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Title 

This  book  should  be  returned  tn  or  before  the  date  last 
marked  below. 


MEDICAL 
ENTOMOLOGY 


Robert  Matheson 

NEW  YORK  STATE  COLLEGE  OF  AGRICULTURE 
CORNELL  UNIVERSITY 


SECOND 
EDITION 


COMSTOCK  PUBLISHING  COMPANY,  INC 

ITHACA,    NEW    YORK,    1950 


First  Edition,  1932 
Copyright  1932  by  Charles  C  Thomas 

Second  Edition,  1950 

Copyright  1950  by 

Comstock  Publishing  Company,  Inc. 


All  rights  reserved.  This  bool{,  or  any  parts  thereof,  must 
not  he  reproduced  in  any  form  without  permission 
in  writing  from  the  publisher,  except  by  a  reviewer  who 
wishes  to  quote  brief  passages  in  a  review  of  the  boo\. 


PRINTED    IN    THE    UNITED   STATES   OF    AMERICA    BY 
THE  VAIL-BALLOU  PRESS,  INC.,  BINGHAMTON,  N.  Y. 


Preface 


MORE  than  seventeen  years  have  passed  since  the  first  edition  of  Med- 
ical Entomology  was  published.  In  the  original  preface  the  important 
role  played  by  insects  and  other  arthropods  in  the  transmission,  causation, 
and  spread  of  human  and  animal  diseases  was  stressed.  Today  no  such  em- 
phasis is  needed,  for  the  important  role  of  insects  in  human  welfare  was 
fully  demonstrated  during  World  War  II.  Recognition  of  the  effects  of 
insect-borne  diseases  on  the  armies  and  navies  of  the  belligerents  has  impelled 
our  medical  and  entomological  services  and  the  governments  of  all  nations 
to  conduct  extensive  investigations  on  all  phases  of  the  problem.  The  results 
of  many  of  these  investigations,  some  of  which  are  continuing,  have  not  yet 
been  published.  In  the  present  work  the  writer  has  attempted,  with  varying 
-iiccess,  to  bring  together  all  data  available  by  the  end  of  1948. 

s  completely  rewritten  text  is  offered  to  the  physician,  the  entomologist, 
the  public  health  worker,  the  student,  and  the  layman  in  order  to  give  them 
an  authoritative  survey  of  our  present  knowledge.  The  writer  has  not  at- 
'empted  to  usurp  the  function  of  the  physician,  so  the  reader  need  not  ex- 
pect to  find  a  discussion  of  treatment;  he  will  find,  however,  a  brief  account 
;>f  the  best  known  methods  of  controlling  the  insects  involved  in  disease 
transmission  or  causation.  Here  great  advances  have  been  made  during  the 
^>ast  few  years.  The  reader  is  warned,  however,  that  all  the  newer  insecticides 
must  be  used  with  care  and  directions  should  be  followed  carefully. 

The  literature  on  insect-borne  diseases  is  voluminous,  widely  scattered  in 
many  and  varied  journals,  monographs,  government  publications,  and  other 
sources,  and  difficult  to  cover  adequately.  For  this  reason  a  list  of  journals, 
textbooks,  and  other -publications  that  will  enable  the  student  to  find  the 
latest  information  is  given  at  the  end  of  the  first  chapter  of  the  present  work. 
Furthermore,  each  chapter  is  provided  with  a  selected  bibliography.  Many 
of  the  references  given  have  long  bibliographies;  these  references  are  starred. 

The  writer  gratefully  acknowledges  his  indebtedness  to  the  numerous 


vi  PREFACE 

authors  whose  publications  he  has  consulted  or  quoted.  Wherever  illusl 
material  is  borrowed,  full  acknowledgment  is  given;  if,  by  accident 
does  not  appear,  due  apology  is  hereby  offered.  To  the  many  colle, 
friends,  and  students  who  have  given  suggestions,  furnished  material,  a 
other  ways  co-operated  with  him,  the  writer  desires  to  tender  his  s: 
thanks.  He  is  under  special  obligation  to  Mr.  Harvey  I.  Scudder  for  *- 
the  galley  proof,  and  to  Mr.  C.  Y.  Chow  for  checking  the  manuscn 
reference  to  malaria  in  China. 

ROBERT  MATIIES 
Ithaca,  New 
September  1949 


Plate  IV.  Left:  Dr.  Leland  Ossian  Howard  (1857-  ),  who  lor  ncany  thirty-five 
years  served  as  Chief  of  the  Bureau  of  Entomology,  United  States  Department  of  Agri- 
culture, and  who  did  more  than  any  other  American  to  establish  the  importance  of  in- 
sects as  agents  in  the  causation  and  spread  of  human  disease.  Right:  Professor  John  Henry 
Comstock  (1849-1931)  in  his  old  office  in  White  Hall,  Cornell  University.  By  his  work 
and  teaching  he  gave  entomology  its  present  position  in  American  universities. 


CHAPTER  I 


Arthropods  and  Human  Disease 


THE  phylum  Arthropoda  plays  a  role  in  human  welfare  that  is  little  under- 
stood by  the  great  majority  of  people.  In  the  sea  the  dominant  animal  life 
is  not  the  larger  fishes,  mammals,  etc.,  but  those  tiny  animals  that  constitute 
the  greater  part  of  the  plankton — the  free-swimming,  minute  Crustacea  on 
which  the  others  rely  for  food.  As  free-living  vegetarians  and  scavengers  they 
people  the  sea  in  vast  numbers  and  perform  their  duties  with  admirable  fitness, 
keeping  great  bodies  of  water  cleaned  of  the  dead  and  dying.  On  the  land 
insects  play  a  similar  but  more  dominant  role.  For  sheer  vastness  of  numbers 
and  incomparable  adaptation  for  meeting  the  vicissitudes  of  life  they  far  out- 
rank any  other  animal  or  plant  association.  (Who  can  count  the  ants  that 
populate  our  fields  and  hillsides  or  the  plant  lice  that  suck  their  nourishment 
from  our  wild  and  cultivated  plants?)  The  part  insects  play  in  agriculture  and 
commerce  has  been  admirably  portrayed  by  a  number  of  writers  and,  at  times, 
overemphasized,  especially  with  respect  to  the  vast  losses  agriculture  suffers 
at  their  hands.  It  is  not  our  purpose  to  enter  such  a  discussion  here;  the  reader 
will  find  references  at  the  end  of  this  chapter  that  will  enlighten  him  on 
this  phase  of  insect  activity.  Sufficient  for  our  purposes  is  the  self-evident  fact 
that,  arthropods,  and  especially  the  class  Hexapoda  (insects),  affect  human 
welfare  at  every  point  and  at  times  endanger  man's  very  existence  or  hold 
in  check  his  advances  in  the  development  of  some  of  the  most  fertile  regions 
of  the  globe.  Medical  entomology  and  parasitology  have  been  recognized  as 
important  fields  of  study  and  research,  not  only  for  the  zoologist,  but  for  the 
physician,  the  veterinarian,  and  the  layman.  World  War  II  amply  dem- 
onstrated the  great  need  for  more  knowledge  of  these  subjects. 

No  more  striking  and  dramatic  story  could  be  told  than  that  of  the  re- 
markable interrelations  which  arthropods  play  in  the  spread  and  maintenance 
of  plant,  animal,  and  human  diseasefclnsects,  long  regarded  and  still  regarded 
as  unworthy  of  serious  consideration  5^  many  of  our  scientists,  have  gradually 
forced  peoples  and  governments  to  devote  some  of  their  resources  to  studies 


2  MEDICAL  ENTOMOLOGY 

too  long  delayed.  Here  only  a  bare  outline  of  these  studies  can  be  offered  and 
a  tribute  paid  to  those  great  medical  leaders  and  others  who  have  laid  down 
their  lives  in  the  investigations  of  insect-borne  diseases/) 

There  are  numerous  early  references  to  insects  as  distributors  of  disease — 
references  made  long  before  the  parasitic  origin  of  disease  was  established.  To 
Mercurialis  (1530-1607),  an  Italian  physician,  is  usually  attributed  the  first 
concrete  observation  that  flies  serve,  in  some  unknown  manner,  to  spread 
disease.  During  the  plague  (Black  Death),  which  ravaged  Europe  in  his  day, 
he  observed  that  flies  may  spread  the  disease  by  feeding  on  the  internal  secre- 
tions of  the  dead  and  dying  and  then  depositing  their  feces  on  the  food  of  the 
well.  Franca  states  that  Souza  (1587)  suspected  flies  of  spreading  yaws  (fram- 
boesia);  Bancroft  (1769)  propounded  a  similar  theory  from  his  observations 
in  Guiana;  and  many  years  later  Castellani  (1907)  demonstrated  that  flies 
do  play  a  part  in  the  dissemination  of  this  disease — obtaining  the  organism 
(Treponema  pertentie)  from  the  sores  of  the  sick  and  passing  it  on  to  the  well. 

It  was  not  till  many  years  later  that  well-defined  theories  of  insect  propaga- 
tion of  disease  were  promulgated.  Such  are  those  of  Beauperthuy  (1854)  and 
Nott  (1848)  relative  to  the  carriage  of  yellow  fever  by  mosquitoes/Beau- 
perthuy  thought  that  mosquitoes  brought  the  disease  from  decomposing 
matter  and  injected  it  into  man  and  this  was  long  before  the  discovery  of 
pathogenic  bacteria  by  Pasteur  in  1857. 

About  the  middle  of  the  nineteenth  century  there  was  a  remarkable  develop- 
ment among  German  doctors  and  scientists  in  the  study  of  helminths.  Herbst 
in  1850  began  the  work  of  experimental  parasitology  when  he  fed  trichinized 
meat  to  dogs  and  obtained  the  adult  worms  in  his  animals;  Kiickenmeister 
in  1852  discovered,  by  feeding  experiments,  that  the  "bladder  worms"  in  rabbits 
were  but  a  stage  in  the  life  cycle  of  tapeworms;  in  1854-1856  he  also  showed 
that  "bladder  worms"  in  pigs  were  but  a  stage  in  the  life  cycle  of  human  tape- 
worms; Virchow  and  Leuckart  in  the  same  decade  determined  the  life  cycle 
of  Trichinella  (Trichina)  and  Leuckart  (1862)  solved  the  mystery  of  hydatid 
cysts.  All  these  and  other  experimental  activities  undoubtedly  fired  the  minds 
and  guided  the  thinking  of  the  rising  generation^ 

s / 

DISEASES  DISCOVERED  TO  BE  TRANSMITTED  BY  INSECTS 

FILARIASIS:  In  1863  Demarquay  discovered  a  larval  nematode  in  cases 
of  chyluria;  they  were  later  seen  by  Wikherer  in  other  cases,  and  Lewis  (1872) 
discovered  that  the  blood  of  man  is  the  normal  habitat  of  this  filarial  worm 
(Filaria  sanguinis  hominis  of  Lewis). 

In  1866  Dr.  Patrick  Manson,  a  young  medical  man  of  imagination  and 


ARTHROPODS  AND  HUMAI^  DISEASE  3 

unbounded  energy,  left  the  shores  of  his  native  country,  England,  and  took 
up  heroic  work  first  at  Formosa  and  later  (1871)  at  Amoy,  China  j(He  in- 
vestigated anything  and  everything  that  came  his  way,  developing  a  remarka- 
ble ingenuity  for  interpreting  old  and  solving  new  problems^He  found  filaria 
abundant  in  the  blood  of  his  Chinese  patients,  established  tfie  "periodicity"  of 
their  appearance  in  the  peripheral  circulation,  and  in  1879  published  the  first 
account  of  an  insect,  Culex  jatigans  (the  house  mosquito  of  the  tropics), 
serving  as  the  intermediate  host  in  the  developmental  cycle  of  a  parasite. 
Though  Manson  traced  the  developmental  cycle  from  the  intestine  through  the 
tjhoracic  muscles,  he  did  not  determine  how  the  parasites  reached  a  new  host. 
He  believed  at  that  time  that  the  life  of  the  mosquito  was  short,  the  females 
dying  after  laying  their  eggs,  and  so  he  formulated  the  theory  that  man  was 
infected  by  drinking  the  water  in  which  infected  mosquitoes  died.  It  was  not 
till  1900  that  the  true  method  was  discovered  by  Low)  Manson's  work  was 
the  real  starting  point  of  medical  entomology.  In  1890  Manson  returned  to 
London,  engaged  in  the  practice  of  medicine,  and  urged  the  development 
of  tropical  medicine.  In  1893  he  evolved  his  mosquito  theory  of  malaria. 
Though  he  never  had  an  opportunity  to  test  his  theory,  he  so  impressed  his 
ideas  on  Dr.  Ronald  Ross  that  the  latter  eventually  made  his  epoch-making 
discovery  in  1897-1898. 

Only  one  other  contribution  by  Manson  can  be  recorded  here.  Loa  loa, 
the  African  eye  worm,  was  long  identified  both  in  America  and  Africa,  but 
nothing  was  known  of  its  life  cycle.  In  1891  Manson  reported  a  new  filaria 
in  the  blood  of  natives  from  the  Congo  and  Old  Malabar,  naming  it  Filaria 
sanguinis  hominis  major  (later  known  as  Micro  filaria  diurna).  On  account 
of  its  diurnal  periodicity  Manson  predicted  that  some  bloodsucking,  day- 
feeding  fly  would  be  found  to  be  the  intermediate  host.  From  talks  with  the 
natives  of  Old  Calabar  he  suggested  that  the  "mangrove  flies,"  Chrysops 
dimidiata  and  Chrysops  spp.,  would  prove  the  correct  flies.  In  1912  Leiper 
confirmed  this  prediction,  and  Kleine  (1915)  worked  out  the  methods  of 
transmission  in  detail. 

Another  remarkable  discovery  should  be  recorded  here;  it,  in  fact,  antedated 
Manson's  work.  Fedschenko  (1869)  demonstrated  that  Cyclops  spp.  (Crusta- 
cea) were  the  intermediate  hosts  of  the  famous  "fiery  serpent"  of  Moses,  the 
dragon  worm,  Dracunculus  medinensis  Linn,  (hence  the  name  of  the  disease, 
dracontiasis).  Manson  (1894)  confirmed  and  extended  the  work  of  Fed- 
schenko. 

MALARIA:  In  1880  Laveran,  working  in  Algeria,  discovered  the  parasite 
of  malaria  in  the  red  blood  cells  of  his  patients.  More  than  ten  years  passed 


4  MEDICAL  ENTOMOLOGY 

before  Laveran's  organism  was  accepted  as  the  causal  agent  of  the  disease. 
Though  much  had  been  learned  about  the  parasite  during  this  time,  little 
progress  was  made  till  Manson  evolved  his  mosquito  theory  and  impressed 
it  on  Ronald  Ross,  a  young  British  surgeon  working  in  India.  So  farfetched 
appeared  Manson's  theory  that  he  was  dubbed  "Mosquito  Manson"  by  his 
distinguished  medical  confreres  and  regarded  as  rather  fit  for  a  lunatic  asylum. 
Curiously  enough,  in  1883  an  American  physician,  A.  F.  A.  King,  had  also 
propounded  a  mosquito  malarial  theory,  which,  unfortunately,  fell  on  deaf 
ears  and  unimaginative  minds.  Under  Manson's  urging  Ross  continued  to 
rwork  and  in  1897  recorded  his  great  discovery  that  "dappled-winged"  mos- 
quitoes served  as  the  definitive  hosts  of  species  of  Plasm  odium.  Ross's  work 
was  done  under  the  most  trying  conditions  and  at  a  time  when  no  one  knew 
mosquitoes  or  their  biology.  His  results  were  fully  confirmed  by  Bastianelli, 
Bignami,  and  Grassi  (1898,  1899),  Manson  (1898),  and  Sambon  and  Low 
(1900).  This  discovery  by  Ross  is  undoubtedly  one  of  the  great  landmarks 
in  medical  history,  for  it  has  led  to  the  reduction,  and  can  lead  to  the  elimina- 
tion, of  the  most  widespread  and  devastating  of  human  diseases. 

PIROPLASMOSIS :  While  the  mosquito  malarial  theory  came  to  fruition 
in  India  and  Europe,  Theobald  Smith,  working  in  Washington,  D.C.,  dis- 
covered the  causative  agent  of  Texas  or  red-water  fever  of  cattle,  Piroplasma 
bigemina,  a  red-blood-cell-inhabiting  protozoan.  In  1893  Smith  and  Kil- 
bourne  published  the  results  of  their  work.  They  demonstrated  that  the 
cattle  tick,  Boophilus  annulatus  Say.  was  the  intermediate  host.  In  addition, 
they  showed  thaTTKe^parasitc  passes  from  the  adult  female  ticks  to  their 
offspring  and  only  young  ticks  (larvae)  infect  new  hosts.  This  is  the  first 
instance  of  a  protozoan  passing  by  way  of  the  egg  to  infect  the  young,  which, 
in  turn,  transmit  the  disease  to  new  hosts.  Many  other  discoveries  in  the  field 
of  protozoan  parasites  of  domestic  animals  have  since  been  made  and  are  of  the 
greatest  importance  to  animal  husbandry.  It  would  take  us  too  far  afield  to 
discuss  them  here. 

TRYPANOSOMIASIS:  From  about  1893  to  the  present  time  the  most 
remarkable  discoveries  have  been  made  in  the  field  of  insect-borne  diseases. 
These  can  be  reviewed  only  briefly.  In  1895  Bruce  discovered  Trypanosoma 
brucei,  the  causative  agent  of  nagana  or  tsetse  fly  disease  of  cattle  in  Zululand 
and  demonstrated  that  the  tsetse  fly,  Glossina^mozsita&s  Westw.,  could  trans- 
mit the  disease  from  the  sick  to  the  well.  It  was  not,  however,  till  1909  that 
Kleine  proved  the  developmental  cycle  in  the  fly  and  showed  the  true  method 
of  transmission.  In  1901  Forde,  in  West  Africa,  observed  a  parasite  in  the 


ARTHROPODS  AND  HUMAN  DISEASE  5 

blood  of  a  European  patient  suffering  from  Gambian  fever;  later  Dutton 
(1902)  recognized  it  as  a  trypanosome  and  described  it  as  Trypanosoma 
gambiense  Dutton;  Castellan!  (1903)  and  Bruce  and  Nabarro  (1903)  proved 
this  trypanosome  was  the  causative  agent  of  sleeping  sickness  and  that  Glossina 
palpalis  R.-D.  was  the  transmitting  fly.  In  1910  Stephens  and  Fantham  de- 
scrfBed  Trypanosoma  rhodgsignsc  as  the  etiological  agent  of  Rhodcsian  sleep- 
ing sickness,  and  Kinghorn  and  Yorke  (1912)  proved  that  Glossina  morsitans 
Westw.  was  the  transmitter.  In  South  America  Chagas  (1909)  demonstrated 
that  a  trypanosome,  T.  cruzi,  was  transmitted  by  a  bug,  Triatoma  megista 
Burm.  This  parasite  is  the  etiological  agent  of  South  American  trypanosomiasis 
or  what  has  been  called  Chagas'  disease. 

YELLOW  FEVER:  While  these  African  investigations  were  being  devel- 
oped, the  American  Arrny  Yellow  Fever  Commission,  consisting  of  Reed, 
Carroll,  Lazear,  and  Agramonte,  made  a  still  more  remarkable  discovery. 
They  demonstrated  (1900)  that  yellow  fever  can  be  transmitted  only  through 
the  agency  of  the  "tiger  mosquito"  or  yellow-fever  mosquito  (Stegomyia 
jasciata,  Aedes  calopus,  Aedes  argenteus — now  known  as  Aedes  jiegygti). 
Though  Carlos  Finlay,  a  Cuban  physician,  had  as  early  as  1881  propounded 
a  mosquito  theory  for  yellow  fever  and  had  extensive  experimental  evidence 
in  support  of  it,  yet  it  must  ever  redound  to  the  glory  of  this  band  of  devoted 
workers  that,  because  of  their  discoveries,  one  of  the  most  deadly  of  human 
diseases  could  now  be  controlled  or  even  eliminated.  Though  Noguchi  (1919) 
announced  that  Leptospira  icteroides  was  the  etiological  agent  and  his  work 
was  accepted  by  many  workers,  his  results  have  since  been  abundantly  dis- 
proved. It  is  now  known  to  be  caused  by  a  recognized  virus,  which  has  been 
studied  in  great  detail.  For  over  a  quarter  of  a  century  it  was  firmly  be- 
lieved that  the  only  transmitter  of  yellow  fever  was  the  "tiger  mosquito"  and 
that  man  was  the  only  animal  susceptible  to  the  disease.  On  this  belief 
prophylactic  measures  against  yellow  fever  were  based,  and  remarkable  results 
were  obtained  in  reducing  and  controlling  outbreaks  of  the  disease.  However, 
in  1928  two  most  important  contributions  were  made  to  the  yellow-fever 
problem.  Stokes  and  his  associates,  working  in  West  Africa,  demonstrated 
that  monkeys,  Macactts  rhesus,  were  susceptible  to  the  disease,  and  since  then 
many  more  species  of  monkeys,  both  from  the  Old  World  and  the  New  World, 
have  been  shown  to  be  susceptible  to  yellow  fever.  In  the  same  year  Bauer, 
working  in  the  same  laboratory,  proved  that  three  other  species  of  mosquitoes 
were  capable  of  transmitting  yellow  fever.  Since  that  date  over  thirty  addi- 
tional species  of  mosquitoes  have  been  shown  to  be  capable  oFtransmitting 
yellow  fever. 


6  MEDICAL  ENTOMOLOGY 

In  1933  Soper  and  his  associates  reported  an  outbreak,  in  parts  o£  Brazil, 
of  what  has  been  designated  as  jungle  yellow  fever.  Since  then  large  areas  in 
South  America  have  been  shown  to  be  endemic  centers  of  this  disease.  Jungle 
yellow  fever  is  identical  with  classical  yellow  fever,  but  its  epidemiology  is 
remarkably  different.  (See  pp.  353-356.)  These  and  other  discoveries  have 
thrown  new  light  on  the  yellow-fever  problem.  The  development  of  an 
effective  vaccine  by  the  workers  of  the  Rockefeller  Foundation  in  1932  has 
provided  one  of  the  most  efficient  methods  to  prevent  and  reduce  yellow-fever 
outbreaks. 

^PLAGUE:  In  1894  Yersin  and  Kitasato  independently  discovered  the  causa- 
tive agent  of  plague,  Pasteurella  pestis,  and  Yersin  demonstrated  that  the  dis- 
ease in  man  was  identical  with  a  plaguelike  disease  of  rodents.  Simond  (1898) 
suggested  that  fleas  _were  agents  in  the  dissemination  of  .plague,  and  his 
experiments  showed  that  he  was  on  the  right  track.  In  1903-1904  Verjbitski 
demonstrated  that  fleas  act  as  vectors  of  the  plague  bacillus,  but  his  results 
were  not  published  till  1908.  The  development  of  the  plague  bacillus  in 
the  gut  of  the  rat  flea  was  independently  discovered  by  Listen  (1905),  and  the 
role  fleas  play  in  the  epidemiology  of  plague  was  fully  determined  by  the 
British  Plague  Commission  (1906-1908).  Finally  Bacot  and  Martin  (1914) 
demonstrated  the  method  of  transmission  of  the  plague  bacilli  by  fleas. 

DENGUE:  Dengue  or  breakbone  fever,  a  disease  of  unknown  etiology, 
was  shown  by  Graham  (1902)  to  be  mosquito-borne,  and  his  results  were  con- 
firmed by  Ashburn  and  Craig  (1907).  Though  the  mosquitoes  with  which 
these  investigators  were  supposed  to  have  worked  have  since  been  shown 
not  to  be  true  vectors,  their  discovery  was  of  great  importance.  The  true  vectors 
have  since  been  shown  to  be  Aedes  aegypti  and  Aedes  albopictus  (see  pp. 
357-358). 

PHLEBOTOMUS  FLIES  AND  DISEASE:  Pappataci  fever  (three-day 
fever  or  sand-fly  fever),  another  disease  of  unknown  etiology,  was  shown  by 
Doerr,  Franz,  and  Taussig  (1909)  to  be  transmitted  by  a  sand  fly,  Phlebotomus 
papatasii  (Psychodidae).  Oroya  fever,  verruga  peruana,  or  Carrion's  disease, 
a  disease  of  rather  high  mortality  in  parts  of  South  America,  was  demon- 
strated by  Townsend  (1913-1914)  to  be  transmitted  by  Phlebotomus  verru- 
carum,  and  his  results  have  been  confirmed  by  Noguchi  and  his  associates 
(1929).  PhleJMomu£S£^h&ye.  also  been  proved  vectors  of  kala  azar,  Oriental 
sore,  and  espundia^(diseases  known  as  -forms  of  leishmanjasis,  the  etiological 
agents  being  species  ol~L^Tsfwania) ,  but  at  the  present  time  (1949)  many 
actual  transmitters  still  remain  unknown. 


ARTHROPODS  AND  HUMAN  DISEASE  7 

SPIROCHETAL  DISEASES:  In  1903  a  peculiar  disease  of  fowls  caused 
by  Spirochaeta  marchouxi  Nuttall  was  shown  by  Marchoux  and  Salimbeni 
to  be  tick-borne,  the  common  fowl  tick,  Argas  persicus  Oken,  being  the  vector. 
Various  recurrent  fevers  of  man  caused  by  Spirochaeta  spp.  have  since  been 
shown  to  be  tick-  or  louse-borne.  Ross  and  Milne  (1904)  first  demonstrated 
that  the  tick,  Ornithodorus  moubata,  is  the  vector  of  African  relapsing  fever 
caused  by  S.  duttoni.  These  conclusions  were  confirmed  and  extended  by 
Dutton  and  Todd  (1905)  working  independently  in  the  Belgian  Congo.  Since 
then  various  species  of  ticks  (Argasidae)  and  lice  (Pediculus  humanus)  have 
been  shown  to  be  the  natural  transmitters  of  the  different  relapsing  fevers  of 
man.  Mackie  (1907),  working  in  India,  first  demonstrated  the  part  played  by 
lice  (Pediculus  corporis)  in  the  dissemination  of  relapsing  fevers. 

TSUTSUGAMUSHI  DISEASE,  KEDANI  FEVER,  FLOOD  FEVER, 
OR  JAPANESE  RIVER  FEVER:  A  serious  disease  in  parts  of  Japan,  China, 
Formosa,  and  other  parts  of  the  Far  East,  tsutsugamushi  was  first  diagnosed 
as  a  distinct  disease  by  Biilz  and  Kawakami  in  1879.  This  peculiar  disease  had 
long  been  believed  by  the  common  people  to  be  associated  with  the  bites  of  a 
red  mite.  Balz  and  Kawakami  concluded  there  was  no  such  association.  Kita- 
sato  (1891-1893),  however,  decided  that  the  bites  of  a  red  mite  did  play  a  role 
in  the  causation  of  the  disease.  The  mite  theory  of  the  transmission  of  the 
disease  has  since  been  fully  confirmed  by  the  work  of  Tanaka  (1899), 
Kitashima  and  Miyajima  (1909,  1918),  Miyajima  and  Okumura  (1917),  and 
others.  The  etiological  agent  was  isolated  by  Nagayo  and  his  associates  (1930) 
and  described  as  a  rickettsia,  R.  orientalis.  During  World  War  II  this  disease 
was  found  to  be  widespread  in  many  Eastern  areas.  The  so-called  "Mossman 
fever"  of  Australia,  "scrub  typhus"  of  Malaya  and  other  parts  of  the  East, 
and  "pseuclotyphoid"  of  Sumatra  were  found  to  be  kedani  fever  and  trans- 
mitted by  mites  (Trombicula  spp;  see  pp.  110-113). 

ROCKY  MOUNTAIN  SPOTTED  FEVER:  This  peculiar  disease  prev- 
alent in  Montana  and  certain  other  Rocky  Mountain  states  was  definitely 
proved  by  Ricketts  (1906)  to  be  transmitted  to  man  by  a  tick,  J^ermacentor 
under "soni  Stiles  (yenustus  Banks).  His  results  have  been  fully  confirmed  by 
various  later  workers,  and  Wolbach  (1916,  1919)  determined  the  causative 
agent  to  be  Dermacentroxenu^ric^ettsi  (Rickettsia  bodies,  so-called).  This 
disease  is  now  widespread  in  the  United  States  (see  pp.  73-74). 

TYPHUS  FEVER:  Though  the  head  and  body  lice  (Pediculus  humanus 
var.  capitis  and  var.  corporis)  have  been  closely  associated  with  man  in  all  his 
long  career,  it  was  not  till  1909  that  Nicolle,  Comte,  and  Conseil,  working  in 


8  MEDICAL  ENTOMOLOGY 

Tunis,  demonstrated  the  role  played  by  the  body  louse  (corporis)  in  the 
spread  of  the  much-dreaded  typhus  or  jail  fever.  These  results  were  confirmed 
by  Ricketts  and  Wilder  (1910)  working  independently  in  Mexico.  Da  Rocha- 
Lima  (1916)  discovered  the  causative  agent  and  named  it  Ricl^ettsia  prowa- 
zelji.  During  World  War  I  (about  1915)  a  peculiar  disease  dubbed  "trench 
fever"  appeared  among  the  troops  of  the  contending  armies  and  was  definitely 
proved  by  various  workers  to  be  disseminated  by  head  and  body  lice  (see 
p.  208).  Topfer  (1916)  designated  what  is  considered  the  causal  agent  as 
Ricf^ettsia  quintana. 

TULAREMIA:  A  peculiar  plaguelike  disease  of  rodents  was  investigated 
by  McCoy  (1911),  and  the  etiological  agent,  Bacterium  titlarense,  was  isolated 
and  described  by  McCoy  and  Chapin  (1912).  In  1911  Pearse,  in  Utah,  described 
a  peculiar  disease  of  man  under  the  title  of  "insect  bites,"  and  this 
disease  later  became  known  as  "deer-fly  fever."  Francis  (1919-1920)  recog- 
nized the  identity  of  "deer-fly  fever"  of  man  and  the  plaguelike  disease  of 
rodents  and  named  the  disease  tularemia.  Francis  and  Mayne  (1921)  dem- 
onstrated that  the  deer  fly,  Chrysops  discalis  (Tabanidac),  was  the  trans- 
mitting insect.  Since  then  a  large  number  of  insects  and  ticks  have  been 
shown  to  be  able  to  transmit  the  disease  in  nature. 

ONCHOCERCIASIS:  Recent  contributions  in  the  field  of  medical  en- 
tomology have  been  the  solving  of  the  life  histories  of  Onchocerca  volvulus 
Leuck.  and  O.  caecutiens  Brumpt  (Nemathelminthes,  family  Filariidae). 
The  former  species  occurs  in  Africa  and  the  latter  in  parts  of  Central  America 
and  Mexico.  Blacklock  (1926)  determined  that  0.  volvulus  passes  part  of  its 
life  cycle  in  black  flies  (Eusimulium  damnosum,  family  Simuliidae)  while 
Hoffman  (1930)  and  Strong  (1931)  demonstrated  that  O.  caecutiens  under- 
goes a  developmental  cycle  in  at  least  three  species  of  black  flies.  Both  these 
round  worms  produce  diseased  conditions  in  man.  These  two  species  are  now 
considered  to  be  one  and  the  same,  O.  volvulus. 

In  recent  years  several  important  diseases  have  been  demonstrated  to  be 
insect-transmitted.  Poliomyelitis,  long  associated  with  some  bloodsucking 
insect  as  a  vector,  has  been  shown  capable  of  being  disseminated  by  filth- 
loving  flies,  as  the  housefly,  blowflies,  and  flesh  flies.  How  important  a  part 
these  flies  play  has  not  been  determined.  St.  Louis  encephalitis,  a  new  virus 
that  appeared  in  epidemic  form  in  St.  Louis  during  1933  and  1937  and  has 
since  been  isolated  in  other  parts  of  the  country,  has  been  shown  to  be  dis- 
seminated to  man  by  mosquitoes.  The  reservoir  of  this  disease  has  been  found 
in  birds,  primarily  fowls,  and  in  the  fowl  mite,  Dcrmanyssus  gallinae.  Japa- 


ARTHROPODS  AND  HUMAN  DISEASE  9 

nese  B  encephalitis,  a  serious  disease  in  Japan  and  other  parts  of  the  East, 
has  also  been  shown  to  be  transmitted  by  mosquitoes.  Equine  encephalo- 
myelitis  (several  different  strains),  primarily  a  disease  of  horses,  appeared  also 
in  man  in  Massachusetts  in  1938  and  in  California  in  the  same  year.  In  1941 
an  extensive  outbreak  of  human  cases  (over  3000)  developed  in  the  western 
prairie  states  of  the  United  States  and  Canada.  Mosquitoes  have  been  proved 
to  be  the  vectors  of  these  diseases. 

OTHER  ASPECTS  OF  DISEASE  TRANSMISSION 

In  the  above  survey  nothing  has  been  said  of  the  mere  mechanical  carriage 
of  pathogenic  organisms  by  insects,  especially  filth-loving  flies.  Very  early, 
flies,  in  the  mind  of  the  common  people  and  the  physicians,  were  associated 
with  disease  outbreaks.  An  abundance  of  flies  during  the  summer  presaged 
an  unhealthy  autumn,  wrote  Sydenham  (r666),  and  since  his  time  a  long  series 
of  physicians  and  others  have  called  attention  to  the  abundance  of  and  the 
dangers  from  filth-loving  flies.  Veeder  (1898)  called  more  specific  attention 
to  the  housefly,  and  Reed,  Vaughan,  and  Shakespeare  (1900)  outlined  the 
role  the  housefly  may  play  in  the  spread  of  typhoid  fever.  Since  then  the 
importance  of  filth-loving  flies  as  possible  disseminators  of  disease-producing 
organisms  has  been  well  established  and  recognized. 

This  brief  historical  survey  will  indicate,  to  some  extent,  the  role  insects  play 
in  the  dissemination  of  human  diseases.  Had  the  writer  attempted  to  include 
animal  diseases  other  than  those  of  man,  the  list  would  have  been  much 
extended  and  the  importance  of  insects,  from  the  point  of  view  of  human 
welfare,  more  strikingly  portrayed.  In  addition,  the  role  insects  play  as  vectors 
of  plant  diseases  has  become,  during  the  past  fifty  years,  almost  as  important 
as  that  in  animal  diseases.  Rand  and  Pierce  gave  an  extended  account  of  the 
subject  up  to  1920,  and  since  then  the  so-called  "mosaics,"  "chloroses,"  and 
other  "virus"  diseases  of  plants  and  their  transmission  by  insects  have  assumed 
even  greater  significance. 

In  the  gut  of  many  insects  are  found  representatives  of  the  protozoan  family 
Trypanosomidae,  under  the  generic  names  Crithidia,  Herpetomonas,  Phyto- 
monas,  Leishmania,  Leptowonas,  and  others  of  doubtful  validity.  The  rela- 
tionships of  some  of  these  forms  to  animal  and  plant  diseases  have  been 
established,  but  the  great  majority  of  them  remain  undetermined.  The  prob- 
lem of  isolating,  ctilturing  these  forms,  and  of  determining  their  relation  to  the 
insects,  to  other  animals,  and  to  plants  is  extremely  difficult.  Progress  has  been 


io  MEDICAL  ENTOMOLOGY 

made,  and  with  the  development  of  microtechnique  we  may  expect  much 
from  the  future. 


FACTORS  INVOLVED  IN  DISEASE  TRANSMISSION 

In  the  study  of  insect-borne  disease,  especially  one  in  which  the  insect 
serves  as  the  definitive  or  intermediate  host,  certain  important  considerations 
must  always  be  kept  in  mind.  Table  i  will  serve  to  call  attention  to  the  more 
important  features  and  indicate  the  far-reaching  significance  of  the  various 
factors  involved.  These  factors  are  (i)  the  parasite  or  etiological  agent;  (2)  the 
definitive  host  and  the  definitive  reservoirs  or  nonreservoirs;  (3)  the  method 
of  transmission;  (4)  the  intermediate  host  and  the  intermediate  reservoirs  or 
nonreservoirs;  and  (5)  the  method  of  transmission.  The  significance  of  these 
facts  can  be  best  illustrated  by  giving  several  examples. 

Table  i.  Three  diseases  and  the  factors  involved  in  their  transmission. 


Malaria 

Yellow  fever 

Sleeping  sickness 

Parasite  (etiologi- 
cal agent) 

Plasmodittm  vivax 
P.  malariae 
P.  jalciparum 

Virus 

Trypanosoma  gambi- 
ense 

Definitive  host 

Anopheles  spp. 
How  many? 

Aedes  aegypti  and 
many  other  spp.  of 
mosquitoes.  How 
many  more? 

Glosslna  palpal  is 
Glossina  spp. 
(How  many?) 

Definitive  host 
reservoirs 

? 

All  not 
definitely  known 

Game  animals? 

Method  of  trans- 
mission 

Sporozoites 
Inoculative 

? 
Inoculative 

Infective  salivary 
trypanosomes 
Inoculative 

Intermediate  host 

Man 
Other  animals? 

Man 
Monkeys 
Other  animals? 

Man 
Domestic  cattle? 

Intermediate  host 
reservoirs 

Man  with  gameto- 
cytes  in  his  blood 
Other  animals  ? 

Monkeys 
Other  animals? 

Domestic  cattle 
Game  animals? 

Method  of  trans- 
mission 

Male  and  female 
gametocytes 
Ingested 

? 

Certain  infective 
blood  types  of  the 
trypanosome 
Ingested 

Examining  such  an  outline,  one  is  immediately  struck  by  the  lacunae,  even 
in  some  of  the  best-known  insect-borne  diseases.  In  malaria  it  is  apparent  that 
the  only  definitive  host  reservoirs  are  mosquitoes  (Anopheles  spp.),  but  how 


ARTHROPODS  AND  HUMAN  DISEASE  11 

long  they  can  remain  infected  is  still  a  matter  of  uncertainty.  The  number 
of  Anopheles  species  that  can  act  and  the  conditions  under  which  they  may 
serve  as  definitive  hosts  are  still  not  well  known,  though  much  progress  has 
been  made  toward  solving  these  problems.  In  yellow  fever  the  etiological 
agent  (parasite)  is  a  virus;  only  recently  have  the  animal  reservoirs  been 
determined  and,  as  yet,  not  all  the  mosquito  transmitters  have  been  recog- 
nized. Many  factors  in  the  problem  of  sleeping  sickness  remain  unsolved.  In 
a  similar  manner,  data  on  all  the  insect-borne  diseases  could  be  assembled  and 
the  numerous  unsolved  problems  pointed  out. 

The  literature  dealing  with  medical  entomology,  parasitology,  and  preven- 
tive medicine  has  become  of  vast  proportions,  especially  during  the  past  fifty 
years.  In  each  field,  and  we  should  include  bacteriology  and  veterinary  medi- 
cine, the  entomologist  will  find  texts,  journals,  reviews,  summaries,  etc.,  that 
he  must  consult  if  he  is  to  keep  abreast  of  the  times.  In  addition  to  the  refer- 
ences given  at  the  end  of  each  chapter,  I  am  appending  to  this  chapter  a  list 
of  the  more  important  journals,  reviews,  summaries,  and  other  publications 
that  the  entomologist  should  consult.  In  many  of  the  texts  listed  will  be  found 
bibliographies,  some  of  them  very  extensive,  and  they  should  be  of  great  benefit 
to  those  who  desire  to  explore  beyond  the  outer  doorway. 

DEFINITION  OF  SOME  OF  THE  TERMS  EMPLOYED  ABOVE 

Definitive  Host.  The  host  in  which  the  sexual  life  of  the  parasite  is  passed. 
Intermediate  Host.  The  host  in  which  the  asexual  stages  of  the  parasite  are 

passed. 
Definitive  Host  Reservoir.  Hosts  in  which  a  natural  supply  of  the  sexual  stage 

of  a  parasite  occurs. 
Intermediate  Host  Reservoir.  Hosts  in  which  a  natural  supply  of  the  asexual 

stages  of  a  parasite  occurs.  (In  using  these  two  terms  the  word  host  is  fre- 
quently omitted.) 
Transmission.  The  passage  of  a  parasite  from  the  intermediate  host  to  the 

definitive  host  or  vice  versa. 
Contaminative.  Infection  or  transmission  is  said  to  be  contaminative  when 

the  pathogenic  organism  gains  entrance  by  way  of  abrasions,  by  fecal  wastes 

deposited  on  the  skin,  etc. 
Inoculative.  This  term  is  applied  when  invasion  of  an  organism  takes  place 

through  the  act  of  biting,  the  organism  being  inoculated  during  the  feeding 

process. 
Ingestive.  This  applies  when  parasites  are  obtained  at  the  time  of  feeding,  the 

infective  stage  being  ingested  per  os. 


12  MEDICAL  ENTOMOLOGY 

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etiology  of  dengue  fever.    Philip.  Jl.  Sci.,  B,  2:  93-147,  1907. 
Bacot,  A.,  and  Martin,  C.  J.    Observations  on  the  mechanism  of  the  transmission 

of  plague  by  fleas.    Jl.  Hyg.,  13  (Plague  Suppl.  in):  423-439,  1914. 
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Accad.  Lincei,  Rendic.,  7  (ii):  313,  1898. 
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Dutton,  J.  E.    Trypanosoma  in  man.     Brit.  Med.  JL,  T,  p.  42;  ii,  p.  881,  1902. 
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Nicolle,  C.    Reproduction  experimentale  du  typhus  exanthematique  chez  le  singe. 

C.  R.  Acad.  Sci.,  Paris,  149:  157-160,  1909, 

,  Comte,  C.,  and  Conseil,  E.    Transmission  experimentale  du  typhus  exanthe- 
matique par  le  pou  du  corps.    Ibid.,  pp.  486-489,  1909. 
Nott,  J.  C.    On  the  origin  of  yellow  fever.    New  Orleans  Med.  and  Surg.  JL, 

4:  563-601,  1848. 
Nuttall,  G.  H.  F.    On  the  role  of  insects,  arachnids,  and  myriapods  as  carriers  in 

the  spread  of  bacterial  and  parasitic  diseases  of  man  and  animals.    Johns  Hopkins 

Hosp.  Rcpts.,  8,  1899. 

Rand,  F.  V.,  and  Pierce,  W.  D.    A  co-ordination  of  our  knowledge  of  insect  trans- 
mission in  plant  and  animal  diseases.    Phytopathology,  10:   189-231,  1920. 
Reed,  Walter.    The  etiology  of  yellow  fever.    Phila.  Med.  JL,  6:  790-796,  1900. 
Rickctts,  H.  T.    The  transmission  of  Rocky  Mountain  spotted  fever  by  the  bite 

of  the  wood  tick  (Dermacentor  occidcntalis).    JL  Amer.  Med.  Assoc.,  47:  358, 

1906. 
,  and  Wilder,  R.  M.    The  transmission  of  typhus  fever  of  Mexico  (tarbar  ditto) 

by  means  of  the  louse  (Pediculus  vestimenti).    Ibid.,  54:  1304-1307,  1910. 
Rocha-Lima,  H.  da.    Zur  Aetiologie  des  Fleckfiebers.    Berlin.  Klin.  Woch.,  53  (i) : 

567,  1916. 
.     Untersuchungen  iiber  Fleckfieber.    Munch.  Med.  Woch.,  63  (No.  39): 

1381-1384,  1916. 

Ross,  Ronald.    Pigmented  cells  in  mosquitoes.    Brit.  Med.  JL,  i,  pp.  550-551, 1898. 
Ross,  R.  H.,  and  Milne,  A.  D.    Tick  fever.    Ibid.,  2,  pp.  1453-1454,  1904. 
Sambon,  L.  W.,  and  Low,  G.    The  malaria  experiments  in  the  Campagna.    Ibid., 

2,  pp.  1679-1682,  1900. 


i4  MEDICAL  ENTOMOLOGY 

Simond,  P.    La  propagation  de  la  pcste.    Ann.  Inst.  Pasteur,  12:  625-687,  1898. 

Smith,  T.,  and  Kilborne,  F.  L.  Investigations  into  the  nature,  causation  and  pre- 
vention of  Texas  or  southern  cattle  fever.  U.S.  Dept.  Agr.,  Bur.  Animal  Ind., 
Bull,  i,  1893. 

Tanaka,  K.  Uber  Aetiologie  und  Pathogenese  der  Kedanikrankheit.  Central. 
Bakt,  I  Abt.  26:  432-439,  1899. 

Veeder,  M.  A.  Flies  as  spreaders  of  sickness  in  camps.  Medical  Rec.,  54:  429- 
430,  1898. 

Verjbitski,  D.  T.  The  part  played  by  insects  in  the  epidemiology  of  plague.  Jl. 
Hyg.,  8:  162-208,  1908. 

Wolbach,  S.  B.  The  etiology  of  Rocky  Mountain  spotted  fever.  Jl.  Med.  Res., 
34:  121-126,  1916. 

.    Studies  on  Rocky  Mountain  spotted  fever.    Ibid.,  41:  1-197,  1919. 

SOME  OF  THE  MORE  IMPORTANT  JOURNALS 

American  Journal  of  Hygiene.     Baltimore,  1921-. 
American  Journal  of  Public  Health.    New  York,  1911-. 
American  Journal  of  Tropical  Medicine.    Baltimore,  1921-. 
Annales  de  1'Institut  Pasteur.    Paris,  1887-. 
Annales  de  parasitologie  humaine  et  comparce.    Paris,  1923-. 
Annals  of  Tropical  Medicine  and  Parasitology.    Liverpool,  1907-. 
Archiv  fur  SchifTs-  und  Tropen-Hygiene.    Leipsic,  1897-. 
Archives  de  1'Institut  Pasteur.    Tunis,  1906-. 
Archives  de  parasitologie.    Paris,  1898-1919. 
Brasil-Medico.    Rio  de  Janeiro,  1887-. 
British  Medical  Journal.    London,  1857-. 
Bulletin  biologique  de  la  France  et  de  la  Belgique.     1869-. 
Bulletin  of  Entomological  Research.    London,  1910-. 
Bulletin  de  1'Institut  Pasteur.    Paris,  1903-. 
Bulletin  de  la  societe  de  pathologic  exotique.    Paris,  1908-. 
Ceylon  Journal  of  Science,  Section  D,  Medical  Science.    Colombo,  1924-. 
Index  Medicus.    Washington,  D.C.,  1879-. 
Indian  Journal  of  Malariology.    Calcutta,  1947-. 
Indian  Medical  Gazette.    Calcutta,  1866-. 
Indian  Medical  Research  Memoirs.    Calcutta,  1924-. 

International  Health  Board,  Annual  Reports  and  Publications.    New  York,  1913-. 
Journal  of  the  American  Medical  Association.    Chicago,  1883-.     (Contains  refer- 
ences to  most  of  the  current  medical  literature.) 
Journal  of  Economic  Biology.    London,  1906-. 
Journal  of  Economic  Entomology.    Geneva,  N.Y.,  1908-. 
Journal  of  Hygiene.    Cambridge,  England,  1901-. 


ARTHROPODS  AND  HUMAN  DISEASE  15 

Journal  of  the  London  School  of  Hygiene  and  Tropical  Medicine.    London,  1911- 

I9I3- 
Journal  National  Malaria  Society.    Pub.  Nat.  Malaria  Soc.,  1942-. 

Journal  of  Parasitology.    Urbana,  111.,  1914-. 
Journal  of  the  Royal  Army  Medical  Corps.    London,  1903-. 
Journal  of  Tropical  Medicine  and  Hygiene.    London,  1898-. 
Kitasato  Archives  of  Experimental  Medicine.    Tokyo,  1917-. 
Liverpool  School  of  Tropical  Medicine,  Memoirs.    Liverpool. 
Malariologia.    Rome,  1908-. 

Medical  Department,  United  Fruit  Company,  Annual  Reports.    New  York,  1912-. 
Memorias  do  Institute  Oswaldo  Cruz.    Rio  de  Janeiro,  1909-. 
Parasitology.    Cambridge,  England,  1908-. 
Philippine  Journal  of  Science,  Series  B.    Manila,  1906-. 
Redia.    Florence,  Italy,  1903-. 

Reports  of  the  Wellcome  Research  Laboratory.    Khartum,  1906-. 
Review  of  Applied  Entomology,  Series  B  (Medical  and  Veterinary).    London, 
1913-.     (Contains  reviews  of  practically  all  literature  in  the  field  of  medical 
and  veterinary  entomology;  each  volume  is  thoroughly  indexed  by  author  and 
subject.) 

Rev.  Inst.  Salubr.  y  Enferm.  Trop.    Mexico,  D.F.,  1939-. 
Royal  Society  of  London,  Proceedings,  Series  B.    London,  1905-. 
Scientific  Memoirs  by  Officers  of  the  Medical  and  Sanitary  Department  of  the 

Government  of  India.    Calcutta. 
Sleeping  Sickness  Bureau  Bulletin.    London,  1908-1912.     (Continued  as  Tropical 

Diseases  Bulletin.) 

Sleeping  Sickness  Commission  of  the  Royal  Society,  Reports.    London,  1903-. 
Transactions  of  the  Congresses  of  the  Far  Eastern  Association  of  Tropical  Medi- 
cine.    1911-. 
Transactions  of  the  Royal  Society  of  Tropical  Medicine  and  Hygiene.    London, 

1907-. 
Tropical  Diseases  Bulletin.    London,  1912-.     (The  most  valuable  publications  for 

it  contains  critical  reviews  of  all  literature  within  its  field;  well  indexed.) 
Tropical  Veterinary  Bulletin.    London,  1912-. 

United  States  Department  of  Agriculture.    Bulletins,   Reports,  Circulars,  etc. 
Washington,  D.C. 

Bureau  of  Animal  Industry,  Bulletins,  Reports,  Circulars,  etc. 
Bureau  of  Entomology,  Bulletins,  Reports,  Circulars,  etc. 

United  States  Public  Health  Service,  Weekly  Reports,  Bulletins,  publications  of 
various  kinds.    Washington,  D.C. 
Hygienic  Laboratory,1  Bulletins,  etc. 

1  Now  known  as  the  National  Institute  of  Health. 


16  MEDICAL  ENTOMOLOGY 

BOOKS  OF  IMPORTANCE  TO  THE  MEDICAL 
ENTOMOLOGIST 

Alcock,  A.    Entomology  for  medical  officers.     2nd  ed.    London,  1920. 

Belding,  D.  L.    Textbook  of  clinical  parasitology.    New  York  and  London,  1942. 

Brumpt,  E.     Precis  de  parasitologie.    4th  ed.     Paris,  1927. 

,  and  Neveu-Lemaire,  M.    Travaux  pratique  de  parasitologie.    Paris,  1929. 

Byam,  W.,  and  Archibald,  R.  G.  (editors).  The  practice  of  medicine  in  the  tropics. 
London,  1921-1923.  3  vols. 

Carpenter,  G.  D.  H.    A  naturalist  on  Lake  Victoria.    London,  1920. 

Castellani,  A.,  and  Chalmers,  A.  J.  Manual  of  tropical  medicine.  3rd  ed.  Lon- 
don, 1919. 

Chandler,  A.  C.     Introduction  to  human  parasitology.     8th  ed.    New  York,  1949. 

Comstock,  J.  H.    An  introduction  to  entomology.     9th  ed.    Ithaca,  N.Y.,  1947. 

Craig,  C.  F.     A  manual  of  the  parasitic  protozoa  of  man.     Philadelphia,  1926. 

,  and  Faust,  E.  C.    Clinical  parasitology.    Philadelphia,  1943. 

Culbertson,  J.  T.     Immunity  against  animal  parasites.     New  York,  1941. 

Doane,  R.  W.    Insects  and  disease.    New  York,  IQIO. 

Ehlers,  V.  M.,  and  Steel,  E.  W.     Municipal  and  rural  sanitation.     New  York,  1927. 

Ewing,  H.  E.    A  manual  of  external  parasites.    Springfield,  111.,  1929. 

Fantham,  H.  B.,  Stephens,  J.  W.  W.,  and  Theobald,  F.  V.  The  animal  parasites  of 
man.  London  and  New  York,  1916. 

Faust,  E.  C.     Human  helminthology.     2nd  ed.     Philadelphia,  1939. 

Folsom,  J.  W.  Entomology,  with  special  reference  to  its  biological  and  economic 
aspects.  3rd  ed.  Philadelphia,  1922. 

Fox,  C.     Insects  and  disease  of  man.     Philadelphia,  1925. 

Hall,  M.  C.  Arthropods  as  intermediate  hosts  of  helminths.  Smithsonian  Misc. 
Coll.,  81,  No.  15,  1929. 

Hegner,  R.  W.,  Root,  F.  M.,  and  Augustine,  D.  L.  Animal  parasitology.  New 
York,  1928. 

,  Root,  F.  M.,  Augustine,  D.  L.,  and  HufT,  C.  G.  Parasitology  with  special 

reference  to  man  and  domesticated  animals.  New  York,  1938. 

Henneguy,  L.  F.    Les  insectes.    Paris,  1904. 

Herms,  W.  B.    Medical  and  veterinary  entomology.    3rd  ed.    New  York,  1939. 

Herrick,  G.  W.  Insects  injurious  to  the  household  and  annoying  to  man.  New 
York,  1926. 

Howard,  L.  O.  A  history  of  applied  entomology.  Smithsonian  Misc.  Coll.,  Vol. 
84,  1930. 

.    The  insect  menace.    New  York,  1931. 

Hull,  T.  G.,  et  al.  Diseases  transmitted  from  animals  to  man.  3rd  ed.  Spring- 
field, 111.,  1947. 

Imms,  A.  D.    A  general  textbook  of  entomology.    3rd  ed.    London,  1934. 


ARTHROPODS  AND  HUMAN  DISEASE  17 

International  Congress  of  Tropical  Medicine  and  Malaria.    Proceedings  of  the 

fourth  International  Congress,  1948.    Washington,  D.C.,  1949.    2  vols. 
Laloy,  L.    Parasitisme  et  mutalisme  dans  la  nature.    Paris,  1926. 
Mackie,  T.  T.,  Hunter,  G.  W.,  and  Worth,  C.  B.    A  manual  of  tropical  medicine. 

Philadelphia,  1945. 

Manson-Bahr,  P.  H.     Manson's  tropical  diseases,     nth  ed.    London,  1940. 
Martini,  E.    Lehrbuch  de  medizinschen  Entomologie.    Jena,  1923. 
Mense,  C.  (editor).    Handbuch  de  Tropen-Krankheiten.    3rd  ed.     1924-1929.    5 

vols. 

Napier,  L.  E.  The  principles  and  practice  of  tropical  medicine.  New  York,  1946. 
Neveu-Lemaire,  M.  Traite  d'helminthologie  medicale  et  vcterinaire.  Paris,  1936. 
Patton,  W.  S.,  and  Cragg,  F.  W.  A  textbook  of  medical  entomology.  Calcutta 

and  London,  1913. 
,  and  Evans,  A.  M.     Insects,  ticks,  mites,  and  venomous  animals  of  medical 

and  veterinary  importance.     Part  i,  Medical;  Part  H,  Public  health.    Croydon, 

England,  1929-1931. 

Riley,  W.  A.,  and  Johannsen,  O.  A.    Medical  entomology.    New  York,  1932. 
Rosenau,  M.  J.    Preventive  medicine  and  hygiene.    5th  ed.    New  York,  1927. 
Ross,  Sir  Ronald.     The  prevention  of  malaria.     London,  1910. 
Roy,  D.  N.     Entomology   (medical  and  veterinary).     Calcutta,   1946. 
Russell,  P.  M.,  West,  L.  S.,  and  Manwcll,  R.  D.     Practical  malariology.    Philadel- 
phia, 1946. 

Scott,  H.  H.    A  history  of  tropical  medicine.    London,  1939.    2  vols. 
Smart,  John.    A  handbook  for  the  identification  of  insects  of  medical  importance. 

British  Museum,  London,  1943.     2nd  ed.,  1948. 
Stiles,  C.  W.,  and  Hassall,  A.     Key-catalogue  of  the  Crustacea  and  arachnoids  of 

importance  in  public  health.     U.S.  Pub.  Hlth.  Serv.,  Hyg.  Lab.  Bull.  148,  1927. 
Strong,  R.  P.    Stitt's  diagnosis,  prevention  and  treatment  of  tropical  diseases. 

Philadelphia,  1943.     2  vols. 
Symposia  (all  by  many  authors): 

A  symposium  on  human  malaria.     (Amer.  Assoc.  Adv.  Sci.,  Pub.  15.)     Wash- 
ton,  D.C.,  1941. 

A  symposium  on  relapsing  fever  in  the  Americas.     (Ibid.,  Pub.  18.)     Washing- 
ton, D.C.,  1942. 

Virus  and  rickettsial  diseases.    Cambridge,  Mass.,  1940. 

Taliaferro,  W.  H.    The  immunology  of  parasitic  infections.    New  York,  1929. 
van  Zwaluwenburg,  R.  H.    The  interrelationships  of  insects  and  roundworms. 

Hawaii  Sugar  Planters  Assoc.,  Bull.  Exp.  Sta.,  No.  20  (Ent.  ser.),  1928. 
Wardle,  R.  A.    The  problems  of  applied  entomology.    New  York,  1929. 
Watson,  M.    Rural  sanitation  in  the  tropics.    New  York,  1915. 
Wenyon,  C.  M.    Protozoology.    London,  1926.    2  vols. 


CHAPTER  II 


The  Arthropoda 


THE  Arthropoda  constitute  the  largest  of  the  animal  phyla.  They  are 
bilaterally  symmetrical  animals.  The  body  is  divided  into  rings  or  seg- 
ments of  which  several  or  many  bear  jointed  appendages.  They  possess  an 
exoskeleton  composed  mainly  of  chitin.  During  growth  the  external  skeleton 
is  periodically  molted  in  its  entirety.  The  nervous  system  consists  of  a  pair  of 
ganglia  to  each  segment,  the  ganglia  being  connected  longitudinally  and  lat- 
erally by  commissures.  It  is  located  below  the  gut  and  forms  a  collar  about  it 
in  the  head  where  the  brain  is  located.  The  blood  circulatory  system  consists 
of  a  longitudinal  dorsal  vessel  or  heart.  It  is  perforated  and  contractile,  the 
pulsations  usually  proceeding  from  the  posterior  to  the  anterior  end.  There 
is  no  closed  system  of  blood  vessels,  the  blood  flowing  freely  about  the  internal 
organs. 

CLASSIFICATION  OF  THE  ARTHROPODA 

The  phylum  is  divided  into  a  rather  large  number  (about  thirteen)  of  classes. 
Only  five  of  these  are  of  interest  to  the  student  of  medical  entomology.  Four 
of  the  five  classes  will  be  dealt  with  in  some  detail  in  the  following  chapters. 
In  order  not  to  burden  the  text  with  too  much  morphological  detail  the  main 
structures  of  each  class  will  be  given  under  the  discussion  of  the  group.  The 
following  key  will  aid  in  separating  the  main  classes  of  the  Arthropoda : 

1.  With  two  pairs  of  antennae  and  usually  at  least  five  pairs  of  ambulatory 

legs;    respiration   by   means   of  blood   gills;    all   aquatic   or   semi- 
aquatic    Crustacea 

2.  Without  antennae;  with  only  four  pairs  of  ambulatory  legs;  respiration 

aerial  by  means  of  trachea  or  the  surface  of  the  body.  (Scorpions, 
spiders,  mites,  etc.)  Arachnida 

3.  With  only  one  pair  of  antennae;  respiration  aerial 4 

4.  With  only  three  pairs  of  legs  and  usually  with  wings  in  the  adult  state. 


THE  ARTHROPODA  19 

(Insects)   Hexapoda 

With  more  than  three  pairs  of  legs;  wings  absent 5 

5.  With  two  pairs  of  legs  on  many  of  the  body  segments.  (Millepedes). 

Diplopoda 

With  one  pair  of  legs  on  each  of  the  body  segments.  (Centipedes). 
Chilopoda 

THE  CLASS  CRUSTACEA 

The  Crustacea  constitute  a  large  class  of  almost  exclusively  aquatic  animals. 
They  occupy  ponds,  lakes,  and  streams  and  are  the  dominant  form  of  animal 
life  in  the  sea.  Some  species,  such  as  sow  bugs  and  pill  bugs,  are  terrestrial  and 
are  generally  found  in  damp  situations.  The  more  common  representatives  are 
the  crayfishes,  lobsters,  shrimps,  water  fleas,  etc.  In  the  waters  of  the  world  they 
play  a  part  closely  parallel  to  that  which  insects  play  on  the  land.  The  great 
majority  are  free-living,  feeding  on  aquatic  plants,  preying  on  animals,  and 
performing  the  important  function  of  scavengers  of  the  waters.  Like  insects, 
many  species  are  represented  by  enormous  numbers  of  individuals,  and  the 
waters  teem  with  their  countless  millions.  The  minute  Crustacea  furnish  the 
main  food  for  the  larger  aquatic  animals.  Despite  their  numbers  and  abun- 
dance, comparatively  few  species  are  known  to  play  a  part  in  the  transmission 
of  human  parasites. 

BRIEF  SYNOPSIS  OF  THE  CRUSTACEA 

The  class  Crustacea  is  divided  into  two  subclasses,  the  Entomostraca  and 
the  Malacostraca.  Both  of  these  subclasses  contain  a  few  species  that  serve  as 
intermediate  hosts  of  human  parasites. 

THE  SUBCLASS  ENTOMOSTRACA:  This  subclass  contains  an  im- 
mense number  of  small  marine  and  fresh-water  forms.  Most  of  them  are 
free-living,  though  some  lead  a  parasitic  life.  They  are  of  great  importance 
since  they  constitute  the  main  food  supply  of  the  larger  aquatic  animals,  espe- 
cially the  fishes.  This  subclass  is  divided  into  four  orders— Phyllopoda,  Ostra- 
coda,  Copepoda,  and  Cladocera.  Although  representatives  of  all  these  orders 
serve  as  intermediate  hosts  of  animal  parasites,  only  the  members  of  the  Cope- 
poda have  been  so  far  involved  in  human  infections. 

THE  SUBCLASS  MALACOSTRACA:  This  group  contains  the  larger 
Crustacea  such  as  the  lobsters,  crayfishes,  and  crabs.  It  is  divided  into  a  number 
of  orders,  of  which  only  the  Decapoda  are  known  to  act  as  intermediate  hosts 
of  human  parasites. 


20  MEDICAL  ENTOMOLOGY 

CRUSTACEA  AND  HUMAN  DISEASE 

A  few  of  the  Crustacea  bear  an  important  relation  to  human  diseases.  Cer- 
tain of  them  act  as  secondary  or  intermediate  hosts  of  human  parasites. 
Dracunculus  medinensis,  the  Guinea  worm,  passes  its  larval  stage  in  various 
species  of  copepods  1  belonging  to  the  genus  Cyclops  (Fig.  i).  Man  and  other 
animals  become  infected  by  drinking  raw  water  containing  parasitized 
Cyclops  spp.  This  disease  has  been  known  from  antiquity,  and  Moses  referred 
to  it  as  "the  fiery  serpent."  When  infected  Cyclops  spp.  are  swallowed,  the 
larvae  of  Dracunculus  medinensis  escape  and  penetrate  the  wall  of  the  stomach 
or  intestine.  They  migrate  through  the  tissues,  lodging  at  last  in  the  sub- 
cutaneous connective  tissue.  It  requires  from  10  to  14  months  for  the  females 
to  reach  maturity.  The  females  measure  from  70  to  no  cm.  in  length.  When 
mature  the  females  produce  blisterlike  lesions  on  the  lower  extremities  as  the 
feet  and  ankles  (Fig.  2)  and  also  on  other  parts  of  the  body.  The  breaking 
of  these  lesions  enables  the  parasites  to  discharge  their  young — small  Hlarial 
worms.  These  are  discharged  whenever  the  infected  member  comes  in  contact 
with  fresh  water.  Dogs,  horses,  cattle,  and  other  animals  serve  also  as  hosts 
of  this  parasite  and  undoubtedly  aid  greatly  in  its  spread  and  prevalence  in 
any  region  where  it  has  become  established.  Owing  to  the  fact  that  no  clinical 
symptoms  appear  until  the  females  arc  mature  and  that  there  is  no  known 
method  of  early  diagnosis,  persons  harboring  this  parasite  may  unknowingly 
spread  it  from  one  region  to  another. 

The  presence  of  this  worm  causes  no  symptoms  of  disease  until  the  forma- 
tion of  the  lesions.  Then  occurs  intense  itching  followed  by  nausea,  vomiting, 
diarrhea,  severe  dyspnea,  and  giddiness.  These  conditions  are  supposed  to  be 
due  to  the  toxic  secretions  of  the  worm. 

The  Guinea  worm  is  widely  distributed.  It  occurs  over  vast  areas  in  Africa, 
Iran,  India,  southern  Russia,  the  islands  of  the  Caribbean  Sea,  the  Guianas,  and 
parts  of  Brazil.  It  is  also  found  in  North  America  in  fur-bearing  animals  such 
as  foxes,  raccoons,  minks,  and  dogs.  There  is  no  effective  treatment  except  the 
removal  of  the  worms.  Prophylaxis  consists  in  drinking  only  boiled  or  filtered 
water  and  in  preventing  infected  persons  from  coming  in  contact  with  water 
used  for  drinking  purposes. 

Another  important  human  parasite,  Diphyllobothrium  latum,  the  broad  fish 
tapeworm,  has  become  well  established  in  certain  sections  of  North  America. 
The  early  larval  stages  of  this  parasite  develop  in  certain  fresh-water  Crustacea 

1  These  are  frequently  called  "water  fleas,"  a  term  that  is  restricted  to  the  cladocerans 
(Daphnia  and  its  allies). 


THE  ARTHROPODA  21 

of  the  genera  Cyclops  and  Diaptomus.  These  infected  crustaceans  are  eaten 
by  plankton-feeding  fishes  such  as  pike,  pickerel,  and  turbot.  Within  the  fish 
the  parasitic  larvae  escape  and  penetrate  through  the  wall  of  the  stomach.  In 
the  course  of  a  few  days  these  larvae  imbed  themselves  in  the  fleshy  tissues, 
where  they  remain  in  a  sort  of  encysted  condition  (plerocercoids) .  Man  be- 
comes infected  by  eating  partially  cooked  or  raw  fish.  The  tapeworm  becomes 
mature  in  from  five  to  six  weeks  after  the  ingestion  of  the  larva  by  man. 


Fig.  i  (left).  Cyclops  sp.,  with  eggs  attached. 

Fig.  2  (center).  Guinea  worm  partially  extracted  from  the  fourth  toe.  (From  Castellani 
and  Chalmers,  Manual  of  Tropical  Medicine.) 

Fig.  3  (right).  Chelicera  of  a  spider,  somewhat  diagrammatic.  D,  duct  from  poison 
gland;  F,  fang;  O,  opening  of  poison  gland;  P,  poison  gland. 

This  parasite  is  widely  distributed  in  Europe,  parts  of  Africa,  and  in  Siberia, 
Japan,  and  Manchuria;  it  is  well  established  in  central  North  America.  The 
plerocercoids  have  been  found  in  fishes  from  most  of  the  large  lakes  of  the 
Canadian  prairies,  from  lakes  in  northern  Minnesota  and  northern  Michigan, 
and  from  the  Greak  Lakes  as  far  east  as  Lake  Erie.  As  cats,  dogs,  foxes,  bears, 
and  probably  other  fish-eating  animals,  as  well  as  man,  are  hosts  of  the  adult 
tapeworm,  the  widespread  distribution  of  this  parasite  is  assured. 

In  man  the  tapeworm  causes  a  rather  serious  disease.  The  clinical  symptoms 
are  those  of  severe  anemia,  reduced  hemoglobin  and  general  weakness. 
Prophylaxis  consists  in  the  thorough  cooking  of  all  fish  intended  for  food. 

The  lung  fluke,  Paragonimus  wester mani,  passes  part  of  its  larval  life  in 
fresh-water  crayfishes  and  crabs.  The  adults  are  found  in  the  lungs  of  man, 
cats,  dogs,  foxes,  wolves,  pigs,  and  many  other  animals.  It  occurs  principally 
in  the  Far  East  (Japan,  Korea,  Formosa,  French  Indo-China,  Siam,  Federated 


22  MEDICAL  ENTOMOLOGY 

Malay  States,  Bengal,  Assam,  Madras,  and  the  Philippines)  and  is  recorded 
from  parts  of  Africa,  the  Dutch  East  Indies  and  in  certain  areas  of  South  and 
Central  America.  The  life  cycle  of  the  fluke  is  rather  complicated,  involving  a 
snail  (a  species  of  the  genus  Melania)  and  then  a  fresh-water  crayfish  or 
crab.  Man  becomes  infected  by  eating  the  raw  flesh  of  these  animals.  The 
nature  of  the  diseased  condition  produced  by  this  worm  in  man  depends  on 
the  localization  of  the  parasite.  Though  normally  a  parasite  of  the  lungs,  it 
may  invade  various  organs,  even  the  brain.  As  no  effective  treatment  appears 
to  be  known,  it  would  seem  imperative  that  only  thoroughly  cooked  meat  of 
fresh-water  crayfishes  and  crabs  should  be  eaten. 

Table  2.  Interrelation  of  Crustacea  and  human  parasites. 


Parasite 

Organ  attacked 

Primary 
hosts 

Intermediate  hosts 

First 

Second 

Dracunculus 

Migrates  through 

Man,  cats, 

Cyclops 

None  required 

medinensis 

subcutaneous 

monkeys, 

bicuspidatus 

(Guinea  worm) 

tissues 

dogs,  foxes, 

C.  corona  t  us 

etc. 

Diphyllobothrium 

Intestine 

Man,  cats, 

Cyclops 

Esox  Indus 

la  turn 

dogs,  foxes, 

strenuus 

Stizostcdion 

(broad  fish 

bears,    pigs, 

Diaptomus 

I'ltreum 

tapeworm) 

mink, 

oregonensis 

S.  canadcnsc 

etc. 

D.  vulgar  is 

S.  griscum 

D.  gracilis 

l^ota  maculosa 

D.  graciliodes 

Pcrca  flavesccns 

and  many  others 

Paragonimus 

Lungs  and 

Man,  cats, 

Melania 

Astacus  japonicus 

wcstermant 

occasionally 

dogs,  wolves, 

liber  tin  a 

A.  si  mil  is 

(lung  fluke) 

other  organs 

pigs,  beavers, 

Melania  spp. 

Potamon  dchaani 

tigers,   etc. 

(snails) 

P.  obtusipes 

and  others 

THE  CLASS  ARACHNIDA 

Scorpions,  Pseudoscorpions,  Spiders,  Mites,  Ticks 

The  Arachnida  are  air-breathing  arthropods.  The  body  is  usually  divided 
into  two  regions — the  cephalothorax,  including  the  fused  head  and  thorax, 
and  the  abdomen.  The  abdomen  may  be  either  segmented  or  unsegmented. 
In  the  mites  and  ticks  the  entire  body  is  fused  and  forms  a  kind  of  sac.  The 
head  appendages  are  highly  modified.  The  antennae  are  lacking  and  the  eyes, 
when  present,  are  rather  simple  and  sessile.  In  the  adults  there  are  four  pairs 
of  ambulatory  legs  and  these  are  attached  to  the  cephalothorax.  The  first  stage 
or  larva  has  only  three  pairs  of  legs.  The  organs  of  respiration,  when  present, 


THE  ARTHROPODA  23 

consist  of  either  tracheae  or  book  lungs.  The  sexes  are  distinct  and  the  meta- 
morphosis is  incomplete,  the  young  closely  resembling  the  adult. 

The  arachnids  suck  the  juices2  of  their  victims  by  means  of  a  sucking 
stomach.  The  mouth  parts  are  adapted  either  for  crushing  their  prey  and 
sucking  up  the  liquid  portions  or  for  piercing  and  cutting  the  tissues  of  their 
hosts  (parasitic  forms)  in  order  to  obtain  blood.  The  mouth  parts  consist  of 
a  pair  of  cheliccrae  3  located  in  front  of  the  mouth  opening;  a  pair  of  pcdipalpi, 
the  palpi  or  palps,  situated  either  at  the  sides  of  the  mouth  or  immediately  be- 
hind it;  and,  in  many  forms,  a  peculiar  structure  known  as  the  hypostome. 
The  hypostome  is  most  highly  developed  in  some  of  the  parasitic  forms  and 
is  fully  discussed  later.  It  is  located,  when  present,  directly  beneath  the  mouth 
opening.  The  structure  of  the  cheliccrae  varies  greatly  in  the  different  orders 
of  the  Arachnida.  In  the  spiders  (Araneida)  each  chelicera  consists  of  a  large 
basal  segment  and  a  terminal  clawlike  one  (Fig.  3).  By  means  of  these 
appendages  the  spider  seizes  and  kills  its  prey.  Near  the  tip  of  the  claw  is 
the  opening  of  the  poison  gland.  In  the  parasitic  forms  (ticks,  etc.)  the  cheli- 
cerae  are  modified  to  serve  as  cutting  and  piercing  organs.  They  are  fully  dis- 
cussed and  illustrated  in  the  following  chapter.  The  pedipalpi  are  more  or 
less  leglike  in  all  the  groups  and  consist  of  four  to  six  segments.  In  the  spiders 
the  pcdipalpi 4  of  the  male  are  greatly  modified  into  very  specialized  organs 
for  the  transference  of  the  semen  to  the  females.  In  many  of  the  ticks  they 
serve  as  organs  for  the  protection  of  the  highly  developed  piercing  organs. 

SYNOPSIS  OF  THE  ARACHNIDA 

The  class  Arachnida  is  divided  into  nine  to  twelve  orders.  From  the  stand- 
point of  the  medical  workers,  only  six  of  these  orders  are  known  to  be  of  im- 
portance. Of  these  six,  only  one,  the  Acarina,  is  of  sufficient  importance  to  be 
treated  in  any  detail.  The  other  five  contain  forms  which  possess  poison  glands. 
Their  bites  or  stings,  when  they  do  attack  humans,  may  be  of  such  severity  as 
to  require  medical  attention.  Certain  of  these  forms  are  treated  in  a  brief 
chapter  (Chapter  xix)  dealing  with  the  poisons  of  arthropods. 

The  following  key  will  aid  in  separating  the  more  common  orders  of 
Arachnida. 


2  The  solpugids  and  the  harvestmen  (daddy  longlegs)  are  supposed  to  take  solid  food. 

3  The  chelicerae  are  homologous  to  the  second  antennae  of  the  Crustacea  and  have 
become  modified  into  prehensile  or  cutting  organs;  the  true  antennae,  the  first  antennae 
of  Crustacea,  are  lost  in  the  spiders.  In  insects  the  true  antennae  are  retained  but  the 
second  antennae  are  lost. 

4  For  an  extended  account  see  Comstock,  The  Spider  Boo\  (1948). 


24  MEDICAL  ENTOMOLOGY 

1.  Abdomen  distinctly  segmented 2 

Abdomen  not  distinctly  segmented 4 

2.  Abdomen  armed  with  a  taillike  prolongation.  (Scorpions)  ....  Scorpionida 
Abdomen  without  a  taillike  prolongation 3 

3.  Palpi  chelate  or  with  pincerlike  claws.  (Pseudoscorpions)  

Pseudoscorpionida 

Palpi  not  chelate  or  without  pincerlike  claws  Pedipalpida 

Solpugida 

4.  Abdomen  joined  to  the  cephalothorax  by  a  short,  narrow  stalk.  (Spi- 

ders)       Araneida 

Abdomen  fused  with  the  cephalothorax,  forming  a  saclike  body  .  .  Acarina 

THE  ORDER  ACARINA 

The  Acarina  are  rather  small  to  minute  arachnids.  The  largest,  such  as 
some  fully  gorged  ticks,  may  reach  a  length  of  nearly  25  mm.,  while  the  small- 
est rarely  exceed  0.25  mm.  in  length.  The  order  contains  a  large  number  of 
species.  Like  the  insects  and  crustaceans,  the  species  arc  noteworthy  for  the 
vast  number  of  individuals.  The  body  is  depressed  dorsoventrally  and  is  un- 
doubtedly an  adaptation  for  their  mode  of  life.  The  head,  thorax,  and  ab- 
domen are  fused,  giving  them  a  saclike  appearance.  In  some  cases  the  cephalo- 
thorax may  be  demarcated  from  the  abdomen  by  a  groove  or  furrow.  The  body 
may  be  partially  or  completely  covered  by  a  scutum  or  shield.  The  mouth  parts 
are  located  either  anteriorly  or  on  the  anterior  ventral  surface.  These  structures 
are  described  in  detail  in  the  discussion  of  the  various  orders  of  mites.  Eyes  are 
either  present  or  absent;  when  present  they  consist  of  simple  convex  facets 
and  are  generally  located  on  the  margin  of  the  scutum  or  on  folds  on  the 
ventral  surface.  The  respiratory  organs,  when  present,  consist  of  tracheae 
connected  to  the  exterior  by  means  of  spiracles.  The  spiracles  are  usually 
located  on  chitinized  plates  and  may  be  either  in  pairs  or  singly.  Some  groups, 
as  the  sarcoptic  and  demodectic  mites,  lack  tracheae,  the  animals  breathing 
directly  through  their  body  wall.  The  sexes  are  distinct,  the  males  generally 
smaller  than  the  females.  The  opening  of  the  reproductive  organs  is  located 
on  the  ventral  surface,  usually  directly  behind  the  mouth  parts.  The  digestive 
system  consists  of  a  straight  tube,  often  supplied  with  numerous  tubular 
branches.  The  anal  opening  is  either  ventral  or  dorsal,  rarely  terminal. 

The  mites  exhibit  a  great  variety  of  habits.  They  live  principally  on  fluid 
nutriment,  which  is  obtained  from  living  plants  or  animals  or  from  decaying 
organic  matter.  Many  are  free-living  and  predaceous,  and  large  numbers  are 
parasitic.  The  parasitic  mites  are  of  great  interest  on  account  of  the  wide  variety 


THE  ARTHROPODA  25 

of  their  habitats.  Many,  like  the  ticks,  are  external  parasites  of  animals,  feeding 
on  the  blood  of  their  hosts;  some,  like  many  Sarcoptidae  and  Demodicidae, 
burrow  in  the  skin  of  their  hosts  and  cause  severe  itching  and  diseased  condi- 
tions; others,  such  as  Halarachnc  spp.  and  Pneumonyssus  spp.,  are  found  in 
the  lungs  of  seals  and  Old  World  monkeys,  respectively ;  some,  like  the  species 
of  Trombidiidae,  are  parasitic  in  their  larval  stage  (chiggers)  but  invariably 
free-living  and  herbivorous  or  predaceous  as  nymphs  and  adults.  Many  species 
attack  birds  and  feed  on  the  scales  and  feathers  or  even  invade  the  lungs,  air 
sacs,  and  hollow  bones  (as  Cytoleichtts  nudus) ;  while  others,  such  as  the 
Tyroglyphidae,  feed  on  stored  food  products,  and  man  may  be  attacked  by 
them  when  handling  such  material.  Of  still  greater  importance  has  been  the 
discovery  that  many  bloodsucking  mites  may  serve  as  intermediate  hosts  of 
various  pathogenic  organisms  of  man  and  animals.  In  recent  years  the  part 
played  by  the  Acarina  in  the  transmission  of  pathogenic  organisms  of  man  and 
animals  has  been  studied  by  numerous  investigators,  and  brief  accounts  of  this 
work  will  be  found  under  the  discussion  of  the  various  groups. 

BRIEF  SYNOPSIS  OF  THE  ACARINA 

The  Acarina  is  divided  into  a  number  of  suborders  (usually  eight),  based 
largely  on  the  structure  of  the  respiratory  system.  Five  of  these  suborders 
contain  mites  that  arc  known  to  be  parasitic  and  have  some  relation  to  man 
either  as  direct  agents  in  producing  diseased  conditions  or  as  vectors  of  patho- 
genic organisms.  The  classification  of  the  order  is  far  from  satisfactory,  but  the 
following  key  will  aid  the  student  in  placing  parasitic  forms: 

KEY  TO  THE  SUBORDERS  AND  SUPERFAMILIES  OF 
PARASITIC  ACARINA5 

1.  Body  vermiform,  much  prolonged  behind;  distinctly  annulate  or  ringed; 

legs  rudimentary  and  apparently  composed  of  only  three  segments;  pa- 
rasitic in  the  hair  follicles  or  sebaceous  glands  of  mammals 

Suborder  BRACHYPODA 

There  is  only  one  superfamily  Demodicoidea 

Body  not  vermiform,  not  prolonged  behind;  not  parasitic  in  the  hair 
follicles  or  sebaceous  glands  of  mammals 2 

2.  Tracheae  present;  spiracular  openings  two,  one  on  each  side  of  the  body 

usually  above  the  third  or  fourth  coxa  or  a  little  behind  them;  spiracles 

5  There  are  more  recent  classifications,  but  this  is  more  easily  understood  and  should 
meet  the  needs  of  most  workers  in  medical  entomology. 


26  MEDICAL  ENTOMOLOGY 

opening  through  distinct  stigmatal  plates Suborder  MESOSTIGMATA 

2a.  Hypostome  large,  furnished  beneath  with  numerous  recurved  teeth; 

venter  with  furrows;  skin  leathery;  large  forms.  (The  ticks)  .... 

Superfamily  Ixodoidea 

2b.  Hypostome  small  without  recurved  teeth  beneath;  venter  without 

furrows  but  often  with  coriaceous  shields 

Superfamily  Parasitoidea 

Tracheae,  when  present,  not  opening  through  lateral  spiracles 3 

3.  Tracheae  usually  present,  the  spiracular  openings  near  or  at  the  bases 

of  the  chelicerae;  larvae  frequently  parasitic,  the  adults  free-living 

Suborder  PROSTJGMATA 

33.  Last  segment  of  the  palpus  never  forms  a  "thumb"  to  the  preceding 

joint;  body  with  few  hairs  Superfamily  Eupodoidea 

3b.  Last  segment  of  the  palpus  forms  a  "thumb"  to  the  preceding  joint, 

which  ends  in  a  claw Superfamily  Trombidoidea 

Tracheae,  when  present,  not  opening  at  the  bases  of  the  chelicerae 4 

4.  Tracheae  present;  body  divided  into  cephalothorax  and  abdomen,  and  the 

abdomen  shows  evidence  of  segmentation;  females  with  a  clavate  hair 

between  the  first  and  second  pair  of  legs Suborder  IIETEROSTIGMATA 

This  suborder  contains  one  Superfamily  Tarsonemoidea 

Tracheae  absent;  no  division  between  cephalothorax  and  abdomen;  ab- 
domen without  true  segmentation;  females  never  with  a  clavate  hair 

between  the  first  and  second  pair  of  legs Suborder  ASTIGMATA 

43.  Surface  of  the  body  with  fine  parallel  lines  or  folds;  tarsi  often  pro- 
vided with  stalked  suckers;  parasitic  in  all  stages,  chiefly  on  verte- 
brates    Superfamily  Sarcoptoidea 

4b.  Surface  of  the  body  without  fine  parallel  lines  or  folds;  tarsi  with- 
out stalked  suckers;  adults  never  true  parasites 

Superfamily  Tyroglyphoidea 

REFERENCES 
CRUSTACEA 

Calmen,  W.  T.    The  life  of  the  Crustacea.    New  York,  1911. 

Essex,  H.  E.  Early  development  of  Diphyllobothrium  latum  in  northern  Minne- 
sota. Jl.  Parasit.,  14:  106-109,  1927. 

Fairly,  N.  H.,  and  Listen,  W.  G.  Studies  on  the  pathology  of  dracontiasis.  Ind. 
Jl.  Med.  Res.,  n:  922,  1924. 

Faust,  E.  C.    Human  helminthology.    Philadelphia,  1939. 


THE  ARTHROPODA  27 

Moorthy,  V.  N.     A  redescription  of  Dracunculus  medinensis.    Jl.  Parasit.,  23:  220- 

224,  1937. 
.     Observations  on  the  development  of  Dracunculus  medinensis  larvae  in 

Cyclops.    Amer.  Jl.  Hyg.,  27:  437-460,  1938. 
,  and  Sweet,  W.  C.    Further  notes  on  the  experimental  infection  of  dogs  with 

Dracunculus  medinensis.    Ibid.,  27:  301-310,  1938. 

Smith,  G.     The  Crustacea.    In  Cambridge  Natural  History,  4:  1-252,  1909. 
Vergeer,  T.     The  broad  tapeworm  in  America.    Jl.  Inf.  Dis.,  44:  i-n,  1929. 
Ward,  H.  B.     Animal  parasites.     In  Abt's  Pediatrics,  8:  912-1065,  1926. 
.     Studies  on  the  broad  fish  tapeworm  in  Minnesota.    Jl.  Amer.  Med.  Assoc., 

92:  389-390,  1929. 
Yoshida,  S.     On  the  intermediate  hosts  of  the  lung  distome,  P.  wcstcrmanni  Ker- 

bcrt.     Jl.  Parasit.,  2:  111-118,1916. 

ARACHNIDA— GENERAL  REFERENCES 

Comstock,  J.  H.     The  spider  book.     Ithaca,  N.Y.,  1948. 

Emerton,  J.  H.     The  common  spiders  of  the  United  States.     Boston,  1902. 

McCook,  C.  American  spiders  and  their  spinning  works.  Philadelphia,  1889- 
1893.  3  vols. 

Warburton,  C.  Scorpions,  spiders,  mites,  ticks,  etc.  In  Cambridge  Natural  His- 
tory, 4:  297-473,  i909- 

AC ARINA— G  EN  ER  AL  REFERENCES 

Banks,  N.  A.     Catalogue  of  the  Acarina  or  mites  of  the  United  States.     Proc.  U.S. 

Nat.  Mus.,  32:  595-625,  1907. 
— «—.     The  Acarina  or  mites.    U.S.  Dept.  Agr.,  Office  of  the  Secretary,  Rept.  108, 

1915. 

Canestrini,  G.     Prospetto  dell'  Acarofauna  italiana.     Padua,  1885-1897.     7  parts. 
Ewing,  H.  E.     A  systematic  and  biological  study  of  the  Acarina  of  Illinois.     Univ. 

111.  Bull.,  Vol.  7,  No.  17,  1910. 
.     The  origin  and  significance  of  parasitism  in  the  Acarina.    Acad.  Sci.  St. 

Louis,  Trans.,  Vol.  21,  No.  i,  1912. 
Vitzhum,  H.  G.    Acari.    In  W.  Kiikenthal  and  T.  Krumbach,  Handbuch  der 

Zoologie,  3  (zwcite  Halite):  i— 160,  1931. 
.     Acarina.  In   Bronns,   Klassen   und   Ordnungen  des  Tierreichs.    Funfter 

Band,  IV  Abteilung,  5  Buch,  1-3  Lieferung:  1-1011.     Leipzig,  1940-1942. 


CHAPTER  III 


The  Order  Acarina;  Ixodoidea 


THE  ticks  constitute  the  superfamily  Ixodoidea.  They  are  readily  distin- 
guished from  all  other  mites  by  the  possession  of  a  pair  of  stigmatal  plates 
(Figs.  4,5)  situated  laterally  above,  and  usually  posterior  to,  the  fourth  pair  of 
legs.  Furthermore  their  large  size  and  leathery  skin  distinguish  them  from  all 
other  mites.  The  superfamily  consists  of  two  families — the  Ixodidae,  in  which 


Fig.  4.  Dcrmacentor  andcrsoni.  Left:  Dorsal  view  of  male.  Right:  Ventral  view  of  male. 
A,  anus;  AG,  anal  groove;  BC,  basis  capituli;  C.  capitulum;  Cr,  cervical  groove;  E,  eye; 
F,  festoons;  Ga,  genital  groove;  GO,  genital  opening;  Lg,  lateral  groove  in  scutum; 
S,  scapula;  Sp,  spiracle;  I-IV,  the  legs. 

the  species  are  recognized  by  the  presence  oi  a  dorsal  shield  or  scutum  and  the 
capitulum  is  located  at  the  anterior  margin  and  is  visible  from  the  dorsal  sur- 
face, and  the  Argasidae,  in  which  the  do^al^shjelc^is  absent  and  the  capitulum' 
is  ventral  and  rarely  visible  from  the  dorsal  view  (Figs.  12-14).  The  capitulum 
is  a  specialized  organ  and  its  structure  is  the  most  characteristic  feature  of 


THE  ORDER  ACARINA  29 

ticks.  The  group  is  not  a  large  one  in  number  of  species.  Probably  not  more 
than  four  hundred  are  known  at  present.  In  number  of  individuals,  ticks  are 
often  very  abundant,  and  constitute  one  of  the  most  important  groups  of  animal 
ectoparasites  and  vectors  of  diseases.  All  ticks  are  parasites  of  vertebrates  and 
are  most  abundant  on  mammals  and  reptiles,  though  they  are  also  common 
on  birds  and  amphibia.  Their  food  consists  entirely  of  blood  and  lymph  taken 
from  their  hosts.  The  life  cycles  of  the  various  species  of  ticks  differ  greatly, 
some  requiring  only  a  single  host,  whereas  others  drop  from  their  hosts  after 
each  feeding  or  remain  on  their  hosts  for  two  feedings  and  then  drop  of! 
(Fig.  20).  Owing  to  their  elastic,  leathery  skins,  ticks,  especially  those  belong- 


Fig.  5.  Dcrmacentor  andersoni.  Left:  Dorsal  view  of  female.  Right:  Ventral  view  of 
female.  A,  anus;  AG,  anal  groove;  BC,  basis  capituli;  Cr,  chelicera;  E,  eye;  F,  festoons; 
Ga,  genital  groove;  GO,  genital  opening;  H,  hypostome;  Mg,  marginal  groove;  P,  palpus; 
Pr,  porose  areas;  Sc,  scutum;  Sp,  spiracle. 

ing  to  the  family  Ixodidac,  can  engorge  an  enormous  amount  of  blood  and 
increase  greatly  in  size  (Fig.  23).  In  general,  ticks  vary  in  size  from  less  than 
2  mm.  to  nearly  25  mm.  (some  fully  gorged  females). 

Ticks  are  widely  distributed  throughout  the  world  but  are  most  abundant 
in  the  tropics  and  subtropics.  Only  two  species,  Ornithodoros  moubata  and 
O^rudis,  are  primarily  restricted  to  man.  Man  is,  however,  used  intermittently 
as  a  host  by  a  rather  large  number  of  species.  In  recent  years  ticks  have  been 
shown  to  be  the  intermediate  hosts  and  distributors  of  a  large  number  of  very 
important  diseases  of  man  and  of  domestic  and  game  animals.  Furthermore, 
tick  bites  arc  known  to  produce  rather  serious  effects,  even  death,  in  man  and 
animals  (lambs  and  calves,  etc.).  On  account  of  these  complicated  interrela- 
tions ticks  have  become  very  important  factors  in  public  health  and  human 
welfare. 


30  MEDICAL  ENTOMOLOGY 

MORPHOLOGY  OF  TICKS 
EXTERNAL  ANATOMY 

THE  IXODIDAE:  The  external  structures  of  ticks  are  primarily  adapted 
to  meet  the  needs  of  parasitic  life.  The  body  is  saclike,  there  being  no  divisions 
between  the  head,  thorax,  and  jihdomgn-  (Figs.  4,5) .  It  is  somewhat  depressed 
dorsoventrally,  especially  so  in  the  imengorgecl  tick  and  in  the  early  stages. 
The  body  bears  on  the  dorsum  a  shield  or  scutum,  which  varies  in  size  and 
shape  according  to  the  species.  In  the  female  the  shield  is  small,  but  in  the 
male  it  almost  covers  the  entire  dorsal  surface  (Figs.  4,5).  The  eyes,  when 
present,  are  located  on  or  near  the  margin  of  the  anterior  half  of  the  scutum 
(Figs.  4,5  E).  There  are  four  pairs  of  legs  (in  the  larvae  only  three  pairs  are 
present). 

THE  CAPITULUM.  Located  in  an  emargination,  the  camerostome,  at 
the  anterior  end  of  the  body  is  the  specialized  head,  false  head^or  capitulum 
(Figs.  4,6).  The  basal  portion,  basis  capituli  (BC),  consists 'of  a  rather  broad, 
dense,  sclerotized  ring,  constricted  somewhat  posteriorly  to  form  a  neck  that 
fits  into  the  anterior  opening  of  the  body  cavity.  Within  and  extending  beyond 
the  ring  are  the  essential  mouth  parts  concerned  in  piercing  the  host  and 
extracting  blood.  The  basis  capituli  varies  in  shape  in  the  different  genera 
of  ticks;  it  may  appear  from  the  dorsal  view  as  hexagonal,  rectangular,  or 
even  triangular  and  may  bear  ridges,  sharp  angles,  or  other  distinguishing 
characteristics.  Females  have  a  pair  of  depressions  on  the  dorsal  surface  of  the 
basis  capituli.  In  these  depressions  lie  the  porose  areas  (Fig.  5  Pr),  which  consist 
of  numerous  open  pores.  They  are  of  considerable  taxonomic  value,  but  their 
exact  function  is  not  known. 

THE  PALPI  OR  PEDIPALPI:  These  structures  arise  from  the  lateroventral  margin 
of  the  basis  capituli.  Each  palpus  consists  of  four  segments  (Fig.  6).  The  first 
segment  is  usually  very  short  and  not  easily  recognized  when  the  capitulum 
is  examined  from  the  dorsal  side.  The  second  and  third  segments  are  longer, 
and  the  fourth  segment  is  located  in  a  deep  pit  or  depression  on  the  third.  The 
fourth  segment  is  usually  furnished  with  a  crown  or  row  of  stiff  hairs,  which 
may  have  a  sensory  function.  In  many  of  the  Ixodidae  the  palpi  are  grooved 
along  their  inner  face  and  form  shields  for  the  chelicerae  and  hypostome.  The 
margins  of  the  grooves  are  commonly  supplied  with  long  or  short  spines  of 
various  shapes  (Fig.  6). 

THE  HYPOSTOME:  A  dartlike  structure,  the  hyjgostpme  (Fig.  6  Hph),  arises 
from  the  median  ventral  surface  of  the  basis  capituli  and  protrudes  forward 


THE  ORDER  ACARINA  31 

directly  beneath  the  mouth  opening  (Fig.  7  Hp).  It  consists  of  a  basaljiortion, 
which  is  smooth  and  convex  ventrally,  and  a  distal  portion,  the  ventral  surface 
of  which  is  provided  with  longitudinal  rows  of  backward-projecting  teeth. 
It  is  divided  by  a  median  fissure  so  that  the  teeth  are  separated  into  two  series 
of  files.  The  number  of  rows  of  teeth  and  the  number  of  teeth  in  the  rows 


Hph 


EA 


Fig.  6.  Ventral  view  of  capitulum  of  Dermaccntor  andersoni.  BC,  basis 
capituli;  CS,  cheliceral  sheath;  EA,  external  article;  Hph,  hypostome;  I  A,  in- 
ternal article;  Pip,  palpus  (I-IV,  segments  of  palpus) ;  Sh,  shaft  of  chelicera. 

differ  in  the  various  species  and  provide  good  characters  for  identification. 
The  hypostome,  when  embedded  in  the  tissues  of  the  animal,  acts  as  an  effective 
anchor  in  maintaining  the  position  of  the  tick.  In  fact,  unless  great  care  is 
exercised  in  removing  ticks,  the  hypostome  is  frequently  left  in  the  host  or  a 
portion  of  the  host's  skin  is  removed  with  the  tick. 

THE  CHELICERAE:  The  chelicerae  are  the  most  important  cutting  organs  of 


32  .       MEDICAL  ENTOMOLOGY 

the  mouth  parts,  and  their  structure  is  complicated.  They  arise  directly  above 
the  mouth  opening  and  consist  of  a  pair  of  cylindrical  shafts,  each  lying  within 
its  sheath,  the  so-called  "chelicera  1  sheaths"  (Figs.  6,8).  The  sheaths  arise  as 
prolongations  of  the  anterior  margin  of  the  basis  capituli  and  lie  in  close  contact 
with  each  other.  The  distal  extremity  of  each  sheath  forms  a  flexible  mem- 
brane, which  invaginates  and  is  attached  to  the  chelicera  directly  behind  the 
digits  or  articles  (Fig.  8  CS).  In  this  way  the  sheath  forms  a  protection  for  the 
digits  when  they  are  withdrawn.  The  outer  surface  of  the  sheath,  except 
the  basal  part,  is  usually  covered  with  minute  denticles,  which  give  it  the  appear- 
ance of  a  fine  file.  Each  ctiiej[i£ejra,  the  so-called  "mandible,"  consists  of  a 


Ge 


Cl 


RM 


DM 


Fig.  7.  Median  longitudinal  section  through  the  capilulum  of  a  tick  to  show  the  rela- 
tions of  the  internal  and  external  parts.  BC,  buccal  cavity;  Cl,  chelicera;  D,  digits  of 
chelicera;  DM,  depressor  muscles  of  capitulum  FM,  flexor  muscles  of  the  digits;  Ge, 
Gene's  organ;  Hp,  hypos  tome;  LM,  levator  muscles  of  capitulum;  MO,  opening  into 
pharynx;  O,  opening  of  salivary  duct;  Ph,  pharynx;  RM,  retractor  muscles  of  chelicera; 
Sc,  scutum;  SD,  salivary  duct.  (Diagrammatic;  after  Nuttall  and  Warburton,  modified.) 

cylindrical  shaft  that  bears  at  its  extremity  the  chelate  digits  (Figs.  6,8).  The 
shaft  is  very  long  and  projects  backward  beyond  the  basis  capituli  into  the 
body.  The  proximal  part  is  dilated  and  to  it  are  attached  the  retractor  muscles 
of  the  chelicerae.  The  distal  portion  is  more  heavily  sclerotized  and  bears  at 
its  extremity  the  digits  or  articles  (Fig.  8).  The  articles  are  usually  two 
in  number:  an  internal  digit  with  sharp  cutting  teeth  articulated  directly  with 
the  shaft  and  activated  by  two  powerful  tendons — an  internal  one  and  an  ex- 
ternal one — arising  from  the  mass  of  muscles  within  the  shaft,  and  an  external 
digit  articulated  with  the  internal  digit  and  provided  with  sharp,  pointed  cusps. 
It  is  these  organs  that  cut  and  lacerate  the  tissues  of  the  host.  A  brief  account 
of  the  method  of  feeding  is  given  later. 


THE  ORDER  ACAR1NA 


33 


THE  BODY:  The  dorsal  portion  of  the  body  bears  a  scutum  or  ^shield.  In 
the  males  the  scutum  covers  practically  the  entire  body  surface  (Fig.  4) ; 
in  the  females  (Fig.  5)  the  scutum  varies  greatly  in  size  and  shape  so  that 
it  serves  as  a  means  of  distinguishing  the  different  species.  It  never  covers 
more  than  a  small  part  of  the  dorsal  surface.  The  scutum  may  be  ornamented 
or  plain  (Figs.  4,5,9),  and  it  bears 
furrows  or  grooves.  The  anterior 
margin  is  usually  deeply  emar- 
ginate;  the  lateral  angles  project 
forward  and  are  called  the  scapu- 
lae (Fig.  4  s).  On  the  dorsal 
surface  of  the  scutum  and  body 
are  several  grooves  that  are  of 
considerable  significance.  These 
are:  (i)  the  cervical  grooves  that 
extend  from  the  inner  angles  of 
the  scapulae  backwards  on  the 
scutum  (Fig.  4  Cr);  (2)  lateral 
grooves  that  extend  along  the 
sides  of  the  scutum  in  the  males 
(Lg) ;  (3)  marginal  grooves,  ex- 
tending longitudinally  near  the 
lateral  margins  of  the  body  in 
the  females  (Fig.  5  Mg).  The 
scutum  may  be  marked  with 
shallow  or  deep  punctures.  On 
the  sides  of  the  scutum,  either 
on  the  edge  or  just  inside  it,  are 
the  eyes,  small  globular  clcva- 


cs 

Sh- 

ET- 

[  

FT- 

. 

•r 
11 

w 

.  8.  Dcrmaccnto 
chelicera,  ventral  vie 


tions   (Figs.  4,5).  Injmany  ticks   greatly  enlarged  to  she 


the  eyes  are  lacking. 
The   ventral   surface    presents 


Art,  points  of  articuh 


mdcrsoni.  Left:  A  single 
Right:  Tip  of  chelicera 
w  the  articles,  ventral  view, 
ion  of  the  internal  article 
iff;  CS,  cheliceral  sheath; 

~,       131',  dorsal  process  of  internal  article;  EA,  exter- 
some  important  structures.  The  nal  arlldc.  ,.r  rclr  ltlor  rendoll  of  internal  ani 

legs  are  prominent  features  and  cle;  FT,  flexor  tendon  of  internal  article;  IA,  in- 
are  numbered  I,  II,  III,  and  IV  tc;rnal  articlc|  M.  muscles,  Sh,  shaft  of  chelicera; 
.„.  \  i  •  •  i  T1'  tendons  of  retractor  muscles  of  chelicera. 

(Fig.  4),  beginning  at  the  ante- 
rior end.  Directly  behind  the  basis  capituli   will  be  found  the  opening  of 
the  genital  organs  in  both  the  males  and  females  (Figs.  4,5  GO).1  Kxtending 

1  The  genital  opening  is  usually  located  between  the  first  or  second  pair  of  legs,  though 
in  the  genus  Jxodcs  it  is  found  between  the  third  pair  of  legs. 


34 


MEDICAL  ENTOMOLOGY 


Fig.  (}.  Ticks.  From  the  top  down:  Dermacentor  variabilis,  the  dog  tick;  Haema- 
phy  salts  leporis-palustris,  the  rabbit  tick;  Rhipicephalus  sangutneus,  the  brown  dog 
tick.  Males  are  at  the  left,  females  at  the  right.  (After  the  U.S.  Bureau  of  Entomology.) 


THE  ORDER  ACARINA 


35 


backwards  from  the  genital  orifice  are  a  pair  of  grooves,  the  genital  grooves 
(Figs.  4,5  Ga).  These  curving  grooves  extend  to  the  posterior  margin  in 
nearly  all  species.  Between  the  genital  grooves  in  the  median  line  and  usually 
far  behind  the  fourth  pair  of  legs  is  the  anal  opening.  Directly  behind  the 
anal  opening  is  the  anal  groove,  the  convexity  directed  backward.  This  groove 
is  present  in  all  species  of  the  Ixodidae  except  in  the  genera  Boophilus  and 


Fig.  JO  (lejt  and  center).  Ventral  view  of  Ixodcs  ricinus,  male;  Ixodes  coofyci,  female, 
ventral  view.  A,  anus;  Ag,  anal  groove;  AP,  anal  plate;  AAP,  adanal  plate;  Gg,  genital 
groove;  GO,  genital  orifice;  H,  hypostome;  MP,  median  plate;  P,  palpus;  PP,  pregenital 
plate;  Sp,  spiracle. 

Fig.  11  (right).  (/)  Fourth  leg  of  Dermacentor  andersoni.  (2)  Tarsus  of  the  first  leg, 
showing  Mailer's  organ  (ho),  c,  coxa;  f,  femur;  pt,  protarsus  t,  tarsus,  ti,  tibia;  tr,  tro- 
chanter. 

Ixodes.  In  Boophilus  the  groove  is  lacking,  whereas  in  Ixodes  the  groove 
surrounds  the  anus  in  front  (Fig.  10) .  On  the  ventral  surface  of  the  males  of  the 
genera  Ixodes,  Boophilus,  and  Rhipicephalus  there  are  various  types  of  scle- 
rotized  shields.  In  Ixodes  these  shields  or  plates  appear  as  nonsalient  struc- 
tures, and  definite  names  have  been  applied  to  them  (Fig.  10).  In  the  other 
genera  the  plates  are  more  or  less  raised  and  usually  consist  of  two  pairs, 
the  adanal  and  accessory  shields. 

Behind  and  above  the  coxae  of  the  fourth  pair  of  legs  are  the  spiracles.  They 
are  located  on  sclerotized  stigmatal  plates  (Figs.  4,5,10).  The  stigmata  are  of 
various  shapes,  circular,  oval,  triangular,  comma-shaped,  etc.  The  spiracular 
openings  are  present  in  the  nymphs  and  adults  but  are  lacking  in  the  larvae. 

THE  LEGS  :  Ticks,  in  the  adult  and  nymphal  stages,  possess  four  pairs  of  legs. 
The  larvae  have  only  three  pairs  (Fig.  19).  Each  leg  consists  of  the  following 
parts:  (i)  Thcjcoxa.  This  is  the  basal  portion  and  is  firmly  and  immovably 


36  MEDICAL  ENTOMOLOGY 

attached  to  the  body  wall.  It  is  often  armed  with  spines,  spurs,  or  teeth  (Fig. 
n).  (2)  The  trochanter.  This  is  attached  to  the  coxa  by  an  intersegmental 
membrane.  It  is  usually  very  short  and  has  a  somewhat  rotatory  movement 
in  its  socketlike  depression  in  the  coxa.  (3)  The  femur.  Following  the  tro- 
chanter is  the  stout,  rather  short  femur.  It  is  usually  smooth  or  provided  with 
a  few  hairs  or  spines.  (4)  Thcjibia.  This  is  sometimes  called  the  patella  and 
is  rather  short  and  stout.  (5)  The  protarsus.  The  tibia  is  followed  by  the 
protarsus.  (6)  The  tarsus.  The  last  segment,  the  tarsus,  which  is  attached  to 
the  protarsus,  has  frequently  a  pseudoarticulation,  indicating  a  two-jointed 


Fig.  12.  Ornithodoros  moubata.  Left:  Ventral  view.  Right:  Dorsal  view.  C,  capitulum; 
Dh,  dorsal  humps;  GO,  genital  opening.  (Redrawn  from  Nuttall  and  Warburton.) 

condition.  (7)  The  claws.  The  tarsus  bears  the  claws,  which  are  located  on  a 
stalk.  (8)  The :  rjujyjllus.  Lying  between  the  claws  is  the  pulvillus,  which  may 
be  present  or  absent  (Fig.  n). 

On  the  tarsus  of  the  first  pair  of  legs  is  a  peculiar  organ  (Fig.  11  ho)  that 
should  not  be  overlooked.  This  is  the  so-called  Hallgr's  organ.  It  consists  of  a 
small  vesicle  containing  sensory  hairs.  Its  cavity  is  connected  with  the  exterior 
by  a  minute  pore.  Hinclle  and  Merriam  (1912)  have  definitely  established 
that  this  organ  has  an  olfactory  function. 

THE  ARGASIDAE:  The  external  anatomy  of  the  Argasidae  differs  from 
that  of  the  Ixodidae.  The  scutum  or  dorsal  shield  is  lacking,  and  on  this 
account  the  Argasidae  have  been  called  the  "soft  ticks."  The  capitulum  is 


THE  ORDER  ACARINA 


37 


located  on  the  ventral  surface,  just  behind  the  anterior  margin  (Figs.  12,13). 
Porose  areas  are  absent.  The  appearance  of  the  dorsal  surface  of  an  argasid  tick 
is  markedly  different  from  that  of  an  ixodid  tick.  (Cf.  Figs.  4,5  and  12-14.) 
The  ventral  surface  possesses  somewhat  similar  structures,  but  the  arrange- 
ment of  the  grooves  is  often  quite  different  (Fig.  14).  The  spiracles  are  located 
just  above  and  in  front  of  the  fourth  pair  of  coxae.  The  stigmatal  plate  is  usually 
small  and  not  so  heavily  sclerotized  (Fig.  15).  Eyes,  when  present,  are  ventral 
in  position  and  are  located  on  longitudinal  ridges  just  above  the  coxae.  Probably 


Fig.  i}.  Argas  persicus.  Dorsal  and  ventral  views  of  female.  (After  Bishopp.) 

one  of  the  most  striking  differences  in  the  external  anatomy  is  the  leglike 
character  of  the  pedipalpi  or  palpi  (Fig.  16).  These  organs  closely  resemble 
the  homologous  structures  in  spiders  and  indicate  the  more  generalized  char- 
acter of  the  argasid  ticks.  The  structure  of  the  legs  is  similar  to  that  of  the 
Ixodidae  except  that  the  pulvillus  is  very  small  or  lacking  and  the  coxae  are 
unarmed  (without  spines  or  teeth) . 

INTERNAL  ANATOMY 

The  internal  anatomy  has  been  studied  by  a  number  of  investigators.  A 
brief  resume  is  here  presented  in  order  that  the  student  may  understand  the 
main  structures  concerned  with  digestion,  respiration,  and  reproduction.  The 


MEDICAL  ENTOMOLOGY 


^••V^   3 

Fig.  14.  Ornithodoros  species.  (/)  Ventral  and  dorsal  views  of  0.  talaje.  (2)  Ventral 
and  dorsal  views  of  0.  hermsi.  (3)  Same  of  0.  tuncata.  (4)  Same  of  0.  parkcri.  G,  genital 
opening;  Ga,  genital  groove;  P,  preanal  groove;  Ta,  transverse  postanal  groove.  (All  after 
Cooley.) 


THE  ORDER  ACARINA 


39 


mouth  parts  have  already  been  described.  It  is  now  necessary  to  indicate  their 
function  and  the  method  of  obtaining  blood.  The  tick,  placed  on  its  host,  pro- 
ceeds to  attach  by  breaking  the  skin  with  the  sharp  cutting  articles  situated 
at  the  ends  of  the  cheliceral  shafts.  The  articles,  controlled  by  powerful  muscles, 
soon  lacerate  the  tissues,  and  the  hypostome  is  forced  into  the  wound.  The 
strong  recurved  teeth  of  the  hypostome  are  firmly  embedded  and  are  forced 
deeper  and  deeper  as  the  chelicerae  cut  the  tissues.  Soon  the  entire  capitulum, 
except  the  palpi,  which  never  enter  the  wound,  are  deep  in  the  flesh  of  the 
host. 


Palp  article^ 


Fig.  75  (Jcjf).  Argas  pcrsicus.  Spiracle.  (After  Nuttall.) 

Fig.  16  (right).  Capitulum  of  Argas  persicus.  (After  Nuttall.) 

Once  the  tick  is  attached,  the  blood  is  extracted  by  means  of  a  powerful 
pumping  pharynx  (Figs.  7,17).  The  buccal  cavity  lies  between  the  palpi  within 
the  anterior  part  of  the  basis  capituli  and  above  the  hypostome.  It  is  tubelike 
and  ends  posteriorly  in  a  small  bayou,  widened  out  laterally,  into  which  open 
the  salivary  ducts.  The  secretion  of  the  salivary  glands  has  been  shown,  in 
some  cases,  to  possess  an  anticoagulin  and  enables  the  tick  to  obtain  a  steady 
flow  of  liquid  nourishment.  Leading  from  the  floor  of  the  buccal  cavity  at  its 
posterior  end  is  the  short  pharynx. 

Sen  (1935,  1937)  describes  a  peculiar  structure  ("stylet")  overlying  the 
entrance  to  and  at  the  anterior  end  of  the  pharynx.  Bertram  (1939)  apparently 
refers  to  the  same  structure  as  the  tongue,  and  Arthur  (1946)  describes  it  in 
detail.  According  to  Bertram  and  Arthur,  this  structure  closes  the  entrance 
to  the  pharynx  when  the  muscles  of  the  pharynx  contract  to  force  the  blood 
into  the  esophagus.  It  thus  prevents  the  backflow  of  the  blood  into  the  wound. 

The  pharynx  is  a  chitinous  tube  richly  supplied  with  dilator  and  contractor 
muscles.  It  terminates  in  the  thin-walled,  short  esophagus,  which  passes 


40  MEDICAL  ENTOMOLOGY 

through  the  brain  and  thence  to  the  stomach  or  mid-intestine.  The  mid- 
intestine  (Fig.  17  St)  consists  of  a  short,  thin  tube  with  numerous  large 
diverticula.  The  diverticula  generally  arise  at  the  anterior  and  posterior  ends 
of  the  mid-intestine.  Their  number,  length,  and  shape  vary  in  the  different 
species.  These  diverticula  are  capable  of  great  distension  and  enable  the  ticks 
to  extract  a  large  amount  of  blood  at  one  feeding.  Ticks  which  drop  oft  their 
hosts  at  each  feeding  are  thus  furnished  with  a  food  supply  that  enables  them 
to  withstand  long  periods  of  starvation.  The  hind  intestine  arises  from  the 
lower  surface  at  the  posterior  end  of  the  mid-intestine.  It  appears  as  a  delicate 
white  cord  and  is  supposed  to  be  largely  functionless  in  most  ticks.  In  some, 
like  Argas  persicus,  discharges  of  wastes  take  place,  but  in  the  great  majority 
of  ticks  excretion  probably  occurs  through  the  Malpighian  tubules,  skin,  and 
other  organs.  The  hind  intestine  terminates  in  a  saclike  rectum.  A  single 
Malpighian  tubule  arises  from  each  side  of  the  rectum.  Each  tubule  is  long 
and  winds  about  and  among  the  internal  organs.  Each  is  more  or  less  filled 
with  a  whitish  substance,  which  is  evacuated  through  the  rectum.  These 
tubules  are  probably  excretory  organs. 

The  salivary  glands,  two  in  number,  lie  in  the  anterior  portion  of  the  body, 
extending  backward  on  each  side  to  the  base  of  or  beyond  the  third  pair  of 
legs  (Fig.  17  Sga).  Each  gland  appears  like  a  small  bunch  of  grapes  and  is 
composed  of  rather  large  secretory  cells  that  pour  out  their  secretions  through 
an  independent  duct.  Each  duct  opens  near  the  base  of  the  buccal  cavity.  An- 
other pair  of  glands  that  appear  to  have  considerable  importance  and  about 
which  little  is  known  are  the  coxal  glands.  These  open  near  the  base  of  the 
first  pair  of  coxae.  They  are  known  to  discharge  a  secretion  while  or  just 
after  feeding  (Argas  and  Ornithodoros).  The  exact  function  of  these  glands 
has  not  yet  been  determined.  It  is  known,  however,  that  certain  spirochetes  are 
transmitted  to  new  hosts  by  means  of  the  fluid  from  these  glands  (e.g.,  Ornitho- 
doros moubata  and  relapsing  fever). 

The  reproductive  system  of  the  female  consists  of  a  duplex  ovary  located 
just  above  the  posterior  end  of  the  mid-intestine.  The  ovary  extends  across 
the  body,  and  each  end  terminates  in  an  oviduct.  The  oviduct  from  each  side 
runs  forward  as  a  long  coiled  tube.  The  oviducts  unite  at  their  anterior  ends 
to  form  the  uterus  (Fig.  17) .  From  the  uterus  the  vagina  leads  to  the  external 
orifice  (Figs.  5,12).  Surrounding  the  vagina  are  various  glands  that  are  active 
at  the  time  of  egg  laying. 

The  male  reproductive  system  consists  of  a  duplex  testis  occupying  a  posi- 
tion similar  to  that  of  the  ovary  in  the  female.  A  vas  deferens  extends  forward 
from  each  end  of  the  testis.  These  unite  near  the  external  orifice.  The  sperm 


THE  ORDER  ACAR1NA 


Fc 


GO 


--  VOa 


Mt 


Fig.  77.  Argas  persicus.  Ventral  view  of  dissection  of  young  female.  The  left  side  of  the 
figure  represents  internal  organs  as  they  appear  after  removal  of  integument;  on  the 
right  side  part  of  the  stomach  and  intestinal  caeca  have  been  removed.  B,  brain;  Cl,  cheli- 
cera;  Fc,  occipital  foramen;  Ga,  glandular  part  of  Gene's  organ;  GC,  caeca  of  gut; 
GO,  Gene's  organ;  H,  heart;  M,  muscles  of  chelicera;  Mt,  Malpighian  tubules;  O,  esopha- 
gus; Ov,  ovary;  Ph,  pharynx;  R,  rectum;  S,  rectal  sac;  Sga,  salivary  gland;  Sp,  spiracle; 
St,  stomach;  UT,  uterus.  (Adapted  from  Robinson  and  Davidson.) 


42  MEDICAL  ENTOMOLOGY 

collects  in  a  lobular  swelling  (seminal  vesicle)  situated  near  the  junction  of  the 
vasa  deferentia.  Here,  in  a  complicated  manner,  the  spermatozoa  are  formed 
into  spermatophores. 

Another  organ  that  requires  description  is  Gene's  organ.  It  is  associated  with 
egg  deposition  (Fig.  7,  Ge).  In  the  Ixodidae  it  is  located  directly  beneath  the 
scutum  and  opens  to  the  exterior  between  the  scutum  and  the  basis  capituli;  in 
the  Argasidae  it  is  just  in  front  of  the  capitulum.  Gene's  organ  is  glandular  in 
structure,  is  present  only  in  the  females,  and  becomes  functional  at  the  time 
of  egg  deposition. 

The  structure  of  the  other  internal  organs  need  not  concern  us  here.  Full 
details  may  be  obtained  by  consulting  the  references. 

SYNOPSIS  OF  THEJXODOIDEA 

The  Ixodoidea  contains  two  families,  the  Argasidae  and  the  Ixodidae.  The 
families  may  be  separated  by  the  following  key : 

1.  Scutum  lacking;  capitulum  ventral,  usually  concealed  beneath  the  anterior 

margin,  and  always  subterminal;  body  alike  in  both  sexes  (Fig.  14) 
Argasidae 

2.  Scutum  present;  in  the  males  the  scutum  extends  over  the  entire  dorsal 

surface;  in  the  females,  nymphs,  and  larvae  only  on  a  portion  of  the 
anterior  dorsal  surface;  capitulum  terminal  and  always  visible  from  the 
dorsal  surface  (Fig.  9) Ixodidae 

THE  FAMILY  ARGASIDAE 

The  family  Argasidae  consists  of  those  ticks  that  lack  a  scutum,  the  so-called 
"soft  ticks."  There  is  very  little  sexual  dimorphism,  the  males  closely  resem- 
bling the  females.  The  capitulum  is  always  inferior,  and  the  spiracles  are  small 
and  located  anterior  to  coxa  IV.  In  the  adults  the  integument  is  leathery, 
wrinkled,  granulated,  mammillated,  or  provided  with  tubercles.  The  palpi 
are  free  and  all  the  segments  are  freely  movable.  The  porose  areas  are  absent. 
The  adults,  even  when  engorged,  never  increase  greatly  in  size;  when  fasting 
their  flattened  appearance  bears  some  resemblance  to  bedbugs.  Their  principal 
hosts  are  birds  (especially  poultry),  domestic  animals,  rodents,  bats,  and  man. 
They  are  found  commonly  in  the  habitats  of  their  hosts  as  in  rodent  burrows, 
bat  roosts,  poultry  houses,  caves,  and  human  abodes  as  well  as  on  the  ground 
where  they  drop  from  their  hosts.  They  appear  to  be  chiefly  nocturnal  in  their 
feeding  habits.  There  are  only  four  well-recognized  genera:  Argas,  Ornitho- 
doros,  Antricola,  and  Otobius. 


THE  ORDER  ACARINA  43 

KEY  TO  THE  GENERA  OF  ARGASIDAE 

1.  Margin  of  the  body  thin  and  acute;  a  sutural  line  separating  the  dorsal 

and  ventral  surfaces  (Fig.  13)   Argas 

Margin  of  the  body  not  thin  and  acute,  but  if  so  no  sutural  line  separating 
the  dorsal  and  ventral  surfaces  (Fig.  14)  2 

2.  Nymphs  with  the  integument  beset  with  spines;  hypostome  well  devel- 

oped; adults  with  the  integument  granular;  hypostome  vestigial  Otobius 
Nymphs  with  the  integument  not  beset  with  spines;  mammillated  or 
tubercular;  hypostome  not  vestigial  in  either  nymphs  or  adults 3 

3.  Hypostome  scooplike  on  dorsal  surface,  broad  at  base.  (Known  from 

bats;  only  2  species)   Antricola 

Hypostome  never  scooplike  on  dorsal  surface,  not  so  broad  at  base.  (On 
various  classes  of  animals  including  bats  and  man;  a  large  genus)  .... 

Ornithodoros 

The  genus  Argas  Latr.  contains  only  a  few  species,  but  some  of  these  are 
world-wide  in  distribution.  The  following  key  will  aid  in  the  identification  of 
the  common  species  : 

1.  Body  nearly  circular,  discoidal vespertilionis  Latr. 

Body  not  circular,  longer  than  broad  2 

2.  Margin  of  body  striate   3 

Margin  of  body  not  striate,  marked  of?  by  distinct  quadrangular  "cell- 
like"  plates  (Fig.  13)   persicus  Oken 

3.  Body  subconical  in  front;  dorsum  marked  with  polygonal  depressed  areas; 

large  species,  15  by  10  mm.  (Known  from  East  Africa)  . .  brumpti  Neum. 
Body  rounded  in  front;  dorsum  marked  with  fine  wrinkles  and  discs  as  in 
persicus  (species  not  so  large).  (Parasitic  on  pigeons  and  widely  dis- 
tributed in  Europe,  North  Africa,  and  northern  South  America;  re- 
ported from  the  U.S.A.)  reflexus  Fabr. 

The  genus  Ornithodoros  Koch  contains  many  important  species  that  attack 
man  and  act  as  vectors  of  serious  diseases.  They  occur  in  many  parts  of  the 
world,  but  none  of  the  species  is  known  to  be  world-wide  in  distribution. 
Nuttall  (1908)  listed  only  n  well-established  species,  but  at  present  nearly  50 
species  have  been  described,  though  some  of  them  are  of  doubtful  validity. 

KEY  TO  THE  MORE  COMMON  SPECIES  OF  ORNITHODOROS 

i.  Cheeks  present  (flaps  at  sides  of  camerostome)  2 

Cheeks  absent 5 


44  MEDICAL  ENTOMOLOGY 

2.  Tarsi  with  humps  (Fig.  12)  though  they  may  be  small.  (From  Brazil) 

brasiliensis  Aragao 

Tarsi  without  humps   3 

3.  Tarsus  IV  with  long  subapical  protuberance 

tholozani  (Labou.  and  Megn.) 

Tarus  IV  without  long  subapical  protuberance 4 

4.  Discs  large  and  easily  seen.  (Southern  U.S.A.  south  to  Argentina) 

(Fig.  14)   talaje  Guerin-Men. 

Discs  very  small  and  inconspicuous.  (Known  only  from  human  abodes; 
Panama,  Colombia,  and  Venezuela) rudis  Karsch 

5.  Integument  not  strongly  mammillated,  appearing  more  or  less  wrinkled; 

dorsum  with  discs,  two  elongate,  parallel  discs  near  front  being  distinc- 
tive. (India,  Persia,  Russian  Turkestan,  Palestine)  . .  lahorensis  Neum. 
Integument  strongly  mammillated;  discs  present  or  absent  but  lacking 
the  two  described  above  6 

6.  Eyes  present 7 

Eyes  absent  8 

7.  Anterior  eyes  much  larger  than  posterior.  (Pacific  coast  of  U.S.A.,  Cali- 

fornia to  Mexico)  coriaceus  Koch 

Anterior  and  posterior  eyes  about  equal  in  size.  (Arabia,  Africa,  India, 
Ceylon)   savignyi  Aud. 

8.  Dorsal  humps  present  on  all  tarsi  and  prominent  (Fig.  12  Dh) 9 

Dorsal  humps,  when  present,  not  on  all  the  tarsi 10 

9.  Tarsus  IV  with  three  humps.  (Hot  dry  areas  of  Africa  from  Lake  Chad 

east  and  south  to  Cape  Colony)  moubata  Murray 

Tarsus  IV  with  one  apical  hump  or  the  hump  might  be  considered  the 
apical  protuberance.   (Southern   Brazil,  Argentina,  Paraguay,  and 

Bolivia)  rostratus  Aragao 

10.  Tarsi  bifurcate  and  with  dorsal  humps.  (Algeria)  foleyi  Parrot 

Tarsi  not  bifurcate  and  without  humps  on  all  or  some  of  the  tarsi n 

u.  Dorsal  humps  absent  from  all  the  tarsi.  (Western  United  States.)  (Fig. 

14) hermsi  Wheeler,  Herms,  and  Meyer 

Some  of  the  tarsi  with  dorsal  humps  12 

12.  Dorsal  humps  on  the  tarsi  very  long;  tarsus  IV  with  subapical  protuber- 

ance or  hump;  mammillae  very  large  and  coarse.  (Southern  Brazil, 

Argentina,  Paraguay,  and  Bolivia) rostratus  Aragao 

Dorsal  humps  not  so  long:  mammillae  not  so  large  and  coarse 13 

13.  Tarsus  IV  without  dorsal  humps  but  with  subapical  protuberance. 

(Mexico)   nicollei  Mooser 


THE  ORDER  ACARINA  45 

Tarsus  IV  without  dorsal  humps  and  without  subapical  protuberance  . .  14 
14.  Mammillae  large  (Fig.  14),  relatively  few  and  not  crowded.  (South- 
western United  States,  Florida,  Mexico)  turicata  Dugcs 

Mammillae  small  (Fig.  14),  crowded,  and  numerous.  (Western  United 
States)    par\eri  Cooley 

The  genus  Otobius  contains  only  two  North  American  species.  O.  megnini 
is  the  "spinose  ear  tick"  of  cattle  and  horses  and  has  been  recorded  from  man. 

0.  lagophilus  Cooley  and  Kohls  is  reported  only  from  cottontail  rabbits  and 
jack  rabbits  from  the  western  United  States  and  Canada.  Both  species  can  be 
easily  recognized  as  nymphs  by  their  spinose  integument.  The  genus  Antricola 
occurs  on  bats  or  in  bat  roosts.  Only  two  species  are  known,  both  from  the 
Americas. 

THE  FAMILY  IXODIDAE 

The  family  Ixodidae  contains  those  ticks  that  have  a  scutum  or  shield  and 
have  been  called  the  "hard  ticks."  Sexual  dimorphism  is  marked,  the  males 
being  completely  covered  on  the  dorsum  by  the  scutum  and  incapable  of  great 
distention;  the  females  may  become  greatly  enlarged  when  engorged,  and  the 
scutum  appears  as  a  small  shield  behind  the  capitulum.  The  capitulum  is 
always  terminal,  and,  in  the  females,  porose  areas  are  present.  This  family 
contains  the  great  majority  of  ticks  and  is  world- wide  in  distribution.  Their 
principal  hosts  arc  mammals,  reptiles,  amphibians,  and  birds.  It  is  not  possible 
to  give  an  adequate  key  to  all  the  described  genera  as  some  of  them  are  rare 
and  not  well  known  or  studied. 

KEY  TO  THE  PRINCIPAL  GENERA  OF  IXODIDAE 

1.  Anal  groove  surrounds  the  anus  in  front  (Fig.  10) ;  eyes  absent.  (World- 

wide in  distribution)   Ixodes 

Anal  groove  curves  about  the  anus  posteriorly  (Fig.  4)  or  is  absent;  eyes 
present  or  absent   2 

2.  Eyes  absent  3 

Eyes  present .4 

3.  Inornate;  festoons  present;  palpi  short,  conical  when  closed  and  segment 

2  projects  laterally  (except  in  rare  cases)  beyond  the  basis  capituli  (Fig. 

9) ;  coxa  I  never  bifid.  (Distribution  world-wide)  Haemaphy salts 

Ornate;  palpi  long,  segment  2  especially  long;  festoons  present.  (Occur 
mainly  on  reptiles;  tropical  and  subtropical) Aponomma 

4.  Anal  groove  absent  or  very  indistinct;  inornate;  eyes  present  and  mar- 


46  MEDICAL  ENTOMOLOGY 

ginal;  festoons  absent;  palpi  very  short,  second  and  third  segments  com- 
pressed and  ridged  dorsally  and  laterally;  males  with  adanal  and  acces- 
sory shields.  (Tropical  and  subtropical)  Boophilus 

Anal  groove  present  and  distinct;  ornate  or  inornate  but  without  all  of  the 
above  combination  of  characters  5 

5.  Ornate;  eyes  and  festoons  present;  eyes  marginal;  abdomen  without  a 

pair  of  terminal  protrusions  capped  by  sclerotized  points 6 

Inornate,  but  if  ornate  (rarely  in  Hyalomma  and  Rhipicephalus)  with  a 
pair  of  abdominal  protrusions  capped  by  sclerotized  points 7 

6.  Palpi  short;  second  palpal  segment  not  twice  as  long  as  wide;  hypostome 

with  the  denticles  arranged  in  6  rows,  3  on  each  side  (expressed  as 
3/3)  and  occupying  most  of  its  length.  (Distribution  world-wide)  .  . 

Dermacentor 

Palpi  long;  sec%ond  segment  twice  as  long  as  wide;  hypostome  with 
denticles  largely  restricted  to  the  apical  half  and  arranged  usually  3/4 
or  4/4.  (Tropical  and  subtropical)  Amblyomma 

7.  Eyes  not  on  the  margin  of  scutum  but  moved  inward;  if  ornate  with 

a  pair  of  abdominal  protrusions  capped  by  sclerotized  points.  (Old 

World,  tropical  and  subtropical)   Hyalomma 

Eyes  located  on  margin  of  scutum;  without  the  abdominal  protrusions  .  8 

8.  Ventral  plates  or  shields  absent  in  both  sexes 9 

Ventral  plates  or  shields  present  in  the  males,  absent  in  the  females;  basis 

capituli  usually  hexagonal  in  dorsal  view.  (Distribution  world-wide) .  . 
Rhipicephalus 

9.  Basis  capituli  rectangular  in  dorsal  view;  coxae  not  increasing  greatly  in 

size  from  I  to  IV;  coxa  IV  without  spines;  spiracles  subcircular.  (Tropi- 
cal America)  Otocentor 

Basis  capituli  hexagonal  in  dorsal  view;  coxae  increasing  greatly  in  size 
from  I  to  IV;  coxa  IV  with  very  long  spines;  spiracle  comma-shaped. 
(Africa)  Rhipicentor 

Over  three  hundred  species  of  ixodid  ticks  have  been  described.  It  is  not 
possible  to  give  keys  to  the  species  included  in  the  different  genera.  In  the 
bibliography  will  be  found  references  in  which  keys  to  the  species  of  certain 
genera  are  given.  These  references  are  indicated  by  a  dagger.  The  genus 
Dermacentor  contains  species  important  as  transmitters  of  human  diseases, 
and  the  following  key  will  aid  in  recognizing  the  North  American  species. 


THE  ORDER  ACARINA 

KEY  TO  THE  IMPORTANT  AMERICAN  SPECIE^ 
DERMACENTOR 

1.  Spurs  on  coxa  I  diverging  from  their  base  outwards.  (Southwestern  U. 

Texas  to  Oregon;  hosts  mainly  rabbits)  parumapertus  Neui, 

Spurs  on  coxa  I  with  proximal  edges  closely  parallel  or  slightly  diverg- 
ing near  apices   2 

2 .  Spiracular  plate  oval,  without  dorsal  prolongation  and  with  goblets  few 

and  large.  (Widespread  in  North  America) albipictus  Pack. 

Spiracular  plate  oval,  with  dorsal  prolongation  and  the  goblets  numerous 
or  moderate  in  numbers  3 

3.  Cornua  long,  especially  so  in  the  males.  (West  coast  from  Oregon  to 

southern  California)   occidentalis  Marx 

Cornua  short  or  of  moderate  length 4 

4.  Goblets  of  Spiracular  plate  very  small  and  numerous.  (Eastern  North 

America  to  Saskatchewan  south  through  central  Texas)  . .  variabilis  Say 
Goblets  of  spiracular  plate  large  and  not  so  numerous  or  densely  packed. 
(Western  North  America,  Saskatchewan  to  British  Columbia  south 
to  northern  New  Mexico)   andersoni  Stiles 

BIOLOGY  OF  TICKS 

Ticks  are  all  external  parasites  of  mammals,  birds,  reptiles,  and  some  am- 
phibia. During  their  life  cycles  they  pass  through  four  stages — egg,  larva, 
njmphj  and  adult.  All  species  oviposit  on  the  ground  or  in  the  habitats  of 
their  hosts,  usually  in  sheltered  places  (Eig.  18).  The  time  required  for  the  de- 
velopment of  the  embryo  within  the  egg  varies  widely  not  only  with  the  species 
but  also  with  temperaturer moisture,  and  other_climatic  factors.  The  hexapod 
^LYf*  (fig*  I9)>.  which  hatches  from  the  egg,  is  very  active  (there  are  a  few 
known  exceptions)  and  seeks  out  its  host  in  various  ways.  After  feeding,  the 
larva  drops  oft  and  molts  on  the  ground  or  remains  on  its  host  an3  molts. 
Thejiymph,  the  next  stage,  possesses  eight  legs,  and  the  tracheal  system  with. 
ksjs£iracles  (lacking  in  the  larva)  are  now  present.  The  external  opening  of 
the  genital  organs  is  still  lacking.  After  another  feeding  the  nymph  again 
leaves  its  host  and  molts,  or  it  may.  remain. aa.d..mQl.t.. on  theJiQ&t.  This  js,  the. 
adult  stage,  which  is  usually  quite  similar  toj^^of^l^jiyjiir^^ 
the  external  genital  ^>nfice  'ls  present.  In  the  Argasidae  there  may  be  several 
nymphal  stages,  but  all  ticks  of  the  family  Ixodidae  have,  as  far  as  known, 
only  a  single  nymphal  stage.  The  adults  arc  not  known  to  molt  but  feed  and 


MEDICAL  ENTOMOLOGY 

Ar  hosts  or  on  the -ground.  Shortly  after  mating  the  ; 

.  In  the  Ixodidae  the  males  usually  die  shortly  after  matinj 

>  after  laying  their  batches  of  eggs.  In  the  Argasidae  the  adults  are 

_,-lived,  the  males  and  females  living  for  a  long  time,  even  several  years. 

.gg  laying  usually  takes  place  after  each  blood  meal. 

Though  the  above  statement  represents  the  general  life  cycle  of  ticks^each 

species  undergoes  its  own  peculiar  developmental  cycle.  Some  ticks  complete 

their  life  cycle  on  a  single  host3  molting  and  mating  without  leavmg~diiC'ri0sT;" 

such  ticks  arc  known  as  one-_host jicks,  as  Boophihts  anniilatus  and  Demia^ 

centor  albipictus;  some  require  two  hosts,  as  Rhipiccphalus  evertsi  and 


Fig.  1  8  (left).  Dcnnaccntor  albipictus.  Female  laying  eggs.   (After  Department  of 
Agriculture,  Division  of  Entomology,  Canada.) 
Fig.  79  (right).  Boophilus  annulatus.  Recently  hatched  larva.  (After  Cotton.) 


f  and  arc^  called  two-host  ticks;  many  others  require 
three  hosts,  dropping  off  after  each  feeding,  and  are  known  as  three-host  ticks, 
as  Dermacentanund.cr-SQni,  D.  variabilis,  and  many  other  species;  and  still  other 
ticks  require  even  more  hosts,  as  many  of  the  argasid  ticks  such  as  Argas 
pcrsiats,  Ornithodoros  monbata,  and  0.  savignyi,  and  may  be  called  many- 
host  ticks.  The  relation  of  ticks  to  their  hosts  is  shown  graphically  in  Fig.  20, 
and  nearly  all  the  known  types  of  life  cycles  are  indicated. 

Sexual  reproduction  occurs  generally  in  ticks,  though  Aragao  (1912,  1936) 
and  Brumpt  (1924)  have  shown  that  Amblyomma  rotundatum  (agamun) 
probably  reproduces  normally  parthem  genetically.  Mating  takes  place,  in 
most  cases,  on  the  host,  the  male  seeking  out  the  female.  In  all  species  so  far 
described,  the  male  attaches  beneath  ihc  female  and  uses  his  mouth  parts  as  an 


THE  ORDER  ACARINA 


Second  nymphal  stage  attacks  hoat  III 
Nymphs  drop  off  when  replete 


Second  nymphal  stage  when  replete 
drops  to  the  ground 


Fig.  20.  Life  cycles  of  ticks.  The  black  areas  (sectors)  represent  the  periods  of  blood 
taking.  Type  I:  Argas  persicus,  Argas  reflexus  (?),  Ornithodoros  sp.  Type  II:  Ornitho- 
doros  monbata,  O.  savignyi.  Type  III:  Ixodes  ricinus,  I.  hcxagonus,  I.  canisuga,  Derma- 
centor  reticulatus,  D.  occidcntalis,  D.  variabilis,  D.  andersoni,  Haemaphysalis  leacht, 
H.  punctata,  II.  kporis-palustris,  Amblyomma  hebraeum,  A.  maculatiim,  A.  cajennense, 
A.  americanum,  Rhipiccphaltts  appendiculatus,  R.  sanguineus,  R.  sinnts.  Type  IV:  Rhi- 
picephalus  evert  si,  Hyalomma  acgyptium.  Type  V:  Boophilus  annulatus,  B.  dugesii, 
Dermacentor  albipictus.  Type  VI:  Otobius  mcgnini.  (There  are  other  types  of  life  cycles 
not  shown  on  the  chart.) 

external  genital  organ.  After  the  male  has  distended  the  vulva  of  the  female 
with  his  mouth  parts,  he  moves  forward  until  his  genital  orifice  is  directly 
over  that  of  the  female.  Then  with  great  rapidity  a  viscid  spermatophore  is 
applied  to  the  vulva  and  is  promptly  received  by  the  female.  The  females  may 
mate  several  times  with  different  males. 


50  MEDICAL  ENTOMOLOGY 

Egg  deposition  in  ticks  is  a  rather  remarkable  performance.  The  eggs  are 
always  found  in  front  of  the  female  (Fig.  18),  whereas  the  genital  opening  is 
on  the  ventral  surface  (Fig.  5).  The  transfer  of  the  eggs  is  accomplished  in 
the  following  manner:  When  ready  to  oviposit  the  female  withdraws  the 
capitulum  as  far  as  possible  within  her  body  and  Gene's  organ  is  extruded. 
The  vulva  is  partially  everted,  and  an  egg  is  protruded  and  rolled  around  until 
it  comes  in  contact  with  the  sticky  Gene's  organ;  when  this  is  done  the  organ"" 
is  withdrawn,  and  the  egg  is  carried  to  the  dorsal  surface  and  pushed  off  in 
front  of  the  tick.  This  process  is  repeated  for  each  egg.  That  it  must  be  a 
laborious  procedure  is  evident  when  it  is  remembered  that  some  ticks  lay  as 
many  as  12,000  eggs.  The  secretion  of  Gene's  organ  is  believed  to  be  protective. 

Many  ticks  are  known  to  be  long-lived  and  to  be  able  to  withstand  long 
periods  of  starvation.  Various  larvae  are  known  to  live  seven  or  eight  months 
or  even  longer  without  any  food;  adults  of  Ornithodoros  moubata  have  sur- 
vived without  food* for  over  a  year;  O.  savignyi  for  over  two  years;  O.  hennsi 
for  four  years;  Argas  persicus  for  three  or  four  years;  A.  reflexus  for  five  years; 
Dermacentor  andersoni  at  least  four  years.  Many  other  species  of  ticks  have 
been  kept  alive  without  food  for  varying  lengths  of  time.  Ruttledge  (1930) 
kept  a  female  of  Argas  brumpti  (collected  in  the  wild)  alive  for  nearly  12 
years;  Francis  (1938)  kept  Ornithodoros  turicata  alive  for  five  years  unfed 
and  infected  with  spirochetes  of  relapsing  fever;  another  group  he  kept  alive 
unfed  for  four  years,  and  then  they  infected  a  monkey  with  relapsing  fever; 
two  and  a  half  years  later  the  same  group  fed  on  a  monkey  and  infected  it 
with  relapsing  fever,  demonstrating  six  and  a  half  years  of  natural  infection. 
In  1942  Francis  records  the  maximum  length  of  life  of  this  tick  under  experi- 
mental conditions  as  9  years  10  months  and  7  days. 

SPECIAL  BIOLOGIES 

Owing  to  the  importance  of  ticks  as  vectors  of  human  and  animal  diseases 
a  few  of  the  life  histories  of  the  more  important  species  need  to  be  given 
in  some  detail. 

THE  FAMILY  ARGASIDAE 

THE  GENUS  ARGAS:  Argas  persicus  (Oken)  is  the  common  fowljick 
(Fig.  13).  The  males  and  females  appear  very  similar  but  may  be  separated 
by  the  shape  of  the  genital  opening.  In  the  males  the  genital  opening  appears 
crescent-shaped,  whereas  in  the  females  it  is  a  narrow  transverse  slit.  The 
mature  female,  unengorged,  measures  from  5  to  8  mm.  in  length  and  the 


THE  ORDER  ACARINA  51 

male  from  4.5  to  6  mm.  The  domestic  fowl  is  the  principal  host,  though  turkeys, 
geese,  and  ducks  are  attacked;  wild  birds  are  also  frequent 


is  occasionally  attacked  when  associated  with  ppu|try. 

The  fowl  tick  has  a  world-wide  distribution  and  occurs  in  the  warm  and  dry 
regions  of  Europe,  Asia,  Africa,  the  Americas,  and  Australia.  The  distribution 
in  North  America  is  shown  in  Fig.  21.  In  our  warm  poultry  houses  it  fre- 
quently occurs  far  north  of  its  range,  as  in  Baltimore,  Maryland. 

The  mature  males  and  females  feed  at  night  and  become  engorged  in  less 
than  an  hour.  Dropping  from  their  hosts  they  seek  shelter  in  any  convenient 
hiding  place.  The  females  deposit  a  batch  of  eggs  after  each  blood  meal,  and 
each  female  may  lay  several  batches  of  eggs.  Over  600  eggs  are  laid  by  the 
average  female.  The  eggs  hatch  in  from  10  days  to  several  weeks.  The  larvae 
attach  to  their  hosts  and  become  engorged  in  about  5  days.  They  drop  from 
their  hosts  and  molt  to  the  first  nymphal  stage  in  about  a  week.  The  first-stage 
nymph  now  feeds  at  night,  and  a  second  molt  takes  place  in  about  another 
week.  Another  molt  occurs  about  a  week  later,  and  the  third-stage  nymph 
after  feeding  usually  molts  to  the  adult.  The  entire  life  cycle  from  egg  to  adult 
may  be  completed  in  about  30  to  40  clays  if  food  and  warmth  are  suitable.  This 
tick  is  a  serious  pest  of  poultry,  killing  young  birds  in  large  numbers.  It  is  the 
vector  of  a  serious  disease  of  fowls,  spirochetosis,  caused  by  Spirochaeta  gal- 
linarum  Blanchard  (S.  marchouxi  Nuttall).  Recently  (1943)  it  has  been 
reported  capable  of  transmitting  anaplasmosis  of  cattle.  It  or  a  closely  allied 
species,  Argas  mianensis,  is  said  to  attack  man  commonly  in  Persia  and 
produces  a  fever  known  as  Mianeh  fever. 

Argas  reflcxus  (Fabr.)  is  primarily  a  parasite  of  pigeons  and  occurs  most 
commonly  in  the  Old  World.  It  also  occurs  in  northern  South  America,  and 
Cooley  (1944)  records  a  few  localities  in  the  United  States.  Why  it  has  not 
spread  among  pigeons  in  this  country  is  not  known.  A.  bntnipti  Neum.  is  our 
largest  known  argasid  tick,  measuring  nearly  20  mm.  in  length.  It  has  been 
taken  only  in  East  Africa  (Somaliland,  Kenya,  and  the  Sudan).  A.  vesper- 
tilionis  (Latr.)  is  a  beautiful  nearly  circular  tick;  it  is  recorded  from  bats  in 
England,  Europe,  North  Africa,  South  Africa,  southern  India,  and  Australia. 
Patton  and  Cragg  reared  this  species  on  bats  in  India;  it  completes  its  life 
cycle  in  about  two  months. 

THE  GENUS  ORN1THODOROS:  Many  species  of  this  genus  are  im- 
portant agents  in  the  transmission  and  dissemination  of  human  diseases.  Only 
a  few  of  the  species  can  be  discussed  here. 

Ornithodoros  moubata  (Murray),  the  eyeless  tampan,  is  probably  the  best 
known  tick  (Fig.  12)  that  prefers  man  as  its  host  in  all  stages.  It  also  feeds  on 


52  MEDICAL  ENTOMOLOGY 

pigs,  goats,  dogs,  shrrp,  and  other  domesticated  animals.  It  is  found  only  in 
Africa,  where  it  is  widely  distributed  in  the  hot  dry  areas  from  Lake  Chad 
eastward  to  the  Red  Sea  and  south  to  the  Cape  Province.  It  is  also  reported 
from  northwestern  Madagascar.  Here  they  are  found  most  commonly  in  the 
rest  houses  along  the  caravan  routes,  in  native  huts,  and  in  the  village  houses. 
The  ticks  prefer  the  dry  places  such  as  about  hearths  and  bed  platforms,  in  the 
cracks  and  crevices  of  the  mud  floors,  in  the  dry  grass  walls,  and  about  the 
doorsills.  The  females  lay  their  eggs  in  batches  at  night,  placing  them  in 
cracks  and  crevices  or  in  hollows  made  in  the  ground.  Each  female  normally 
lays  several  batches  of  eggs,  a  batch  after  each  blood  meal.  Jobling  (1925) 
records  each  female  as  laying  from  600  to  over  1200  eggs.  The  eggs  hatch  in 
from  eight  days  to  two  or  three  weeks.  The  larvae,  however,  do  not  leave  the 
eggs  but  remain  within  the  shells  and  molt  to  the  nymphal  stage  in  about  four 
days.  According  to  Jobling,  the  males  undergo  four  molts  and  the  females 
five  molts  before -reaching  maturity.  Both  the  nymphs  and  adults  are  noc- 
turnal and  feed  primarily  at  night.  The  nymphs  require  about  a  half-hour 
to  become  engorged  and  then  drop  from  their  hosts.  The  adults  are  long-lived 
and  can  live  for  several  years.  This  tick  is  the  important  vector  of  African 
relapsing  fever  throughout  its  range., 

Ornithodoros  savignyi  (Aud.),  the  eyed  tampan,  closely  resembles  0.  mou- 
bata  but  is  easily  distinguished  by  the  possession  of  two  pairs  of  eyes,  all  about 
the  same  size.  The  life  history  of  this  tick  is  very  similar  to  that  of  0.  moubata. 
The  females  oviposit  after  each  blood  meal,  and  the  total  number  of  eggs 
varies  widely.  CunlifTe  (1922)  reports  a  total  of  400  under  laboratory  condi- 
tions. Under  experimental  conditions  the  life  cycle  from  egg  to  adult  varied 
from  60  to  over  103  days.  Its  hosts  are  various  domestic  animals  as  horses, 
cattle,  camels,  dogs,  pigs,  goats,  but  it  seems  to  prefer  man  (Bedford,  1934). 
Its  distribution  in  Africa  closely  corresponds  to  that  of  0.  moubata,  and  in 
addition  it  is  found  in  parts  of  Arabia  and  India.  Senevet  (1937)  reports  it 
from  Tunisia,  Algeria,  and  North  Africa  generally.  It  is  known  to  be  a  vector 
of  relapsing  fever. 

Ornithodoros  hermsi  Wheeler,  Herms,  and  Myer  is  a  comparatively  small 
tick  (Fig.  14),  not  much  more  than  half  the  size  of  O.  turicata.  It  may  be 
recognized  by  the  size  and  the  absence  of  dorsal  humps  on  tarsus  I.  It  has  been 
taken  only  at  high  elevations  (3000  to  9000  feet)  in  the  mountainous  regions 
of  the  western  United  States  (California,  Colorado,  Oregon,  Washington, 
Nevada,  and  Idaho).  The  tick  is  primarily  a  parasite  of  small  mammals,  as  the 
western  chipmunks,  Eutamias  spp.,  and  probably  other  rodents.  It  has  been 
taken  in  the  nests  of  its  hosts,  and  Davis  (1939)  reports  taking  many  ticks 


THE  ORDER  ACARINA 


53 


in  chipmunks'  nests  in  old  Douglas  fir  (Pseudotsuga  taxijolia)  stumps  in  east- 
ern Colorado  at  an  elevation  of  8800  feet.  Wheeler  (1943)  gives  a  full  account 
of  the  biology  of  this  tick.  The  females  deposit  their  eggs  in  batches,  the  maxi- 
mum number  obtained  being  232.  The  eggs  hatch  in  9  to  24  days  (under 
constant  temperature  of  75°  F.  and  90  per  cent  humidity);  there  may  be  two 
larval  stages  and  three  or  four  nymphal  stages.  The  normal  time  for  develop- 
ment from  the  egg  to  the  adult  stage  is  about  four  and  one-half  months. 
The  adults  are  apparently  long-lived,  as  Wheeler  kept  some  females  for  over 


Fig.  21.  Distribution  of  argasid  ticks  in  the  United  States.  A.  persicus,  generally  south 
of  the  line  of  dashes,  and  two  isolated  spots,  one  in  British  Columbia,  and  one  in  Balti- 
more, Md.;  Ornithodoros  turicata,  generally  south  of  line  of  dashes  and  north  indicated 
by  circles;  0.  parfyeri,  generally  west  of  line  of  dots;  O.  hermsi,  places  collected  indicated 
by  X's;  0.  corlaceus,  indicated  by  stars.  (After  Cooley  and  others.) 

four  years  without  any  food,  and  others  by  occasional  feedings  for  more  than 
six  and  one-half  years.  This  tick  is  known  to  be  a  vector  of  relapsing  fever  in 
many  parts  of  its  range. 

Ornithodoros  turicata  (Duges)  is  a  large  tick  (Fig.  14)  and  is  widely  dis- 
tributed in  the  southwestern  United  States  (Fig.  21),  Florida,  and  parts  of 
central  Mexico.  It  is  frequently  found  in  great  numbers  in  caves,  in  holes  of 
burrowing  animals,  and  in  camps.  Its  hosts  include  nearly  all  our  domestic 
animals,  rodents,  snakes,  and  terrapins  as  well  as  man.  Hoffman  (1930)  reports 
them  as  abundant  in  pigsties  in  central  Mexico.  Under  experimental  condi- 
tions Francis  (1938)  reared  the  tick  from  egg  to  adult  in  nine  months  and 


54  MEDICAL  ENTOMOLOGY 

ten  days.  He  found  four  nymphal  stages,  though  five  nymphal  stages  were 
observed  in  four  females  and  only  three  nymphal  stages  in  one  male.  The 
species  is  an  excellent  vector  of  relapsing  fever,  and  Davis  (1943)  has  dem- 
onstrated transovarial  transmission  to  the  fifth  generation,  securing  a  100 
per  cent  infection  with  the  fifth  generation.  He  concludes  that  this  tick  may 
be  a  more  efficient  "spirochactal  reservoir"  than  the  rodent  hosts.  Francis 
(1938)  obtained  transmission  of  relapsing  fever  in  infected  ticks  after  four 
years  of  starvation;  two  and  a  half  years  later  he  demonstrated  the  presence 
of  the  spirochetes  in  ticks  that  had  only  one  feeding  during  that  period  (six 
and  a  half  years). 

Ornithodoros  parpen  Cooley  (Fig.  14)  is  very  similar  to  O.  turicata  but 
may  be  recognized  by  the  much  smaller  mammillae.  It  has  been  taken  in 
widely  separated  areas  in  nine  western  states  from  Washington  south  to 
southern  California  and  east  to  Colorado  (Fig.  21).  Jellison  (1940)  took  large 
numbers  in  the  nests  of  the  burrowing  owl,  Speotyto  cunicularia,  and  found 
the  larvae  of  this  tick  engorged.  Its  principal  hosts  are  recorded  as  Citellus  spp., 
Cynotnys  spp.,  Marmota  sp.,  Peromysctts  sp.,'Lepus  sp.,  Sylvilagus  sp.,  Mustela 
sp.,  and  man  (Cooley,  1944).  Davis  (1941)  reared  large  numbers  of  this  tick 
and  records  two  nymphal  stages  for  some  males  and  three  to  four  nymphal 
stages  for  females  and  males.  The  average  developmental  time  from  larval 
feeding  varied  from  about  53  days  to  over  250  days.  This  tick  is  an  efficient 
vector  of  relapsing  fever,  and  Davis  (1943)  has  shown  experimentally  that  it 
can  transmit,  in  all  stages,  the  spotted  fevers  of  the  United  States,  Colombia, 
and  Brazil  with  equal  facility  even  to  the  second  and  fourth  generation 
through  the  egg.  He  suggests  that  this  tick  may  serve  as  a  "spotted  fever 
reservoir"  in  nature  and  may  occasionally  infect  man.  The  tick  is  apparently 
long-lived  as  Davis  has  kept  nymphs  and  adults  for  four  years  without  feeding. 

Ornithodoros  talaje  (Gucrin-Men.)  occurs  from  California  and  Kansas 
south  to  Argentina.  In  the  tropics  and  subtropics  of  the  Americas  it  is  cosmo- 
politan and  is  frequently  present  in  large  numbers.  In  the  United  States  it 
is  recorded  from  California,  Nevada,  Arizona,  Kansas,  Texas,  and  Florida. 
This  tick  (Fig.  14)  has  been  confused  with  O.  rudis  Karsch  and  O.  kellyi 
Cooley  and  Kohls,  and  it  is  difficult  to  interpret  the  published  accounts.  Its 
hosts  are  known  to  be  various  mammals,  birds,  and  reptiles.  The  larval  stage 
is  most  common  on  rats  in  Panama,  and  in  the  United  States  this  tick  has  been 
taken  in  association  with  rodents.  Dunn  (1931,  1933)  reports  it  in  houses 
attacking  man,  and  the  later  stages  were  found  in  beds  and  other  parts  of  the 
homes.  The  larva  of  this  species  requires  a  long  time  to  feed  (several  days) 
and  then  leaves  the  host  and  molts  twice  before  feeding  again.  There  are  three 


THE  ORDER  ACARINA  55 

to  four  nymphal  stages,  but  the  nymphs  require  only  a  few  hours  to  feed. 
Under  laboratory  conditions  Davis  (1942)  has  reared  this  species  in  eight 
months.  The  principal  hosts  of  the  larvae  are  various  species  of  rats,  though 
Dunn  has  taken  them  on  chickens,  opossums,  monkeys,  cats,  and  dogs  in 
Panama.  This  tick  is  known  to  be  a  transmitter  of  relapsing  fever  in  Panama, 
Colombia,  and  Guatemala;  relapsing  fever  spirochetes  have  been  recovered 
from  ticks  captured  in  Arizona  and  Texas. 

Ornithodoros  \dleyi  Cooley  and  Kohls  is  noted  here  because  it  has  been 
confused  with  O.  talaje.  As  far  as  known,  this  is  a  parasite  of  bats,  and  it  has 
been  reported  under  the  name  talaje  from  houses  in  New  York,  Wisconsin, 
and  Minnesota  (Matheson,  1931 ;  Herrick,  1935;  and  Riley,  1935).  It  apparently 
occurs  in  places  where  bats  live  or  roost.  It  also  has  been  reported  from  houses 
in  Illinois,  Iowa,  and  Pennsylvania  (Cooley,  1944).  In  one  house  in  New  York 
it  has  been  present  since  1925,  the  last  tick  being  found  about  December  13, 
1940. 

Ornithodoros  rudis  Karsch  (O.  vcncziielcnsis  Brumpt;  0.  migonei  Brumpt) 
is  closely  allied  to  O.  talaje,  and  these  two  species  have  been  confused  in  litera- 
ture. However,  man  is  the  only  known  host  of  O.  nidis,  which  is  a  house 
dweller,  often  occurring  in  large  numbers  in  primitive  dwellings  where  it 
hides  during  the  day  in  cracks,  crevices,  holes,  bedding,  and  similar  places.  It 
is  a  night  feeder.  The  larvae  feed  rapidly  and  molt  after  feeding;  there  are  two 
to  four  nymphal  molts.  Under  experimental  conditions  the  life  cycle  from 
egg  to  adult  may  occupy  only  three  months  (Davis,  1942).  Its  known  dis- 
tribution is  Panama,  Colombia,  Venezuela,  and  Paraguay.  It  is  the  important 
transmitter  of  relapsing  fever  in  Panama,  Colombia,  and  Venezuela.  Davis 
(1943)  has  shown  that  the  causative  agents  of  the  spotted  fevers  of  Colombia, 
of  Brazil,  and  of  the  United  States  can  be  conserved  in  the  tissues  of  this  tick 
for  343  days,  191  days,  and  243  days,  respectively;  furthermore,  the  Colombian 
spotted-fever  agent  was  transmitted  through  the  egg  to  the  next  generation. 
Davis  did  not  get  transmission  by  the  bites  of  this  tick. 

Ornithodoros  coriaceus  Koch,  the  pjaroello,  is  a  large  tick  and  is  much  feared 
on  account  of  its  bite.  It  occurs  in  many  parts  of  California  extending  from 
near  San  Francisco  south  along  the  coast  (Fig.  21)  in  the  more  mountainous 
regions  into  Mexico,  where  Hoffman  (1930)  records  it  as  native  to  the  hot  and 
temperate  regions  along  the  Pacific  coast  to  Chiapas.  Herms  (1939)  found  it 
commonly  in  deer  beds  among  the  low  scrub  oaks.  It  is  a  parasite  of  large 
mammals  and  bites  man  freely.  Herms  (1916)  gives  its  life  history,  under  ex- 
perimental conditions,  as  requiring  about  15  months  from  egg  to  egg.  He  also 
reared  mature  males  in  about  four  months.  The  larvae  require  several  days  (8 


56  MEDICAL  ENTOMOLOGY 

or  more)  to  engorge,  and  then  undergo  two  molts  before  feeding  again. 
There  are  three  to  six  nymphal  stages.  The  nymphs  and  adults  feed  very 
rapidly,  becoming  engorged  in  10  to  40  minutes.  The  females  lay  several 
batches  of  eggs  and  may  live  for  several  years.  The  bite  of  this  tick  is  very 
severe.  It  is  not  known  to  transmit  any  disease. 

A  goodly  number  of  other  species  of  Ornithodoros  have  been  recorded  as 
biting  man  and  some  of  them  as  playing  a  part  in  the  transmission  of  disease. 
O.  brasiliensis  Aragao  is  reported  from  Brazil  and  bites  man  but  is  not  known 
to  transmit  disease.  O.  rostratus  Aragao  occurs  in  Argentina,  Paraguay,  Brazil, 
and  Bolivia.  It  is  said  to  occur  in  houses  and  its  bite  is  severe.  0.  nicollei 
Mooser  was  described  from  Mexico,  where  it  occurs  in  native  huts;  Davis 
(1943)  gives  its  life  history,  reports  it  readily  infected  with  the  rickettsiae 
of  the  spotted  fevers  of  the  United  States,  Colombia,  and  Brazil,  and  has 
proved  transovarial  transmission.  The  tick  has  been  taken  from  dogs,  species 
of  Neotoma,  man,  and  a  rattlesnake.  O.  delanoei  Roubaud  and  Colas-Belcour 
was  described  from  porcupine  burrows  in  Morocco.  It  is  a  large  species,  the 
female  being  18  mm.  in  length.  The  same  authors  (1936)  give  an  account  of 
its  life  history,  concluding  that  it  requires  about  five  or  six  years  from  egg  to 
maturity  (under  experimental  conditions).  O.  erraticus  (Lucas)  [0.  maro- 
canus  Velu]  occurs  throughout  the  western  littoral  of  the  Mediterranean  and 
south  to  Senegal.  Brumpt  (1936)  records  this  tick  as  infected  with  Spirochaeta 
duttoni  at  Dakar;  it  is  a  vector  of  relapsing  fever  in  Spain  and  parts  of  North 
Africa.  It  is  found  commonly  in  pigsties  and  burrows  of  various  animals  such 
as  porcupines,  jackals,  and  rats.  O.  jolcyi  Parrot  was  described  from  Algeria 
and  reported  as  feeding  on  man.  O.  tholozani  (Laboulbene  and  Megnin) 
[=  O.  papillipes  Birula]  is  reported  from  the  Caucasus,  Turkestan,  Iran, 
Syria,  Palestine,  and  the  island  of  Cyprus.  It  is  known  to  transmit  relapsing 
fever  in  Russia  and  Cyprus.  Russian  workers  report  it  as  living  at  least  25 
years.  Its  hosts  are  camels,  chickens,  porcupines,  jerboas,  and  various  rodents. 
It  readily  feeds  on  man  and  is  found  in  human  dwellings.  0.  lahorensis  Neum. 
is  widely  distributed  in  Russian  Turkestan,  Iran,  Transcaucasia,  Tibet,  Pales- 
tine, Asia  Minor,  and  Cyrenaica;  it  is  also  found  in  India  (the  Punjab).  It 
is  not  known  to  transmit  relapsing  fever  but  transmits  anaplasmosis  of  sheep. 
Its  bite  is  severe  and  is  recorded  as  killing  sheep.  0.  normandi  Larrousse  is 
reported  as  abundant  near  El  Kef,  Tunisia;  it  bites  man  readily. 

THE  GENUS  OTOBIUS:  This  genus  has,  at  present,  only  two  well- 
defined  species.  O.  megnini  (Duges),  more  generally  known  as  Ornithodoros 
megnini,  is  the  spinose  ear  tick.  It  lives  in  the  ears  of  its  hosts,  which  are  mainly 
horses  and  cattle.  It  also  attaches  to  the  ears  of  mules,  asses,  sheep,  goats,  hogs, 


THE  ORDER  ACARINA  57 

dogs,  cats,  coyotes,  deer,  rabbits,  and  some  other  animals.  It  receives  its  name 
from  the  spiny  last  nymphal  stage,  which  is  the  stage  most  commonly  seen  in 
the  ears  of  its  host.  This  stage  leaves  the  host  and  molts  on  the  ground  into 
a  smooth,  typical  tick;  however,  the  large  hypostome  of  the  nymph  is  replaced 
by  a  vestigial  one.  The  adult  does  not  feed.  The  female  lays  her  eggs  on  the 
ground,  and  the  larvae  on  hatching  are  very  active.  Reaching  the  ears  of  their 
hosts,  they  attach  deep  down  in  the  folds  and  become  fully  engorged  in  about 
a  week.  Then  follows  the  larval  molt;  there  is  a  second  molt  soon  after,  and 
this  is  the  last  nymphal  stage,  the  spinose  stage.  The  entire  life  cycle  may  be 
completed  in  a  month  and  a  half  under  favorable  conditions,  or  it  may  be 
greatly  prolonged.  The  adults  may  survive  for  a  year  or  more.  This  tick  was 
originally  described  from  Mexico  but  has  become  widely  distributed  through- 
out many  parts  of  the  world.  In  North  America  it  extends  from  British  Colum- 
bia south  and  east  to  Kentucky  and  North  Carolina.  I  have  taken  this  species  in 
the  ears  of  cattle  shipped  from  Texas  to  Ithaca,  New  York.  The  species  is 
widespread  in  Mexico  and  parts  of  South  America.  Brumpt  (1936)  states  that 
it  is  well  established  in  the  Transvaal  and  other  parts  of  South  Africa.  Kingston 
(1936)  reports  it  in  the  ear  of  a  gelding  that  had  been  born  and  reared  in 
Australia.  This  tick  has  been  reported  found  several  times  in  the  ears  of 
man. 

Recently  Cooley  and  Kohls  (1940)  described  another  species,  O.  lagophilus, 
from  rabbits.  The  species  occurs  in  the  northwestern  United  States  and  British 
Columbia. 

In  addition  to  the  species  mentioned  above  many  others  are  known.  The 
genus  Ornithodoros  contains  several  species  described  from  bats,  bat  roosts, 
or  bat  dung,  as  well  as  from  other  hosts. 

THE  FAMILY  IXODIDAE 

This  family  contains  the  vast  majority  of  ticks  distributed  among  some  10 
or  12  genera.  Only  a  few  of  the  more  important  species  can  be  treated  here. 

'  THE  GENUS  BOOPHILUS:  Boophilus  annulatus  (Say)  (Figs.  22,23)  « 
the  common  cattle  tick  of  North  America  and  Mexico.  In  the  United  States 
it  is  normally  restricted  to  south  of  37°  North  latitude,  and  in  this  area  the 
tick  has  been  largely  eliminated  by  dipping  and  other  practices;  where  pres- 
ent it  is  under  strict  quarantine  control.  The  tick  is  a  one-host  tick.  The  females 
deposit  their  eggs  on  the  ground,  each  female  laying  from  3000  to  over  5000 
eggs.  The  incubation  period  of  the  eggs  depends  largely  on  temperature  and 
moisture  and  varies  from  19  days  (minimum)  in  summer  to  180  or  more 
days  in  late  autumn,  with  varying  periods  between  these  extremes  during  the 


58  MEDICAL  ENTOMOLOGY 

rest  of  the  year  (Graybill,  1941).  The  seed  ticks  are  very  active  and  climb  up 
blades  of  grass  and  various  objects  to  await  a  passing  host.  The  larvae  can 
survive  long  periods — from  a  maximum  of  85  days  for  eggs  hatching  in  July 
to  234  days  for  eggs  hatching  in  October.  The  developmental  period  on  the 
host  (larva,  nymph,  adult)  varies  from  20  to  65  days.  Mating  takes  place  on 
the  host,  and  the  female  after  engorging  drops  off;  egg  laying  begins  in  from 
three  days  to  as  long  as  nearly  100  days  (females  dropping  in  November) .  This^ 
tick  is  a  very  important  species  as  it  transmits  the  organism  (Piroplasma 
bigemina)  of  the  so-called  Texas  fever,  red-water  fever,  or  hemoglobinuria. 


Fig.  22.  The  cattle  tick  (Boophilus  annulattis}.  Male,  ventral  view. 
(After  Salmon  and  Stiles.) 

This  was  demonstrated  by  Smith  and  Kilbournc  (1893),  and  they  showed 
that  the  organism  develops  in  the  red  blood  cells  of  cattle,  destroying  them. 
The  tick  in  feeding  obtains  the  infective  stage  of  this  parasite,  which  under- 
goes a  developmental  cycle  (later  elucidated  by  Dennis,  1932)  and  is  passed 
on  to  the  young  of  the  tick  through  the  egg  (the  so-called  transovarial  or 
hereditary  transmission).  It  is  of  interest  to  note  that  this  was  the  first  tick  that 
was  shown  to  be  an  intermediate  host  of  a  protozoan  parasite  and  the  first  case 
of  proven  transovarial  transmission  of  any  parasite.  The  principal  hosts  of  this 
tick,  besides  cattle,  are  horses,  mules,  sheep,  goats,  and  probably  deer. 

A  number  of  species  or  subspecies  of  this  tick  have  been  described  from  vari- 
ous parts  of  the  world:  Boophilus  australis  Fuller  from  Australia,  the  Philip- 


THE  ORDER  ACARINA  59 

pine  Islands,  the  Dutch  East  Indies,  India,  and  South  America;  B.  microplus 
Canestrini  from  South  America,  Central  America,  West  Indies,  Mexico, 
Florida  and  probably  other  parts  of  the  world;  B.  decolorutus  Koch  from 
South  Africa.  Minning  (1934,  1936)  has  added  a  number  of  doubtful  species. 

THE  GENUS  DERMACENTOR:  This  genus  contains  some  very  im- 
portant North  American  species.  The  principal  characters  that  readily  dis- 
tinguish this  genus  are  as  follows:  ornate,  with  eyes  and  festoons  (always  ir) ; 
basis  capitulum  quadrangular  in  dorsal  view;  coxae  I  to  IV  gradually  in- 
creasing in  size,  with  coxa  IV  very  large;  coxa  I  always  bifid;  anal  groove 
posterior;  males  without  ventral  shields. 

In  North  America  Cooley  (1938)  describes  seven  species,  and  probably  over 
twenty  species  are  at  present  known  from  the  world.  No  species  are  known 
from  South  America  (Cooley,  1938). 

Dcrmacentor  variabilis  (Say),  the  dog  tick  (Fig.  9)  or  wood  tick,  is  widely 
distributed  in  North  America  east  of  a  line  drawn  from  eastern  Montana 
south  to  Texas;  it  also  occurs  in  Canada  east  of  Saskatchewan;  another  area 
is  in  California  west  of  the  Cascade  and  Sierra  Nevada  Mountains  (Fig.  24). 
It  is  most  abundant  along  the  Atlantic  seaboard  from  Massachusetts  south  to 
Florida  and  in  certain  inland  areas  such  as  southern  Iowa  and  parts  of  Wis- 
consin and  Minnesota  (Bishopp  and  Smith,  1938).  This  is  a  three-host  tick. 
The  adults  prefer  large  mammals  such  as  dogs  (the  preferred  host),  cattle, 
horses,  hogs,  sheep,  man,  and  a  wide  variety  of  wild  animals.  The  adults 
require  from  5  to  14  days  to  engorge.  Mating  takes  place  on  the  host.  Dropping 
from  the  host  the  females  lay  their  eggs  in  some  secluded  place  on  the  ground; 
each  female  lays  from  4000  to  6500  eggs.  The  eggs  hatch  in  from  26  to  40  days 
(depending  on  the  temperature),  and  the  larvae  can  survive  without  food 
for  at  least  n  months.  The  principal  larval  hosts  are  mice  (Peromyscus,  Micro- 
tits,  and  Pity my s  spp.),  and  the  time  of  attachment  varies  from  2  to  14  days. 
The  larvae  then  drop  from  their  hosts  and  molt  to  the  nymphal  stage.  Nymphs 
can  survive  at  least  six  months  without  food.  The  nymphs  attach  to  the  same 
host  as  the  larvae  and  engorge  in  from  3  to  10  days.  Dropping  from  the  hosts, 
the  nymphs  molt  to  the  adult  stage  in  from  three  weeks  to  a  much  longer 
period.  The  entire  life  cycle  from  egg  to  adult  varies  from  54  days  to  much 
longer,  depending  on  the  available  food  supply  and  the  temperature.  This 
tick  is  the  important  vector  of  Rocky  Mountain  spotted  fever  and  tularemia 
in  parts  of  its  range, 

Dermacentor  andersoni  Stiles  (yenustus  Banks)  is  commonly  caller)  t^e 
"Rocky  Mountain  spotted-fever  tick"  (Figs.  4,5)  as  it  was  first  shown  to  be  the 
vector  of  a  peculiar  disease  of  man  called  "Rocky  Mountain  spotted  fever." 


60  MEDICAL  ENTOMOLOGY 

Its  distribution  is  restricted  to  parts  of  the  western  United  States  and  western 
Canada  (Fig.  24).  Its  greatest  abundance  is  in  the  northern  part  of  the  Rocky 
Mountain  region  of  the  United  States,  and  there  it  is  most  common  in  areas 
"where  the  predominating  vegetation  is  low,  brushy  and  more  or  less  open, 
i.e.,  in  areas  where  there  is  good  protection  for  the  small  mammalian  hosts 
of  the  larvae  and  nymphs  and  sufficient  forage  to  attract  the  large  hosts,  either 
wild  or  domestic,  of  the  adult  ticks.  It  is  relatively  quite  scarce  in  heavily  tim- 
bered areas  or  country  of  a  strictly  grassland,  prairie  type"  (Parker  et  al.t 


Pig.  23  (lejt).  The  cattle  tick  (tioophilus  annulatus).  Fully  gorged  female.  (After 
Salmon  and  Stiles.) 

Fig.  24  (right).  General  distribution  of  Dcnnaccntor  variabilis  (dotted  area)  and 
D.  andcrsoni  (lined  area)  in  North  America. 

1937).  At  present  it  is  known  from  14  western  states — Washington,  Oregon, 
California,  Nevada,  Arizona  (northern  part),  New  Mexico  (northern  edge), 
Utah,  Colorado,  Idaho,  Wyoming,  Montana,  and  the  western  edge  of  North 
and  South  Dakota  and  Nebraska;  it  is  also  present  in  southern  British  Colum- 
bia (dry  regions  of  the  Kootenay  district  and  north),  southern  Alberta,  and 
southern  Saskatchewan.  The  tick  has  been  spreading,  and  it  may  eventually 
occupy  a  much  wider  range  where  suitable  hosts  and  conditions  exist. 
This  tick  is  a  three-host  tick,  and  its  life  cycle  is  interesting  and  complicated. 


THE  ORDER  ACARINA  61 

The  fertilized  females  drop  from  the  larger  hosts  during  April,  May,  and 
June  or  early  July.  They  deposit  their  eggs  in  some  protected  place  on  the 
ground,  each  female  laying  from  2000  to  8000  eggs  over  a  period  of  about  a 
month.  The  eggs,  depending  on  temperature  and  other  factors,  hatch  in  from 
one  to  two  months.  The  larvae  attach  to  some  of  the  smaller  mammals, 
particular  rodents,  as  the  ground  squirrel  (Citdlus  columbianus) ,  pine  squirrel 
(Sciurus  hudsonicus  richardsoni),  chipmunks  (Eutamias  spp,),  and  most  of 
the  other  native  rodents  as  porcupines,  prairie  dogs,  and  various  species  of 
rabbits.  As  Cooley  remarks,  "Almost  any  mammal  that  is  available  is  used." 
The  larvae  become  engorged  in  two  to  eight  days  and  drop  from  their  hosts. 
Molting  takes  place  on  the  ground,  and  the  nymphs  normally  pass  the  winter 
unfed.  During  the  following  spring  and  summer  the  nymphs  attach  to  the 
same  type  of  hosts  as  those  of  the  larvae.  After  engorgement  the  nymphs  drop 
from  their  hosts,  molt  on  the  ground,  and  pass  the  second  winter  as  unfed 
adults.  The  following  season  the  adults  attach  to  the  larger  mammals,  pre* 
ferring  horses,  cattle,  sheep,  bears,  coyotes,  mountain  goats,  deer,  man,  and 
also  the  jack  rabbits,  snowshoe  rabbits,  and  porcupines,  but  usually  riot  any  of 
the  smaller  rodents.  The  presence  of  the  larger  mammals  seems  essential  for  the 
maintenance  of  this  tick  in  abundance.  They  attach  from  March  to  July  each 
year  and  mate  on  the  hosts.  The  complete  cycle  from  egg  to  egg  thus  requires 
two  years,  though  there  are  many  variations  due  to  the  failure  to  find  suitable 
hosts,  climatic  factors,  and  other  "conditions.  The  most  striking  features  of 
the  life  cycle  are  its  length,  two  years,  and  the  change  of  hosts— from  small 
rodents,  as  larvae  and  nymphs  to  the  larger  mammals  as  adults.  This  tick  is 
a  very  important  vector  of  Rocky  Mountain  spotted  fever,  tularemia,  "Q" 
fever,  and  Colorado  tick  fever;  it  is  the  cause  of  tick  paralysis. 

Dermacentor  occidentalis  Marx  can  be  recognized  by  the  long  cornua  and, 
at  present,  its  restricted  distribution.  It  is  known  only  from  the  Pacific  coast 
along  the  Coastal  Ranges  'and  Cascade  Range  from  northern  Oregon  to 
southern  California.  Cooley  (1938)  reports  it  as  very  abundant  in  southern 
Oregon.  This  is  a  three-host  tick.  The  adults  attach  to  cattle,  horses,  deer,  dogs. 
mules,  asses,  and  man.  The  larvae  and  nymphs  attach  mostly  to  the  smaller 
rodents,  such  as  ground  squirrels,  wood  rats,  chipmunks,  and  rabbits,  and 
occasionally  to  larger  animals.  The  larvae,  nymphs  and  adults  engorge  on 
their  hosts  in  three  to  six  or  more  days,  and  the  entire  life  cycle  may  be  com- 
pleted in  less  than  three  months.  In  nature  this  tick  may  be  found  at  all 
seasons.  It  is  a  serious  pest  of  cattle.  It  also  readily  attaches  to  man  qnrl  its 
bite  is  severe.  At  present  it  is  known  to  transmit  tularemia  and  it  is  strongly 


62  MEDICAL  ENTOMOLOGY 

juspected  of  transmitting  Rocky  Mountain  spotted  fever.  Experimentally  it 
can  transmit  spotted  fever  in  all  stages,  from  stage  to  stage,  and  through  the 
egg  to  the  larvae. 

•Dermacentor  parumapertus  Nctim.  is  primarily  a  rabbit  tick,  as  rabbits  (all 
species)  are  the  hosts  of  all  stages.  It  is  rarely  found  on  other  hosts.  The 
species  occurs  in  the  southwestern  United  States,  from  Oregon,  southern 
Idaho,  and  southern  Wyoming  south  to  Mexico  and  east  to  Kansas  and  central 
Texas.  Parker  et  al.  (1937)  have  shown  stage-to-stage  survival  of  Rocky  Moun- 
tain spotted  fever  in  this  tick,  and  it  seems  probable  that  the  tick  may  serve  as 
an  agent  in  maintaining  the  virus  in  nature  in  rabbits. 

Dermacentor  albipictus  (Pack.),  the  moose  or  elk  tick,  is  markedly  different 
from  all  other  species  of  Dermacentor  as  it  is  a  one-host  tick.  Its  hosts  are  the 
larger  domestic  and  game  animals,  such  as  cattle,  horses,  elk,  moose,  and  deer. 
The  ticks  are  present  on  their  hosts  only  during  the  winter  season,  from  Sep- 
tember (usually)  to  early  spring.  The  females  lay  their  eggs  on  the  ground, 
and  when  they  hatch  the  larvae  bunch  together  and  are  torpid  during  the 
warmer  months;  they  become  active  at  the  approach  of  cold  weather  and 
seek  out  their  hosts.  Once  attached,  the  tick  completes  its  life  cycle,  only 
dropping  when  the  adult  stage  is  reached.  This  tick  is  widely  distributed 
throughout  North  America  and  is  frequently  a  serious  pest  of  elk,  moose,  deer, 
and  horses  in  its  northern  range  in  Canada.  Thomas  and  Cahn  (1932)  report 
this  tick  to  be  a  vector  of  a  serious  disease  of  moose  in  northern  Minnesota  and 
adjacent  regions  of  Ontario. 

THE  GENUS  IXODES:  The  species  of  this  genus  can  be  recognized  readily 
by  the  anal  groove  curving  around  the  anus  in  front.  They  are  inornate,  with- 
out eyes,  and  lack  festoons.  Males  differ  from  females:  they  have  ventral 
plates,  i  median,  i  anal,  and  2  adanals  (a  pregenital  and  2  epimeral  plates  may 
also  be  present) ;  they  are  normally  much  smaller  than  the  females.  Over  one 
hundred  species  have  been  described,  but  probably  not  over  fifty  can  be  con- 
sidered good  species.  Comparatively  little  is  known  about  their  biology,  dis- 
tribution, bionomics,  or  hosts;  a  few  species  have  been  thoroughly  studied. 

Ixodcs  ricinus  (Linn.)  2  is  probably  world-wide  in  distribution.  Its  hosts 
include  cattle,  dogs,  horses,  cats,  deer,  foxes,  sheep,  man,  and  other  animals. 
It  is  a  thrpe-hp.<ff  fink.  As  it  is  the  vector  of  louping  ill  of  sheep  in  Great  Britain 
(northern  England  and  Scotland)  it  has  been  studied  intensely  in  recent  years. 
The  tick  appears  to  require  a  moist  climate  (70  to  80  per  cent  relative  humid- 
ity) for  its  best  development.  MacLeod  (1932-1936)  reports  the  female  lays 
2400  to  3200  eggs;  the  eggs  hatch  in  4  to  10  weeks;  the  larval  and  nymphal 

2Cooley  (1945)  does  not  consider  that  this  tick  occurs  in  North  America. 


THE  ORDER  ACARINA  63 

stages  are  usually  completed  in  from  16  to  20  weeks.  He  found  the  males  and 
females  can  live  nearly  two  years,  the  larvae  two  years,  and  the  nymphs  over 
a  year,  without  feeding.  The  rapidity  of  development  depends  on  the  various 
stages  finding  available  hosts.  It  is  probable  that  it  normally  requires  almost 
a  year  for  the  complete  life  cycle.  Recently  this  tick  has  been  found  to  transmit 
louping  ill  of  sheep  in  the  U.S.S.R.  (Silber  and  Shubladze,  1945).  Louping 
ill  has  also  been  reported  from  man.  This  tick  is  also  the  most  important 
vector  of  piroplasmosis  (Babesia  bovis)  of  cattle  in  Europe. 

Ixodes  pacificus  Cooley  and  Kohls  (usually  called  calijornicus  Banks) 
closely  resembles  Ixodes  ricinus.  It  occurs  commonly  along  the  Pacific  coast 
from  southern  British  Columbia  to  Mexico  west  of  the  Cascade  Mountains. 
The  adults  attack  a  wide  range  of  animals  including  man.  The  immature 
stages  also  attach  to  cold-blooded  animals  and  birds.  As  it  is  a  three-host  tick, 
it  may  prove  of  some  importance  in  the  transmission  of  disease. 

Ixodes  cooled  Pack,  is  a  common  tick  in  the  eastern  United  States  and 
occurs  on  a  variety  of  animals  such  as  woodchucks,  foxes,  squirrels,  skunks, 
weasels,  dogs,  and  cows.  It  is  not  an  uncommon  tick  on  humans.  The  author 
has  nine  records  from  humans:  two  ticks  taken  from  the  eyelids  of  children, 
two  from  the  shoulders  of  adults,  four  from  the  head  and  neck,  and  one  from 
below  the  breast — all  were  from  the  central  New  York  region.  This  tick  has 
not  been  studied  to  determine  whether  it  can  transmit  any  disease.  Ixodes 
holocyclus  Neum.  occurs  in  India,  Australia,  and  the  East  Indies.  Its  life  cycle 
is  quite  similar  to  that  of  7.  ricinus.  It  has  a  wide  range  of  hpsts,  including  man. 
7.  pilosus  is  widespread  in  South  and  East  Africa.  The  last  two  species  are 
notorious  for  the  production  of  "tick  paralysis"  in  man  and  animals. 

THE  GENUS  AMBLYOMMA:  This  is  a  large  genus  of  ornate  ticks;  they 
abound  principally  in  the  tropical  and  subtropical  regions.  They  may  be  recog- 
nized by  the  long  palpi  and  hypostome;  the  second  segment  of  the  palpus  is 
over  twice  as  long  as  it  is  wide,  and  the  hypostome  is  armed  with  teeth  only  on 
the  apical  half.  Eyes  and  festoons  are  present.  Although  over  ninety  species 
have  been  described,  Cooley  (1944)  lists  only  seven  species  from  North  Amer- 
ica. The  species  are  most  abundant  in  South  America  and  Africa  and  are  very 
difficult  to  diagnose. 

Amblyomma  americanum  (Linn.),  the  lone-star  tick  (Fig.  25),  is  easily 
identified  by  the  solitary  white  spot  on  the  posterior  margin  of  the  scutum  of 
the  female.  It  is  widely  distributed  in  the  United  States  east  of  central  Texas 
north  to  southern  Iowa  and  east  to  the  Atlantic  seaboard.  It  is  recorded  as 
abundant  in  the  Ozark  region  and  occurs  commonly  along  the  south  Atlantic 
coast  and  in  the  canebrakes  of  Louisiana  and  Mississippi  as  well  as  in  wooded 


64  MEDICAL  EJ-ITOMOLOGY 

regions  of  many  of  the  southern  states.  It  is  a  three-host  tick,  and  in  its 
southern  range  it  breeds  throughout  the  year.  The  larvae  and  nymphs  occur 
on  a  wide  range  of  hosts  including  birds;  all  stages  attack  many  different  mam- 
mals such  as  cattle,  horses,  hogs,  and  man.  Its  bite  is  very  painful  and  may 
be  followed  by  suppurating  sores.  The  larvae,  nymphs,  and  adults  can  survive 
nearly  a  year  or  longer  without  food.  This  tick  is  a  vector  of  Rocky  Mountain 
spotted  fever  (Texas  and  Oklahoma),  is  a  suspected  vector  of  "Q"  fever  and 
tularemia,  and  is  reported  as  a  transmitter  of  a  new  clinical  syndrome, 
"Bullis"  fever. 


Fig.  25.  Left:  Amblyomma  cajennense.  Right:  A.  americanum.  Adult  females. 

Amblyomma  cajennense  (Fabr.)  is  distributed  from  the  southern  tip  of 
Texas  south  through  Central  America,  Panama  and  south  along  the  Atlantic 
seaboard  to  Argentina.  Unlike  the  lone-star  tick  the  scutum  has  an  extensive 
pale  pattern  (Fig.  25),  and  the  internal  spur  of  coxa  I  is  about  one-half  as 
long  as  the  external  spur.  It  is  a  three-host  tick  and  all  stages  readily  attach  to 
man.  Where  it  occurs  in  abundance,  it  is  very  annoying  to  all  domestic  animals 
and  many  wild  animals,  and  man  suffers  very  severely  from  its  attacks.  As  the 
tick  is  very  small  (3  to  3.5  mm.  in  length  in  the  female),  it  easily  gains  access 
through  clothing.  The  bites  are  very  deep  owing  to  the  long  mouth  parts  and 
frequently  develop  into  sores  that  are  difficult  to  heal.  In  Brazil  and  Colombia 
it  is  the  recognized  vector  of  spotted  fevers  (Brazilian  spotted  fever  and  Tobia 
fever).  These  diseases  are  presumably  identical  with  Rocky  Mountain  spotted 
fever,  and  A.  cajennense  may  prove  a  suitable  vector  when  this  disease  is  intro- 
duced into  southern  Texas. 

Amblyomma  maculatum  Koch  is  an  important  pest  of  livestock  along  the 
Atlantic  and  the  Gulf  coasts,  extending  from  South  Carolina  west  to  Texas.  It 
also  occurs  throughout  South  and  Central  America.  The  larval  and  nymphal 


THE  ORDER  ACARINA  65 

stages  attach  to  birds  and  some  of  the  smaller  wild  mammals;  the  adults  attach 
in  the  ears  and  when  abundant  produce  inflammation  and  swelling.  The 
points  of  attack  furnish  ideal  places  for  infestation  with  screw  worms,  which 
may  result  in  the  death  of  the  animals. 

Amblyomma  hebraeum  Koch,  the  bont  tick,  is  widespread  in  South  Africa. 
It  is  a  three-host  tick  and,  in  all  stages,  attaches  to  man  as  well  as  to  many 
domestic  and  game  animals.  In  its  range  it  is  a  vector  of  tick-bite  fever  of  man 
and  heart  water  of  cattle,  sheep,  and  goats.  Many  other  species  of  Amblyomma 
occur  in  Africa  and  are  important  pests  of  domestic  and  game  animals,  and 
some  are  vectors  of  serious  diseases. 

THE  GENUS  RHIPICEPHALUS:  The  ticks  of  this  genus  are  practically 
always  inornate,  with  eyes  on  the  margins  of  the  scutum  and  with  festoons. 
When  viewed  dorsally  the  capitulum  is  generally  hexagonal  in  outline.  The 
males  are  smaller  than  the  females  and  possess  ventral  shields.  Over  thirty 
species  are  recognized,  and  of  these  more  than  twenty  are  known  from  Africa. 
In  North  America  there  is  one  species,  which  is  world-wide  in  distribution. 

Rhipicephalus  sanguineus  (Latr.),  the  brown  dog  tick  (Fig.  9),  is  widely 
distributed  in  the  United  States  and  occurs  in  most  of  the  temperate  and 
tropical  regions  of  the  world.  It  was  first  reported  from  southern  Texas  in  1912, 
and  since  then  it  has  spread  to  most  parts  of  the  continent.  It  is  primarily  a 
pest  of  dogs  and  has  not  been  reported  as  a  pest  of  man  in  the  United  States. 
In  the  temperate  climates  this  tick  seeks  warm  places  such  as  houses,  dog 
kennels,  and  similar  places  where  it  may  pass  generation  after  generation. 
In  warmer  climates  it  occurs  out  of  doors,  often  in  great  numbers.  It  is  a  three- 
host  tick  and  all  stages  develop  readily  on  dogs.  Under  favorable  conditions 
the  entire  life  cycle  from  the  egg  to  the  adult  may  be  completed  in  less  than 
two  months.  In  the  North  this  tick  often  becomes  very  abundant  in  private 
homes  where  dogs  are  allowed  to  wander  at  will.  They  may  be  found  in 
cracks  and  on  the  walls,  floors,  and  ceilings.  They  are  difficult  to  eradicate. 
In  some  parts  of  the  world,  as  about  the  Mediterranean  region  and  in  Africa, 
this  tick  is  known  to  attach  to  man.  It  is  also  reported  attacking  man  in 
Mexico.  It  is  a  vector  of  several  diseases.  It  is  known  to  transmit  boutonneuse 
fever  and  Kenya  tick  typhus  and  has  been  shown  experimentally  to  be  capable 
of  transmitting  Rocky  Mountain  spotted  fever  and  Spanish  relapsing  fever; 
it  is  also  implicated  in  tick-bite  fever  and  "Q"  fever.  Bustamente  et  al.  (1946) 
have  found  this  tick  naturally  infected  with  Rocky  Mountain  spotted  fever 
in  Mexico.  It  is  an  important  vector  of  canine  piroplasmosis  (Babesia  canis) 
or  malignant  jaundice  of  dogs;  this  disease  is  common  in  the  Mediterranean 
region  and  South  Africa  and  has  recently  been  reported  from  Florida. 


66  MEDICAL  ENTOMOLOGY 

Other  species  of  this  genus  are  important  vectors  of  serious  diseases  of 
domestic  animals  in  various  parts  of  Africa.  R.  appendiculatus,  R+  capensis, 
R.  evertsi,  and  R.  simus  are  vectors  of  East  Coast  fever  of  cattle;  the  last  two 
are  also  involved  in  the  transmission  of  red-water  fever  of  cattle;  R.  simus, 
R.  sanguincus,  and  R.  bursa  are  vectors  of  bovine  anaplasmosis  (Anaplasma 
marginale) ;  and  other  species  are  known  to  transmit  several  different  diseases. 

THE  GENUS  HAEMAPHYSALIS:  The  ticks  of  this  genus  are  small, 
eyeless,  and  inornate  but  with  festoons.  The  second  segment  of  the  palpus 
projects  laterally  at  its  base  and  gives  the  capitulum  a  triangular  appearance 
in  dorsal  view.  More  than  fifty  species  have  been  described,  but  only  a  few 
of  them  are  known  to  play  any  part  in  disease  transmission. 

Haemaphysalis  leporis-palustris  (Pack.),  the  rabbit  tick  (Fig.  9),  plays  an 
intermediate  but  important  part  in  the  transmission  of  Rocky  Mountain 
spotted  fever  and  tularemia.  According  to  Green  and  his  associates  (1943), 
the  favorite  host  of  this  tick  in  all  stages  is  the  snovvshoe  hare,  the  second  most 
important  host  is  the  ruffed  grouse,  and  the  cottontail  rabbit  is  the  third.  In 
addition,  this  tick  is  reported  from  more  than  sixty  species  of  ground-loving 
birds,  from  many  different  rodents,  and  occasionally  from  domestic  animals. 
The  larvae  and  nymphs  are  the  stages  most  commonly  found  on  birds.  It 
is  not  known  to  attach  to  man;  only  one  case  has  been  reported  by  Brown 
(1946)  in  Alberta,  Canada.  The  tick  is  a  three-host  tick  and  feeds,  in  the 
North,  during  the  spring,  summer,  and  autumn.  It  hibernates  in  all  stages  on 
the  ground.  In  the  South  the  tick  is  found  on  its  hosts  throughout  the  year.  The 
life  cycle  may  be  completed  in  as  short  a  time  as  75  clays,  or  it  may  be  greatly 
prolonged  if  hosts  and  conditions  are  not  favorable.  All  stages  of  the  tick  are 
capable  of  surviving  long  periods  of  starvation.  The  importance  of  this  tick 
lies  in  its  ability  to  transmit  Rocky  Mountain  spotted  fever  and  tularemia 
among  the  reservoir  hosts.  If  infected  the  tick  can  transmit  these  diseases  to 
susceptible  hosts  at  each  feeding.  The  rabbit  tick  is  widely  distributed  from 
Alaska  and  Canada  throughout  the  United  States  and  Central  and  South 
America  to  Argentina. 

Haemaphysalis  leachi  (Aud.)  is  an  important  tick  with  a  wide  distribution 
in  Africa,  Asia,  and  throughout  the  Australasian  region.  It  is  the  vector  of 
canine  piroplasmosis  (Babesia  canis)  and  is  reported  as  a  transmitter  of  tick- 
bite  fever  in  South  Africa.  PL  humerosa  of  Australia  has  been  shown  to 
transmit  "Q"  fever  among  bandicoot  rats,  a  natural  reservoir  of  the  disease, 
while  H.  bispinosa  is  thought  to  be  one  of  the  vectors  to  man.  Other  ticks  are 
recorded  as  playing  a  role  in  the  transmission  and  maintenance  of  this  disease 
in  Australia. 


THE  ORDER  ACARINA  67 

4    TICKS  AND  DISEASE 

Our  knowledge  o£  ticks  and  the  role  they  play  in  the  causation  of  diseased 
conditions  in  man  and  other  animals  and  in  the  transmission  of  pathogenic 
organisms  has  greatly  increased  during  the  past  few  years.  Smith  and  Kil- 
bourne  (1893)  were  the  first  to  prove  that  the  ordinary  cattle  tick,  Boophilus 
annulatus  (Say),  is  the  vector  of  Texas  fever,  red-water  fever,  or  hemo- 
globinuria  of  cattle.  Furthermore  they  showed  that  the  organism  Piroplasma 
bigemina  is  passed  through  the  egg  to  the  larva.  Infection  occurs  when  larvae 
descended  from  infected  mothers  feed  on  nonimmune  cattle.  This  was  the 
first  demonstration  of  the  passage  of  a  pathogenic  protozoan  from  the  parent 
to  the  offspring.  During  the  intervening  years  a  large  number  of  ticks  have 
been  shown  to  be  the  vectors  of  many  serious  diseases  of  man  and  other  ani- 
mals. At  present  the  interrelations  of  ticks  and  disease  may  be  roughly  classi- 
fied as  follows: 

1.  Direct  effects  produced  by  their  bites. 

2.  Causation  of  paralysis,  known  as  "tick  paralysis." 

3.  Hosts  and  vectors  of  pathogenic  organisms. 

TICK  BITES 

Tick  bites  arc  at  times  rather  serious.  In  many  domestic  and  game  animals 
the  loss  of  blood  is  often  great;  frequently  the  mass  attack,  especially  in  young 
animals,  results  in  death  or  weakness,  which  exposes  them  to  disease  or 
destruction  by  their  enemies.  Moose  and  elk  have  frequently  been  reported 
as  weak  and  dying  from  mass  attacks  of  Dermacentor  albipictus,  and  young 
cattle  are  undoubtedly  killed  by  attacks  of  Boophilus  annulatus.  When  ticks 
bite  there  is  injected  into  the  wound  the  secretions  of  the  salivary  glands,  which 
in  some  cases  are  known  to  possess  an  anticoagulin  and  in  others  a  toxin. 
Whatever  may  be  present,  the  bites  of  certain  species  produce  ugly  ulccrations, 
which  are  difficult  to  heal  and  which  offer  ideal  conditions  for  the  invasion 
of  pathogenic  organisms  or  the  attacks  of  myiasis-producing  flies.  Widely 
varying  effects  are  reported  by  different  workers.  This  should  be  expected  since 
insect  bites  affect  different  people  in  the  most  varied  ways.  When  a  tick  has 
buried  its  capitulum  deeply,  it  should  be  removed  with  great  care.  Holding 
the  lightened  end  of  a  cigarette  to  the  tick  will  usually  cause  it  to  loosen  its 
hold.  It  should  then  be  carefully  removed  and  not  crushed  by  hand  but  stamped 
on  or  placed  in  alcohol.  Crushing  it  might  result  in  infection  if  the  tick  hap- 
pened to  be  carrying  some  pathogenic  organisms.  Another  method  o£  tick 
removal  (said  to  be  effective  by  those  using  it)  is  to  place  a  piece  of  adhesive 


68  MEDICAL  ENTOMOLOGY 

tape  over  the  tick,  attaching  it  firmly  on  both  sides  of  the  tick.  This  will  cause 
the  tick  to  withdraw  its  mouth  parts  and  it  then  can  be  removed  without 
tearing  the  flesh.  The  wound  should  be  treated  by  some  antiseptic  such  as 
alcohol,  and,  if  a  physician  is  available,  he  should  be  consulted.  Should  infec- 
tion result  the  physician  will  have  a  better  chance  to  give  the  correct  treatment. 
Table  3  lists  ticks  that  are  recorded  as  producing  severe  wounds  on  man  by 
their  bites.  The  bites  of  many  other  ticks  are  annoying,  but  little  information 
can  be  found  about  them. 

Table  3.  Ticks  whose  bites  may  have  severe  effects  on  man. 


Species 

Effect  of  bite 

Authority 

Argas  mianensis 

Severe;  produces  fever 

Nuttall  and  others 

A.  brumpti 

Bite  severe  and  wound 
pruriginous  for  long  time. 
After  25  years  nodules 
still  persist  at  location 
of  bite 

Brumpt  (1927) 

Ornithodoros 

Extensive  ecchymosis 

Patton  (1913) 

savignyi 

O.  gurneyi  (Australia) 
on  Kangaroo 

Reported  to  cause  paralysis, 
blindness,   and    unconscious- 

Man. Trop.  Mcd.  (1945) 

ness 

O.  turicata 

Effects  severe 

Nuttall  (1908)  and  others 

O.  ro  stratus 

Bites  severe 

Davis  (1945) 

O.  talaje 

Effects  severe 

Nuttall  and  others 

O.  moubata 

Bites  of  nymphs,  severe? 

Nuttall  (1908) 

O.  lahorensis 

Bites  severe 

Vogel  (1927) 

O.  brasilienscs 

Bites  severe 

Davis  in  Man.  Trop.  Med. 

I  x  odes  ricinus 

Bites  often  accompanied 
by  paralysis 

Nuttall  (1908) 

I.  ricinus  (?) 

Severe,  followed  often  by 
ulceration  or  glandular 
involvement 

Mail  and  Gregson  (1938) 

/.  pacificus  (calijornicus) 

Bite  severe  and  reactions 
often  follow 

Various  authors 

Amblyomma  cajennense 

Severe,  often  followed  by 
sores  difficult  to  heal 

Various  authors 

TICK  PARALYSIS 


Tick^£aralysis  is  a  peculiar  disease  found  mostly  in  young  childrea~and.. 
domestic  animals,  such  as  sheep,  dogs,  cattle,  and  goats,  when  attacked^  by 


THE  ORDER  ACARINA  69 

certain  sgecies  of  ticks.  Thej)aralysisis_iisually  .preceded  by  muscular  weak- 
ness andjnability  J:o  co-ordinate  the  movements  oj^thelegs,  followed  in  a  few 
hours  by_ji  more  or  less  complete  flaccid  paralysis  of  the  lower  limbs.  The 
paralysis  extends  rapidly  _upjward,  involving  the  arms  and  neck;  speech  and 
deglutition  become..  difficulty  and,  if  trie  tick  is  not  found  and  removed,  death 
results  from  respiratory  paralysis..  In  many  cases  a  marked  rise  in  temperature 
occurs.  In  North  America  the.  ticks  involved  are  Dermacentor  andersoni  and 
D.  variabilis;  there  is  also  a  possibility  that  a  species  of  Ixodes  may  play  a  part 
in  British  Columbia.  When  these  ticks  attach  at  the  base  of  the  skull,  on  the 
head,  or  along  the  spine,  paralysis  may  result.  If  the  tick  or  ticks  are  removed 
before  paralysis  reaches  the  respiratory  state,  recovery  is  usually  prompt  and 
rapid.  Todd  (1914)  reviews  the  history  of  tick  paralysis  in  British  Columbia. 
For  a  long  time  practicing  physicians  in  British  Columbia  have  known  this 
disease  was  associated  with  tick  bites.  Todd  (1914)  gives  the  records  of  ten 
cases  reported  by  different  physicians,  and  all  except  one  recovered  promptly 
after  the  removal  of  a  tick  (Dermacentor  andersoni).  He  also  gives  details  of  a 
series  of  experiments  with  this  tick;  he  obtained  paralysis  in  a  puppy  and 
lambs  but  failed  with  monkeys  and  guinea  pigs.  Had  wen  (1913)  and  Nuttall 
(1914)  confirmed  these  results  by  producing  paralysis  in  sheep  and  dogs  by 
the  bites  of  D.  andersoni.  McCormack  (1921)  records  13  cases  of  tick  paralysis 
in  young  children  and  one  of  a  girl  21  years  old.  All  recovered  when  the  ticks 
were  discovered  and  removed  except  in  one  case  in  which  the  tick  was  not 
noted  till  after  death.  Nuttall  (1914)  lists  13  cases  as  observed  by  Dr.  Temple 
in  Oregon.  Cogswell  (1923)  lists  6  cases  in  children  in  'Montana.  Mail  and 
Gregson  (1938)  report  26  cases  from  British  Columbia  during  the  period 
from  1910  to  1931;  of  these  four  died.  Dermacentor  andersoni  was  the  tick 
involved.  They  also  state  that  they  have  records  of  at  least  150  cases  from  the 
province.  Robinson  and  Carroll  (1938)  report  a  single  case  of  tick  paralysis 
in  a  young  girl  from  Georgia  caused  by  the  bite  of  Dermacentor  variabilis. 
Recovery  was  rapid  when  they  found  and  removed  two  ticks  from  the  parietal 
region  of  the  skull.  Gibbes  (1938)  lists  a  case  of  a  young  woman  in  South 
Carolina  who  was  suffering  from  a  peculiar  paralysis  when  she  was  admitted 
to  a  hospital.  The  accidental  finding  and  removal  of  a  tick  from  the  back 
of  the  scalp  brought  almost  immediate  recovery.  The  tick  was  undoubtedly 
Dermacentor  variabilis.  Undoubtedly  physicians  have  treated  many  other  cases 
of  which  we  have  no  record.  Ticks  do  not,  in  all  cases,  produce  paralysis 
when  they  attach  to  young  ^children^but,  when  children 


^ 

QCSS  accompanied  j^njibUityj^Q  the  legs,  searcri 

should  be  made  at  ..once  for  ticks  and  they  should  be  carefully  removedT 


70  MEDICAL  ENTOMOLOGY 

Tick  paralysis  also  occurs  among  sheep.  Hadwen  (1913)  reports  many 
cases  among  lambs  in  British  Columbia.  Hearle  (1933)  reports  an  outbreak  of 
paralysis  among  steers  in  British  Columbia.  Out  of  900  steers  100  became 
paralyzed  and  65  died.  Moillett  (1937)  records  200  steers  stricken  in  a  herd  of 
638  in  the  same  province;  of  these  26  died.  In  all  cases  D.  andersoni  was  the 
tick  involved.  In  Australia  paralysis  in  lambs,  dogs,  and  children  is  caused 
by  Ixodes  holocydus  Neum.  Ferguson  (1924)  reports  eight  deaths  of  children 
in  Australia  from  tick  paralysis,  all  caused,  he  believes,  from  the  bites  of 
Ixodes  holocydus.  Ross  (1926)  records  numerous  experiments  with  this  tick 
on  dogs  but  was  unable  to  determine  the  exact  agent  producing  paralysis  and 
death.  Tick  paralysis  has  also  been  reported  from  South  Africa  caused  by  the 
bites  of  Ixodes  pilosus  Koch.  Veneroni  (1928)  reports  two  cases  of  tick 
paralysis  in  Italian  Somaliland  from  bites  on  the  neck  by  the  tick  Rhipi- 
cephalus  simus  Koch.  In  Europe  Ixodes  ricinus  (Linn.)  is  known  to  cause 
a  paralysis  by  its  bites. 

This  peculiar  ascending  motor  paralysis  has  been  reported  from  widely 
separated  regions  of  the  world  and  is  caused  by  at  least  six  different  species 
of  ticks.  As  the  onset  of  the  disease  may  easily  be  mistaken  for  poliomyelitis, 
it  is  essential  that  in  all  cases  of  paralysis  of  children  search  should  be  made 
for  the  presence  of  ticks.  As  a  prophylactic  measure  all  people,  especially  chil- 
dren, that  camp,  play,  or  live  in  tick-infested  regions  should  be  carefully 
examined  each  day  for  ticks.  The  head  should  be  combed  with  care  since  the 
small  unengorged  ticks  are  not  easily  located.  If  ticks  are  found,  report  to  a 
physician  so  that  any  sign  of  sickness  may  be  treated  at  once.  In  all  cases  re- 
move the  ticks  so  that  the  head  is  not  left  buried  in  the  wound.  If  the  head 
is  left,  have  a  physician  remove  it. 

TICKS  AS  VECTORS  AND  HOSTS  OF  PATHOGENIC  ORGANISMS 
AND  VIRUSES 

Human  Diseases 

During  the  past  fifty  years  ticks  have  been  discovered  to  be  the  active 
vectors  and  hosts  of  many  animal  and  human  diseases.  Smith  and  Kilbourne 
(1893)  first  demonstrated  the  relation  of  Boophilus  annulatus  (Say)  and 
hemoglobinuria  or  red-water  fever  of  cattle.  The  causative  agent  of  this  dis- 
ease is  a  minute  protozoan,  Piroplasma  bigemina,  which  lives  within  and  de- 
stroys the  red  corpuscles.  It  is  a  very  serious  disease,  and  no  adequate  treat- 
ment is  known  except  the  control  of  the  ticks.  A  similar  disease  of  cattle  in 
Europe,  caused  by  Babcsia  bovis,  is  transmitted  by  the  ticks  Ixodes  ricinus, 


THE  ORDER  ACARINA  71 

/.  hexagonus,  and  probably  other  species.  Numerous  otber  diseases  of  animals 
are  transmitted  by  ticks,  but  space  does  not  permit  of  more  than  a  mention 
here. 

RELAPSING  JFEVERS ;  OF  MAN  (Tick-borne) :  In  recent  years  a  large 
number  of  relapsing  fevers,  caused  by  Spirochacta  spp.  (often  referred  to 
under  the  generic  names  Spirillum,  Treponema,  or  Borrelia)  have  been  recog- 
nized by  different  workers.  These  relapsing  fevers  are  characterized  by  re- 
peated attacks  of  fever,  the  attacks  tasting  from  Tnree  to  five  days.  The  periods 
of  apyrexia  vary  from  five  to  ten  days.  The  causative  agents  of  these  fevers 
are  species  of  Spirochaeta  that  are  present  in  the  blood,  cerebrospinal  fluid, 
and  other  body  fluids  and  are  most  abundant  during  attacks  of  fever.  During 
the  apyrexial  periods  they  may  apparently  be  absent  from  the  blgod^^trearn 
though  experimental  infection  work  has  demonstrated  their  presence.  The 
vectors  of  the  various  species  of  Spirochacta  are^ticks  and  lice,  though  other 
arthropods.  inay-at^tijiies_play.A.pait..  The  presence  of  thejjpirochetes  in  the 
blood  stream  during*  the  entire  infection  period  is  of  great  significance4  espe- 
cially when  prophylactic  measures  are  considered.  Spjirgchs£ta..jrjeff.Htrsntif 
(Lebert),  often  referred  to  as  S.  obermeieri,  was  the  first jsjjgcics.  observed  to 
infest  the  blood  of  man.  It  was  first  seen  by  Obermeier  in  1868  and  was  de- 
scribed and  named  by  Lebert  in  1874.  Ross  and  Milne  (1904)  were  the  first  to 
demonstrate  that  a  peculiar  fever  of  West  Africa  was  caused  by  a  spirochete 
(now  known  as  Spirochaeta  duttoni)  and  that  the  spirochete  was  transmitted 
to  man  by  a  tick,  Qrnithodoros  moubata  (Murray).  Later,  but  independently, 
Dutton  and  Todd  (1905)  demonstrated  that  Q.  moubata  was  the  vector  of  this 
spirochete.  Furthermore  they  proved  that  the  newly  hatched  offspring  of  iat 
fected  ticks  were  capjible  of  transmitting  the  disease.  Since  then  it  has  been 
shown  that  infection  in  the  tick  can  pass  through  the  eggs  even  to  the  third 
generation.  At  present  numerous  species  of  spirochetes  have  .been  described 
from  the  blood  of  man  and  animals.  More  than  12  species  have  been  described 
as  occurring  In  man,  but  there Js  no  general  agreement  that  these  are  all  dis- 
tinct species.  Some  authorities  consider  them  to  be  nothing  more  than  strains 
of  the  one  species,  S.  recurrentis. 

Tick  relapsing  fevers  are  widely  distributed  throughout  the  world,  being 
recorded  from  Europe,  Asia,  Africa,^orth,  South,  and  Central ,  A_m£iiea^and 
Mexico.  In  NortrT  America  tick  relapsing  fever  is  known  from  at  least  13 
western  states  and  the  southern  part  of  British  Columbia.  Though  relapsing 
fever  was  first  recognized  by  Meader  (1915)  in  Colorado  and  other  physicians 
in  California  (1922)  and  Texas  (1927),  it  was  not  till  1930  that  Weller  and 
Graham  showed  it  to  be  tick-borne.  They  demonstrated  that  Ornithodoros 


72  MEDICAL  ENTOMOLOGY 

turicata  was  the  vector.  Since  then  at  least  two  other  species  of  Ornithodoros 
have  been  recognized  as  active  vectors  in  the  United  States.  In  practically  all 
cases  the  spirochetes  are  passed  from  generation  to  generation  through  the 
eggs,  and  Davis  is  of  the  opinion  that  the  active  reservoirs  of  the  spirochetes 
are  the  ticks  rather  than  the  susceptible  animals  such  as  rodents  on  which  so 
many  of  the  ticks  feed.  Table  4  will  give  in  brief  form  the  known  tick  vectors 
and  the  present  distribution  of  the  disease.  The  distribution  of  the  ticks  is 
usually  much  more  extensive  than  that  of  the  disease.  Undoubtedly  other 
species  are  involved,  but  data  on  them  are  not  available. 

Table  4.  Tick  relapsing  fever. 


Vector 

Distribution  of  ticks 

Known  occurrence  of  disease 
(and  name  of  spirochete  strain) 

Ornithodoros 

Southwestern  U.S.A., 

New  Mex.,  Kansas,  Okla., 

turicata 

Florida,  and  Mexico 

Texas,  Mexico  (S.  turicatae) 

0,  hermsi 

Calif.,  Col.,  Ore., 

Calif.,  Col.,  Idaho,  Nev.,  Wash., 

Wash.,  Nev.,  Idaho 

British  Columbia  (?)   (S.  hermsi) 

(At  high  elevations, 

3000  ft.-f-) 

O.  parfcri 

Nine  western  states 

California.  (Ticks  with  spirochetes 

from  Wash,  to  southern 

also   taken    in    Idaho,    Mont.,    Nev., 

Calif,  and  east  to 

Wyo.,  and  Utah) 

Mont,  and  Col. 

(S.  par^eri) 

O.  talaje 

Calif,  to  Kansas, 

Panama,  Colombia,  and  Guatemala 

south  to  Argentina 

(S.  venezuelensis) 

O.  rudis 

Panama,  Colombia, 

Panama,  Colombia,  Venezuela 

(venezuelensis) 

Venezuela,  Paraguay 

(S.  vcnezuclcnsis) 

(A  house  tick) 

0.  moubata 

Africa  from  Lake  Chad 

Throughout  the  range  of  the  tick 

east  to  Red  Sea  and 

(S.  duttoni) 

south  to  Cape  Province 

0.  savignyi 

Same  area  as  O.  moubata, 

Probably  throughout  its  range 

also  North  Africa, 

(S.  duttoni?) 

Arabia,  and  India 

O.  erraticus 

Western  littoral  of 

Southern  Spain  and  parts  of  Africa 

Mediterranean,  Spain 

(5.  hispanicum) 

south  to  Senegal  in 

Africa 

O.  tholozani 

Caucasus,  Iran,  Syria, 

Cyprus,  parts  of  Russia  (S.  sp.?) 

(papittipes) 

Palestine,  Cyprus 

0.  nereensis 

Turkmenia  (Russia) 

Turkmenia  (Russia)  (S.  sp.?) 

THE  ORDER  ACARTNA  73 

The  method  q£_transrnission  o£  the  spirochejgs, by.. the  various  specie^, of. 
ticks  is  not  known  in  all  cases.  The  ticks  obtain  the  spirochetes  when  feeding 
on  the  blood  of  animals  that  are  infected.  In  the  tick  the  spirochetes  multiply 
by  transverse  fission.  The  spirochetes  invade  the  tissues  and  body  cavity  of  the 
tick.  When  an  infected  tick  bites  a  new  host,  the  spirochetes  gain  entrance 
either  through  the  coxal  fluid  glands,  which  eject  their  secretion  (as  in  0. 
moubata)  or  by  way  of  the  bite  as  in  0.  turicata,  0.  parpen,  0.  hermsi,  0. 
tholozani,  and  probably  others  (Davis,  1945). 

,  ROCKY  MOUNTAIN  SPOTTED  FEVER:  Ever  since  the  settlement 
of  Montana  there  has  appeared  in  certain  regions,  particularly  the  Bitter  Root 
Valley,  a  peculiar  and  very  fatal  disease  of  man.  The  disease  was  first  recog- 
nized here  about  1890.  It  is  characterized  by  sudden  onset,  a  high  fever,  severe 
arthritic  and  muscular  pains,  and  a  profuse  petechial  eruption  in  the  skin,  ap- 
pearing first  on  the  ankles,  wrists,  and  forehead  but  later  usually  spreading 
all  over  the  body.  In  fatal  cases  the  disease  runs  a  rapid  course,  the  patient 
dying  from  the  sixth  to  the  twelfth  day.  If  the  fever  falls  and  the  patient  lives 
two  weeks,  recovery  is  usually  rapid.  There  are  two  strains  of  the  disease,  a 
mild  and  a  virulent  type,  and  these  appear  to  be  present  in  most  of  the  regions 
in  which  it  occurs.  The  mortality  rate  varies  from  about  80  per  cent  for  the 
virulent  strain  to  about  4  to  6  per  cent  for  the  mild  strain.  This  disease  is 
designated  "Rocky  Mountain  spotted  fever"  from  its  place  of  apparent  origin. 
It  is  noncontagious,  highly  infectious,  and  transmitted  to  man  by  ticks.  Wilson 
and  Chowning  (1902-1904)  first  advanced  the  theory  that  the  disease  was 
tick-borne  and  Ricketts  (1906-1909)  and  his  co-workers  demonstrated  that 
the  disease  is  primarily  an  infection  of  small  mammals  (rodents) ;  that  large 
mammals,  except  man,  are  not  susceptible;  and  that  the  tick,  Dermacentor 
andersoni,  is  the  transmitting  agent  for  man.  Wolbach  (1919)  described  and 
named  the  parasite  Dermacentroxenus  ricfettsL  For  many  years  this  disease 
was  known  only  from  a  restricted  area  in  the  Rocky  Mountain  region.  Rum- 
reich,  Dyer,  and  Badger  (1931)  demonstrated  the  disease  in  the  eastern 
United  States  and  reported  cases  from  rural  areas  in  Delaware,  Maryland, 
Pennsylvania,  Virginia,  North  Carolina,  and  the  District  of  Columbia  during 
the  summer  of  1930.  Later  they  proved  that  the  vector  was  the  dog  tick, 
Dermacentor  variabilis.  Since  then  the  disease  has  been  found  rather  wide- 
spread throughout  the  United  States.  At  present  the  disease  is  also  known 
from  western  Canada  (British  Columbia  and  Alberta)  and  many  parts  of 
South  America  and  Mexico.  In  South  America  this  disease  has  been  called 
exanthematic  typhus  of  Sao  Paulo,  Tobia  fever  of  Colombia,  Choix  or  Pinta 


74  MEDICAL  ENTOMOLOGY 

fever  in  Mexico,  and  Minas  Geraes  typhus  in  Brazil.  The  tick  vector  in  South 
America  is  Amblyomma  cajennense. 

The  relation  of  ticks  to  this  disease  may  be  considered  under  two  headings : 
maintenance  in  nature  and  transmission  to  man. 

MAINTENANCE  IN  NATURE  :  The  following  species  of  ticks  are  known  to  trans- 
mit, or  can  transmit  experimentally,  the  rickettsiae  among  the  reservoir 
hosts  (mainly  rodents) :  Dermacentor  andersoni  (mainly  by  the  larvae  and 
nymphs) ;  Dermacentor  variabilis  (all  stages) ;  Dermacentor  occidentalis  (all 
stages);  Rhipicephalus  sanguineus3  (experimentally);  Amblyomma  ameri* 
canum  (all  stages);  Amblyomma  cajennense  (experimentally  and  probably 
in  nature);  Ornithodoros  par^eri  (all  stages  experimentally);  Ornithodoros 
nicollei  (all  stages,  experimentally).  In  addition,  all  these  ticks  pass  the  rickett- 
siae through  the  eggs  to  their  young  so  that  the  natural  reservoir  in  rodents 
can  be  maintained  or  greatly  increased.  Another  tick  that  is  undoubtedly  very 
important  in  many  areas  is  the  rabbit  tick,  Haemaphysalis  leporis-palustris. 
This  tick  does  not  attack  man,  but  it  can  transmit  the  rickettsiae  from  rabbit 
to  rabbit  and  thus  maintain  an  adequate  source  for  those  ticks  that  bite  man 
and  also  feed  on  rabbits. 

TRANSMISSION  TO  MAN:  Only  those  ticks  that  become  infected  and  feed  on 
man  can  transmit  the  disease.  Dermacentor  andersoni  (adults)  is  the  vector 
throughout  its  range  (western  Canada  and  western  United  States) ;  Derma- 
centor occidentalis  is  probably  a  vector  in  the  United  States  in  western  Cali- 
fornia and  parts  of  Oregon;  Amblyomma  americanum  (all  stages)  is  a  vector 
in  some  parts  of  the  United  States  (known  only  at  present  as  a  vector  in  Texas 
and  Oklahoma);  in  Brazil  and  Columbia  Amblyomma  cajennense  is  re- 
ported as  the  vector.  In  addition,  other  species  may  play  a  part  as  Ornithodoros 
parJ^eri,  which  Davis  (1943)  has  shown  to  be  an  effective  transmitter  in  all 
stages  and  through  the  egg  even  to  the  fourth  generation.  The  same  worker 
(1943)  has  shown  that  Ornithodoros  nicollei  is  a  good  experimental  vector  of 
the  rickettsiae  of  the  spotted  fevers  of  Brazil,  Colombia,  and  Mexico  in  all 
stages  and  through  the  egg  to  the  next  generation.  As  this  tick  feeds  readily 
on  man  and  dogs,  it  is  probably  a  vector  in  its  range. 

The  incubation  period  in  man  after  infection  by  a  tick  varies  from  2  to 
12  days.  In  recent  years  a  vaccine  has  been  developed  that  gives  good  promise. 
It  is  said  to  be  erTective  for  nearly  one  year,  and  if  it  does  not  confer  entire 
immunity  it  at  least  reduces  to  a  minimum  the  danger  of  a  fatal  termination 
of  the  disease. 


3  Recently  found  naturally  infected  in  Sonora,  Mexico  (Mariotte  et  a!.t  1945). 


THE  ORDER  ACARINA  75 

TULAREMIA:  Tularemia  is  a  plaguelike  disease  of  rodents,  particularly  of 
rabbits  and  hares,  caused  by  Pasteurdla  tularensis  (Bacterium  tularense).  The 
disease  was  discovered  in  rats  in  California  by  McCoy  in  1910.  The  bacterium 
was  isolated  from  squirrels  and  described  by  McCoy  and  Chapin  in  1912. 
Francis  (1919,  1920)  demonstrated  that  the  so-called  "deer-fly  fever"  of  man 
in  Utah  and  the  plaguelike  disease  of  rodents  are  identical  and  caused  by  the 
same  organism;  he  later  (1921)  named  the  disease  "tularemia."  The  disease 
is  highly  infectious  to  man  and  is  transmitted  by  various  arthropods  either  by 
their  bites,  their  crushed  bodies,  or  their  feces  or  by  the  tissues  or  body  fluids  of 
infected  rodents;  it  is  also  occasionally  water-borne.  The  disease  is  widespread 
in  the  United  States  and  is  reported  from  the  following  countries :  Japan  (1925), 
Russia  (1928),  Nor  way  (1929),  Canada  (1930),  Sweden  (1931),  Austria  (1935), 
Germany,  Czechoslovakia,  and  Turkey  (1936),  Alaska  (1937,  no  human  cases 
but  the  organism  was  isolated  from  rabbit  ticks),  and  from  Tunisia. 

NATURAL  RESERVOIRS:  There  are  numerous  natural  reservoir  hosts.  Burroughs 
et  al.  (1945)  list  44  hosts  from  the  world,  distributed  among  birds,  insectivores, 
rodents,  carnivores,  and  ungulates.  They  list  4  birds  (ruffed  grouse,  bobwhite, 
sage  hen,  and  horned  owl),  3  carnivores  (cat,  dog,  and  coyote),  20  rodents, 
and  sheep  from  the  United  States.  Jellison  and  Parker  (1945)  present  rather 
conclusive  evidence  that  the  main  source  of  human  infection  in  the  United 
States  is  from  cottontail  rabbits  (Sylvilagus  spp.)  particularly  S.  floridantis.  Of 
the  14,000  cases  reported  in  the  United  States  (up  to  1942)  fully  90  per  cent 
are  traceable  directly  to  infection  from  cottontail  rabbits;  only  40  cases  oc- 
curred beyond  the  range  of  these  rabbits.  Jack  rabbits  are  known  reservoirs  and 
are  an  indirect  source  of  human  infection  through  the  agency  of  ticks  and  deer 
flies.  In  the  same  manner  many  rodents  are  indirect  sources  of  human  infection. 

TRANSMISSION  TO  MAN:  Human  infection  is  mainly  through  contact  with 
reservoir  hosts,  particularly  rabbits.  The  bacterium  (Pasteurdla  tularensis)  is 
so  infectious  that  it  can  pass  directly  through  the  human  skin,  and  thus  man 
is  readily  infected  by  handling  infected  animals,  their  flesh,  or  body  fluids;  by 
contact  with  the  fecal  wastes  or  body  fluids  of  the  vectors;  by  eating  partially 
cooked  infected  rabbits,  squirrels,  and  others;  or  by  handling  or  drinking 
infected  water.  Jellison  and  Parker  state  that  90  per  cent  of  the  human  cases 
in  the  United  States  result  from  handling  infected  rabbits;  the  other  10  per 
cent  of  the  cases  are  traceable  to  handling  other  infected  rodents,  sheep,  game 
birds,  or  other  animals  or  by  transmission  by  arthropods.  Certain  arthropods 
play  an  important  part  in  maintaining  this  natural  reservoir  and  also  in  trans- 
mitting the  disease  to  man.  Francis  (1921)  was  the  first  to  demonstrate  the 


76  MEDICAL  ENTOMOLOGY 

transmission  of  tularemia  from  infected  animals  (the  jack  rabbit)  to  man  by 
the  deer  fly,  Chrysops  discalis  (Fig.  161).  Parker,  Spencer,  and  Francis  (1924) 
demonstrated  that  Dermacentor  andersoni  and  Haemaphysalis  leporis-palustris 
could  transmit  the  disease  and  that  the  bacterium  passes  from  stage  to  stage 
of  the  ticks.  In  1926  Parker  and  Spencer  reported  the  survival  of  the  bacterium 
through  the  egg  to  the  young  of  Haemaphysalis  leporis-palustris  and  Derma- 
centor andersoni.  Philip  and  Jellison  (1934)  showed  stage-to-stage  and 
generation-to-generation  survival  of  this  bacterium  in  Dermacentor  variabilis. 
Dermacentor  occidentalis  and  D.  marginatus  have  also  been  shown  to  play 
some  part  in  this  disease  complex. 

Although  most  of  the  human  infection  in  North  America  is  traceable  to 
contact  with  rabbits,  it  must  be  borne  in  mind  that  ticks,  particularly  Hae- 
maphysalis  leporis-palustris,  Dermacentor  andersoni,  D.  variabilis,  and  other 
bloodsucking  arthropods,  are  of  great  importance  in  maintaining  the  disease 
among  the  natural  reservoirs.  Furthermore  the  disease  can  be  water-borne  as 
shown  by  Scott  (1940)  and  Jellison  et  al.  (1942)  in  the  case  of  beavers  and  by 
Karpoflf  and  Antonoff  (1936)  in  the  case  of  water  rats  in  Russia.  In  both  in- 
stances the  water  was  shown  to  be  highly  infectious  when  handled  or  drunk. 
Mosquitoes  may  also  play  a  part  in  the  infection  of  man  and  among  the 
reservoir  hosts,  as  shown  by  Philip  (1932). 

*  AUSTRALIAN  "Q"  FEVER,  AMERICAN  "NINE-MILE  FEVER": 
"Q"  fever  was  first  recognized  as  a  distinct  entity  by  Derrick  (1937)  in  Aus- 
tralia. It  occurred  among  meat  handlers  and  slaughterers  in  a  restricted  area 
about  Brisbane.  The  causative  organism  was  isolated  and  described  as  Ricfett- 
sia  burneti  by  Burnet  and  Freeman  (1937).  "Nine-Mile  fever"  was  recognized 
near  Nine  Mile  Creek  in  Montana  in  1938,  and  the  infectious  agent  was  iso- 
lated from  the  tick  Dermacentor  andersoni  by  Davis  and  Cox  (1938);  the 
human  case  (a  laboratory  worker)  was  described  by  Dyer  (1938).  Cox  (1939) 
named  the  organism  Ric^ettsia  diaporica.  It  now  seems  well  established  that 
these  two  isolated  diseases  are  identical.4  In  Australia  the  reservoir  appears 
to  be  in  bandicoot  rats  (Isodon  torosus),  three  out  of  103  tested  being  natu- 
rally infected.  All  species  of  bush  animals  tested  proved  susceptible  to  infection. 
The  tick  Haemaphysalis  humerosa  taken  from  bandicoots  proved  infectious, 
and  bandicoots  in  certain  areas  showed  a  high  agglutination  rate  (34  per  cent). 
Although  this  tick  does  not  normally  bite  man,  it  is  suggested  that  it  main- 
tains the  reservoir  and  that  Ixodes  holocyclus  (which  readily  bites  bandicoots, 
man,  and  other  animals)  may  transmit  the  disease  among  the  bandicoots  and 


4  Recently  the  generic  name  hds  been  changed  to  Coxiella. 


THE  ORDER  ACARINA  77 

to  man.  The  rickettsiae  develop  in  the  epithelium  lining  of  the  gut  of  the  tick 
so  that  the  lumen  and  fecal  wastes  are  heavily  charged.  The  feces  are  highly  in- 
fective, even  when  dry  and  powdery,  to  broken  or  injured  skin.  Transmission 
is  only  through  fecal  wastes  of  infected  ticks  entering  the  wound  made  by 
the  bite  or  by  the  dry  infective  fecal  wastes  gaining  access  to  wounds  or  by  way 
of  the  respiratory  tract.  Other  potential  tick  vectors  are  Haemaphysalis  bispi- 
nosa  and  Rhipicephalus  sanguincus. 

In  North  America  Ric\ettsia  diaporica  has  been  isolated  from  Dermacentor 
andersoni  in  Montana  and  Wyoming,  from  Dermacentor  occidentalis  in 
Oregon  and  California,  and  from  Amblyomma  americanum  in  Texas  (Lib- 
erty County).  Davis  (1943)  demonstrated  that  Ornithodoros  moubata  could 
be  infected  by  feeding  on  infected  guinea  pigs  and  could  transmit  the  infec- 
tion by  feeding  up  to  428  days  following  the  infective  feeding,  and  that  trans- 
mission through  the  eggs  was  obtained  to  the  F2  generation.  The  infective 
agent  was  conserved  in  the  tissues  of  the  tick  for  at  least  670  days.  With  O. 
hermsi  transmission  took  place  by  feeding  up  to  772  days  after  the  infective 
meal,  and  the  infectious  agent  was  conserved  in  the  tissues  for  at  least  979  days; 
there  was  no  transmission  through  the  egg. 

In  Australia  176  cases  in  humans  with  three  deaths  are  recorded  up  to  1942. 
In  North  America,  cases  (15,  with  one  death  in  Washington,  D.C.)  have 
occurred  in  laboratory  workers,  and  the  infection  is  believed  to  be  due  to 
the  inhalation  of  infected  tick  feces  or  dust  from  cultures  while  the  persons 
were  working  with  experimental  animals.  In  cases  involving  the  respiratory 
tract  the  disease  is  more  serious.  Recently  an  outbreak  was  reported  at  Amarillo, 
Texas,  among  slaughter-house  workers  (55  cases).  Elkland  (1947)  records  a 
case  in  Montana  probably  contracted  from  Dermacentor  andersoni  in  the  wild. 
Huebner  et  al.  (1948)  located  an  endemic  center  of  "Q"  fever  in  southern 
California  (117  cases  during  1947).  They  also  report  recovering  Ric\ettsia 
burneti  from  raw  milk  in  several  dairies.  Jellison  and  his  co-workers  (1948) 
recovered  the  organism  Ricftettsia  (Coxiella)  burneti  not  only  from  raw  milk 
but  from  butter  made  from  unpasteurized  milk.  They  also  found  the  spinose 
ear  tick,  Otobius  megnini  (Duges),  naturally  infected. 

During  World  War  II  extensive  outbreaks  of  "Q"  fever  occurred  among 
Allied  troops  in  Italy  and  Axis  troops  in  the  Balkans  (Balkan  grippe)  and 
in  Greece.  Cases  were  also  reported  from  ^Panama.  Workers  in  research 
laboratories,  especially  among  those  handling  the  cultures  of  Ric^ettsia  burneti, 
were  infected.  As  a  result  of  intensive  studies  of  these  outbreaks  it  seems  estab- 
lished that  there  may  be  several  strains  of  "Q"  fever,  but  all  appear  to  be  identi- 
cal from  the  standpoint  of  reciprocal  cross  immunity,  complement  fixation, 


78  MEDICAL  ENTOMOLOGY 

and  agglutination  absorption  tests.  Unfortunately  nothing  was  learned  re- 
garding the  sources  of  the  infection,  the  animal  reservoirs,  or  the  methods  of 
transmission  unless  we  accept  the  one  known  method — the  inhalation  of  the 
infectious  agent  (Amer.  //.  Hyg.,  44,  1946). 

.  COLORADO  TICK  FEVER:  This  disease  is  of  unknown  etiology.  It  is 
reported  from  various  portions  of  the  mountainous  areas  of  Colorado,  wide 
areas  of  Wyoming,  and  parts  of  Idaho.  Parker  et  al.  (1937)  state  that  it  was  first 
observed  in  1907  but  not  regarded  as  a  distinct  entity  till  1930.  The  disease 
is  associated  with  the  bite  of  Dermacentor  andcrsoni  but  is  distinct  from  Rocky 
Mountain  spotted  fever;  there  is  no  rash  and  the  fever  is  of  the  remittent  type. 
The  disease  rarely  proves  fatal. 

'  BULLIS  FEVER:  This  peculiar  disease  is  named  after  Camp  Bullis  in 
Texas,  where  the  first  cases  were  recognized  by  Woodland  et  al.  (1943).  In 
1943  over  485  cases  were  isolated  among  the  troops;  later  Anigstein  and  Bader 
reported  that  some  1000  cases  were  observed.  All  reports  indicate  that  the  vector 
is  the  tick  Amblyomma  americanum,  as  practically  all  cases  had  numerous  tick 
bites  and  this  tick  is  the  common  and  most  abundant  tick  in  the  area  and  readily 
bites  man.  Steinhaus  and  Parker  (1944)  report  a  filter-passing  agent  from  the 
tick  Haemaphysalis  leporis-palustris,  taken  from  rabbits,  but  the  authors  do 
not  conclude  that  this  virus  may  be  the  causative  agent  of  Bullis  fever. 

.  TICK  TYPHUS:  Tick  typhus  has  been  described  from  widely  separated 
regions.  The  etiology  of  the  disease  is  unknown.  The  disease  is  reported  from 
Russia  (central  Siberia),  where  Bocharova  (1945)  reports  that  it  is  tick-borne 
and  the  vector  Dermacentor  nuttalli  Olenev;  he  also  found  natural  infection 
in  this  species  in  the  wild.  Natural  infection  was  found  in  a  number  of  rodents, 
including  the  domestic  rat.  Singh  (1943)  reports  a  case  of  typhus  fever  from 
Meerut,  India,  that  Megaw  (1943)  calls  a  typical  case  of  tick  typhus.  Walsh 
(1945)  reports  an  epidemic  of  tick  typhus  in  East  Africa,  and  Tovar  (1945) 
indicates  that  the  disease  is  widespread  in  the  Americas  but  not  yet  detected. 
It  would  seem  that  this  disease  entity  is  not  well  understood.  Kenya  tick 
typhus  is  said  to  be  almost  similar  to  boutonneuse  fever. 

>  BOUTONNEUSE  FEVER  (Fievre  Exanth&natique  de  Marseille) :  This 
disease  was  first  reported  from  Tunisia  by  Conor  and  Bruch  (1910).  It  is  now 
known  to  occur  all  along  the  Mediterranean  littoral  from  Portugal  to  Romania, 
and  it  has  recently  been  reported  from  Ethiopia.  The  causative  organism  has 
been  described  by  Brumpt  (1932)  under  the  name  Ricfyttsia  conori.  This 
organism  has  been  recovered  from  the  tick  Rhipicephalus  sanguineus,  which 


THE  ORDER  ACARINA  79 

is  the  known  vector  throughout  the  Mediterranean  region.  The  reservoir  hosts 
are  the  dog  (most  important),  certain  rodents  as  the  spermophile  Citellus  citel- 
lus,  the  white  rat,  and  mice.  In  the  tick  the  rickettsia  is  transmitted  from  stage 
to  stage  and  also  through  the  egg  to  the  larvae.  The  disease  belongs  to  the 
"spotted-fever  group." 

Kenya  tick  typhus  is  thought  to  be  identical  with  boutonneuse  fever,  and 
Roberts  (1935)  has  shown  that  Rhipicephalus  sanguineus  is  the  vector  in 
Kenya  of  what  is  frequently  called  "tropical  typhus."  The  etiological  agent 
has  been  described  as  Rickettsia  ricfyettsi  conori. 

'  SOUTH  AFRICAN  TICK-BITE  FEVER:  This  disease  is  closely  related 
to  the  spotted  fevers  and  is  caused  by  a  rickettsia,  variously  known  as  Rickettsia 
ricfyettsi  conori  or  as  a  distinct  variety,  R.  r.  pijperi.  It  was  recognized  as  a  dis- 
tinct clinical  disease  in  South  Africa  sometime  before  1930.  Gear  (1938,  1939) 
reports  the  disease  in  the  Witwatersrand  as  severe,  the  reservoir  being  dogs 
and  the  vector  the  dog  tick,  Haemaphy 'salts  leachi.  Amblyomma  hebraeum 
is  also  a  vector,  but  it  is  stated  that  only  the  larval  stage  transmits  the  disease. 
The  disease  is  nearly  always  associated  with  tick  bites,  the  primary  sore  being 
described  as  a  tache  noire,  and  is  accompanied  by  lymphadenitis.  The  dog  tick, 
Haemaphysalis  leachi,  can  transmit  the  disease  in  all  stages  and  also  by 
transovarial  transmission  through  the  egg;  it  is  thus  considered  a  reservoir 
of  the  disease.  Rhipicephalus  sanguineus  is  also  reported  as  a  potential 
vector.  The  distribution  of  the  disease  is  not  fully  known. 

.  RUSSIAN  SPRING-SUMMER  ENCEPHALITIS  OR  TICK-BORNE 
ENCEPHALITIS :  This  is  the  only  human  encephalitis  known  to  be  trans- 
mitted by  ticks.  It  is  recorded  from  parts  of  European  Russia,  Siberia,  and 
parts  of  the  maritime  province  of  the  Far  East  of  Russia  (always  in  well- 
demarcated  virgin-forest  regions).  Various  Russian  investigators  have  shown 
that  the  tick  Ixodes  persulcatus  Schulze  is  the  natural  vector.  This  tick  occurs 
only  in  the  forested  regions,  and  the  disease  is  transmitted  to  those  who  work 
in  the  forests.  The  tick  has  a  two-  or  three-year  cycle,  and  infection  of  the 
ticks  occurs  when  they  feed  on  the  wild  rodents  that  are  the  reservoirs.  The 
virus  is  transmitted  in  the  ticks  from  stage  to  stage  and  to  the  young  through 
the  eggs.  Russian  workers  have  shown  that  there  are  two  peaks  of  infection, 
one  in  the  spring  and  another  in  the  summer.  The  first  is  from  the  feeding 
of  the  overwintering  ticks,  and  the  second  is  probably  from  the  young  that 
hatch  from  eggs  laid  during  the  spring  months.  There  are  indications  that 
Dermacentor  silvarum,  Haemaphysalis  concinna,  and  H.  japonica  may  also 
serve  as  vectors  since  they  have  been  found  naturally  infected. 


80  MEDICAL  ENTOMOLOGY 

ST.  LOUIS  ENCEPHALITIS:  See  pages  95,  367. 
Animal  Diseases 

In  addition  to  the  human  diseases  many  diseases  of  domestic  and  game 
animals  are  also  transmitted  by  ticks.  A  few  of  these  may  be  mentioned  here. 

PIROPLASMOSIS,  RED-WATER  FEVER,  TEXAS  FEVER,  OR 
HEMOGLOBINURIA  OF  CATTLE:  For  a  brief  statement  see  page  58. 
In  North  America  this  disease  (caused  by  Piroplasma  bigemina)  is  transmitted 
by  Boophilus  annulatus;  in  Australia,  the  Philippine  Islands,  the  Dutch  East 
Indies,  India,  and  parts  of  South  America  by  Boophilus  australis;  and  in  South 
Africa  by  Boophilus  decoloratus.  Boophilus  microplus  is  the  vector  in  parts  of 
South  America,  the  West  Indies,  and  probably  other  parts  of  the  world.  In 
East  Africa  this  disease  is  also  transmitted  by  Rhipicephalus  appendiculatus 
and  R.  evertsi.  In  Europe  a  similar  disease  caused  by  Babesia  bovis  is  trans- 
mitted by  Ixodes  ricinus.  The  etiological  agent  is  transmitted  from  larva  to 
nymph,  from  nymph  to  adult,  and  through  the  egg  to  the  young.  Malignant 
jaundice  of  dogs  is  a  serious  disease  caused  by  Babesia  cams  and  is  transmitted 
by  the  brown  dog  tick  (Rhipicephalus  sanguineus)  in  the  United  States 
(Florida,  where  it  was  first  discovered  in  North  America  in  1934),  Asia, 
North  Africa,  and  India;  by  Dermacentor  reticulatus  in  Europe;  and  by 
Haemaphysalis  leachi  in  South  Africa.  The  parasite  is  passed  by  infected 
females  through  the  egg  to  the  larvae.  "Carceag"  of  sheep  and  goats  is  caused 
by  Babesia  motasi.  The  disease  occurs  in  eastern  and  southeastern  Europe  and 
its  known  vector  is  Rhipicephalus  bursa,  a  one-host  tick.  The  etiological  agent 
is  passed  through  the  egg  to  the  larvae,  but  infection  is  said  not  to  take  place 
till  the  tick  has  reached  the  adult  stage  on  its  host.  Two  diseases  of  horses 
are  caused  by  species  of  Babesia.  Babesia  caballi  is  reported  from  southern  and 
southeastern  Europe  and  from  the  Caucasus  region  of  Russia.  The  disease  is 
very  similar  to  Texas  fever  and  Dermacentor  reticulatus  is  the  vector.  Babesia 
equi  occurs  in  southern  Europe,  Africa,  southern  Asia,  and  South  America. 
In  South  Africa  Rhipicephalus  evertsi  is  the  known  vector.  In  adult  horses 
and  other  members  of  the  Equidae  the  disease  (biliary  fever)  is  highly  virulent. 
Species  of  Babesia  have  been  described  from  many  other  animals,  but  little 
is  known  about  them  or  their  vectors. 

ANAPLASMOSIS :  Theiler  (1910)  recognized  the  small,  coccuslike  bodies 
on  the  periphery  of  many  of  the  red  blood  cells  of  cattle  suffering  from  a 
specific  disease  (now  known  as  "anaplasmosis")  and  named  them  Anaplasma 
marginale.  These  had  previously  been  seen  by  Smith  and  Kilborne  (1893), 


THE  ORDER  ACARINA  81 

who  did  not  correctly  interpret  them.  In  reality  they  had  animals  suffering 
from  the  two  diseases,  anaplasmosis  and  piroplasmosis.  These  two  diseases  are 
now  well  recognized,  and  anaplasmosis  has  been  found  in  at  least  22  states 
of  our  country  as  well  as  in  South  Africa.  The  disease  is  restricted  to  cattle 
.  and  frequently  proves  very  serious,  with  a  mortality  varying  from  5  per  cent 
to  over  50  per  cent.  Ticks  are  the  important  vectors,  and  numerous  species 
have  been  incriminated.  Rees  (1934)  lists  the  following:  Boophilus  annulatus, 
B.  microplus,  B.  decoloratus,  Dermacentor  andersoni,  D.  variabilis,  Hyalomma 
lusitanicum,  Ixodes  ricinus,  I.  scapularis,  Rhipicephalus  sanguineus,  R.  bursa, 
and  R.  simus.  To  these  can  be  added  Dermacentor  occidentalis,  D.  albipictus, 
and  some  others  of  doubtful  proof.  At  the  present  time  only  Boophilus  annula- 
tus, Dermacentor  andersoni,  and  D.  occidentalis  have  been  proved  capable 
of  transmitting  the  etiological  agent  to  their  offspring  through  the  egg.  In 
addition,  many  bloodsucking  flies  may  act  as  mechanical  carriers,  such  as 
the  Tabanidae  (at  least  seven  species),  and  mosquitoes  (several  species). 
Probably  one  of  the  most  important  methods  of  transmission  is  from  infected 
surgical  instruments  used  in  dehorning,  bloodletting,  castrations,  etc. 

EAST  COAST  FEVER :  A  serious  disease  of  cattle  largely  confined  to  the 
eastern  coastal  region  of  Africa  though  it  is  reported  from  India  and  Trans- 
caucasia is  East  Coast  fever.  It  is  caused  by  a  minute  protozoan,  Theileria 
parva.  This  parasite  occurs  in  the  red  blood  cells,  but  the  schizogonous  cycle 
takes  place  in  the  spleen,  lymph  nodes,  and  some  other  organs.  When  the 
stage  in  the  red  blood  cells  is  taken  by  ticks,  particularly  Rhipicephalus  appen- 
diculatus,  it  undergoes  a  complicated  life  cycle  in  the  tick  and  finally  infected 
forms  are  found  in  the  salivary  glands  (Cowdry,  1932).  Transmission  takes 
place  when  an  infected  tick  feeds  on  a  susceptible  animal.  There  is  no  trans- 
ovarial  passage  of  the  parasite.  Infection  can  pass  from  larvae  to  nymphs  and 
nymphs  to  adults.  Qtfier  proven  vectors  are  Rhipicephalus  evertsi,  R.  simus 
(only  in  adults),  and  a  Hyalomma  species  closely  allied  to  impressum. 

FOWL  SPIROCHETOSIS:  This  is  a  serious  disease  of  fowls  caused  by 
Spirochaeta  gallinarum  Blanchard  (marchouxi  Nuttall).  Its  primary  vector 
is  the  soft  tick,  Argas  persicus.  The  disease  is  recorded  from  Brazil,  Egypt,  the 
Sudan,  India,  Australia,  Europe  (Germany),  and  the  Transcaucasus  region. 
The  fowl  mite,  Dermanyssus  gallinae,  has  been  suspected  as  a  vector,  but 
the.  work  of  Rastegaieff  (1936)  would  seem  to  disprove  this  idea,  though 
Hungerford  and  Hart  (1937)  indicate  that  this  mite  may  serve  as  a  mechani- 
cal transmitter.  Zulzer  (1937)  states  that  mosquitoes  (which  species?)  serve 
as  vectors  and  that  there  is  a  cyclical  development  in  them. 


82  MEDICAL  ENTOMOLOGY 

OTHER  DISEASES :  There  are  other  diseases  of  domestic  animals  which 
are  transmitted  by  ticks,  such  as  Nairobi  sheep  disease  transmitted  by  Rhipi- 
cephalus  appendiculatus  and  Amblyomma  hebraeum,  louping  ill  of  sheep 
transmitted  by  Ixodes  ricinus,  heartwater  of  sheep,  cattle,  and  goats  in  Africa 
transmitted  by  Amblyomma  hebraeum  and  A.  variegatum,  and  some  others 
about  which  little  is  known. 

TICK  CONTROL 

At  the  present  time  no  adequate  specific  treatments  are  known  for  tick-borne 
diseases  of  man  and  animals  except  for  the  relapsing  fevers  of  man.  The  in- 
travenous injection  of  neoarsphenamine  or  other  arsenic  compounds  usually 
brings  about  the  complete  elimination  of  the  spirochetes  of  relapsing  fevers. 
However,  the  disease  runs  a  tedious  course,  and  prophylactic  measures  are  to 
be  preferred  rather  than  treatment  after  infection.  In  the  case  of  malignant 
jaundice  of  dogs  (caused  by  Babesia  cants)  and  in  illnesses  caused  by  some  of 
the  other  larger  species  of  Babesia,  the  administration  of  Trypan  Blue  is  known 
to  give  good  results.  Such  treatments  cannot  be  applied  to  dogs,  cattle,  or 
horses  except  in  the  case  of  very  valuable  animals.  In  general,  it  may  be  stated 
that  the  control  of  ticks  is  the  most  essential  and  effective  method  of  keeping 
these  diseases  in  check.  However,  the  development  of  vaccines  and  serum 
treatments  should  prove  of  great  value,  and  much  progress  may  be  looked  for 
in  these  fields. 

On  domestic  animals,  as  cattle,  horses,  dogs,  etc.,  the  most  efficient  method 
of  destroying  ticks  is  by  dipping  or  spraying.  The  dip  or  spray  employed  is 
usually  an  arsenical  one.  Each  country  has  its  own  official  dip.  That  recom- 
mended by  the  United  States  Department  of  Agriculture  is  as  follows: 

Sodium  bicarbonate    24  pounds 

Arsenic  trioxide  (white  arsenic)  8  pounds 

Pine   tar    i  gallon 

Water    500  gallons 

This  material  is  prepared  in  a  large  dipping  vat.  The  vat  is  so  arranged  that 
the  cattle  are  driven  into  it  one  by  one,  swim  through  it,  and  walk  out  at  the 
other  end  by  means  of  an  inclined,  cleated  plane.  They  are  then  held  a  short 
time  in  a  dripping  pen,  the  drip  running  back  into  the  vat.  By  consistent  pe- 
riodic treatments  large  areas  have  been  completely  cleared  of  cattle  ticks,  as 
for  instance  most  of  the  southern  United  States. 

However,  the  problem  of  controlling  such  ticks  as  Ornithodoros  spp.,  Argas 
spp.,  and  those  that  normally  attach  only  to  wild  animals  is  a  much  more 


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Dermacentor  andersoni, 
D.  variabilis,  Ixodes  holot 
clus,  I.  pilosus,  I.  ricinus 

Sec  summary  p.  72 

Dermacentor  andersoni,  D 
parumapertus,  D.  vartabili 
D.  occidentalis,  Amblyomi 
americanum,  A.  cajennens 
Rhipicephalus  sanguineus, 
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collei,  Haemaphysalis  lepo, 
palustris 

Ixodes  holocyclus, 
Haemaphysalis  humerosa 

Dermacentor  andersoni, 
D.  occidentalis,  Ornithodo 
moubata,  O.  hermsi, 
Amblyomma  americanum 
Rhipicephalus  sanguineus 

Rhipicephalus  sanguineus 

Haemaphysalis  leachi, 
Amblyomma  hebraeum 

Dermacentor  andersoni 

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86  MEDICAL  ENTOMOLOGY 

difficult  one.  Many  of  these  ticks  are  not  known  to  act  as  vectors  of  disease- 
producing  organisms,  but  others,  as  Haemaphysalis  Ieporis-pali4stris,  serve  as 
agents  in  maintaining  the  natural  reservoir.  Ornithodoros  moubata,  which 
lives  principally  in  and  around  human  habitations,  can  probably  be  effectively 
controlled  by  proper  housing  and  cleanliness.  In  the  case  of  the  two-  or  three- 
host  ticks  that  live  primarily  on  wild  animals  we  have  little  knowledge  or 
experience  on  which  to  base  control  measures.  The  only  large-scale  work  car- 
ried on  is  that  against  Dermacentor  andersoni  in  parts  of  Montana.  Here  the 
natural  reservoir  of  the  human  disease,  Rocky  Mountain  spotted  fever,  is  the 
native  rodents.  The  main  efforts  have  been  directed  toward  the  destruction 
of  the  rodent  hosts  (squirrels,  ground  squirrels,  rabbits,  etc.)  by  means  of 
poison  baits  and  the  killing  of  the  adult  ticks  by  the  dipping  of  horses  and 
cattle.  By  destroying  the  hosts  of  the  larvae  and  nymphs  it  is  hoped  to  starve 
out  the  ticks.  Though  this  work  has  proved  somewhat  successful,  it  is  difficult 
to  see  how  it  could  be  employed  for  many  tick  species.  Recently  a  tick  parasite, 
Ixodiphagtts  cauctirtei  du  Buysson,  was  discovered  in  France  and  has  been 
introduced  into  Montana  and  the  eastern  United  States.  The  parasite  is  known 
to  attack  a  number  of  different  species  of  ticks.  It  is  hoped  that  the  employ- 
ment of  this  parasite  on  a  large  scale  may  bring  about  a  decided  reduction  in 
the  disease-distributing  species  of  ticks. 

Personal  prophylaxis  must  be  relied  on  as  the  most  effective  means  of 
avoiding  tick-borne  diseases.  In  tick-infested  regions  sleeping  or  sitting  on 
the  ground  should  be  avoided,  and  camping  places  should  be  selected  with 
care.  The  use  of  suspended  hammocks  for  sleeping  purposes  is  most  essential. 
The  clothing  should  be  rather  coarse  and  loose  and  the  legs  well  protected 
by  laced  high  boots  or  wrap  puttees.  Before  entering  dwellings  or  prepared 
camps  for  the  night,  all  clothing  should  be  carefully  examined  and  adhering 
ticks  destroyed.  If  convenient,  a  complete  change  of  clothing  is  the  wisest 
precaution.  Each  evening  the  clothing  worn  during  the  day  should  be  care- 
fully examined  for  adhering  ticks.  Only  by  careful  attention  can  infestation 
by  ticks  be  avoided.  This  is  well  illustrated  in  the  case  of  Dermacentor  ander- 
soni. Though  the  most  exacting  precautions  have  been  observed  in  the  tick- 
control  work  in  Montana,  yet  at  least  five  men  have  died  through  contracting 
the  disease  in  some  unknown  manner. 

Since  the  discovery  of  the  effectiveness  of  various  DDT  combinations  in 
controlling  mosquitoes,  lice,  fleas,  and  other  insects,  experiments  have  been 
conducted  with  this  material  against  ticks.  Areas  infested  with  various  species 
of  ticks  have  been  sprayed,  but  the  results  are  not  very  gratifying.  A  certain 
amount  of  control  is  indicated  with  such  species  as  Dermacentor  variabilis 


THE  ORDER  ACARINA  87 

and  Amblyomma  americannm.  Fair  control  of  Rhipicephalus  sanguineus  has 
been  obtained  when  10  per  cent  DDT  dusts  have  been  applied  in  houses.  In 
all  probability  some  effective  agent  against  ticks  may  be  developed.  No  satis- 
factory repellent  has  been  developed. 

REFERENCES  5 

American  Association  for  the  Advancement  of  Science.     A  symposium  on  relapsing 

fever  in  the  Americas.     (Pub.  18)  Washington,  D.C.,  1942. 

.    Rickettsial  diseases  of  man.    Washington,  D.C.,  1948.     (A  symposium.) 

*Aragao,  H.  de  B.    Ixodidas  brasileiros  e  de  alguns  paizes  limitrophes.    Mem.  do 

Instit.  Oswaldo  Cruz,  31:  769-843,  1936. 
Arthur,  D.  R.     The  feeding  mechanism  of  Ixodes  ricinus  L.     Parasitology,  37: 

154-161,  1946. 
Badger,  L.  F.,  and  Dyer,  R.  E.     An  infection  of  the  Rocky  Mountain  fever  type. 

U.S.  Pub.  Hlth.  Repts.,  49:  463-470,  1931. 
*Banks,  N.  A.     A  revision  of  the  Ixodidae,  or  ticks,  of  the  United  States.     U.S. 

Dept.  Agr.,  Div.  Ent.,  Tech.  Ser.  15,  1908. 
Bates,  L.  B.,  Dunn,  L.  H.,  and  St.  John,  J.  H.     Relapsing  fever  in  Panama.     Amer. 

Jl.  Trop.  Med.,  i:  183-210,  1921. 
Bedford,  G.  A.    A  synoptic  check  list  and  hosts  of  the  ectoparasites  found  in  South 

African  mammalia.     i8th  Rept.  Dir.  Vet.  Serv.  and  Animal  Ind.,  Union  of 

South  Africa,  pp.  223-523,  1932.     Onderstepoort  Jl.  Vet.  Sci.  and  Animal  Ind., 

7  (Suppl.  i):  69-110,  1936. 
Bequaert,  J.     Synopsis  des  tiques  du  Congo  beige.     Rev.  Zool.  Bot.  Afr.,  20:  209- 

251,  1931. 
.    The  ticks  or  Ixodoidea  of  the  northeastern  United  States  and  eastern  Canada. 

Entomologica  Americana,  25:  73-232,  1946. 
Bertram,  D.  S.    The  structure  of  the  capitulum  in  Ornithodoros.     Ann.  Trop.  Med. 

Parasit.,  33:  229-258,  1939. 
Bishopp,  F.  C.    Ticks  and  the  role  they  play  in  the  transmission  of  diseases.    Rept. 

Smithsonian  Inst.  for  1933,  pp.  389-406,  1935. 
,  and  Trembley,  H.  L.    Distribution  of  certain  North  American  ticks.    Jl. 

Parasit.,  31:  1-54,  1945. 
,  and  Wood,  H.  P.    The  biology  of  some  North  American  ticks  of  the  genus 

Dcrmacentor.    Parasitology,  6:  153-187,  1913. 
Burnet,  F.  M.,  and  Freeman,  M.    Experimental  studies  on  the  virus  of  "Q"  fever. 

Med.  Jl.  Australia,  2:  299-305,  1937. 
Burroughs,  A.  R.,  et  at.    A  field  study  of  latent  tularemia  in  rodents  with  a  list  of 

all  known  naturally  infected  vertebrates.    Jl.  Inf.  Dis.,  76  (2):  115-119,  1945. 

5  This  is  only  a  partial  list.  Articles  with  bibliographies  are  starred;  with  extensive 
bibliographies,  double-starred. 


88  MEDICAL  ENTOMOLOGY 

Christophers,  S.  R.    The  anatomy  and  histology  of  ticks.    Sci.  Mem.  Med.  and 

Sank.  Depts.  India,  n.s.  23,  1906. 
Chumakov,  M.  P.    Further  study  of  the  area  of  distribution  and  peculiarities  of 

the  epidemiology  of  tick-borne  encephalitis  in  the  European  part  of  the  U.S.S.R. 

In  Russian.    Summary  in  Rev.  Appl.  Ent.  (B):  117,  1946. 
Cogswell,  W.  F.    Tick  paralysis.     Mont.  State  Bd.  Hlth.,  Spl.  Bull.  26:  47-49, 

1923. 
Cooley,  R.  A.    The  genera  Dermacentor  and  Otocentor  (Ixodoidea)  in  the  United 

States.    Nat.  Inst.  Hlth.  Bull.  171,  1938. 

-  .    Determination  of  Ornithodoros  species.    In  Symposium  on  relapsing  fevers 
in  the  Americas.    Amer.  Assoc.  Adv.  Sci.,  Pub.  18:  77-84,  1942. 

-  .    The  genera  Boophilus,  Rhipicephalus  and  Haemaphysalis  (Ixodoidea)  of 
the  new  world.    Nat.  Inst.  Hlth.,  Bull.  187,  1946. 

-  ,  and  Kohls,  G.  M.    The  Argasidae  of  North  America,  Central  America  and 
Cuba.    Amer.  Mid.  Natural.,  Monograph  i,  1944. 

-  ,  and  Kohls,  G.  M.    The  genus  Amblyomma  in  the  United  States.    Jl.  Parasit., 
30:  77-1  1  1,  1944. 

Cox,  H.  R.    Ricfettsia  diaporica  and  American  "Q"  fever.    Amer.  Jl.  Trop.  Med., 

20:  463-469,  1940. 
Cunlifle,  N.,  and  Nuttall,  G.  H.  F.    Some  observations  of  the  biology  and  structure 

of  Ornithodoros  moubata  Murray.     Parasitology,  13:  327-347,  1921. 
Davis,  Gordon  E.     Ornithodoros  par^cri;  distribution  and  host  data;  spontaneous 

infection  with  relapsing  fever  spirochetes.    U.S.  Pub.  Hlth.  Repts.,  54:  1345- 


-  .    Bacterium  tularense:  its  persistence  in  the  tissues  of  the  argasid  ticks  Ornitho- 
doros turicata  and  O.  parferi.    Ibid.,  55:  676-680,  1940. 

-  .    Ornithodoros  par\eri  Cooley:  observations  on  the  biology  of  this  tick.    Jl. 
Parasit.,  27:  425-433,  1941. 

-  .    Tick  vectors  and  life  cycles  of  ticks.    In  Symposium  on  relapsing  fever  in 
the  Americas.    Amer.  Assoc.  Adv.  Sci.,  Pub.  18:  67-76,  1942. 

-  .    Studies  of  the  biology  of  the  argasid  tick,  Ornithodoros  nicollei  Mooser.    Jl. 
Parasit.,  29:  393-395,  1943. 

-  .     Relapsing  fever:  the  tick,  Ornithodoros  turicata  as  a  spirochaetal  reservoir. 
U.S.  Pub.  Hlth.  Repts.,  58:  839-842,  1943. 

-  .    American  Q  fever;  experimental  transmission  by  the  argasid  ticks  Ornitho- 
doros moubata  and  O.  hermsi.    Ibid.,  pp.  984-987,  1943. 

-  .    The  tick  Ornithodoros  rudis  as  a  host  to  the  rickettsiae  of  the  spotted  fevers 
of  Colombia,  Brazil  and  the  United  States.    Ibid.,  pp.  1016-1020,  1943. 

-  .    Experimental  transmission  of  the  rickettsiae  of  spotted  fevers  of  Brazil, 
Colombia  and  the  United  States  by  the  argasid  tick,  Ornithodoros  parpen.    Ibid., 
pp.  1201-1208,  1943. 

-  .    Experimental  transmission  of  the  richettsiae  of  spotted  fevers  of  Brazil, 


THE  ORDER  ACARINA  89 

Colombia  and  the  United  States  by  the  argasid  tick,  Ornithodoros  nicollei. 

Ibid.,  pp.  1742-1744,  1943. 
Derrick,  E.  H.    "Q"  fever,  a  new  fever  entity.    Med.  Jl.  Australia,  2:  281-299,  T937* 

.    Ricfettsia  burnetl:  the  cause  of  "Q"  fever.    Ibid.,  p.  14,  1939. 

.    The  epidemiology  of  "Q"  fever.    Jl.  Hyg.,  43:  357-361,  1944. 

Dios,  R.  L.,  and  KnopofI,  R.    Sobre  Ixodoidea  de  la  Republica  Argentina.    Rev 

Inst.  Bact.  (Buenos  Aires),  6:  359-412,  1935. 
Dunn,  L.  H.    The  ticks  of  Panama,  their  hosts,  and  the  diseases  they  transmit. 

Amer.  Jl.  Trop.  Med.,  3:  91-104,  1923. 
.    Notes  on  two  species  of  South  American  ticks,  Ornithodoros  talaje  Guerin- 

Men.  and  0.  venezuelensis  Brumpt.    Jl.  Parasit.,  13:  177-182,  1927. 
.     Studies  on  the  South  American  tick,  Ornithodoros  venezuelensis,  in  Colom- 
bia.   Ibid.,  pp.  249-255,  1927. 
**Eysell,  Adolf.    Zecken.    In  Handbuch  der  Tropenkrankheiten,  edited  by  Carl 

Mense,  i :  1-40, 1924. 
Fairchild,  G.  B.     An  annotated  list  of  blood-sucking  insects,  mites,  and  ticks  from 

Panama.    Amer.  Jl.  Trop.  Med.,  23:  569-591,  1943. 
Ferguson,  E.  W.    Deaths  from  tick  paralysis  in  human  beings.     Med.  Jl  Australia, 

2(i4):  346-34^  I924- 
*Fielding,  J.  W.    Australasian  ticks.    Ser.  Pub.  (Trop.  Div.)  Australia  Dept. 

Hlth.,  No.  9,  1926. 
*Fotheringham,  W.,  and  Lewis,  E.  A.     East  coast  fever;  its  transmission  by  ticks 

in  Kenya  Colony.    Parasitology,  29:  504-523,  1937. 
Francis,  Edward.    Microscopic  changes  of  tularaemia  in  the  tick,  Dermacentor 

under sonl,  and  the  bedbug,  Cimex  lectularius.    U.S.  Pub.  Hlth.  Repts.,  42: 

2763-2772,  1927. 
* .    Arthropods  in  the  transmission  of  tularaemia.    Trans.  4th  Internat.  Cong. 

Ent.,  2:  929-944,  1929. 
.    The  longevity  of  fasting  and  non-fasting  Ornithodoros  turicata  and  the 

survival  of  Spirochaeta  obcrmclerl  within  them.    In  Symposium  on  relapsing 

fever  in  the  Americas.    Amer.  Assoc.  Adv.  Sci.,  Pub.  18:  85-88,  1942. 
,  et  al.    Tularaemia  Francis,  1921:  a  new  disease  of  man.    U.S.  Pub.  Hlth. 

Serv.,  Hyg.  Lab.  Bull.  130,  1922.     A  series  of  articles  by  Francis  and  his  as- 
sociates. 
Gear,  J.,  and  de  Meillon,  B.    The  common  dog  tick,  Haemaphy  sails  leachl  as  a 

vector  of  tick  typhus.    S.  Afr.  Med.  JL,  13:  815-816,  1939. 
Graybill,  H.  W.    Studies  on  the  biology  of  the  Texas-fever  tick.    U.S.  Dept.  Agr., 

Bur.  Animal  Ind.,  Bull.  130,  1911. 
Green,  R.  G.     Virulence  of  tularaemia  as  related  to  animal  and  arthropod  hosts. 

Amer.  Jl.  Hyg.,  38:  282-292,  1943. 
,  et  al.    A  ten-year  population  study  of  the  rabbit  tick,  Haemaphysalis  leporis- 

palustrls.    Ibid.,  pp.  260-281,  1943. 


9o  MEDICAL  ENTOMOLOGY 

Hadwen,  Seymour.  On  "tick  paralysis"  in  sheep  and  man  following  bites  of 
Dermacentor  venustus,  with  notes  of  the  biology  of  the  tick.  Parasitology, 
6:  283-297,  1913. 

,  and  Nuttall,  G.  H.  F.  Experimental  "tick  paralysis"  in  the  dog.  Ibid., 

6:  298-301,  1913. 

Hammon,  W.  McD.    The  arthropod-borne  encephalitides.    Amer.  Jl.  Trop.  Med., 

28:  515-525*  J948- 
Hooker,  W.  A.,  Bishopp,  F.  C.,  and  Wood,  H.  P.    The  life  history  and  bionomics 

of  some  North  American  ticks.    U.S.  Dept.  Agr.,  Bur.  Ent.,  Bull.  106,  1912. 
Howard,  C.  W.    A  list  of  the  ticks  of  South  Africa,  with  descriptions  and  keys 

to  all  of  the  forms  known.    Ann.  Transvaal  Mus.  (Pretoria),  i:  73-170,  1908. 
Huebner,  R.  J.     Report  of  an  outbreak  of  "Q"  fever  at  the  National  Institute  of 

Health.    Amer.  Jl.  Hyg.,  37:  431-440,  1947. 
,  et  al.    "Q"  fever  studies  in  southern  California.     U.S.  Pub.  Hlth.  Repts., 

63:  214-222,  1948. 
,  Jellison,  W.  L.,  and  Beck,  M.  D.    Q  fever — a  review  of  current  knowledge. 

Ann.  Intern.  Med.,  30:  495-509,  1949. 
*Hunter,  W.  D.,  and  Bishopp,  F.  C.    The  Rocky  Mountain  spotted  fever  tick. 

U.S.  Dept.  Agr.,  Bur.  Ent.,  Bull.  105,  1911. 
** ,  and  Hooker,  W.  A.    Information  concerning  the  North  American  fever 

tick,  with  notes  on  other  species.    Ibid.,  Bull.  72,  1907. 
Jellison,  W.  L.    The  geographical  distribution  of  Rocky  Mountain  spotted  fever 

and  Nuttall's  cottontail  in  the  western  United  States.    U.S.  Pub.  Hlth.  Repts., 

60:  958-961,  1945. 
,  and  Parker,  R.  R.     Rodents,  rabbits  and  tularaemia  in  North  America. 

Amer.  Jl.  Trop.  Med.,  25:  349-362,  1945. 

,  et  al.  Epizootic  tularaemia  in  the  beaver,  Castor  canadensis,  and  the  con- 
tamination of  stream  water  with  Pastcurdla  tularcnsis.  Amer.  Jl.  Hyg.,  36:  168- 

182,  1942. 
,  et  al.     Occurrence  of  Coxiella  burneti  in  the  spinose  ear  tick,   Otobius 

megnini.    U.S.  Pub.  Hlth.  Repts.,  63:  1483-1489,  1948. 
,  et  al.^  Recovery  of  Coxiella  burneti  from  butter  made  from  naturally  infected 

and  unpasteurized  milk.    Ibid.,  63:  1712-1713,  1948. 
Lahille,  F.    Contribution  a  1'etude  des  Ixodides  de  la  Republique  Argentine. 

Anales  Ministero  Agr.,  seccion  de  Zootechnia,  Bact.,  Veterin.  y  Zool.,  2:  1-166, 

1905. 
Lewis,  E.  A.    A  study  of  the  ticks  of  Kenya  Colony.    Bull.  Dept.  Agr.  Kenya, 

No.  7,  1934. 
.    The  ticks  of  East  Africa.    Emp.  Jl.  Exp.  Agr.,  7  (27) :  261-270;  7  (28) :  299- 

3<>4>  1939- 
McCaffrey,  D.    The  effects  of  tick  bites  on  man.    Jl.  Parasit.,  2:  193-194,  1916. 


THE  ORDER  ACARINA  91 

McCormack,  P.  D.  Paralysis  in  children  due  to  the  bites  of  wood  ticks.  Jl.  Amer. 
Med.  Assoc.,  77:  260-263,  1921. 

MacLeod,  J.  Ixodcs  ricinus  in  relation  to  its  physical  environment.  Parasitology, 
26:  282,  1934;  27:  123-144,  489-500,  1935;  28:  295-319,  1936. 

Mail,  G.  A.,  and  Gregson,  J.  D.  Tick  paralysis  in  British  Columbia.  Jl.  Canad. 
Med.  Assoc.,  39:  532-537,  1938. 

Mariotte,  C.  O.,  et  al.  Hallazgo  del  Rhipicephalus  sangulneus  Latreille  infectado 
naturalmente  con  fieber  manchada  de  las  Montanas  Rocosas  en  Sonora  (Mexico). 
Rev.  Inst.  Salub.  y  Enferm.  Trop.,  5:  297-300,  1944. 

Mazzotti,  L.  Transmission  experiments  with  Spirochaeta  turicata  and  S.  vene- 
zudcnsis  with  four  species  of  Ornithodoros.  Amer.  Jl.  Hyg.,  38:  203-206,  1943. 

Milne,  A.  The  ecology  of  the  sheep  tick,  Ixodes  ricinus  L.  Parasitology,  36:  142- 
*57>  J945;  38:  27-50,  1947. 

Moilliet,  T.  K.  A  review  of  tick  paralysis  in  cattle  in  British  Columbia.  Proc. 
Em.  Soc.  B.C.,  33:  35-39,  1937. 

Neumann,  L.  G.    Ixodidae.    In  Das  Tierrich,  Lieferung  26,  1911. 

Newstead,  R.  Ticks  and  other  blood-sucking  Arthropoda  (in  Jamaica).  Ann. 
Trop.  Med.  Parasit.,  3:  421-469,  1909. 

Nuttall,  G.  H.  F.  The  Ixodoidea  or  ticks,  spirochaetosis  in  man  and  animals, 
piroplasmosis.  The  Harben  Lectures,  1908.  Jl.  Roy.  Inst.  Pub.  Hlth.,  July, 
Aug.,  and  Sept.,  1908. 

.    On  symptoms  following  tick-bites  in  man.    Parasitology,  4:  80^-93,  1911. 

.     Tick  paralysis  in  man  and  animals.    Ibid.,  7:  95-104,  1914. 

,  Cooper,  W.  F.,  and  Robinson,  L.    The  structure  and  biology  of  Haemaphy- 

sails  punctata  Cancstrini  and  Fanzago.    Ibid.,  i:  152-180,  1908. 

** ,  Warburton,  C.,  et  al.    A  monograph  of  the  Ixodoidea.'    Part  i.  Argasidae, 

1908.  Part  2.  Sect,  i,  Classification;  Sect,  n,  The  genus  Ixodes,  1911.  Part  3.  The 
genus  Haemaphysalis,  1915.  Part  4.  The  genus  Amblyomma  (by  L.  E.  Robin- 
son), 1926.  (This  work  constitutes  the  outstanding  contribution  to  our  knowl- 
edge of  the  ticks.  Bibliographies  complete  and  extensive.  Beautifully  illus- 
trated with  colored  plates  and  line  drawings.) 

Parker,  R.  R.  Quail  as  a  possible  source  of  tularaemia  infection  in  man.  U.S. 
Pub.  Hlth.  Repts.,  44:  999-1000,  1929. 

.    Rocky  Mountain  spotted  fever.    Mont.  State  Bd.  Ent.,  7th  Biennial  Rept., 

pp.  39-62,  1929. 

,  and  Kohls,  G.  M.    American  Q  fever;  the  occurrence  of  Rict^cttsia  disporlca 

in  Amblyomma  amcricanum  in  eastern  Texas.  U.S.  Pub.  Hlth.  Repts.,  58: 
1510-1511,  1943. 

,  Philip,  C.  B.,  and  Davis,  G.  E.    Tularaemia.    Ibid.,  47:  479-487,  1932. 

' ,  Philip,  C.  B.,  and  Jellison,  W.  L.    Rocky  Mountain  spotted  fever.    Amer. 

Jl.  Trop.  Med.,  13:  341-379*  '933- 


**. 


92  MEDICAL  ENTOMOLOGY 

Parker,  R.  R.,  and  Spencer,  R.  R.    Hereditary  transmission  of  tularaemia  infection 

by  the  wood  tick,  Dermacentor  andersoni  Stiles.    U.S.  Pub.  Hlth.  Repts.,  41: 

1403-1407,  1926. 
,  and  Steinhaus,  E.  A.    American  and  Australian  Q  fevers.    Ibid.,  58:  523- 

527,  1943. 
** ,  et  al.    Ticks  of  the  United  States  in  relation  to  disease  in  man.    Jl.  Econ. 

Ent.,  30:  51-69,  1937. 
**"Q"  fever.    Amer.  Jl.  Hyg.,  44,  1946.     (All  of  No.  i  is  devoted  to  articles  on 

this  disease  by  numerous  authors.) 
*Rees,  C.  W.    Transmission  of  anaplasmosis  by  various  species  of  ticks.    U.S. 

Dept.  Agr.,  Tech.  Bull.  418,  1934. 
Robinson,  L.  E.,  and  Davidson,  J.    The  anatomy  of  Argas  persicus  (Oken  1818). 

I — III.     Parasitology,  6:  20-48,  217-256,  382-424,  1914. 
Ross,  I.  C.    The  bionomics  of  Ixodes  holocyclus  Neumann,  with  a  redescription 

of  the  adult  and  nymphal  stages  and  a  description  of  the  larvae.    Ibid.,  16:  365- 

381,  1924. 
.    An  experimental  study  of  tick  paralysis  in  Australia.    Ibid,,  18:  410-429, 

1926. 
Rumreich,  A.,  Dyer,  R.  E.,  and  Badger,  L.  F.    The  typhus-Rocky  Mountain 

spotted  fever  group.    U.S.  Pub.  Hlth.  Repts.,  49:  470-480,  1931. 
*Salmon,  D.  E.,  and  Stiles,  C.  W.    The  cattle  ticks  (Ixodoidea)  of  the  United 

States.    U.S.  Dept.  Agr.,  Bur.  Animal  Ind.,  i7th  Rept.,  pp.  380-491. 
Samson,  K.    Zur  Anatomic  und  Biologic  von  Ixodes  ricinus  L.    Zeit.  Wiss.  Zool., 

93:  185-236,  1909. 

Sen,  S.  K.    The  mechanism  of  feeding  in  ticks.     Parasitology,  27:  355-368,  1935. 
Silber,  L.  A.,  and  Shubladze,  A.  K.    Louping-ill  in  the  USSR.    Amer.  Rev.  Sov. 

Med.,  2:  339-341,  1945- 
Smith,  C.  N.,  Cole,  M.  M.,  and  Gouck,  H.  K.    Biology  and  control  of  the  American 

dog  tick.    U.S.  Dept.  Agr.,  Tech.  Bull.  905,  1946 
Smith,  D.  J.  W.     Studies  in  the  epidemiology  of  "Q"  fever.     Aus.  Jl.  Exp.  Med. 

Sci.,  20:  213-217,  1942. 
Smith,  T.,  and  Kilbourne,  F.  L.    Investigations  into  the  nature,  causation,  and 

prevention  of  Texas  or  southern  cattle  fever.    U.S.  Dept.  Agr.,  Bull,  i,  1893. 
Stiles,  C.  W.    The  taxonomic  value  of  the  microscopic  structure  of  the  stigmal 

plates  in  the  tick  genus  Dermacentor.    Pub.  Hlth.  and  Marine-Hosp.  Serv.,  U.S. 

Hyg.  Lab.,  Bull.  62,  1910. 
Todd,  J.  L.    Tick  paralysis.    Jl.  Parasit.,  i:  55-64,  1914. 

.    Tick  caused  paralysis.    Jl.  Canad.  Med.  Assoc.,  9:  994-996,  1919. 

Toumanofi,  C.    Les  Tiques  (Ixodoidea)  de  1'Indochine.    Inst.  Pasteur  Indochine, 

Saigon,  1944. 
Warren,  Joel.    Epidemic  encephalitis  in  the  Far  East.    Amer.  Jl.  Trop.  Med.,  26: 

417-436,  1946. 


THE  ORDER  ACARINA  93 

Weller,  B.,  and  Graham,  G.  M.    Relapsing  fever  in  central  Texas.    Jl.  Amer.  Med. 

Assoc.,  95:  1834-1835,  1930. 
Wheeler,  C.  M.    A  contribution  to  the  biology  of  Ornlthodoros  hermsi  Wheeler, 

Herms  and  Meyer.    Jl.  Parasit.,  29:  33-41,  1943. 
*Wolbach,  S.  B.     Studies  on  Rocky  Mountain  spotted  fever.    Jl.  Med.  Res.,  41: 

1-197,  1919. 


CHAPTER  IV 


The  Order  Acarina;  Parasitoidea, 

Sarcoptoidea,  Trombidoidea, 

Tarsonemoidea,  Tyroglyphoidea, 

and  Demodicoidea 


THE  PARASITOIDEA 

THE  Parasitoidea  contain  at  least  three  rather  large  families.  Their  struc- 
ture allies  them  with  the  ticks.  Tracheae  are  present  and  open  through 
a  pair  of  spiracles  located  on  spiracular  plates  placed  usually  ahove  and  be- 
tween the  third  and  fourth  coxae.  The  mouth  parts  are  well  developed  and 
consist  of  chelate  or  piercing  chelicerae,  an  unarmed  hypostome,  and  a  pair 
of  small  palpi.  The  ventral  surface  lacks  furrows,  but  sclerotized  plates  are 
generally  present.  Only  one  family,  the  Dcrmanyssidae,  is  of  interest  here. 
The  members  of  this  family  may  be  recognized  as  they  are  all  true  parasites 
of  reptiles,  birds,  and  mammals.  The  chelicerae  are  needlelike  or  shearlike, 
usually  without  teeth.  Ventral  and  anal  plates  are  nearly  always  present  and 
separate;  a  dorsal  plate  is  present  but  covers  only  a  part  of  the  body.  Only 
two  genera  of  this  large  family  are  known  to  contain  species  that  may  attack 
man  or  be  found  associated  with  the  transmission  of  disease.  These  two 
genera  may  be  separated  by  the  following  couplet : 

1.  Chelicerae  shearlike,  both  arms  present  (Fig.  26)  Liponyssus  l 

2.  Chelicerae  needlelike  and  long  (Fig.  26)  Dermanyssus 


1  This  genus  and  a  number  of  related  genera  were  separated  by  Ewing  (1923)  and 
placed  in  a  subfamily,  Liponyssinae;  later  Vitzthum  (1931)  created  the  family  Uponys- 
sidae  for  these  genera;  recently  da  Fonseca  (1948)  changed  the  family  name  to  Macronys- 
sidae. 


THE  ORDER  ACARINA 


95 


Dermanyssus  gallinae  (Linn.)  is  the  common  chicken  mite  (Fig.  27).  It  is 
bloodsucking  in  habit  and  usually  feeds  at  night  when  the  fowls  are  roosting. 
The  mites  engorge  rapidly  and  leave  their  hosts  to  spend  the  day  hidden  away 
in  cracks,  crevices,  and  trash  about  poultry  houses.  The  eggs  are  laid  in  the 
trash  and  rubbish;  they  hatch  in  three  to  four  days.  The  larval  and  nymphal 
life  occupies  ten  days  to  two  weeks.  The  mites  will  attack  persons  handling 
infested  fowls  or  sleeping  in  or  near  infested  poultry  houses.  Though  the 
mites  cause  a  marked  dermatitis  in  humans,  it  is  said  they  do  not  obtain 


Fig.  26.  (A)  Chelicera  of  Liponys- 
sus  bacoti.  (B)  Chelicera  of  Derma- 

nyssus  gallinae. 


Fig.  27.  Dermanyssus  gallinae,  the 
chicken  mite.  Dorsal  view.  (After 
Ewing.) 


human  blood.  Avoidance  of  the  mites  is  all  that  is  necessary  to  reduce  the 
dermatitis  as  they  dc  not  live  long  on  the  human  body.  Recently  it  has  been 
shown  by  Smith  et  al.  (1944,  1945,  1946)  that  the  chicken  mite  appears  to  be 
the  natural  transmitter  and  reservoir  of  the  St.  Louis  encephalitis  virus  among 
chickens.  Furthermore  these  workers  demonstrated  that  the  virus  is  passed 
through  the  eggs  to  the  offspring  of  the  mites.  As  chickens  are  also  reservoirs 
of  this  virus  and  as  Culex  pipiens  (the  common  house  mosquito)  is  a  common 
feeder  on  chickens  and  on  man,  it  is  well  established  that  this  mosquito  is  an 
important  vector  of  this  disease  to  man.  Here  we  have  the  complex  of  the 
chicken  mite  maintaining  the  virus  in  chickens  and  the  mosquito  (Culex 
pipiens)  transferring  the  virus  to  man.  The  mosquito  may  also  serve  as  a 


96  MEDICAL  ENTOMOLOGY 

vector  from  chicken  to  chicken.  An  adequate  control  o£  the  chicken  mite 
might  aid  in  the  reduction  of  the  incidence  of  this  disease  among  men. 
Howitt  et  al.  (1948)  recovered  the  virus  of  eastern  equine  encephalomyelitis 
from  Dermanyssus  gallinae  taken  in  nature  in  Tennessee;  they  also  isolated 
the  virus  in  the  chicken  lice,  Menopon  pallidum  Nitsch.  and  Eomenacanthus 
stramineus  (Nitsch.)  taken  from  poultry.  This  is  the  first  recovery  of  this  virus 
from  insects  in  nature. 


Fig.  28.  Dermanyssus  (Allodermanyssui)  sanguineus.  Lcff:  Ventral  view  of  female. 
Right:  Dorsal  view  of  female.  (Redrawn  and  modified  from  H'rst.) 

Dermanyssus  (Allodermanyssus)  sanguineus  Hirst  is  a  parasitic  mite  on 
rats  and  mice.  It  was  described  from  Egypt  in  1914.  The  female  can  be  easily 
separated  from  D.  gallinae  by  the  possession  of  two  dorsal  shields,  the  posterior 
one  being  small  and  circular  (Fig.  28).  D.  sanguineus  was  first  reported  from 
America  in  1923  by  Ewing,  though  collected  in  Washington  in  1909.  At 
present  it  is  known  from  New  York,  Philadelphia,  Boston, 'Indianapolis,  and 
Tucson  as  well  as  from  Washington,  D.C.  In  1946  a  peculiar*  febrile  disease  of 
unknown  etiology  appeared  in  parts  of  New  York  City.  Huelbner  et  al.  (1946) 
reported  this  disease  (Rickettsialpox)  as  due  to  a  rickettsia,  \Vhich  he  named 

\ 


THE  ORDER  ACARINA  97 

Rickettsia  a\ari.  This  rickettsia  was  recovered  from  the  mite  and  from  patients 
suffering  from  the  disease;  mice  were  infected  by  mites  carrying  the  rickettsia. 
During  the  summer  of  1946  over  100  cases  of  human  infection  were  reported 
from  New  York  City. 

Liponyssus  bursa  (Berlese)  and  Liponyssus  sylviarum  Canestrini  and  Fan- 
zago  are  mites  that  commonly  infest  poultry,  and  man  may  be  attacked 
when  handling  infested  birds.  L.  bacoti  (Hirst)  is  frequently  called  the  tropi- 
cal rat  mite  (Fig.  29)  as  it  was  originally  described  from  Egypt  and  was 
thought  to  be  mainly  distributed  in  tropical  countries.  It  is  now  known  to  be 


Fig.  29.  Liponyssus  bacoti,  the  tropical  rat  mite.  Dorsal  and  ventral  views.  (After  Dove 
and  Shelmire,  Journal  of  Parasitology,) 

widely  distributed  in  many  parts  of  the  world  including  the  United  States.  In 
America  it  is  known  from  many  states  and  occurs  at  least  as  far  north  as  New 
York  and  Minnesota,  This  mite  is  primarily  a  parasite  of  rats,  but  it  readily 
attacks  man,  especially  in  such  places  as  buildings,  granaries,  storehouses,  pub- 
lic buildings,  stores,  or  even  private  homes  where  rats  are  abundant.  The  mite 
feeds  only  on  blood.  The  nymphs  and  adults  drop  from  their  hosts  after 
each  blood  meal;  thus  the  mite  may  feed  on  a  variety  of  different  animals 
during  its  life  cycle.  This  feeding  habit  is  well  adapted  to  the  transmission  of  a 
blood  virus  or  parasite.  The  life  cycle  is  comparatively  short.  The  eggs  hatch 
in  about  four  days  and  the  adult  stage  may  be  attained  12  days  later.  Dove  and 
Shelmire  found  that  at  least  four  blood  meals  are  necessary  to  rear  a  larva  to 


98  MEDICAL  ENTOMOLOGY 

the  adult  stage.  The  only  known  way  to  control  the  mites  is  to  destroy  the  rats. 
DDT  might  prove  an  effective  control  method  in  rat-infested  buildings 
where  killing  of  the  rats  is  not  feasible. 

Shelmire  and  Dove  (1931)  described  a  large  number  of  cases  of  dermatitis 
caused  by  this  mite.  The  eruptions  appeared  as  urticarial  wheals  varying  in 
size  from  that  of  a  pinhead  to  that  of  a  split  pea.  On  children  urticarial  welts, 
papules,  and  vesicles  are  often  present.  Severe  pruitus  may  result,  and  sec- 
ondary infections  may  occur  from  scratching.  The  author  has  received  several 
reports  of  severe  infestations  of  this  mite  in  large  manufacturing  plants  in  New 
York  state.  The  mites  gradually  disappeared  with  the  destruction  of  the  rats. 

The  above  authors  also  proved  experimentally,  with  rats  and  guinea  pigs, 
that  this  mite  can  transmit  endemic  (murine)  typhus.  They  showed  that  the 
infection  in  mites  is  transmitted  to  their  offspring,  the  young  larvae  from 
infected  mothers  producing  typical  murine  typhus  in  guinea  pigs  by  their 
bites.  Later  they  demonstrated  that  the  mite  is  capable  of  maintaining  the 
infection  in  wild  rats  and  concluded  that  rats  are  important  reservoirs  of 
murine  typhus,  a  fact  that  is  now  well  known. 

Philip  and  Hughes  (1948)  have  demonstrated  that  this  mite  can  transmit 
experimentally  rickettsialpox  (Rickettsia  afari)  and  have  presented  data  that 
indicate  transovarial  transmission  of  the  parasite. 

THE  SARCOPTOIDEA 

This  superfamily  is  restricted  to  atracheate  mites,  parasitic  on  animals, 
mainly  birds,  mammals,  and  insects.  Many  of  the  external  structures  generally 
found  in  mites  are  greatly  reduced  or  lacking.  The  mouth  parts  arc  modified 
and  reduced  so  that  the  parts  cannot  be  distinguished  easily  (Fig.  30).  The 
palpi,  so  prominent  in  the  ticks,  are  almost  lacking  in  segmentation  and  are 
often  more  or  less  fused  with  the  mouth  parts.  The  chelicerae  are  reduced  to 
mere  sclerotized  rods  or  blades;  a  hypostome  is  lacking.  The  skin  of  the 
body  is  marked  with  fine  parallel  folds,  and  it  bears,  especially  on  the  dorsal 
surface,  minute  setae,  stout  spines,  and  cones  or  modifications  of  them.  The-- 
legs  are  short  and  frequently  modified  for  clasping.  Usually  the  legs,  or  some 
of  them,  terminate  in  a  stalked  sucker  or  long  hair.  The  two  anterior  pairs 
are  widely  separated  from  the  two  posterior  pairs. 

The  sarcoptoid  mites  live  on  their  hosts  throughout  their  life,  mating  and 
egg  laying  taking  place  on  their  hosts.  They  infest  the  skin,  tissues,  hairs,  or 
feathers  of  their  hosts.  Sexual  dimorphism  is  usually  marked,  the  males  pos- 
sessing special  structures  for  clasping  or  holding  the  females.  The  principal 


THE  ORDER  ACARINA  99 

families  may  be  separated  by  the  following  key  (adapted  from  Banks  and 
Ewing) :  * 

KEY  TO  FAMILIES  OF  SARCOPTOIDEA 

i.  With  special  apparatus  for  clinging  to  hairs,  usually  either  modified 
legs  or  chelicerae.  Parasitic  on  mammals.  (Contains  no  species  of 

known  medical  importance)  Listrophoridae 

No  such  special  clinging  apparatus  2 


---Ch 


Ar- 


Fig.  30.  Lefl:  Dorsal  view  of  capitulum  of  Psoroptes  communis  var. 
cuniculi.  Right:  A  single  chelicera,  greatly  enlarged.  Ar,  articulation 
of  internal  part  of  chelicera;  BC,  basis  capitulum;  C,  Chi,  Chz,  cheli- 
cerae; M,  the  muscle;  K,  a  keellike  structure  on  basis  capitulum;  P, 
palpus;  Si,  Si,  Ss,  spines. 

2.  Bird-infesting  mites,  living  on  or  among  the  feathers;  usually  heavily 

sclerotized     Analgesidae 

Mites  not  living  on  or  among  the  feathers  of  birds;  soft-bodied  mites 3 

3.  Parasitic  on  insects  only Canestrimidae 


joo  MEDICAL  ENTOMOLOGY 

Parasitic  in  or  on  the  living  tissues  of  vertebrates 4 

4.  Vulva  longitudinal;  parasitic  in  the  skin  and  tissues  of  birds  (mainly 

the  air  passages  and  air  cells)  Cytoleichidae 

Vulva  transverse;  parasitic  in  or  on  the  skin  of  mammals  and  birds 

Sarcoptidae 

THE  FAMILY  SARCOPTIDAE 

Species  of  this  family  produce  skin  diseases  of  man  and  other  animals  known 
under  such  names  as  scabies,  sarcoptic  itch,  "Norwegian  itch,"  "barber's 
itch,"  psoroptic  itch,  acariasis,  etc.  The  species  are  all  skin-infesting  and  live 
primarily  beneath  the  scabby  incrustations  that  their  activities  induce.  Certain 
species  (Sarcoptes  spp.)  are  burrowing  in  their  habit  and  form  tunnels  below 
the  surface  of  the  skin.  Though  a  considerable  number  of  genera  have  been 
described  in  this  family  only  a  few  of  them  are  of  interest  here.  These  may  be 
separated  by  the  following  key. 

KEY  TO  GENERA  OF  SARCOPTIDAE 

1.  Suckers  of  the  tarsi  with  segmented  pedicels;  males  with  anal  suckers 

(Fig.  32  A)  Psoroptes 

Pedicels  of  the  suckers  not  segmented  or  suckers  may  be  absent  (Fig.  315) 

2 

2.  Females  with  tarsal  suckers  lacking  on  all  the  legs;  anal  opening  ter- 

minal; parasitic  on  birds Cnemidocoptes 

Females  with  tarsal  suckers  on  some  of  the  legs 3 

3.  Tarsal  suckers  on  all  the  legs  of  the  male  and  on  the  first,  second,  and 

fourth  of  the  female.  (Species  infest  horses  and  cattle)  Chorioptes 

Tarsal  suckers  not  arranged  as  above;  suckers  on  the  first,  second,  and 
fourth  pairs  of  legs  of  the  male;  on  the  first  and  second  pairs  of  the 
female  (Fig.  31  B) 4 

4.  Anal  opening  on  the  dorsal  surface;  dorsal  surface  of  the  body  with  only 

short,  sharp  setae  Notoedres 

Anal  opening  terminal  or  partially  ventral;  dorsal  surface  of  the  body 
with  pointed  scales  and  blunt,  stout  spines  (Fig.  31  A) Sarcoptes 

THE  GENUS  SARCOPTES  LATREILLE  1806:  Sarcoptes  contains  those 
species  that  produce  the  true  scabies  or  itch  of  man  and  animals.  Whether 
there  is  only  one  species  with  numerous  varieties  or  a  number  of  distinct 
species  attacking  different  animals  is  still  a  much-disputed  question.  Further- 
more, whether  the  various  so-called  species  on  different  animals  will  attack 


THE  ORDER  ACARINA  101 

man  has  not  been  determined  for  many  of  them.  It  is  preferable  to  follow  the 
practice  of  recognizing  only  one  valid  species  and  listing  as  varieties  or  sub- 
species those  found  on  different  animals.  The  type  species  is  Sarcoptes  scabiei 
de  Geer,  found  on  man,  though  it  is  often  written  S.  scabiei  var.  hominis 
(Hering). 
Sarcoptes  scabiei  :ft\\t  human  itch  mite  has  been  carefully  studied  by  several 


Fig.  37.  (A}  and  (#)  Dorsal  and  ventral  views  o£  Sarcoptes  scabiei.  (C)  Sarcoptes 
scabiei  in  its  burrow  in  the  skin.  (D)  Pcdiculoides  ventricosus,  mature  female  before  the 
development  of  its  young.  (£)  P.  ventmcosus,  female,  showing  the  abdomen  greatly 
swollen  by  the  developing  young  (D  and  E  not  drawn  to  the  same  scale),  a,  anal  opening; 
e,  eggs  in  burrow;  f,  female  at  end  of  burrow;  s,  suckers. 

workers,  especially  in  recent  years.  The  adult  female  (Fig.  31)  measures 
330  to  450  microns  in  length  and  250  to  350  microns  in  width.  The  male  is 
considerably  smaller,  a  little  more  than  half  the  size  of  the  female.  The  dorsal 
surface  of  the  body  is  marked  with  numerous  parallel  lines  except  in  atf 
anterior  median  area;  stout,  blunt  spines  and  irregular  scales  are  prestnt  and 
arranged  as  shown  in  Fig.  31.  Several  pairs  of  long  and  short  hairs  are  also 
present.  The  number,  arrangement,  length,  and  shape  of  these  structures  seem 
to  be  of  some  systematic  significance.  The  ventral  surface  is  smooth  except  for 


102  MEDICAL  ENTOMOLOGY 

a  few  hairs  or  bristles.  The  anterior  two  pairs  of  legs  are  widely  separated  from 
the  posterior  two  pairs.  The  most  striking  structures  are  the  epimeres  or 
chitinous  supports  for  the  legs|(Fig.  31  B).  The  epimeres  of  the  first  pair  of 
legs  are  united  and  form  a  narrow  rod  lying  in  the  median  line;  those  of  the 
second  pair  do  not  unite  but  lie  on  either  side  of  the  body.  The  epimeres  of  the 
last  two  pairs  of  legs  are  not  so  prominent  except  in  the  male  where  they 
unite.  The  tarsal  suckers  consist  of  unsegmented  pedicels  and  are  present  on 
the  first  and  second  pairs  of  legs  of  the  female  and  on  the  first,  second,  and 
fourth  of  the  male. 

LIFE  CYCLE  iiThis  mite  and  its  various  subspecies  excavate  horizontal,  tor- 
tuous tunnels  in  the  upper  epidermis,  the  horny  layer  (Fig.  31).  In  man  these 
burrows  are  usually  found  on  definite  areas  of  the  body,  particularly  between 
the  fingers,  wrists,  elbows,  axillae,  region  of  the  groin  and  external  genital 
organs,  back  of  the  knees,  ankles,  and  toes.  In  children  all  parts  of  the  body 
may  be  infested;  in  women  the  undersides  of  the  breasts  are  said  to  be  favorite 
locations/According  to  Munro  definite  egg  burrows  are  made  by  the  mature 
female.  She  bores  directly  into  the  skin,  becoming  completely  concealed  in 
from  a  few  minutes  to  nearly  an  hour.  Burrowing  usually  continues,  and 
2  to  5  mm.  is  excavated  daily,  fcgg  laying  commences  with  the  burrowing  and 
continues  for  about  four  to  five  weeks.  The  eggs  are  deposited  directly  behind 
the  female  (Fig.  31),  and  normally  she  deposits  one  or  two  eggs  each  day.  The 
exact  number  of  eggs  laid  by  a  single  female  has  not  been  determined  but 
probably  40  to  50  is  about  the  average.  The  eggs  hatch  in  from  three  to  four 
days.  The  larvae  leave  the  parent  burrow  and,  passing  to  the  surface  of  the 
skin,  enter  hair  follicles  or  penetrate  the  skin  between  hairs;  vesicles  may  form. 
The  larval  stage  lasts  from  two  to  three  days.  The  larva  then  molts  in  its 
burrow.  There  are  two  nymphal  stages,  the  nymphs  making  narrow,  shallow 
burrows.  Mating  takes  place  in  the  burrows^he  males  seeking  out  the  females, 
though  Mellanby  (1943)  thinks  mating  occurs  on  the  surface  of  the  skin, 
frhe  fertilized  female  then  proceeds  to  form  an  ovigerous  burrow.  The  entire 
life  cycle  from  egg  to  adult  varies  from  8  to  15  days.  The  adults  live  for  three 
to  five  weeks.  As  the  life  cycle  is  comparatively  brief,  a  mild  infection  may 
become  marked  in  a  short  time.f  According  to  Mellanby,  it  requires  several 
weeks  before  an  infection  becomes  apparent  and  requires  medical  attention. 
He  has  also  shown  that  in  man  (some  900  cases)  the  average  number  of  adult 
female  mtfes  per  patient  rarely  exceeds  fifty.  However,  many  severe  infesta- 
tions have  been  reported,  and  the  number  of  mites  must  have  been  large  or 
secondary  infection  (bacterial1;  occurred. 


THE  ORDER  ACARINA  103 

EFFECT  ON  HosTf  The  initial  attack  is  without  definite  symptoms  for  the  first 
few  weeks.  As  the  host  becomes  sensitized,  the  presence  of  the  mites  in  the 
skin  causes  intense  itching,  especially  at  night  when  the  warmth  induces  the 
mites  to  greater  activity.'lncessant  scratching  follows,  and  the  effects  of  the 
scratching  may  be  more  serious  than  the  work  of  the  mites.  ftVhere  the  egg 
channels  are  formed  and  the  larvae  and  nymphs  burrow  in  the  skin,  small 
serous  vesicles  appear.  Scratching  ruptures  these  vesicles,  and,  on  healing, 
minute  crusts  are  formed.  In  severe  infestations  secondary  complications  may 
follow,  such  as  infection  with  Streptococcus  specieslDiagnosis  of  scabies  must 
rest  on  finding  the  mites  and  the  burrows  in  the  skin.  The  mites  are  not  present 
in  the  vesicles  but  usually  close  beside  them  at  the  end  of  linear,  shallow  bur- 
rows. As  scabies  may  be  masked  or  confounded  with  other  skin  diseases,  it  is 
essential  that  the  mite  be  found  before  a  final  diagnosis  is  made. 
I  Sarcoptic  mites  are  not  easily  transferred  by  simple  contact,  though  cases 
of  such  are  on  record.  The  most  common  methods  are  by  close  contact  with 
infected  persons,  as  by  sleeping  with  them,  by  cohabitation,  by  using  their 
clothing  or  bedding,  or,  among  children,  by  playing  and  holding  hands. 
Munro  has  shown  that  the  cast-off  clothing  of  infected  persons  remains  capable 
of  infecting  others  for  at  least  n  days  if  the  clothing  is  moist;  if  the  clothing  is 
dry,  infection  dies  out  in  two  or  three  days.i  During  the  First  and  Second 
World  Wars  there  were  severe  outbreaks  of  sarcoptic  itch  in  the  various  armies. 
These  outbreaks,  though  marked  among  the  troops,  were  also  present  in  the 
general  population  of  many  countries.  Mellanby  (1943)  states  that  in  Great 
Britain  the  normal  population  showed  an  infection  rate  of  about  i  per  cent 
in  1939  anc^  this  increased  to  about  5  per  cent  in  many  parts  of  the  country 
during  the  war.  The  average  for  the  country  as  a  whole  was  about  2  per  cent. 
Women,  especially  young  women,  showed  an  incidence  about  twice  as  great 
as  did  males. 

TREATMENT:  Persons  infected  with  sarcoptic  itch  should  obtain  medical  atten- 
tion. During  the  last  world  war  several  effective  treatments  were  developed,  and 
these  proved  easy  of  application.  The  American  Army  formula  was  known 
under  the  code  name  NBIN  and  consisted  of  the  following  compounds  Ibenzyl 
benzoate  68  per  cent;  DDT  6  per  cent;  benzocaine  12  per  centl'Tween  80, 
14  per  cent  (all  by  weight).  For  treatment  the  concentrate  should  be  diluted 
at  the  rate  of  one  part  to  five  parts  of  water.  Before  applying  treatment  the 
infected  person  should  take  a  hot  bath,  scrubbing  the  lesions  vigorously  with 
a  tincture  of  green  soap.  The  dilution  may  then  be  applied  either  by  a  sponge 
or  as  a  spray,  and  the  whole  body  should  be  carefully  covered.  The  patient 


104  MEDICAL  ENTOMOLOGY 

should  not  bathe  for  at  least  24  hours.*|Many  reliable  proprietary  brands  are 
on  the  market  as  benzyl  benzoate  solutions,  benzyl  benzoate  ointment,  or 
other  trade  names.  These  are  said  to  be  very  effective,  and  the  patient  should 
follow  the  directions  of  the  manufacturer.  One  thorough  treatment  by  these 
preparations  usually  gives  complete  cure,  though  it  may  be  well  to  follow  this 
by  a  second  about  a  week  later.  ^The  British  formula  as  given  by  Mellanby 
(1943)  is  very  easy  to  prepare  and  is  said  to  be  very  easy  on  patients  with 
tender  and  abraded  skins.  It  is  as  follows:  "Benzyl  benzoate,  200  mils;  Stearic 
acid,  20  gr.;  Triethanolamine,  6  mils;  water  to  produce  1000  mils.  Heat  the 
benzyl  benzoate  and  stearic  acid  together  until  the  latter  is  dissolved.  Mix 
the  triethanolamine  with  the  water  and  then  pour  into  the  warm  benzyl 
benzoate  acid  mixture  and  stir."  This  makes  a  good  emulsion  and  is  very  easy 
on  the  skin.  Other  mixtures  are  also  on  the  market  but  those  with  benzyl 
benzoate  as  the  prime  ingredient  are  preferred.  Where  these  compounds  can- 
not be  obtained  the  sulphur  ointment  (10  to  15  per  cent)  may  be  used,  but 
this  requires  at  least  three  treatments  morning  and  evening  without  bathing. 
Bathing  should  precede  the  first  treatment  and  follow  the  last.  In  all  cases  the 
clothing  and  bedding  of  infected  patients  should  be  sterilized  by  laundering 
or  by  dry  heat. 

JThe  so-called  "Norwegian  itch"  is  caused  by  the  same  species  of  Sarcoptcs 
but  oftentimes  is  marked  by  gigantic  crusts  due  to  long  infestations.  Another 
disease  called  "craw-craw"  in  parts  of  Africa  is  characterized  by  nodular  and 
scabby  dermatitis  but  has  been  shown  to  be  caused  by  Sarcoptes.^ 

Other  Sarcoptes:  Itch  mites  have  been  described  from  many  different  mam- 
malian hosts.  Over  18  to  20  different  species  or  varieties  are  known,  as  S.  equi 
(from  the  horse),  S.  cants  (from  the  dog),  S.  ovis  (from  the  sheep),  S.  suis 
(from  the  pig),  and  S.  bovis  (from  the  ox).  Nearly  all  recent  work  indicates 
that  these  are  not  separable  on  morphological  characters  but  appear  as 
physiological  races  or  varieties  of  the  one  species  S.  scabiei  de  Geer.  If  this  is 
true,  can  man  become  infected  by  the  animal-infesting  forms?  There  are 
many  records  of  man's  becoming  infected  with  some  of  these  forms,  especially 
by  S.  scabiei  var.  equi  (by  grooms  and  others  attending  infested  horses),  by 
var.  caprae  and  var.  ovis  (by  goat  and  sheep  herders) .  During  a  recent  epidemic 
of  scabies  of  cattle  by  S.  scabiei  var.  bovis  in  the  northeastern  United  States 
there  were  many  reports  of  human  infection,  but  so  far  as  the  writer  is  aware 
these  infestations  were  of  a  temporary  nature. 

THE  GENUS  PSOROPTES  GERVAIS  1841:  Species  of  Psoroptes  are 
nonburrowing  itch  mites  that  possess  tarsal  suckers  with  jointed  pedicels 


THE  ORDER  ACARINA  105 

(Fig.  32).  Like  Sarcoptes,  rather  numerous  species  of  Psoroptes  have  been 
described  from  various  animals.  P.  communis  var.  ovis  (Hering)  produces  a 
serious  disease  of  sheep,  psoroptic  itch  or  scab.  The  mite  causes  the  wool  to  fall 
out  or  to  mat  together  and  severe  scabby  incrustations  to  form,  and,  in  general, 
the  infected  animals  present  a  scraggy  and  dilapidated  appearance.  This  dis- 
ease is  widespread  in  sheep-raising  regions  but  can  be  controlled  by  the  use 


Fig,  32.  Left:  A  common  nonburrowing  itch  mite,  Psoroptes  communis.  Right:  A 
hair-follicle  mite,  Demodex  Jolliculorum.  A,  segmented  pedicel  o£  sucker. 

of  appropriate  dipping  solutions.  Other  varieties  are  P.  communis  var.  cqui, 
on  horses;  var.  bovis,  on  cattle;  var.  cuniculi  (Fig.  32),  on  rabbits.  (This  variety 
on  rabbits  seems  to  prefer  the  ears  and,  in  laboratory  animals,  causes  them  to 
swell  enormously.  Frequently  they  penetrate  deeply  into  the  ear  and  cause 
death.)  Many  other  varieties  from  different  animals  have  been  recognized. 

OTHER  GENERA:  Species  of  the  genus  Notocdrcs  infest  cats  and  rats. 
They  are  found  principally  about  the  ears,  snout,  tail,  and  anogenital  region 
or  among  the  fine  hairs  of  the  lower  part  of  the  legs.  The  itch  produced  is 


io6  MEDICAL  ENTOMOLOGY 

rather  severe.  The  species  on  cats  or  rats  may  also  occur  on  man.  Gordon  et  al. 
(1943)  give  an  extended  account  of  the  habits  and  biology  of  this  mite. 
Chorioptes  equi  causes  a  mange  on  the  feet  of  horses  and  C.  bovis  produces  a 
mange  on  cattle.  Cnemidocoptes  mutans  affects  fowls,  causing  a  rather  serious 
disease  known  as  scaly  leg;  C.  gallinae  is  found  at  the  base  of  feathers  and 
is  known  as  the  "depluming  mite." 

THE  TROMBIDOIDEA 

The  Trombidoidea  constitute  a  large  group  of  mites  that  are  mainly  free- 
living,  feeding  on  plant  juicejs,  or  they  are  predaceous;  some  are  parasitic  while 
others  are  free-living  in  the  nymphal  and  adult  stages  and  parasitic  in  the  larval 
stage.  They  are  trarhenfe  mjre.s.  the  spiracles  located  on  or  near  the  basesof  the 
cheliccrae.  The  mouth  parts  are  either  prominent  and  raptorial  or  they  are 
modified  for  piercing  ancrsucking.  The  last  segment  of  the  palpus  is  modified 
into  a  thumblike  structure  capable  of  apposing  the  clawlike  extension  of  the 
penultimate  segment.  The  body  is  never  strongly  sclerotized,  and  chitinous 
plates  are  rarely  present. , - 

This  group  is  divided  into  a  number  of  families,  six  or  more.  Only  one 
family,  the  Tjjimhidiidae,  is  of  interest  here  as  it  contains  species  that  are  fre- 
quently parasitic  in  the  larval  stages,  oi\  man  and  other  animals.  Parasitic 
forms  are  known  in  some  of  the  other  families  and  a  few  have  been  reported 
as  annoying  to  man,  but  they  are  of  minor  importance.  This  family  is  fre- 
quently divided  into  two  subfamilies,  the  Trombidiinae  and  the  Trombi- 
culinae.  Recently  Ewing  (1944)  has  recognized  these  as  distinct  families. 
They  may  be  separated  by  the  following  brief  key : 

1.  Abdomen  of  adults  and  nymphs  strongly  constricted  somewhat  in  front 

of  the  middle;  eyes,  when  present,  never  stalked.  Eggs  laid  singly. 
Larvae  parasitic  on  vertebrates Trombiculinae 

2.  Abdomen  of  adults  and  nymphs  not  constricted;  eyes  usually  present 

and  frequently  stalked.  Eggs  laid  in  clusters.  Larvae  parasitic  on  in- 
vertebrates       Trombidiinae 

THE  SUBFAMILY  TROMBICULINAE 

To  this  subfamily  belong  the  harvest  mites,  the  chigger  mitcs^and  others  that 
are  parasitic  on  vertebrates  during  their  larval  stage  and  arc  free-living  in  the 
nymphal  and  adult  stages.  Many  of  these  mites  are  brilliantly  colored— red, 
scarlet,  or  spotted  with  variegated  colors.  They  bear  various  names  as  "diig- 
gers,"  "harvest  mites,"  "scrub  mites,"  bete  rouge,  and  rottget.  Until  recently 


THE  ORDER  ACARINA  107 

only  a  few  genera  were  known,  but  at  the  present  time  some  26  genera  and  a 
large  number  of  species  have  been  described;  many  or  most  of  them  are  from 
the  Oriental  and  Australasian  regions.  Michener  (1946)  states  that  13  genera 
are  known  from  the  Western  hemisphere,  and  these  include  about  90  species. 
Of  these  90  species  only  8  are  known  as  adults  or  have  been  reared  to  the 
adult  stage.  The  species  are  based  mainly  on  the  larval  state  since  very  few 
(10  species)  have  been  reared  to  the  adult  stage.  The  following^pecies  are  of 
interest  because  of  their  constant  attacks  on  man  or  as  vectors  of  important 
diseases. 


/ 


Fi^.  33.  Eutrombicula  alfreddugesii  (Oudemans).  Left:  Larva  (North  American  chig- 
ger),  greatly  enlarged.  Right:  Adult,  a,  abdomen;  ae,  anterior  eye;  as,  anterolateral  seta; 
dp,  dorsal  plate;  hs,  humeral  seta;  Is,  lateral  seta;  ms,  median  seta;  p,  pseudostigma; 
pa,  palpus,  pc,  palpal  claw;  pe,  posterior  eye;  po,  pseudostigmatic  organ;  ps,  posterolateral 
seta.  (From  Manual  of  Tropical  Medicine,  courtesy  W.  B.  Saunders;  modified  from 
Ewing.) 

Eutrombicula  alfreddugesii  (Oudemans)  [Leptus  irritans  of  literature] 
>is  thc^common  chigger  (Fig.  33)  that  aj^acks  mnn  in  North  America.  It  is 
generally  distributed  from  New  York  to  Minnesota,  southward  to  the  Gulf 
of  Mexico  and  in  Mexico.  In  the  southern  states  it  is^ery  prevalent  during  the 
summer  months^  and  its  attacks  are  very  annoying.  The  larval  mites  are  very 
minute  and  easily  penetrate  the  clothing.  They  attach  by  means  of  their  hooked 
chelicerae  and  armed  palpi.  The  method  of  feeding  is  very  interesting.  The 
chelicerae  are  inserted  in  the  skin,  frequently  about  a  hair  follicle  and  usually 


io8  MEDICAL  ENTOMOLOGY 

under  or  near  clothing  where  there  is  pressure.  The  mite  then  injects  into  the 
tissues  a  fluid  that  has  a  remarkable  effect.  This  fluid  liquefies  the  immediate 
tissues,  but  the  surrounding  tissues  become  hardened  and  form  a  tube,  fre- 
quently referred  to  as  the  stylostome  or  hypostome  (Fig.  34).  The  liquefied 
tissues  are  ingested  by  the  mite,  and  as  feeding  continues  the  tube  becomes 
lengthened  as  more  of  the  tissues  are  dissolved.  The  stylostome  may  become 
as  long  as  the  mite,  and  when  the  mite  releases  its  hold  this  tube  is  left  in  the 
tissues.  The  effect  of  the  digestive  juices  is  to  cause  severe  itching  followed 

by  a  marked  dermatitis.  Incessant  scratch- 
ing may  bring  about  secondary  infection, 
and  the  result  may  be  dangerous.  After 
feeding,  the  larval  mites  drop  to  the 
ground  and  later  molt  to  the  eight-legged 
nymphal  stage.  The  nymphs  are  not 
parasitic  and  probably  feed  on  vegetable 
matter.  This  is  also  true  of  the  adults. 
The  females  deposit  their  eggs  singly  on 
the  ground.lHow  many  generations  de- 
velop in  a  summer  season  does  not  seem 
to  be  known /In  the  larval  stage  this  mite 
attacks  all  sorts  of  vertebrates  as  rabbits, 
Fig.  34.  A  diagrammatic  illustration  mice,  rats,  snakes,  turtles,  poultry,  and 
of  the  formation  of  the  stylostome  by  a  quail. /Jenkins  (1947)  gives  a  concise  ac- 
Ncoschongastia  sp.  in  the  ear  of  a  rat.  r  ,  c 

Ch,  chelicerae  of  mite;  Sty,  stylostome.  count  of  reannS  several  generations  of 

this  mite  and  also  of  E.  masoni.  He  reared 

the  nymphs  in  soil  in  jars,  feeding  them  on  the  eggs  of  mosquitoes  (Aedes 
aegypti) .  At  the  present  time  this  mite  is  not  known  to  transmit  any  human 
disease. 

Eutrombicula  batatas  (Linn.),  known  as  the  "patatta"  mite  of  Surirlam, 
occurs  from  Surinam  to  Panama, /north  to  Puerto  Rico,  Florida,  Alabama, 
and  parts  of  Mexico.  According  to  Michener  (1946),  the  adults  are  found  in 
open  sunlight  areas  among  short  grass.  The  females  lay  their  eggs  on  the 
ground.  The  eggs  hatch  in  four  to  five  days  into  what  has  been  called  the 
"deutovum"  stage  of  mites  (the  eggshell  bursting  and  showing  a  quiescent 
undeveloped  larva,  Fig.  35).  This  stage  lasts  six  to  seven  days,  and  from  it 
emerges  an  active,  six-legged,  reddish  larvga.  The  larvae  occur  on  the  grass  or 
weeds,  often  in  great  numbers,  especially  about  houses  where  domestic  ani- 
mals such  as  chickens  are  numerous.  The  larvae  readily  attach  to  man, 
domestic  animals,  rats,  or  birds.  On  man  they  seem  to  settle  mostly  in  the 


Fig.  35.  A  chigger  mite,  Eutrombicula  batatas  (Linn.),  (a)  Dorsal 
view  of  adult.  (£)  Dorsal  view  of  nymph.  (<r)  Dorsal  view  of  larva. 
(J)  Lateral  view  of  deutovum.  (<?)  The  egg.  (All  to  the  same  scale; 
After  Michcner,  Annals  oj  the  Entomological  Society  oj  America?) 


j  io  MEDICAL  ENTOMOLOGY 

groin  region,  under  the  armpits,  under  the  belt  line,  or  on  the  ankles  under 
the  socks.  They  remain  attached  for  three  to  six  days  and  then  drop  from  their 
hosts.  Within  the  larval  skin  the  protonymph  appears,  and  later  the  first 
nymphal  stage  emerges  from  the  larval  and  protonymph  integuments  in  six 
or  seven  days  after  the  larva  dropped  from  its  host.  The  eight-legged,  dull-red 
nymph  Jnnks  like  the  adult  except  in  size.  The  nymphs  remain  on  the  ground, 
but  their  exact  food  was  not  determined.  In  about  two  weeks  or  longer  the 
nymphs  become  quiescent  and  in  about  a  week  transform  to  adults.  The 
adults  have  been  kept  alive  for  at  least  45  days.  Though  the  exact  food  of 
the  nymphs  and  adults  was  not  determined,  Michener  suggests  that  they  live 
on  the  soil  moisture  rich  in  organic  matter  as  they  possess  sucking  mouth  parts. 
This  species  is  not  known  to  transmit  any  disease. 

Trombicula  autumnalis  (Shaw)  is  a  very  troublesome  mite  in  various  parts 
of  Europe.  It  is  a  pest  not  only  of  man  but  of  horses,  cattle,  dogs,  cats,  and 
rabbits.  According  to  Fuss  and  Hansen  (1933),  it  produces  on  man  a  severe 
dermatitis  with  inflammation,  necrosis  of  the  epidermis,  and  hyperemia.  The 
itching  is  intense. 

Trombicula  a\amushi  (Brumpt)  occurs  over  extensive  areas  of  Japan,  For- 
mosa, parts  of  Korea,  and  the  Pescadores,  and  it  is  reported  from  the  Malay 
Peninsula.  This  species  is  of  great  importance  as  it  is  known  to  be  the  vector 
of  Japanese  river  fever,  tsutsugamushi  disease,  or,  as  it  is  frequently  called, 
kedani  fever.  The  life  history  of  this  mite  and  its  relation  to  tsutsugamushi  dis- 
ease were  rather  fully  elaborated  by  Japanese  workers  between  1900  and  1918. 
In  World  War  II  tsutsugamushi  disease  appeared  among  American  and  Al- 
lied troops  in  various  parts  of  the  South  Pacific  and  Burma  theaters  of  opera- 
tions. As  a  result  extensive  and  intensive  investigations  have  been  carried  on 
and  much  new  data  obtained. 

T.  afymushi  (Fig.  36),  like  other  mites  parasitic  in  the  larval  stage,  not  only 
feeds  on  man  but  attacks  mice,  rats,  and  other  rodents.  It  is  especially  fond  of 
the  voles  (Microtus  montebelli  in  Japan)  in  the  ears  of  which  it  seems  to 
congregate.  The  period  of  larval  attachment  is  three  to  four  days.  The  method 
of  feeding  is  similar  to  that  of  Eutrombicula  aljreddugesii.  (This  is  believed 
to  be  true  of  all  the  parasitic  larval  mites  of  the  subfamily  Trombiculinae.) 
Leaving  the  host  the  larvae  seek  shelter  in  the  ground,  where  they  transform 
to  nymphs  in  from  two  to  three  weeks.  The  nymphs  are  said  to  feed  only  on 
plant  juices  or  decaying  organic  matter.  The  nymphal  period  lasts  some  three 
to  ten  or  more  weeks  (no  very  accurate  data  seem  to  be  available  6n  the  activi- 
ties and  length  of  the  nymphal  life) .  The  adults  live  on  the  ground  and  are 
said  to  feed  on  plant  juices.  They  are  known  to  hibernate  during  the  winter 


THE  ORDER  ACARINA 


in  Japan.  In  the  spring  the  females  deposit  their  eggs  singly  on  the  ground 
under  trash  or  other  covering.  Unfortunately  very  few  new  data  have  been 
obtained  on  the  life  cycles,  habits,  or  biology  of  the  various  species  of  mites 
occurring  in  the  regions  where  kedani  fever  is  now  known  to  be  prevalent. 


Fig.  36.  Larva  of  Trombicula  aJ(amushi.  A,  abdomen;  Ae>  anterior  eye;  As,  anterolateral 
seta;  Bes,  basal  segment  of  chelicera;  Ds,  dorsal  shield  or  plate;  Gs,  branched  galeal  seta; 
H,  one  of  the  dorsal  hairs;  Hs,  humeral  seta;  Ms,  median  seta;  P,  pseudostigma;  Pa,  pal- 
pus; PC,  palpal  claw;  Pe,  posterior  eye;  Po,  pseudostigmatic  organ;  Ps,  posterolateral  seta. 
(Modified  from  Hirst.) 

Trombicula  deliensis  Walch  was  described  from  Sumatra.  It  is  distributed 
in  many  parts  of  Malaya,  northern  India  (Simla  Hills),  the  East  Indies, 
northern  Australia,  and  probably  in  other  parts  of  southeastern  Asia.  It  occurs 
on  various  species  of  rats  and  other  rodents  and  readily  attacks  man. 

Trombicula  fletcheri  Womersley  and  Heaslip  was  described  in  1943.  It 


H2  MEDICAL  ENTOMOLOGY 

is  found  commonly  in  the  New  Guinea  area  and  readily  attacks  man.  It  is  a 
common  parasite  of  rats  and  bandicoots  and  is  recorded  from  several  other 
hosts.  Little  seems  to  be  known  of  its  life  history,  and  its  distribution  is,  as 
yet,  not  fully  known.  Trombicula  walchi  was  described  by  Womersley  and 
Heaslip  from  the  New  Guinea  area,  but  many  authorities  seem  to  think  it  is 
the  same  as  T.  deliensis. 

Many  other  species  of  Trombicula  and  related  genera  have  been  described 
from  the  southwest  Pacific  area,  but  little  is  known  about  their  biology  or 
distribution.  Trombicula  hirsti  Sambon  is  generally  called  the  "scrub  mite" 
of  parts  of  Australia;  T.  wichmanni  Oudemans,  is  said  to  be  a  pest  in  the 
Celebes  and  New  Guinea;  Leeutvenhoetya  australiensis  Hirst  is  troublesome 
in  New  South  Wales. 

CONTROL  OF  MITES:  Very  effective  mite  repellents  were  developed 
during  the  recent  world  war.  Briefly  these  are: 

(1)  Dimethyl  phthalate  or  dibutyl  phthalate  used  as  liquids  on  all  openings 
of  the  clothing.  These  are  applied  by  hand  or  the  entire  clothing  can  be 
sprayed.  In  using  them  apply  liberally  along  all  openings  and  especially  about 
the  socks  and  edges  of  trousers.  These  materials  can  also  be  used  to  impreg- 
nate clothing.  These  solutions  can  be  purchased  and  the  directions  of  the 
manufacturer  should  be  followed. 

(2)  Benzyl  benzoate  as  developed  in  the  NBIN  formula  for  the  control 
of  sarcoptic  itch  mites  is  also  effective  (see  pp.  103-104).  Clothing  is  impreg- 
nated with  this  mixture  and  it  withstands  several  launderings  or  even  longer. 

(3)  Benzyl  benzoate  alone  also  gives  excellent  repellent  effect  when  cloth- 
ing is  impregnated  with  it.  The  repellent  effect  persists  even  after  four  or  five 
launderings. 

(4)  Other  repellents  have  been  tested  but  not  sufficiently  to  warrant  their 
use  at  the  present  time, 

TROMBICULID  MITES  AND  DISEASE:  The  attacks  of  various  species 
of  mites  throughout  the  world  usually  result,  in  man,  in  a  marked  dermatitis 
accompanied  by  intense  itching.  The  scratching  of  the  areas  may  induce  sec- 
ondary infections  that  may  be  serious.  However,  it  is  as  vectors  of  disease  that 
certain  species  are  dangerous. 

Tsutsugamushi  disease  was  recognized  in  man  in  Japan  as  early  as  1878, 
and  Baelz  and  Kawakami  (1879)  published  on  account  of  what  they  described 
as  "Japanese  river  fever."  The  disease  was  confined  to  overflow  areas  of  certain 
river  valleys.  The  natives  associated  it  with  the  bite  of  a  red  mite  (akamushi). 
Japanese  workers,  between  1893  and  1918,  fully  established  that  the  mite, 


THE  ORDER  ACARINA  113 

Trombicula  akamushi,  was  the  vector  of  the  disease;  that  rodents,  principally 
the  vole,  Microtus  montebelli,  were  the  reservoir;  and  that  the  virus  is  .passed 
through  the  egg  to  the  young  of  the  infected  mites.  They  also  described  the 
life  cycle  of  the  mite  and  largely  determined  its  distribution  in  Japan  and 
Formosa.  In  1930  Nagayo  and  his  associates  discovered  the  etiological  agent 
and  named  it  Ric^ettsia  orientalis.  It  is  now  well  established  that  the  reservoir 
of  this  disease  is  in  rats,  mice,  voles,  and  other  rodents;  the  mites  obtain  the 
rickettsiae  while  feeding  on  infected  hosts,  and  these  are  passed  through  the 
nymphal  stage  to  the  adults  and  by  the  adults  through  the  eggs.  Larvae  from 
infected  mothers  then  transmit  the  disease  to  man  when  they  feed  on  him. 
The  point  of  feeding  by  infected  larvae  usually  shows  a  distinct  scar  (eschar) . 
The  incubation  period  in  man  is  7  to  10  days  or  may  be  prolonged  to  14  days. 
The  mortality  rates  vary,  but  range  from  60  per  cent  for  older  persons  to  15 
per  cent  for  the  n-  to  20-year  age  group  in  Japan.  Blake  et  al.  (1946)  give  an 
over-all  death  rate  of  30  per  cent  in  Japan.  Throughout  southeast  Asia,  the 
islands  of  the  southwest  Pacific,  and  Australia  various  typhuslike  diseases  have 
been  described  such  as  Mossman  fever  from  Australia,  scrub  typhus  from 
Malaya,  pseudotyphus  from  Sumatra,  endemic  typhus  from  India,  and  tropical 
typhus  from  Indo-China.  During  World  War  II  these  diseases  were  investi- 
gated by  a  large  number  of  workers  with  the  result  that  all  these  diseases  were 
declared  to  be  manifestations  of  tsutsugamushi  disease.  At  present  this  disease 
occurs  in  India,  Ceylon,  Burma,  Indo-China,  Malaya,  Sumatra,  Java,  Borneo, 
Celebes,  New  Guinea,  northeast  Australia,  New  Britain,  Bougainville,  parts 
of  the  Philippines,  Formosa,  Japan,  Korea,  and  probably  parts  of  China.  The 
vectors  are  Trombicula  a\amushi,  T.  deliensis,  T.  fletcheri,  T.  walchi 
(  —  deliensis),  and  probably  others.  The  reservoirs  of  Ricftettsia  orientalis  are 
in  voles  (especially  Microtus  montebelli  in  Japan),  in  wild  rats  of  various 
species,  and  in  other  rodents.  McCulloch  (1944,  1946)  reports  Schongastia 
blestowei  and  Trombicula  wichmanni  as  probable  vectors  on  epidemiological 
evidence. 

THE  TARSONEMOIDEA 

This  superfamily  includes  a  large  number  of  mites  that  are  primarily  plant- 
inhabiting  or  that  infest  foods  of  various  kinds.  A  few  species  are  known  to 
be  parasitic,  and  one  species,  under  certain  conditions,  may  attack  man. 
Acarapis  woodi  Rennie  lives  in  the  tracheae  of  honeybees  and  produces  a 
serious  disease  of  the  adults  known  as  "Isle  of  Wight  disease."  Two  species 
have  been  recorded  as  invading  the  tracheae  of  grasshoppers  (Wehrle  and 
Welch,  1925). 


ii4  MEDICAL  ENTOMOLOGY 

Pediculoides  ventricosus  Newport,  the  grain  itch  mite,  is  a  predaceous  mite 
(Fig;  31)  that  feeds  on  the  larvae  of  various  insects  infesting  seeds,  grains, 
plants,  or  their  products.  It  feeds  on  the  larvae  of  the  Angoumois  grain  moth 
(Sitrotroga  cerealella  Oliv.),  the  pink  bollworm  of  cotton  (Pectinophora 
gossypiella  Saunders),  the  joint  worms  (Isosoma  grande  Riley  and  /.  tritici 
Fitch),  the  bean  and  pea  weevils  (Mylabris  quadrimaculatus  Fabr.  and  M. 
obtectus  Say),  and  others.  There  is  marked  sexual  dimorphism  in  this  mite 
(Fig.  31).  The  abdomen  of  the  fertilized  female  becomes  greatly  swollen  as 


Fig.  37.  Lesions  produced  on  man  by  the 
bites  of  Pediculoides  ventricosus.  (After 
Webster.) 


F:g.  38.  Demodex  cants.  Base  of  a  seba- 
ceous gland  of  a  dog  packed  with  Demo- 
dex  canis. 


the  eggs  hatch  within  the  body  of  the  mother,  and  the  young  are  retained  till 
they  reach  sexual  maturity.  A  single  female  may  give  birth  to  as  many  as  270 
sexually  mature  mites.  In  seeds,  grain,  straw,  cotton,  beans,  or  other  plant 
material  infested  with  the  insect  larvae  noted  above,  this  mite  may  occur  in 
enormous  numbers.  Man  is  attacked  when  handling  such  infested  material 
or  sleeping  on  infested  straw,  or  when  he  in  other  ways  comes  in  contact  with 
large  numbers  of  the  mites.  On  man  their  bites  produce  a  rashlike  dermatitis, 
which  may  cover  the  entire  body  (Fig.  37).  The  rash  appears  12  to  16  hours 
after  the  attack  and  consists  of  wheals  and  papules  of  varying  size.  Vesicles  or 
pustules  may  develop,  and  the  attacked  areas  may  become  very  red  and  have 


THE  ORDER  ACARINA  115 

a  burning,  itching  sensation.  Fever  and  sweating  are  recorded  as  concomitants 
in  some  cases.  Ciarrocchi  (1928)  describes  an  epidemic  of  pruriginous  derma- 
titis in  Italy  caused  by  this  mite.  Its  attacks  have  been  recorded  from  widely 
scattered  regions  of  the  world.  Diagnosis  of  this  rash  must  be  based  on  the 
occupation  or  sleeping  habits  of  the  patient  and  the  discovery  of  the  mites. 
Treatment  consists  of  avoiding  further  infestation;  recovery  will  be  rapid.  In 
severe  cases  the  rash  may  be  reduced  by  bathing  in  warm,  soapy  water,  fol- 
lowed by  the  application  of  a  mild  talcum  powder. 

THE  TYROGLYPHOIDEA 

The  mites  belonging  to  this  superfamily  are  minute  and  abound  on  dried 
fruits,  other  foodstuffs,  roots,  and  bulbs.  Man  becomes  infested  from  handling 
infested  products.  Vanilla  pods  and  beans  are  often  heavily  infested,  and  a 
dermatitis,  known  as  "vanillism,"  frequently  occurs  among  vanilla  workers. 
It  is  believed  to  be  caused  by  the  mite  Tyroglyphns  siro  Linn.  Copra  itch 
is  a  common  dermatitis  among  workers  in  the  copra  mills  and  was  first  de- 
scribed by  Castellani  in  Ceylon.  It  is  caused  by  Tyroglyphus  longior  var.  castel- 
lani  Hirst.  This  dermatitis  may  affect  copra  workers  in  all  parts  of  the  world. 
A  so:called  "grocers'  itch"  is  caused  by  Glyciphagus  prunorum  Hermann 
(G.  domesticus  de  Geer),  which  often  abounds  in  grocery  stores.  The  derma- 
titis caused  by  these  mites  may  be  mistaken  for  scabies  or  other  types  of  skin 
diseases.  For  the  purpose  of  diagnosis  the  history  of  the  patient's  work  may 
often  give  a  clue  to  the  causative  agent.  Treatment  consists  of  various  oint- 
ments and  the  avoidance  of  mite-infested  plants  or  foodstuffs. 

As  mites  of  this  family  abound  in  foodstuffs,  they  have  been  recorded  many 
times  from  fecal  examinations.  Whether  they  cause  any  trouble  in  the  in- 
testinal tract  does  not  seem  to  be  known.  Mekie  (1926)  has  reported  the 
infection  of  the  urinary  tract  by  three  species,  Tarsonemus  floricolus  C.  and  F., 
Glyciphagus  domesticus  de  Geer,  and  Tyroglyphus  longior  Gerv.  He  also  re- 
viewed previously  reported  cases.  Hinman  et  al.  (1934)  reported  a  case  of 
intestinal  myiasis  due  to  Tyroglyphus  longior  Gerv.  It  is  difficult  to  conjecture 
how  such  infection  takes  place  except  through  uncleanly  habits. 

THE  DEMODICOIDEA 

The  Demodicoidea,  the  hair-follicle  mites,  are  a  highly  aberrant  group  of 
mites.  They  are  parasitic  in  the  hair  follicles  and  sebaceous  glands  of  mammals. 
They  are  very  elongate  (Fig.  32),  the  legs  are  reduced  to  mere  stumps,  the 
abdomen  is  vermiform,  and  the  mouth  parts  are  modified,  minute,  and  fitted 


n6  MEDICAL  ENTOMOLOGY 

for  piercing.  The  superfamily  contains  but  a  single  family,  the  Demodicidae, 
and  one  genus,  Demodex.  The  hair-follicle  mites  of  different  animals  are  ex- 
tremely difficult,  if  not  impossible,  to  differentiate  as  distinct  species.  Hirst 
(1919)  has  brought  more  or  less  order  out  of  the  chaos  and  has  redefined  the 
various  forms. 

Demodex  jolliculorum  Simon  is  the  hair-follicle  mite  of  man.  It  is  abundant 
in  some  countries,  but  it  is  said  to  be  rare  in  North  America.  It  lives  deep  down 
in  the  hair  follicles  and  sebaceous  glands.  The  entire  life  cycle  is  passed  on 
the  host  so  that  the  infection  gradually  spreads.  It  is  not  considered  of  any 
pathogenic  importance  to  man. 

Demodex  can  is  Ley  dig  (Figs.  38,39)  attacks  dogs  and  is  cosmopolitan  in 
distribution.  It  causes  the  follicular  or  red  mange  of  the  dog.  The  disease  is 
serious  and  there  is  no  known  successful  treatment.  D.  cati  Megnin  parasitizes 
the  cat;  D.  bovis  Stiles,  cattle;  D.  equi  Raillet,  horses.  Other  species  are  found 


Fig.  59.  A  gland  from  a  dog,  showing  Demodex  cams  along  the  entire  gland. 

on  different  mammals.  Baker  (1946)  reports  a  serious  infection  of  a  cow  with 
demodectic  mange.  The  mange  appeared  as  enlarged  nodules,  and  each 
nodule  when  opened  contained  an  enormous  mass  of  the  mites  in  all  stages. 
This  type  of  mange  is  apparently  very  rare.  Several  workers  have  recorded 
D.  canis  parasitizing  man,  but  Hirst  regards  these  cases  as  doubtful. 

THE  CLASS  PENTASTOMIDA 

The  tongue  worms  and  their  allies 

This  aberrant  group  has  had  a  varied  taxonomic  career,  having  been  placed, 
at  one  time  or  another,  with  the  Cestoda,  Nematoda,  and  Hirudinea.  Van 
Beneden  (1848)  placed  it  in  the  Arthropoda,  and  Sambon  (1922)  established 
its  position  as  in  the  Acarina  though  now  it  is  regarded  as  a  distinct  class. 

The  adults  are  elongate,  legless,  cylindrical,  or  flattened  worms  divided 
externally  by  conspicuous  rings  that  are  not  true  segments.  The  mouth  is 
provided  with  a  chitinous  armature,  which  is  located  before,  behind,  or  be- 
tween two  pairs  of  hollow,  retractile,  fanglike  hooks  (Figs.  40,41).  The  sexes 


THE  ORDER  ACARINA 


117 


are  distinct,  the  males  smaller  than  the  females.  There  is  no  separation  of  the 
head,  thorax,  or  abdomen.  Anteriorly  the  most  conspicuous  features  are  the 
hollow  fangs  or  retractile  hooks.  At  their  bases  open  a  number  of  glands,  the 
secretion  of  which  is  supposed  to  have  a  hemolytic  action.  The  internal  struc- 
ture is  very  simple.  The  mouth  opens  into  a  pharynx,  which  connects  with  a 
short  esophagus.  The  pharynx  is  supplied  with  muscles,  which  undoubtedly . 


Fig.  40.  (/)  Armillifer  armillatus,  female.  (2)  Male.  (Both  drawn  to  the  same  scale.) 
(3)  Head  of  A .  armillatus  to  show  the  fangs.  (4)  Nymphal  stage  of  same  species  in  liver. 
(5)  Recently  hatched  larva  of  same  species.  (6)  Fully  developed  embryo  within  the  egg 
of  Poroccphalus  subulijer.  (All  modified  from  Sambon.) 

serve  to  exert  a  sucking  action.  The  esophagus  opens  into  the  mid-gut  or 
stomach,  which  is  somewhat  capacious  and  extends  the  entire  length  of  the 
body  to  the  rectum.  There  is  no  trace  of  circulatory  or  respiratory  organs.  The 
nervous  system  is  vestigial.  The  main  organs  appear  to  be  for  reproductive 
purposes  as  the  ovaries  and  testes  are  well  developed.  In  the  females  the 
opening  of  the  vagina  is  either  at  the  anterior  or  posterior  end  of  the  body. 

Hey  mans  and  Vitzthum  (1936)  in  an  extensive  paper  divide  the  Pentasto- 
mida  into  two  orders,  which  may  be  separated  by  the  following  scheme: 


1 1.8-  MEDICAL  ENTOMOLOGY 

1.  Hooks  located  on  fingerlike  processes  or  slight  swellings  of  the  body  back 

of  the  mouth ;  genital  opening  anterior  in  both  sexes 

Order  Cephalobaenida 

Two  families:  Cephalobaenidae  (in  lungs  of  snakes  and  lizards); 

Reighardiidae  (in  air  sacs  of  birds)  2 

2.  Hooks  not  so  located  but  arranged  on  each  side  of  the  mouth  either 

in  a  straight,  curved,  or  arched  line;  genital  opening  of  the  female 

posterior  Order  Porocephalida 

Two  families:  Porocephalidae  (body  cylindrical;  adults  in  lungs  of 
reptiles;  young  in  a  great  variety  of  vertebrates  including  man); 
Linguatulidae  (body  flattened;  adults  in  nasal  passages  of  dog  and 
cat  family;  young  in  all  sorts  of  mammals  including  man) 

As  far  as  known  all  species  of  this  class  have  a  complicated  life  cycle,  the 
larval  and  nymphal  stages  in  one  host  and  the  adults  in  another.  Linguatula 
serrata  occurs  in  the  adult  stage  in  the  nasal  passages  and  frontal  sinuses  of 
dogs  (occasionally  in  man  and  some  herbivores),  where  they  suck  blood.  They 
cause  a  severe  catarrh,  suppuration,  and  bleeding.  The  eggs  of  the  parasite  are 
discharged  in  the  mucus  and  wastes  from  the  nostrils,  infecting  water  or 
vegetation.  If  these  eggs  are  eaten  by  rabbits,  sheep,  goats,  etc.,  or  by  man,  the 
larvae  escape  from  the  eggs,  migrate  through  the  intestinal  walls,  and  usually 
locate  in  the  liver,  or  other  organs  where  the  nymphal  development  takes  place. 
In  a  short  time  the  larva  (Fig.  40)  becomes  encapsulated  by  the  host-tissue 
reaction  and  nymphal  development  proceeds.  In  about  five  or  six  months  the 
nymphs  become  mature;  they  then  possess  two  pairs  of  hooks  and  measure 
4  to  6  mm.  in  length.  The  body  is  divided  into  numerous  rings,  each  bordered 
posteriorly  by  a  row  of  closely  set  spines.  Within  the  cysts  the  nymphs  may 
live  at  least  two  or  three  years.  If,  however,  raw  liver  or  other  organs  con- 
taining these  nymphs  are  eaten  by  dogs  or  man,  the  nymphs  gain  access  to 
the  nasal  passages  via  the  mouth  or  esophagus  and  there  reach  maturity.  In 
Europe  dogs  are  frequently  parasitized  and  humans  not  uncommonly  harbor 
the  nymphs  in  their  internal  organs.  Hobmaier  and  Hobmaier  (1940)  give 
a  clear  account  of  the  life  cycle  of  Linguatula  rhinaria,  a  parasite  of  brown 
rats  and  dogs.  Their  account  differs  in  many  details  from  the  records  of  other 
workers. 

In  Africa  man  is  frequently  parasitized  by  Armillijer  armillatus  (Fig.  40) . 
This  species  is  found  as  a  mature  parasite  in  pythons  and  other  snakes;  its  inter- 
mediate hosts  are  primarily  monkeys  and  apes,  although  carnivores  and  other 
animals  have  also  been  reported  as  infected.  The  natives  of  certain  parts  of 


THE  ORDER  ACARINA  1^9 

Africa  regard  python  steaks  as  delicacies,  and  as  a  result  frequently  become 
infected  by  eating  raw  meat.  Infection  may  also  take  place  by  eating  raw  vege- 
tables or  drinking  water  contaminated  with  the  eggs  of  the  parasite.  Human 
infection  is  common  in  many  parts  of  West  Africa,  the  nymphs  being  recovered 
at  autopsies.  Cannon  (1942)  reports  the  death  of  an  African  woman  due  to  an 
extremely  heavy  infection  of  the  colon  by  encysted  nymphs  of  this  species. 
A.  moniliformis  is  parasitic  in  the  respiratory  tract  of  pythons,  and  records 
of  human  infections  are  rather  rare  (three  so  far  recorded,  one  from  Manila, 
one  from  Sumatra,  and  one  from  a  Tibetan  in  China). 


Fig.  41,  Porocephalus  clavattis.  Mature  female  from  the  lung  cavity  of  a  South  Ameri- 
can snake.  The  central  figure  shows  the  head  with  the  four  characteristic  fangs. 

Porocephaliasis  is  the  usual  term  employed  to  designate  human  infection 
with  species  of  Pentastomida.  Sambon  in  1910  and  1915  summarized  the 
known  human  cases  up  to  that  time.  It  appears  that  when  few  nymphs  are 
present  in  man  the  ill  effects  are  not  serious;  when  large  numbers  occur  the 
effects  may  be  dangerous,  but  there  is  no  method  of  diagnosing  their  presence. 
Most  of  the  present  information  of  human  infections  is  based  on  findings  at 
autopsies  or  from  abdominal  operations. 

In  America  two  cases  of  porocephaliasis  are  on  record.  As  no  species  of 
Armillifer  are  known  from  the  Americas,  it  is  thought  the  infections  may 
have  been  due  to  the  nymphal  stage  of  Porocephalus  crotali  of  rattlesnakes 
or  an  allied  form.  Penn  (1942)  reports  P.  crotali  as  being  found  commonly  in 
the  larval  and  nymphal  stages  in  muskrats  (Ondatra  zibethica  rivalled)  in 


120  MEDICAL  ENTOMOLOGY 

Louisiana  and  the  adults  in  the  water  moccasin  (Agfystrodon  piscivorui) .  The 
adults  live  in  the  lung  cavities  of  the  snakes  and  the  eggs  are  discharged  in  the 
sputum.  When  the  infected  sputum  is  eaten  by  the  muskrat,  the  eggs  hatch 
in  the  small  intestine  and  the  larvae  migrate  to  the  liver  and  lungs,  where  they 
become  encapsulated  in  the  tissues.  The  nymphs  become  mature  in  about 
three  months.  When  infective  muskrats  are  eaten  by  the  water  moccasin  the 
nymphs  migrate  up  the  esophagus  and  into  the  tracheae  and  lungs,  where 
they  develop  to  adults. 

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THE  ORDER  ACAR1NA  121 

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1945- 


THE  ORDER  ACARINA  123 

,  and  Woodward,  T.  E.    Tsutsugamushi  disease  (scrub  or  mite  borne  typhus) 

in  the  Philippine  Islands  during  American  re-occupation  in  1944-45.    II.  Ob- 
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1942. 

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2  (10):  246-249,  1923. 

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causation  of  the  eruptive  fevers  and  other  diseases  of  man.  Preliminary  con- 
siderations based  upon  an  ecological  study  of  typhus  fever.  Ann.  Trop.  Med. 
Parasit.,  22:  67-132,  1928. 

Sergent,  Et.  Sur  le  Demodex  jolliculorum  var.  hominis  dans  le  cerumen.  Arch. 
Inst.  Pasteur  Algerie,  18:  238,  1940. 

Shelmire,  B.,  and  Dove,  W.  E.  The  tropical  rat  mite,  Liponyssus  bacoti  Hirst. 
Jl.  Amer.  Med.  Assoc.,  96:  579-584,  1931. 

Snyder,  F.  M.,  and  Morton,  F.  A.  Materials  as  effective  as  benzyl  benzoate 
for  impregnating  clothing  against  chiggers.  Jl.  Econ.  Ent.,  39:  385-386, 
1946. 

,  and  Morton,  F.  A.  Benzyl  benzoate-dimethyl  phthalate  mixture  for  im- 
pregnation of  clothing.  Ibid.,  40:  586-587,  1947. 

Warburton,  C.  Sarcoptic  scabies  in  man  and  animals.  Parasitology,  12:  265- 
300,  1920. 

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the  larval  trombiid  mites  attacking  man.    Ibid.,  20:  228-236,  1928. 

Webster,  F.  M.  A  predacious  mite  proves  noxious  to  man.  U.S.  Dept.  Agr.,  Bur. 
Ent.,  Circ.  118,  1910. 

Wharton,  G.  W.  Observations  on  Ascoschongastia  indica  (Hirst,  1915) 
(Acarinida,  Trombiculidae).  Ecological  Monog.,  16:  151-184,  1946. 

,  and  Hardcastle,  A.  B.  The  genus  Neoschongastia  (Acarinida;  Trombi- 
culidae) in  the  western  Pacific  area.  Jl.  Parasit.,  32:  286-322,  1946. 

Willcocks,  F.  C.  The  predacious  mite,  Pediculoides  ventricosus  Newpt.  Agr. 
Jl.  of  Egypt,  4:  31-51, 1914. 

Williams,  R.  W.  A  contribution  to  our  knowledge  of  the  bionomics  of  the  com- 
mon North  American  chigger,  Eutrombicula  aljreddugesii  (Oudemans)  with  a 
description  of  a  rapid  method  of  collection.  Amer.  Jl.  Trop.  Med.,  26:  243-250, 
1946, 


124  MEDICAL  ENTOMOLOGY 

Womersley,  H.    A  revision  of  the  Australian  Trombidiidae.    Rec.  S.  Australia 

Mus.,  6:  74-100,  1937. 
.    Further  notes  on  the  Australian  Trombidiidae  with  description  of  new 

species.    Trans.  Roy.  Soc.  S.  Australia,  63:  149-166,  1939. 
.  A  revision  of  the  Microtrombidiinae  (Acarina,  Trombidiidae)  of  Australia 

and  New  Guinea.    Rec.  S.  Australian  Mus.,  8:  293-355,  1945. 
,  and  Heaslip,  W.  G.    The  Trombiculinae  (Acarina)  or  itch  mites  of  the 

Austro-Malayan   and   Oriental   regions.    Trans.   Roy.   Soc.   S.   Australia,   67: 

68-142,  1943. 
,  and  Heaslip,  W.  G.     Notes  on  and  additions  to  the  Trombiculinae  and 

Leeuwenhoekiinae  (Acarina)  of  Australia  and  New  Guinea.    Ibid.,  68:  82,  1944. 

CLASS  PENTASTOMIDA 

Cannon,  D.  A.     Linguatulid  infestation  of  man.     Ann.  Trop.  Med.  Parasit.,  36: 

160-167,  J942- 
Darling,  S.  T.,  and  Clark,  H.  C.    Linguatula  serrata  (larva)  in  a  native  Central 

American.     Arch.  Internal  Med.,  9:  401-405,  1912. 
Faust,  E.  C.     Linguatulidae  (order,  Acarina)  from  man  and  other  hosts  in  China. 

Amer.  Jl.  Trop.  Med.,  7:  311-325,  1927. 
Heymons,  R.,  and  Vitzthum,  H.  G.     Beitrage  zur  Systematik  der  Pentastomiden. 

Zeit.  Parasitenk.,  8:  1-103,  1936. 
Hobmaier,   A.,  and   Hobmaier,  M.     On   the  life -cycle  of  Linguatula  rhinaria. 

Amer.  Jl.  Trop.  Med.,  20:  199-210,  1940. 
Noc,  F.     Sur  1'embryon  acariforme  et  les  stades  larvaires  des  Linguatulides.     Bull. 

Soc.  Path.  Exot.,  16:  340-346,  1923. 
Penn,  G.  H.    The  life  history  of  Porocephalus  crotali,  a  parasite  of  the  Louisiana 

muskrat.     Jl.  Parasit.,  28:  277-283,  1942. 
Sagredo,  N.    Linguatula  rhinaria  (Pentastoma  denticulatum)  in  den  Lungen  des 

Menschen.     Virchow's  Arch.  Path.  Anat.  Physiol.,  251:  608-615,  J924- 
Sambon,  L.  W.    Porocephaliasis  in  man.    Jl.  Trop.  Med.  and  Hyg.,  13:  17-24, 

212-217,  258-262,  1910;  15:  321-327,  371-374,  1912;  16:  97-100,  1913. 

.    A  synopsis  of  the  family  Linguatulidae.     Ibid.,  25:  188-206,  391-428,  1922. 

Southwell,  T.    On  a  collection  of  Linguatulidae  in  the  Liverpool  School  of  Tropical 

Medicine.    Ann.  Trop.  Med.  Parasit.,  18:  515-531,  1924 


CHAPTER  V 


The  Hexapoda:  Insects 


^  I  ^HE  class  Hexapoda  contains  an  enormous  assemblage  of  species,  every- 
J-.  where  present  and  always  abundant  in  all  regions  of  the  world.  They 
are  small  animals  possessing  a  body  made  up  of  transverse  segments;  their  seg- 
ments are  grouped  into  three  distinct  regions,  the  head,  thorax,  and  abdomen. 
The  segmentation  shows  most  distinctly  in  the  abdomen  and  thorax,  whereas 
in  the  head  the  segments  have  become  fused,  forming  a  highly  chitinized  box. 
The  number  of  segments  is  generally  stated  as  twenty.  These  are  distributed 
as  follows:  6  constitute  the  head,  3  compose  the  thorax,  and  u  form  the 
abdomen.  Typically  each  segment  of  the  primitive  arthropod  bore  a  pair  of 
appendages,  but  in  insects  many  of  these  have  been  lost.  There  are  readily 
visible  but  three  pairs,  the  legs,  which  are  attached  to  the  segments  of  the 
thorax.  The  other  appendages  have  been  lost  (as  in  the  abdomen)  or  modified 
for  other  purposes  (as  the  mouth  parts,  antennae,  eyes,  and  external  genital 
appendages).  In  addition,  the  great  majority  of  insects  possess  a  pair  or  two 
pairs  of  wings  attached  to  the  dorsolateral  angles  of  the  second  and  third 
thoracic  segments.  Insects  breathe  by  means  of  a  highly  complicated  system  of 
tracheae,  which  penetrate  every  portion  of  the  body  and  open  externally  by 
special  orifices,  the  spiracles,  situated  at  the  sides  of  the  body. 

The  animals,  as  characterized  above,  constitute  a  vast  assemblage,  number- 
ing nearly  a  million  described  species.  They  far  outnumber,  in  species,  all 
other  animals  combined,  while  in  individuals  their  vast  multitudes  are  like 
the  sands  of  the  sea — uncountable.  Who  can  estimate  the  ants  of  a  single 
hillside,  the  aphids  of  an  orchard,  or  the  flies  of  a  city  ?  As  a  group,  insects  are 
considered  to  be  the  most  successful  of  all  forms  of  terrestrial  animal  life,  yet 
man  treats  them  with  scant  respect. 

EXTERNAL  ANATOMY 

Externally  the  body  of  an  insect  is  composed  of  transverse  segments  (20), 
which  may  or  may  not  bear  appendages.  These  segments  are  grouped  into 


i26  MEDICAL  ENTOMOLOGY 

three  regions,  head,  thorax,  and  abdomen  (Fig.  42).  The  surface  layer  of 
the  body  is  called  the  body  wall  or  integument.  It  is  more  or  less  rigid  and 
forms  the  skeleton  within  which  all  the  organs  and  fleshy  parts  are  enclosed; 
but  the  external  covering  is  flexible  along  certain  transverse  and  longitudinal 
lines  and  at  other  points,  thus  permitting  a  great  variety  of  movements.  The 
hardened  portion  of  the  body  wall  is  due  to  the  deposition  of  various  substances 
in  the  chitin  and  it  is  variously  distributed;  usually  lines  (sutures)  delimit 
the  sclerotized  areas,  which  are  called  sclerites.  The  arrangement  of  sclerites 
and  their  separating  sutures  constitutes  the  major  feature  of  the  external 
anatomy  of  insects. 


Fig.  42.  Lateral  view  of  a  grasshopper  to  illustrate  the  principal  external  structures  of  an 
insect.  (Wings  of  one  side  removed.)  Ant,  antenna;  Cx,  coxa;  E,  compound  eye;  F,  femur; 
O,  ocellus;  Ovi,  ovipositor;  PN,  pronotum;  Sp,  spiracles;  Tar,  tarsus;  Tb,  tibia;  Tn,  tym- 
panum of  ear;  Tr,  trochanter;  W,  wing. 

THE  BODY  WALL 

The  body  wall  is  a  continuous  structure,  and  the  apparent  segmentation  is 
due  to  infoldings.  It  completely  surrounds  the  insect.  It  also  extends  internally 
and  forms  the  lining  of  the  fore  and  hind  intestine;  the  tracheae  are  only 
invaginations  of  the  body  wall.  The  only  external  openings  are  the  mouth,  the 
anus,  the  spiracles,  and  those  of  the  genital  organs.  The  body  wall  is  composed 
of  a  single  layer  of  epidermal  cells  supported  on  a  noncellular  membrane 
(basement  membrane).  Outside  these  cells  lies  the  cuticula,  a  product  of  the 
epidermal  cells  (Fig.  43).  The  cuticula  may  be  soft  and  pliable,  but  it  is  usually 
sclerotized  into  definite  areas,  the  sclerites.  The  cuticula  is  not  a  homogeneous 
structure.  It  is  stratified  into  two  primary  layers,  the  endocuticula  and  the 


THE  HEXAPODA:  INSECTS  127 

exocuticula,  and  externally  it  is  protected  by  a  very  thin  layer  called  the 
epicuticula  (Fig.  43).  The  two  primary  layers  are  composed  mainly  of  chitin, 
whereas  the  epicuticula  is  nonchitinous.  Chitin  is  a  soft,  pliable  substance  that 
is  insoluble  in  water,  alcohol,  ether,  dilute  acids,  or  alkalies.  It  becomes  hard- 
ened by  the  deposition  of  various  substances,  mainly  in  the  exocuticula.  The 
epicuticula  is  very  thin  and  is  largely  impermeable  to  water.  Most  of  the 
pigments  are  found  in  the  exocuticula.  The  body  wall  is  rarely  smooth 
externally.  On  it  are  small  spicules,  hairs,  spines,  ridges,  scales,  setae,  or  other 
excrescences.  Many  of  these  are  merely  projections  of  the  cuticula;  others,  such 
as  stout  spines,  glandular  hairs,  and  sense  hairs,  take  their  origin  from  the 
underlying  epidermis. 


Tr 


Bm 


Fig.  43.  Left:  Diagrammatic  longitudinal  section  of  the  body  wall  of  an  insect. 
Right:  More  enlarged  and  detailed  sketch  of  a  portion  of  a  body  wall  to  show 
structure.  Bm,  basement  membrane;  C,  sclerotized  portion  of  wall  of  segment; 
En,  endocuticula;  Ep,  epicuticula;  Ex,  exocuticula;  Hp,  Hypodermis  or  epi- 
thelial cells;  S,  seta;  T,  the  nonsclerotized  part  of  body  wall  between  two  seg- 
ments; Tr,  a  trichogen  cell. 

Each  segment  of  the  body  is  composed  of  a  dorsal,  lateral,  and  ventral  area. 
In  each  of  these  areas  definite  parts,  sclerites,  may  occur,  and  these  are  separated 
by  sutures.  These  sclerites  bear  names,  and  the  terminology  becomes  quite 
complex  in  some  of  the  highly  specialized  insects.  In  general,  there  are  recog- 
nized for  each  segment  a  dorsal  sclerite,  the  tergum  or  notum;  two  lateral 
sclerites,  the  pleurites;  and  a  ventral  sclerite,  the  sternum.  Each  of  these  may 
be  divided  into  a  number  of  smaller  sclerites. 


THE  HEAD 

The  head  is  composed  of  a  number  of  fused  segments  (usually  regarded 
as  six),  and  these  are  so  intimately  consolidated  as  to  form  a  hard  case,  the 


I28  MEDICAL  ENTOMOLOGY 

head  capsule.  Externally  several  distinct  head  sclerites  may  be  recognized, 
especially  in  the  more  generalized  insects.  Some  of  these  are  delimited  by 
sutures,  but  most  of  them  are  fused  so  that  the  names  refer  to  areas  rather 
than  distinct  sclerites.  Fig.  42  will  illustrate  the  structure  as  found  in  a  gen- 
eralized insect  and  the  terms  employed.  The  main  sclerites  are  the  two  that 
form  the  vertex  (Fig.  44);  the  front  or  frons,  an  unpaired  sclerite  lying  in 
front  of  the  arms  of  the  epicranial  suture;  the  clypeus,  a  simple  sclerite  attached 
to  the  anterior  margin  of  the  front  and  usually  fused  with  it;  the  labrum,  a 
flaplike  structure  attached  to  the  clypeus  (this  structure  is  usually  included 
with  the  mouth  parts  though  it  is  strictly  part  of  the  head  capsule) ;  and  the 
genae,  paired  structures  located  below  and  somewhat  behind  the  eye.  That 
portion  of  the  head  behind  the  vertex  and  the  dorsal  or  posterior  surface  is 
known  as  the  occiput.  In  the  more  specialized  insects  the  sclerites  listed  above 
become  fused  or  modified,  but  in  general  the  areas  are  designated  by  the 
names  indicated. 

The  Appendages  of  the  Head 

The  six  segments  that  form  the  head  have  not  lost  all  their  primitive 
appendages  though  they  have  become  highly  modified  and  perform  dif- 
ferent functions.  The  appendages  still  present  in  the  adult  consist  of  the 
following:  (i)  a  pair  of  compound  eyes,  modified  appendages  of  the  first 
head  segment;  (2)  a  pair  of  antennae,  which  arise  from  segment  two;  (3)  a 
pair  of  mandibles,  appendages  of  segment  four;  (4)  a  pair  of  maxillae,  ap- 
pendages of  segment  five;  (5)  a  pair  of  appendages  that  unite  to  form  the 
labium,  the  second  maxillae  of  authors,  appendages  of  segment  six.  The 
appendages  of  segment  three  are  lost  in  the  adult  insect  though  vestiges  of 
them  are  present  in  the  embryo.  The  modified  head  appendages  thus  consist 
of  eyes,  antennae,  and  mouth  parts. 

THE  MOUTH  PARTS :  The  mouth  parts  of  insects  may  be  quite  simple, 
as  in  the  grasshopper  (Fig.  45),  or  they  may  be  very  complicated,  as  in  the 
bloodsucking  insects  (Fig.  79)  and  the  muscoid  flies  (Fig.  47) .  In  general,  three 
types  of  mouth  parts  may  be  recognized,  the  mandibulate  type,  the  piercing 
and  sucking  type,  and  the  nonpiercing  and  sucking  type.  There  are,  of  course, 
many  modifications  of  these  types. 

The  Mandibulate  Type  (Fig.  45) :  In  this  type  the  mouth  parts  consist  of  a 
labrum,  a  movable  flap  attached  to  the  clypeus  and  overlying  the  upper  margin 
of  the  mouth;  a  pair  of  mandibles  lying  directly  below  the  labrum  and  moving 
laterally;  a  pair  of  maxillae  arising  below  the  mandibles  and  of  rather  com- 


THE  HEXAPODA:  INSECTS 
cs    Y     FS  o 


129 


Fig.  44,  (a)  Frontal  view  of  the  head  of  a  grasshopper  (Mclanoplus  sp.).  (£)  Lateral 
view  of  the  head  of  a  grasshopper,  (c)  Posterior  view  of  the  head  of  a  grasshopper 
(Romalca  sp.).  (d)  Sectional  view  of  head  of  grasshopper  to  show  the  internal  structures 
(d  modified  from  Snodgrass).  Ant,  antenna;  Ap,  point  of  invagination  for  the  anterior 
arm  of  the  tentorium;  At,  anterior  arm  of  tentorium;  Cb,  cibarium;  Clp,  clypeus;  Cls, 
clypeal  or  epistomal  suture;  Cr,  crop;  Cs,  coronal  suture;  Csl,  cervical  sclerites;  Cx,  con- 
dyles  of  the  mandible;  Da,  dorsal  arm  of  tentorium;  E,  eye;  Fr,  foramen  magnum; 
Fs,  frontal  suture;  Ft,  front  or  frons;  Ge,  gena;  Hphy,  hypopharynx;  Lb,  labium;  LbPlp, 
labial  palpi;  Lm,  labrum;  M,  mentum  of  labium;  md,  mandible;  MO,  mouth  opening; 
MX,  maxilla;  MxPlp,  maxillary  palpi;  O,  ocelli;  Oc,  occipital  sclerite;  Ocs,  occipital  suture; 
Pa,  posterior  arm  of  tentorium;  Pge,  postgena;  Ph,  pharynx;  Pt,  point  of  invagination  of 
posterior  arm  of  tentorium;  R,  genal  suture  or  ridge;  S,  submentum  of  labium;  SD,  sali- 
vary duct;  T,  tentorium  with  its  arms;  V,  vertex. 


i^o  MEDICAL  ENTOMOLOGY 

plicated  structure;  and  a  labium,  closing  the  lower  surface  of  the  mouth  and 
formed  by  the  fusion  of  a  pair  of  appendages  (the  second  maxillae).  On  the 
under  surface  of  the  labrum  and  forming  the  roof  of  the  mouth  is  a  fleshy 
organ  known  as  the  epipharynx  (Fig.  45) .  It  is  supplied  with  sense  hairs  and 
is  supposed  to  function  as  an  organ  of  taste.  This  structure  becomes  highly 
developed  in  many  sucking  insects  and  serves  as  part  of  the  piercing  apparatus 
as  well  as  part  of  the  channel  through  which  blood  is  drawn.  (Examples: 
mosquito,  Fig.  97;  tabanus,  Fig.  156.)  From  the  floor  of  the  mouth  cavity,  at 
the  base  of  the  labium,  there  arises  a  fleshy  organ,  the  hypopharynx  or  lingua. 
The  hypopharynx  bears  the  opening  of  the  common  salivary  duct  and  in  many 
insects  becomes  an  important  part  of  the  mouth. 

The  mandibulate  type  of  mouth  parts  is  regarded  as  the  primitive  arrange- 
ment of  the  head  appendages  entering  into  the  formation  of  the  organs  for 
obtaining  food.  These  appendages  have  become  highly  modified  in  many 
insects  and,  in  some  cases,  as  in  the  lice  and  muscoid  flies,  are  so  changed 
that  the  parts  have  not  been  definitely  homologized  with  those  of  the  primitive 
type.  The  various  types  of  mouth  parts  found  in  bloodsucking  insects  are 
discussed  more  in  detail  under  the  different  groups  but  one  or  two  simple 
bloodsucking  types  may  be  compared  with  the  mouth  parts  of  the  grasshopper. 

Mouth  Parts  of  the  Bedbug  (Cirnex  lectularius) :  In  the  bedbug  the  mouth 
parts  are  rather  highly  specialized.  The  labium  (Fig.  46  La)  has  become 
greatly  elongated  and  divided  into  three  well-defined  segments.  Along  its 
dorsal  surface  there  is  a  groove  or  gutter  within  which  lie  the  piercing  organs, 
the  mandibles  and  maxillae.  The  segments  of  the  labium  are  flexible  and  can 
be  telescoped  on  each  other  by  internal  muscles.  Each  mandible  is  a  delicate, 
chitinous,  needlelike  rod,  which  arises  deep  in  the  head  and  terminates  in  a 
sharp  point,  the  distal  part  being  supplied  with  fine  recurved  teeth  (Fig.  46  M) . 
The  maxillae  (Mx),  arise  close  beside  the  mandibles  but  are  stouter  and  slightly 
longer.  They  are  grooved  on  the  inner  face  and,  just  in  front  of  the  hypo- 
pharynx,  form,  by  apposition,  two  canals  (Fig.  46).  They  are  interlocked 
throughout  their  entire  length  and  firmly  adhere  even  when  dissected  out  of 
the  head.  In  cross  section  the  two  canals  are  distinctly  shown,  the  larger  one 
serving  as  the  food  channel  up  which  the  blood  is  drawn  by  the  pharyngeal 
pump;  the  smaller  one  is  the  channel  down  which  the  secretions  of  the  salivary 
glands  are  forced  into  the  wound  by  the  salivary  pump.  The  labrum  or 
labrum-epipharynx  is  a  large  structure  lying  over  the  base  of  the  labium.  On 
the  under  surface,  lying  at  the  base  of  the  labium,  is  the  fine-pointed  hypo- 
pharynx  (Fig.  46  Hyp)  through  which  is  discharged  the  salivary  secretion 
into  the  groove  formed  by  the  maxillae.  The  salivary  pump  is  a  complicated 


THE  HEXAPODA:  INSECTS 


13* 


Fig,  45.  Mouth  parts  of  a  grasshopper.  {A)  Frontal  view  of  the  labrum  attached  to  the 
clypeus.  (B)  Looking  into  the  mouth  of  a  grasshopper  with  the  mandibles  removed  and 
the  labrum  turned  back.  (C)  The  lower  side  of  a  mandible  with  the  tendons  in  place. 
(D)  The  upper  side  of  a  mandible.  (E)  and  (F)  The  right  and  left  maxillae  as  viewed 
from  the  lower  or  ventral  side.  (G)  The  labium  as  viewed  from  the  lower  side.  C,  cardo; 
Cd,  socket  for  condyle  of  mandible;  Clp,  clypeus;  Cx,  condyles  of  mandibles;  Ephy,  epj- 
pharynx;  Fc,  area  over  which  fits  the  base  of  the  mandible;  Ga,  galea;  Gl,  glossa;  Hphy,. 
hyopharynx;  IN,  cutting  teeth  of  mandible;  Lb,  labium;  LbPlp,  labial  palpi;  Lc,  lacinia; 
Lm,  labrum;  M,  opening  into  mouth;  Mb,  molar  portion  of  mandible;  Met,  mentum; 
MX,  upper  or  dorsal  surface  of  maxilla;  MxPlp,  maxillary  palpi;  Pgl,  paraglossae;  Plf, 
palpigerj-Sga,  subgalca;  Sm,  submentum;  St,  stipes,  Ten,  tendons;  Tr,  torma. 


MEDICAL  ENTOMOLOGY 


F/^.  46.  The  mouth  parts  of  the  bedbug  (Cimex  lectularius}.  (a)  Frontal  view  of  the 
mouth  parts  and  part  of  the  head.  (£)  Ventral  view  of  the  pharynx  and  salivary  gland  con- 
nections with  the  hypopharynx.  (c)  The  salivary  pump  partially  opened,  (d)  Cross  section 
of  the  maxillae  and  mandibles.  Ant,  antenna;  C,  extension  of  body  cavity  into  maxilla; 
Cl,  clypeus;  E,  eye;  Fc,  food  channel;  Hyp,  hypopharynx;  La,  labium;  Lb,  labrum;  LG, 
labial  gutter;  M,  tip  of  mandible,  greatly  enlarged;  Md,  mandible;  Ms,  muscles  that  move 
the  piston;  MX,  maxilla;  P,  piston  head;  Ph,  pharynx;  PR,  piston  rod;  O,  esophagus; 
SC,  salivary  channel;  Sd,  salivary  duct;  SG,  common  duct  of  salivary  glands;  Sp,  salivary 
pump. 

organ,  but  its  structure  and  function  have  been  elucidated  by  Patton  and 
Cragg  (1913)  and  Puri  (1924).  It  is  located  on  the  ventral  surface  of  the 
hypopharynx;  it  is  cup-shaped  in  general  appearance  and  about  one-tenth  the 
size  of  the  pharyngeal  pump.  Its  posterior  end  is  closed  by  an  elastic  membrane, 
a  part  of  which  is  invaginated  to  form  a  chitinized  piston  (Fig.  46).  Posteriorly 


THE  HEXAPODA:  INSECTS  133 

the  piston  is  continued  as  a  flattened  rod  to  which  retractor  muscles  are 
attached  on  each  side.  The  salivary  duct  opens  into  the  pump  on  the  ventral 
side  by  a  crescent-shaped  opening.  The  working  of  the  pump  is  brought 
about  by  the  movement  of  the  piston.  When  the  piston  is  withdrawn,  salivary 
secretion  is  drawn  into  this  chamber.  The  relaxation  of  the  retractor  muscles 
is  followed  by  the  recoil  of  the  elastic  posterior  membrane  of  the  pump,  which 
forces  the  piston  into  the  chamber  and  the  saliva  is  sent  down  the  duct  in  the 
maxillae  into  the  wound.  The  recoil  of  the  piston  closes,  at  the  same  time, 
the  opening  of  the  salivary  duct  leading  from  the  glands.  The  saliva  in  blood- 
sucking insects  seems  to  perform  certain  definite  functions,  either  to  prevent 
coagulation  or  to  induce  blood  flow  to  the  invading  mouth  parts,  jj 
|  Another  important  organ  in  connection  with  the  bloodsucking  type  of 
mouth  parts  is  the  pumping  pharynx  or  pharyngeal  pump,  an  organ  whose 
special  function  is  to  pump  the  blood  from  the  host  and  pass  it  on  to  the 
intestine.  In  the  bedbug  the  organ  is  well  developed.  It  is  pear-shaped  in  out- 
line, but  flattened  dorsoventrally.  In  sectional  view  the  lumen  appears  as  a 
transverse  slit.  The  pumping  action  is  brought  about  by  powerful  dilator 
muscles  attached  to  the  dorsal  surface;  these  dilate  the  pharyngeal  cavity,  and 
blood  flows  in  through  the  food  channel  (Fig.  46).  The  relaxation  of  the 
muscles  allows  the  resilient  chitinous  walls  to  come  together  and  thus  probably 
forces  the  blood  on  through  the  esophagus.  | 

Mouth  Parts  of  Other  Bloodsucking  Insects:  In  other  bloodsucking  insects 
various  modifications  occur.  In  the  mosquito  (Fig.  97),  it  is  the  labrum- 
epipharynx  that  forms  the  food  channel.  These  organs,  together  with  the 
mandibles  and  maxillae,  constitute  the  piercing  apparatus.  The  salivary  secre- 
tion is  pumped  into  the  wound  through  a  channel  in  the  hypopharynx.  The 
pharyngeal  pump  is  well  developed  and  functions  as  in  the  bedbug,  though 
here  the  pharynx  must  connect  with  a  different  food  channel.  The  structures 
employed  by  various  insects  in  piercing  a  host  and  withdrawing  blood  are 
in  need  of  more  detailed  study,  and  some  of  these  problems  will  be  stressed 
under  the  discussion  of  the  various  bloodsucking  groups. 

Mouth  Parts  of  Some  Muscoidean  Plies:  Another  type  of  mouth  parts  of 
great  interest  to  the  medical  entomologist  is  that  found  in  many  of  the 
muscoidean  flies  as,  for  example,  the  housefly,  the  flesh  flies,  the  bluebottle 
flies,  and  others.  Here  the  food  is  taken  in  one  of  three  ways:  (i)  the  flies 
may  obtain  their  food  in  liquid  form  as  nectar,  milk,  sugar  solutions,  the 
liquid  exudates  of  decaying  substances  (as  pus,  fecal  matter,  sewage,  etc.), 
perspiration,  serum  exudates  from  wounds,  moisture  from  around  the  eyes, 


i34  MEDICAL  ENTOMOLOGY 

or  other  sources;  (2)  or  they  may  liquefy  soluble  substances  such  as  sugar  by 
regurgitating  liquid  from  their  intestines  or  by  using  the  salivary  secretion 
and  then  suck  up  such  fluids  by  their  mouth  parts;  (3)  or  they  can  ingest 
larger  particles  by  applying  the  mouth  opening  directly  to  soft  substances.  This 
type  is  very  complicated  and  may  be  best  illustrated  by  the  mouth  parts  of 
the  housefly. 

In  the  housefly  the  mouth  parts  constitute  an  elongated  proboscis,  which, 
when  not  in  use,  is  partly  withdrawn  into  the  head  capsule.  When  the  fly  is 
about  to  feed,  the  proboscis  is  extended  by  compression  of  the  body,  thereby 
forcing  blood  into  the  open  spaces  of  the  proboscis,  and  the  tracheae  and  air 
sacs  become  distended  with  air  (Fig.  47).  The  proboscis  then  hangs  downward 
from  the  head  capsule.  This  distension  may  be  produced  artificially  by  soaking 
the  head  in  10  per  cent  caustic  potash,  then  placing  it  under  a  dissecting 
microscope,  and  pressing  on  it  with  a  needle;  the  proboscis  and  labella  may 
be  extended  and  partially  contracted  at  will.  The  proboscis  may  be  divided 
into  three  distinct  regions — the  rostrum,  the  haustellum,  and  the  oral  disc 
(Fig-  47)- 

THE  ROSTRUM  (Fig.  47  R)  :  In  side  view  the  rostrum  appears  like  a  truncated 
pyramid,  the  base  attached  to  the  head  capsule.  Its  wall  (W)  consists  of  a  rather 
tough  chitinous  membrane  that  is  attached  to  the  ventral  margin  of  the  head 
and  is  continuous  with  that  of  the  haustellum  and  the  oral  disc.  Within  the 
membrane  is  the  large  pharyngeal  sclerite  or  fulcrum  (Fig.  47  Fa),  and 
within  the  fulcrum  lies  the  pumping  pharynx  and  its  dilator  muscles.  In  side 
view  the  fulcrum  appears  like  a  Spanish  stirrup  iron,  while  the  frontal  aspect 
presents  an  inverted  vaselike  appearance.  The  sides  of  the  fulcrum  are  roughly 
triangular  in  outline  and  are  produced  at  their  proximal  ends  into  a  pair  of 
stout  cornua.  The  anterior  angles  are  joined  by  the  clypeus  (tormae  of  Peter- 
son) and  the  anterior  arch  (Fig.  47).  Posteriorly  they  are  joined  by  a  thinner 
convex  plate,  the  posterior  plate,  which  forms  the  rear  wall  of  the  pharynx. 
The  anterior  wall  of  the  pharynx  consists  of  a  thin  chitinous  plate,  thickened 
along  its  median  line  to  form  a  sharply  delimited  chitinous  rod,  the  median 
ridge.  To  this  ridge  are  attached  the  dilator  muscles  of  the  pharynx.  Its  distal 
end  terminates  opposite,  and  in  close  contact  with  the  prepharynx  (hyoid 
sclerite)  ^The  pharynx  unites  at  its  proximal  end  with  the  esophagus,  and  its 
distal  end  joins  the  tube  formed  by  the  mouth  parts  by  way  of  the  hyoid 
sclerite,  which  surrounds  the  buccal  opening.  By  means  of  the  retractor  mus- 
cles the  anterior  wall  of  the  pharynx  is  withdrawn  from  the  posterior  wall, 
and  by  this  action  liquid  food  is  sucked  up  through  the  mouth  parts  and 
passed  into  the  esophagus.  Below  the  fulcrum,  on  either  side  of  the  middle  line, 


THE  HEX  APOD  A:  INSECTS 


135 


there  are  two  slightly  chitinized  plates.  From  each  of  these  arises  a  single- 
jointed,  somewhat  club-shaped  maxillary  palpus)  Near  the  border  of  the  max- 
illary plates  there  arises  on  each  side  of  the  fulcrum  a  sinuous,  strongly 
sclerotized  rod;  the  apices  of  these  rods  articulate  in  small  pits  at  the  sides  of  the 
broad  base  of  the  labrum-cpipharynx  and  function  in  the  extension  and  retrac- 
tion of  the  proboscis(  Below  the  palpi  the  rostrum  narrows  and  merges  with 
the  haustellum.'j 


MO 


Fig.  47.  A  somewhat  lateral  view  of  the  proboscis  of  the  housefly  (Mnsca  domestica). 
R,  rostrum;  H,  haustellum,  OD,  oral  disc;  MO,  mouth  opening;  Cxc,  a  main  collecting 
channel  of  the  psaulotracheac;  DSc,  cliscal  sclerite;  Fc,  fcxxl  channel  bAtffcen  the  hypo- 
pharynx  (Hp)  and  the  labrum  (Lm);  Fu,  fulcrum  seen  in  outline  beneath  the  chitinous 
membrane  (W);  Hp,  hypopharyiix;  LA,  label  la;  Lg,  labial  gutter;  Lm,  labrum;  MR, 
maxillary  rods  (stipes);  MxPlp,  maxillary  palpi;  Ptr,  pseudotracheae;  Th,  theca;  W, 
membrane  of  proboscis. 

THE  HAusTELLt'M  (Figs.  47,48) :  The  haustellum  (H)  is  attached  to  the  distal 
end  of  the  rostrum  and  gradually  narrows  to  its  junction  with  the  oral  disc. 
In  the  housefly,  as  in  many  of  the  higher  Diptera,  all  the  mouth  parts  are 
not  present.  The  mandibles  and  maxillae  are  lacking  though  the  palpi  of  the 
maxillae  still  persist.  The  mouth  parts  consist  of  the  labrum-epipharynx, 
the  liypopharynx,  and  the  labium.  The  rear  portion  of  the  haustellum  is  the 
lubium.  Its  structure  is  complicated  and  not  well  understood.  The  posterior  sur- 
face consists  of  a  large,  concave  sclerite,  the  mentum  or  theca,  which  is 
articulated  with  the  base  of  the  haustellum;  its  apex  rests  on  peculiar  rods 
that  articulate  with  the  oral  disc.  The  anterior  face  of  the  labium  is  deeply 
grooved  (labial  groove),  and  the  margins  of  the  groove  are  supported  by 


136  MEDICAL  ENTOMOLOGY 

stout  rods  (Fig.  48  LR)  that  extend  from  the  base  to  articulate  with  the 
discal  sclerite.  The  mentum  and  the  anterior  groove  are  connected  on  each 
side  by  tough  membranes,  Lying  in  the  labial  groove  or  gutter  are  the  labrum- 
epipharynx  and  the  hypopharynx.  The  labrum-epipharynx  (Lm)  is  in  front. 
It  consists  of  an  elongate,  pointed  organ  that  is  deeply  channeled  on  its  posterior 
face  (Fig.  48).  The  hypopharynx  lies  directly  behind  the  labrum-epipharynx; 
it  is  an  elongate  bladelike  structure  (Hp)  with  a  groove  in  its  anterior  face. 
The  margins  of  these  two  fit  closely  into  each  other  and  thus  form  the  food 
channel  (Fc).  The  tips  of  the  labrum-epipharynx  and  hypopharynx  extend 
to  the  opening  formed  by  the  discal  sclerite;  their  bases  are  united  and  lead 
to  the  mouth  opening,  which  lies  between  thern.  ) 

CTIIE  ORAL  DISC  (Figs.  47,48)  :  The  oral  disc  (OD)  consists  of  the  discal  sclerite 
(DSc)  and  the  labella,  the  two  large  lobes  that  arise  from  the  discal  sclerite. 
The  labella  are  shown  fully  expanded  in  the  figures.  When  not  in  use  they  are 
greatly  reduced  in  size.  The  oral  disc  articulates  to  the  distal  part  of  the  haustel- 
lum  by  means  of  two  joints.  The  anterior  joint  is  formed  by  the  junction  of 
the  labellar  rods  to  the  discal  sclerite  by  means  of  tendons.  The  discal  sclerite 
is  somewhat  horseshoe-shaped,  the  opening  being  anterior;  posteriorly  there 
extends  a  stout  thickening  of  the  sclerite.  This  sclerite  surrounds  the  mouth 
or  oral  opening,  and  to  it  are  attached  the  pseudotracheal  membrane  and 
the  prestomal  teetK^The  posterior  joint  of  the  oral  disc  is  formed  by  a  pair  of 
rods  (the  sigma  or  metofurcal  bars)  that  rest  on  two  arms  of  the  triradiate 
labellar  sclerite  or  furca.  These  rods  arise  from  the  forks  of  the  mentum 
(Fig.48Th). 

The  two  labellar  lobes  are  completely  separated  from  each  other  by  a  deep 
fissure,  which  is  continuous  anteriorly  with  the  labial  groove  or  gutter;  the 
fissure  extends  some  distance  on  the  posterior  face.  Each  labellum  contains  a 
large  hemocele  and  is  filled  with  blood  when  extended.  In  the  resting  condi- 
tion the  two  inner  walls  of  the  labella  are  in  close  contact,  but  when  feeding 
they  are  widely  separated.  As  the  walls  are  very  soft  they  can  be  molded  to 
any  surface  on*  which  the  fly  is  feeding.  The  inner  surface  of  each  labellum 
is  traversed  by  a  series  of  channels  that  resemble  tracheae,  hence  are  called 
"pseudotracheae"  (Figs.  47,48  Ptr).  Through  these  pseudotracheae  the  fly 
sucks  up  its  liquid  food.  As  the  size  of  the  opening  to  these  channels  deter- 
mines what  materials  the  fly  can  ingest,  the  structure  of  these  organs  is  of  the 
utmost  importance.  The  inner  wall  of  each  labellum  consists  of  a  very  thin, 
structureless  membrane  in  which  lie  the  pseudotracheal  channels.  These  chan- 
nels all  converge  to  the  prostomum  or  opening  bounded  by  the  discal  sclerite. 
In  each  labellum  are  30  to  32  of  these  grooves;  the  upper  9  or  10  and  the  lower 


THE  HEXAPODA:  INSECTS  137 

15  or  16  unite  to  form  collecting  channels  (Figs.  47,48  Cxc),  and  the  middle 
5  or  6  open  directly  into  the  prostomum.  Each  pseudotracheal  channel  is  kept 
open  by  means  of  incomplete  rings  of  chitin.  Each  chitinous  ring  is  bifid  at 
one  end  and  simply  expanded  at  the  other.  The  rings  are  closely  set  and 
alternate  so  that  a  bifid  end  faces  an  expanded  end,  and  then  an  expanded  end 
faces  a  bifid  end.  Looking  along  the  surface  of  a  channel  there  appears  a 
series  of  alternate  bifid  and  expanded  ends  of  chitinous  rings  (Fig.  48  d,e,j) . 
The  membrane  of  the  labellum  is  stretched  taut  over  all  these  rings  except 
between  the  bifid  ends  and  the  line  between  the  expanded  ends  and  the  forks. 
Therefore,  the  only  openings  into  the  channel  itself  are  between  the  forks 
of  the  bifid  end  of  each  ring  and  a  zigzag  fissure  extending  the  whole  length 
of  the  channel.  The  openings  between  the  bifid  ends  have  been  called  the 
"interbifid  grooves."  During  feeding  the  membrane  is  stretched  so  taut  that 
the  zigzag  fissure  is  practically  closed  and  the  only  food  that  can  enter  is 
through  the  interbifid  grooves.  The  size  l  of  the  interbifid  grooves  determines 
the  size  of  the  solid  particles  that  can  pass  into  the  food  channel.  This  position 
of  feeding  has  been  termed  by  Graham-Smith  "the  filtering  position."  .,) 

By  separating  the  labella  further  there  is  brought  into  play  the  prestomal 
teeth  (Fig.  49).  These  teeth  arise  from  the  lateral  margin  of  the  discal  sclerite, 
five  on  each  side.  Each  tooth  consists  of  a  chitinous  strip,  serrate  on  its  distal 
extremity,  and  lies  between  the  openings  of  two  pseudotracheae.  Graham- 
Smith  (1930)  has  shown  that  instead  of  one  row  of  prestomal  teeth  there 
are  four  rows  in  the  blowfly  (Calliphora  erythrocephala).  This  also  appears 
to  be  the  condition  in  the  housefly.  The  first  three  chitinous  strips  that  sur- 
round the  pseudotracheal  openings  into  the  oral  cavity  are  not  bifid  but 
sharply  pointed  (Fig.  49  O).  These  may  correspond  to  the  extra  teeth  described 
for  the  blowfly.  Following  these  are  the  ordinary  chitinous  rings  that  keep 
the  pseudotracheae  open. 

(^Recently  Graham-Smith  has  described  three  methods  of  feeding  by  the 
blowfly;  the  housefly,  in  all  probability,  feeds  in  the  same  fashion.(The  first 
method,  the  filtering  method,  has  already  been  described.  By  further  separat- 

1  Graham-Smith  has  measured  these  interbifid  spaces  and  the  channels  in  several 
of  our  common  flies.  These  are  here  appended. 

Pseudotracheae,  Interbifid  spaces, 

diameter  (mm.)  diameter  (mm.) 

Proximal            Distal  Proximal          Distal 

end                 end  end                 end 

Calliphora  erythrocephala                           0.02                 o.oi  0.006               0.004 

Sarcophaga  carnaria                                    0.02                 o.oi  0.005               0.004 

Lucilia  caesar                                               0.02                 o.oi  0.006               0.004 

Fannia  canicularis                                       o.oi 6               0.008  0.006               0.004 

Musca  domestica                                         0.016               0.008  0.004               0.003 


Fig.  48.  Detailed  illustrations  of  the  mouth  parts  of  the  housefly  (Musca  domestica). 
(a)  Lateral  view  of  the  proboscis  of  the  housefly.  (£)  Frontal  view  of  the  proboscis  with 
the  labella  expanded,  (c)  Cross  section  (somewhat  diagrammatic)  of  the  middle  of  the 
haustellum.  (d)  View  of  a  pseudotracheal  channel  (highly  magnified)  as  seen  through 
the  integument  of  the  labellum;  the  right  half  illustrates  the  details  of  a  channel  with 
the  ch  Hi  nous  rings  in  place;  the  upper  left  side  shows  two  interbifid  grooves  in  the  in- 
tegument with  the  chitinous  rings  showing  through;  the  lower  left  corner  shows  a  single 
interbifid  groove  which  leads  to  an  interbifid  space,  (e)  A  single  chitinous  ring  in  side 
view  showing  the  attachment  of  the  interbifid  groove  to  the  forks  of  the  ring.  (/)  Two 
chitinous  rings  as  they  are  arranged  in  a  pseudotracheal  channel  (partial  side  view). 
H,  haustellum;  OD,  oral  disc;  R,  rostrum;  A,  anterior  arch  of  fulcrum;  Ap,  anterior  wall 
of  pharynx;  Cl,  clypeus;  Cxc,  main  collecting  channels;  DSc,  discal  sclerite;  F,  fissure 
along  the  surface  of  the  pseudotrachea;  Fc,  food  channel;  Fu,  fulcrum;  Hp,  hypopharynx; 
IG,  interbifid  groove;  IS,  interbifid  space,  LA,  labellum;  Lm,  labrum;  LR,  labellar  rods; 


THE  HEXAPODA:  INSECTS 


139 


ing  the  labella  the  prestomal  teeth  can  be  brought  into  action  and  used  for 
scraping — the  scraping  position.  By  an  extreme  folding  back  of  the  labella 
the  mouth  or  oral  opening  can  be  brought  into  direct  contact  with  the  food, 
and  then  comparatively  large  objects  can  be  ingested,  as  the  eggs  of  helminths. 
By  various  manipulations  of  these  methods  the  fly  can  feed  on  a  great  variety 
of  substances.  Furthermore,  liquid  can  be  regurgitated  (the  vomit  drop)  to 
dissolve  what  has  been  scraped  loose  (Fig.  50).  Graham-Smith  also  states 
that  the  prestomal  teeth,  moistened  with  infected  vomit,  appear  to  be  excellent 


Fig.  49.  Looking  into  the  mouth  opening  of  the  housefly  (only  a  small  part 
is  shown).  ACCH,  anterior  collecting  channel;  DS,  discal  sclerite;  MO,  mouth 
opening;  O,  openings  to  the  pseudotracheal  channels,  PCCH,  posterior  collect- 
ing channel;  PT,  prestomal  teeth. 

instruments  for  the  intradermal  introduction  of  pathogenic  organisms.  Sites 
on  the  body  most  likely  to  be  selected  for  scraping  are  mucus  and  conjunctival 
surfaces,  recent  abrasions,  and  wounds,  ; 

The  mouth  parts  of  other  insects  that  afTect  man  are  briefly  discussed  under 
the  different  species  described  in  the  following  pages. 

LSc,  labellar  sclerite;  M,  membranous  portion  of  the  pseudotracheal  channel;  MO,  open- 
ing to  the  food  channel;  MR,  maxillary  rods  (stipes);  Mt,  mentum;  MxPlp,  maxillary 
palpus;  O,  esophagus;  Ph,  pharynx;  Pph,  hyoid  or  prepharyngeal  sclerite;  Pr,  pseudo- 
tracheal ring  of  ehitin  (the  dotted  portion  indicates  the  position  of  the  ring  at  the  rear  of 
the  channel);  Ptr,  pseudotracheae;  Sc,  salivary  channel  in  hypopharynx;  SD,  salivary 
duct;  Sp,  salivary  pump  or  syringe;  Th,  theca  or  mentum;  W,  membranous  wall  of 
proboscis. 


i4o  MEDICAL  ENTOMOLOGY 

THE  ANTENNAE:  The  antennae  are  the  modified  appendages  of  the 
second  head  segment.  Each  antenna  arises  from  a  small  antennal  sclerite  situ- 
ated in  the  antennal  fossa.  The  antennae  show  various  modifications  in  the 
different  orders  and  names  have  been  applied  to  them  such  as  setaceous,  fili- 
form, clavate,  and  capitate.  Some  of  the  types  found  in  insects  of  medical  im- 
portance are  shown  in  Fig.  51.  The  number  of  antennal  segments  varies 
widely.  The  first  segment  is  known  as  the  scape  and  the  second  as  the  pedicel; 


Fig.  50.  The  housefly,  Musca  domestica,  showing  the  .vomit  spot  at  the  tip  of  labella. 
(Modified  from  Hewitt.) 

the  remaining  segments  constitute  the  flagellum  (Fig.  51).  The  various  func- 
tions of  the  antennae  are  not  well  known.  It  has  been  fully  established  that 
the  sense  organs  of  touch  and  smell  are  present  on  the  antennae  and  possibly 
also  some  of  the  organs  of  taste. 

THE  THORAX 

The  thorax  is  the  second  region  of  the  body.  It  is  attached  to  the  head  by 
an  intersegmental  region  known  as  the  neck.  The  neck  is  not  sclerotized 
except  for  a  few  small  sclerites,  the  cervical  sclerites.  The  thorax  consists  of 
three  segments  and  bears  the  wings  and  legs.  The  segments  are  known  as  the 
prothorax,  mcsothorax,  and  metathorax  (Fig.  52) .  The  terms  pro,  meso,  and 
meta  are  used  to  designate  the  first,  second,  and  third  segments  of  the  thorax 
and  also  the  various  part|  of  these  segments.  For  example,  the  protergum, 
proepisternum,  etc.,  refer  to  the  tergum  and  episternum  of  the  prothorax.  The 


THE  HEXAPODA:  INSECTS  141 

pleuron  of  each  thoracic  segment  is  usually  divided  into  two  sclerites — the 
anterior  one  being  called  the  episternum  (Fig.  52  Eps)  and  the  posterior 
the  epimeron  (Epm) — and  these  bear  the  prefixes,  pro,  meso,  or  meta  to  indicate 
to  which  segment  they  belong.  Each  segment,  in  its  simplest  form,  consists  of 


Fig.  51.  Various  types  of  insect  antennae.  (/)  Musca  domestica.  (2)  Wohljahrtia  vigil. 
(3)  Aedes  acgypti.  (4)  Glossina  paJpalis.  (5)  Tabanus  flauiis.  (6)  Cimcx  lectularis.  (7) 
Xenopsylla  cheopis.  (Not  drawn  to  the  same  scale.)  A,  arista;  ds,  dorsal  suture  or  seam; 
Fl,  flagellum;  p,  pedicel;  s,  scape. 

a  dorsal  region,  the  tergum  or  notum;  a  ventral  region,  the  sternum;  and  two 
sides,  the  pleura  (singular  pleuron)  or  pleurites.  Each  of  these  regions  may 
consist  of  one  or  several  sclerites  separated  by  sutures.  A  rather  simple  type 
of  thorax  is  that  of  the  grasshopper  (Fig.  52) .  It  is  more  or  less  cylindrical  in 
shape.  Here  the  tergum  (PN)  of  the  prothorax  is  greatly  enlarged;  it  overlies 
a  large  part  of  the  mesothorax  and  extends  down  on  the  sides  to  near  the 


I42  MEDICAL  ENTOMOLOGY 

attachment  of  the  first  pair  of  legs.  Only  a  small  portion  of  the  lateral  wall  is 
visible — the  episternum  (Epst)  of  the  prothorax;  the  epimeron  is  entirely 
concealed  and  lies  underneath  the  lower  end  of  the  tergum. 

The  mesothorax  is  shown  in  dotted  lines  beneath  the  pronotum.  The  epi- 
sternum (Epso)  and  the  epimeron  (Epm2)  are  well  developed,  and  from 


Epi, 


b 


Fig.  52.  The  external  structure  of  the  thorax  of  a  grasshopper  (Mclanoplns  difterenti- 
alis).  (a)  Prothorax  with  the  leg  attached.  (£)  Lateral  view  of  the  incso-  and  metathorax 
(pterothorax)  with  the  first  segment  of  the  abdomen;  the  prothorax  sketched  in  outline. 
(c)  Ventral  view  of  the  entire  thorax.  Cx,  coxa;  Epnis,  Epnn,  epimera  of  nieso-  and 
metathorax;  Epsi,  Epsi,  Epss,  episterna  of  pro-,  mcso-,  and  rnetathorax;  F,  femur;  iS, 
sternum  of  first  abdominal  segment;  iiSp,  iiiSp,  spiracles  of  second  and  third  thoracic 
segments;  L,  lateral  lobes  of  the  metasterna;  PN,  pronotum;  S,  a  suture;  Si,  Sj,  S.t,  pro-, 
meso-,  and  metasterna;  Sa,  invaginations  of  sternal  apodcmes  (furcae);  iSp,  first  spiracle 
of  abdomen;  T,  tympanum;  Ta,  tergum  of  mesothorax;  Tar,  tarsus;  Tb,  tibia;  Te,  tergum 
of  first  abdominal  segment;  Tg,  tergum  of  metathorax;  Tr,  trochanter;  W,  cut  end  of 
wings;  WP,  wing  processes.  " 

their  lower  ends  arises  the  second  pair  of  legs.  The  metathorax  is  also  large 
and  the  pleurites  (Eps;{  and  Epm;{)  are  well  outlined.  Their  tergal  portions 
underlie  the  pronotum  and  the  wing  bases.  It  is  well  to  note  that  the  meso- 
and  metathorax  of  the  grasshopper  are  each  much  larger  than  the  prothorax, 
owing  to  the  presence  of  wings.  This  enlargement  is  to  provide  for  the 
processes  for  wing  attachment  and  the  large  muscles  needed  to  move  these 


THE  HEX  APOD  A:  INSECTS  143 

organs  of  flight.  In  the  Diptera,  where  only  the  mesothoracic  wings  are 
present,  the  mesothorax  (Fig.  53)  is  greatly  enlarged  and  appears  to  occupy 
the  entire  thoracic  region.2  In  the  Culicidae  the  thorax  is  distinctly  wedge- 
shaped,  the  thick  part  of  the  wedge  occupying  the  dorsal  surface.  The  pro- 
thorax  is  greatly  reduced.  The  pronotum  is  represented  by  two  sclerotized 
areas  on  each  side  (Fig.  53  PN,PPN)  the  anterior  pair  being  joined  by  a  narrow 
membrane  lying  in  front  and 

J  °  WTO 

somewhat  beneath  the  mesono- 
tum.  The  posterior  pronotum  has 
generally  been  called  the  proep- 
imeron  and  probably  corre- 
sponds to  the  humeral  callus  of 
the  higher  Diptera.  The  pleuron 
consists  of  a  small  episternum  as 
in  the  grasshopper.  The  meso- 
thorax occupies  the  greater  part 
of  the  thorax.  The  mesonotum 
(Mcs)  extends  from  the  head  to 
the  scutcllum  (Sc)  and  appears  to 
occupy  the  entire  dorsal  surface. 
The  scutellum  (Sc)  belongs  to 
the  mesothorax  and  is  separated 
from  the  mesonotum  by  a  distinct 
suture.  Viewed  from  the  dorsal 
surface  it  is  trilobed  and  each  lobe 
bears  a  distinct  group  of  bristles. 
Directly  behind  and  below  the 
scutellum  is  a  large,  smooth,  chitinized  area,  the  postnotum  (P).  The  side  of 
the  thorax  is  largely  made  up  of  the  mesopleuron.  It  begins  directly  in  front  of 
the  mesothoracic  spiracle  (iiSp)  and  extends  to  the  suture  cephalad  of  the 
metathoracic  spiracle  (iiiSp).  Unlike  that  of  the  grasshopper,  the  episternum  in 
the  flies  is  divided  into  two  distinct  parts,  the  so-called  mesanepisternum  and 
the  meskatepisternum.  The  latter  sclerite  is  generally  called  the  sternopleuron 
in  all  the  Diptera.  The  mescpimeron  is  a  large,  rectangular-shaped  sclerite.  Be- 
hind it  lies  the  metathorax,  greatly  reduced  in  size  and  united  rather  firmly  to 
the  abdomen.  The  metanotum  (N)  appears  as  a  very  narrow  band  lying  be- 
hind the  postnotum  and  articulating  with  the  tergum  of  the  first  abdominal 

2  The  thorax  of  the  various  orders  of  insects  treated  in  this  work  is  discussed  under 
the  groups  in  later  chapters. 


Fig.  55.  Lateral  view  of  the  thorax  of  a  mos- 
quito (Psorophora  sp.).  C,  cervical  slccrite;  Cx, 
coxa;  EpiTb,  Epms,  cpimcra  of  the  meso-  and 
metathorax;  Epsi,  Epsz,  Epsa,  episterna  of  the 
pro-,  meso-,  and  metathorax;  H,  haltere;  iiSp, 
iiiSp,  spiracles  of  meso-  and  metathorax;  M, 
meron;  Mes,  mesonotum;  N,  notum  of  meta- 
thorax; P,  postnotum  of  mesothorax;  PN,  prono- 
tum; PPN,  postpronotum;  Sc,  scutellum;  Stn, 
sternum;  WP,  cut  ends  of  wing. 


I44  MEDICAL  ENTOMOLOGY 

segment.  Laterally  the  metathoracic  spiracle  is  found  in  the  me.tepisternum, 
and  directly  behind  this  sclerite  is  the  metepimeron,  rather  faintly  delimited 
from  it.  Directly  above  the  latter  sclerite  is  found  the  haltere  (H).  Located 
above  and  between  the  coxae  of  the  second  and  third  pair  of  legs  is  the  so- 
called  meron  (M). 

In  the  mosquitoes,  as  in  nearly  all  the  Diptera,  the  pleural  sclerites  bear 
groups  of  hairs  or  spines  that  are  of  great  taxonomic  significance.  For  an 
account  of  the  pilotaxy,  see  pages  256-258. 

The  Appendages  of  the  Thorax 

THE  LEGS  (Fig.  54)  :  Each  segment  of  the  thorax  bears  a  pair  of  legs.  Each 
leg  is  articulated  to  the  thorax  by  its  basal  segment,  the  coxa,  located  in  the 
membranous  area  between  the  pleural  plates — the  episternum  and  epimeron 
and  the  adjacent  parts  of  the  sternum.  An  insect's  leg  consists  of  five  distinct 
parts : 

The  coxa  (Cx)  varies  greatly  in  size  and  shape  in  different  insects.  It  may 
be  firmly  attached  to  the  body  wall  or  very  movable,  as  in  the  housefly  and 
grasshopper. 

The  trochanter  (Tr)  is  a  small  segment  of  varying  shape  and  forms  the 
attachment  point  for  the  next  segment,  the  femur.  <+• 

The  femur  (F)  is  usually  an  elongated  segment  and  may  be  greatly  en- 
larged as  in  jumping  and  leaping  insects;  e.g.,  grasshoppers  and  fleas. 

The  tibia  (Tb)  is  usually  slender,  nearly  always  as  long  or  longer  than  the 
femur,  and  frequently  bears  many  stout  hairs  or  spines.  The  tip  may  be 
armed  with  special  spines. 

The  tarsus  (Tar)  is  generally  divided  into  segments,  five  being  the  most 
common  number.  There  may,  however,  be  only  one  segment  as  in  the  lice,  two 
in  plant  lice,  three  in  some  grasshoppers,  etc.  The  first  segment  is  frequently 
greatly  elongated  and  has  been  called  the  metatarsus.  Some  of  the  segments 
may  be  heavily  armed  with  spines  or  stout  setae.  The  last  segment  is  generally 
provided  with  a  pair  of  claws  (Fig.  54  C).  The  claws  arise  from  a  special 
elongation  of  the  last  joint.  The  claws  are  frequently  modified  and  adapted 
for  various  purposes  and  are  moved  by  rather  powerful  retractor  muscles. 
In  some  groups,  as  the  lice,  and  some  Mallophaga,  there  is  only  a  single 
claw,  which  is  adapted  for  clinging  to  hairs.  The  claws  may  be  simple, 
toothed,  equal  in  size,  or  one  claw  may  be  much  larger  than  the  other. 

On  the  ventral  surface  of  the  claws  and  attached  to  the  membrane  of  the 
last  tarsal  segment  is  a  pair  of  membranous  pads,  the  pulvilli  (Fig.  54  P).  Each 
pulvillus  may  be  provided  on  its  ventral  surface  with  numerous,  glandular 


THE  HEXAPODA:  INSECTS  145 

hairs,  the  so-called  tenent  hairs.  It  is  by  means  of  these  tenent  hairs  (each 
one  is  connected  with  a  gland)  that  flies  are  enabled  to  walk  on  ceilings,  glass, 
and  other  smooth  surfaces.  The  sticky  excretion  gathers  up  all  sorts  of  bac- 
teria, spores,  cysts,  and  filth  and  distributes  them.  Between  the  pulvilli  and 
below  them  is  a  long,  narrow,  hairy  spine,  the  empodium  (E).  The  empodium 
varies  greatly  in  different  insects.  It  may  be  hairlike,  it  may  be  a  stout  spine, 
or  it  may  be  padlike  and  then  it  is  said  to  be  pulvilliform. 


Fig.  54.  The  legs  of  insects,  (a)  Hind  leg  of  a  grasshopper,  (b)  Tarsus  and  pretarsus  of 
leg  of  grasshopper,  (c)  Leg  of  housefly  (Musca  domestica).  (d)  Pretarsus  of  housefly,  (e) 
Tip  of  tarsus  and  pretarsus  of  fly  (Stratiomys).  A,  arolium;  C,  claw;  Cx,  coxa;  E,  empo- 
dium; F,  femur;  P,  pulvillus;  PI,  unguitractor  plate;  Ptr,  pretarsus;  T,  tendon  of  muscle 
attached  to  unguitractor  plate;  Tb,  tibia;  Tar,  tarsus;  Tr,  trochanter. 

THE  WINGS:  Probably  the  most  important  appendages  of  the  thorax' 
are  the  wings.  They  are  not  true  appendages  but  are  outgrowths  from  the 
dorsolateral  margins  of  the  meso-  and  metathorax. 

In  insects  with  incomplete  metamorphosis,  as  the  Orthoptera  and  Hemip- 
tera,  the  external  development  of  the  wings  may  be  easily  observed.  In  holo- 
metabolous  insects,  as  the  Diptera,  Lepidoptera,  and  other  orders,  the  wings 
are  developed  internally  during  the  larval  growth  and  only  become  exposed  as 


146 


MEDICAL  ENTOMOLOGY 


the  wing  pads  at  the  time  of  pupation.3  The  great  majority  of  insects  possess 
two  pairs  of  wings,  though  the  Diptera  have  only  one  pair,  the  metathoracic 
wings  being  represented  by  the  halteres  or  balancers,  vestiges  of  what  may 
have  been  originally  wings  (Fig  53  H).  Some  orders  are  wingless,  as  the 
Anoplura  (lice)  and  Siphonaptera  (fleas),  though  they  undoubtedly  de- 
scended from  winged  ancestors.  The  Apterygota  consists  of  two  or  three 
orders  in  which  the  wingless  condition  is  primitive. 

The  wing  as  seen  in  an  adult  insect  consists  of  two  fused  membranes.  The 
longitudinal  thickenings,  the  veins  (Fig.  55),  are  more  heavily  chitinized 
areas  laid  down  around  the  cavities  through  which  tracheae  supplied  the 
developing  wings  with  air.  The  complete  system  of  veins  in  a  wing  is  called 


Fig.  55.  Hypothetical  tracheation  of  a  wing  of  a  primitive  nymph.  (After  Comstock.) 

its  venation  or  neuration.  The  venation  presents  excellent  characters  in  sys- 
tematic work,  and  various  systems  of  naming  these  veins  have  developed  in 
each  order.  Comstock  and  later  Comstock  and  Needham  developed  what 
they  called  the  hypothetical  type  of  venation  (Fig.  55)  of  a  primitive  winged 
insect.  As  all  winged  insects  are  believed  to  have  descended  from  a  common 
ancestor,  many  extensive  studies  have  been  carried  on  to  interpret  the  vena- 
tion of  the  wings  in  the  various  orders.  As  a  result  of  Comstock  and  Need- 
ham's  work,  a  uniform  system  of  naming  the  veins  was  evolved,  though  un- 
fortunately it  has  not  been  adopted  by  all  taxonomic  workers.  In  fact,  there 
are  many  systems  and  each  author  follows  his  own  bent  in  naming  the  veins. 
In  medical  entomology  it  is  necessary  to  have  a  thorough  knowledge  of  the 
venation  in  the  Diptera,  and  the  discussion  here  is  largely  restricted  to  that 
order. 


3  For  a  full  account  of  the  development  of  wings  and  wing  venation,  consult  Comstock 
(1918,  1947)  or  Imms  (1934). 


THE  HEXAPODA:  INSECTS  147 

The  principal  veins  in  an  insect's  wing  consist  of  a  series  of  longitudinal 
veins  and  a  few  definite  cross  veins.  Modification  of  the  hypothetical  type 
takes  place  through  addition  or  reduction,  mainly,  reduction  in  the  dipterous 
wing.  Reduction  occurs  through  fusion  of  veins  or  their  loss.  These  modifica- 
tions are  differently  interpreted  by  various  workers  so  that  uniformity  cannot 
be  looked  for  in  taxonomic  work.  The  arrangement  of  the  veins  and  cross 
veins  in  the  hypothetical  type  is  shown  in  Fig.  55.  The  following  table  gives 
the  nomenclature  of  the  veins  according  to  the  Comstock-Needham  system 
and  to  the  system  used  extensively  by  the  students  of  the  Diptera. 

Terminology  Comstoc\-  Abbreviations 

of  Need  ham 

dipterists  terminology 

Costal  Costa  C 

Auxiliary  vein  Subcosta  Sc 

ist  longitudinal  vein  Radius  one  R, 

2nd  longitudinal  vein  Radius  two  and  three  R2  and  R3 

3rd  longitudinal  vein  Radius  four  and  five  R4  and  R5 

4th  longitudinal  vein  Media  one  M,  and  M2 

Media  two 

5th  longitudinal  vein  Media,  3rd,  and  M:i  and  Cu,  or  Cu 

Cubitus,  or  Cubitus 
alone 
6th  longitudinal  vein  Anal  veins  lA,  2A,  3A 

Figs.  56  and  57  present  die  wing  of  a  Tubanus  species  with  the  veins  and 
cells  labeled  according  to  the  Comstock-Needham  system  and  that  com- 
monly used  by  dipterists. 

The  costa  (C)  is  the  thickened  frontal  margin  of  the  wing;  the  anterior 
border  is  generally  called  the  costal  border. 

The  subcosta  (Sc)  is  directly  behind  the  costa  and  parallel  to  it;  it  is  generally 
known  as  the  auxiliary  vein  (Fig.  57  a)  by  dipterists.  In  the  Diptera  the  sub- 
costa is  rarely  branched. 

The  radius  lies  directly  behind  the  subcosta  and,  in  the  hypothetical  type, 
is  five-branched.  In  Tabanus  the  radius  is  four-branched,  R;{  having  been  lost 
by  fusion  with  Ro.  The  first  branch,  R,,  is  simple  and  corresponds  to  the  first 
longitudinal  (Fig.  57  ist).  Near  the  base  of  the  wing  a  short  branch,  the 
radial  sector  (Fig.  56  Rs),  arises,  which  divides  into  two  branches,  the  posterior 
branch  again  dividing.  The  first  branch  constitutes  the  2nd  longitudinal  vein 
(Fig.  57  2nd) ;  the  posterior  branch  with  its  two  divisions  is  the  3rd  longitudinal 


i48 


MEDICAL  ENTOMOLOGY 


The  media  extends  through  the  middle  of  the  wing.  In  Tabanus  it  is  three- 
branched  (Fig.  56  Mj,  M2,  M3).  The  first  two  branches  constitute  the  4th 
longitudinal  vein  (Fig.  57  4th). 

The  cubitus  is  typically  two-branched  and  with  the  posterior  branch  of 
media  (M3)  constitutes  the  5th  longitudinal  vein  (Fig,  57  5th). 


Fig.  56.  Wing  of  Tabanus  sp.  with  the  veins  and  cells  labeled  according  to 
the  Comstock-Needham  system. 


costal 


2nd 


3rd 


6th 


5th 


Fig.  57.  Wing  of  Tabanus  sp.  with  the  veins  and  cells  labeled  in  accordance 
with  the  system  followed  by  students  of  the  Diptera  (flies). 

The  anal  veins  are  the  two  or  three  veins  (ist,  2nd,  and  3rd  when  present) 
lying  behind  the  cubitus.  In  the  Diptera  the  first  anal  vein  is  greatly  reduced 
or  absent.  It  is  frequently  represented  by  a  furrow,  the  anal  furrow,  which  is 
close  behind  the  cubitus.  The  second  anal  vein  is  well  preserved  (Fig.  56  2d  A) 
and  corresponds  to  the  6th  longitudinal  (Fig.  57  6th). 

The  cross-veins  include  several  well-marked  veins.  These  are  (i)  the 
humeral  (h),  (2)  the  radio-medial  (r-m),  known  also  as  the  anterior  cross- 
vein  (ac),  and  (3)  the  medio-cubital  (m-cu),  commonly  called  the  posterior 


THE  HEXAPODA:  INSECTS  149 

cross-vein  (discal  cross-vein  of  Williston;  Fig,  57  pc).  The  radio-medial  or 
anterior  cross-vein  is  very  constant,  and  its  location  will  always  give  a  clue 
to  the  venation  of  the  wing.  Another  important  cross-vein  is  the  medial  (m). 
The  areas  of  the  wings  bounded  by  veins  are  called  ceils.  In  the  Comstock- 
Needham  nomenclature  the  cell  takes  the  name  of  the  vein  lying  immediately 
in  front  of  it  (Fig.  56) .  In  the  older  system  the  names  of  the  cells  are  rather 
arbitrary,  and  it  is  at  times  difficult  to  interpret  an  author's  work  unless  he  is 
very  specific  in  his  explanations  (Fig.  57). 

THE  ABDOMEN 

The  abdomen  constitutes  the  third  region  of  the  body  (Fig.  58).  It  is 
composed  of  a  series  of  segments  that  retain  the  rather  primitive  annular  form. 


DV 


viS 


viiS 


viiiS 


viiiSp 


Fig.  5<S.  Lateral  view  of  the  abdomen  of  a  grasshopper  (Melanoplus  differentialif'). 
Cer,  cercus;  Cxc,  coxal  cavity;  E,  egg  guide;  Ep,  epiproct;  Epma,  epimeron  of  3rd  thoracic 
segment;  Lc,  lateral  commisure;  Ovi,  ovipositor  consisting  of  the  dorsal  valves  (DV), 
ventral  valves  (VV),  and  inner  valves  (IV);  Pp,  paraproct  or  podical  plate;  Ss  sternum  of 
third  thoracic  segment;  iS-viiiS,  first  to  eighth  abdominal  sterna;  iSp-viiiSp,  one  to  eight 
spiracles;  iT-xiT,  one  to  eleven  tergites  or  terga;  T,  tympanum. 

Each  segment  has  a  large  tergum  and  a  well-developed  sternum.  The  pleural 
region  is  nearly  always  membranous,  though  differentiated  sclerites  may 
sometimes  occur.  When  the  abdomen  of  a  grasshopper  is  examined,  it  will 
be  observed  that  the  terga  and  sterna  closely  approach  each  other  while  the 
pleurum  is  represented  by  a  folded  membrane,  the  longitudinal  conjunctiva. 
The  abdomen  consists  of  eleven  segments,  the  last  three  or  four  being  modi- 
fied to  form,  with  the  modified  appendages,  the  clasping  organs  of  the  male  or 
the  ovipositor  of  the  female  (genitalia).  Though  eleven  segments  are  con- 
sidered the  primitive  number,  it  is  often  difficult  to  recognize  more  than  eight 


150  MEDICAL  ENTOMOLOGY 

or  even  less.  This  is  due  to  their  reduction  or  modification  in  the  higher 

orders  such  as  the  Diptera  and  Hymenoptcra. 
The  terminal  segments  with  their  appendages  are  highly  modified  in  many 

insects  to  form,  in  the  males,  the  most  bizarre  types  of  clasping  organs.  As 

the  parts  entering  into  the  external  genitalic  structures  have  not  been  homolo- 

gized  throughout  the  various  orders,  it 
does  not  seem  worth  while  to  discuss 
them  as  they  occur  in  the  more  gen- 
eralized groups.  These  structures  will  be 
dealt  with  in  some  detail  in  those  groups 
that  are  of  importance  from  the  stand- 
point of  medical  entomology. 

INTERNAL  ANATOMY 


The  internal  anatomy  of  insects  can  be 
referred  to  only  briefly.  Those  structures 
that  chiefly  interest  the  medical  entomolo- 
gist will  be  outlined  in  brief  detail,  i.e.,  the 
F/e.  50.  Diagrammatic  cross  section    j.  t  .  ,  i 

t  L     i i  •  i  r  L     LJ  c  digestive  system  and  its  appendages,  the 

of  the  third  segment  or  the  abdomen  of       °  '  rr          °    ' 

a  grasshopper  to  show  position  of  mus-  respiratory  system,  the  blood,  the  muscu- 

cles  and  some  of  the  internal  organs,  lar  system,  and  the  reproductive  system. 

Em,  external   lateral  muscles;   F,    fat 

body;  Fc,  food  channel  or  alimentary   T  cvQTPlv/f 

canal;  H,  heart;  L,,  internal  lateral  mus-   THE  DIGESTIVE  SYSTEM 

clc;  la,  lateral  apodemes  of  sternum;   AND  ITS  APPENDAGES 

Lm,  lateral  internal  dorsal  muscle;  Mi, 

median  internal  dorsal  muscles;  mp,       The  most  striking  feature  of  an  insect 

Malpighian  tubules;  P,  an  external  mus-    is  that  the  body  wall  (pig      ^  £orms  the 

cle;  ps,  perivisceral  sinus  for  blood;  R.     ,    ,  .   .  . 

reproductive  organs;  &,  &,  dorsal  and  skeleton,  giving  support  and  protection  to 

ventral  sinuses;  Ta,  ventral  diaphragm;   the  internal  organs.  The  body  wall  may 

Tn,  dorsal  diaphragm;  Tr,  trachea;  V,  represent  the  wall  of  a  cylinder.  The  ali- 

ventral I  muscles;  VX)  ventral  nerve  cord.  j  .  , 

(Modified  from  Snodgrass.)  ... 

central  position  in  the  cylinder  and  con- 
nects the  mouth  opening  with  that  of  the  anus.  It  may  be  barely  as  long  as  the 
body  or  it  may  be  coiled  and  doubled  on  itself,  making  several  convolutions. 
Above  it  lies  the  heart,  and  the  nerve  chain  is  ventral  (Fig.  59).  The  digestive 
system  is  composed  of  the  following  parts :  (i)  fore-intestine,  (2)  mid-intestine, 
(3)  hind-intestine,  (4)  salivary  glands,  (5)  Malpighian  tubules,  and  (6) 
accessory  glands  (Fig.  60). 


THE  HEXAPODA:  INSECTS  151 

FORE-INTESTINE:  The  fore-intestine  begins  at  the  rear  of  the  buccal 
cavity.  Its  anterior  end  is  a  rather  wide-open  channel  into  which  the  food  is 
passed  after  mastication.  This  leads  directly  into  the  pharynx,  which,  in 
mandibulatc  insects,  is  a  thin-walled  tube.  In  insects  with  piercing  mouth 
parts  the  pharynx  is  an  organ  of  suction  and  is  provided  with  powerful  muscles. 
By  the  contraction  of  these  muscles  the  pharynx  acts  as  a  pumping  organ 
(Fig.  60).  The  pharynx  leads  into  the  esophagus,  a  thin-walled  tube,  which 
may  terminate  in  a  crop,  followed  by  a  proventriculus  or  gizzard.  In  most 
of  the  bloodsucking  Diptera  the  gizzard  is  reduced  to  a  valve  that  opens  into 
the  mid-intestine.  In  addition  to  these  structures  the  esophagus  may  have  one 


Fig.  60.  Diagrammatic  sectional  view  of  the  internal  structures  of  a  female  mosquito. 
C,  cardiac  or  csophageal  valve;  Cer,  cercus;  D,  dorsal  diverticula;  E,  esophagus;  F,  food 
channel;  H,  hind-intestine;  M,  Malpighian  tubules;  Ov,  ovary;  Ovi,  oviduct;  Ph,  pharynx; 
Pph,  pharyngcal  pump;  S,  salivary  duct;  Sg,  salivary  glands;  Sm,  stomach;  Sp,  salivary 
pump;  Spa,  spermatheca;  V,  ventral  diverticula  of  esophagus. 

to  three  diverticula  or  food  reservoirs  (Fig.  60),  as  they  are  called.  These 
diverticula  are  very  large  in  the  mosquito  but  their  exact  function  is  not 
well  known. 

THE  MID-INTESTINE:  The  mid-intestine  or  stomach  (Fig.  60)  extends 
from  the  proventriculus  to  the  insertion  of  the  Malpighian  tubules.  It  may  be 
short  and  saclike  or  it  may  be  long  and  coiled.  It  is  in  this  portion  of  the 
alimentary  tract  that  digestion  and  most  of  the  absorption  take  place.  The 
mid-intestine  is  joined,  in  many  cases,  to  the  fore-intestine  by  what  has  been 
termed  the  esophageal  valve  (Fig.  60  C).  The  esophageal  valve  is  absent  in 
the  lice  (Anoplura)  and  the  bedbug.  In  many  insects  the  food  contained  in 
the  mid-gut  is  surrounded  by  a  delicate  membrane,  the  peritrophic  membrane, 
which  originates  from  a  group  of  cells,  the  cardiac  cells,  located  at  the  juncture 


152  MEDICAL  ENTOMOLOGY 

of  the  epithelium  of  the  fore-  and  mid-intestine.  The  peritrophic  membrance  is 
present  in  the  majority  of  insects.4 

THE  HIND-INTESTINE:  The  origin  of  the  hind-intestine  is  marked  by 
the  insertion  of  the  Malpighian  tubules.  In  many  insects  the  hind-gut  is 
divided  into  three  fairly  well  defined  regions — the  ileum,  the  colon,  and  the 
rectum  (Fig.  61). 

STRUCTURE  OF  THE  INTESTINE:  The  fore-  and  hind-intestine  are 
of  ectodermal  origin.  Internally  each  is  lined  with  a  thin  intima,  which  is 
continuous  with  the  cuticula  of  the  body  wall.  The  intima  may  be  very  thick 
as  in  the  gizzard  (proventriculus).  Beneath  the  intima  is  a  single  layer  of 
epithelial  cells  that  is  continuous  with  the  epidermis.  A  basement  membrane 
underlies  the  epithelial  cells.  The  fore-intestine  is  surrounded  by  a  layer  of 
longitudinal  muscle  fibres  overlaid  by  a  thin  band  of  circular  muscle  fibers. 
In  the  hind-intestine  the  muscle  layers,  from  within,  are  first  circular,  then 
longitudinal,  and  usually  again  circular.  The  mid-intestine  is  of  entodermal 
origin.  It  lacks  the  internal  lining  of  intima  and  is  composed  of  a  single  layer 
of  epithelial  cells  resting  on  a  basement  membrane.  It  is  surrounded  by  a  layer 
of  circular  muscles  overlaid  by  a  thin  sheet  of  longitudinal  fibers.  The  entire 
intestine  outside  the  muscle  layers  is  surrounded  by  a  thin  sheet  known  as 
the  peritoneal  membrane.  The  peritoneal  membrane  may  then  be  considered 
as  the  inner  lining  of  the  body  cavity  or  hemocele. 

THE  SALIVARY  GLANDS:  These  are  the  most  important  glands  con- 
nected with  the  fore-intestine,  and  they  often  play  a  significant  role  in  the 
transmission  of  parasites  (Figs.  60-62).  The  glands  are  paired  structures  and 
lie  on  each  side  of  the  intestine  in  the  hemocele.  Each  gland  consists  of  a 
cellular  part  and  a  duct  that  unites  with  its  fellow  from  the  opposite  side  to 
form  a  common  salivary  duct.  The  common  duct  opens  at  the  base  of  the 
hypopharynx  and,  in  some  of  the  bloodsucking  insects,  extends  throughout 
its  length  (Fig.  97) .  These  glands  vary  greatly  in  size  and  complexity.  In  the 
mosquito  the  glands  are  quite  large  and  occupy  a  considerable  space  in  the 
thorax.  Each  gland  of  the  mosquito  is  trilobcd,  with  a  central  gland  and  two 
lateral  glands  (Fig.  62).  The  ducts  of  the  three  glands  from  each  side  unite 
into  one,  and  this  in  turn  joins  its  fellow  from  the  opposite  side  to  form  a 
common  salivary  duct.  At  its  point  of  entrance  into  the  hypopharynx  there 
is  a  muscular  pump  that  forces  the  secretion  into  the  wound  made  at  the  time 


4  Wigglcsworth  (1930)  states  that  it  is  absent  in  the  Hemiptera,  adult  Lepidoptera, 
and  some  Coleoptera. 


THE  HEXAPODA:  INSECTS 


Fig.  61.  (a)  The  digestive  tract  of  the  housefly  with  the  main  parts  labeled.  (I?)  The 
salivary  syringe  to  show  details  (highly  magnified).  A^ anal  opening;  F,  fulcrum  in  head 
of  fly;  HI,  hind-intestine;  I,  mid-intestine  extending  trom  proventriculus  (PR)  to  in- 
sertion of  Malpighian  tubules  (T);  M,  muscles  to  syringe;  O,  esophagus;  Od,  esophageal 
diverticulum  or  crop;  P,  pharynx;  PR,  proventriculus;  R,  rectum;  Sd,  salivary  duct  lead- 
ing to  hypopharynx  from  salivary  syringe;  Sga,  salivary  glands;  Sp,  salivary  syringe; 
T,  Malpighian  tubules;  V,  valve  to  prevent  backflow  of  salivary  fluid. 


i54  MEDICAL  ENTOMOLOGY 

of  obtaining  blood.  In  many  insects  the  salivary  glands  function  for  the  secre- 
tion of  silk,  as  in  the  caterpillars  and  the  larvae  of  many  Hymenoptera. 

The  functions  of  the  secretion  of  the  salivary  glands  of  bloodsucking  in- 
sects are  not  well  understood.  It  is  known  that  in  the  mosquito  the  secretion  is 
injected  into  the  wound,  causing  the  irritation  and  swelling.  How  this  is 
brought  about  is  not  known.  In  some  insects  the  secretion  possesses  an  anti- 
coagulin  (Anopheles  rossi  and  A.  jamesii),  but  in  others  such  a  function  has 


Fig.  62.  Left:  The  left  half  of  the  salivary  gland  of  Anopheles  punctipcnnis.  Center: 
Cross  section  of  the  glands.  Right:  Cross  section  of  a  gland  from  Culcx  pipicns  showing 
masses  of  sporo/.oites  of  bird  malaria.  Cg,  central  gland;  Lg,  lateral  gland;  Sd,  salivary 
duct. 

not  been  demonstrated.  Metcalf  (1945)  has  shown  that  the  salivary  glands  of 
Anopheles  quadrimaculatus  contain  an  anticoagulin  that  is  thermostable  and 
active  at  dilutions  of  i  :io,ooo;  they  also  contain  a  powerful  agglutinin  for  most 
vertebrate  blood  but  not  for  chicken  or  turtle  blood.  Cornwall  and  Pattern 
have  shown  that  the  saliva  of  a  muscid  (Musca  crassirostris)  contains  a  power- 
ful anticoagulin,  whereas  Stomoxys  calcitrant  (the  stable  fly)  has  no  anti- 
coagulin. Lester  and  Lloyd  find  that  the  salivary  secretions  of  Glossina  flies 
possess  a  powerful  anticoagulin.  Yorke  and  Macfie  report  that  the  salivary 
secretion  of  Anopheles  maculipennis  agglutinates  red  blood  cells  and  also 


THE  HEXAPODA:  INSECTS  155 

possesses  an  anticoagulin  and  that  the  secretions  of  Culex  pipiens  and  Aedes 
aegypti  do  not  possess  an  agglutinin  nor  do  they  contain  an  anticoagulin.  Mc- 
Kinlcy  determined  that  an  emulsion  of  the  glands  of  Aedes  aegypti,  when 
injected  intradermally,  caused  a  severe  itching  and  characteristic  wheals  on 
susceptible  persons;  it  does  not  possess  an  anticoagulin  nor  does  it  hemolyze 
blood.  It  has  also  been  shown  that  some  species  of  horseflies  (Tabanidae) 
possess  an  anticoagulin  in  their  salivary  glands.  Puri  has  shown  that  the 
saliva  of  the  bedbug  causes  the  severe  irritation  and  that  it  contains  an 
anticoagulin.  As  bloodsucking  insects  must  ingest  their  blood  meal 
through  a  very  minute  channel,  it  would  seem  essential  that  some  agent  or 
agents  be  present  to  prevent  the  coagulation  of  the  blood  here  or  in  the  esoph- 
agus in  order  to  allow  it  to  flow  freely  into  the  mid-gut  where  digestion  takes 
place. 

THE  MALPIGHIAN  TUBULES:  The  Malpighian  tubules  (Figs.  60,61) 
are  usually  elongated  tubes  that  arise  at  the  junction  of  the  mid-  and  hind- 
intestine.  In  their  origin  they  belong  to  the  hind-gut.  Their  number  varies 
but  they  generally  occur  in  multiples  of  two,  the  usual  number  being  four  or 
six.  In  the  Culicidac  there  are  live,  but  most  of  the  Diptera  possess  four.  Each 
Malpighian  tubule  arises  at  the  anterior  end  of  the  hind-gut  and  terminates 
blindly  in  the  hcmocele.  Though  they  are  usually  single,  branching  may  occur 
or  two  may  unite  to  form  a  common  opening  into  the  intestine  (Fig.  61).  In 
structure  each  tube  is  composed  of  a  ring  of  epithelial  cells  surrounding  a 
central  channel.  Each  cell  possesses  a  prominent  nucleus,  which  may  be  much 
branched.  The  epithelial  layer  of  cells  rests  on  a  basement  membrane  sur- 
rounded by  a  delicate  peritoneal  sheath.  The  function  of  these  tubules  is  now 
generally  regarded  as  excretory,  extracting  waste  from  the  blood  and  storing  it 
in  the  cells  or  passing  it  to  the  hind-intestine.  The  Malpighian  tubules  are  of 
great  interest  to  the  parasitologist  because  within  them  certain  parasites 
undergo  part  of  their  life  cycles,  for  example,  Dirofdaria  immitis  (Fig.  63), 
a  rilarial  roundworm  infecting  the  dog. 

THE  RESPIRATORY  SYSTEM 

The  respiratory  system  of  insects  consists  of  a  paired  series  of  tubes,  tracheae, 
which,  by  branching,  ramify  through  all  parts  of  the  body  and  its  appendages. 
These  tubes  arise  as  invagi nations  of  the  body  wall  and  are  usually  located 
on  the  pleura  of  the  second  and  third  thoracic  and  first  eight  abdominal  seg- 
ments (Fig.  42).  The  external  openings  are  called  spiracles,  and  the  usual 
number  is  ten  pairs.  The  spiracle  is  usually  surrounded  by  a  chitinous  ring, 


156  MEDICAL  ENTOMOLOGY 

the  peritreme,  and  opens  into  an  atrium  or  air  chamber.  From  the  air  chamber 
extends  a  trachea,  which  branches  and  unites  with  its  fellows  to  form  longi- 
tudinal and  transverse  connections.  From  these  main  trunks  innumerable 
branches  extend  to  all  the  tissues  and  organs  of  the  body.  The  spiracle,  in  its 
simplest  form,  consists  of  an  opening  to  the  exterior  to  admit  air.  There  is, 
however,  extreme  variation  in  the  structure  of  spiracles,  and  many  possess  a 
rather  complicated  apparatus  for  closure  and  for  excluding  dust,  dirt,  and 
moisture.  In  many  insects  a  single  spiracle  may  have  several  openings  (Fig. 
194).  The  trachea  consists  of  a  tube  lined  internally  with  intima  arranged  in 
such  a  way  that  the  thickenings  form  a  spiral  (Fig.  64).  These  spiral  thicken- 
ings (taenidia)  keep  the  trachea  distended  and  allow  the  free  passage  of  air. 


Fig.  63  (lejt).  Malpighian  tubule  from  Acdes  vexans  (a  mosquito)  containing  three 
larval  filarial  worms,  Dirofilaria  immitis  (dog  filaria).  These  developed  17  days  after  the 
mosquito  fed  on  the  blood  of  a  dog  containing  microfilaria. 

Fig.  64  (right).  Small  section  of  a  trachea  to  show  structure,  e,  epithelium;  i,  intima; 
t,  taenidia. 

The  tracheae  finally  terminate  in  tracheoles,  which  are  the  essential  organs 
for  respiration.  The  tracheoles  are  minute  tubes  that  lack  a  chitinous  lining  and 
penetrate  the  various  tissue  cells  to  furnish  the  needed  air. 

In  addition  to  the  respiratory  system  described  above,  various  modifica- 
tions are  found.  In  aquatic  insects  there  may  be  tracheal  gills,  as  in  mosquito 
larvae  (Fig.  105),  and  blood  gills  (which  are  rare),  as  in  the  larvae  of  some 
species  of  Chironomus  and  Simulium. 

In  order  to  indicate  the  distribution  of  spiracles  the  following  classification 
is  much  used  (mostly  applied  to  dipterous  larvae) : 

1.  Holopneustic — Spiracles  all  open  and  arranged  on  thorax  and  first  7  or  8  ab- 

dominal segments. 

2.  Hemipneustic — One  or  more  spiracles  closed. 

(i)  Peripneustic—Usually  spiracles  of  wing  bearing  segments  closed. 


THE  HEXAPODA:  .INSECTS  157 

(2)  Propneustic — Only  first  pair  of  thoracic  spiracles  open.  Example:  pupae 

of  mosquitoes. 

(3)  Metapneustic — Only  the  last  pair  of  spiracles  is  open.  This  type  is  found  in 

mosquito  larvae,  some  parasitic  larvae  as  Hypoderma  spp.  (warble 
flies),  and  others. 

(4)  Amphipneustic — The  first  and  last  pair  of  spiracles  are  open.  Example: 

larvae  of  the  Muscidae. 

THE  BLOOD 

The  blood  is  generally  a  colorless  fluid  that  circulates  freely  in  the  hemocele, 
bathing  directly  all  the  internal  organs  and  tissues.  In  some  insects  it  may  be 
colored  from  the  absorbed  food  substances  or  may  contain  hemoglobin 
(rare) .  In  the  plasma  are  found  several  types  of  leucocytes,  but  their  functions 
are  not  well  known.  One  type  possesses  a  phagocytic  function,  and  these  cells 
undoubtedly  play  an  important  role.  The  blood  is  kept  in  circulation  by  a  dorsal 
pumping  organ,  the  heart.  The  heart  is  a  tube  that  extends  from  near  the 
caudal  extremity  to  the  head.  It  is  usually  closed  at  the  posterior  end  and 
terminates  in  a  nonpulsating  anterior  vessel,  the  aorta.  In  the  heart  there  are 
paired  ostioles  or  openings.  The  pulsations  of  the  heart  travel  from  behind 
forward  so  that  the  blood  flows  in  at  the  ostioles  and  is  then  forced  cephalad  by 
the  wavelike  muscular  contractions,  being  discharged  through  the  aorta.  The 
ostioles  are  so  constructed  that  they  admit  the  entry  of  the  blood,  but  as  the 
contraction  waves  passes  forward,  backflow  in  the  heart  itself  and  to  the  hemo- 
cele is  prevented. 

THE  MUSCULAR  SYSTEM 

The  muscles  of  insects  are  all  internal.  The  body  wall  and  various  invagina- 
tions  (apodemes,  furca,  etc.)  furnish  the  points  of  origin,  and  the  insertion 
points  are  those  portions  or  parts  of  the  body  to  be  moved.  As  a  rule,  insect 
muscles  are  composed  of  numerous  fibers  enclosed  in  sheaths  and  appear 
almost  colorless,  transparent,  or  yellowish  white;  they  are  soft  and  gelatinous. 
The  number  of  muscles  is  large  and  their  arrangement  very  complicated.  In 
their  histological  structure  all  the  muscle  fibers  are  cross-striated  and  present 
a  beautiful  appearance  to  the  microscopist.  To  the  parasitologist  and  medical 
entomologist  the  normal  histology  is  of  considerable  significance,  for  in  some 
muscle  tissues  certain  Nematodes  pass  part  of  their  life  cycle  (Wuchereria 
bancrofti,  in  the  thoracic  muscles  of  the  mosquitoes;  Loa  loa  in  similar  muscles 
of  Tabanidae) . 


i58 


MEDICAL  ENTOMOLOGY 


THE  REPRODUCTIVE  SYSTEM 

In  practically  all  insects  the  sexes  are  distinct.  The  female  reproductive 
organs  (Fig.  65)  consist  of  the  ovaries,  paired  structures;  each  ovary  is  com- 
posed of  a  variable  number  of  egg  tubes  or  ovarioles;  the  ovarioles  from  each 
side  open  into  an  oviduct;  the  oviducts  unite  to  form  a  common  duct,  the 
vagina,  which  opens  to  the  exterior  ventral  of  the  anal  opening.  Attached 
to  the  vagina  and  opening  into  it  are  usually  found  a  pair  of  accessory  glands 


Fig.  65.  Female  reproductive  system  of  Anopheles  punctipcnnis.  Ag,  accessory  gland; 
Ov,  ovary;  Ovd,  oviduct;  Sp.  spcrmatheca;  V,  vagina. 

and  a  pouch  (there  may  be  several),  the  spermatheca,  for  the 'reception  and 
storage  of  the  sperm.  As  the  majority  of  insects  probably  mate  but  once,  and 
the  female  oviposits  over  a  long  period  of  time,  it  is  essential  that  a  storage 
place  be  provided  for  the  sperm. 

The  male  reproductive  organs  consist  of  a  pair  of  testes  composed  of 
testicular  follicles;  from  each  testis  extends  a  canal,  the  vas  deferens,  which 
unites  near  the  exterior  with  its  fellow  to  form  the  ejaculatory  duct.  Usually 
each  vas  deferens  is  enlarged  along  its  course  to  form  a  sac,  the  vesicula 


THE  HEX  APOD  A:  INSECTS  159 

seminalis,  in  which  the  spermatozoa  congregate.  There  is  also  generally  a 
pair  of  accessory  glands.  The  ejaculatory  duct,  at  its  terminal  section,  is  enclosed 
in  a  chitinous  tube  that  forms  the  intromittent  organ  or  aedeagus.  The  aedeagus 
or  penis  is  a  variable  structure,  and  around  it  often  develop  a  most  com- 
plicated grouping  of  clasping  and  holding  organs. 

THE  METAMORPHOSIS  OF  INSECTS 

The  great  majority  of  insects,  in  the  course  of  their  postembryonic  develop- 
ment, undergo  remarkable  changes  in  form  or  metamorphosis;  the  beautiful 
butterfly  was  once  a  caterpillar;  the  May  beetle,  a  grub;  the  housefly,  a  footless 
maggot.  The  most  obvious  changes  are  external,  though  the  internal  meta- 
morphosis is  even  more  complicated  and  as  yet  not  well  understood.  Practically 
all  insects  lay  eggs  and  these  develop  externally  to  the  mother.  In  some  insects 
the  embryonic  development  may  be  completed  before  the  egg  is  laid,  as  in 
many  plant  lice  and  flesh  flies;  the  egg  may  hatch  and  the  larva  develop  in  a 
uteri nelike  cavity  in  the  mother,  as  in  the  Glossina  flies,  the  sheep  tick  or  ked, 
and  all  the  Piipipara;  or  partial  embryonic  development  may  take  place  before 
egg  laying,  as  in  the  bedbug.  There  are  two  general  types  of  postembryonic 
development — incomplete  metamorphosis  (hemimetabolous),  and  complete 
metamorphosis  (holometabolous).  Those  insects  that  do  not  undergo  changes 
in  form  during  growth  are  called  ametabolous  (these  include  the  two  primitive 
orders,  Thysanura  and  Collembola). 

THE  EGG:  The  eggs  of  insects  vary  greatly  in  their  shape,  size,  and  mark- 
ings. Attention  here  is  directed  only  to  the  eggs  of  those  insects  that  are 
annoying  to  man  or  his  domestic  animals.  These  eggs  all  possess  a  distinct  shell 
and  arc  laid  on  or  near  the  food  on  which  the  young  are  to  feed.  The  egg  of  the 
bedbug  (Fig.  71)  is  quite  large  and  distinctive;  that  of  the  louse  is  attached 
to  hairs  or  clothing  and  possesses  a  structure  for  attachment  (Fig.  81);  the 
housefly  deposits  large,  smooth,  white  eggs  (Fig.  173).  Frequently  the  most 
distinguishing  characteristic  of  the  eggs  of  certain  insects  is  the  manner  of 
oviposition.  Thus  the  mosquito,  (Culex  spp.,  lays  its  eggs  in  rafts  (Fig.  in) 
on  the  surface  of  the  water;  horseflies  (Tabanidae)  deposit  their  eggs  in 
masses  glued  to  the  leaves  or  stems  of  aquatic  or  semiaquatic  plants  (Fig.  158). 

The  young  larva  escapes  from  the  egg  either  by  breaking  the  shell  with 
its  mandibles  or  mouth  hooks,  by  pushing  off  a  cap  by  means  of  an  air  cushion 
(lice);  or  by  breaking  the  shell  with  a  special  apparatus  known  as  an  egg 
burster  or  hatching  spines.  Such  hatching  spines  are  easily  seen  on  the  dorsal 
surface  of  the  head  of  the  first-stage  mosquito  larva. 


160  MEDICAL  ENTOMOLOGY 

INSECTS  WITH  INCOMPLETE  METAMORPHOSIS:  The  most 
striking  feature  of  this  type  of  metamorphosis  is  the  development  of  wings  as 
external  outgrowths  of  the  mesothoracic  and  metathoracic  segments.  In  all 
other  respects  except  in  size  and  the  rudimentary  condition  of  the  genital 
appendages,  the  young  (generally  called  nymphs)  resemble  the  adults.  A  good 
example  is  a  grasshopper  or  a  bug.  Furthermore  in  this  type  of  metamorphosis 
the  life  of  the  young  and  of  the  adult  is  essentially  the  same:  they  live  in  the 
same  situation  and  feed  on  the  same  food.5  The  adults  are  provided  with  wings 
giving  them  increased  power  of  locomotion.  The  power  of  flight  gives  them 
a  wider  feeding  range  and  provides  for  the  more  rapid  spread  of  the  species 
and  more  successful  mating. 

INSECTS  WITH  COMPLETE  METAMORPHOSIS:  In  this  group  the 
young  and  adults  are  totally  unlike  in  appearance.  Familiar  examples  are 
the  caterpillars,  which  develop  into  moths  or  butterflies;  maggots,  which 
later  become  flies;  and  grubs,  which  transform  to  beetles.  The  young  stage 
is  generally  known  as  the  larva.  When  the  larva  has  reached  maturity,  it 
ceases  to  feed  and  proceeds  to  undergo  a  most  remarkable  change.  It  now 
either  spins  a  silken  cocoon  (most  moths),  forms  a  cell  in  the  ground  (many 
beetles),  seeks  out  some  sheltered  place,  uses  the  last  larval  skin  as  a  shelter 
(many  Diptera),  attaches  itself  to  some  support  (butterflies  and  some  beetles), 
or  in  other  ways  makes  provision  for  the  changes  that  are  to  follow.  The 
last  larval  skin  is  now  cast  ofT  (except  in  many  Diptera),  and  a  new  stage,  the 
pupa,  appears  (Fig.  103).  Within  the  pupa  many  of  the  larval  tissues  are 
broken  down  and  rebuilt  to  form  the  adult.  From  the  pupal  skin  emerges  an 
entirely  new  form,  the  adult. 

The  most  striking  characteristics  of  this  type  of  metamorphosis  are:  (i)  the 
larval  stage  occupies  an  entirely  different  habitat  and  requires  different  food 
from  that  of  the  adult;  (2)  the  wings  are  developed  internally  during  the 
larval  period  and  only  appear  externally  as  wing  pads  (Fig.  103)  in  the  pupal 
stage;  and  (3)  a  resting  stage  appears,  the  pupa,  within  which  the  larval  tissues 
are  broken  down  and  the  adult  is  rebuilt  from  histoblasts  or  embryonic  tissues. 

GROWTH  IN  INSECTS 

The  growth  period  in  insects  is  restricted  to  the  nymphal  or  larval  stage. 
Growth  in  the  nymphal  and  larval  stages  is  accomplished  by  a  periodic  shed- 

5  This  last  statement  does  not  apply  to  three  orders,  the  May  flies,  stone  flies,  and  the 
dragonflies,  whose  nymphs  are  aquatic  and  adults  aerial.  Comstock  has  designated  this 
type  as  incomplete  or  hemimetabolous,  and  the  type  represented  by  the  Orthoptera, 
Hemiptera,  Anoplura,  etc.,  as  paurometabolous  or  gradual  metamorphosis. 


THE  HEXAPODA:  INSECTS  161 

ding  of  the  skin,  molting.  As  the  skeleton  is  external,  no  increase  in  size  beyond 
a  certain  expansion  can  take  place  after  the  cuticula  has  hardened.  This  dif- 
ficulty is  overcome  by  molting.  When  a  larval  stage  has  reached  its  full  growth, 
the  cuticula  splits  at  some  convenient  place  and  a  new  larva  crawls  out  pro- 
vided with  a  soft  external  skin  capable  of  considerable  extension.  The  new 
cuticula  is  laid  down  beneath  the  old  before  the  latter  is  shed.  Molting  takes 
place  at  regular  intervals  and  the  number  of  molts  varies  in  different  groups 
of  insects.  In  the  mosquito  the  larva  molts  four  times  before  the  pupal  stage 
is  reached;  in  most  of  the  higher  Diptera  only  three  molts  occur;  in  the  beetles 
and  moths  five  or  more  may  occur;  in  other  groups  three  to  many  molts  may 
take  place.6  During  the  larval  growth  large  quantities  of  food  are  stored  up  as 
fat.  This  food  supply  is  largely  used  up  during  the  pupal  period,  being  em- 
ployed in  the  development  of  the  tissues  of  the  adult. 

The  adult,  though  it  feeds,  does  not  increase  in  size.  Molting  does  not  occur, 
and,  once  the  external  skeleton  is  fully  hardened,  no  great  expansion  of  body 
size  is  possible.  Food  is  now  taken  to  provide  for  the  adult  activities  and  the 
development  of  eggs  and  sperm.  In  many  insects  the  adults  do  not  feed  but 
depend  on  the  store  of  food  carried  over  from  the  larvae. 

SYNOPSIS  OF  INSECT  CLASSIFICATION 

The  Hexapoda  or  insects  constitute  an  immense  assemblage  of  species; 
probably  more  than  800,000  species  have  already  been  described,  and  new 
ones  are  constantly  being  discovered.  The  class  is  divided  into  two  subclasses, 
the  Apterygota  and  Pterygota.  The  Apterygota  contain  the  wingless,  primi- 
tive insects,  and  these  are  included  in  two  orders,  the  Thysanura  and  the 
Collembola.  The  Pterygota  include  all  the  other  insects  whether  wingless  or 
not.  The  wingless  condition  of  the  forms  included  here  is  not  a  primitive 
one  but  acquired.  The  Pterygota  are  divided  into  a  number  of  orders  but  rarely 
do  workers  agree  as  to  the  exact  number  or  their  arrangement.  It  is  proposed 
here  to  give  a  brief  synopsis  of  only  those  orders  that  contain  important  species 
annoying  to  man  or  his  animals.7  These  include  only  eight  or  nine  of  the 
twenty  to  nearly  forty  orders  now  recognized.  Of  these  orders  the  most  im- 
portant are  the  Hemiptera,  the  Anoplura,  the  Diptera,  and  the  Siphonaptera. 
The  other  orders,  the  Orthoptera,  Lepidoptera,  Coleoptera,  and  Hymenoptera, 
contain  forms  that  may  act  as  mechanical  carriers  of  disease  organisms 


6  The  intervals  between  molts  or  ecdyses  are  called  stadia;  the  form  of  the  larva  or 
nymph  during  a  stadium  is  called  an  instar. 

7  For  a  full  account  the  reader  is  referred  to  works  by  Comstock,  Sharp,  Imms,  Kellogg, 
Brues  and  Melander,  and  Matheson,  all  indicated  in  the  References. 


162  MEDICAL  ENTOMOLOGY 

(Orthoptera),  produce  diseased  conditions  by  their  poisonous  hairs  (Lepidop- 
tera)  or  stings  (Hymenoptera),  cause  ill  effects  by  their  vesicating  substances 
(cantharidin  of  blister  beetles),  or  serve  as  intermediate  hosts  of  helminths 
(Coleoptera,  Orthoptera,  etc.).  It  is  not  proposed  to  treat  these  four  orders 
in  any  detail,  but  they  are  discussed  briefly  in  the  last  chapter  and  mentioned 
in  a  few  other  places.  The  following  simple  key  will  serve  to  place  those 
insects  that  are  of  great  importance  to  man: 

KEY  TO  THE  PRINCIPAL  ORDERS  OF  INSECTS  (ADULTS) 
OF  MEDICAL  IMPORTANCE 

1.  Wingless  insects 2 

Winged  insects    9 

2.  Free-living  forms,  not  parasitic  3 

Not  free-living,  ectoparasites  5 

3.  Abdomen  sharply  constricted  at  base;  cerci  absent  Hymenoptera 

Abdomen  not  sharply  constricted  at  base,  broadly  joined  to  the  thorax; 

cerci  present  or  absent  4 

4.  Mouth  parts  fitted  for  biting;  flattened  insects;  body  without  scales. 

(Many  cockroaches) Orthoptera 

Mouth  parts  consisting  of  a  proboscis  coiled  up  beneath  the  head;  body 
usually  covered  with  scales  or  long  hairs.  (Wingless  moths)  Lepidoptera 

5.  Mouth  parts  formed  for  piercing  and  sucking 6 

Mouth  parts  adapted  for  biting.  (Biting  lice)   .     (Mallophaga)  Anopltira 

6.  Body  strongly  compressed  (flattened  from  side  to  side) ;  antennae  in 

grooves  visible  from   above;   legs   fitted  for  jumping  or   running. 

(Fleas)     Siphonaptcra 

Body  not  compressed  but  may  be  flattened  from  above  down;  antennae 
not  in  grooves,  visible  or  not  from  dorsal  surface 7 

7.  Antennae  short,  located  in  pits  and  not  visible  from  dorsal  surface. 

(Louse  flies;  Pupipara)  Diptera 

Antennae  fully  exposed 8 

8.  Tarsus  with  one  claw  and  fitted  for  clinging  to  hairs.  (Sucking  lice; 

Siphunculata)     Anoplura 

Tarsus  with  two  claws  and  not  adapted  for  clinging  to  hairs  .  .  Hemiptera 

9.  With  a  single  pair  of  membranous  wings;  hind  pair  represented  by 

short  processes  (halteres  or  balancers)    Diptera 

With  two  pairs  of  wings 10 

10.  The  two  pairs  of  wings  unlike  in  structure  or  texture n 

The  two  pairs  of  wings  similar  in  structure  or  texture 13 


THE  HEXAPODA:  INSECTS  163 

11.  The  front  wings  hard  and  horny,  shell-like,  and  without  distinct  vena- 

tion. Hind  wings  thin  and  membranous;  mouth  parts  for  chewing. 

(Beetles)    Coleoptera 

The  front  wings  not  as  described  above 12 

12.  The  front  wings  parchmentlike  with  a  network  of  veins;  hind  wings 

folded  fanlike  beneath  the  front  wings;  mouth  parts  for  chewing 

Orthoptera 

The  front  wings  leathery  at  base  and  membranous  on  apical  portion 

(Fig.  68) ;  mouth  parts  fitted  for  piercing  and  sucking 

(Heteroptera)     Hemiptera 

13.  Wings  covered  more  or  less  densely  with  scales;  mouth  parts  fitted  for 

sucking  and,  when  at  rest,  coiled  up  under  the  head Lepidoptera 

Wings  not  covered  with  scales;  mouth  parts  fitted  for  biting  or  sucking 
but  never  coiled  up  under  head 14 

14.  Mouth  parts  enclosed  in  a  jointed  beak  and  fitted  for  piercing  and 

sucking;  they  are  located  at  the  posterior  part  of  the  head,  just  in 

front  of  the  first  pair  of  coxae (Homoptera)  Hemiptera 

Mouth  parts  not  enclosed  in  a  jointed  beak;  in  normal  position 

Hymenoptera 

REFERENCES 

**Berlcsc,  Antonio.    Gii  insetti;  loro  organizzazione,  sviluppo,  abitudini  e  rap- 

porti  coU'uomo.     Milan,  1909. 

Brues,  C.  T.,  and  Melander,  A.  L.     Key  to  the  families  of  North  American  in- 
sects.    1915. 
,  and  Melander,  A.  L.     Classification  of  insects.     Bull.  Mus.  Comp.  Zool., 

Harvard  Univ.,  1932. 

**Carpentcr,  G.  H.    The  biology  of  insects.    London,  1928. 
*Comstock,  J.  H.    An  introduction  to  entomology.    Ithaca,  N.Y.,  1947. 

.     The  wings  of  insects.     Ithaca,  N.Y.,  1918. 

Cornwall,  J.  W.,  and  Patton,  W.  S.     Some  observations  on  the  salivary  secretion 

of  the  common  blood-sucking  insects  and  ticks.     Ind.  Jl.  Med.  Res.,  2:  569-593, 

1914. 

**Costa-Lima,  A.  da.    Insetos  do  Brasil.     1939-1945.     5  vols. 
**Essig,  E.  O.    College  entomology.     New  York,  1942. 
**Folsom,  J.  W.,  and  Wardle,  R.  A.    Entomology  with  special  reference  to  its 

ecological  aspects.    4th  ed.    Philadelphia,  1934. 
Graham-Smith,  G.  S.    Further  observations  on  the  anatomy  of  the  proboscis  of  the 

blow-fly,  Calliphora  erythrocephala  L.    Parasitology,  22:  47-114,  1930. 
Henneguy,  L.  F.    Les  Insectes.    Paris,  1904. 


164  MEDICAL  ENTOMOLOGY 

*Imms,  A.  D.    A  general  textbook  of  entomology.    3rd  ed.    London,  1934. 
Lester,  H.  M.  O.,  and  Lloyd,  L.     Notes  on  the  process  of  digestion  in  tsetse-flies. 

Bull.  Ent.  Res.,  19:  39-60,  1928. 
McKinley,  E.  B.    The  salivary  gland  poison  of  the  Aedes  (argenteus)  aegypti. 

Proc.  Soc.  Exp.  Biol.  Med.,  26:  806-809,  1929. 

**Matheson,  R.    Entomology  for  introductory  courses.     Ithaca,  N.Y.,  1947. 
Maxwell-Lefroy,  H.,  and  Howlett,  P.M.    Indian  insect  life.    Calcutta,  1909. 
Packard,  A.  S.    A  textbook  of  entomology.    New  York,  1898. 
Patton,  W.  S.,  and  Cragg,  F.  W.     A  textbook  of  medical  entomology.    London, 

*9*3- 

,  and  Evans,  A.  M.  Insects,  ticks,  mites,  and  venomous  animals  of  medical 

and  veterinary  importance.  Part  I.  Medical.  Croydon,  England,  1929. 

Puri,  I.  M.  Studies  on  the  anatomy  of  Cimcx  lectularius.  Parasitology,  16:  84-97, 
269-278,  1924. 

**Schroeder,  Chr.  (editor).  Handbuch  der  Entomologie.  Jena,  1928,  1929.  2 
vols. 

Sharp,  David.  Insects.  In  Cambridge  Natural  History,  vols.  V  and  VI.  Lon- 
don, 1895,  1899. 

**Snodgrass,  R.  E.    Principles  of  insect  morphology.     New  York,  1935. 

Tillyard,  R.  J.    The  insects  of  Australia  and  New  Zealand.     Sydney,  1926. 

Wigglesworth,  V.  B.  The  formation  of  the  peritrophic  membrane  in  insects,  with 
special  reference  to  the  larvae  of  mosquitoes.  Quart.  Jl.  Micros.  Sci.,  73:  593— 
616,  1930. 

.    The  principles  of  insect  physiology.    New  York,   1939. 

Yorke,  W.,  and  Macfie,  J.  W.  S.  The  action  of  the  salivary  secretion  of  mos- 
quitoes and  of  Glossina  tachinoidcs  on  human  blood.  Ann.  Trop.  Med.  Parasit., 
18:  103-108,  1924. 


CHAPTER  VI 


The  Orders  Orthoptera 
and  Hemiptera 


'"THHE  order  Orthoptera  includes  such  insects  as  cockroaches,  grasshoppers, 
-L  crickets,  and  related  groups.  They  possess  chewing  mouth  parts  (Fig.  45) 
and  normally  two  pairs  of  wings,  of  which  the  outer  (tegmina)  pair  is  more 
or  less  parchmentlike  with  distinct  veins;  the  lower  or  hind  wings  are  thin 
and  folded  fanlike  when  at  rest.  Metamorphosis  is  gradual.  Though  the  order 
contains  many  species  that  are  destructive  to  vegetation  (practically  all  are 
vegetarians),  only  a  single  family  is  of  interest  here. 

THE  FAMILY  BLATTIDAE— THE  COCKROACHES 

Cockroaches  are  primarily  inhabitants  of  the  tropical  and  subtropical  re- 
gions. They  are  easily  recognized  by  their  oval,  flattened  bodies;  long,  filiform 
antennae;  and  legs  fitted  for  running  or  walking.  The  head  is  almost  concealed 
by  the  prothorax  and  is  bent  downward  so  that  the  mouth  parts  project  be- 
tween the  first  pair  of  legs.  Most  of  the  species  live  in  the  wild  in  their  natural 
habitats.  At  least  four  species,  however,  have  become  largely  domesticated  and 
have  invaded  our  homes,  restaurants,  hotels,  food-storage  warehouses,  commer- 
cial establishments  of  all  kinds,  and  similar  places  where  food  and  warmth 
are  available.  These  species  are  all  voracious  feeders,  attacking  almost  any 
vegetable  or  animal  matter.  They  are  largely  nocturnal  in  activity,  and  warm 
kitchens,  laundries,  bakehouses,  restaurants,  and  hotels  are  their  favorite 
haunts.  Unlike  most  insects  the  females  produce  special  egg  cases  within  their 
genital  armature.  When  ready  for  egg  laying  the  female  excretes  a  special 
substance  that  forms  an  egg  case  (ootheca)  composed  of  two  parallel  rows. 
As  each  egg  sac  is  formed,  an  egg  is  passed  into  it  either  from  the  right  or  left 
ovary.  This  continues  till  a  purselike  capsule  is  completed.  It  may  be  seen  ex- 
tending from  the  end  of  the  abdomen  when  it  is  about  ready  to  be  dropped. 


r66  MEDICAL  ENTOMOLOGY 

Each  species  produces  its  own  type  of  ootheca  (Fig.  66).  The  oothecae  are 
dropped  at  convenient  places,  and  the  eggs  normally  hatch  in  a  month  or  two. 
The  female  may  carry  the  egg  case  till  the  eggs  are  ready  to  hatch  as  in  the 
case  of  the  German  roach  (Blatella  germanica). 


Fig.  66.  Egg  case  of  Blatta  orientdis. 

The  four  common,  more  or  less  domesticated  species  (Fig.  67)  are  Blatella 
germanica  (the  German  roach  or  croton  bug),  Blatta  orientalis  Linn,  (the 
oriental  roach),  Periplaneta  amencana  Linn,  (the  American  roach),  and 
Periplaneta  australasiae  Fabr.  (the  Australian  roach).  Another  species,  the 
brown-banded  roach  (Supella  supellectilium  Serv.),  has  become  established 
in  the  southern  United  States  and  to  some  extent  in  the  North.  These  species 
may  be  recognized  by  the  aid  of  the  following  key  (adults)  : 

1.  Tegmina  in  male  not  reaching  the  end  of  the  abdomen,  covering  only 

about  two-thirds  of  it;  in  female  tegmina  represented  by  small  pads. 
Length  about  i  inch.  Almost  black  without  any  markings  (Fig.  67)  . . 

Blatta  orientalis 

Tegmina  in  both  males  and  females  reaching  or  extending  beyond  the 
end  of  abdomen;  if  not  covering  the  abdomen  then  marked  with  two 
light  bands,  one  at  base  of  wings  and  another  about  one-third  of  length 
from  base 2 

2.  Length  of  insect  rarely  more  than  %  inch 3 

Length  more  than  i  inch 4 

3.  Color  uniformly  pale  brown  with  two  parallel  dark  stripes  on  pro- 

notum  (Fig.  67)  Blatella  germanica 

Color  uniformly  dark  brown  with  two  pale  bands  near  the  base  of  teg- 
mina, one  at  base  and  another  a  third  of  the  length  from  the  base 

Supella  supellectilium 

4.  Thorax  yellow  with  two  large  blotches  of  chestnut  brown;  tegmina  lack- 

ing a  yellow  submarginal  stripe  along  basal  third.  Length  from  i%  to 

2  inches  (Fig.  67) Periplaneta  amencana 

Thorax  yellow,  with  base  and  one  or  two  central  spots  black;  tegmina 
with  a  pale-yellow,  submarginal  stripe  along  basal  third.  Length  about 
i  inch  Periplaneta  australasiae 

The  German  roach  or  croton  bug  (Blatella  germanica)  is  the  smallest  house- 
hold roach.  It  is  world-wide  in  distribution  and  the  commonest  species  in 


ORTHOPTERA  AND  HEMIPTERA 


rig.  67.  Cockroaches.  (/)  Blatta  oncntalis  (female),  (j)  Blatta  oricntahs  (male),  (j) 
Blattella  germanica  (female).  (4)  Preiplaneta  americana  (male).  (From  British  Museum, 
after  Laing.) 

homes,  restaurants,  hotels,  and  similar  places.  The  developmental  period  from 
the  hatching  of  the  eggs  to  the  adult  stage  is  from  three  to  four  months;  the 
adults  live  from  six  to  ten  months.  The  American  roach  (Periplaneta  ameri- 
cana) requires  nearly  a  year  to  complete  its  developmental  cycle  though  this  var- 
ies greatly.  The  adults  live  a  year  or  more.  This  roach  is  common  on  board  ships 
and  in  warehouses,  sugar  refineries,  meat-packing  establishments,  zoological 


168  MEDICAL  ENTOMOLOGY 

gardens,  city  dumps,  and  similar  places.  In  America  it  commonly  invades  our 
homes.  Gould  and  Deay  (1940)  describe  migrations  of  this  species  from  place 
to  place  in  the  North.  In  the  South  along  the  Gulf  coast  it  is  common  in  palm 
trees,  and  nightly  flights  take  place.  It  is  known  to  be  able  to  make  long  flights. 
The  oriental  roach  (Blatta  orientalis)  is  almost  jet  black  in  color  and  is 
primarily  a  house  pest,  preferring  dark,  warm  basements,  kitchens,  and  similar 
places.  If  food  and  favorable  conditions  of  warmth  and  moisture  are  available, 
the  developmental  cycle  from  egg  to  adult  requires  nearly  a  year.  The  Aus- 
tralian roach  (Periplaneta  australasiae)  is  somewhat  smaller  than  the  Ameri- 
can roach  and  is  easily  recognized  by  the  pale-yellow  streak  on  the  tegmina. 
It  is  said  not  to  be  common  in  houses  but  prefers  greenhouses  and  such  places. 
In  addition,  many  other  roaches  occur  in  tropical  and  subtropical  regions, 
and  some  of  these  may  be  distributed  by  commerce  and  adapt  themselves  to 
our  homes  and  warm  buildings.  In  recent  years  the  brown-banded  roach 
(Supella  supellectilium  Serv.)  has  spread  into  many  parts  of  the  United  States 
and  has  become  a  house  pest,  especially  in  cities.  It  occurs  as  far  north  as 
Massachusetts,  Wisconsin,  South  Dakota,  and  central  California.  Unlike 
other  roaches  this  gregarious  species  prefers  cupboards,  shelves  in  closets, 
behind  pictures  and  moldings,  desks,  and  such  places. 

COCKROACHES  AND  HUMAN  DISEASE:  On  account  of  their  om- 
nivorous and  filthy  habits  and  close  association  with  man,  cockroaches  have 
long  been  suspected  of  disseminating  pathogenic  organisms.  As  they  feed 
on  man's  food  and  his  fecal  wastes,  roam  at  will  through  his  household,  and 
invade  food  shops,  bakeries,  meat-packing  and  food-storage  plants,  and  similar 
places,  it  would  be  surprising  if  they  did  not  distribute  all  kinds  of  organisms 
that  are  capable  of  surviving  passage  through  their  intestines  or  carriage  on 
their  bodies.  Although  various  authorities  have  shown  that  viable  bacteria 
can  pass  through  the  intestines  of  roaches  and  be  carried  on  their  bodies,  yet 
nothing  has  been  established  of  the  importance  of  roaches  in  disease  dissemina- 
tion. Barber  (1914)  demonstrated  that  viable  organisms  of  cholera  pass  through 
the  intestines,  but  there  are  many  other  methods  of  dissemination  of  much 
greater  significance.  This  is  true  also  of  such  diseases  as  tuberculosis,  typhoid, 
leprosy,  and  dysenteries,  the  etiological  agents  of  which  can  survive  passage 
through  their  intestines  and  be  carried  on  their  bodies.  Such  protozoan  cysts 
as  those  of  Endamoeba  histolytica,  Endamoeba  colt,  and  Giardia  intestinalis, 
survive  and  this  may  be  of  some  significance.  Investigations  in  Peru  demon- 
strated that  7  per  cent  of  the  house-infecting  cockroaches  were  carriers  of 
viable  cysts  of  Endamoeba  histolytica  (Schneider  and  Schields).  As  intermedi- 
ate hosts  of  helminths  they  are  of  considerable  importance.  All  four  common 


ORTHOPTERA  AND  HEMIPTERA  169 

cockroaches  serve  as  intermediate  hosts  of  the  roundworms,  Gonglyonema  pul- 
chrum  (which  is  reported  from  rats  and  man),  G.  neoplasticum  (which  pro- 
duces a  carcinoma  in  the  stomach  of  rats;  not  reported  from  man),  G.  orientate 
(a  parasite  of  rats),  and  the  acanthocephalid,  Monilijormis  monilijormis  (a 
parasite  of  rats  and  occasionally  of  man) . 

CONTROL  OF  COCKROACHES :  As  roaches  are  lovers  of  filth  and  prefer 
darkened  corners,  cracks,  and  out-of-the-way  places,  the  first  procedure  is  a 
thorough  clean-up  and  the  destruction  of  all  wastes.  When  this  has  been  done, 
an  application  of  sodium  fluoride  is  one  of  the  most  effective  methods  of  con- 
trol. Commercial  sodium  fluoride,  either  pure  or  diluted  with  a  carrier  such  as 
ground  gypsum,  chalk,  or  other  diluent  to  give  50  per  cent  sodium  fluoride, 
dusted  or  blown  into  all  cracks,  crevices,  and  runways  and  about  sinks,  tables, 
shelves,  or  other  hiding  places  will  quickly  kill  roaches.  As  the  roaches  run 
over  the  powder,  it  sticks  to  their  bodies  and  in  cleaning  themselves  they 
ingest  the  material,  which  proves  a  prompt  poison.  Of  course,  sodium  fluoride 
should  not  be  used  near  food  or  where  there  is  a  possibility  of  contaminating 
food.  One  treatment  should  be  allowed  to  remain  for  several  days,  and  the 
application  is  best  made  during  the  evening  hours.  The  exposed  dust  should 
be  cleaned  up,  but  all  in  the  cracks,  crevices,  and  similar  places  should  be 
allowed  to  remain  since  the  powder  remains  effective  almost  indefinitely.  This 
treatment  should  be  repeated  if  all  roaches  are  not  destroyed  by  the  first 
application. 

Phosphorous  pastes  are  purchasable  and  are  quite  effective.  Smear  the  paste 
inside  cardboard  rolls  and  place  them  in  the  runways  of  the  roaches.  The 
pastes  are  particularly  valuable  in  very  damp  climates  because  powders  may 
harden  and  not  be  effective. 

DDT  as  a  powder  or  as  a  spray  is  very  effective  if  properly  and  thoroughly 
applied.  The  dust  should  contain  from  10  to  20  per  cent  of  DDT,  and  all 
cracks,  crevices,  areas  behind  objects,  baseboards,  and  runways  should  be 
liberally  covered  with  the  mixture.  The  visible  dust  may  be  removed  in  a 
few  days  but  not  that  from  the  cracks  and  crevices.  The  application  should 
be  repeated  in  about  five  or  six  weeks  to  kill  any  young  that  may  have  hatched 
from  eggs.  A  5  per  cent  DDT  oil  spray  is  also  effective  but  usually  slower  in 
action.  Spray  thoroughly  and  heavily  with  5  per  cent  DDT  in  refined  kero- 
sene oil  or  as  a  5  per  cent  emulsion.  Carefully  apply  to  all  cracks,  crevices, 
under  draining  boards,  about  sinks,  on  all  runways,  behind  baseboards,  and 
in  similar  places.  Avoid  contaminating  food.  The  residual  effect  of  the  DDT 
will  act  for  a  considerable  time. 

Probably  the  most  effective  insecticide  for  the  control  of  cockroaches  is  the 


170  MEDICAL  ENTOMOLOGY 

recently  developed  commercial  product  known  as  chlordane.  This  material 
can  be  obtained  from  dealers,  and  full  directions  for  its  use  will  be  found 
on  the  containers.  Normally  a  2  per  cent  solution  is  most  effective.  A  com- 
bination spray  containing  5  per  cent  DDT  and  2  per  cent  chlordane  is  now 
on  the  market  and  is  used  as  directed  by  the  manufacturers. 

THE  ORDER  HEMIPTERA:  SUBORDER  HETEROPTERA 

The  True  Bugs 

IThe  order  Hemiptera  consists  of  two  suborders,  the  Heteroptera  and 
Homoptera.  The  Homoptera  contain  no  insects  known  to  be  of  medical 
importance.  They  are  all  primarily  vegetarians  sucking  the  sap  from  plants 


Fig.  68.  Some  hemelytra  of  the  Heteroptera.  (A)  Diagrammatic  illustration  of 
hemelytra  with  the  areas  labeled.  (B)  Hemelytron  of  an  Anthocoridae  (Triphleps).  (C) 
Hemelytron  of  a  Coreidae  (Leptocoris) .  (D)  Hemelytron  of  a  Miridae  (Poecilocapsus). 
c,  cuneus;  cl,  clavus;  co,  corium;  e,  emboliurn;  m,  membrane.  (Modified  from  Comstock.) 

of  all  kinds.lThe  Heteroptera  are  also  mainly  vegetarians,  but  a  few  families 
are  predaceous,  sucking  the  blood  of  other  insects  or  attacking  animals  in- 
cluding man.  Their  chief  characteristics  are  the  possession  of  two  pairs  of 
wings  (except  the  wingless  forms) :  the  fore  wings  are  thickened  at  their 
bases  (Fig.  68),  and  the  membranous  extremities  overlap  on  the  back;  the 
hind  wings  are  thin  with  few  veins.  The  mouth  parts  consist  of  a  jointed  beak 
(Fig.  46)  which  contains  the  piercing  and  sucking  organs;  the  beak  arises 
from  the  front  part  of  the  head.  The  metamorphosis  is  graduafl 

The  true  bugs  are  abundant  in  species  and  individuals.  Many  species  are 
very  injurious  to  plants  on  account  of  their  habit  of  piercing  and  sucking  the 
sap;  some  are  beneficial  as  they  feed  on  noxious  insects.  t)nly  two  families 
contain  species  that  are  known  to  be  injurious  to  man  as  bloodsuckers  and 
as  carriers  and  intermediate  hosts  of  pathogenic  organism^  Other  families 
have  certain  species  that  may  occasionally  attack  manjand  a  list  of  these  is 


ORTHOPTERA  AND  HEMIPTERA  171 

given  at  the  end  of  this  chapter.  The  following  brief  key  will  aid  in  recogniz- 
ing the  principal  families  that  may  be  noxious  to  man: 

KEY  TO  THE  FAMILIES  OF  THE  HETEROPTERA 
RECORDED  AS  BITING  MAN 

1.  Antennae  shorter  than  the  head  and  concealed  in  depressions  on  the 

underside  of  the  head  beneath  the  eyes.  All  forms  aquatic 2 

Antennae  as  long  as  or  longer  than  the  head  and  fully  exposed 3 

2.  Hind  tarsi  consisting  of  two  segments,  the  last  bearing  two  distinct  claws; 

large  flattened  bugs.  Fore  wing  with  the  membranous  portion  with 

distinct  veins.  (The  giant  water  bugs;  Fig.  75)  Belostomatidae 

Hind  tarsi  consisting  of  three  segments,  the  first  very  short  and  indis- 
tinct; tarsal  claws  setiform;  head  deeply  inserted  into  prothorax.  (Boat- 
shaped  bugs,  the  back  swimmers)  Notonectidae 

3.  Beak  composed  of  three  segments 4 

Beak  composed  of  four  sfgments     6 

4.  Beak  stout,  lying  in  j  cross-striated  groove  hut  not  reaching  the  middle 

coxae;  ocelli,  when  present,  placed  distinctly  behina  ihe  eyes  or  behind 

a  transverse  dtfpression.  (The  assassin  bugs)  Reduyiidae 

Beak  elongate^  extending  to  middle  coxae  and  groove  not  cross-striateu',' 

ocelli,  wh:,n  prcsent,  not  placed  as  above 5 

5-  Ocelli  absent.  fore  wings  reduced,  without  membrane  or  vestigial.  (The 

bedbug*)  Cimicidae 

Ocelli  Present;  fore  wings  usually  well  developed;  embolium  present 

(Fi?.  68).  Membrane  of  fore  wings  veinless  or  with  indistinct  veins. 

(*\owcr  bugs)    Anthocoridae 

6.  Front  jegs  fittecl  for  seizing  prey;  fore  tibiae  and  usually  the  front  femora 

armed  with  stout  spines  which  interlock Nabidae 

Froiit  legs  fitted  for  walking,  normal 7 

7.  Fror,t  wjng  with  a  V-shaped  portion  (cuneus)  at  the  apex  of  the  hard- 

ef    d  base  of  the  wing  (Fig.  68) ;  membrane  with  one  or  two  closed 

>.  (Leaf  bugs)  Miridae 

wings  not  as  described  above 8 

absent.  (Cotton  stainers)  Pyrochorridae 

present;  no  transverse  depression  in  front  of  the  ocelli 9 

rane  of  fore  wing  with  five  simple  veins  arising  from  its  base. 

nch  bugs)   Lygaeidae 

ane  of  fore  wing  with  many,  usually  anastomosing,  veins  arising 
transverse  basal  vein.  (Squash  bugs)  Corcidae 


1^2  MEDICAL  ENTOMOLOGY 

THE  FAMILY  CIMICIDAE— THE  BEDBUGS 

This  is  the  well-known  bedbug  family.  The  most  distinctive  features  are 
the  depressed  bodies,  fitting  them  for  creeping  into  cracks  and  crevices;  the 
absence  of  wings  except  for  the  small  padlike  elytra  (remnants  of  the  fore 
wings,  Fig.  69);  the  beak  is  segmented  and  lies  in  a  groove  on  the  ventral 
surface  of  the  head  and  thorax;  the  head  is  short  and  broad  and  bears  a  pair 
of  prominent  compound  eyes;  the  ocelli  are  absent;  the  antennae  are  four 
segmented  | 

|  The  family  contains  three  principal  genera,  Cimex,  Oeciacus,  and  Haema- 
tosiphom  (Some  five  or  six  others  have  been  described.)  The  entire  family  con- 
tains not  over  35  well-defined  species. 

j|  THE  GEN,JJS  CIMEX:  Several  species  have  been  described  as  belonging 
to  this  genus.AOnly  two  of  them  are  consistent  parasites  of  man.  The  common 
bedbug,  Cimex  lectularius  Linn.,  and  the  tropical  bedbug,  Cimex  hemipterus 
Fabr.,  are  persistent  invaders  of  huma^  nabitJ^ons  anc^  ^ve  primarily  on 
human  blood|though  they  readiVy  teed  on  rabbits,  m\ce»  wmte  rats>  and  fowls. 
\Cimex  lectularius  Linn,  (the  bedbug,  wall  louse,  maV°gany  flat>  etc-)  is  tne 
common  bedbug  (Fig.  69)  of  the  temperate  zones.  Its  bodv  is  flattened  dorso- 
ver^aiiy  and  is  well  adapted  to  its  mode  of  life.  The  adult  mtasures  4  to  5  mm- 
in  length  and  about  3  mm.  in  width.  It  is  reddish  brown  in  color-  The  head 
is  broad  and  flat  and  fits  rather  neatly  into  the  deeply  concave  ailterior  Part  of 
the  prothorax.  The  antennae  are  four-segmented;  the  last  two  segments  are 
elongate  and  much  thinner  than  the  precedindJThe  eyes  are  pro,minent  ancl 
deeply  pigmented.  The  beak  is  three-segmented  and  lies  in  a  groove  reacn,ing 
the  middle  coxaej  The  mouth  parts  are  fully  explained  on_pages  130-^  J^ne 
thorax  appears  as  a  single  segment,  the  large  anterior  part  being  the  protn°rax- 
Dorsally  the  mesothorax  may  be  distinguished  by  the  attachment  of  the  i ecluced 
fore  wings.  The  metathorax  lies  beneath  and  behind  the  fore  win^Sl  The 
abdomen  consists  of  eight  visible  segments;  the  terminal  ones  (the  ni« uh  and 
tenth)  are  modified  for  sexual  purposes|((Fig.  70) . 

A  great  many  insects  possess  a  distinctive  odor,  and  this  is  especi         true 
of  bedbugs,  the  "bedbuggy"  odor  of  infested  dwellings  being  very          ''ecl 
and  easily  recognized  by  anyone  familiar  with  it.  (The  odor  of  the  1 
produced  by  special  stink  glands,  which,  in  the  nymphs,  open  on  t 
surface  of  the  abdomen  and  on  the  ventral  side  of  the  last  thoracic  f 

of  the  adult.  Puri  has  described  these  glands  in  great  detail;  he  cons  r 

function  to  be  defensive  and  sexual, 
The  males  and  females  of  bedbugs  can  be  recognized  easily.  Ir  ie 


ORTHOPTERA  AND  HEMIPTERA  173 

(Fig.  70)  the  abdomen  gradually  narrows  from  the  third  segment  to  the 
rather  pointed  tip,  where  are  located  the  genitalia.  In  the  female  the  abdomen 
does  not  narrow  so  much,  and  the  tip  is  broadly  rounded  (Fig.  70).  The 
external  genital  organ  of  the  male  consists  of  a  sclerotized,  sharply  pointed 
aedeagus,  which  arises  from  the  interior  of  the  ninth  segment.  It  is  directed 
to  the  left  side  (seen  from  the  dorsal  surface).  When  not  extended  it  lies  in 
a  groove  of  the  segment.  The  aedeagus  is  grooved  on  its  inner  face,  and  at  its 


I'ig.  (>().  The  bedbug,  Cimcx  lectularms.  Female.   (Courtesy  De- 
partment of  Agriculture,  Division  of  Entomology,  Canada.) 

base  lies  the  penis.  The  anal  opening  is  in  front  of  the  tenth  segment,  which 
appears  to  surround  i Jjln  the  female  the  external  genital  organs  consist  of  the 
genital  opening  surrounded  and  supported  by  sclerotized  plates  or  gona- 
pophyses.  On  the  ventral  surface  of  the  abdomen  of  the  female  there  is  a 
rather  sharp  and  deep  depression  or  slit  on  the  posterior  margin  of  the  fourth  1 
segment,  about  halfway  between  the  median  line  and  the  margin.  This  leads 
to  a  peculiar  organ  known  as  the  organ  of  Berlese.  It  is  through  this  organ 
that  the  male  fertilizes  the  female,  the  sperm  being  introduced  into  it  and 
not  into  the  genital  opening  at  the  time  of  copulation/  In  mating  the  male 

1  In  reality  the  fifth  segment  as  the  first  visible  abdominal  segment  is  the  second. 


174  MEDICAL  ENTOMOLOGY 

inserts  the  aedeagus  into  the  slit,  the  penis  passes  down  the  groove  and  ejects 
the  sperm  into  the  opening  of  the  organ  of  Berlese. 

1  BIONOMICS:  Bedbugs  are  primarily  parasites  of  man,  though  they  feed  on 
fowls,  mice,  and  white  rats  and  are  frequently  serious  pests  of  rabbits  in  rab- 


Fig.  jo.  Clmcx  lectulanus.  Upper:  Tip  of  abdomen  of  male  (ventral  view) .  Lower:  Tip 
of  the  abdomen  of  female  (ventral  view).  AD,  aedeagus;  AO,  anal  opening;  CA,  cauda; 
G,  groove  in  aedeagus  along  which  penis  moves  in  act  of  copulation;  GO,  genital  opening 
guarded  by  two  pairs  of  gonopophyses;  GP  VIII  and  GP  IX,  gonopophyses  of  the  eighth 
and  ninth  segments;  GR,  groove  in  the  ninth  segment  for  the  reception  of  the  aedeagus; 
P,  hairy  process  of  the  ninth  segment;  SP,  spiracle;  VIII,  IX,  X,  eighth,  ninth,  and  tenth 
segments. 

bitries.  They  are  nocturnal  in  their  feeding  habits  and  during  the  day  hide 
in  convenient  cracks,  crevices,  or  other  hiding  places  in  sleeping  rooms;  under 
loosened  wallpaper  and  moldings;  in  cracks  in  the  flooring,  old  wooden 
bedsteads,  and  the  creases  and  folds  of  mattresses;  under  bedding;  and  in 
places  where  mice,  white  rats,  or  rabbits  are  reared.  As  they  are  gregarious, 


ORTHOPTERA  AND  HEMIPTERA  175 

large  numbers  may  be  found  in  infested  rooms.  Mating  takes  place  at  irregular 
intervals,  and  the  eggs  are  laid  in  the  hiding  places  of  the  bugs.  The  egg  (Fig. 
71)  when  laid  is  pearly  white,  gradually  changing  to  a  yellowish  white.  It 
measures  1.02  mm.  in  length  by  0.44  mm.  in  width.  The  shell  is  distinctly 
reticulated  and  has  a  cap  or  lid  that  is  pushed  off  when  the  nymph  emerges. 
Each  female  is  capable  of  laying  from  75  to  200  eggs.  Titschack  records  a  single 
female  that  laid  541  eggs.  The  eggs  are  not  all  laid  at  one  time  but  usually  in 
ones,  twos,  threes,  or  small  batches  each  day.  Cragg  records  that  a  caged 
female,  when  supplied  with  food  and  its  mate,  laid  174  eggs  in  105  days  and 


Fig.  ji  (Icjt).  The  egg  of  the  bedbug,  Cimex  lectularius. 

Fig.  72  (right).  A  large  reduviid  bug  from  South  America,  Pangstrongylus  (Triatoma) 
me  gist  us. 

only  ceased  laying  at  the  approach  of  cold  weather.  The  adults  live  a  long  time, 
at  least  six  or  seven  months  to  a  year.  They  can  also  withstand  long  periods 
of  starvation,  especially  during  cold  weather  when  they  become  inactive. 
Adults  have  been  kept  alive  without  food  for  a  year,  and  the  nymphs  can 
withstand  varying  periods  of  starvation,  70  days  or  moreJ 

JLiFE  HISTORY:  The  egg  hatches  in  from  six  to  seven  days  (longer  if  the 
temperature  is  low) .  The  first-stage  nymph  is  very  active  and  closely  resembles 
the  adult  except  in  size.  It  will  feed  rather  promptly.  After  feeding,  the  nymph 
hides  in  some  convenient  place  to  digest  its  blood  meal  and  prepares  to  molt 
to  the  second  instar.  There  are  five  molts,  and  the  nymph  takes,  practically 
always,  only  a  single  blood  meal  between  molts.  According  to  Jones,  the 
development  period  from  egg  to  adult  is  a  little  over  30  days  (the  experi- 


176  MEDICAL  ENTOMOLOGY 

ments  were  carried  out  at  a  temperature  of  27°  C.  and  a  relative  humidity  of 
75  per  cent;  the  nymphs  were  fed  to  repletion  between  each  molt).  He  found 
the  length  of  the  instars  to  be:  first  instar,  5  days;  second,  4.5  days;  third,  4.2 
days;  fourth,  4.6  days;  and  the  fifth,  6  days.  The  nymphal  life  may  be  greatly 
prolonged  by  low  temperatures,  lack  of  food,  or  other  factors  affecting  de- 
velopment. Both  the  nymphs  and  adults  feed  rapidly,  repletion  being  reached 
in  5  to  10  minutes.  Jones  has  shown  the  amount  of  blood  required  from  the 
first  instar  to  adult  is  only  0.0156  grams  for  the  males  and  and  0.0209  grams 
for  the  females.  The  number  of  generations  per  year  varies  greatly,  being 
largely  dependent  on  food  supply,  temperature,  and  humidity.  During  the 
winter  season  the  bedbug  is  usually  inactive  but  will  feed  and  breed  under 
favorable  conditions.  In  warm  climates  it  probably  breeds  throughout  the  year,/ 
and  the  number  of  generations  is  probably  five  or  six  or  more.  In  colder  cli- 
mates there  are  said  to  be  three  or  four  generations,  but  no  definite  number 
can  be  given  as  the  reproductive  and  developmental  rates  are  so  dependent 
on  food  supply  and  warmth. 

1  DISTRIBUTION:  This  bedbug  is  cosmopolitan,  being  found  throughout  the 
temperate  regions  of  the  world  and  probably  in  many  tropical  areas,  though 
another  species,  Cimex  hemipterus,  is  the  abundant  tropical  bedbug;*1 

idmex  hemipterus  (Fabr.)  is  the  so-called  "tropical  bedbug"  and  is  widely 
distributed  throughout  the  tropical  and  subtropical  regions,  especially  Asia. 
It  closely  resembles  the  ordinary  bedbug  but  can  be  distinguished  by  the 
lateral  margins  of  the  prothorax  being  rounded  and  the  concave  depression 
for  the  reception  of  the  head  being  shallower.  The  habits  of  the  nymphs  and 
adults  are  very  similar  to  those  of  the  common  bedbug.  The  life  history  is 
almost  identical.  Dunn  found  that  the  time  from  the  hatching  of  the  egg  to 
the  adult  varied  from  30  to  40  days.  The  most  interesting  feature  was  that 
each  nymphal  stage  required  from  two  to  four  meals  instead  of  one.  The 
adults  live  from  six  to  .eight  months.  Each  female  is  capable  of  laying  from 
about  100  to  439  eggs.  4 

)''  . 

DISPERSAL!  Bedbugs  are  gregarious  and  remain  close  to  their  food  supply; 

their  dispersal  is  mainly  through  man's  activities.  As  bedbugs  readily  hide 
in  clothing  and  the  eggs  are  laid  in  all  their  places  .of  concealment,  their  dis- 
tribution is  largely  dependent  on  man's  carrying  them  from  place  to  place 
with  his  household  goods  or  his  clothing.  A  single  impregnated  female  ac- 
cidentally introduced  into  a  household  will  soon  produce  a  good-sized  colony .| 
Furthermore,  bedbugs  are  active  migrants  and  will  readily  pass  from  one 
person  to  anotherlThis  has  been  seen  again  and  again  in  crowded  railway 


ORTHOPTERA  AND  HEMIPTERA  177 

cars,  boats,  buses,  and  other  public  conveyances.  In  crowded  city  houses,  apart- 
ments, and  tenements  they  will  travel  along  the  water  and  heating  pipes, 
especially  if  their  food  supply  has  been  removed.  Bedbugs  are  frequently  re- 
ported as  very  abundant  in  movie  houses.  Again  bedbugs  are  capable  of  with- 
standing long  periods  of  starvation,  especially  during  cold  weather,  and 
unfrequented  houses,  as  summer  hotels,  cottages,  and  similar  places  may 
remain  infested  from  year  to  year.  As  they  are  known  to  feed  on  birds,  white 
rats,  rabbits,  and  mice  (Patton  and  Evans  record  that  they  fed  them  on  rats, 
cats,  dogs,  monkeys,  rabbits,  guinea  pigs,  and  a  calf),  they  can  probably 
obtain  food  to  tide  them  over  periods  of  man's  absence.  MacGregor  mentions 
an  interesting  case  of  dispersal.  In  the  East  African  campaign  of  World  War  I 
bedbugs  invaded  the  cork  lining  of  the  helmets  of  the  soldiers.  As  the  helmets 
were  piled  together  at  night,  all  soon  became  infested  and  the  soldiers  com- 
plained of  bugs  attacking  their  heads. 

if  BEDBUGS  AND  HUMAN  WELFARE:  Bedbugs  affect  man  in  two 
ways:  (i)  by  their  bites  and  bloodsucking  propensities;  (2)  by  the  possibility 
of  their  carrying  disease-producing  organisms  or  acting  as  hosts  of  parasites 
in  some  phase  of  the  latter's  developmental  cycle.1 

I  BITES:  Many  persons  suffer  severely  from  the  bites  of  bedbugs;  many  do 
not  suffer  at  all  or  even  know  when  they  are  bitten;  and  others  appear  immune 
to  their  attacks.  Puri  (1924)  has  shown  that  the  salivary  secretion  is  the  cause 
of  the  irritation  and  that  it  contains  a  rather  strong  anticoagulin.' Children 
suffer  most  from  bedbug  bites.  In  susceptible  persons  there  is  severe  irritation, 
hardened  wheals  may  develop  at  the  sites  of  the  bites,  and  secondary  infection 
may  follow.  In  severe  cases  there  may  be  a  marked  nervous  reaction  accom- 
panied by  digestive  disorders.  Stiles  records  a  case  diagnosed  as  neurasthenia 
and  treated  as  such;  an  examination  of  the  patient's  room  showed  an  abun- 
dance of  bedbugs;  after  fumigation  a  pint  of  bedbugs  was  collected  and  the 
patient  promptly  recovered.  Unfortunately  there  is  very  little  data  on  the 
effect  of  continued  attacks  of  bedbugs.  When  abundant  they  cause  loss  of 
sleep,  loss  of  blood,  nervous  reactions,  digestive  disturbances  and,  in  general, 
reduce  the  vitality  so  that  people,  especially  children,  are  more  susceptible  to 
prevalent  diseases. 

|  BEDBUGs^Np  DISEASE  :  Owing  to  the  close  relation  of  man  and  bedbugs  it  has 
long  been  thought  such  bloodthirsty  parasites  must,  in  some  way,  be  asso- 
ciated with  disease  transmission.  Though  intensive  research  has  been  carried 
out  along  this  line,  nearly  all  the  results  are  either  negative  or  inconclusive. 
Bedbugs  have  been  shown  experimentally  capable  of  transmitting  bubonic 


178  MEDICAL  ENTOMOLOGY 

plague  (Pasteurdla  pestis)  even  as  long  as  48  days  after  an  infective  meal,  yet 
there  is  no  evidence  that  they  play  a  part  in  human  transmission.  Many 
experiments  with  pathogenic  organisms  such  as  those  of  leprosy,  tuber- 
culosis, and  typhoid  fevers  have  given  negative  results.  Extensive  experiments 
with  bedbugs  and  the  causative  agents  of  kala  azar  (Leishmania  donovani) 
and  of  Oriental  sore  (Leishmania  tropicd)  have  resulted  in  failure  to  transmit 
even  under  the  most  favorable  conditions.  In  the  case  of  relapsing  fevers 
(Spirochaeta  spp.)  all  experiments  have  failed,  though  the  bedbugs  can  be 
infected  and  the  spirochctes  remain  alive  in  the  gut  or  the  coelomic  fluid  for 
considerable  periods.  No  transmission  took  place  by  the  bites  of  infected 
bedbugs  though  transmission  of  the  spirochetes  was  effected  by  crushing 
infected  bedbugs  on  the  scarified  skin  of  experimental  animals  or  by  injecting 
the  hemolymph  of  such  bedbugs.  When  relapsing  fevers  become  epidemic 
in  the  presence  of  numerous  bedbugs,  human  infection  may  occur,  though 
usually  the  ordinary  human  lice  (Pedicitlus  humanus)  are  present  and  are 
effective  transmitters.  Brumpt  has  shown  that  the  bedbug  (both  species)  can 
be  infected  with  Trypanosoma  crnzi  (causative  agent  of  Chagas*  disease),  and 
he  caused  animal  infection  through  the  feccs.  This  work  was  confirmed  by 
Mayer  and  da  Rocha-Lima.  No  infection  occurred  by  the  bites  of  infected 
bedbugs.  Francis  has  shown  that  Cimex  lectularius  can  transmit  tularemia 
(Bacterium  tularense)  from  mouse  to  mouse  by  its  bites  up  to  71  days  after 
the  bugs  had  their  infective  meal.  Mice  also  contracted  the  disease  by  eating 
bedbugs  that  had  been  infected  65  to  100  days  previously.  He  also  showed 
that  the  feces  of  infected  bugs  contained  the  virulent  organisms  of  tularemia  at 
all  times  to  at  least  250  days  after  the  date  of  infection. 

OTHER  SPECIES  OF  CIMICIDAE:  Leptocimex  boueti  (Brumpt)  oc- 
curs in  French  West  Africa  and  is  quite  widely  distributed.  According  to 
Joyeux  (1913)  its  life  history  is  very  similar  to  that  of  the  ordinary  bedbug 
as  it  readily  feeds  on  man.  It  may  be  recognized  by  its  very  long  legs  and  much 
narrower  body.  Cimex  pilosellus  Horvath  and  C.  pipistrelli  (Jenyns)  are 
common  parasites  of  bats,  the  former  in  America  and  the  latter  in  Europe. 
These  bugs  will  invade  sleeping  rooms  and  attack  man  when  their  normal 
hosts  are  driven  away.  In  the  genus  Oeciacus  the  body  is  clothed  with  long 
hairs  and  the  last  two  segments  of  the  antennae  are  but  slightly  thinner  than 
the  preceding  ones,  and  about  equal  in  length;  the  front  margin  of  the  pro- 
notum  is  shallowly  concave.  O.  vicarius  Horvath,  the  common  bedbug  of 
swallows  in  North  America,  will  invade  dwellings  when  their  nests  are  located 
on  houses  and  infested  with  this  bug;  O.  hirundinis  (Jenyns),  the  barn-swallow 
bug  of  Europe,  will  also  attack  man  and  its  bite  is  said  to  be  severe.  Cimexopsis 


ORTHOPTERA  AND  HEMIPTERA  179 

nyctalis  List  has  been  recorded  in  Nebraska  as  attacking  man,  though  its 
normal  hosts  are  thought  to  be  chimney  swifts  (Chaetura).  Hacmatosiphon 
inodora  (Duges)  is  a  large  bug  that  normally  infests  poultry  houses  in  the 
southwestern  United  States  and  Mexico;  it  has  also  been  reported  from  Flor- 
ida. It  sometimes  invades  houses  and  frequently  becomes  a  serious  pest.  Its 
bite  is  severe. 

CONTROL  OF  BEDBUGS  During  World  War  II  an  almost  perfect 
method  for  the  control  of  bedbugs  was  developed.  By  the  proper  use  of  DDT 
bedbugs  can  not  only  be  controlled  but  eliminated  from  all  their  breeding 
places.  Depending  on  the  place  to  be  treated  either  a  5  per  cent  DDT  solution 
or  emulsion  can  be  used.  Where  it  is  not  feasible  to  use  a  spray,  a  10  per  cent 
dust  may  be  employed,  though  it  does  not  give  such  satisfactory  results. 

The  5  per  cent  DDT  spray  (solution  or  emulsion)  can  be  applied  by  a  small 
hand  sprayer,  by  a  knapsack  type  sprayer,  or  by  power  equipment.  In  treat- 
ing an  infested  room  or  building  it  is  essential  first  to  clean  the  place.  Then 
spray  all  beds,  especially  the  mattresses,  bedsprings,  joints,  and  corners,  thor- 
oughly with  a  wet  spray,  not  a  mist.  Then  treat  all  cracks,  crevices,  especially 
behind  baseboards,  picture  frames,  loose  wallpaper,  and,  if  the  place  is  badly 
infested,  every  part  of  the  room.  The  spray  will  kill  all  bedbugs  it  covers,  but 
many  may  not  be  reached.  However,  the  residual  DDT  on  the  walls,  bedding, 
and  beds  will  kill  all  bugs  that  come  in  contact  with  it.  Experiments  have 
shown  that  the  residual  action  is  very  lasting,  at  least  a  year.  If  spraying  cannot 
be  used,  dust  with  a  10  per  cent  DDT  powder  on  mattresses,  bedding,  cracks, 
crevices,  and  similar  places.  The  bedbugs  will  be  killed  by  walking  over  the 
powder.  By  the  proper  and  timely  application  of  any  of  these  methods  bedbugs 
can  be  eliminated. 

Sulphur  fumigation  is  also  effective  but  it  involves  much  more  labor  and 
trouble.  When  sulphur  is  used,  the  rooms  must  be  prepared  by  the  closure 
of  all  cracks,  crevices  (as  around  doors  and  windows),  keyholes,  and  other 
openings  by  pasting  over  them  strips  of  heavy  brown  paper.  (Thin  flour  paste 
or  merely  water  will  serve  for  temporary  attachment;  soak  the  brown  paper 
in  water  till  saturated;  then  apply  it  and  it  will  stick  for  several  hours.)  All 
metallic  objects  and  fabrics  that  might  be  bleached  by  the  sulphur  fumes 
should  be  removed.  Metals  that  cannot  be  removed  should  be  coated  with 
vaseline.  Large  openings  such  as  fireplaces  must  be  closed.  The  sulphur  is 
used  at  the  rate  of  four  pounds  to  1000  cubic  feet  of  space.  The  sulphur  should 
be  burned  in  a  large  iron  pan  or  pot  placed  on  bricks  in  a  galvanized  tub 
containing  some  water.  This  will  take  care  of  any  spilling  and  prevent  injury 
to  the  floors.  Pour  a  small  amount  of  denatured  alcohol  on  the  sulphur  (aboul 


i8o  MEDICAL  ENTOMOLOGY 

a  cup  to  four  pounds  of  the  sulphur)  and  ignite  the  alcohol.  Several  such  out- 
fits may  be  placed  in  different  parts  of  the  place  to  be  fumigated.  All  should 
be  started  at  about  the  same  time.  Then  the  building  should  remain  closed 
for  several  hours,  at  least  four  or  five.  Sulphur  candles  may  also  be  used,  but 
great  care  should  be  employed  to  avoid  danger  from  fire  and  enough  candles 
must  be  burned. 

Fumigation  with  hydrocyanic  acid  gas  is  a  very  effective  control  method 
but  should  be  undertaken  only  by  responsible  personnel.  The  building  to  be 
fumigated  should  be  prepared  as  for  sulphur  fumigation.  The  necessary 
ingredients  are  sodium  or  potassium  cyanide  (these  can  be  obtained  in  the 
form  of  small  eggs,  each  weighing  about  one  ounce),  a  commercial  grade  of 
sulphuric  acid,  and  water.  It  requires  at  least  one  ounce  of  the  cyanide  for 
each  100  cubic  feet  of  space.  The  mixture  is  prepared  as  follows: 

Sodium  cyanide  (95  to  97  per  cent  purity)    i  ounce 

Sulphuric   acid    i  ]X>   fluid  ounces 

Water   2  fluid  ounces 

In  the  fumigation  of  a  building,  the  cubic  contents  must  be  calculated,  the 
distribution  of  the  fumigation  pots  should  be  designated,  and  the  amount 
of  ingredients  for  each  pot  determined.  The  equipment  should  consist  of  five- 
to  eight-gallon  earthenware  crocks.  The  crocks  should  be  placed  on  thick  folds 
of  paper  to  avoid  injury  from  splashing.  In  each  of  the  crocks  place  the  deter- 
mined amount  of  water  and  then  add  the  sulphuric  acid,  pouring  slowly  (never 
the  reverse  process).  Beside  each  crock  place  the  determined  amount  of  sodium 
cyanide,  preferably  in  a  thin  paper  bag.  When  all  is  in  readiness  start  at  the 
top  floor  and  drop  the  cyanide  into  the  jars,  passing  to  the  floors  below  as 
rapidly  as  possible.  The  gas  is  very  light  and  is  given  off  very  rapidly.  The 
house  or  building  should  be  kept  closed  for  at  least  12  hours  and  then  aired 
by  opening  the  windows  and  doors  from  the  outside.  Keep  open  for  another 
6  to  12  hours  before  entering  unless  gas  masks  are  used.  Fumigation  with 
hydrocyanic  acid  gas  should  be  undertaken  only  by  trained  persons  and  gas 
masks  should  be  used. 

Another  fumigation  method  is  the  use  of  thin  discs  impregnated  with 
liquid  hydrocyanic  acid.  These  discs  (Zyklon  discoids)  are  conveniently 
packed,  and  full  directions  for  their  use  are  furnished.  Gas  masks  should  be 
employed  when  using  such  discs.  Pyrethrum  aerosol  bombs  are  also  effective 
and  they  are  nonpoisonous. 

In  most  of  our  states  and  particularly  our  large  cities  the  Boards  of  Health 
have  strict  regulations  governing  the  use  of  poisonous  gases.  Such  rules  and 
regulations  should  be  carefully  followed  before  attempting  any  fumigation. 


ORTHOPTERA  AND  HEMIPTERA  181 

THE  FAMILY  REDUVIIDAE-THE  ASSASSIN  BUGS 

The  Reduviiclae  is  a  large  family  of  predaceous  bugs  that  suck  the  blood 
and  lymph  of  their  prey.  At  least  400(3  species  are  known.  They  feed  mainly 
on  other  insects  and  on  each  other.  However,  certain  groups  attack  man  and 
some  of  these  are  important  vectors  of  human  and  other  animal  diseases.  Their 
bites  are  frequently  severe  and  often  difficult  to  heal.  The  assassin  bugs  are 
rather  elongate,  active,  large  insects.  The  beak  is  stout,  three-segmented,  and 
capable  of  inflicting  a  painful  wound.  The  head  is  freely  movable  and  more  or 
less  elongate,  and  the  eyes  are  conspicuous.  The  ocelli  arc  prominent  when 
present  and  the  antenna  is  four-segmented.  The  family  is  divided  into  a  large 
number  of  subfamilies  and  numerous  genera.  Although  nineteen  subfamilies 
are  listed  by  Usinger  (1943),  only  about  three  contain  genera  that  are  at  present 
known  to  plague  man,  and  some  of  these  are  not  of  great  importance.  The 
following  brief  summary  may  aid  in  recognizing  these  subfamilies: 

KEY  TO  THE  SUBFAMILIES  HAVING  SPECIES  THAT 
ATTACK  MAN 2 

1.  Beak  divided  into  3  segments  and  fits  into  a  cross-striated  groove;  stout, 

short,  not  reaching  the  middle  coxae;  ocelli,  when  present,  placed  dis- 
tinctly behind  the  eyes  or  behind  a  transverse  depression 

Family  Reduviidae  2 

2.  Wing  membrane  with  one  or  more  closed  cells;  front  coxae  not  greatly 

elongated,  usually  less  than  twice  as  long  as  broad  and  not  extending 
beyond  apex  of  head   3 

3.  Pronotum  constricted  behind  the  middle;  ocelli  present.  Subfamily  Pira- 

tinae  (Genera  Melanolestes,  Rasahus,  and  others;  Fig.  74) 
Pronotum  constricted  at  or  near  the  middle 4 

4.  Ocelli  present  and  located  behind  the  compound  eyes;  second  antennal 

segment  not  subdivided 5 

5.  Head  rarely  constricted  behind  the  eyes.  Elongate;  ocelli  located  on 

oblique  elevations  or  tubercles  at  posterolatcral  angles  of  the  long,  cylin- 
drical head;  dorsal  abdominal  glands  absent  ....  Subfamily  Triatomi- 
nae  (Here  belong  Psamntolestes,  Rhodnius,  Eratyrus,  Panstrongylus, 
Triatoma,  and  others) 
Head  transversely  constructed  behind  the  eyes;  eyes  not  stalked;  antennae 


2  Keys  to  the  genera  and  species  of  Triatominae  will  be  found  by  consulting  the  ref- 
erences at  the  end  of  the  chapter. 


1 82  MEDICAL  ENTOMOLOGY 

not  inserted  on  long,  oblique  tubercles;  dorsal  scent  glands  present 

(Reduvius,  Spiniger,  and  others)   Subfamily  Reduviinae 

The  Subfamily  Triatominae 

The  known  members  of  this  subfamily  as  at  present  restricted  feed  exclu- 
sively by  sucking  the  blood  of  vertebrates.  Though  widely  distributed,  the 
great  majority  of  the  species  are  predominantly  American.  A  few  species 
occur  in  the  Oriental  and  African  regions,  and  Triatoma  rubrojasciata  (De 
Geer)  is  tropicopolitan.  Usinger  (1944)  recognizes  9  genera  and  40  species 
and  subspecies  from  North  and  Central  America,  Mexico,  Panama,  and  the 
West  Indies.  Costa  Lima  (1940)  recognizes  9  genera  and  44  species  from  Brazil 
and  neighboring  countries.  Neiva  and  Lent  (1941)  list  14  genera  and  89  species 
from  the  world.  The  study  of  this  subfamily  is  of  great  importance  in  the 
Americas  since  the  discovery  by  Chagas  (1909)  that  a  certain  species,  Pan- 
strongylus  megistus,  is  the  intermediate  host  of  a  disease  (Chagas'  disease) 
caused  by  Trypanosoma  cnizi.  Since  then  a  large  number  of  species  have  been 
shown  to  harbor  the  trypanosome  and  many  of  them  to  transmit  the  disease. 
Only  a  few  of  the  species  can  be  discussed  here  with  a  list  of  the  more  im- 
portant vectors  of  the  disease  and  their  known  distribution. 

Panstrongylus  megistus  (Burm.)  was  the  first  species  shown  by  Chagas  to 
be  the  natural  vector  of  the  disease  that  bears  his  name.  The  species  is  widely 
distributed  in  Brazil,  British  Guiana,  and  Paraguay.  This  bug  is  primarily 
domestic  and  hides  in  cracks,  crevices,  or  any  available  cover  during  the  day. 
At  night  it  comes  out  to  feed  and  its  bite  is  not  recorded  as  severe.  The  adults 
measure  from  30  to  32  mm.  in  length.  They  are  black,  with  regularly  arranged 
red  markings  on  the  prothorax,  wings,  and  abdomen  (Fig.  72).  They  are 
strong  fliers  and  readily  migrate  from  house  to  house.  The  female  lays  her 
eggs  in  batches  (8  to  12  in  a  batch)  in  the  cracks,  crevices,  and  holes  in  the 
floors  and  walls.  Each  female  lays  from  160  to  220  or  more  eggs.  The  eggs 
hatch  in  from  8  to  30  days.  The  nymphs  feed  on  humans  at  night.  There  are 
five  nymphal  stages  and  each  nymphal  stage  requires  a  number  of  blood  meals. 
The  entire  life  cycle  from  egg  to  adult  varies  from  260  to  300  days. 

Triatoma  rubrojasciata  (De  Geer)  is  widely  distributed  in  the  Oriental  re- 
gions, parts  of  the  Ethiopian  region,  neotropical  region,  the  West  Indies,  Cen- 
tral America,  and  Florida  in  the  United  States.  It  is  quite  domestic  in  its  habits 
and  its  bite  is  rather  severe.  Its  life  history  is  very  similar  to  that  of  the  preceding 
species.  Patton  and  Cragg  found,  under  experimental  conditions,  that  the 
life  cycle  from  egg  to  adult  required  from  four  and  one-half  to  five  months. 

Triatoma  sanguisuga  (Le  Conte)  is  the  big  bedbug  or  conenose  (Fig.  73) 


ORTHOPTERA  AND  HEMIPTRRA  183 

of  the  south  and  western  United  States,  extending  north  to  Pennsylvania  and 
west  to  Kansas,  Texas,  and  Mexico;  it  is  reported  from  Panama.  It  infests 
poultry  houses  and  the  adults  invade  human  habitations.  The  adult  is  1 8  to 
20  mm.  in  length,  flattened,  and  dark  brown  in  color  with  pinkish  or  reddish- 


Fig.  75.  The  bloodsucking  conenose,  Triatoma  sanguisuga.  (a)  and 
Nymphal  stages.  (<:)  Adult,  (d)  Lateral  view  of  adult  to  show  long  beak. 
(After  Marlatt.) 

orange  areas  on  the  abdomen,  on  the  tips  and  bases  of  the  hemelytra,  and  along 
the  anterior  and  lateral  margins  of  the  pronotum.  Recently  several  subspecies 
have  been  described  but  on  rather  minor  characters. 

The  life  histories  of  a  number  of  species  have  been  fully  elucidated  in  recent 
years:  Euratyrus  cuspidatus  Stal  and  Panstrongylus  geniculatus  (Latr.)  by 
Hase  (1932);  Rhodnius  prolixus  Stal  by  Buxton  (1930);  Triatoma  dimidiata 
'(Latr.)  by  Campas  (1923);  and  Paratnatoma  hirsuta  Barber  (two-year  life 


184  MEDICAL  ENTOMOLOGY 

cycle),  T.  rubida  uhleri  (Neiva),  one-year  life-cycle,  T.  lecticularius  occulata 
(Neiva),  one-year  life  cycle,  T.  gerstaecferi  (Stal),  one-year  life  cycle,  T. 
longipes  Barber  (two-year  life  cycle),  and  T.  protracta  (Uhler),  one-year  life 
cycle,  all  by  Usinger  (1944). 

.  TRIATOMINAE  AND  THEIR  RELATION  TO  DISEASE:  BITES: 
The  bites  by  a  number  of  species  are  known  to  be  severe  but  others  cause  little 
if  any  reaction.  Numerous  records  of  severe  reaction  from  their  bites  are 
known.  However,  Wood  (1942)  tested  eight  common  species  (Triatoma  pro- 
tracta woodi,  T.  longipes,  T.  gerstaecl^cri,  T.  lecticularius,  T.  sanguisuga,  T. 
rubida,  and  Paratriatoma  hirsuta)  without  any  ill  effects  except  a  tickling 
sensation. 

DISEASE:  The  only  disease  so  far  definitely  associated  with  these  bugs  is 
Chagas'  disease  caused  by  Trypanosoma  cruzi.  In  1909  Chagas  announced  suc- 
cessful transmission  of  an  unknown  disease  in  Brazil  by  Panstrongylus  megis- 
tus  caused  by  a  trypanosome  and  described  by  him  as  Trypanosoma  cruzi. 
This  disease  was  later  differentiated  as  a  specific  entity  and  bears  the  name  of 
Chagas'  disease.  The  disease  is  widespread  and  occurs  from  Argentina  through 
much  of  South  America,  Panama,  Central  America,  and  Mexico.  The  disease 
is  characterized  by  fever,  swelling  of  the  eyelids  and  face,  enlargement  of 
various  lymphatic  glands,  and  destruction  of  the  cardiac  muscles  of  the  heart, 
the  cells  of  the  spleen  and  the  brain,  and  endothelial  tissue  cells  generally 
throughout  the  body.  The  disease  appears  in  two  forms,  acute  and  chronic. 
In  the  acute  stage  death  may  occur  in  two  to  four  weeks,  In  the  chronic  state, 
mostly  in  adults,  the  disease  runs  a  varied  course.  At  present  there  seems  to  be 
no  adequate  treatment. 

TRANSMISSION:  The  various  species  (see  Table  6)  obtain  the  trypanosomes 
from  the  infected  reservoir  hosts  when  taking  blood.  In  the  bug  the  trypano- 
somes develop  only  in  the  lumen  of  the  intestinal  tract.  First  they  develop 
into  crithidial  forms  in  the  stomach;  migrating  posteriorly  they  transform  to 
smaller  forms  and  give  rise  to  the  metacylic  (infective)  trypanosomes.  These 
are  discharged  in  the  feces,  and  infection  in  man  takes  place  when  the  feces 
are  deposited  at  the  time  the  bug  is  feeding  or  soon  after.  They  gain  access  to 
the  body  through  abrasions  of  the  skin  (by  scratching  or  otherwise)  or  the 
mucous  membranes  of  the  mouth,  conjunctiva  of  the  eyes,  or  other  moist  mem- 
branes. Other  animals  become  infected  in  a  similar  manner  or  by  eating  in- 
fected bugs.  The  life  cycle  in  the  bug  requires  6  to  15  days,  and  once  infected 
the  bug  remains  capable  of  transmitting  the  disease  for  a  long  time,  at  least 
one  or  two  years  according  to  some  authorities.  In  man  the  incubation  period 


ORTHOPTERA  AND  HEMIPTERA  185 

is  10  to  12  days  and  the  trypanosomes  may  be  found  in  the  blood  during  this 
period.  Later  they  disappear  from  the  blood  and  are  found  in  the  Leishmania 
form  in  the  cardiac  muscles  and  in  cells  of  the  spleen,  liver,  brain,  and  most  of 
the  tissues.  From  time  to  time  the  trypanosome  form  appears  in  the  circulating 
blood  and  man  may  serve  as  a  reservoir  for  the  bugs.  As  this  disease  is  wide- 
spread, it  has  become  of  great  importance.  Though  the  trypanosome  is  present 
in  many  triatome  bugs  in  the  United  States,  no  human  case  has  been  discovered. 
However,  these  infected  bugs  do  bite  humans  and  Packchanian  (1943)  has 
produced  a  typical  infection  in  a  human  being  with  trypanosomes  from  Texas 
(crushed  infected  Triatoma  heidemanni).  He  also  infected  monkeys  (Macacus 
rhesus}  and  deer  mice  (two  species).  He  recovered  the  trypanosomes  from  all 
cases  and  cultured  them.  Despite  this  experimental  evidence  no  human  cases 
of  Chagas'  disease  have  been  isolated  in  the  United  States.  Undoubtedly  some 
must  occur,  but  they  have  not  been  diagnosed  as  such. 

Table  6.  Tritomc  bugs  found  naturally  infected  and  their  distribution. 


Species 

Triatoma  barberi  Usinger  Mexico 

Triatoma  brasilicnsis  Neiva  Brazil 

Triatoma  chagasi  Brumpt  and  Gomes  Brazil 

Triatoma  dclpontei  Romana  and  Abalos  Argentina 


Distribution 


18. 
19. 


Triatoma  dimidiata  (Latr.) 

Triatoma  gcrstaecl^cri  (Stal) 
Triatoma  hcgncri  Maz/.otti 
Triatoma  injestans  (Klug.) 

Triatoma  JecticuJarius  (Stal) 

(hcidcnmanni  Neiva) 
Triatoma  longipcs  Barber 
Triatoma  phyllosoma  (Burm.) 

var.  longipennis  (Usinger) 
var.  pallidipennis  (Stal) 
var.  picturata  (Usinger) 
Triatoma  platcnsis  Neiva 
Triatoma  protracta  (Uhler) 

var.  woodi  (Usinger) 
Triatoma  rubida  uhlcri  (Neiva) 
Triatoma  rubrojasciata  (de  Geer) 
Triatoma  rubrovaria  (Blanchard) 
Triatoma  sangnisuga  (Lee.) 

var.  ambigua  (Neiva) 
var.  indictiva   (Neiva) 

Triatoma  spinolai  Porter 
Triatoma  vitticcps  (Stal) 


Mexico,  Central   America,   Panama, 

Venezuela,  Peru 

Mexico,  U.S.A. 

Mexico 

Brazil  south  to  Argentina, 

Chile,  Peru 

U.S.A.  (Texas) 

U.S.A.    (Arizona) 

Mexico 

Mexico 

Mexico 

Mexico 

Argentina 

California,  New  Mexico,  Arizona,  Texas 

Texas 

U.S.A.  (California  and  Arizona) 

Tropical  regions  of  world 

Argentina,  Chile,  Uruguay 

U.S.A.,  Mexico,  Panama 

U.S.A. 

U.S.A.  (Arizona,  New  Mexico, 

Texas)  and  Mexico 

Chile 

Brazil 


i86 


MEDICAL  ENTOMOLOGY 


20.  Dipetalogaster  maxim  us  Usinger 

21.  Eutriatoma  maculata  (Erichson) 

22.  L-Mtriatoma  nigromaculata  (Stal) 

23.  Eutriatoma  oswaldol  (Neiva  and  Pinto) 

24.  Eutriatoma  patagonica  del  Pontc 

25.  Eratyrus  cuspidatus  Stal 

26.  Ncotriatoma  circummaculata   (Stal) 

27.  Panstrongylus  geniculatus  (Latr.) 

28.  Panstrongylus  megistus  (Burm.) 

29.  Panstrongylus  rujotuberculatus 

(Champion) 

30.  Rhodnius  brumpti  Pinto 

31.  Rhodnius  domcsticus  Neiva  and  Pinto 

32.  Rhodnius  pallesccns  Stal 

33.  Rhodnius  prolixus  Stal 

34.  Cavernicola  pilosa  Barber 

35.  Psammolestes  arthuri  (Pinto) 


Mexico  (cape  region  of 

Baja  California) 

Brazil  north  to  Venezuela 

Venezuela 

Argentina 

Argentina 

Panama,  Colombia, 

Venezuela 

Argentina,  Uruguay 

Argentina  north  to 

Venezuela,  Panama 

Paraguay,  Brazil  north  to 

Venezuela 

Panama,  Ecuador,  Venezuela 

Brazil 

Brazil 

Panama 

Brazil  north  to  Colombia, 

San  Salvador,  Mexico 

Brazil 

Venezuela 


In  addition  to  the  list  of  species  given  above,  a  long  series  of  other  Hemip- 
tera  are  recorded  as  capable  of  acting  as  vectors  of  Chagas'  disease.  Some  of 
these  are  dm  ex  lectularhis,  C.  hemipterus,  C.  stadleri,  Leptocimex  boutei, 
Oeciactts  hirundinis,  and  Haematosiphon  inodora.  The  following  ticks  are 
also  indicated:  Ornithodoros  moubata,  O.  talaje,  O.  venezuelensis  (rudis), 
O.  conlceps,  O.  lahorensis,  O.  nicollei,  Amblyomma  cajennense,  and  Rhipi- 
cephalus  sanguineus. 

The  vectors  of  Chagas'  disease  do  not,  in  most  cases,  normally  live  in  human 
dwellings  but  feed  on  a  great  variety  of  wild  animals.  Many  of  these  animals 
serve  as  a  reservoir  for  the  trypanosome  since  none  of  the  bugs  are  known  to 
transmit  Trypanosoma  cruzi  to  their  offspring.  Furthermore  many  of  the 
triatomes  feed  on  more  or  less  specific  hosts,  and  a  large  number  of  these  hosts 
have  been  examined  and  found  to  harbor  Trypanosoma  cruzi  either  in  their 
blood  or  as  Leishmania  forms  within  tissue  cells.  From  these  hosts  the  triatome 
bugs  obtain  their  infection  and  may  transmit  it  to  man.  Some  of  the  known 
reservoirs  are:  armadillos  (8  or  more  species)  in  Brazil,  Panama,  Mexico,  and 
Texas  (mostly  Dasypus  novemcinctus  and  its  varieties) ;  bats  in  Panama  and 
California  (Artibeus  jamaicensis,  Carollia  perspicullata  azteca,  Desmodus 
rotundas  murinus,  Glossophaga  soricina  leachi,  Phyllostomus  hastatus  pana- 
mensis,  and  Uroderma  bilobatum  in  Panama;  Antrozous  pallidus  pact  feus  in 
California) ;  cats  and  dogs  in  Brazil,  Panama,  Guatemala,  and  Mexico;  house 
mice  in  the  United  States;  opossums  in  Honduras,  Panama,  and  the  United 


ORTHOPTERA  AND  HEMIPTERA  187 

States;  wood  rats  (Neotoma  species)  in  Mexico,  California,  Texas,  and  other 
states.  In  addition,  many  animals  are  easily  infected  experimentally  as  mice 
(10  or  more  species),  monkeys,  rats,  rabbits,  dogs,  and  many  others. 

OTHER  REDUVIID  BUGS  THAT  SUCK  BLOOD;  A  large  number  of 
reduviid  bugs  have  been  recorded  as  occasionally  attacking  man,  and  their 
bites  frequently  prove  very  annoying.  The  following  are  the  most  important 
species  : 

Rhodnius  prolixus  Stal  is  a  domestic  bug  prevalent  in  parts  of  South  America 
and  San  Salvador.  It  readily  bites  man  and  is  the  natural  vector  of  Chagas' 
disease  in  Venezuela. 

Reduvius  personatus  Linn.  (Fig.  74)  has  received  a  rather  bad  reputation 
for  attacking  people  and  has  been  called  the  "kissing  bug."  This  bug  is  com- 
monly found  in  houses  in  many  parts  of  the  world.  The  nymphs  are  covered 
with  a  sticky  substance  to  which  dirt,  dust,  and  floss  adhere.  They  are  said  to 
feed  on  bedbugs,  flies,  etc.,  and  the  nymphs  are  frequently  called  the  "masked 
bedbug  hunters."  The  adult  is  almost  coal  black,  very  active,  and  attracted  to 
lights.  It  measures  about  20  mm.  in  length.  When  handled  roughly  as  in 
attempts  to  remove  them  when  they  alight  on  the  face  or  hands,  they  bite 
readily  and  fiercely.  Herms  quotes  reporting  physicians  as  stating,  "In  a  few 
minutes  after  the  bite  the  patient  develops  nausea,  palpitation  of  the  heart, 
rapid  breathing,  rapid  pulse,  followed  by  profuse  urticaria  all  over  the  body." 
Like  all  other  insect  bites,  the  effects  depend  largely  on  the  susceptibility  of 
the  individual. 

Rasahus  biguttatus  Say  (Fig.  74)  and  Rasahus  thoracicus  Stal  are  known 
as  the  "Corsairs."  The  former  occurs  in  the  southern  states  and  the  West  Indies, 
the  latter  in  the  western  part  of  the  United  States  and  probably  Mexico.  The 
bites  of  these  bugs  are  quite  severe  and  have  been  confused  with  spider  bites. 

Arilus  cristatus  Linn,  the  "wheel  bug,"  so-called  because  of  the  cogwheellike 
crest  on  the  prothorax,  is  normally  predaceous  on  other  insects.  Hall  (1924) 
records  a  young  girl  being  bitten  twice  by  this  bug  on  her  little  finger.  This 
was  followed  by  severe  pain,  and  growths  resembling  papillomas  developed 
at  the  sites  of  the  bites.  The  growths  persisted  for  months,  and  the  finger 
remained  warmer  than  the  others  for  over  a  year.  The  bug  is  distributed  in 
North  America  from  New  Jersey  southward. 

Mdanolestes  picipes  H.  S.  (Fig.  74)  is  an  almost  coal-black  bug  found  com- 
monly throughout  North  America.  There  are  well-authenticated  records  of 
its  biting  man.  It  is  found  under  stones,  logs,  moss,  etc.,  and  will  bite  if  handled 
roughly.  It  is  also  reported  as  flying  into  houses,  being  attracted  by  the  lights, 
and  biting.  Its  bite  is  said  to  be  severe. 


1 88  MEDICAL  ENTOMOLOGY 

Mdanolestes  abdominalis  H.S.  is  also  recorded  as  biting  man.  It  is  widely 
distributed  in  North  America  and  has  about  the  same  habits  as  M.  picipes. 

Many  other  species  of  Hemiptera  have  been  reported  as  occasionally  attack- 
ing man.  The  reports  of  the  effects  of  their  bites  vary  so  widely  that  no  general 
statement  regarding  them  can  be  made.  It  should  be  borne  in  mind  that  the 
bite  of  a  bug  is  always  more  or  less  complicated  not  only  by  the  susceptibility 
of  the  individual  to  protein  substances  (fluid  from  the  salivary  or  poison 


Fig.  74.  Three  reduviids  that  commonly  bite  man.  (A)  Reduvius  personatus  (the  so- 
called  "kissing  bug").  (B)  Me/anolestes  picipes.  (C)  Rasahns  biguttatus. 

glands  of  the  bug)  but  also  to  any  contamination  present  on  the  proboscis. 
The  latter  feature  seems  often  to  be  overlooked  when  the  ill  effects  of  a  bite 
are  described.  The  following  incomplete  list  will  give  some  idea  of  the  numer- 
ous observations  recording  the  bloodsucking  habits  of  bugs  : 

Nabidae 
Nabis  capsijormis  Germar.  Cosmopolitan  in  the  tropics. 

Anthocoridae 

Anthocoris  musculus  Say.  Biting  hop  pickers. 
Anthocoris  sylvestris  Linn.  Europe. 
Anthocoris  \ingi  Brumpt.  Sudan. 
Anthocoris  insidiosus  Say.  North  America.  Several  records  of  this  bug  biting 

man. 

Cardiastethus  elegans  Uhl.  Panama.  From  bats. 
Lyctocoris  campestris  Fabr.  Europe  and  North  America. 

Pyrochorridae 

Clcrada  apicicornis  Sign.  Widely  distributed  in  the  tropics. 
Dysdcrcus  superstitiosus  Fabr.  Africa. 


ORTHOPTERA  AND  HEMIPTERA 

Lygaeidae 

Leptodemus  minutus  Jakovleff .  Mediterranean  region. 
Geocoris  hconi  Puton  and  G.  scutdlaris  Puton.  North  Africa. 

Miridae  (Capsidae) 

Plagionathus  obscurus  Uhler.  North  America. 
Lygus  pratensis  Linn.  North  America,  Europe,  Asia. 

Notonectidae 

These  are  aquatic  insects,  the  so- 
called  "back  swimmers."  Practically 
all  the  larger  species  will  bite  if  handled 
roughly.  The  bite  is  quite  severe. 

Belostomatidae 

These  are  the  giant  water  bugs  (Fig. 
75)  and  include  the  largest  of  our 
Hcmiptera;  some  species  exceed  three 
inches  in  length.  They  are  found  com- 
monly in  stagnant,  water.  The  adults 
are  strongly  attracted  to  lights  and 
hence  have  been  called  "electric  light 
bugs."  Their  bites,  especially  those  of 
the  larger  species,  are  quite  severe.  The 
author  has  recorded  the  death  of  a 
good-sized  woodpecker,  killed  by 
Lethocerus  americanus;  the  bug  had 
inserted  its  beak  deep  into  the  back 
part  of  the  skull. 


Fig.  75.  A  giant  water 
bug,   Ecnacus   griseus. 


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tularius)   in  the  transmission  of  relapsing  fever.     Warsaw,   1930.     In  Polish. 

Rev.  Appl.  Ent.  (B):  18,  1930. 
Davis,  D.  J.,  et  al.     Triatoma  sanguisiiga  (Leconte)  and  T.  ambigua  Neiva.  as 

natural  carriers  of  Trypanosoma  cruzi  in  Texas.     U.S.  Pub.  tilth.  Repts.,  58: 

353-354'  1943- 
Dove,  W.  E.     Summary  of  DDT  experiments  on  insects  that  afTect  man  and 

animals.     Soap,  14:  8-14,  1946. 
Dunn,  L.  H.     The  tropical  bedbug  in  relation  to  the  transmission  of  relapsing 

fever  of  Panama.    Amer.  Jl.  Trop.  Med.,  3:  345-350,  1923. 
.     Life-history  of  the  tropical  bedbug  (Cimex  rotundatus}  in  Panama.     Ibid., 

4:  77~83>  J924- 
Fracker,  S.  B.    A  systematic  outline  of  the  Reduviidae  of  North  America.    Iowa 

Acad.  Sci.,  19:  217-252,  1914. 
Francis,  Edward.    The  transmission  of  tularaemia  by  the  bedbug,  Cimex  lee- 

tularius.    U.S.  Pub.  Hlth.  Serv.,  Hyg.  Lab.,  Bull.  130:  24-37,  1922. 
Girault,  A.  A.     Preliminary  studies  on  the  biology  of  the  bedbug,  Cimex  lee- 

tularius  Linn.     Jl.  Econ.  Biology,  5:  88-91,  1910;  7:  163-188,  1912. 
Hall,  M.  C.    Lesions  due  to  the  bite  of  the  wheelbug,  Arilus  cristatus  (Hemiptera, 

Reduviidae).    Arch.  Internal  Med.,  33:  513-515,  1924. 


I92  MEDICAL  ENTOMOLOGY 

Horvath,  G.    Revision  of  the  American  Cimicidae.    Ann.   Hist.  Nat.  Hung. 

(Budapest),  10:  257-262,  1912. 
Howard,  L.  O.    The  insects  to  which  the  name  "kissing  bugs"  became  applied 

during  the  summer  of  1899.    U.S.  Dept.  Agr.,  Div.  Ent.  Bull.  22:  24-30,  1900. 
Hussey,  R.  F.     A  bibliographical  notice  on  the  reduviid  genus  Triatoma.     Psyche, 

29:  109-123,  1922. 
Jones,  R.  M.     Some  effects  of  temperature  and  humidity  as  factors  in  the  biology 

of  the  bedbug  (Cimex  lectularius  Linn.).     Ann.  Ent.  Soc.  Amer.,  23:  105-119, 

1930. 

Joyeux,  Charles.     Biologic  de  Clmex  boueti.     Arch.  Parasit.,  16:  140-146,  1913. 
Larrousse,    F.    Etude    biologique    et    systematique    du    genre    Rhodnius    Stal. 

(Hemiptera,  Reduviidae).     Ann.  Parasit.  Hum.  Comp.,  5,  63-89,  1927. 
McCiure,  H.  E.    The  bite  of  Melanolestes  picipes.    Ent.  News,  46:  138-139,  1935. 
Marlatt,  C.  L.    The  bedbug  and  cone-nose.    U.S.  Dept.  Agr.,  Div.  Ent.  Bull.  4: 

32-42,  1896. 
Mazzotti,  L.     Experimental  infection  of  Haematosiphon  inodorus  (Duges)  with 

Trypanosoma  cruzi  Chagas.     Bull.  Brokl.  Ent.  Soc.,  36:  67-68,  1941. 
Mellanby,  K.     A  comparison  of  the  physiology  of  the  two  species  of  bedbugs  which 

attack  man.     Parisitology,  27:  111-122,  1935. 
.     Fertilization  and  egg  production  in  the  bedbug,  Cimex  lectularius  L.     Ibid., 

31:  I93-I99.I939- 
.     The  physiology  and  activity  of  the  bedbug  (Cimex  lectularius)  in  a  natural 

infestation.     Ibid.,  pp.  200-211,  1939. 
Monteiro,  }.  L.     Sobre  a  transmissao  do  virus  da  febre  amarella  pelas  fezes  de 

presevejos  infectados.     Brasil-Meclico,  43:   1037-1040,   1929. 
Myers,  L.  E.     The  American  swallow  bug,  Oeciacus  vicarius  Horvath.     Parasitol- 

ogy,  20:  159-172,  1928. 
Myers,  }.  G.    Facultative  blood-sucking  in  phytophagous  Hemiptera.    Ibid.,  21: 

472-480,  1929. 
Neiva,  A.     Informaqois  sobrc  biolojia  do  Conor hinus  megistus  Burm.     Mem.  do 

Instit.  Oswaldo  Cruz,  2:  206-212,  1910. 

,  and  Lent,  H.     Sinopse  dos  triatomideos.     Rev.  Ent.,  12:  61-92,  1941. 

Pinto,  C.     Ensaio  monographico   dos   reduvideos   hematophagos   o   "barbeiros." 

Rio  de  Janeiro,  1925. 
Ponte,  E.  del.    Catalogo  descriptico  de  los  generos  Triatoma  Lap.,  Rhodnius  Stal., 

y  Eratyrus  Stal.     Rev.  Inst.  Bact.  (Buenos  Aires),  5:  855-937,  I93°- 
Puri,  I.  M.    Studies  on  the  anatomy  of  Cimex  lectularius.    i,  n.    Parasitology, 

16:  84-97,  269-278,  1924. 
Readio,  P.  A.    Studies  on  the  biology  of  the  Reduviidae  of  America,  north  of 

Mexico.    Univ.  Kansas  Sci.  Bull.,  17:  5-291,  1927. 
Richardson,  H.  H.    Studies  of  methyl  bromide,  chloropicrin,  certain  nitriles  and 

other  fumigants  against  the  bedbug.    Jl.  Econ.  Ent.,  36:  420-426,  1943. 


ORTHOPTERA  AND  HEMIPTERA  193 

Rivnay,  E.  Studies  in  tropisms  of  the  bedbug,  Cimex  Icctularius  L.  Parasitology, 
24:  121-136,  1932. 

Rosenholz,  H.  P.  Die  Rolle  der  Wanzen  in  der  Epidemiologie  des  Rikkfallfiebers. 
Central.  Bakt.  I  Abt.,  Orig.,  102:  179-213,  1927. 

.  Weitere  Untersuchungen  iiber  die  Rolle  der  Wanzen  in  der  Epidemiologie 

des  Ruckfallriebers.  Ibid.,  103:  348-353,  1927. 

Roubaud,  E.  Adaptation  spontanee  de  la  punaise  des  lit  (Cimex  lectularius)  en 
milieu  obscuricole,  aux  rongeurs  domestiques.  Bull.  Soc.  Path.  Exot.,  21:  224- 
226,  1928. 

Rozeboom,  L.  E.  Triatoma  dimidiatu  Latr.,  found  naturally  infected  with  Try- 
panosoma  cruzi  Chagas  in  Panama.  Amer.  Jl.  Trop.  Med.,  16:  481-484,  1936. 

Sherrard,  C.  Five  fuinigants  for  disinfestation  of  bedding  and  clothing;  a  com- 
parative study  of  insecticide  properties.  U.S.  Pub.  Hlth.  Repts.,  57:  753-759, 
1942. 

Torre-Bueno,  J.  L.     Biting  bugs.     Bull.  Brokl.  Ent.  Soc.,  26:  176,  1931. 

Usinger,  W.  E.  The  Triatominae  of  North  and  Central  America  and  the  West 
Indies  and  their  public  health  significance.  U.S.  Pub.  Hlth.  Serv.,  Bull.  288, 
1944. 

Wood,  F.  D.,  and  Wood,  S.  F.  On  the  distribution  of  Trypanosoma  in  the  south- 
western United  States.  Amer.  Jl.  Trop.  Med.,  18:  207-212,  1938. 

Yorke,  W.    Chagas'  disease:  a  critical  review.    Trop.  Dis.  Bull.,  34:  275-300, 


CHAPTER  VII 


The  Order  Anoplura: 
The  Biting  and  Sucking  Lice 


THE  order  Anoplura  contains  the  sucking  lice  and  the  biting  lice  of 
mammals  and  birds.  It  has  been  generally  held,  and  still  is  by  some,  that 
these  two  groups  constitute  distinct  orders,  the  Siphunctilata  (the  sucking 
lice) and  the  Mallophaga  (the  biting  lice).  However,  all  the  recent  morphologi- 
cal and  biological  evidence  seems  to  indicate  that  the  two  groups  arc  so  closely 
related  that  they  constitute  but  suborders  of  the  Anoplura. 

CHARACTERISTICS 

v  The  Anoplura  are  wingless  insects  that  live  permanently  as  ectoparasites  on 
mammals  and  birds,  upon  whose  hairs  (and  clothes  in  man)  or  feathers  they 
cement  their  eggs, The  antennae  are  short,  three-  to  five-jointed;  the  eyes  are 
reduced  or  absent;  the  ocelli  are  lacking.  The  mouth  parts  arc  strikingly  modi- 
fied cither  for  piercing  and  sucking  blood  (Siphunctilata)  or  for  feeding  on 
the  scales,  feathers,  scurf,  and  wastes  of  the  skin  (Mallophaga).  The  thoracic 
segments  are  more  or  less  fused;  the  legs  are  rather  short  and  fitted  for  cling- 
ing; the  tarsi  are  one-  or  two-jointed  and  terminate  in  one  or  two  claws.  The 
metamorphosis  is  incomplete. 

The  order  contains  two  suborders,  the  Siphunculata  and  the  Mallophaga. 
The  Mallophaga  are  not  known  to  transmit  disease. 

THE  SUBORDER  SIPHUNCULATA 

The  Siphunculata  or  sucking  lice  are  all  permanent  ectoparasites  of  mam- 
mals. The  mouth  parts  (Fig.  79)  are  highly  modified  and,  when  at  rest,  are 
retracted  within  a  divertictilum  that  opens  into  the  floor  of  the  pharynx  at 
its  anterior  end.  The  thoracic  segments  are  fused  (except  in  the  genus  Haema- 


THE  ORDER  ANOPLURA  195 

tomyzus) ;  the  tarsi  are  one-segmented  and  terminate  in  a  single  claw  which 
is  fitted  for  grasping  and  clinging  to  hairs. 

The  Siphunculata  is  a  very  small  group  (only  somewhat  over  200  species 
have  been  described  from  the  world),  consisting  exclusively  of  bloodsucking 
ectoparasites  of  mammals.  At  the  present  time  four  families  are  recognized.1 
Of  these  families  only  one,  the  Pediculidae,  contains  species  that  affect  man 
himself.  The  following  simple  key  will  aid  in -distinguishing  the  families: 

1.  Head  prolonged  as  a  narrow  tube;  tibiae  lacking  a  thumblike  process 

opposing  the  claw;  prothorax  distinct.  (Pflly  one  genus  and  one  species, 

Haematomyzuselephantis,on  elephants) Haematomyzidae 

Head  not  prolonged  as  a  tube;  tibiae  with  a  thumblike  process  (Fig.  78) 
opposing  the  claw;  prothorax  not  distinct  2 

2.  Body  distinctly  flattened;  sparsely  clothed  with  setae  or  spines  that  are 

arranged  in  more  or  less  definite  rows;  parasites  on  land  mammals  ....  3 
Body  rather  thick  and  stout;  clothed  with  stout,  heavy  spines,  and,  in 

some  cases,  scales.  Parasites  exclusively  on  marine  mammals 

Echinophtheriidae 

3.  Eyes  present,  pigmented;  head  not  retracted  into  the  thorax.  Parasites  of 

man,  monkeys,  and  apes Pediculidae 

Eyes  absent  or  vestigial;  head  rather  deeply  retracted  into  the  thorax. 
(This  family  contains  more  than  half  of  the  described  species  of  lice) 
Haematopinidae 

THE  FAMILY  PEDICULIDAE 

The  family  Pediculidae 2  has  been  divided  into  two  subfamilies,  the  Pedi- 
culinae  and  the  Pedicininae.  The  former  are  characterized  by  a  five-jointed 
antenna  and  occur  on  man,  monkeys,  and  apes;  the  latter  have  the  antenna 
three-jointed  (indistinctly  five-jointed)  and  are  found  on  monkey**. The 
entire  family  contains  some  four  genera  and  less  than  twenty  species  and 
varieties,  many  of  them  scarcely  deserving  the  designation  of  more  than  races. 
The  forms  known  from  man  are  Pediculus  humanus  Linn.,  of  which  there 
are  two  varieties  or  races — P.  humanus  var.  capitis  de  Geer  (the  head  louse) 
and  P.  humanus  var.  corporis  de  Geer  (the  body  louse) — and  Phthirus  pubis 
(Linn.)  (the  groin,  crab,  or  pubic  louse) . 

xEwing  (1929)  recognizes  six  families,  but  the  creation  of  two  new  families  for  a 
few  rather  aberrant  species  does  not  seem  warranted. 

2Ewing  (1929)  has  created  a  new  family  for  the  pubic  louse  (Phthirus  pubis  Leach); 
has  accepted  most  of  Fahrenholz's  genera  and  species;  and,  at  the  same  time,  has  de- 
scribed a  number  of  new  varieties. 


196  MEDICAL  ENTOMOLOGY 

THE  HEAD  LOUSE:  Pediculus  humanus  var.  capitis  de  Geer  (Fig.  76) 
is  the  head  louse  of  man.  This  variety  or  race  is  found  principally  on  the 
head,  living  amongst  the  hair,  on  which  it  cements  its  eggs.  It  is  found  most 
commonly  at  the  back  of  the  head  and  above  the  ears,  though  the  entire  scalp 
may  be  infested.  It  also  may  occur  on  the  eyebrows  and  the  hairy  parts  of  the 
body,  and  I  have  seen  the  eyelashes  of  an  infant  with  a  louse  deeply  embedded 
at  the  base  of  nearly  every  hair.  On  the  average  it  is  smaller  than  the  body 
louse.  The  female  measures  about  2.4  to  3.3  mm.  in  length  and  the  male  aver- 


Fig.  76.  The  human  louse,  Pediculus  humanus.  Male  at  left,  female  at  right.  (After 
Nuttall.) 

ages  about  2  mm.  It  is  grayish  in  color,  with  the  margins  of  the  abdomen 
somewhat  darker  or  almost  black.  In  the  male  (Figs.  76,80)  the  abdomen  is 
rounded  at  the  posterior  end  and  the  male  genital  organ,  the  aedeagus,  is  easily 
visible  and  usually  extruded;  in  the  female  the  terminal  portion  of  the  abdomen 
is  deeply  cleft  (Fig.  76). 

THE  HEAD:  In  this  louse  the  head  is  rounded  in  front  and  rather  bluntly 
pointed;  it  is  sharply  constricted  at  the  insertion  of  the  antennae,  then  bulges 
sharply  and  gradually  narrows  to  the  neck.  The  neck  is  short  but  permits  of 
considerable  movement.  The  antennae  are  short  and  five-jointed.  The  eyes 
are  prominent,  heavily  pigmented,  but  without  facets.  The  thorax  appears  as 


THE  ORDER  ANOPLURA  197 

a  consolidated  box  widening  posteriorly.  To  it  are  attached  the  legs,  and  there 
is  a  single  pair  of  spiracles  on  the  mesothoracic  segment.  The  abdomen  con- 
sists of  nine  segments,  seven  of  which  can  be  easily  counted.  The  margins  are 
festooned  and  chitinized  to  form  darkly  pigmented  plates  on  which  spiracles 
are  located.  There  are  six  pairs  of  abdominal  spiracles. 

THE  LEGS:  This  louse  has  stout  legs,  well  fitted  for  clasping  and  holding. 
The  coxa,  trochanter,  femur,  and  tibia  are  well  developed  (Fig.  77).  The 


finale  lav 


Fig.  77  (left).  Pediculus  humanus.  Male  with  parts  labeled.  (After  Nuttall,  Para- 
sitohgy.) 

Fig.  78  (right).  Pediculus  humanus.  Terminal  portion  of  first  left  leg  of  male.  C,  claw; 
L,  lamella;  S,  sensory  spines;  Sp,  chitinous  spine  of  thumb;  T,  tibial  thumb;  Tar,  tarsus; 
Tb,  tibia.  (After  Nuttall.) 

tarsus  consists  of  a  single  segment  and  bears  a  stout,  recurved  claw.  The  claw 
can  be  firmly  apposed  to  a  peculiar  extension  of  the  inner  distal  end  of  the 
tibia,  the  so-called  "tibial  thumb"  (Fig.  78).  The  tibial  thumb  bears  a  promi- 
nent spine,  and  by  apposing  the  claw  against  it  the  louse  can  attach  very  firmly 
to  hairs,  In  the  male  the, tibial  thumb  is  better  developed  than  in  the  female. 

MOUTH  PARTS  i  The  mouth  parts  (Fig.  79)  of  lice  are  extremely  complicated. 
They  have  been  fully  elucidated  by  Sikora  (1916),  Harrison  (1916),  Peacock 
(1918),  and  Florence  (1921),  but  these  workers  are  not  entirely  in  agreement. 
At  the  front  of  the  head  is  found  a  tubelike  projection,  the  haustellum.  It  is  ' 


198 


MEDICAL  ENTOMOLOGY 

Ph  B 


Fc 


Fig.  79.  The  mouth  parts  of  a  louse  (Pediculus  humanus).  (a)  Longitudinal  section  of 
the  head  to  show  the  relation  of  the  various  parts.  (&)  The  stylets  removed  and  shown 
more  in  detail,  (c)  The  tip  of  the  ventral  stabber  or  stylet  (greatly  enlarged),  (d)  Re- 
construction of  the  mouth  parts  near  the  anterior  end  to  show  passage  of  food  canal  be- 
tween the  dorsal  slabbers  or  stylets.  B,  brain;  D,  denticles  or  teeth;  DSt,  dorsal  stylet; 
F,  forks  of  the  stylets;  Fc,  food  channel;  Hphy,  hypopharynx;  Lm,  labru'm;  O,  esophagus; 
P,  proboscis;  Ph,  pharynx;  Pph,  prepharynx;  Sc,  ventral  sac  holding  the  stylets;  Sd,  sali- 
vary duct;  Sg,  subesophageal  ganglion;  VSt,  ventral  stylet.  In  d  the  arrows  indicate  the 
direction  of  the  passage  of  blood  and  salivary  fluid.  (Redrawn  and  modified  after  various 
authors.) 

convex  above  and  has  an  open  slit  on  the  ventral  side.  Within  the  haustellum 
are  minute  denticles  (15-16),  the  buccal  teeth.  When  the  louse  feeds,  these 
denticles  are  everted  and  they  serve  as  holdfasts  or  anchors  while  the  main 
mouth  parts  are  brought  into  play.  The  food  channel  extends  from  the 
haustellum  to  the  pharynx.  Ventral  of  the  food  channel  and  extending  to  the 
posterior  end  of  the  head  is  a  long,  narrow  diverticulum,  which  opens  an- 


THE  ORDER  ANOPLURA  199 

teriorly  near  the  buccal  plate.  Within  this  divcrticulum  lie  the  piercing  mouth 
parts.  They  consist  of  dorsal  and  ventral  piercers  or  stabbers.  The  dorsal 
stabber  is  a  single  stylet;  the  ventral  consists  of  two  stylets  closely  appressed  to 
each  other.  The  piercers  resemble  long-handled,  two-pronged  forks,  the  prongs 
being  posterior.  Between  the  dorsal  and  ventral  stabbers  lies  the  salivary  duct 
or  pipe.  All  these  structures  are  supplied  with  a  complicated  muscular  system 

(Fig- 79)- 

METHOD  OF  FEEDING:  When  ready  to  feed,  the  louse  applies  its  head  to  the 
skin.  By  muscular  action  the  haustellum  is  everted  and  the  teeth  are  anchored 
in  the  skin.  The  stabbers  are  brought  forward,  passing  into  the  skin  along  with 
the  salivary  duct.  Salivary  secretion  is  poured  into  the  wound  (Nuttall,  1917, 
has  shown  that  this  secretion  possesses  an  anticoagulin),  and  the  pumping 
pharynx  (Fig.  79)  pumps  the  blood  with  great  rapidity.  The  pumping  action 
and  the  passage  of  the  blood  into  the  pharynx  and  thence  to  the  esophagus  and 
intestine  can  be  seen  most  readily  in  freshly  molted  individuals.3 

THE  DIGESTIVE  SYSTEM:  The  digestive  system  (Fig.  80)  consists  of  a  simple 
thin-walled  esophagus  that  opens  into  a  rather  large  intestine.  The  mid- 
intestine  narrows  posteriorly  into  the  hind-intestine  at  the  point  of  entrance  of 
the  Malpighian  tubules.  The  hind-intestine  curves  forward,  then  backward 
to  the  anal  opening.  There  is  a  large  rectal  ampulla.  The  salivary  glands  consist 
of  two  pairs — a  pair  of  tubular  glands  and  a  pair  of  kidney-shaped  glands. 
Each  gland  has  a  duct  that  opens  independently  into  the  base  of  the  diverti- 
culum  containing  the  mouth  parts.  Here  they  connect  with  the  salivary  duct 
lying  between  the  stabbers. 

LIFE  CYCLE:  Adult  females  of  the  head  louse  begin  oviposition  in  from  24 
to  ^6  hours  after  emergence  from  the  last  nymphal  skin,  and  each  lays,  on"  an 
average,  six  to  seven  eggs  a  day.  The  total  number  of  eggs  produced  by  a  single 
female  docs  not  seem  to  be  definitely  known  though  Bacot  obtained  a  maxi- 
mum of  141  eggs;  Buxton  (1946)  reports  an  average  of  270  to  300  eggs  per 
female.  The  eggs  are  cemented  to  hairs  (Fig.  81  A)  and  are  practically 
always  deposited  with  the  cap  directed  away  from  the  base  of  the  hair.  They 
measure  from  0.9  to  i  mm.  in  length.  The  small,  whitish  er  ~s  are  usually 
known  as  "nits."  The  eggs  hatch  in  from  five  to  nine  days  when'  kept  at  tem- 
peratures (30°  to  35°  C.)  normal  to  the  habitat  of  the  lice.  When  ready  to 


8  For  a  full  and  extended  account  of  the  ,niouth  parts  and  their  action  the  reader  is 
referred  to  the  works  of  Harrison,  Sikora,  Peacock,  and  Florence.  The  above  account 
is  necessarily  brief  and  is  abstracted  largely  from  these  workers. 


200  MEDICAL  ENTOMOLOGY 

emerge  the  nymph  employs  a  novel  method  to  open  the  lid  or  cap  of  the  egg. 
Air  is  pumped  in  through  the  mouth  parts  and  gradually  extruded  from  the 
anus  until  a  cushion  of  air  is  obtained  of  sufficient  pressure  to  force  open  the 
cap.  The  fore  part  of  the  nymph,  which  has  acted  like  a  stopper,  is  forced  out; 


Fig.  80  (left).  Pcdiculus  humanus.  Internal  anatomy  of  male  louse;  parts  fully  labeled. 
(After  Nuttall,  Parasitology.) 
Fig.  8 1  (right).  Eggs  of  human  lice.  (A)  Pcdiculus  humanus.  (B)  Phthirus  pubis. 

pumping  continues  and  the  nymph  is  gradually  forced  out  of  the  shell.  The 
nymph  begins  feeding  promptly  within  a  few  hours.  There  are  three  molts 
before  the  adult  stage  is  reached.  The  length  of  the  life  cycle  has  been  accurately 
determined  by  Nuttall  and  is  as  follows: 

Egg  stage  7  days 

ist  nymphal  stage 4  days 


THE  ORDER  ANOPLURA  20* 

2nd  nymphal  stage 3  days 

3rd  nymphal  stage 2  days         - 

Total   16  days 

The  length  of  the  life  cycle  may  be  somewhat  prolonged  by  low  temperatures 
or  lack  of  food.  The  adults  live  about  30  days. 

THE  BODY  LOUSE:  Pediculus  humanus  var.  corporis  dc  Geer,4  the  body 
louse,  is  found  principally  on  the  body  and  oviposits  generally  on  the  clothing. 
In  practically  all  characteristics  it  agrees  with  capitis,  though  it  averages  slightly 
larger  in  size.  About  the  only  distinguishing  characters  are  its  habitat  and 
its  preference  for  laying  its  eggs  on  the  clothing  rather  than  on  the  hairs. 
Nuttall  has  shown  that  capitis  will  oviposit  on  cloth  and  that  corporis  will  lay 
its  eggs  on  the  body  hairs.  Such  eggs  have  been  found  naturally  on  the  body 
hairs  of  persons  infested  with  this  louse.  The  life  history  of  the  body  louse  is 
very  similar  to  that  of  the  head  louse.  Nuttall  has  shown  that  the  female  lays 
from  275  to  300  eggs,  ovipositing  at  the  rate  of  about  ten  a  day.  The  eggs  hatch 
in  from  six  to  nine  days  and  the  entire*  life  cycle  from  egg  to  egg  may  be  as 
short  as  16  days.  The  optimum  temj^f  rntlirr  for  its  fH^l^p"™*"1"  l'r  3n°  tn  y>°  r:. 

BIONOMICS  OF  LICE:  FEEDING  HABITS:  The  method  of  feeding  has  al- 
ready been  described.  Whereas  starved  lice  will  gorge  to  excess,  those  present 
on  the  body  feed  whenever  hungry.  They  feed  most  commonly  at  night  or 
yvheruhe  host  is  resting.  JThe  act  of  feeding  usually  occupies  three  to  ten  min- 
utes (Nuttall),  though  other  authorities  record  even  as  long  as  two  or  three 
hours,  the  lice  sucking  intermittently.  The  young  lice  begin  feeding  almost 
immediately  after  hatching,  and,  if  conditions  are  favorable,  continue  to 
feed  at  varying  intervals  throughout  life.  As  the  lice  feed  and  the  intestine  fills 
with  blood,  excreta  are  commonly  voided  in  more  or  less  profusion.  This  is  a 
very  important  fact  when  the  methods  of  transmission  of  pathogenic  organisms 
are  considered. 

HABITAT:  The  head  louse  (capitis)  is  primarily  an  inhabitant  of  the  head. 
It  may  occur  and  establish  itself  on  other  hairy  parts,  as  the  beard,  pubic 
region,  and  chest.  The  body  louse  (corporis)  is  largely  confined  to  the  clothing 
on  which  it  lays  its  eggs.  Nuttall  has  recorded  a  severe  infestation  of  capitis  on 
the  pubic  region.  Many  observers  record  the  presence  of  corporis  on  the  body 
and  the  deposition  of  its  eggs,  though  not  commonly,  on  the  hairs  of  the  breast, 
axillae,  perianal,  and  pubic  regions.  This  is  especially  true  when  the  infestation 


4  Under  the  rules  of  nomenclature  this  name  should  be  Pediculus  humanus  humanus 
Linn. 


202  MEDICAL  ENTOMOLOGY 

is  severe.  These  observations  are  of  great  importance  when  delousing  opera- 
tions are  considered.  It  is  useless  to  delouse  by  change  of  clothing  after  an 
ordinary  bath.  If  the  eggs  are  present  on  the  body  hairs,  the  person  will  be 
soon  as  lousy  as  ever. 

ACTIVITIES:  Lice  are  very  active,  crawling  about  with  remarkable  speed. 
Nuttall  observed  a  female  of  corporis  travel  at  the  rate  of  one  metre  in  three 
minutes,  and  it  is  evident  lice  can  run  a  distance  equal  to  the  length  of  a  man's 
body  in  a  few  minutes.5  They  have  been  seen  wandering  about  rooms,  crawl- 
ing up  walls,  and,  not  uncommonly,  moving  about  railway  carriages  and 
'busses.  They  are  more  active  when  warm,  corporis  climbing  more  than  twice 
as  fast  at  30°  C.  than  at  17°  C.  At  o°C.  they  are  immobile;  at  10°  C.  they  move 
slowly;  at  20°  C.  they  are  fairly  active;  and  at  30°  C.  they  are  very  active  (about 
the  temperature  of  their  normal  habitat).  At  38  °  to  40°  C.  they  become  wildly 
active  and  soon  die  from  exhaustion.  The  thermal  death  point  is  about  44°  C. 
(112°  F.).  Lice  become  very  active  on  persons  with  fever,  migrating  from  the 
patients  in  large  numbers;  when  a  person  dies  the  lice  soon  abandon  the 
body  and  scatter.  These  important  facts  should  be  remembered  when  attend- 
ing persons  suffering  with  relapsing  or  typhus  fever. 

Both  the  head  and  body  lice  are  very  gregarious,  tending  to  congregate  in 
large  numbers  in  particular  places.  This  habit  may  account  for  the  density  of 
a  primary  infestation  before  active  spreading  takes  place.  Nuttall  has  cal- 
culated that  a  single  female  may  have  1918  descendants  during  her  lifetime 
(about  30  days),  and  the  offspring  of  her  daughters,  during  their  lifetime, 
would  be  112,778,  a  rather  large  population  to  be  produced  in  about  48  days. 

5  It  may  be  well  to  recall  here  the  poem  by  Robert  Burns  entitled,  "To  a  Louse,  on 
seeing  one  on  a  lady's  bonnet  at  church,"  in  which  he  described  very  accurately  the 
roaming  activities  of  these  creatures: 

"Ha!  where  yc  gaun,  ye  crowlin'  ferlic! 
Your  impudence  protects  you  sairly: 
I  canna  say  but  ye  strunt  rarely, 

Owrc  gauze  and  lace; 
Though,  faith,  I  fear  ye  dine  but  sparely 

On  sic  a  place. 

"Now  haud  you  there,  ye're  out  o'  sight, 
Below  the  fatt'rils  snug  and  tight; 
Na  faith  ye  yet!  ye'll  no  be  right 

Till  ye've  got  on  it, 
The  very  tapmost,  towering  height 

O'  Miss's  bonnett." 


THE  ORDER  ANOPLURA  203 

MODES   OF    DISSEMINATION    AND   INFESTATION!    It    should    DC   recalled   that   lice 

are  very  active,  can  attach  easily  to  hair  or  cloth,  and  cling  thereto  very 
tenaciously;  they  can  survive  for  a  maximum  of  ten  days  without  food.  Lice 
can  readily  pass  from  head  to  head  when  in  contact;  lice,  clinging  to  stray  hairs, 
clamber  quickly  to  any  warm  body  surface  near  at  hand;  caps  or  hats  worn  by 
lousy  persons  and  hung  in  close  contact  with  others,  as  in  schools  and  public 
places,  undoubtedly  serve  to  spread  them.  Hairs  from  lousy  persons  are  often 
scattered  in  public  conveyances,  and  these  falling  on  other  people's  clothing 
may  start  an  infestation.  Persons  suffering  from  head  lice  are  constantly  scratch- 
ing, and  hairs  bearing  nits  (eggs)  are  continually  dropping,  frequently  on 
scats  and  cushions  of  railway  carriages,  busses,  etc.  Probably  the  most  common 
method  of  acquiring  lice  is  through  contact  with  infested  clothing,  bedding, 
brushes,  etc. 

THE  CRAB  LOUSE:  Phthirus  pubis  (Linn.).,  the  groin,  pubic,  or  crab 
louse  (Fig.  82),  is  a  very  distinctive  louse.  It  is  usually  confined  to  the  pubic 
and  perianal  regions,  though  it  is  recorded  from  the  head,  eyebrows,  eyelashes, 
the  axillae,  breast,  and  beard.  Herms  records  seeing  soldiers  infested  from 
their  ankles  to  their  necks,  and  Nuttall  also  observed  similar  conditions  among 
soldiers  he  examined  in  England.  However,  the  main  site  of  infestation  is  the 
pubic  and  perianal  region.  The  prevalence  of  this  louse  among  the  general 
population  is  not  known.  Grccnough  (1888)  records  that  in  the  examination  of 
864  verminous  patients  admitted  to  a  hospital  in  Boston  3  per  cent  were 
infested  with  the  crab  louse.  From  personal  knowledge  the  author  is  led  to 
believe  that  this  louse  is  quite  widely  prevalent,  but  very  few  records  are  kept. 
It  is  restricted  to  man  as  a  host,  though  there  are  some  records  of  dogs  being 
infested.  Further  investigation  is  needed  to  learn  whether  the  clog  may  be  a 
normal  host  and  serve  as  an  animal  reservoir  of  this  louse. 

The  crab  louse  is  grayish  white  in  color;  it  measures  1.5  to  2  mm.  in  length 
and  is  nearly  as  broad  as  long.  It  remains  almost  immobile  upon  the  host, 
the  hind  legs  grasping  two  hairs.  In  this  position  it  continues  to  feed  inter- 
mittently for  hours  or  clays,  rarely  removing  its  mouth  parts  from  their 
position  in  the  host.  During  its  entire  life  it  remains  near  its  first  point  of 
attachment,  withdrawing  its  mouth  parts  only  at  the  time  of  molting.  As  it 
feeds  it  defecates  frequently,  voiding  blood  and  wastes  intermingled.  This 
frequent  defecation  soon  renders  its  surroundings  filthy. 

LIFE  CYCLE:  Nuttall  gives  an  excellent  account  of  the  biology  of  this  species. 
Mating  takes  place  on  the  host  and  the  eggs  (Fig.  81  B)  are  deposited  on  the 
hairs,  close  to  the  base.  The  total  egg  production  of  a  single  female  has  not  been 


204  MEDICAL  ENTOMOLOGY 

accurately  determined,  though  Nuttall  records  26  eggs  laid  by  one  during  a 
period  of  12  days  (the  female  died  17  days  after  reaching  sexual  maturity).  The 
eggs  hatch  in  from  7  to  8  days.  The  young  nymph  attaches  within  a  few  hours, 
and  the  first  molt  takes  place  in  from  5  to  6  days;  the  second  molt  in  9  to  10 
days;  and  the  third  molt  in  from  13  to  17  days.  The  complete  life  cycle  from 
egg  to  egg  occupies  from  34  to  41  days.  The -nymphs  or  adults  cannot  survive 
very  long  when  removed  from  the  host,  a  maximum  of  two  days  being 
recorded. 


Fig.  82.  The  pubic  louse,  Phthirus  pubis.  Female. 

DISSEMINATION:  The  crab  louse  is  usually  spread  during  coitus,  but  there 
are  many  other  ways  in  which  persons  may  become  infested.  Some  of  these 
are  the  use  of  common  or  piled  bath  towels  in  dormitories,  gymnasiums,  etc.; 
contact  with  hairs  bearing  eggs  or  lice  that  may  drop  on  clothing,  bedding, 
the  seats  of  public  toilets,  etc.,  as  the  result  of  scratching  by  infested  persons; 
the  throwing  or  piling  together  of  undergarments,  athletic  suits,  etc.  Under 
crowded  conditions  a  single  infested  individual  may  distribute  them  to  an 
entire  family  or  group  of  people  with  whom  he  or  she  comes  constantly  in 
contact. 


THE  ORDER  ANOPLURA  205 

LICE  AND  DISEASE 
HEAD  AND  BODY  LICE 

The  head  and  body  lice  of  man  affect  him  in  two  principal  ways:  through 
the  direct  effects  of  their  bites  and  by  the  transmission  of  pathogenic  or- 
ganisms. 

BITES :  The  bites  of  lice  have  a  very  marked  effect  on  most  people,  though 
some  persons  are  apparently  immune  to  their  attacks  (Moore  and  Hirsch- 
felder  record  an  experimental  individual  on  which  lice  refused  to  feed)  and 
others  become  immune  after  continued  attack.  The  bites  produce  minute  hem- 
orrhagic  spots,  which  are  found  most  frequently  over  the  neck,  back,  breast, 
and  abdomen.  These  spots  are  accompanied  by  an  urticaria,  often  with  intense 
itching,  leading  to  scratching  and  frequent  secondary  infection.  Among  persons 
(as  tramps,  vagabonds,  chronic  drunkards,  and  children  living  under  filthy 
conditions)  who  harbor  lice  for  years,  the  skin  back  of  the  head,  over  the 
breast,  and  on  the  neck,  back,  or  any  part  frequently  bitten  becomes  roughened, 
thickened,  and  deeply  pigmented  (melanoderma),  producing  what  is  com- 
monly called  "vagabonds'  disease."  As  the  body  louse  attacks  most  frequently 
at  night  or  when  the  host  is  resting,  it  causes  a  great  deal  of  irritation,  loss  of 
sleep,  and  restlessness,  which  may  induce  irritability  and  an  anemic  condition, 
especially  in  children.  Insomnia  and  neurasthenia  may  result  from  continued 
infestation.  Moore  (1918)  records  rather  severe  effects  from  the  experimental 
feeding  of  lice  on  himself.  After  feeding  700  to  800  lice  twice  each  day,  he 
developed  almost  at  once  a  tired  feeling,  an  irritable  and  pessimistic  state  of 
mind,  and  an  illness  resembling  grippe  with  a  body  rash.  All  these  effects  rap- 
idly disappeared  when  the  lice  were  removed  and  feeding  discontinued. 

DISEASES :  There  are  at  least  three  important  human  diseases  transmitted 
by  lice:  (i)  epidemic  typhus;  (2)  trench  fever;  and  (3)  relapsing  fever.  An- 
other disease,  endemic  typhus  or  murine  typhus,  is  mainly  associated  with  rats 
and  rat  parasites,  since  fleas  and  mites  are  the  transmitters  among  rats  and 
to  man  (see  pp.  98,  560) ;  human  lice  are  also  capable  of  acting  as  vectors. 

EPIDEMIC  TYPHUS,   OLD  WORLD  TYPHUS,  JAIL  FEVER,  TYPHUS  EXANTIIEMATICUS, 

LOUSE  TYPHUS,  ETC.:  Typhus  is  an  acute  infectious  disease  caused  by  Ricfatsia 
prowazety  da  Rocha-Lima  (1916)  and  is  transmitted  by  the  human  louse, 
Pediculus  humanus  Linn.  The  disease  is  characterized  by  sudden  onset,  high 
fever,  severe  headache,  and  marked  prostration,  followed  on  the  fourth  or  fifth 
day  by  a  pinkish  body  rash.  The  course  of  the  disease  is  rapid,  a  fall  in  tempera- 


206  MEDICAL  ENTOMOLOGY 

ture  occurring  on  the  twelfth  to  the  fourteenth  day,  followed  by  a  rapid  recovery 
or  death.  The  mortality  rate  varies  from  5  per  cent  to  as  high  as  70  per  cent  in 
severe  epidemics. 

Typhus  fever  is  world-wide  in  distribution  and  may  occur  wherever  human 
lice  are  abundant.  Epidemics  have  occurred  in  most  parts  of  the  world.  It  is 
prevalent  principally  in  the  cooler  climates  where  people  are  compelled  to 
wear  heavy  clothing  and  bathing  and  clothing  changes  are  infrequent.  Out- 
breaks are  most  frequent  in  the  winter  because  of  the  crowding  of  the  poorer 
classes,  bad  sanitary  conditions,  and  lack  of  adequate  food,  inducing  general 
debility.  The  disease  is  practically  always  associated  with  poverty  and  unsani- 
tary living  conditions  or,  under  war  conditions,  with  famine,  national  poverty, 
political  upheavals,  or  revolutions.  Severe  epidemics  occurred  during  World 
War  I  in  Serbia,  Romania,  and  Poland,  and  the  aftermath  witnessed  severe 
outbreaks  in  Poland  and  Russia.  In  World  War  II  epidemics  threatened  in 
areas  overrun  by  the  various  armies  as  in  Italy  and  North  Africa,  but  these 
were  soon  halted  by  the  use  of  DDT. 

That  lice  are  the  transmitters  of  typhus  was  first  demonstrated  by  Nicolle 
and  his  associates  in  1909  in  Tunis,  North  Africa.  They  succeeded  in  transmitt- 
ing typhus  from  infected  monkey  to  uninfected  monkey  by  body  lice.  These 
results  were  fully  confirmed  by  Ricketts  and  Wilder  (1910),  Goldberger 
(1912),  and  others  in  various  parts  of  the  world.  These  workers  stated  that  the 
transmission  was  by  the  bites  of  the  louse;  this  is  now  known  not  to  be  the 
case.  The  causative  organism  was  discovered  by  da  Rocha-Lima  (1916),  and 
the  complicated  method  of  transmission  by  lice  has  since  been  fully  elucidated. 
Man  is  believed  to  be  the  reservoir  of  the  disease.  Lice  feeding  on  typhus  pa- 
tients ingest  the  rickettsiae  that  are  in  the  circulating  blood  during  the  febrile 
period  (the  third  to  the  loth  day).  In  the  lice  the  rickettsiae  invade  the  epi- 
dermal cells  lining  the  stomach  and  mid-gut;  here  they  multiply  in  enormous 
numbers  and  cause  the  cells  to  burst  and  liberate  them.  This  developmental 
cycle  requires  from  five  to  nine  days.  The  infected  louse  now  feeds  on  a  new 
patient  and  infection  may  occur  in  one  of  three  ways:  (i)  the  louse  in  feeding 
defecates  and  the  rickettsiae  in  the  feces  may  enter  the  wound  or  the  abra- 
sions that  result  from  scratching;  (2)  the  louse  is  crushed  by  the  patient  and 
the"  contents  of  the  intestine  of  the  louse  are  spread  over  the  skin  to  enter 
wounds  or  scratches;  (3)  the  feces  of  infected  lice  may  fall  on  mucous  mem- 
branes about  the  eyes,  the  mouth,  or  other  exposed  mucous  surfaces.  In  addi- 
tion, it  has  been  demonstrated  that,  though  infected  feces  may  become  dry  and 
powdery,  the  rickettsiae  are  still  infective  and  may  be  scratched  into  the  skin 
or  rubbed  on  mucous  surfaces  or  they  may  be  air-borne  and  gain  access  to 


THE  ORDER  ANOPLURA  207 

mucous  surfaces  (from  feces  contaminating  bedding,  clothing,  and  so  forth). 
The  rickettsiae  in  man  invade  the  cytoplasm  of  the  cells,  and  the  incubation 
period  varies  from  8  to  12  days.  No  successful  treatment  is  known.  At  present 
a  fairly  effective  vaccine  has  been  developed  from  killed  rickettsiae  and  is 
being  used  with  considerable  success.  The  prevention  of  infection  is  of  the 
greatest  importance  in  controlling  or  preventing  an  outbreak.  This  involves 
effective  louse  control  (see  pp.  211-213),  cleanliness,  improved  living  condi- 
tions, adequate  bathing  and  laundering  facilities,  and  the  prevention  of  louse- 
infected  people  from  entering  the  areas. 'Mass  vaccination  is  of  importance 
where  it  can  be  done  effectively.  There  is  no  known  animal  reservoir  of 
epidemic  typhus  except  man.  However,  the  monkey  lice  (Pedicinus  longiceps 
and  P.  albidus)  have  been  shown  capable  of  transmitting  the  disease  to 
monkeys  and  the  rat  louse,  Polyplax  spinulosa,  of  transmitting  the  disease 
among  rats.  The  rickettsiae  are  not  known  to  be  transmitted  by  lice  to  their 
young  (in  fact  most  infected  lice  are  said  to  die).  The  sources  of  epidemic  out- 
breaks are  not  known. 

BRILL'S  DISEASE:  Although  generally  regarded  as  a  form  of  murine  or  endemic 
typhus,  Brill's  disease  has  been  shown  to  be  a  mild  form  of  epidemic  typhus  and 
is  transmitted  by  the  human  louse. 

ENDEMIC  TYPHUS,  MURINE  TYPHUS,  OR  FLEA  TYPHUS:  This  is  a  mild  typhuslikc 
disease  caused  by  Ric\ettsia  mooseri  (typhi}  and  is  transmitted  to  man  by  the 
bites  of  infected  fleas,  infective  flea  feces,  or  the  eating  of  food  contaminated 
by  urine  from  infected  rats.  The  body  louse,  Pcdicidus  humanus  corporis,  can 
also  transmit  the  disease. 

That  rats  (the  brown  rat,  Rattus  norvegicus,  and  others)  and  probably  mice 
are  the  reservoirs  of  the  rickettsiae  has  been  well  demonstrated  by  Dyer, 
Rumreich,  and  their  associates  (1931,  1932), 'Mooser  and  his  co-workers  in 
Mexico,  and  many  others.  More  recently  Brigham  (1937)  has  isolated  a  strain 
from  a  field  mouse  (Peromy  setts  polionotus  polionotus)  from  a  rural  district 
in  southern  Alabama,  and  the  same  author  (1937)  has  shown  mice,  various 
species  of  rats,  flying  squirrels,  cotton  mice,  golden  mice,  and  wood  rats 
to  be  susceptible  to  infection.  Among  rats  the  vectors  are  fleas  (Xenopsylla 
cheopis,  Nosopsyllus  jasciatus,  and  probably  others),  the  rat  louse  (Polyplax 
spinulosa),  and  the  tropical  rat  mite  (Liponyssus  bacoti).  Brigham  (1941)  re- 
covered a  strain  of  typhus  from  the  sticktight  flea,  Echidnophaga  gallinacea, 
collected  from  rats  in  Georgia,  and  Alicata  (1942)  transmitted  endemic  typhus 
by  this  flea. 

The  disease  in  man  (apparently  it  has  little  effect  on  rats  or  other  rodents) 


2o8  MEDICAL  ENTOMOLOGY 

is  mild,  and  the  death  rate  is  less  than  5  per  cent  in  the  United  States.  In  man 
the  incubation  period  varies  from  6  to  14  days  followed  by  fever  and  a  rash. 
Recovery  normally  occurs  in  two  or  three  weeks.  Eskey  (1943)  reports  some 
20,000  cases  in  the  United  States  from  1932  to  1941  but  indicates  that  this  was 
probably  less  than  20  per  cent  of  the  actual  cases.  As  the  main  source  of  human 
infection  is  rats,  the  control  or  eradication  of  these  pests  would  practically 
eradicate  the  disease. 

Murine  typhus  is  widely  distributed  in  the  southern  United  States,  extend- 
ing northward  into  New  York,  Ohio,  Iowa,  and  California;  it  is  widespread 
in  Mexico,  parts  of  South  America,  Africa,  southern  and  western  Europe,  the 
Near  East,  eastern  Asia,  and  nearby  areas. 

TRENCH  FEVER:  Trench  fever,  or  Volhynia  fever,  was  first  diagnosed  as  a 
clinical  entity  in  1915  during  World  War  I.  It  is  believed  to  be  caused  by 
RicJ^ettsia  quintana  (R.  tvolhynicd),  but  this  has  not  been  definitely  proved.  It 
is  a  specific  relapsing  fever  transmitted  to  man  by  the  body  louse,  Pedicttlus 
humanus  corporis,  through  the  infected  feces  only.  It  is  not  transmitted  by  the 
bites  of  infected  lice,  nor  is  it  known  to  be  transmitted  through  the  eggs. 
During  World  War  I  trench  fever  is  said  to  have  caused  about  25  per  cent  of 
all  cases  of  illness  in  the  British  Army  in  France  and  the  disease  was  very 
prevalent  in  the  German  and  Austrian  Armies.  Byam  (1923)  reports  800,000 
cases  among  the  Allied  armies  in  France  during  the  four  years  of  the  war. 
Outbreaks  occurred  in  Egypt  and  Mesopotamia  as  well  as  in  Europe.  During 
World  War  II  the  disease  was  rare. 

In  man  the  organism  of  trench  fever  is  present  in  the  blood,  and  the  blood 
is  infective  to  lice  from  the  first  day  of  the  disease.  In  lice  there  is  a  develop- 
ment period  of  five  to  nine  days  before  the  excreta  are  infective.  The  louse 
remains  infective  as  long  as  it  lives.  The  excreta  retain  their  virulence  for  a 
long  time,  at  least  four  months.  Man  becomes  infected  by  scratching  the 
excreta  into  the  injured  skin,  crushing  the  lice,  or  in  any  way  that  brings  the 
infective  fecal  wastes  into  the  blood  stream.  In  man  the  incubation  period 
varies  from  10  to  30  days  (Mackie  et  aL,  1945).  The  onset  is  sudden  with 
severe  headache,  weakness,  vertigo,  and  fever  of  103°  to  104°  F.  The  fever 
soon  subsides  (one  to  two  weeks)  and  is  followed  by  several  relapses  (three 
to  five).  During  the  disease  there  is  usually  a  rash  on  the  chest,  back,  and 
abdomen.  Recovery  is  slow  (frequently  prolonged)  and  the  sequelae  are,  in 
many  cases,  serious.  As  there  is  no  successful  treatment,  the  control  of  lice  is 
very  important.  In  man  there  is  only  a  fleeting  immunity  and  reinfection  may 
occur  within  six  months. 


THE  ORDER  ANOPLURA  209 

RELAPSING  FEVER:  There  are  two  types  of  this  disease,  tick-borne  (see  pp. 
71-73)  and  louse-borne.  Species  of  Spirochaeta  are  the  causative  agents  of 
the  disease,  but  no  agreement  seems  to  have  been  reached  as  to  the  species 
concerned.  Spirochaeta  recurrent!*  (Lebert)  is  usually  regarded  as  the  louse 
species.  There  is  doubt  about  the  possibility  or  probability  that  tick-borne 
species  can  also  be  transmitted  by  lice  or  vice  versa.  The  two  diseases,  typhus 
and  louse-borne  relapsing  fever,  frequently  occur  about  the  same  time  in  the 
same  areas,  or  they  may  be  separated  by  a  few  years.  Mackie  (1907)  first 
demonstrated  that  the  body  louse  (Pediculus  hunt  anus  corporis]  served  as  the 
vector  in  India  in  an  area  where  typhus  had  never  been  recorded.  This  work 
was  confirmed  by  many  investigators  in  North  Africa  and  other  parts  of  the 
world.  According  to  Chung  and  Feng  (1936),  the  developmental  cycle  in  the 
louse  is  as  follows.  The  louse  feeding  on  a  patient  obtains  the  spirochetes  in  its 
blood  meal.  Most  of  the  ingested  spirochetes  are  soon  digested,  disappearing 
within  six  to  eight  hours.  A  few,  however,  penetrate  the  wall  of  the  intestine 
and  appear  in  the  coelomic  fluid  in  about  two  hours,  and  numbers  are  seen 
within  eight  hours.  At  the  same  time  dead  spirochetes  appear  in  the  feces. 
Within  the  body  cavity  the  spirochetes  multiply  by  transverse  division  and 
soon  appear  in  all  parts  of  the  body.  They  do  not  invade  the  tissues  nor  are 
they  transmitted  through  the  egg  or  through  the  feces.  Within  the  louse  the 
spirochetes  persist  as  long  as  the  louse  lives  (19  days  or  more).  Infection  of 
man  takes  place  by  crushing  the  lice  directly  on  the  skin  by  the  fingers  or 
other  means,  whereby  the  spirochetes  gain  entrance  through  abrasions,  or  by 
scratching,  thus  permitting  their  access  to  the  blood.  The  vectors  are  both  the 
body  and  head  lice. 

Relapsing  fever  has  occurred  in  epidemic  form  in  most  parts  of  the  world. 
It  is  associated  with  lousiness  in  jails,  armies,  overcrowded  and  poverty  stricken 
areas,  famines,  wars,  and  political  disturbances.  ^Though  the  clinical  entity  of 
the  disease  was  recognized  in  the  early  part  of  trie  nineteenth  century,  it  was 
not  till  1873  that  the  etiological  agent  was  described  by  Obermeier  and  named 
Protomycetum  recurrentis  by  Lebert  in  1874,  now  called  Spirochaeta  recur- 
rentis  (Lebert) .  Epidemics  have  been  recorded  from  many  countries  and  cities 
as  in  Dublin  (1739  and  later),  parts  of  Scotland  (1842-1844  and  later),  Eng- 
land (1847-1848  and  later),  Russia  (1833, 1863,  and  later),  Germany  (1868  and 
later),  most  of  Asia,  Egypt  (1851,  1884,  and  later),  most  of  India  (1852  and 
later),  North  Africa,  West,  central,  and  parts  of  East  Africa  (to  the  present 
time)  and  China;  it  is  not  known  from  Australasia.  The  disease  has  been 
recorded  from  the  eastern  coastal  cities  of  North  America  (1844,  1847,  1871) 


210  MEDICAL  ENTOMOLOGY 

but  is  apparently  absent  at  the  present  time.  It  also  occurs  in  some  parts  of 
South  America. 

During  and  after  World  War  I  great  epidemics  swept  over  Poland,  central 
Russia,  Romania,  and  Serbia.  In  Romania  alone  there  were  over  one  million 
cases  of  typhus  and  more  of  relapsing  fever  in  a  population  of  five  million. 
The  most  recent  great  epidemic  swept  over  central  Africa,  appearing  first 
in  French  Guinea  in  1921,  and  gradually  spread  southward  to  Nigeria,  east- 
ward to  the  Anglo-Egyptian  Sudan,  and  northward  to  various  areas.  By  1928 
it  had  subsided,  though  during  the  epidemic  it  is  estimated  about  10  per  cent 
of  the  population  died.  In  French  Sudan  and  the  Niger  area  over  80,000  died 
within  two  years.  (Scott,  1939).  Though  some  of  the  newer  arsenical  drugs 
appear  to  act  effectively  in  the  cure  of  relapsing  fever,  yet  the  most  important 
measure  is  the  control  of  lice.  Where  lice  are  adequately  controlled,  louse-borne 
diseases  soon  disappear. 

OTHER  LICE 

Phthirus  pubis  has  not,  apparently,  been  extensively  experimented  with  as 
an  agent  in  the  transmission  of  disease.  "It  is  not  known  to  serve  as  a  vector  of 
any  infective  disease"  (Nuttall,  1918).  Todd  (1922)  states  that  it  may  transmit 
relapsing  fever.  The  main  effects  of  this  louse  are  local.  Pruritus  is  usually  the 
first  symptom  and  leads  to  scratching  and  secondary  infections.  With  many 
persons  no  ill  effects  are  evident  though  pale  bluish-gray  maculae  mark  the 
sites  of  the  bites. 

Another  interesting  relation  of  lice  (other  than  human  lice)  to  man  is 
that  a  species  of  dog  lice,  Trichodectes  canis  de  Geer  6  (a  species  of  Mallo- 
phaga),  serves  as  the  intermediate  host  of  the  dog  tapeworm  (Dipylidium 
caninum  Linn.).  This  tapeworm  is  found  occasionally  in  man,  particularly 
children.  The  dog  harbors  the  tapeworm,  and  the  defecated  proglottids  with 
their  eggs  become  entangled  in  the  hairs  of  the  host.  If  these  eggs  are  de- 
voured by  the  lice,  the  cysticercoid  stage  develops  in  them.  The  dog  becomes 
infected  by  swallowing  the  infected  lice.  Persons  handling  and  petting  infected 
dogs  may  accidentally  become  infected  through  swallowing  a  louse  contain- 
ing the  cysticerci.  This  most  commonly  occurs  with  children  that  play 
with  dogs  harboring  this  species  of  tapeworm. 

Another  interesting  relation  is  that  of  the  rabbit  louse,  Haemodipsus  ventri- 
cosus  Denny  (Siphunculata).  Francis  (1921)  showed  experimentally  that  this 


6  Other  intermediate  hosts  are  the  dog  and  cat  fleas  (Ctenocephalides  canis  and  C.  felts) 
and  the  human  flea  (Pulex  irritans). 


THE  ORDER  ANOPLURA  211 

louse  is  an  active  agent  in  the  dissemination  of  tularemia  (Bacterium  tularense) 
from  rabbit  to  rabbit.  This  is  undoubtedly  one  of  the  means  by  which  this 
disease  is  transmitted  in  nature,  and  it  thus  aids  in  maintaining  a  natural 
reservoir  from  which  man  may  become  infected. 

CONTROL  OF  LICE 

The  problem  of  the  control  of  lice  may  well  be  discussed  under  two  distinct 
heads:  (i)  personal  cleanliness  and  debusing;  (2)  public  cleanliness  and  mass 
debusing.7 

DELOUSING  OF  THE  INDIVIDUAL 

PERSONAL  CLEANLINESS:  Personal  cleanliness  is  probably  the  most 
effective  measure  against  lousiness.  However,  the  religion  of  cleanliness,  both 
personal  and  public,  has  not  become  universal,  and  there  still  exists,  among 
all  peoples  and  nations,  a  proportion  of  the  population  that  may  be  called  "the 
great  unwashed."  Unfortunately,  cleanliness  is  not  always  a  concomitant  of 
what  may  be  called  a  rising  civilization.  Furthermore,  there  are  many  super- 
stitions in  regard  to  lice,  their  presence  being  taken  to  indicate  good  health, 
vigor,  fertility,  protection  against  disease,8  etc.  Owing  to  the  dangers  of  disease 
transmission,  everyone  should  take  the  utmost  precaution  against  infestation. 
Certain  simple  rules  should  be  followed  as  far  as  possible:  (i)  avoid  all  con- 
tact with  lousy  persons  and  their  effects;  (2)  avoid  overcrowding  whenever 
possible;  (3)  bathe  at  least  once  a  week,  using  plenty  of  hot  water  and  soap, 
and  rub  dry  with  a  rough  towel;  (4)  wear  underwear  at  all  times  and  make 
a  complete  change  at  least  once  each  week ;  to  use  no  underwear  is  an  unclean 
habit  and  invites  lousiness;  (5)  wash  the  head  carefully  at  frequent  intervals; 
comb  and  brush  it  at  least  once  a  day  and  keep  it  clean  at  all  times;  (6)  avoid 
unclean  bedding,  especially  blankets;  when  traveling,  carefully  inspect  the 
bedding  before  retiring;  (7)  carefully  inspect  the  head  and  body  at  frequent 


7  Lousing  is  the  correct  term  to  use  in  this  connection  but  it  has  fallen  into  disuse, 
owing,  no  doubt,  to  the  decreasing  lousiness  of  peoples.  To  louse,  according  to  the  Oxford 
English  dictionary,  means  "to  clear  of  lice,  to  remove  lice."  "Howe  handsome  it  is  to  lye 
and  sleepe,  or  to  lowze  themselves  in  the  sunshine"  (Spenser,  View  of  the  Present  State 
of  Ireland,  1633).  "To  York  House,  where  the  Russian  Ambassador  do  lie;  and  there 
I  saw  his  people  go  up  and  down  lousing  themselves"  (Pepys*  Diary,  June  6,  1663). 
(From  Nuttall.) 

8  "Ten  lice  boiled  in  milk  with  plenty  of  salt  and  taken  on  an  empty  stomach  was 
certain  to  cure  jaundice,  a  very  common  complaint  among  the  Lapps  in  Spring"  (The 
Story  of  San  Michele  by  Axel  Munthe). 


212  MEDICAL  ENTOMOLOGY 

intervals,  especially  if  you  have  been  exposed  to  contacts  with  lousy  individ- 
uals; (8)  in  case  of  infestation,  vigorous  treatment  should  be  adopted  at  once. 

HEAD  LICE  (P.  humanus  capitis) :  In  mild  infestations  the  lice  and  the  nits 
(eggs)  can  be  removed  by  hand  picking  and  vigorously  combing  with  a  fine- 
toothed  comb.  Frequent  washing  and  combing  will  usually  eliminate  a  mild 
infestation.  If  lice  are  abundant  or  even  if  only  a  few,  they  can  be  quickly 
destroyed  by  one  of  the  newer  lousicides.  A  10  per  cent  DDT  (by  weight)  in 
some  carrier  as  pyrophyllite  is  very  effective.  Dust  the  head  thoroughly  (about 
a  spoonful  of  the  powder)  and  rub  the  dust  in  vigorously  with  the  hands.  Also 
rub  some  into  the  eyebrows  and  beard  (if  present);  avoid  getting  any  into 
the  eyes.  The  head  should  not  be  washed  for  24  hours  or  longer.  This  will 
kill  all  the  lice  but  not  the  eggs.  Use  the  same  treatment  a  week  or  ten  days 
later  to  kill  any  lice  that  have  hatched.  Two  thorough  treatments  even  on 
heads  with  dense  hair  will  eliminate  lice.  Another  treatment  is  by  the  use 
of  liquid  solutions  of  DDT.  When  using  these,  follow  carefully  the  directions 
of  the  manufacturer  as  given  on  the  containers. 

BODY  LOUSE  (P.  humanus  corporis) :  As  this  louse  is  found  mainly  on  the 
clothing,  a  thorough  treatment  of  the  clothing,  especially  the  underwear,  is  the 
most  effective  method.  Sift  a  10  per  cent  DDT  powder  thoroughly  over 
the  insides  of  the  underwear,  carefully  rubbing  it  into  all  the  seams.  Apply  the 
same  treatment  to  the  insides  of  trousers  (in  the  case  of  women,  treat  the  insides 
of  skirts),  shirts,  and  caps.  If  such  garments  arc  worn  without  washing,  a 
single  treatment  is  good  for  three  weeks.  If  washed  in  warm  soapy  water,  the 
clothing  will  still  be  effective  for  a  short  period.  If  new  infestation  is  avoided, 
a  single  treatment  should  be  effective.  In  case  of  constant  exposure  to  infesta- 
tion, as  on  the  part  of  nurses,  social  workers,  medical  officers,  or  others  work- 
ing among  lousy  persons,  especially  when  typhus  or  relapsing  fever  is  prev- 
alent, the  underclothing  may  be  impregnated  with  a  DDT  emulsion  or 
DDT  may  be  mixed  with  a  dry-cleaning  fluid.  Such  emulsions  can  be  prepared 
or  purchased. 

CRAB  LOUSE  (Phthirus  pubis) :  This  louse  may  be  controlled  by  dusting  the 
groin  region,  the  arm  pits,  or  other  hairy  portions  of  the  body  with  a  10  per 
cent  DDT  dust.  Rub  in  thoroughly  and  do  not  bathe  for  at  least  twenty-four 
hours.  Follow  with  a  second  treatment  in  a  week  to  ten  days  to  kill  any  lice 
that  have  hatched. 


THE  ORDER  ANOPLURA  213 

MASS  DELOUSING 

In  armies  or  among  lousy  populations  it  is  often  necessary  to  use  mass 
delousing  methods.  These  methods  were  developed  and  refined  during  World 
War  II.  The  simplest  method  used  in  Naples,  Italy  (1943-1944),  to  control  an 
epidemic  of  typhus  was  the  use  of  DDT  as  a  10  per  cent  dust  (by  weight).  By 
means  of  small  hand  blowers  the  dust  was  blown  between  all  layers  of  the 
clothing,  particular  attention  being  paid  to  undergarments.  This  was  accom- 
plished by  blowing  down  the  back,  down  the  front,  up  the  sleeves,  down  the 
trouser  legs,  and  up  the  legs  to  cover  the  entire  body  and  clothes  with  the  dust. 
If  such  dusted  clothing  is  worn  for  a  week  or  longer,  all  the  lice  and  those 
hatching  from  eggs  will  be  destroyed.  Such  a  mass  delousing  can  be  carried 
out  effectively  only  under  police  regulations  acting  under  the  orders  of  the 
medical  authorities. 

To  carry  out  a  mass  delousing  program  requires  legal  regulation,  for  it 
necessitates  not  only  destroying  the  lice  on  the  persons  but  also  those  on  dis- 
carded or  recently  worn  clothing.  This  may  be  carried  out  effectively  by  organ- 
izing definite  delousing  stations,  as  is  done  by  the  Army  and  Navy  and  at 
ports  of  entry  to  any  country.  In  such  a  station  arrangements  are  made 
that  all  worn  clothing  in  addition  to  those  on  the  individual  must  be 
brought.  All  such  clothing,  including  what  is  worn,  is  placed  in  a  gastight  bag 
in  which  is  placed  the  required  amount  of  methyl  bromide  in  glass  ampoule, 
or  the  clothing  is  labeled  and  placed  in  gastight  chambers  for  treatment  with 
methyl  bromide.  In  the  bag  the  ampoule  is  broken,  and  in  45  minutes  the  bag 
may  be  opened  and  the  clothes  taken  out  and  shaken.  They  are  now  ready 
for  wear.  In  the  gas  chambers  masses  of  clothing  can  be  treated.  While  the 
clothing  is  being  treated,  the  unclothed  individuals  may  take  a  bath.  They 
arc  then  sprayed  with  a  lousicide  such  as  the  NBIN  formula  (see  p.  103)  used 
by  our  Army  and  Navy.  The  individual  now  receives  his  clothing,  all  the  lice 
on  his  body  and  his  clothing  having  been  killed.  By  such  a  method  400  to  500 
can  be  treated  each  day  in  a  small  station;  larger  units  can  handle  more.  In 
addition,  mobile  units  can  be  used  where  isolated  groups  have  to  be  treated. 

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Dyer,  R.  E.    The  control  of  typhus  fever.     Amer.  JL  Trop.  Med.,  21:  163-183, 

1941. 
}  Rumreich,  A.,  and  Badger,  L.  F.    Typhus  fever.    U.S.  Pub.  Hlth.  Repts., 

46:  334-338, 1931. 

Eskey,  C.  R.    Murine  typhus  control.    Ibid.,  58:  631-638,  1943. 
Ewing,  H.  E.    Sucking  lice  from  jack  rabbits.    Amer.  Jl.  Trop.  Med.,  4:  547- 

551,  1924. 


THE  ORDER  ANOPLURA  215 

.    A  revision  of  the  American  lice  of  the  genus  Pediculus,  together  with  a 

consideration  of  their  geographical  and  host  distribution.     Proc.  U.S.  Nat.  Mus., 

68,  art.  19,  1926. 

.    The  sucking  lice  of  American  monkeys.    Jl.  Parasit.,  24:  13-33,  1938. 

Fahrenholz,  H.  von.    Lause  verschiedener  Menschenrassen.    Zeit.    Morph.     An- 

throp,  17:  591-602,  1915. 
.    Bibliographic  der   Lause-(Anopluren)    Literatur   nebst   Verzeichnis   der 

Lausearten  nach  den  Wohntieren  geordnet.    Zeit.  Angew.  Ent.,  6:   106-160, 

1920. 
Ferris,  G.  F.    A  catalogue  and  host  list  of  the  Anoplura.     Proc.  Calif.  Acad.  Sci., 

4th  ser.,  6:  129-213,  1916. 

.    Contributions  toward  a  monograph  of  the  sucking  lice.     Parts  i-vm.     Stan- 
ford University,  1919-1935. 
*Florence,  L.    'The  hog  louse,  Haernatopinus  suis  Linne:  its  biology,  anatomy,  and 

histology.    Cornell  Univ.  Agr.  Exp.  Sta.,  Mem.  51,  1921. 
Foster,  M.  H.    Preliminary  report  on  carbon  tetrachloride  vapor  as  a  delousing 

agent.    U.S.  Pub.  Hlth.  Repts.,  33:  1823-1827,  1918. 
Francis,  E.    Experimental  transmission  of  tularaemia  in  rabbits  by  the  rabbit 

louse,  llaemodipsus  vcntricosus  (Denny).     Ibid.,  36:  1747-1753,  1921. 
Goldberger,  J,  and  Anderson,  J.  F.     The  transmission  of  typhus  fever  with  especial 

reference  to  transmission  by  the  head  louse  (Pediculus  capitis}.    Ibid.,  27:  297- 

307,  1912. 
Greene,  E.  M.    Pediculosis  in  Boston's  public  schools.     Boston  Med.  and  Surg. 

Jl,38:7o-7i,i898. 

**Grinnell,  M.  E.,  and  Hawes,  L.  L.     Bibliography  on  lice  and  man  with  partic- 
ular reference  to  war-time  conditions.     U.S.  Dept.  Agr,  Biblio.  Bull,  i,  1943. 
Harrison,  L.  A.     A  preliminary  account  of  the  structure  of  the  mouthparts  of  the 

body  louse.    Proc.  Cambridge  Phil.  Soc,  18:  207-226,  1916. 
Hindle,  E.     Notes  on  the  biology  of  Pediculus  humanus.    Parasitology,  9:  259- 

265,  1917. 
Hinman,  E.  H.    History  of  typhus  in  Louisiana.    Amer.  Jl.  Pub.  Hlth,  26:  1117- 

1124,  1936. 

Hutchinson,  R.  H.     A  note  on  the  life-cycle  and  fertility  of  the  body  louse  (Pedi- 
culus corporis).    Jl.  Econ.  Ent,  11:  404-406,  1918. 
.    Experiments  with  steam  disinfectors  in  destroying  lice  in  clothing.    Jl. 

Parasit,  6:  65-78,  1919. 
Jones,  H.  A.,  et  al.    Experimental  impregnation  of  underwear  with  pyrethrum 

extract  for  the  control  of  body  lice.    War  Medicine,  6:  323-326,  1944. 
Keilin,  D,  and  Nuttall,  G,  H.  F.     Iconographic  studies  on  Pediculus  humanus. 

Parasitology,  22:  i-io,  1930. 
Latta,  R.    Methyl  bromide  fumigation  for  the  delousing  of  troops.    Jl.  Econ. 

Ent,  37:  103,  1944. 


216  MEDICAL  ENTOMOLOGY 

Mackie,  F.  P.    The  part  played  by  Pediculus  corporis  in  the  transmission  of  re- 
lapsing fever.    Brit.  Med.  Jl.,  2:  1706-1709,  1907. 
Maxcy,  K.  P.    An  epidemiological  study  of  endemic  typhus  (Brill's  disease)  in 

the  southeastern  United  States.    U.S.  Pub.  Hlth.  Repts.,  41:  2967-2995,  1926. 
Megaw,  }.  W.  D.    Louse-borne  typhus.    Brit.  Med.  JL,  2,  pp.  401-403:  433-435, 

1942. 
Moore,  W.    The  effects  of  laundering  upon  lice  (Pediculus  corporis)  and  their 

eggs.    Jl.  Parasit.,  5:  61-68,  1918. 
.    An  interesting  reaction  to  louse  bites.    Jl.  Amer.  Med.  Assoc.,  71:  1481- 

1482,  1918. 
,  and  Hirschfelder,  A.  D.    An  investigation  of  the  louse  problem.     Res.  Pub. 

Univ.  Minn.,  8  (4):  r-86,  1919. 
Mooser,  H.,  Castaneda,  M.  R.,  and  Zinsser,  H.     Rats  as  carriers  of  Mexican  typhus 

fever.    Jl.  Amer.  Med.  Assoc.,  97:  231-233,  1931. 
,  Castaneda,  M.  R.,  and  Zinsser,  H.    The  transmission  of  the  virus  of  Mexican 

typhus  from  rat  to  rat  by  Polyplax  sptnulosus.    Jl.  Exp.  Med.,  54:  567-569,  1931. 
,  and  Dummer,  C.    Experimental  transmission  of  endemic  typhus  of  the 

southeastern  United  States  by  the  body  louse.    Jl.  Inf.  Dis.,  46:  170-172,  1930. 
Nicollc,  C.     Reproduction  experimental  du  typhus  exanthematique  chez  le  singe. 

C.  R.  Acad.  Sci.,  Paris,  149:  157-160,  1909. 
,  Blaizot,  L.,  and  Conseil,  E.    Etiologie  de  la  fievre  recurrente;  son  mode  de 

transmission  par  le  pou.    Ann.  Inst.  Pasteur,  27:  204-225, 1913. 
**Nuttall,  G.  H.  G.     Bibliography  of  Pediculus  and  Phthirus.    Parasitology,  10: 

1-42,  1917. 
.    The  part  played  by  Pediculus  humanus  in  the  causation  of  disease.    Ibid., 

pp.  43-79,  1917. 

.    The  biology  of  Pediculus  humanus.    Ibid.,  pp.  80-185,  1917. 

.    The  pathological  effects  of  Phthirus  pubis.    Ibid.,  pp.  375-382,  1918. 

.    The  biology  of  Phthirus  pubis.    Ibid.,  pp.  383-405,  1918. 

.    Combating  lousiness  among  soldiers  and  civilians.    Ibid.,  pp.  411-586, 

1918. 

.    The  biology  of  Pediculus  humanus.    Ibid.,  11:  201-220,  1919. 

.    The  systematic  position,  synonymy,  and  iconography  of  Pediculus  humanus 

and  Phthirus  pubis.    Ibid.,  pp.  329-346,  1919. 
.    On  Fahrenholz's  purported  new  species,  subspecies,  and  varieties  of  Pedi- 

culus:  a  criticism  of  methods  employed  in  describing  Anoplura.    Ibid.,   12: 

136-153,  1920. 
Peacock,  A.  D.    The  structure  of  the  mouth  parts  and  mechanism  of  feeding  in 

Pediculus  humanus.    Ibid.,  n:  98-117,  1918. 
Shattuck,  G.  C.    Typhus  fever  in  Boston  and  a  review  of  the  newer  methods  of 

diagnosing  typhus.    Amer.  Jl.  Trop,  Med.,  2:  225-250,  1922, 


THE  ORDER  ANOPLURA  217 

Sikora,  H.  Beitrage  zur  Biologic  von  Pediculus  vestimcntl.  Central.  Bakt.,  I 
Abt.,  Orig.,  76:  523-537,  1915. 

.  Beitrage  zur  Anatomic,  Biologic  und  Physiologic  der  Kleiderlaus  (Pedi- 
culus vestimenti  Nitzsch.)  i.  Anatomic  des  Verdauungstraktus.  Arch.  Schiflf. 
Trop.  Hyg.,  20:  5-76,  1916. 

Sobel,  }.  Pediculosis  capitis  among  school  children.  New  York  Med.  Jl.,  98: 
656-664,  1913. 

Strong,  R.  P.  Trench  fever  report  of  Commission,  Medical  Research  Committee, 
American  Red  Cross.  New  York,  1918. 

Topping,  N.  H.,  and  Dyer,  R.  E.  Apparent  extension  of  typhus  in  the  United 
States.  Amer.  Jl.  Trop.  Med.,  23:  37-42,  1943. 

U.S.  Department  of  Agriculture.  DDT  and  other  insecticides  and  repellents. 
Mis.  Pub.  No.  606,  1946. 

Wolbach,  S.  B.,  Todd,  J.  L.,  and  Palfrey,  F.  W.  The  etiology  and  pathology 
of  typhus;  being  the  main  report  of  the  Typhus  Research  Commission  of  the 
League  of  Red  Cross  Societies  to  Poland.  Cambridge,  Mass.,  1922. 

Zinsser,  H.     Rats,  lice  and  history.     Boston,  1935. 

.  The  rickettsia  diseases:  varieties,  epidemiology  and  geographical  distribu- 
tion. Amer.  Jl.  Hyg.,  25:  430-463,  1937. 


CHAPTER  VIII 


The  Diptera:  Flies 


^  I  ^HE  Diptera  are  insects  with  only  one  pair  of  membranous  wings  (in 
JL  some  groups  the  wings  are  lacking  or  vestigial)  which  are  borne  by  the 
mesothorax  (Fig.  83);  the  second  pair  of  wings  is  represented  by  a  pair  of 
short,  knobbed,  filiform  organs,  the  halteres  (Fig.  53).  The  mouth  parts  are 
suctorial,  usually  forming  a  proboscis  and,  in  some  groups,  adapted  for  pierc- 
ing. The  larvae  are  legless  and  their  respiratory  system  is  reduced  (generally 
amphipneustic) ;  the  pupae  are  usually  free  or  enclosed  in  the  last  larval  skin 
(puparium).  The  metamorphosis  is  complete. 

The  Diptera  constitute  a  very  large  order:  over  80,000  species  have  been 
described  from  the  world  and  at  least  10,000  from  North  America.  Many 
of  the  species  are  very  abundant  in  individuals  and  are  world-wide  in  distribu- 
tion. Furthermore,  they  vary  extremely  in  their  habits  both  as  larvae  and  as 
adults.  The  adults  are  mainly  diurnal,  feeding  on  nectar,  the  exudates  from 
plant  and  animal  wounds,  or  decaying  animal  or  vegetable  matter;  some  arc 
predaceous,  as  the  robber  flics  (Asilidae),  while  large  groups,  and  sometimes 
almost  entire  families,  have  acquired  the  bloodsucking  habit  and  attack  a 
great  variety  of  hosts.  The  larvae  may  be  scavengers,  as  the  blowflies,  flesh 
flies,  bluebottle  flies,  etc.,  parasites  on  man  and  animals,  as  in  the  myiasis- 
producing  flies  (see  pp.  492-533),  or  parasites  on  other  insects  (all  the  Tachini- 
dae,  some  of  the  Sarcophagidae,  etc.).  Many  are  injurious  to  man's  crops;  others 
are  beneficial,  destroying  noxious  insects  (the  larvae  of  the  Syrphidae  are  usu- 
ally predaceous  and  feed  on  a  great  variety  of  insects;  those  of  the  Tachinidae 
are  also  beneficial)  ;  while  many  others  feed  on  wastes  of  all  kinds  and,  in  many 
cases,  are  highly  beneficial. 

The  bloodsucking  habits  of  the  adults;  the  propensity  of  many  flies  to 
feed  on  fecal  or  decaying  wastes  and  human  and  animal  foods;  their  search 
for  moisture  on  mucous  membranes,  exudates  from  sores,  wounds,  or  dis- 
charges from  diseased  tissues;  and  the  domestic  habits  of  many  species — all 
render  the  group  of  great  importance  to  man.  In  addition  to  these  extremely 


THE  DIPTERA:  FLIES  219 

annoying  habits,  many  flies,  both  bloodsucking  and  nonbloodsucking,  are  now 
known  to  be  the  vectors  or  hosts  in  the  developmental  stages  of  many  parasites 
pathogenic  to  man  and  animals.  Here  may  be  mentioned  mosquitoes  and 
malaria,  yellow  fever,  dengue,  filariasis,  encephalitis  (and  other  diseases); 
Glossina  flies  and  sleeping  sickness  or  trypanosomiasis;  houseflies  and  typhoid 
fever,  diarrheas,  (and  other  diseases);  Phlebotomus  flies  and  Oroya  fever, 
kala  azar,  and  pappataci  fever.  Viewing  the  group  as  a  whole  we  may  roughly 


Fig.  83.  A  common  flesh  fly,  Sarcophaga  bullata.  A,  arista  of  antenna;  Al,  axil- 
lary lobe;  MES,  mesonotum,  which  occupies  practically  all  of  the  dorsal  surface 
of  the  thorax;  O,  ocelli;  SCT,  the  scutellum  of  the  mesonotum;  TS,  transverse 
suture. 

classify  the  disease  relationships  of  flies  to  man  and  animals  in  the  following 
categories : 

1.  Flies,  bloodsucking  in  habit,  act  as  carriers  of  pathogenic  organisms.  The 
carriage  may  be  mechanical,  that  is,  the  fly  feeding  on  the  blood  of  a  diseased 
animal  may  go  directly  to  another  susceptible  animal  to  complete  its  meal  and 
inoculate  living  organisms  present  in  or  on  its  proboscis;  the  fly  may  also  act  as 
a  host  in  the  developmental  cycle  of  the  organism,  as  mosquitoes  do  in  malaria. 

2.  Flies,  nonbloodsucking  in  habit,  may  deposit  their  eggs  or  living  larvae  in 
wounds,  sores,  cavities,  on  the  surface  or  hairs  of  the  body,  or  on  food,  and  the 


220  MEDICAL  ENTOMOLOGY 

larvae  developing  cause  serious  diseased  conditions  (myiasis-producing  larvae) . 

3.  Bloodsucking  and  nonbloodsucking  flies  may  act  as  the  intermediate 
hosts  of  helminths  of  man  and  animals.  Examples:  Culex  fatigans  and  Wuche- 
reria  bancrojti  of  man;  Culex  pipiens,  Aedes  vexans,  etc.,  and  Dirofilaria  im~ 
mitis  of  dogs;  Simulium  damnosum,  S.  metallicum,  and  Onchocerca  volvulus 
of  man;  Chrysops  spp.  and  Loa  ha  of  man;  Musca  domestica  and  Choano- 
taenia  infundibulum  of  poultry;  and  many  others. 

4.  Nonbloodsucking  flies  that  seek  moisture  about  mucous  membranes, 
either  diseased  or  not,  or  that  feed  on  fecal  or  other  human  or  animal  wastes, 
liquids,  or  discharges  from  wounds  may  distribute  pathogenic  organisms  on 
their  bodies  or  by  way  of  their  intestinal  tracts.  The  organisms  obtained  with 
the  food  may  be  digested  but,  if  not,  may  be  passed  with  the  feces  or  the  so- 
called  "vomit  spots"  of  many  flies.  A  large  number  of  flies  are  involved  in  these 
relations  and  our  knowledge  of  them  is  far  from  complete. 

STRUCTURE 

The  structure  of  the  Diptera  can  be  dealt  with  only  very  briefly,  and  then 
only  those  characters  mainly  concerned  with  classification  and  in  the  transmis- 
sion of  disease  can  be  treated. 

THE  HEAD  (Figs.  83,84)  :  In  flies  the  head  is  free  and  movable  and  usually 
of  relatively  large  size.  It  bears  the  large  compound  eyes  which  may  be  con- 
tiguous on  the  vertex  (holoptic)  or  widely  separated  (dichoptic).  Ocelli  are 
generally  present  and  usually  three  in  number,  located  between  or  slightly 
behind  the  eyes  on  the  vertex.  The  antennae  are  of  varied  forms  (Fig.  51)  and 
furnish  excellent  characters  for  classification.  The  mouth  parts  are  formed  for 
sucking  (Fig.  47),  lapping,  or  piercing  (Fig.  97).  Their  structure  varies  greatly 
in  the  different  families  and  details  will  be  given  in  the  treatment  of  those 
families  (for  a  general  account  see  pp.  133-139).  In  the  specialized  Diptera 
(suborder  Cyclorrhapha)  there  will  be  observed  a  small  inverted  U-shaped 
suture  immediately  above  the  antennae,  the  frontal  suture  (Fig.  84).  This 
suture  represents  the  opening  through  which  the  ptilinum,  a  bladderlike  struc- 
ture, was  extruded  at  the  time  the  adult  emerged  from  its  puparium.  The  ptili- 
num is  forced  out  by  internal  pressure  and  the  cap  of  the  puparium  is  broken 
off;  its  usefulness  now  ended,  it  is  withdrawn  into  the  head  and  the  frontal 
suture  marks  the  point  of  withdrawal.  The  median  area  extending  from  the 
frontal  suture  to  the  ocelli  and  lying  between  the  rows  of  bristles  (frontal 
bristles)  is  the  frontal  vitta.  A  small  area  above  and  between  the  bases  of  the 
antennae  is  known  as  the  frontal  lunule. 


THE  DIPTERA:  FLIES 


Fig.  84.  The  areas  and  setae  of  the  head  of  the  blowfly,  CaUiphora  viridesccn 
(After  Walton.) 


222  MEDICAL  ENTOMOLOGY 

THE  THORAX:  the  thoracic  region  is  largely  composed  of  the  meso- 
thorax,  both  the  prothorax  and  metathorax  being  greatly  reduced  (Fig.  85) . 
The  interpretation  of  the  various  sclerites  of  the  thoracic  region  is  still  much 
in  dispute  so  that  conventional  terms,  with  no  special  morphological  value,  are 
widely  used.  This  is  especially  true  of  the  terms  used  to  designate  the  various 
groups  of  bristles  or  macrochaetae  (Fig.  85).  The  wings  of  the  Diptera  consist 
of  a  single  pair,  the  second  pair  being  reduced  and  represented  by  the  halteres. 
The  wings  are  thin  and  membranous,  usually  naked  or  with  microscopic  setae. 
In  the  Psychodidae  (moth  flies)  the  wings  are  covered  with  fine  hairs,  while 
in  the  Culicidae  (mosquitoes)  the  margin  of  the  wing  bears  a  fringe  of  scales 
and  most  of"  the  veins  are  also  scaled  (Fig.  93).  The  venation  of  the  wings  is 
much  used  in  the  classification  of  this  order.  It  corresponds  rather  closely  to 
the  hypothetical  type  (Fig.  55).  The  names  applied  to  the  veins  and  the  cells 
will  be  found  on  pages  145-149.  Fig.  86  shows  in  detail  the  modifications  found 
in  the  more  specialized  Diptera  (Muscidae)  with  all  the  veins  and  cells  fully 
labeled. 

In  many  families  the  posterior  margin  of  the  wing,  near  its  base,  is 
notched,  the  axillary  incision;  the  lobe  thus  somewhat  detached  is  called  the 
posterior  or  axillary  lobe  (Fig.  86).  In  addition,  the  axillary  lobe  may  be 
greatly  expanded  (many  muscoidean  flies)  and  folded  beneath  the  wing  base. 
When  fully  developed  there  are  two  extra  lobes,  one  above  the  other  (Fig. 
83).  These  lobes  are  called  the  calypteres,  alulae,  or  squamae,  and  are  desig- 
nated the  upper  and  lower  respectively. 

The  legs  vary  greatly  in  length  and  stoutness.  They  consist  of  the  usual 
parts  (Fig.  54).  The  tarsi  are  usually  five-jointed  and  may  terminate  in  pul- 
villi.  Between  the  pulvilli  there  often  exists  a  third  structure,  the  empodium, 
which  may  be  bristlelike  or  padlike. 

From  the  standpoint  of  taxonomy  the  wing  venation,  antennal  characters, 
and  the  arrangement  of  the  bristles  of  the  head,  thorax,  and  at  times  the 
abdomen  constitute  very  essential  characters.  The  arrangement  of  the  bristles 
are  of  especial  importance  in  many  of  the  groups  of  Diptera  that  are  of  great 
interest  to  the  medical  entomologist. 

CHAETOTAXY  OF  THE  DIPTERA 

Muscoidean  Flies  (Myodaria) 
THE  HEAD: 

The  arrangement  of  the  bristles  and  the  parts  on  which  they  occur  are 
fully  illustrated  in  Fig.  84.  A  frontal  view  and  a  lateral  view  of  the  head  are 
shown  in  the  two  upper  figures  and  all  the  bristles  are  named.  These  are: 


THE  DIPTERA:  FLIES  223 

/.  Facial  Bristles:  A  series  of  bristles  on  each  side  borne  by  the  vibrissal 
ridge,  above  the  vibrissae. 

2.  Frontal  Bristles:  A  row  of  bristles  on  each  side  of  the  frontal  vitta;  the 
lower  ones  directly  above  the  frontal  suture  or  base  of  the  antennae  are 
often  called  the  trans jrontals  ;  and  the  upper  one  to  four,  the  frontals. 

3.  Pronto-orbital  Bristles:  One  or  several  bristles,  usually  in  a  row,  be- 
tween the  frontal  bristles  and  the  eye.  They  are  located  on  the  genovertical 
plate. 

4.  Lateral  Facial  Bristles:  One  or  two  bristles  at  times  present  on  the 
sides  of  the  face  below  the  eye  (marked  "sometimes  called  cruciate"  in  the 
figure). 

5.  Ocellar  Bristles:  A  pair,  the  greater  ocellars,  are  situated  on  the  ocellar 
triangle  just  back  of  the  median  ocellus;  they  always  point  forward  and 
diverge.  The  lesser  ocellars  are  small  bristles  located  in  lines  back  of  the 
greater  ocellars  and  consist  of  a  variable  number. 

6.  Vertical  Bristles:  Two  pairs,  an  inner  and  outer  pair,  situated  on  the 
vertex  and  inserted  more  or  less  behind  the  upper  and  inner  corners  of  the 
compound  eye. 

7.  The  Vibrissae:  A  pair  of  stout  bristles,  one  on  each  side  of  the  lower 
part  of  the  face,  near  or  above  the  oral  margin. 

8.  The  Beard:  The  beard  is  represented  as  a  mass  of  fine  bristles  present 
on  the  lower  portion  of  the  occiput  and  cheek. 

9.  The  Arista:  A  prominent  bristle,  arising  from  the  third  segment  of  the 
antennae.  It  may  be  bare,  partially  or  completely  plumose,  or  modified  in 
other  ways  (Fig.  51). 

The  parts  of  the  head  on  which  the  above-described  bristles  are  borne  are 
fully  explained  in  the  figure. 

THE  THORAX  (Fig.  85) 

THE  SUTURES  AND  RECiIONS:  The  following  sutures  of  the  thorax 
are  of  importance  in  determining  areas  of  the  thorax: 

1.  The  Transverse  Suture  is  an  impressed  line  extending  across  the  meso- 
notum,  terminating  a  little  in  front  of  the  root  of  the  wing. 

2.  The  Notopleural  or  Dorsopleural  Suture  extends  from  the  humeral 
callus  to  the  mesopleural  suture  and  separates  the  mesonotum  from  the 
pleuron. 

j.  The  Mesopleural  Suture  extends  downward  from  in  front  of  the  wing 
to  the  sternopleural  suture,  separating  the  mesopleuron  from  the  pteropleu- 


224  MEDICAL  ENTOMOLOGY 

4.  The  Sternopleural  Suture  separates  the  mesopleuron  from  the  sterno- 
pleuron. 

The  areas  bounded  by  these  sutures  are  all  named  in  the  lateral  view  of  the 
thorax  (Fig.  85). 

THE  THORACIC  BRISTLES:  The  bristles  of  the  thorax  and  their  ar- 
rangement are  of  great  importance  and  a  mastery  of  them  is  essential  for 
any  systematic  work  with  the  higher  Diptera.  Their  importance  is  also 
accepted  in  other  groups  (Culicidae,  etc.).  The  more  important  bristles  are: 

1.  Acrostichals:  Two  rows  of  bristles,  one  on  each  side  of  the  median  line 
of  the  mesonotum.  The  transverse  suture  separates  them  into  the  anterior 
and  posterior  acrostichals. 

2.  Dorsocentrals:  A  row  on  each  side,  next  to  and  parallel  with,  the  acrosti- 
chals. The  transverse  suture  divides  them  into  the  anterior  and  posterior 
dorsocentrals. 

j.  Discal  Scutellars  and  Marginal  Scutellars:  The  discal  scutellars  usually 
consist  of  a  pair  of  bristles  on  the  dorsal  portion  of  the  scutellum;  the  mar- 
ginal scutellars  form  a  distinct  row  of  large  bristles  on  the  margin  of  the 
scutellum. 

4.  The  Humerals:  One  or  more  bristles  situated  on  the  humeral  callus. 

5.  The  Hypopleural  Row:  A  row  of  bristles  running  in  a  more  or  less 
vertical  direction  on  the  hypopleura  (usually  directly  below  the  posterior 
spiracle  or  above  the  hind  coxa).  The  bristles  may  be  grouped  in  a  tuft. 

6.  The  Intra-alars:  A  row  of  two  or  three  bristles  just  laterad  of  the  posterior 
dorsocentrals. 

7.  The  Mesopleural  Row:  A  prominent  row  of  bristles  in  front  of  the  meso- 
pleural  suture  and  below  the  dorsopleural  suture. 

8.  The  Notopleurah:  Usually  two  bristles  inserted  directly  above  the  dorso- 
pleural suture,  between  the  humeral  callus  and  the  root  of  the  wing. 

9.  Post-alar s:  Bristles  on  the  post-alar  callus  directly  back  of  the  supra-alar 
row  and  the  intra-alars. 

w.  Post-humerals:  Two  or  three  bristles  located  just  behind  the  humeral 
callus  on  the  mesonotum. 

//.  Prescutellar  Row:  A  name  applied  to  the  row  of  bristles  just  in  front 
of  the  scutellum  and  consisting  of  the  caudal  dorsocentrals  and  acrostichals. 

12.  Presuturals:  One  or  more  bristles  just  in  front  of  the  outer  end  of  the 
transverse  suture  and  above  the  presutural  depression. 

/j.  The  Sternopleurals:  One  or  several  bristles  on  the  sternopleura  and 
directly  below  the  Sternopleural  suture.  These  are  often  arranged  two  in 


THE  DIPTERA:  FLIES 


225 


Fig.  85.  The  principal  external  structures  of  the  thorax  of  the  blowfly, 
Calliphora  viridesccns,  and  the  arrangement  of  the  macrochaetae.  (After 
Walton.) 

front  and  one  behind  (written  "sternopleurals  2:1");  one  in  front  and  two 
behind  (1:2);  two  in  front  and  two  behind  (2:2) ;  etc. 

14.  The  Sub-lateral  Row:  Frequently  the  anterior  posthumerals  and  the 
inner  presutural  are  treated  as  a  row  and  bear  the  above  name. 


226  MEDICAL  ENTOMOLOGY 

15.  The  Supra-alar  Row:  Usually  one  to  four  bristles  in  a  row  above  the 
root  of  the  wing  between  the  notopleurals  and  the  post-alars. 

CLASSIFICATION  OF  THE  DIPTERA 

The  Diptera  are  divided  into  two  suborders,  the  Orthorrhapha  or  the 
straight-seamed  flies  and  the  Cyclorrhapha  or  the  circular-seamed  flies. 

The  Orthorrhapha  includes  those  flies  in  which  the  pupa  escapes  from  the 
last  larval  skin  through  a  transverse  or  T-shaped  slit  near  the  anterior  end, 
or  by  a  transverse  slit  between  the  seventh  and  eighth  abdominal  segments. 
The  larva  usually  has  a  well-developed  or  somewhat  reduced  head.  The 


*s 


Fig.  86.  Wing  of  Calliphora  viridcscens  (=  C.  lividd)  with  veins  and  cells  labeled. 
(After  Walton,  Entomological  News.) 

pupa  is  naked,  never  enclosed  in  the  last  larval  skin.  The  adults  are  either 
slender  flies  with  long  and  many-jointed  antennae  or  robust  flies  with  re- 
duced antennae.  The  venation  of  the  wing  is  simple  (Figs.  56,57) . 

The  Cyclorrhapha  include  those  flies  in  which  the  pupa  is  not  naked  but 
is  enclosed  in  the  last  larval  skin — the  puparium.  The  adult  emerges  through 
a  round  opening  made  by  pushing  of!  a  cap  at  the  anterior  end  by  means  of 
the  ptilinum.  The  adults  possess  a  frontal  lunule  that  is  delimited  by  the 
frontal  suture  (Fig.  84).  The  wing  venation  is  more  complicated  (Fig.  86). 

SUBORDER  ORTHORRHAPHA 

This  suborder  is  divided  into  two  series  that  are  difficult  to  differentiate 
as  there  are  no  well-defined  and  clear-cut  separating  characters. 


THE  DIPTERA:  FLIES  227 

SERIES  I,  NEMOCERA  (Nematocera) :  In  this  series  the  larva  possesses 
a  well-developed  head  with  mandibulate  mouth  parts;  the  pupa  is  free,  not 
enclosed  in  the  last  larval  skin.  The  adults  have  long  antennae,  many-jointed 
(8  to  1 6  or  more),  usually  longer  than  the  head  and  thorax,  and  the  joints 
nearly  similar;  the  palpi  are  pendulous,  consisting  of  one  to  five  segments. 
The  anal  cell  (ist  A)  is  not  narrowed  toward  the  margin  of  the  wing  and 
the  discal  cell  is  generally  absent  (Fig.  86) . 

The  Ncmocera  include  some  twelve  or  more  families  of  flies.  Only  four 
of  these  families  contain  species  known  to  be  of  medical  importance;  in  two 
of  these  families  only  a  small  group  of  species  is  of  significance. 

SERIES  II,  BRACHYCERA:  In  this  series  the  larval  head  is  usually  re- 
duced, generally  retractile,  the  mandibles  acting  vertically  instead  of 
horizontally;  the  pupa  is  free.  The  antennae  are  shorter  than  the  head  and 
thorax,  generally  three-jointed;  the  last  segment  is  elongate  and  often  an- 
nulate; style  or  arista,  when  present,  is  terminal,  palpi  are  porrect,  one-  or 
two-jointed.  Discal  cell  usually  present  and  the  anal  cell  is  closed  or  narrowed 
before  the  margin  of  the  wing  (Figs.  56,57) . 

THE  SUBORDER  CYCLORRHAPHA 

This  suborder  includes  a  large  number  of  families.  Their  classification  is 
in  a  very  unsatisfactory  condition  since  well-defined  differentiating  characters 
have  not  been  found.  At  present  the  suborder  is  divided  into  two  series,  the 
Aschiza  and  the  Schizophora. 

SERIES  I,  THE  ASCHIZA:  In  this  series  the  adults  do  not  possess  a 
frontal  suture,  or  it  is  restricted;  the  ptilinum  is  nonpersistent,  not  being 
retained  after  the  adult  emerges  from  the  puparium.  The  series  contains 
four  families  of  which  one,  the  Syrphidae  or  hover  flies,  is  of  medical  im- 
portance (see  pp.  524-527). 

SERIES  II,  THE  SCHIZOPHORA:  The  adults  possess  a  frontal  suture, 
well  marked,  and  the  ptilinum  persists  as  a  structure  retained  within  the 
head,  directly  behind  the  suture.  This  series  is  composed  of  a  large  number 
of  families,  many  of  them  of  the  greatest  interest  to  the  medical  entomologist. 
It  is  generally  divided  into  two  sections,  the  Myodaria  and  the  Pupipara. 

Section  I,  Myodaria:  The  Myodaria  or  muscoidean  flies  is  the  largest  group 
of  Diptera,  including  many  families  and  probably  more  than  half  of  all  the 
living  species  of  flies.  This  section  is  further  divided  into  two  subsections, 
the  Acalypteratae  and  the  Calypteratae. 

In  the  Acalypteratae  the  squamae  or  calypteres  are  small  or  vestigial  and 


228  MEDICAL  ENTOMOLOGY 

do  not  conceal  the  halteres;  the  transverse  suture  of  the  thorax  is  usually 
not  distinct.  This  group  contains  many  families  of  small,  to  very  small,  flies; 
a  few  are  of  importance  to  man  and  are  discussed  on  pages  527-528. 

In  the  Calypteratae  the  squamae  or  calypteres  are  well  developed,  large,  and 
frequently  conceal  the  halteres;  the  transverse  suture  of  the  thorax  is  distinct 
and  prominent.  The  flies  are  moderate  to  large  in  size.  Here  belong  the  house- 
flies,  flesh  flies,  blowflies,  etc. 

Section  II,  Pupipara:  The  Pupipara  is  a  remarkable  groUp  of  flies.  They  are 
all,  except  Braula,  bloodsucking  ectoparasites  of  mammals  and  birds.  Their 
structure  has  been  greatly  modified  to  fit  them  for  their  parasitic  habits. 
Their  bodies  are  tough,  leathery,  and  the  abdomen  is  indistinctly  segmented; 
they  may  be  winged  or  wingless  and  the  mouth  parts  are  fitted  for  piercing 
and  sucking  blood.  Larval  development  takes  place  within  a  uterinelike 
structure  of  the  female  (except  Braula),  and  the  young  are  deposited  as 
full-grown  larvae.  Some  of  the  species  are  of  importance  as  they  attack 
domestic  and  game  animals  and  act  as  vectors  of  disease  (the  sheep  tick  or 
ked,  Melophagus  ovinus  and  Trypanosoma  melophagium,  the  causative  agent 
of  sheep  trypanosomiasis;  Lynchia  maura  and  Haemoproteus  columbae  of 
pigeons). 

It  is  not  feasible  to  prepare  a  key  to  all  the  families  of  Diptera  that  affect 
man.  The  following  table  will  aid  in  separating  the  more  important  families 
of  Diptera  that  are  of  medical  importance: 

KEY  TO  THE  PRINCIPAL  FAMILIES  OF  DIPTERA  (ADULTS) 

ASSOCIATED  WITH   HUMAN  DISEASE  OR  KNOWN 

AS  BLOOD  SUCKERS 

1.  Flies  of  a  leathery  or  horny  texture,  living  in  the  adult  stage  as  blood- 

sucking ectoparasites  on  birds  or  mammals;  they  may  be  winged, 
wingless,  or  with  vestigial  wings;  abdomen  not  distinctly  divided 
into  segments;  the  antennae  are  short  and  inserted  in  small  pits,  not 

easily  seen.  (The  group  Pupipara)  2 

Flies  not  as  described  above:  abdomen  with  distinct  segments;  never 
external  parasites  living  as  adults  on  birds  or  mammals;  antennae  not 
inserted  in  pits,  usually  easily  seen;  usually  with  one  pair  of  wings  4 

2.  Head  small,  narrow,  folded  back  in  a  groove  in  the  thorax.  Wingless. 

Parasites  of  bats  Nycteribiidae 

Head  not  as  described  above,  in  normal  position 3 

3.  Palpi  elongate,  forming  a  sheath  for  the  piercing  mouth  parts.  Usually 


THE  DIPTERA:  FLIES  229 

winged  with  the  veins  crowded  anteriorly.  Parasites  of  birds  and 

mammals  Hippoboscidae 

Palpi  not  forming  a  distinct  sheath  for  the  piercing  mouth  parts  but 
broad  and  leaflike.  Winged  or  wingless  and  in  the  winged  forms  the 
veins  evenly  distributed.  Parasites  of  bats  Streblidac 

4.  Antenna  consisting  of  eight  or  more  freely  movable,  nearly  similar 

segments;  anal  cell  (Fig.  93)  widens  toward  the  margin  of  the  wing. 

The  group  Nemocera  5 

Antenna  consisting  of  not  more  than  four  or  five  well-defined  segments; 
the  segment  beyond  the  second  may  appear  as  more  or  less  consoli- 
dated into  rings  or  annuli 9 

5.  The  costal  vein  is  not  continued  beyond  the  apex  of  the  wings;  hairs 

and  scales  seldom  present  (Fig.  145)  6 

The  costal  vein  surrounds  the  wing;  hairs,  often  dense,  on  the  wing  or 
scales  present  on  the  veins,  especially  on  costa  and  posterior  margins 
of  wing 8 

6.  Antenna  shorter  than  the  thorax,  composed  of  ten  or  eleven  closely 

united,  similar  segments;  never  plumose;  legs  strong,  the  hind  pair 
more  or  less  dilated:  body  thickset;  wings  broad  with  few  veins. 

(Black  flies)   Simuliidae 

Antenna  longer  than  the  thorax,  usually  bushy  with  long  hairs.  In 
general  not  as  described  above 7 

7.  Dorsum  of  thorax  with  a  longitudinal  groove;  wings  narrow  and,  in 

life,  held  more  or  less  roof  like;  mouth  parts  not  fitted  for  piercing. 

(None  are  known  to  be  of  medical  importance;  the  gnats)  

Chironomidae 

Dorsum  of  thorax  without  a  longitudinal  groove;  wings  held  flat  and 
superimposed  over  each  other  when  at  rest;  wings  often  spotted 

(Fig.  153).  Mouth  parts  fitted  for  piercing.  (Punkies)  

(Heleidae)    Ceratopogonidae 

8.  Small  mothlike  flies;  mouth  parts  very  short;  wings  and  body  clothed 

with  long  hairs;  wings  with  long  parallel  veins;  scales  on  wings  ab- 
sent   Psychodidae 

A.  Wings  with  the  second  longitudinal  vein  three-branched,  the 

third  branch  arising  near  the  base.  (Fig.  88).  Not  known 

to  be  of  medical  importance Subfamily  Psychodinae 

AA.  Wings  with  the  second  longitudinal  vein  three-branched,  the 

third  branch  arising  near  the  middle  of  wing  (Fig.  88). 

(Of  great  medical  importance)  . . .  Subfamily  Phlebotominac 


230  MEDICAL  ENTOMOLOGY 

Not  mothlike  flies;  posterior  margin  of  wings  and  most  of  the  veins 

with  coarse  scales  (Fig.  93);  mouth  parts  elongate,  slender,  well 

adapted  for  piercing  (most  species) .  (The  mosquitoes)   ....  Culicidae 

9.  Antenna  consisting  of  four  or  five  segments,  the  segment  beyond  the 

second  may  appear  as  more  or  less  consolidated  into  rings  but  can 

be  easily  counted  (3  to  8  rings) ;  squamae  large.  (Horseflies)   

Tabanidae 

Antenna  consisting  of  only  three  segments 10 

10.  Last  segment  of  antenna  small  and  ending  in  an  elongate  style  or 

arista  (Fig.  162) .  (The  snipe  flies)   Rhagionidae 

Last  segment  much  larger  than  the  others  and  with  a  dorsal  arista 
either  bare  or  plumose  (Fig.  51  /)  or  a  terminal  arista n 

11.  Wing  with  stout  veins  (2  or  3)  near  the  inner  costal  border;  other 

veins  are  weak  and  extend  outward  to  the  wing  margin;  no  cross 

veins Phoridac 

Wing  not  as  described  above  12 

12.  Anal  cell  elongate  reaching  nearly  to  the  margin  of  the  wing;  a  spurious 

or  false  vein  present  between  the  third  and  fourth  longitudinal  veins; 

usually  brightly  colored,  flower-loving  flies  (F"ig.  211)  Syrphidae 

Anal  cell  short,  truncate  (Fig.  172  a) ;  spurious  vein  absent 13 

13.  Second  antenna!  segment  with  a  longitudinal  cleft  or  suture  on  its  up- 

per outer  edge  (Fig.  51  ds);  squamae  usually  conspicuous;  thorax 

generally  with  a  conspicuous  transverse  suture 14 

Second  antennal  segment  without  a  longitudinal  cleft  on  its  upper, 
outer  edge;  squamae  usually  small  or  very  small;  thorax  usually  with- 
out a  complete  transverse  suture  18 

14.  Mouth  parts  vestigial.  (The  warble  flies  and  botflies,  including  Cutere- 

bridae  and  Hypodermatidae)   Oestridac 

Mouth  parts  well  developed  and  functional 15 

15.  Hypopleura  without  a  well  developed  row  of  bristles  below  the  pos- 

terior spiracle  (Fig.  85).  Small  hairs  may  be  present.  Arista  of  antenna 
usually  hairy  or  plumose.  (Houseflies,  stable  flies,  glossina  flies)   .... 

Muscidae   (and   Anthomyiidae) 

Hypopleura  with  a  well-developed  row  of  bristles  (Fig.  85)  or  tuft 
of  bristles  16 

16.  Postscutellum  and  postnotum  appearing  in  side  view  as  double  con- 

vexities (double  chin  effect  under  the  scutellum).  Usually  strongly 

bristled  flies.  All  parasites  as  larvae,  mostly  on  other  insects 

Tachinidae 


THE  DIPTERA:  FLIES  231 

Postscutellum  not  strongly  developed  so  that  only  the  single  convex 
postnotum  appears  in  side  view 17 

17.  Flies  in  which  the  coloration  is  largely  metallic,  blues,  dark  blues,  black, 

or  shades  of  green.  A  few  species  are  not  metallic  but  have  golden 
hairs  on   the  thorax  among  the  bristles   (Pollenia)\  usually   four 

notopleural  bristles  present.  (The  blowflies)  Calliphoridae  1 

Flies  in  which  coloration  is  mainly  gray,  silvery,  intermixed  with  darker 
colors;  rarely  more  than  two  notopleural  bristles  present.  (The  flesh 
flies)  Sarcophagidae 1 

18.  Mouth  parts  vestigial,  sunk  in  a  tiny  oval  pit;  large,  brownish,  fuzzy 

flies  (15  mm.  or  more).  (Horse  botflies;  Figs.  206-208)  Gasterophilidae 
Mouth  parts  well  developed,  not  sunk  in  a  pit 19 

19.  Subcosta  vestigial;  if  present  it  extends  but  a  short  distance  beyond 

the  humeral  cross  vein  but  does  not  reach  the  costa 20 

Subcosta  present  and  extending  to  the  costa  (but  must  be  looked  for 
with  care  as  it  is  almost  concealed  beneath  the  base  of  the  ist  longi- 
tudinal    21 

20.  Sixth   longitudinal  and  anal  veins  absent;  ocellar  triangle   large  as 

compared  with  size  of  head;  subcosta  only  present  at  base  and  ap- 
pears as  a  minute  fold;  costa  with  only  one  fracture  (Fig.  178).  Very 

small  flics  (i  to  3  mm.).  (Eye  gnats)  Chloropidae 

Sixth  longitudinal  vein  and  usually  anal  vein  present;  subcosta  more 
distinct  but  docs  not  reach  the  costa;  costa  with  two  fractures.  (The 
fruit  flies)  . Drosophilidae 

21.  Palpi  vestigial.  Small,  shiny  black,  brown,  or  reddish  flies  with  few 

bristles.  Head  spherical  and  abdomen  wasp-shaped Sepsidae 

Palpi  well  developed.  Also  small  flics  but  not  of  the  shape  indicated 
above.  (The  cheese  skipper)  Piophilidae 

A  KEY  TO  THE  LARVAE   OF  SOME  OF  THE  FAMILIES  OF 
DIPTERA  MENTIONED   IN  THE   KEY   TO  THE  ADULTS 

i.  Head  well  developed,  enclosed  in  a  horny  capsule,  not  retractile;  mouth 

parts  normal,  the  mandibles  moving  laterally  in  feeding  2 

Head  not  well  developed  but  if  partially  developed  the  mandibles  move 
vertically,  parallel  to  each  other  or  obliquely  inward;  or  with  no  visible 

1  These  two  family  names  are  retained  here  though  the  grouping  of  the  genera  of 
the  Musciclac,  Calliphoridae,  and  Sarcophagidae  varies  with  different  specialists.  These 
,  names  are  still  in  common  usage  in  medical  literature  and  include  the  most  important 
genera  affecting  man  and  animals. 


232  MEDICAL  ENTOMOLOGY 

head,  and  the  anterior  end  pointed  and  provided  with  mouth  hooks 
or  reduced  parts  (Figs.  159,160,173);  or  the  entire  larva  grublike, 
rounded  at  both  ends  (Fig.  210) ;  or,  possessing  an  elongated  siphon  at 
end  o£  abdomen  (Fig.  211)  7 

2.  Aquatic  or  semiaquatic  larvae,  living  only  in  swift  streams  or  in  tree- 

holes,  mud,  edges  of  ponds,  or  in  open  water 3 

3.  Prolegs  lacking  on  all  segments  of  the  body 4 

Prolegs  present  on  some  segments  of  the  body  (Fig.  149) 6 

4.  Head  distinct;  thorax  and  abdominal  segments  divided  secondarily  into 

annuli  or  rings,  usually  each  ring  with  a  dorsal  plate;  respiratory 

openings  on  prothorax  and  anal  segments  (amphipneustic)  

Psychodinae 

Head  distinct;  the  segments  of  thorax  and  abdomen  without  secondary 
divisions  and  otherwise  differing  from  above  couplet 5 

5.  Thoracic  segments  fused,  forming  a  more  or  less  greatly  enlarged  portion, 

distinctly  thicker  than  the  abdomen  (Fig.  105)  ;  respiration  by  spiracles 
located  at  end  of  elongated  tube  (siphon)  or  flattened  posterior  spiracles 

(metapneustic).  (Mosquitoes,  see  pp.  250-332)  Culicidae 

Thoracic  and  abdominal  segments  about  equal  in  diameter,  the  thoracic 
segments  not  greatly  enlarged;  larvae  snakelike  (Fig.  152  C)  with 

rather  smooth  bodies.  (Culicoides,  Bezzia,  and  others;  punkies)   

(Heleidae)  Ceratopogonidae 

6.  Two  prolegs  on  each  of  abdominal  segments  i  and  2;  tracheae  ending  in 

a  pair  of  discs  on  eighth  abdominal  segment Dixidae 

Prolegs  (usually  only  a  single  one)  confined  to  the  prothoracic  segment; 

posterior  end  of  larva  with  an  adhesive  disc  for  attachment.  (Larvae 

confined  to  more  or  less  swift  water;  black  flics)   Simuliidae 

Prolegs  present  on  prothorax  and  posterior  end  of  body  or  they  may  be 

reduced;  never  as  above.  (Gnats)  (Tendipcdidae)  Chironomidae 

Larva  with  well-developed  head  and  provided  with  stout  bristly  hairs  or 
spines  (Fig.  90  b) ;  body  with  similar  hairs;  tip  of  abdomen  with  two 

groups  of  long  hairs;  abdomen  with  prolegs.  (Sand  flies)  

Phlebotominae 

7.  Larvae  cylindrical  pointed  at  both  ends;  mandibles  present,  hooklike,  and 

move  vertically,  parallel  to  each  other;  respiratory  organs  (spiracles) 
located  in  a  vertical  cleft,  and  usually  on  the  tip  of  a  posterior  siphon 

(Fig.  160)  Tabanidae 

Larvae  not  as  described  above 8 

8.  Stout,  grublike  larvae  (aquatic)  with  a  long  telescopic  terminal  siphon. 


THE  DIPTERA:  FLIES  233 

(Rat-tailed  maggots;  Fig.  211)  (in  part)  Syrphidae 

Larvae  not  as  described  above.  For  identification  of  larvae  which  do  not 
agree  with  any  of  the  above  descriptions,  consult  the  key  given  on 
pages  531-533- 

REFERENCES 

Aldrich,  J.  M.  A  catalogue  of  North  American  Diptera.  Smithsonian  Misc. 
Colls.  46,  Washington,  1905. 

Curran,  C.  H.  The  families  and  genera  of  North  American  Diptera.  New  York, 
1934.  (A  valuable  book.) 

Fauna  of  British  India.  The  Diptera.  London,  1912-1940.  5  vols.  (Ex- 
tremely valuable  for  workers  in  the  East.) 

Lindner,  Erwin  (editor).  Die  Fliegen  der  palaearktischen  Region.  Stuttgart, 
1925-1935.  (A  series  of  volumes;  various  parts  have  been  published.) 

Walton,  W.  R.  An  illustrated  glossary  of  chaetotaxy  and  anatomical  terms  used 
in  describing  Diptera.  Ent.  News,  20:  307-319,  1909. 

Williston,  S.  W.  Manual  of  North  American  Diptera.  New  Haven,  Conn., 
1908. 


CHAPTER  IX 


The  Psychodidae: 

The  Moth  Flies,  Owlet  Midges, 

and  Sand  Flies 


THE  members  of  this  family  are  long-legged,  small  mothlike  flies  rarely 
exceeding  5  mm.  in  length  (Fig.  87).  Their  bodies  and  wings  are 
densely  clothed  with  hairs.  The  wings  (Fig.  88)  are  either  oval  or  lanceolate 
in  shape  and,  when  at  rest,  are  held  rooflike  or  in  an  arched  manner  over  the 


Fig.   8j.   A   sand   fly,   Phlebotomus   vcrruciinim 
Hertig.) 


.    (From  a  photograph  presented  by 


abdomen.  The  venation  is  simple,  consisting  mainly  of  longitudinal  veins. 
The  mouth  parts  are  short  and  not  well  adapted  for  piercing  (subfamily 
Psychodinae)  or  rather  long  and  fitted  for  bloodsucking  (Fig.  89),  the 


THE  PSYCHODIDAE  235 

subfamily  Phlebotominae.  The  antennae  are  long,  slender,  and  consist  of  12 
to  16  segments,  each  usually  with  short  hairs.  The  two  subfamilies,  Psychod- 
inae  and  Phlebotominae,  may  be  readily  separated  by  the  characters  given 
in  the  key  (pp.  228-231). 

The  majority  of  known  species  belong  in  the  subfamily  Psychodinae  in 
which  the  mouth  parts  are  not  adapted  for  bloodsucking.  The  adults  are 
usually  whitish,  small,  mothlike,  and  are  commonly  found  about  kitchens 
and  outhouses,  along  creeks  filled  with  decaying  wastes,  and  about  sewage 
disposal  plants  where  they  may  breed  in  vast  numbers  and  the  adults  be 
very  annoying.  The  larvae  occur  in  decaying  vegetable  wastes,  sewage,  dung, 
exuding  sap  on  trees,  fouled  streams,  and  similar  situations.  None  of  the 
species  are  known  to  be  of  medical  importance,  though  their  abundance  may 
be  annoying  at  times. 


Fig.  88.  Left:  The  wing  of  a  Phlcbotomus  sp.  Right:  The  wing  of  a  Psychoda  sp.  The 
veins  and  margins  of  wings  are  clothed  with  long  hairs  but  these  are  omitted,  av, 
auxiliary  or  subcostal  vein.  The  numbers  indicate  the  longitudinal  veins. 

*  In  the  subfamily  Phlebotominac  the  adults  (usually  called  sandflies)  are 
bloodsucking,  the  mouth  parts  being  well  adapted  for  piercing  (Fig.  89). 
This  group  contains  but  a  single  genus,  Phlebotomtts,  which  has  been  divided 
into  a  number  of  not  well  defined  subgenera.  In  recent  years  this  family  has 
been  studied  rather  intensively,  especially  in  those  areas  where  pappataci 
fever,  kala  azar,  leishmaniasis,  and  Oroya  fever  occur.  Larrouse  (1921)  re- 
corded 5  species  from  Europe,  7  from  Africa,  7  from  Asia,  and  12  from  the 
Americas.  Sinton  (1928)  listed  28  species  from  Asia,  and  Dyar  (1929)  re- 
ported 21  species  from  the  Americas,  only  one  being  found  in  North  America. 
Barretto  (1947)  lists  over  150  species  from  the  Americas,  6  of  which  are 
from  North  America.  Adler  (1946)  reports  10  species  from  the  island  of 
Cyprus  alone.  Kirk  and  Lewis  (1946)  report  44  species  from  the  Ethiopian 
region.  Yao  and  Wu  (1941)  list  13  species  from  China;  Theodor  (1948)  re- 
ports 127  species  and  34  varieties  from  the  Old  World. 

•DISTRIBUTION:  Phlebotomus  flies  arc  widely  distributed  throughout 
the  subtropical  and  tropical  regions  of  the  world.  They  do  not  occur  very 


236 


MEDICAL  ENTOMOLOGY 


far  within  the  temperate  zones,  being  confined  between  40°  South  and  40° 
North  latitude  in  the  Americas.  In  Europe  and  Asia  they  occur  to  about  45° 
North  latitude  but  their  southern  limit  is  not  known.  They  are  not  known 
to  occur  in  tropical  mountain  areas  above  8000  feet  (P.  verrucamm  in  Peru) . 
Though  widely  distributed,  the  species  are  usually  restricted  to  more  or  less 
definite  regions  that  provide  breeding  grounds  and  adequate  sources  for 
blood.  Their  flight  range  is  very  limited,  scarcely  exceeding  100  to  200  yards 
from  their  breeding  grounds. 


Fig.  89.  Mouth  parts  of  Phlcbotomus  sergenti  (somewhat  diagrammatic). 
Ant,  antennae;  CI,  clypeus;  E,  eye;  Hphy,  hypopharynx  showing  the  salivary 
gutter  extending  throughout  its  length;  Lb,  labium;  LbEp,  labrum-epipharynx; 
M,  mandible;  MX,  maxilla;  MxPlp,  maxillary  palpus. 

BIONOMICS:  The  biology,  under  experimental  conditions,  of  a  con- 
siderable number  of  American  species  (over  25)  has  been  reported  during 
the  past  ten  years.  Unfortunately  not  a  single  American  species  has  been 
found  breeding  under  natural  conditions  though  the  habitats  and  activities 
of  the  adults  of  a  number  of  species  seem  to  be  well  known.  The  larval 
habitats  of  several  European  and  Asiatic  species  have  been  discovered  in 
certain  areas,  but  many  details  of  their  activities  are  still  lacking.  Phlcbotomus 
papatasii  Scopoli  (Fig.  90),  the  vector  of  three-day  fever  or  pappataci  fever, 
has  been  studied  extensively  in  the  Mediterranean  region  and  in  India.  This 
species  is  the  important  vector  of  pappataci  fever  throughout  its  range.  It 
occurs  around  the  Mediterranean  region  and  along  the  North  African  area 
south  to  the  Anglo-Egyptian  Sudan  east  through  the  former  Italian  Somali- 
land  to  Calcutta  and  north  into  Central  Asia.  The  adults  are  partial  to  hu- 


THE  PSYCHODIDAE  237 

man  blood  and  invade  buildings,  attacking  during  the  evening  and  at  night. 
Their  bites  are  severe  and  the  later  irritation  is  almost  intolerable  to  susceptible 
persons.  They  are  not  capable  of  long  flights — only  a  few  yards  (50  or  more) — 
but  they  have  been  taken  in  barracks  over  25  feet  from  the  ground,  and 
Anderson  (1939)  reports  more  cases  of  fever  among  soldiers  in  Peshawar 
occupying  the  second  story  than  those  on  the  ground  floor.  He  reports  taking 
the  adults  70  feet  above  the  ground  level.  During  the  day  they  hide  in  holes 
and  cracks  of  walls,  crevices,  tree  holes,  dark  rooms,  latrines,  and  any  place 
of  darkness  and  freedom  from  air  currents.  The  adult  life  is  believed  to  be 
comparatively  short,  probably  not  over  two  to  three  weeks.  Under  experi- 


Fig.  90.  Phlebotomus  papatasii  Scop,  (a)  Larva,  first  instar.  (£)  Sketch  of  adult  larva. 
(c)  Pupa  with  larval  skin  attached,  (d)  Adult  female,  resting  position.  (After  Byam  and 
Archibald,  The  Practice  of  Medicine  in  the  Tropics;  from  Nevvstead.) 

mental  conditions  the  species  is  easily  reared  when  the  necessary  larval  food, 
such  as  moist  soil  with  adequate  decaying  animal  and  plant  wastes,  is  pro- 
vided. The  females  require  blood  meals  for  the  development  of  the  eggs. 
After  the  flies  mate  eggs  are  laid  in  small  batches,  preferably  in  cracks  and 
crevices  of  the  soil.  Several  batches  are  usually  laid  and  blood  meals  are 
required  between  each  batch.  Anderson  (1939)  reared  this  species  in  31  days 
at  Peshawar,  India,  where  the  temperature  ranged  from  80°  to  84°  F.  at  night 
to  100°  to  107°  F.  during  the  day.  He  fed  the  larvae  on  desiccated  rabbit  feces 
and  earth.  During  cool  weather  the  larval  life  is  much  prolonged,  to  60  days 
or  more.  Whittingham  and  Rook  (1923)  reared  this  species  in  Malta  from 
egg  to  adult  in  42  days.  There  are  four  larval  stages,  and  hibernation  takes 
place  in  the  fourth  larval  stage.  The  main  larval  habitats  were  in  loose  soil, 
cracks  of  buildings,  embankments,  but  not  in  wet  soil.  Recently  Uns worth  and 


238  MEDICAL  ENTOMOLOGY 

Gordon  (1946)  succeeded  in  establishing  and  maintaining  a  colony  for  ex- 
perimental work  at  the  University  of  Liverpool. 

Phlebotomus  argentipes  has  been  studied  in  the  region  of  Calcutta,  India^ 
It  is  one  of  the  important  vectors  of  kala  azar.  Smith  et  al.  (1936)  report  its 
primary  breeding  grounds  as  in  the  soil  within  a  range  of  20  yards  of  dwellings, 
cattle  sheds,  and  similar  places  where  there  is  vegetation  and  contamination 
of  the  ground.  The  larvae  were  found  mostly  in  the  first  three  or  four  inches 
and  localization  was  frequent.  Though  this  species  seems  to  prefer  cattle 
blood,  yet  it  will  attack  humans.  It  is  widespread  in  India  east  and  south  of 
a  line  drawn  from  Simla  to  Bombay  (Sinton,  1932).  It  also  occurs  in  Burma. 

Phlebotomus  sergenti  is  widely  distributed  in  the  Near  and  Middle  East, 
in  North  Africa,  Mesopotamia,  Iran,  and  northwest  India.  It  is  an  important 
vector  of  Oriental  sore. 

In  North  America  six  species  of  Phlebotomus  are  now  known.  Only  one 
species,  P.  diabollcus  Hall,  is  known  to  bite  man.  Very  little  is  known  of  its 
biology,  though  it  has  been  reared  in  captivity  and  its  life  cycle  requires  28 
to  50  days.  The  species  is  known  only  from  southwestern  Texas.  Its  breeding 
grounds  have  not  been  discovered.  No  species  of  Phlebotomus  have  been 
found  north  of  line  from  Washington,  D.C.,  to  San  Francisco. 

In  Mexico  and  Central  America  9  species  are  listed  by  Barretto  (1946), 
while  in  South  America  over  136  species  are  recognized  by  the  same  author 
(1947).  These  species  are  widely  distributed  over  South  America  south  to 
Buenos  Aires  and  east  of  a  line  drawn  from  Lima,  Peru,  to  Buenos  Aires. 
No  species  are  recorded  from  Chile.  Only  a  few  of  the  species  can  be  men- 
tioned here. 

Phlebotomus  intermedius  Lutz  and  Neiva  (  =  lutzi),  a  vector  of  muco- 
cutaneous  leishmaniasis  and  of  kala  azar  (experimental),  is  widely  distributed 
in  South  America  from  Venezuela  to  Argentina,  though  most  records  are 
from  Brazil,  Paraguay,  and  Argentina.  Bayma  (1936),  Chagas  (1938)  and 
Barretto  (1940)  have  reared  this  species  under  experimental  conditions.  The 
eggs  were  obtained  from  captured  females  and  the  larvae  reared  in  earth 
(rich)  usually  supplied  with  animal  or  decomposing  vegetable  matter  under 
proper  moisture  and  temperature  conditions.  At  the  optimum  temperature 
of  26°  to  27°  C.  the  life  cycle  from  egg  to  adult  required  36  days;  if  the  tem- 
peratures were  lowered  to  20°  to  22°  C.  it  required  52  or  more  days.  Unfortu- 
nately nothing  seems  to  be  known  about  their  natural  breeding  places.  The 
adults  are  crepuscular  and  nocturnal  in  their  feeding  habits.  They  are  more 
or  less  domestic  in  their  habits  and  readily  enter  buildings  for  human  or 
other  animal  blood. 


THE  PSYCHODIDAE  239 

Phlebotomus  verrucarum  Townsend  is  the  well-known  vector  of  Oroya 
fever  or  verruga  peruana.  It  occurs  only  in  the  high  mountain  canyons  in 
Peru  (between  6°  and  13°  South  latitude)  especially  in  the  Rimac  and  Santa 
Eulalia  Valleys  at  elevations  of  800  to  nearly  3000  meters.  Its  distribution  out- 
side these  valleys  is  not  well  known.  The  adults  occur  abundantly  in  certain 
areas  in  these  valleys,  especially  in  houses  and  less  abundantly  in  caves,  crev- 
ices, or  other  outdoor  situations.  Though  it  has  been  reared  many  times  under 
experimental  conditions,  its  natural  breeding  grounds  seem  to  have  escaped 
the  most  diligent  search.  The  life  cycle  at  temperatures  of  23°  to  25°  C.  is 
completed  in  6  to  8  or  more  weeks.  Breeding  continues  throughout  the  year, 
though  in  cold  weather  hibernation  takes  place  in  the  last  larval  stage  (4th 
instar).  The  adults  are  constant  invaders  of  human  habitations  and  prefer 
human  blood,  feeding  primarily  during  the  evening  hours  and  at  night.  They 
also  feed  on  dogs,  monkeys,  donkeys,  and  the  larger  mammals.  The  other 
two  species  usually  associated  with  P.  verrucarum  in  these  high  canyons  and 
valleys  are  P.  noguchli  Shannon  and  P.  pentensis  Shannon.  According  to 
Hertig  (1942),  P.  nogtichii  rarely  enters  houses,  does  not  feed  on  man,  and 
its  only  known  hosts  arc  field  mice;  P.  pentensis  occurs  in  caves  but  also  enters 
houses  and  feeds  on  dogs  and  man. 

With  the  more  or  less  definite  proof  (confirmed  in  1940)  that  the  various 
human  Icishmania  diseases  are  transmitted  by  species  of  Phlebotomus,  the 
study  of  these  insects  received  great  impetus  in  South  America  where  muco- 
cutancous  and  cutaneous  leishmaniases  (caused  by  Leishmania  braziliensis 
and  L.  tropica)  are  widely  distributed;  the  more  recent  discovery  of  kala  azar 
in  Brazil  by  Chagas  (1936)  added  greatly  to  the  necessity  for  these  studies. 
The  work  of  Barretto  (1940  to  1947)  and  others  led  to  the  recognition  of  112 
new  species  in  South  America  since  1936,  out  of  a  total  of  136  species.  In 
addition,  the  biology,  at  least  under  experimental  conditions,  of  nearly  20 
species  has  been  reported  when  previously  only  three  or  four  species  had  been 
reared.  Experimental  work  on  the  transmission  of  these  diseases  by  various 
species  of  Phlebotomus  has  greatly  increased.  At  present  six  species  have  been 
incriminated  as  vectors  of  Leishmania  braziliensis  experimentally  or  have 
been  found  naturally  infected;  at  least  two  species  have  been  shown  capable 
of  transmitting  kala  azar  under  experimental  conditions.  The  importance 
of  Phlebotomus  species  as  transmitters  of  disease  is  well  recognized;  this  is 
particularly  true  in  Central  and  South  America  and  in  Mexico. 

Unfortunately  the  study  of  the  species  of  Phlebotomus  is  so  difficult  that 
only  specialists  in  the  group  are  qualified  to  make  identifications  of  the  adults. 
These  are  based  on  the  structures  of  the  male  genitalia  (Fig.  91),  of  the 


240 


MEDICAL  ENTOMOLOGY 


spermatheca  of  the  females,  of  the  hypopharynx,  and  of  other  minute  charac- 
ters. The  larvae  are  distinctive  (Fig.  90)  hut  no  one  has  ventured  to  offer 
keys  to  separate  even  the  species  that  have  been  reared. 


DC 


DC 


Io 


Fig.  p/.  Male  gcnitalia  of  Phlcbotomus  vcrrucarum.  DC,  dorsal  clasper;  Dsp, 
dorsal  side  piece;  la,  intermediate  appendage;  Io,  intromiltent  organ;  Vc,  ventral 
clasper. 

PHLEBOTOMUS  AND  DISEASE 

PAPPATACI  FEVER,  THREE-DAY  FEVER,  OR  SAND-FLY 
FEVER:  This  disease  is  endemic  throughout  the  Mediterranean  region,  India, 
Ceylon,  parts  of  China,  East  Africa,  and  parts  of  South  America.  The  disease 
is  characterized  by  sudden  onset,  fever  of  103°  to  104°  F.,  which  usually  falls 
on  the  third  day,  severe  headache,  and  pains.  Recovery  is  usually  slow  bur 


THE  PSYCHODIDAE  241 

mortality  is  nil.  The  etiological  agent  is  a  virus  that  has  not  been  isolated. 
It  is  present  in  the  blood  stream  24  hours  before  the  onset  o£  the  disease  and 
disappears  in  from  24  to  48  hours  of  the  disease.  Doerr  and  his  associates 
(1908,  1909)  demonstrated  that  P.  papatasii  could  transmit  the  virus  of  this 
disease,  and  their  work  has  been  confirmed  by  numerous  investigators.  The 
fly  obtains  the  virus  during  its  presence  in  the  blood  stream  of  patients  suf- 
fering from  the  disease.  In  the  fly  there  is  an  incubation  period  of  six  to  nine 
days  before  the  fly  is  capable  of  transmitting  the  virus.  The  incubation  period 
in  man  is  from  three  to  ten  days.  Whittingham  and  Rook  (1923)  demon- 
strated that  infected  sand-flies  can  transmit  the  virus  to  their  offspring,  and 
Moshkovsky  (1937)  obtained  similar  results.  Sabin  et  aL  (1944)  were  unable 
to  confirm  these  results.  Though  this  disease  is  present  in  regions  where 
P.  papatasii  is  not  known  to  occur,  yet  no  other  vector  has  been  discovered  or 
incriminated  up  to  the  present  time.  There  is  no  known  animal  reservoir 
except  man. 

OROYA  FEVER,  VERRUCA  PERUANA,  OR  CARRION'S  DISEASE: 
Oroya  fever  and  verruga  peruana  were  long  regarded  as  distinct  diseases,  or 
different  manifestations  of  the  same  disease  as  held  by  Peruvian  physicians. 
Oroya  fever  is  the  severe  form  of  the  disease  and  is  characterized  by 
high  fever  and  anemia,  often  resulting  in  death.  Verruga  peruana  is  the 
cutaneous  form  involving  verrucous  eruptions  or  nodules,  with  usually  few 
deaths.  The  former  has  been  called  "Carrion's  disease"  after  Daniel  Carrion, 
a  student  at  Lima,  who,  on  August  27,  1885,  infected  himself  with  blood  from 
a  verruga  nodule  and  developed  Oroya  fever  from  which  he  died,  thus 
apparently  proving  that  the  two  diseases  were  in  some  manner  connected. 
The  disease  is  restricted  to  high,  narrow,  mountainous  valleys,  principally 
on  the  western  slopes  of  the  Andes  in  Peru  between  6°  and  13°  South  latitude. 
It  has  recently  been  reported  from  southern  Colombia,  Ecuador,  and  the 
eastern  slopes  of  the  Andes,  thus  extending  the  known  distribution  to  2°  North 
latitude.  The  disease  appears  to  be  restricted  to  elevations  of  from  2500  to 
about  8000  feet  in  these  areas.  Practically  all  persons  living  in  the  zones  of 
the  disease  suffer  from  the  disease  and  become  immune.  However,  it  is  very 
deadly  to  nonimmunes  as  demonstrated  during  1870  when  over  7000  persons 
died  while  trying  to  build  a  railway  from  Lima  to  Oroya.  Later  epidemics 
occurred  during  the  construction  of  bridges  and  tunnels. 

The  etiological  agent  is  Bartonella  bacillijormis  Strong  et  al.  (1915).  This 
organism  occurs  in  the  red  blood  cells  and  the  reticulo-endothelial  cells  of 
the  lymphatic  system  and  the  viscera.  It  has  been  successfully  cultured,  and 
infections  have  been  produced  in  monkeys  with  these  cultures,  though  ap- 


242  MEDICAL  ENTOMOLOGY 

parently  only  the  verruga  type;  no  case  of  Oroya  fever  has  been  produced 

in  monkeys. 

TRANSMISSION:  Townsend  (1913,  1914)  was  the  first  to  incriminate  Phle- 
botomus  flies  as  the  vectors  and  he  described  P.  verrucafiim  as  the  transmitter 
in  the  high  valleys  of  PcruJHis  experiments,  though  not  absolutely  conclu- 
sive, demonstrated  that  his  assistant  (out  of  three  sleeping  in  the  verruga 
area)  came  down  with  the  disease  after  being  bitten  by  sand  flies  (55  bites) 
through  accidental  exposure  of  his  arms  while  sleepfng  under  a  net.  The 
other  two  were  not  bitten.  A  second  case  was  of  a  British  sailor  who  permitted 
himself  to  be  bitten  by  wild  sand  flies  and  who  developed  what  appeared  to 
be  the  disease,  but  confirmation  of  this  was  apparently  never  established. 
"It  is  most  unfortunate  that  this  experiment  should  have  resulted  incon- 
clusively for  lack  of  definite  diagnosis  of  the  subject's  various  clinical  symptoms, 
since  it  is  the  only  recorded  human  transmission  experiment  with  Phleboto- 
mus"  (Hertig,  1942).  Townsend's  work  was  not  confirmed  till  Noguchi  and 
his  associates  (1929)  succeeded  in  transmitting  the  disease  to  monkeys  by 
crushed,  infected  Phlebotomus  verrucarum  sent  from  Peru  to  New  York  by 
Shannon.  Though  much  experimental  work  has  been  done  on  the  trans- 
mission of  this  disease,  the  results  are  not  very  gratifying.  Battistini  (1929, 
1931)  succeeded  in  infecting  monkeys  both  from  the  bites  of  wild  flies  and 
from  the  injection  of  suspensions.  Hertig  (1942)  succeeded  in  infecting  five 
out  of  eight  monkeys  by  the  bites  of  wild  sand  flies  taken  in  the  verruga  zone 
in  Peru.  He  also  succeeded  by  using  inoculations  of  cultures  of  Bartonella 
bacilltjormls.  In  no  case  did  he  observe  a  typical  case  of  Oroya  fever  but  he 
did  demonstrate  the  presence  of  the  etiological  agent  in  the  experimental 
animals.  Hertig's  (1042)  work  has  apparently  proved  that  only  P.  verrucarum 
is  the  vector  in  the  Peru  area  as  P.  noguchii  does  not  bite  humans  and  rarely 
enters  houses;  P.  peruensis  is  usually  scarce  and  is  restricted  to  the  upper  part 
of  the  zone  of  verruga  disease  in  the  Rimac  and  Eulalia  Valleys.  Hertig 
(1942)  was  unable  to  find  any  developmental  cycle  of  the  etiological  agent 
in  the  sand  flies,  though  he  found  massive  infections  of  the  proboscides  of  both 
males  and  females,  taken  in  the  wild,  with  organisms  not  quite  typical  of 
B.  bacilli formis.  What  relation  these  massive  infections  have  in  relation  to 
verruga  is  still  undetermined.  At  the  present  time  only  P.  verrucarum  has  been 
definitely  incriminated  as  a  vector,  yet  no  direct  human  infection  by  the  bites 
of  this  species  has  been  made.  As  the  disease  has  been  found  in  areas  in 
Colombia  and  Ecuador,  other  species  of  Phlebotomus  must  be  involved. 
There  is  no  known  animal  reservoir  except  man. 

As  there  is  no  known  treatment  for  either  Oroya  fever  or  the  verruga 


THE  PSYCHODIDAE  243 

stage,  it  would  seem  that  the  use  of  DDT  might  prove  effective  in  destroying 
the  adults  either  by  direct  spraying  or  by  residual  effects.  Some  of  the  new 
repellents  might  also  prove  efficient.  As  their  breeding  grounds  have  never 
been  found,  nothing  can  be  done  in  the  control  of  larvae. 

KALA  AZAR  OR  VISCERAL  LEISHMANIASIS:  "Kala-azar  is  an 
acute,  sub-acute  or  chronic  infectious  disease  caused  by  a  protozoan  parasite, 
Leishmania  donovani  Ross,  1903  or  L.  injantum  Nicolle,  1908,  occurring  in 
children  and  adults,  and  characterized  by  splenic  and  hepatic  enlargements, 
an  irregular  remittent  fever,  progressive  anaemia,  leucopenia,  cachexia,  and  a 
high  mortality"  (Archibald,  1921).  This  disease  has  a  wide  distribution 
around  the  Mediterranean,  is  local  in  the  Sudan,  Transcaucasia,  Turkestan, 
Kenya,  French  Equatorial  Africa,  and  Nigeria,  and  covers  an  extensive  area 
in  northeast  India  and  in  China  from  Canton  north  to  Peking,  extending 
deep  into  Manchuria  with  many  scattered  areas  in  other  parts  of  China. 
Recently  (1936  and  later)  it  has  been  found  in  northeastern  Brazil,  and  the 
Chaco  region  of  the  Argentine,  with  scattered  reports  of  cases  in  various 
other  parts  of  South  America.  Before  the  development  of  the  newer  treat- 
ments with  various  antimony  compounds  (1915)  the  death  rate  was  about 
95  per  cent  of  cases  (Napier,  1946).  Still  newer  and  better  treatments  have 
been  developed  so  that  the  disease  is  not  the  terror  it  was  in  the  days  when 
vast  numbers  died  in  epidemic  waves,  such  as  swept  through  Bengal,  Assam, 
and  other  parts  of  India.  After  the  discovery  of  the  causal  organism  intense 
search  followed  to  determine  the  method  of  transmission.  It  can  only  be 
transmitted  from  the  sick  to  the  well  by  some  stage  of  the  parasite  Leishmania 
donovani,  and  this  would  require  some  vector  as  all  other  means  of  transmis- 
sion had  been  negative.  Phlebototmts  flies  were  early  suspected  (Sergents, 
1904)  as  vectors  of  leishmania  and  certain  species  when  fed  on  the  blood  of 
kala  azar  patients  showed  the  same  development  stages  in  their  intestines 
as  in  artificial  cultures — the  leptomonad  stage.  Yet  despite  the  development 
of  this  flagellate  stage  and  its  migration  forward  to  the  esophagus,  pharynx, 
and  buccal  cavity  of  the  experimental  flies,  all  efforts  to  obtain  infection  in 
experimental  animals  or  human  volunteers  proved  failures.  However,  Shortt 
ct  al.  (1931),  Napier  ct  al.  (1933),  and  Smith  and  Murkirjee  (1936)  reported 
successful  infections  of  hamsters  by  the  bites  of  infected  P.  argentipes.  These 
consisted  of  only  three  apparently  successful  transmissions  out  of  a  large  num- 
ber of  trials.  Though  numerous  experiments  were  carried  out  with  these  flies, 
it  was  not  till  Smith  ct  al.  (1940)  recognized  the  significance  of  what  are  now 
called  "blocked"  flies  that  rapid  progress  was  made  in  solving  the  relation 
of  Phlebotomus  flies  to  kala  azar  transmission.  They  discovered  that  when 


244  MEDICAL  ENTOMOLOGY 

flies  were  fed  on  infected  blood  and  later  fed  on  plant  juices  such  as  that  of 
raisins,  the  anterior  end  of  the  intestine,  the  esophagus,  and  the  pharynx  be- 
came so  plugged  with  the  developing  leptomonad  stage  that  the  flies  could 
not  successfully  obtain  a  blood  meal.  They  would  try  to  feed  again  and  again 
but  in  so  doing  liberated  great  numbers  of  what  may  be  called  the  infective 
stage  of  the  parasite  into  the  host.  Experiments  with  "blocked"  infected  P. 
argentipes  by  these  investigators  readily  demonstrated  the  transmission  of  kala 
azar  to  mice  and  hamsters  (1940,  1941).  Finally  Swanimath  et  at.  (1942), 
using  the  same  technique,  successfully  transmitted  kala  azar  by  "blocked" 
infected  flies  to  five  human  volunteers.  All  bitten  by  these  flies  developed  the 
disease  within  five  to  eight  months.  These  were  the  first  successful  infections 
of  man  and  the  transmission  problem  seems  solved  for  this  species  of  Phle- 
botomus.  Whether  this  may  also  prove  true  for  other  species  suspected  of 
transmitting  leishmania  diseases  remains  to  be  determined. 

DERMAL  LEISHMANIASIS:  The  form  of  the  disease  that  occurs  most 
commonly  about  the  Mediterranean  region  is  dermal  leishmaniasis,  though 
the  visceral  (kala  azar)  is  also  present,  especially  in  Greece,  Crete,  and  scat- 
tered in  all  the  area.  It  is  mainly  a  children's  disease  here,  hence  the  name  of 
the  parasite,  Leishmania  infanturn  (this  is  now  considered  identical  with 
L.  donovant).  Dogs  in  this  region  are  heavily  infected  and  serve  principally 
as  the  source  of  human  infection.  (Apparently  dogs  have  not  been  found 
infected  in  India,  though  they  are  known  to  be  infected  in  North  China.) 

VECTORS  OF  KALA  AZAR  AND  DERMAL  LEisHMANiAsis:  In  India  the  principal 
vector  is  Phlebotomus  argentipes  and  the  distribution  of  the  disease  cor- 
responds closely  with  the  known  distribution  of  the  fly.  In  China  the  accepted 
vector  (though  apparently  no  human  infections  have  been  proved  by  experi- 
mental work)  is  P.  chincnsis  and  probably  P.  scrgenti  mongolensis;  in  the 
Mediterranean  area  it  is  mainly  P.  perniciosus,  though  in  Greece  P.  major  is 
the  vector  (Malmos,  1947) ;  in  the  eastern  Mediterranean  P.  papatasii  is  in- 
volved, but  in  North  Africa  P.  sergenti  is  considered  important.  In  the  Sudan 
and  other  parts  of  Africa  the  vectors  have  not  been  determined.  In  South 
America  Chagas  (1939,  1940)  incriminated  P.  intermedius  (=  lutzt)  and 
P.  longipalpis.  With  the  known  ease  with  which  these  flies  can  be  raised  under 
laboratory  conditions,  it  should  not  be  long  before  experiments  with  "blocked" 
flies  should  give  adequate  data  on  the  principal  vectors  throughout  the  world. 

ORIENTAL  SORE;  ALEPPO,  BAGDAD,  OR  DELHI  BOIL;  ETC.: 
This  is  a  cutaneous  leishmaniasis  caused  by  Leishmania  tropica.  The  disease 
is  widespread  about  the  Mediterranean  basin;  in  Africa  south  to  Angola  on 


THE  PSYCHODIDAE  245 

the  west  and  to  the  Sudan  and  Abyssinia  on  the  east;  in  Arabia,  Mesopotamia, 

Iran,  southern  Russia,  India,  China;  and  throughout  southern  Mexico,  Cen- 

tral America,  and  all  of  South  America  except  Chile.  The  disease  is  restricted 

to  the  skin,  forming  ulcers,  and  a  single  infection  is  said  to  confer  immunity. 

Transmission  may  be  by  direct  contact  with  the  ulcers.  In  some  countries 

children  are  inoculated  in  those  parts  of  the  body  where  the  healed  scar  will 

not  be  observed.  However  the  main  agents 

in  the  transmission  of  L.  tropica  are  Phle- 

botomus  flies.  Adler  and  Ber  (1941)  re- 

port successful  transmission  of  L.  tropica 

by  P.  papatasii  in  Palestine.  They  obtained 

28  lesions  from  the  bites  of  26  infected  sand 

flies.  In  India  P.  papatasii  and  P.  sergenti 

are  considered  the  vectors;  in  Italy  P. 

macedonicum  is  reported  as  a  vector;  in 

North  Africa  P.  sergenti  probably  is  the 

vector;  in  the  Americas  no  definite  species 

have  been  incriminated. 

Mucocutaneous  leishmaniasis  or  espun- 
dia  is  an  ulcerating  infection  of  the  skin 

that  may  also  involve  the  margins  of  the       F'S>  9^  Photograph  of  worker  with 
,    ,  f    ,  IT-     Leishmania  lesion  developing  in  ear. 

nose  and  the  mucosa  of  the  mouth.  It  is 


(Arfow  ^^  £o 

caused  by  Leishmania  brasihensis.  The 
disease  is  widespread  in  South  and  Central  America  and  as  far  north  as 
Yucatan.  In  many  rural  areas  as  in  Minas  Geraes  in  Brazil  and  in  Yucatan 
among  the  chicle  workers  (Fig.  92)  this  is  a  serious  disease.  The  transmitters 
are  species  oiPhlebotomus  and  the  following  have  been  incriminated  in  South 
America:  P.  arthuri  (?),  P.  fischeri  (Pessoa  and  Coutinho,  1941),  P.  inter- 
medius  (Aragao,  1922,  1927),  P.  migonci  (Pessoa  and  Coutinho,  1941,  and 
others),  P.  pessoai  (Pessoa  and  Coutinho,  1940,  1941),  and  P.  whitmani 
(Pessoa  and  Coutinho,  1941). 

RESERVOIRS 

In  the  Mediterranean  region  dogs  are  probably  the  chief  reservoir  of  kala 
azar  though  cats  play  a  part;  dogs  are  also  known  to  be  naturally  infected 
in  China,  but  not  in  India.  Experimentally  many  animals  are  readily  in- 
fected as  guinea  pigs,  rabbits,  gerboas,  gerbils,  hamsters,  jackals,  dogs,  and 
monkeys.  The  reservoirs  of  L.  tropica  and  L.  brasiliensis  are  probably  man 


246  MEDICAL  ENTOMOLOGY 

though  certain  species  of  monkeys,  dogs,  cats,  rats,  mice,  guinea  pigs,  and 
others  can  be  experimentally  infected. 

CONTROL  OF  SAND  FLIES 

So  little  is  known  about  the  breeding  grounds  of  sand  flies  that  it  would 
be  impossible  to  indicate  any  measures  that  might  be  of  value  in  reducing 
the  abundance  of  flies.  In  the  case  of  P.  papatasii  proper  building  measures  to 
reduce  cracks,  crevices,  etc.,  in  walls  might  be  of  some  aid.  P.  sergenti  might 
be  reduced  by  avoidance  of  contaminating  the  ground  about  homes  with 
animal  or  vegetable  wastes.  Nothing  is  known  about  the  breeding  grounds  of 
the  other  species.  The  adults  might  be  adequately  controlled  by  the  proper 
use  of  DDT  sprays  in  buildings,  cracks,  crevices,  or  known  places  where  the 
adults  rest  during  the  day.  If  applied  in  sufficient  quantities  the  residual 
effect  might  be  lasting.  Hertig  and  Fairchild  (1948)  demonstrated  the  effec- 
tiveness of  5  per  cent  DDT  (by  weight)  in  kerosene  in  Peru  during  the  years 
1945-1947.  House  spraying  and  spraying  of  stone  walls,  resting  caves,  shelters 
of  all  kinds,  and  suspected  breeding  areas  gave  excellent  control  and  the 
residual  effect  was  very  lasting  (12  to  19  months  on  stone  walls).  This  treat- 
ment to  be  most  effective  should  be  applied  to  all  buildings,  all  shelters,  stone 
walls,  caves,  and  other  places  where  sand  flies  rest  since  the  above  authors 
found  that  untreated  areas  only  75  to  100  yards  distant  were  still  swarming 
with  the  flie.s.  This  method  of  control  should  be  very  effective  for  sand  flies 
in  many  parts  of  the  world  owing  to  their  resting  and  flight  habits.  Further- 
more, their  long  larval  cycle  would  prevent  rapid  multiplication  and  thus 
reduce  the  number  of  treatments.  In  addition  to  controlling  the  sand  flies, 
other  insects  as  mosquitoes  and  houseflies  would  be  greatly  reduced. 

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Shannon,   R.   C.    Entomological   investigations    in    connection    with    Carrion's 

disease.    Amer.  Jl.  Hyg.,  10:  78-111,  1929. 
Sinton,  J.  A.    Some  new  species  and  records  of  Phlebotomus  from  Africa.    Ind. 

Jl.  Med.  Res.,  18:  171-193,  1930- 
.    Notes  on  some  Indian  species  of  the  genus  Phlebotomus.    Diagnostic  tables 

for  the  females  of  the  species  recorded  from  India.    Ibid.,  20:  55-72,  1932. 

** .    Diagnostic  tables  for  the  males.    Ibid.,  21:  417-428,  1933. 

Smith,  R.  O.  A.,  Haider,  K.  C.,  and  Ahmed,  I.    Further  investigations  on  the 

transmission  of  kala  azar.    I-IV,  VI.    Ibid.,  28:  575-579>  58l~584>  585~59I> 

1940;  29:  783-787,  799-802,  1941. 
9  et  al.    Identification  of  larvae  of  the  genus  Phlebotomus.    Ibid.,  21:  66 1- 

667,  1934. 
,ctal.    Bionomics  of  P.  argentipes.    I,  II.    /&</.,  24:  295-308,  557-562,  1936. 


THE  PSYCHODIDAE  249 

Sun,  C.  J.,  and  Wu,  C.  C.    Notes  on  the  study  of  kala-azar  transmission.    Chinese 

Med.  Jl.,  52:  665-673,  1937. 
Swaminath,  C.  S.,  Shortt,  H.  E.,  and  Anderson,  L.  A.  P.    Transmission  of  Indian 

kala-azar  to  man  by  the  bites  of  Phlcbotomus  argentipes.    Ind.  Jl.  Med.  Res., 

30:  473-477,  1942.     (First  successful  transmission  from  man  to  man.) 
Theodor,  O.     On  African  sandflies.    Bull.  Ent.  Res.,  22:  469-478,  1931. 
.     Observations  on  the  hibernation  of  Phlebotomus  papatasii.    Ibid.,  25:  459- 

472,  1934. 
.     On  some  sandflies  (Phlebotomus)  of  the  sergenti  group  in  Palestine.    Ibid., 

38:  91-98,  1947. 
.    Classification  of  the  old  world  species  of  the  subfamily  Phlebotominae. 

Ibid.,  39:  85-116,  1948. 
Townsend,  C.  H.  T.     A  Phlcbotomus  the  practically  certain  carrier  of  verruga. 

Science,  n.s.,  38:  194-195,  1913. 
.     Progress  in  the  study  of  verruga.     Transmission  by  bloodsuckers.     Bull. 

Ent.  Res.,  4:  125-128,  1913. 
.     The  transmission  of  verruga  by  Phlcbotomus.    Jl.  Amer.  Med.  Assoc.,  61: 

1717,  1913. 
.     The  vector  of  verruga,  Phlcbotomus  vcrrucarum  sp.n.    Ins.  Ins.  Mens.,  i: 

107-109,  1913. 
.    Human  case  of  verruga  directly  traceable  to  Phlebotomus  verrucarum. 

Ent.  News,  25:  40,  1914. 
.     On  the  identity  of  verruga  and  Carrion's  fever.     Science,  n.s.,  39:  99-100, 

1914. 
.     The  history,  etiology,  transmission  of  Peruvian  verruga  with  an  outline 

of  the  asexual  cycle  of  its  causative  organism.    West  Coast  Leader,  Lima,  Mar. 

8,  1927. 
Unsworth,  K.,  and  Gordon,  R.  M.    The  maintenance  of  a  colony  of  Phlebotomus 

papatasii  in  Great  Britain.     Ann.  Trop.  Med.  Parasit.,  40:  219-227,  1946. 
Wu,  C.  C.,  and  Sun,  C.  J.     Notes  on  the  study  of  kala-azar  transmission.     Chinese 

Med.  JL,  Suppl.  2:  579-591,  1938. 
Yao,  Y.  T.,  and  Wu,  C.  C.    Notes  on  the  Chinese  species  of  the  genus  Phlebotomus. 

Sandflies  of  Hainon  Island.     Trans.  Cong.  Far  East.  Assoc.  Trop.  Med.  (loth 

Cong.,  Hanoi,  1938). 
,  and  Wu,  C.  C.     Sandflies  of  Nanning  and  Tienapo,  Kwangsi.     Chinese 

Med.  JL,  59:  67-76,  1941. 


CHAPTER  X 


Mosquitoes:  Their  Structure, 
Biology,  and  Classification 


Culicidae  or  mosquitoes  are  easily  recognized  by  their  characteristic 
JL    wing  venation  and  the  presence  of  a  fringe  of  scales  on  the  posterior 
margin  of  the  wing  and  on  the  veins  (Fig.  93).  They  are  slender,  soft- 
textured  flies  with  long  antennae  (Fig.  95).  The  segments  of  the  antennae 
bear  whorls  of  hairs;  in  most  of  the  males  the  whorls  of  hairs  are  so  dense 


2da 


Fig.  93.  Wing  of  Anopheles  walJ(eri  labeled  according  to  the  Comstock-Needharn 
terminology,  with  the  usual  terms  employed  by  dipterists  in  parentheses.  The  veins: 
C,  costal;  Sc,  subcostal  (auxiliary);  Ri  (ist  longitudinal):  Rz  and  Ra  (2nd  longitudinal); 
R<  +  5  (yd  longitudinal);  Mi +  2  (qth  longitudinal);  GUI  -f-  Cua  ($th  longitudinal);  ada 
(6th  longitudinal);  r-m,  radio-medial  cross-vein  (anterior  cross-vein);  m-cu,  medio- 
cubital  cross-vein  (posterior  cross-vein).  The  cells:  a,  Sc  (subcostal) ;  b,  Ri  (ist  marginal) ; 
c,  Ra  (2nd  marginal);  d,  Ra  (submarginal);  e,  Rs  (ist  posterior);  f,  Ma  (2nd  posterior); 
g,  Ms  (yd  posterior);  h,  GUI  (qth  posterior);  i,  ist  A  (anal  cell);  j,  2nd  A  (axillary 
cell).  (After  Matheson.) 

as  to  give  the  antennae  a  bushy  appearance  (Fig.  96).  The  family  is  divided 
into  two  subfamilies:  the  Chaoborinae  in  which  the  mouth  parts  are  short 
and  not  adapted  for  piercing;  and  the  Culicinae  in  which  the  mouth  parts 
are,  in  most  species,  fitted  for  piercing  and  sucking  blood.  Not  all  the  species 
of  the  Culicinae  take  blood;  the  males  do  not  take  blood. 


MOSQUITOES  251 

The  larvae  of  the  Culicidae  are  all  aquatic.  In  the  Chaoborinae  the  larvae 
are  predaceous,  the  antennae  being  modified  for  grasping  organs  (Fig.  94). 1 
In  the  Culicinae  the  antennae  are  not  so  modified  and  food  is  obtained  by 
the  action  of  the  mouth  brushes  (Fig.  107).  The  thorax  consists  of  three 
fused  segments,  always  wider  than  the  abdomen.  The  abdomen  consists  of 
nine  segments  and  is  without  appendages.  The  eighth  segment  bears  a  pair 


Fig.  94.  Larva  of  Chaoborinae.  Upper:  Larva  of  Mochlonyx  cinctipes.  Center:  Chao- 
borus  punctipennis.  Lower:  Eucorethra  under  woodi.  A,  air  sac;  Ant,  prehensile  antennae. 

of  spiracles,  either  at  the  end  of  a  long  tube,  the  siphon  (Fig.  105)  or  the 
siphon  may  be  absent  (Fig.  106).  The  pupae  of  the  Culicinae  are  all  aquatic, 
active,  comma-shaped.  The  anterior  portion  (cephalothorax)  is  enlarged  and 
provided  with  a  pair  of  horns  or  trumpets,  the  respiratory  organs  (Fig.  103). 
The  abdomen  consists  of  eight  segments  (nine  or  ten  are  recognized),  the 
eighth  segment  bears  a  pair  of  paddles  and  each  paddle  has  a  midrib. 


1  The  Chaoborinae  are  not  further  treated  here. 


MEDICAL  ENTOMOLOGY 


Fig.  95.  Aedes  vexans,  female.  ABD,  abdomen;  ANT,  antenna;  E,  eye;  F,  femur; 
H,  haltere;  MES,  mcsonotum;  MXP,  maxillary  palpus;  PB,  proboscis;  SCT,  scutellum; 
TB,  tibia;  TAR,  tarsus  with  its  five  segments. 


MOSQUITOES 


Fig.  96.  Aedes  vexans,  male.  Lettering  as  in  Fig.  95. 


254  MEDICAL  ENTOMOLOGY 

THE  STRUCTURE  OF  MOSQUITOES 
THE  ADULT 

The  more  general  features  of  an  adult  mosquito  are  shown  in  figures  95,96. 
The  head  is  nearly  globose  and  is  borne  on  a  slender  neck.  The  compound  eyes 
are  prominent,  large,  and  occupy  most  of  the  lateral  areas  of  the  head;  the 
ocelli  are  lacking.  The  small  median  area  between  the  eyes  is  called  the  ver- 
tex while  the  broader  portion  back  of  the  vertex  is  generally  known  as  the 
occiput.  The  front  or  frons  lies  in  front  of  the  vertex  and  bears  the  antennae. 
Anterior  to  the  frons  and  separated  from  it  by  a  suture  is  the  clypeus,  a  short, 
usually  nude,  snoutlike  projection  (Fig.  97  Clp).  The  antennae  arise  on  the 
sides  of  the  frons  between  the  eyes.  Each  antenna  consists  of  15  segments.  The 
first,  the  scape,  is  very  small  and  hidden  beneath  the  large,  globular  second 
segment,  the  torus.  The  remaining  segments  (13)  are  filamentous  and  form 
the  flagellum.  Each  segment,  except  the  first,  of  the  flagcllum  has  a  basal  whorl 
of  hairs,  which  are  usually  long  and  bushy  in  the  males  (Fig.  96)  and  shorter 
and  sparser  in  the  females  (Fig.  95). 

THE  MOUTH  PARTS :  In  the  female  the  mouth  parts  (Fig.  97)  consist  of 
an  elongated  proboscis  within  which  lie  the  piercing  stylets.  The  proboscis  is 
the  labium  (Lb),  a  hollow  cylindrical  tube,  narrowly  open  along  its  dorsal 
face  and  terminating  in  two  pointed  lobes,  the  labellae.  The  stylets  within  the 
labium  consist  of  (i)  the  labrum,2  a  long,  sclerotized,  sharply  pointed  rod 
that  is  grooved  on  its  ventral  surface;  in  cross  section  it  appears  U-shaped,  the 
opening  of  the  U  closed  by  a  delicate  membrane  (Fig.  97) ;  (2)  the  mandibles 
(md),  a  pair  of  delicate,  linear-lanceolate  structures  lying  close  beside  and 
behind  the  labrum;  (3)  the  hypopharynx  (Hphy),  a  thin  lanceolate  structure 
that  is  more  or  less  closely  applied  to  the  thin  mandibles  and  labrum;  (4)  the 
maxillae  (Mx),  a  pair  of  thin,  sclerotized  shafts,  each  terminating  in  a  some- 
what enlarged  tip  that  bears  a  row  of  small,  retrorse  teeth;  (5)  a  pair  of  4  to  5- 
jointed  maxillary  palpi  (MxPlp).  The  maxillary  palpi  arise  at  the  anterior 
margin  of  the  head,  just  beneath  the  clypeus.  The  palpi  differ  in  the  two  sexes. 
In  the  females  (Culicini)  the  palpi  are  much  shorter  than  the  proboscis;  in  the 
males3  they  are  usually  densely  haired  and  generally  longer  than  the  pro- 
boscis, with  the  last  two  segments  angled  upward  and  tapered  to  a  point 


2  This  is  often  referred  to  as  the  labrum-epipharynx,  but  here  we  shall  use  the  word 
labrum  to  indicate  both  structures. 

3  In  the  males  of  certain  genera  and  in  some  species  of  other  genera  the  palpi  of  both 
males  and  females  are  similar. 


MOSQUITOES  255 

(Fig.  125) .  In  the  females  of  the  Anophelini  the  palpi  are  straight  and  about 
as  long  as  the  proboscis  (except  in  the  genus  Bironella) ;  in  the  males  the  palpi 
are  nearly  as  long  as  or  longer  than  the  proboscis  while  the  last  two  segments 
are  stouter,  somewhat  flattened,  bent  upward,  and  rounded  at  the  apex  (Fig. 


Fig.  97.  Mouth  parts  of  female  mosquito.  Lejt:  Frontal  view  of  the  head  of  a  mosquito 
with  the  mouth  parts  removed  from  the  labium  and  the  tips  of  the  parts  greatly  enlarged. 
Center:  Cross  section  and  isometric  view  of  the  arrangement  of  the  piercing  parts.  Right: 
A  female  in  the  act  of  taking  blood.  Ant,  antenna;  Clp,  clypeus;  F,  food  channel;  Hphy, 
hypopharynx;  L,  labella;  Lb,  Labium;  LbEp,  labrum-epipharynx  or  simply  labrum;  md, 
mandible;  MX,  maxilla;  MxPlp,  maxillary  palpus;  Sc,  salivary  channel. 

The  mouth  parts  of  the  male  are  greatly  modified.  The  mandibles,  when 
present,  being  greatly  reduced,  and  the  maxillae  being  thin  and  delicate  and 
usually  greatly  reduced  or  almost  absent. 

The  action  of  the  mouth  parts  in  taking  blood  may  be  observed  by  allowing 
a  mosquito  to  bite.  When  a  satisfactory  site  is  selected,  the  labellae  are  pressed 
close  to  the  skin.  By  muscular  action  and  pressure  the  cutting  mouth  parts 


256  MEDICAL  ENTOMOLOGY 

are  forced  through  the  skin  and  soon  all  the  mouth  parts  except  the  labium 
are  deeply  embedded;  the  basal  half  of  the  labium  is  bent  back  exposing  the 
other  mouth  parts,  and  blood  can  be  seen  streaming  up  the  food  channel; 
the  apical  part  of  the  labium  still  holds  the  piercing  parts  in  the  groove  and 
undoubtedly  steadies  them. 

THE  THORAX:  The  thorax  is  distinctly  wedge-shaped,  the  base  upper- 
most. The  sides  of  the  wedge  form  the  pleura  and  the  apex  bears  the  legs.  It 
is  composed  of  three  segments,  the  second  and  third  being  solidly  fused  to- 
gether. The  spiracles  appear  as  prominent  black-rimmed  apertures  on  seg- 
ments two  and  three.  The  prothorax  (ist  segment)  is  normally  greatly 
reduced  and  consists  of  the  two  lobes  located  just  back  of  the  head  (these 
lobes  are  usually  widely  separated  when  viewed  from  the  dorsum),  the 
postpronotum  (Fig.  98  PPn)  and  the  proepisternum  (propleurum).  The  pro- 
sternum  lies  between  the  first  pair  of  coxae.  The  second  and  third  thoracic 
segments  are  solidly  fused  together  as  in  most  Diptera.  The  dorsal  surface  is 
composed  almost  entirely  of  the  large  mcsonotum  and  scutellum  (dorsum 
of  the  second  thoracic  segment) ;  back  of  the  scutellum  is  the  small,  usually 
smooth  postnotum  (Fig.  98  9).  The  sides  of  meso-  and  metathorax  are  divided 
into  several  scleritcs.  The  names  and  position  of  these  sclerites  are  fully  ex- 
plained in  Figs.  98  and  99.  On  these  sclerites  are  certain  setae  or  bristles  that 
have  been  assigned  definite  names.  They  are  of  much  importance  and  form 
landmarks  for  the  placing  of  many  of  our  species  in  their  respective  genera. 
These  groups  are  as  follows  (Figs.  98,99)  :  (i)  pronotal  group  (Pn),  a  varying 
number  of  setae  massed  on  the  pronotal  lobes;  (2)  proepisternal  or  propleural 
group  (Ps),  a  single  stout  seta  or  a  mass  of  them  on  the  proepisternum;  (3) 
postpronotal  group  (PPn),  one  or  several  setae  arranged  more  or  less  in  a 
row  just  in  front  of  the  ridge  on  the  posterior  margin  of  the  postpronotum; 
(4)  spiracular  group  (Sp),  a  row  of  setae  just  in  front  of  the  anterior  spiracle 
and  behind  the  postpronotal  ridge;  (5)  postspiracular  group  (P  Sp),  a  num- 
ber of  setae  located  on  the  upper  portion  of  the  mesanepisternum  and  directly 
behind  the  anterior  spiracle;  (6)  prealar  group  (Pa),  a  small  group  on  the 
dorsoposterior  projection  of  the  sternopleuron ;  (7)  sternopleural  group  (St  P), 
a  group  consisting  of  a  variable  number  of  setae  located  near  the  posterior 
margin  of  the  sternopleuron  and  often  crossing  it  (the  location  of  these  setae 
varies);  (8)  upper  mesepimeral  group  (UMe),  a  group  located  on  the  upper 
portion  of  the  mesepimeron;  and  (9)  lower  mesepimeral  group  (LMe),  one 
to  several  setae  on  the  lower  portion  of  the  mesepimeron. 

The  dorsal  area  of  the  thorax  offers  comparatively  few  characters  of  value 
in  systematic  work  except  coloration  patterns  and  the  arrangement  of  setae 


MOSQUITOES 


257 


Fig.  98.  Lateral  views  of  the  thorax  of  mosquitoes.  (/)  Uranotaenia  lowii.  (2)  Culiseta 
morsitans.  (3)  Anopheles  punctipcnnis.  (4)  Psorophora  ciliata.  (5)  Megarhinus  septen- 
trionaUs.  The  sclerites  of  the  thorax  (2) :  i,  pronotum  (prothoracic  lobe) ;  2,  proepister- 
num;  3,  postpronotum;  4,  mesanepisternum;  5,  sternopleuron;  6,  mesepimeron;  7,  mete- 
pisternum;  8,  prealar  area;  9,  postnotum;  10,  metepimeron;  n,  meteusternum;  m,  meron. 
The  setae  (4):  LMe,  lower  mesepimeral;  Pa,  prealar;  Pn,  pronotal;  PPn,  posterior  pro- 
notal  or  postpronotal ;  Ps,  proepisternal;  P  Sp,  postspiracular;  Sp,  spiracular;  St  P, 
sternopleural;  UMe,  upper  mesepimeral.  The  dorsal  portion  extending  from  I  to  9  repre- 
sents the  mesonotum  (2). 


MEDICAL  ENTOMOLOGY 


Fig.  99.  Lateral  views  of  the  thorax  of  mosquitoes.  (6)  Orthopodomyia  signi/era.  (7) 
Deinocerites  pseudes.  (8}  Wyeomyia  smithii.  (9)  Culcx  pipicns.  (/o)  Mansonia  pcrtur- 
bans.  (//)  Aedcs  vexans.  Explanations  as  in  Fig.  98. 

and  scales.  The  scutellum  is  separated  by  a  transverse  suture  from  the  mesono 
tum.  In  all  the  genera  except  Anopheles  and  Megarhinus  the  scutellum  is 
trilobed,  and  each  lobe  generally  bears  stiff  bristles  and  usually  scales;  in  the 
above-named  genera  the  scutellum  is  arcuate  or  rounded  behind  and  the 
bristles  arranged  evenly  on  it. 


MOSQUITOES  259 

THE  WINGS :  The  wings  are  long  and  narrow  (Fig.  93) .  The  venation 
is  characteristic  and  the  presence  of  scales  is  very  distinctive  o£  this  family. 
The  scales  are  frequently  of  different  colors  or  may  be  distributed  so  as  to  give 
definite  patterns  (Fig.  126).  The  terminology  of  the  wing  veins  and  cells 
varies.  The  Comstock-Needham  system  and  that  used  by  most  dipterists  is 
illustrated  in  Fig.  93.  As  the  venational  pattern  varies  very  little  throughout 
the  family,  the  form,  shape,  and  color  of  the  scales  and  their  arrangement 
frequently  offer  excellent  characters  in  separating  species  (Fig.  131).  The 
second  pair  of  wings  are  represented  by  small  knoblike  structures,  the  halteres 
(Fig.  96  H). 

THE  LEGS :  The  legs  are  long  and  slender  (Fig.  96) .  Each  leg  consists  of 
the  usual  parts,  coxa,  trochanter,  femur,  tibia,  and  a  5-segmented  tarsus.  The 
coxa  is  short,  stout,  and  connects  with  the  ventral  portion  of  the  thorax. 
The  trochanter  is  a  small,  short  segment  connecting  the  coxa  to  the  long  femur. 
The  tibia  is  slender  and  about  as  long  as  the  femur.  The  tarsus  is  usually 
very  long  and  the  segments  vary  in  length,  though  the  first  one  is  much  the 
longest.  The  last  segment  bears  a  pair  of  claws  or  ungues.  The  claws  vary 
greatly  in  size  and  those  of  the  hind  legs  are  generally  smaller  than  those  of 
the  other  legs.  In  the  females  the  claws  are  usually  simple,  that  is,  they  do 
not  bear  teeth  except  in  most  species  of  the  genera  Aedes,  Psorophora,  Haema- 
gogus,  Armigeres,  and  some  others.  In  the  males  the  claws  of  the  first  pair  of 
legs  (and  sometimes  also  the  second  pair)  are  usually  toothed,  though  in 
anophelines  one  claw  is  usually  reduced  and  the  other  is  toothed.  In  nearly 
all  species  there  is  present  a  small  hairy  seta  (empodium)  between  the  bases 
of  the  claws;  in  the  genus  Culex  there  is,  in  addition,  a  pair  of  thin  padlike 
structures  (pulvilli)  beneath  the  claws  that  is  diagnostic  for  this  genus. 

THE  ABDOMEN:  The  abdomen  is  narrowly  elongate,  nearly  cylindrical, 
and  consists  of  ten  segments,  the  first  eight  of  which  are  distinct.  Each  seg- 
ment is  composed  of  a  tergite  that  extends  down  the  sides  and  is  connected 
with  the  sternite  by  a  pleural  membrane.  The  successive  segments  are  joined 
by  thin  membranes  (intersegmental  membranes).  In  all  the  culicines  both 
the  dorsal  and  ventral  surfaces  are  usually  covered  with  dense  scales;  in  the 
anophelines  scales  are  practically  absent  or  present  in  restricted  areas.  Six 
pairs  of  spiracles  are  present  on  the  second  to  seventh  segments.  In  the 
female  the  abdomen  is  pointed,  as  in  Aedes,  or  truncate,  as  in  Culex.  The 
ninth  segment  is  reduced,  and  between  it  and  the  eighth  lies  the  opening  of 
the  female  reproductive  organs.  The  tenth  segment  is  greatly  reduced  and 
bears  the  cerci  and  anal  opening.  In  the  male  the  terminal  abdominal  seg- 


26o  MEDICAL  ENTOMOLOGY 

ments  are  modified  for  sexual  purposes.  Shortly  after  emergence  from  the 
pupa  (usually  within  24  hours)  the  eighth,  ninth,  and  tenth  segments  un- 
dergo an  axial  torsion  through  an  arc  of  180°  so  that  the  dorsal  surface  be- 
comes ventral  and  the  ventral  dorsal.  The  tip  of  the  abdomen  back  of  the 
eighth  segment  is  generally  called  the  hypopygium,  male  genitalia,  or,  by 
some,  terminalia. 


9T- 


Fig.  100.  Male  genitalia  of  Aedes  stimulans.  AL,  apical  lobe;  BL,  basal  lobe  of  side- 
piece;  BP,  basal  plate;  C,  claw  or  spine  of  clasper;  Cl,  clasper;  Clsp,  claspette;  F,  filament 
of  claspette;  IF,  interbasal  fold;  L(),  lobe  of  ninth  tergite;  Mes,  mesosome;  P,  paramere; 
Sp,  sidepiece;  108,  tenth  sternite;  pT,  ninth  tergite. 

MALE  GENITALIA:  The  structure  of  the  male  genitalia  affords  excellent 
characters  for  the  identification  of  species  and  an  understanding  of  these 
structures  is  essential.  Figs.  100-102  show  the  main  structures  to  be  observed 
in  the  genera  Aedes,  Culex,  and  Anopheles. 

As  the  terminal  segments  (8th  to  loth)  of  the  male  abdomen  undergo  an 


MOSQUITOES  261 

axial  torsion  of  1 80°,  it  is  essential  to  remember  that  ventral  becomes  dorsal 
and  dorsal  ventral.  The  terms  lower  and  upper  will  be  used  in  their  ordinary 
sense  but  all  morphological  terms  as  dorsal,  ventral,  and  names  of  sclerites 
will  be  employed  with  their  correct  meaning.  Typically  the  genitalia  struc- 


L9 


Fig.  1 01.  Male  genitalis  of  Culex  pipicns.  Cl,  clasper;  D,  dorsal  bridge;  L,  leaf 
of  subapical  lobe;  Lp,  lobe  of  ninth  tergite;  Mes,  mesosome;  Si,  subapical  lobe; 
Sp,  sidepiece;  loS,  tenth  sternite  or  paraprocts;  pT,  ninth  tergite;  V,  ventral 
bridge. 

tures  begin  with  the  ninth  segment;  this  segment  consists  of  a  complete  ring, 
more  or  less  sclerotized,  especially  on  the  dorsal  aspect.  The  tergite  (9T,  ixT) 
may  possess  lobes  (Lp,  T)  or  the  lobes  may  be  greatly  reduced  or  almost 
absent.  From  within  the  ring  of  the  ninth  segment  arises  a  pair  of  large, 
hollow,  forcepslike  appendages.  The  basal  parts  are  stout  and  are  called 


262  MEDICAL  ENTOMOLOGY 

sidepieces,  or  coxites  (Sp),  or  basistyles.  The  apical  appendage  of  each  is  long 
and  normally  narrow  (CL),  or  it  may  be  expanded  (Psorophora)  or  modified 
into  the  most  bizarre  shapes  (Wyeomyia) ;  it  is  called  the  clasper  or  dististyle. 
Each  sidepiece  may  bear  a  basal  lobe  (Fig.  100  BL)  or  the  lobe  may  be  lacking 
or  the  lobe  may  be  replaced  by  several  stout  spines  (Fig.  102  Ps),  parabasal 
spines.  There  may  be  an  apical  lobe  (Fig.  100  AL),  the  lobe  may  be  subapical 
in  position  as  in  Culex  (Fig.  101,  SI),  or  it  may  be  absent.  In  anophelines  there 
is  usually  present  an  internal  spine  (Fig.  102  IS).  Arising  from  a  basal  fold  that 
aids  in  uniting  the  sidepieces  are  the  claspettes  (Clsp)  ;  in  the  Culicini  {Aedes, 
Psorophora,  etc.;  absent  in  the  genus  Culex}  these  structures  may  be  very 
complicated;  in  the  Anophelini  they  are  represented  by  lobes,  the  outer  or 
dorsal  and  inner  or  ventral  lobes  (Fig.  102  Dl  and  VI).  In  the  median  plane, 
lying  directly  above  and  extending  beyond  the  ninth  tergite  are  the  sclerotized 
parts  of  the  tenth  segment  (los),  the  proctiger.  The  structures  here  involved 
have  been  variously  designated  and  differ  greatly  in  the  different  genera.  The 
tenth  sternite  (ios)  is  usually  well  developed  in  such  genera  as  Aedes,  Culex, 
Culiseta,  Psorophora,  Mansonia,  and  others.  In  Anopheles  the  tenth  sternite 
is  vestigial,  only  the  membranous  anal  lobe  (Fig.  102  Lb)  being  present.  Be- 
tween the  sternites  and  beneath  them  or  the  anal  lobe  is  located  the  meso- 
some  (Mes)  or  phallosome,  a  sclerotized  tubelike  structure  surrounding  the 
penis.  It  is  supported  and  held  in  position  by  the  basal  plates  (Fig.  100  BP)  and 
the  parameres  (P).  The  mesosome  varies  greatly  in  the  different  genera  and 
furnishes  characters  for  the  differentiation  of  genera  and  species.  In  Anopheles 
the  mesosome  is  a  long,  slender  tube  with  or  without  apical  leaflets  (Fig.  102) ; 
in  other  genera  it  may  assume  bizarre  shapes  as  in  Cul&P^Fig.  101). 

THE  PUPA 

The  pupa  is  the  stage  from  which  the  adult  emerges.  All  pupae  are  aquatic, 
active,  take  no  food,  and  are  comma-shaped  (Fig.  103).  The  enlarged  anterior 
half  contains  the  future  head  and  thorax  of  the  developing  adult.  The  more 
slender  portion  represents  the  abdomen  and  is  composed  of  eight  segments 
(nine  or  ten  can  be  recognized)  and  a  pair  of  paddles  or  fins  (Fig.  103). 
Arising  from  the  thorax  is  a  pair  of  respiratory  horns  or  trumpets,  which 
break  through  the  surface  film  of  the  water  when  the  pupa  float  to  the  surface 
and  permit  air  to  enter  through  the  spiracles  located  within  the  horns.) 

The  abdomen  of  pupae  is  provided  with  various  hairs  and  spines,  and  these 
have  been  studied  by  various  workers  in  attempts  to  use  them  for  identifica- 
tion purposes.  Though  a  goodly  number  of  pupae  have  been  figured  and 
described,  the  number  is  not  sufficiently  large  to  permit  us  to  hope  that  species 


Fig.  102.  Male  genitalia  of  Anopheles  quadrimaculatus.  Upper:  Lower  or 
dorsal  view.  Lower:  Lateral  view.  C,  claw  or  spine  of  clasper;  Cl,  clasper;  Clsp, 
claspettes;  Dl,  dorsal  lobe  of  claspette;  IS,  internal  spines;  L,  leaflets  of  meso- 
some;  Lb,  anal  lobe;  Mes,  mesosome  or  phallosome;  Ps,  basal  or  parabasal 
spines  of  sidepiece;  Sp,  sidepiece  or  coxite;  viiiS,  ixS,  eighth  and  ninth  sternites; 
T,  lobe  of  ninth  tergite;  viiiT,  ixT,  eighth  and  ninth  tergites;  VI,  ventral  lobe 
of  claspette. 


264  MEDICAL  ENTOMOLOGY 

identification  by  pupae  may  become  well  established.  The  characters  most 
frequently  used  are  the  structure  of  the  paddles  and  the  arrangement  of  the 
hairs  and  spines.  Anopheline  pupae  can  usually  be  recognized  in  that  spine 
A  of  segments  3  to  7  is  stout,  peglike,  single,  and  located  at  the  apical  angles, 
while  the  same  spine  on  segment  8  is  in  the  same  position  and  fringed.  In  other 
pupae  spine  A  is  usually  branched  and  not  located  at  the  exact  apical  angle 
(Fig.  104). 


Fig.  103.  Pupae  of  mosquitoes.  Lejt:  Aedes  cinereus.  Right:  Anopheles  punctipennis. 
P,  paddles;  R,  respiratory  horns. 

THE  LARVA  (Fourth  instar) 

The  larvae  of  all  known  species  are  aquatic  and  their  structure  adapts  them 
to  life  in  the  water  (Fig.  113).  The  larva  (Figs.  105,106)  is  legless  and  con- 
sists of  a  prominent  head,  a  large,  boxlike  unsegmented  thorax,  and  a  slender 
abdomen  of  nine  segments. 

.  The  head  is  normally  well  sclerotized  and  bears  the  mouth  parts,  the  an- 
tennae, eyes,  the  remarkable  mouth  brushes,  and  an  arrangement  of  hairs 
or  tufts.  The  mouth  parts  (Fig.  107)  consist  of  a  labrum  (often  referred  to  as 
the  preclypeus),  a  pair  of  mandibles,  a  pair  of  maxillae,  and  the  labium.  These 
are  typical  mandibulate  mouth  parts.  The  mouth  brushes  are  remarkable 
structures  as  by  their  vigorous  and  rapid  movement  they  direct  the  food  into 


Fig.  104.  Pupal  chactotaxy.  Left:  Typical  arrangement  of  hairs  of  an  anopheline.  Right: 
Typical  arrangement  of  hairs  of  a  nonanopheline.  The  numbers  and  letters  refer  to  the 
hairs  on  each  abdominal  segment.  (After  Penn.) 


266  MEDICAL  ENTOMOLOGY 

the  mouth  cavity  or  serve  to  capture  their  prey  (some  Psorophora,  Megar- 
hinus).  It  has  been  shown  by  Becker  (1938),  Cook  (1944),  and  Farnsworth 
(1947)  that  the  activity  of  the  mouth  brushes  is  due  to  muscular  .action  and 
elasticity  of  the  cuticula.  Fig.  107  illustrates  the  muscles  and  structures  in- 
volved in  this  movement.  The  external  and  internal  messorial  muscles  (aem, 
aim)  by  pulling  the  palatal  bar  to  a  more  anterior  position  depress  the  mouth 
brushes.  The  median  palatal  muscle  (mpa)  would  then  contract  and  cause 
the  brushes  to  return  to  their  original  position.  Hence  by  the  rapid  action  of 
these  muscles  along  with  the  elasticity  of  the  cuticula  the  mouth  brushes  are 
set  in  active  vibration.  (Consult  Farnsworth,  1947.) 

The  antenna  consists  of  a  single  segment  and  it  terminates  in  a  hair  and 
certain  terminal  spines;  in  the  culicines  subterminal  spines  are  present.  A 
tuft  of  hairs,  a  single  hair,  or  a  branched  hair  (the  antennal  hair  tuft)  is 
located  near  the  middle  of  the  shaft.  The  eyes  are  located  on  the  sides  of  the 
head.  The  large  anterior  eyes  are  the  developing  eyes  of  the  adult  and  back  of 
them  is  located  the  small  larval  eyes.  The  various  paired  hairs  on  the  head 
are  given  names,  numbers,  or  letters  according  to  the  individual  worker.  In 
the  culicine  and  anopheline  larvae  the  principal  head  hairs  are  illustrated 
and  named  in  Figs.  105  and  no. 

The  thorax  bears  a  large  number  of  hairs  and  they  are  so  arranged  as  to 
indicate  the  pro-,  meso-,  and  metathoracic  segments.  The  usual  numbers  ap- 
pK  ^d  to  these  hairs  or  groups  are  shown  in  Figs.  105  and  109.  In  the  anophe- 
lines  the  character  of  these  hair  groups  is  of  considerable  importance  in  the 
identification  of  species.  Many  of  these  have  been  given  names,  which  are 
indicated  under  the  illustrations. 

The  abdomen  consists  of  nine  segments.  On  the  dorsal  surface  of  the  eighth 
abdominal  segment  are  the  openings  of  the  respiratory  system,  which,  in  all 
the  Culicini,  consists  of  a  long  siphon  (Fig.  105  S)  through  which  a  pair  of 
tracheal  tubes  run  to  the  tip;  these  tracheae  can  be  opened  or  closed  by  a  series 
of  apical  valves  which  surround  the  spiracles;  in  all  anophelines  the  siphon  is 
absent  and  the  spiracles  open  through  a  stigmatal  plate  (Figs.  106,109).  The 
ninth  segment  is  usually  more  slender,  is  attached  ventroposteriorly  to  the 
eighth,  and  points  ventrally  and  backwards.  Its  integument  is  more  or  less 
sclerotized  forming  the  dorsal  plate  or  saddle  (Fig.  105  DP).  This  saddle  may 
completely  surround  (ring)  the  segment  (as  in  Psorophora,  some  Aedes)  or 
be  open  along  its  ventral  median  face.  Beyond  the  saddle  the  segment  appears 
fleshy  and  bears  at  its  tip  the  anal  opening  and  four  (rarely  two)  thin,  taper- 
ing appendages,  the  tracheal  or  anal  gills.  In  addition,  the  ninth  segment  bears 
two  important  structures,  the  dorsal  brush,  consisting  of  two  sets  of  longer  or 


LHT- 


Head 


YB 


Fig.  705.  Dorsal  view  of  larva  of  Aedcs  stimulans.  The  eighth  and  ninth  segments  and 
the  siphon  are  turned  lateral  so  as  to  give  a  side  view  of  them.  A  AT,  anteantennal  hair 
tuft;  AG,  anal  gills;  Ant,  antenna;  AT,  antennal  tuft;  C,  comb;  DH,  dorsal  brush;  DP, 
dorsal  plate  or  saddle;  E,  eyes;  LAT,  lateral  abdominal  tufts;  LHT,  lower  head  tuft  or 
hair;  Mb,  mouth  brushes;  P,  pecten;  S,  siphon  or  air  tube;  SD,  subdorsal  hair  tufts  of  the 
abdomen;  SHT,  siphonal  or  air  tube  tuft;  St,  stigma;  UHT,  upper  head  tuft  or  hair; 
VB,  ventral  brush;  1-9,  segments  of  abdomen.  The  small  numbers  on  thorax  and  segment 
4  of  abdomen  indicate  the  arrangement  of  the  setae. 

267 


Head 


Fig.  106.  Larva  of  Anopheles  punctipennis.  Cl,  inner  clypeal  hairs;  DP,  dorsal  plate; 
H,  float  hairs  or  palmate  tufts;  O,  outer  clypeal  hairs;  P,  pecten;  St,  stigma  of  spiracle. 


Fig.  707.  Mouth  parts  of  a  mosquito  larva  (Anopheles) .  Upper:  Ventral  view  of  head. 
Lower  left:  A  single  mandible.  Lower  right:  A  maxilla.  Ant,  antenna;  Lb,  labium;  M, 
mentum;  MB,  mouth  brushes  (see  Fig.  io8)\  Md,  mandible;  Mu,  muscles  of  mandible; 
MX,  maxilla;  MxPlp,  maxillary  palpus;  Sm,  submentum. 


270  MEDICAL  ENTOMOLOGY 

shorter  hair  tufts  (Fig.  105  DB,  only  one  set  is  shown;  the  other  is  on  the 
opposite  side)  located  at  the  posterodorsal  angle;  and,  in  most  mosquito  larvae, 
a  ventral  brush,  consisting  of  unpaired  hair  tufts  extending  from  the  ventro- 


Fig.  108.  Internal  view  looking  down  toward  the  mouth  brushes  to  show  the  attach- 
ments that  move  the  brushes.  Aem,  tendon  attaching  the  external  messorial  muscle;  Aim, 
same  for  the  internal  messorial  muscle;  Bib,  base  of  brush;  Lb,  larval  mouth  brush;  Lpp, 
lateral  palatal  plate;  Mb,  median  bristles;  Mes,  messor;  Ml,  median  lobe;  Mpa,  median 
palatal  muscle;  Ppb,  posterior  palatal  bar;  Ta,  sclerite;  Tg,  transverse  girdle.  (After 
Farm  worth.) 

apical  edge  to  a  greater  or  less  distance  forward;  the  distal  tufts  usually  have 
sclerotized  bases  forming  a  sort  of  grid  or  barred  area.  In  the  culicines  the 
siphon  or  air  tube  has  one  to  several  pairs  of  subventral  hair  tufts  or  a  median 
row  of  hair  tufts  and,  usually  on  the  basal  half,  a  paired  row  of  short,  spine- 
like  teeth,  the  pecten  (Fig.  105  P).  In  some  genera  the  pecten  may  be  absent. 


MOSQUITOES  271 

In  all  anophelines  each  side  of  the  stigmatal  structure  has  a  sclerotized  plate 
that  bears  a  distal  row  of  spines  of  varying  length — the  pecten  (Fig.  109)  or, 
as  it  is  sometimes  called,  the  comb.  The  true  comb  is  borne  laterally  on  the 
eighth  segment  (Fig.  105  C)  and  is  found  in  anophelines  only  in  the  first- 
stage  larva.  The  comb  consists  of  a  patch  of  scales  arranged  in  various  ways. 
Each  scale  may  be  toothlike,  fringed  with  spinules  or  with  stout  branches,  and 
arise  independently  or  be  attached  to  a  sclerotized  plate. 


Fig.  io().  Left:  Dorsal  view  of  spiracle  of  larva  of  Anopheles,  Right:  Pecten  of  larva  of 
Anopheles,  Ap,  anterior  plate  or  flap;  Fl,  lateral  flap  or  ear;  M,  dorsal  plate;  Pip,  posterior 
spiracle  plate;  Sp,  spiracle. 

In  recent  years  the  chaetotaxy  or  arrangement  of  hairs  and  spines  on  the 
thorax  and  abdomen  of  mosquito  larvae  has  been  closely  studied,  and  names 
or  numbers  or  both  have  been  assigned  to  them.  Fig.  no  presents  the  num- 
bering system  as  interpreted  by  Hurlbut  (1938)  for  anophelines,  and  Fig.  105 
shows  similar  numbers  assigned  by  the  author  to  culicines.  However,  there 
is  great  variation  among  workers  and  usually  each  author  explains  his  system. 

THE  EGG 

The  eggs  (Fig.  in)  of  mosquitoes  are  rather  characteristic  and  well  pro- 
tected by  several  layers — the  thin  vitelline  membrane  which  surrounds  the 
yolk  (the  chorion,  exo-  and  endochorion)  and  a  heavily  sclerotized  outer  shell 
which  externally  is  frequently  patterned  with  small  bosses  or  reticulations 
(Fig.  112).  At  the  anterior  pole  is  the  micropyle,  a  minute  opening  for  the 
entrance  of  the  sperm;  the  micropyle  is  usually  surrounded  by  a  ring  of  small 
bosses  forming  a  kind  of  rosette.  The  eggs  of  culicines  are  generally  elongate 


272 


MEDICAL  ENTOMOLOGY 


Fig.  no.  The  chaetotaxy  of  the  fourth  instar  larva  of  Anopheles  wal^eri',  the  hairs  are 
all  numbered  i  to  14.  (/)  Thorax  and  first  five  abdominal  segments;  the  right  half  is 
dorsal,  the  left  ventral.  (2)  Leaflet  of  palmate  tuft.  (3)  Leaflet  of  hair  i  of  metathorax. 
(4)  Leaflet  of  hair  i  of  second  abdominal  segment  (5)  The  spiracular  apparatus,  dorsal 
view.  (6)  Sixth  and  seventh  abdominal  segments;  right  dorsal,  left  ventral.  (7)  Dorsal 
view  of  head.  (8)  Ventral  view  of  head.  (9)  Tip  of  antenna,  (/o),  (//),  (72)  Basal 
tubercles  of  pro-,  meso-,  and  metathoracic  pleural  hairs.  (73)  Inner  clypeal  hair.  (14) 
Anterior  part  of  the  frontoclypeus.  (75)  Tip  of  left  maxillary  palpus.  (76)  Lateral  aspect 
of  eighth,  ninth,  and  tenth  abdominal  segments.  (After  Hurlbut.) 


MOSQUITOES 


273 


Fig.  in.  Eggs  of  various  species  of  mosquitoes,  (a)  Egg  mass  of 
Culex  pipiens.  (b}  Egg  mass  of  Culiseta  inornata.  (<:)  Egg  of  Aedes 
aegypfi.  (d)  Egg  of  Anopheles  punctipcnnis,  dorsal  view.  (<?)  The 
same,  ventral  view.  (/)  Egg  of  Anopheles  quadrimaculatus ,  dorsal 
view,  (g)  Egg  of  Anopheles  crucians.  (From  Howard,  Dyar,  and 
Knab.) 


Fig.  112.  Egg  of  A/iophclcs  wal1(cri.  E,  chorion;  F,  frill; 
Fl,  floats.  (From  Hurlbut.) 

oval  and  may  be  laid  singly  (as  in  Aedes)  or  in  masses  (as  in  many  Culex 
spp.).  The  eggs  of  anophelines  are  strikingly  different  from  those  of  the 
culicines.  The  egg  is  generally  boat-shaped,  flattened,  slightly  convex  or  con- 
cave dorsally,  and  strongly  convex  ventrally  (Fig.  112).  The  chorion  is  modi- 
fied to  form  a  frill,  which  partially  or  completely  surrounds  the  upper  portion. 


274 


MEDICAL  ENTOMOLOGY 


In  addition,  a  pair  of  characteristic  floats  or  air  sacs  on  each  side  enables  the  egg 
to  float  freely  on  the  surface  of  the  water  (Fig.  112  Fl).  The  extent,  arrange- 
ment of  the  floats,  coloration,  and  certain  other  features  have  all  been  studied 
and  have  been  found  quite  valuable  in  identifying  species  of  Anopheles,  espe- 
cially of  closely  related  forms  or  races  as  A.  maculipennis  of  Europe.  Causey, 
Deane,  and  Deane  (1944)  nave  studied  the  eggs  of  thirty  Brazilian  species  of 
anophelines  and  have  been  able  to  identify  species  on  egg  characters. 


f'S-  "3-  Larvae  of  mosquitoes  (Acdcs  spp.)  resting  and  feeding  at  the  surface  of  the 
water;  note  the  long  ana!  siphon  or  breathing  tube;  note  the  curled  up  pupae  among 
them. 

THE  BIOLOGY  OF  MOSQUITOES 

All  mosquitoes  undergo  a  complete  metamorphosis,  i.e.,  from  the  egg  hatches 
a  larva  which  feeds  and  grows;  the  larva,  when  mature,  transforms  into  an 
active  pupa  (Fig.  113);  from  the  pupa  there  later  emerges  the  adult.  The 
larval  and  pupal  stages  occur  only  in  water  (Fig.  113).  The  eggs  of  all  known 
species  are  laid  on  water,  near  water,  or  in  places  where  water  is  likely  to  be 
at  some  later  date  (as  in  many  Aedes  spp.,  Psorophora  spp.,  and  some  others). 
All  mosquito  larvae  molt  four  times,  the  last  molt  disclosing  the  pupa.  In  the 
study  of  the  larva  the  fourth  instar,  which  is  the  stage  before  the  last  molt,  is 
called  the  mature  larva,  and  it  is  this  stage  that  is  used  almost  exclusively  for 


MOSQUITOES  275 

identification  purposes.  Studies  on  the  earlier  stages  have  been  made,  but  not 
much  success  has  resulted  in  identifying  species  except  in  certain  small  groups. 
It  is  not  our  purpose  here  to  give  an  extended  account  of  mosquito  bionomics. 
The  literature  in  this  field  is  so  vast  and  has  increased  so  enormously  during 
the  past  few  years  that  the  reader  must  consult  special  papers  dealing  with 
groups  or  individual  species.  For  our  North  American  species  consult  King, 
Bradley,  and  McNeel  (1942),  Matheson  (1944),  or  Carpenter,  Middlekauff, 
and  Chamberlain  (1946).  The  following  account  is  mainly  concerned  with 
those  species  known  to  be  or  suspected  of  being  transmitters  of  important 
diseases. 

CULICINE  MOSQUITOES 

The  vast  majority  of  our  species  belong  in  the  tribes  Culicini  and  Sabethini 
and  are  generally  referred  to  as  the  culicine  mosquitoes. 

THE  GENUS  CULEX:  Probably  one  of  the  most  abundant,  most  wide- 
spread, and  generally  conceded  most  annoying  mosquitoes  is  one  that  belongs 
to  the  genus  Culex,  the  common  house  mosquito  Culex  pipiens  Linn.4  (Fig. 
114).  Not  only  is  it  annoying  by  its  bites  but  it  is  the  transmitter  of  several  im- 
portant diseases  of  man  and  other  animals. 

The  house  mosquito  is  widely  distributed  throughout  the  Holarctic  region; 
in  South  America  it  is  found  south  of  the  39th  parallel  of  latitude,  in  East 
Africa  from  Egypt  south  to  the  Cape  and  west  to  eastern  Belgian  Congo,  in 
Madagascar,  and  probably  in  other  regions.  This  species  passes  the  winter  as 
fertilized  females,  hibernating  in  various  shelters  such  as  attics,  cellars,  cow- 
sheds, stables,  and  outbuildings  of  all  kinds  where  protection,  adequate  mois- 
ture, and  semidarkncss  are  found.  The  males  all  die  with  the  approach  of 
winter.  It  is  probable  that,  in  the  warmer  portions  of  the  range  of  this  species, 
continuous  breeding  may  occur,  though  at  a  much  reduced  rate  as  indicated 
by  several  recent  workers.  In  the  temperate  regions  hibernation  is  the  general 
rule.  Enormous  numbers  of  females  may  pass  the  winter  in  very  small  shelters. 
I  have  estimated  from  careful  counts  of  definite  areas  that  over  100,000  hiber- 
nated in  a  small  dark  cellar  not  over  four  feet  by  six  feet  with  a  height  of  only 


4  According  to  Marshall  (1938)  and  other  European  workers  this  species  rarely  feeds 
on  man  but  mainly  on  birds.  They  state  that  another  species,  so  closely  similar  that  it  is 
difficult  to  recognize  it,  is  the  troublemaker.  To  this  species  has  been  assigned  the  name 
Culex  mo/estus  Forskal.  This  is  the  one  that  prefers  mammalian  blood  but  can  reproduce 
generation  after  generation  without  blood  ("autogeny");  C.  pipiens  requires  blood  for 
egg  development  and  it  prefers  the  blood  of  birds. 


276 


MEDICAL  ENTOMOLOGY 


Fig.  //f  Culex  piplens.  Female. 


MOSQUITOES  277 

seven  feet.  Scarcely  a  pin  point  could  be  found  on  which  a  mosquito  did  not 
cling  to  ceiling,  walls,  hanging  ropes,  and  a  pump,  which  occupied  the  center 
of  the  small  room.  During  the  cold  weather  the  hibernating  individuals  show 


Fig.  7/5.  Breeding  places  <>i  iiiirqniiucs.  Upper:  View  across  a  marsh  area 
with  many  pools  and  sluggish  streams  in  which  breed  Aedes  vexans  and  Ano- 
pheles pnnctipcnnis.  Loner:  A  hog  wallow  where  Aedes  vexans  and  Culex 
pipiens  breed  in  enormous  numbers. 

little  activity  though  occasionally  they  may  invade  the  warmer  rooms  in  search 
of  blood.  With  the  approach  of  spring,  activity  is  resumed  and  the  females 
seek  suitable  places  for  oviposition.  Depending  on  the  locality,  egg  laying 
begins  in  May  or  June  or  possibly  earlier.  Each  female  deposits  from  100  to 


278  MEDICAL  ENTOMOLOGY 

400  or  more  eggs  in  a  boat-shaped  mass  (Fig.  in  a)  on  or  close  to  the  surface 
of  standing  water  well  protected  from  the  winds.  Each  egg  is  cylindrical  and 
tapers  to  the  end  away  from  the  water.  The  favorite  breeding  grounds  are 
rain-water  barrels,  cisterns,  tanks,  garden  pools  stocked  with  aquatic  plants, 
slow-flowing  polluted  streams,  flooded  latrines,  cesspools,  polluted  ponds  (Fig. 
115),  catch  basins,  sagging  gutters,  and  almost  any  water-filled  container. 

Depending  on  the  temperature,  the  eggs  hatch  in  from  one  to  three  days 
or  occasionally  longer.  The  young  larva  escapes  from  the  lower  end  of  the  egg 
and  swims  actively  about  in  the  water.  During  warm  weather  the  larval  de- 
velopment is  very  rapid,  the  pupal  stage  being  reached  in  seven  to  ten  days.  In 
cold  weather,  larval  development  may  be  greatly  delayed.  The  larvae  (Fig. 
116)  are  very  active,  swimming  with  ease  and  rapidity  by  sudden  jerks  of  the 
body.  Being  somewhat  heavier  than  water,  they  rise  to  the  surface  by  a  rapid 
wriggling  of  the  body  from  side  to  side,  break  through  the  surface  film  with 
their  air  tubes,  and  rest,  the  body  sloping  at  an  angle.  During  all  this  time, 
the  mouth  brushes  are  in  motion,  sweeping  small  particles  into  the  alimentary 
canal  along  with  a  certain  amount  of  water. 

The  pupal  period  is  short,  usually  only  two  or  three  days.  The  pupa  nor- 
mally rests  at  the  surface,  the  air  tubes  piercing  the  surface  film.  When  dis- 
turbed, it  swims  rapidly  downward  by  means  of  violent  abdominal  contrac- 
tions. The  tip  of  the  abdomen  is  provided  with  two  broad  paddles,  which 
greatly  aid  in  pupal  movement.  Being  lighter  than  water,  the  pupa,  when 
quiet,  rises  to  the  surface  again.  As  the  time  for  the  emergence  of  the  adult 
approaches,  the  pupa,  when  disturbed,  descends  with  difficulty  and  rises  more 
rapidly.  The  time  occupied  in  the  transformation  from  pupa  to  adult  is  very 
short.  The  pupa  will  be  seen  to  straighten  out  the  abdomen  and  air  appears 
between  the  pupal  skin  and  the  adult.  The  pupa  now  seems  almost  silvery 
white,  and  its  specific  gravity  being  greatly  reduced,  the  whole  cephalothorax 
and  part  of  the  abdomen  touch  the  surface.  The  pupal  skin  now  splits  in  the 
median  line  of  the  cephalothorax  and  the  dorsum  of  the  adult  appears  in  the 
slit.  By  constant  pressure  the  slit  widens  and  two  transverse  slits  appear  on 
each  side.  Slowly  the  adult  works  its  way  out,  using  the  pupal  skin  as  a  float 
and  balancing  itself  with  great  care.  In  two  or  three  minutes  the  insect,  now 
swollen  with  engorged  air,  stands  poised  on  its  previous  prison  cell,  and  is 
soon  ready  for  its  initial  flight.  At  first  the  adult  is  almost  colorless,  but  in  a 
few  hours  the  permanent  color  pattern  appears. 

The  entire  life  cycle  from  egg  to  adult  occupies  from  10  to  14  days.  Genera- 
tion after  generation  follows  throughout  the  summer  season  and  breeding  only 
stops  with  the  approach  of  cold  weather.  Culex  pipicns  may  be  found  breeding 


MOSQUITOES 


279 


Fig.  ii 6.  Larva  of  Culex  pipiens. 


28o  MEDICAL  ENTOMOLOGY 

as  late  as  November  in  the  region  of  central  New  York,  it  is  one  of  our  domestic 
mosquitoes,  that  is,  it  breeds  and  lives  in  close  proximity  to  human  habitations. 
In  the  tropical  and  subtropical  regions  of  the  world  it  is  replaced  by  Culex 
jatigans  Wied.  (quinqucfasciatus  Say),  a  closely  allied  species.  It  is  not  always 
possible  to  separate  these  two  species;  reliance  must  be  placed  on  a  study  of  the 
male  genitalia,  and  even  this  may  not  be  satisfactory  where  the  two  species 
overlap.  The  larvae  are  practically  identical.  Both  species  breed  in  similar  situa- 
tions, invade  houses,  bite  during  the  evening  hours  and  at  night.  The  tropical 


Fig.  7/7.  A  productive  roadside  pool  in  western  Canada.  In  early  spring 
Aedes  spencer ii  is  present,  followed  by  A.  vexans  and  A.  dorsalis;  later  in  Au- 
gust A.  spcncerii,  Culex  tarsalis,  and  Culiseta  inornata  are  found.  (After 
Rcmpel.) 

species  is  said  to  be  intensely  anthropophilic  (NAVMED,  983.  1946)  and  has 
a  recorded  flight  range  of  three  to  four  miles. 

Culex  tarsalis  Coquillett  is  easily  recognized  by  the  broad  apical  and  basal 
white  bands  on  the  hind  tarsi,  the  tibiae  with  apices  and  bases  banded  with 
white,  and  a  broad  whitish  ring  on  the  proboscis.  In  addition,  the  femora  and 
tibiae  have  narrow  longitudinal  lines  of  white  scales  on  outer  and  inner  sides 
and  a  series  of  black  V-shaped  markings  on  the  ventral  surface  of  the  abdomen. 
This  is  a  very  important  species  as  it  probably  is  the  important  vector  of 
encephalitis  of  man  and  animals  in  North  America.  It  has  a  wide  distribution 
throughout  the  western  United  States  and  western  Canada,  especially  in  the 
plains.  Freeborn  (1926)  reports  it  as  the  most  widespread  mosquito  in  Cali- 


MOSQUITOES  281 

fornia;  Rees  (1943)  regards  it  as  a  major  pest  in  Utah  because  of  its  abundance 
and  wide  distribution;  Rempel  reports  it  very  abundant  some  years  in  Sas- 
katchewan; Cox  (1944)  states  it  is  widespread  and  abundant  in  Texas.  Its 
general  distribution  is  southern  British  Columbia  eastward  through  the  Cana- 
dian prairie  provinces  to  Michigan,  south  through  the  central,  southern,  and 
western  states  and  Mexico.  The  adults  are  fierce  biters  and  readily  enter  houses, 
normally  attacking  at  dusk  and  after  dark.  The  common  breeding  places  are 
in  fresh  or  foul  ground  pools  (Fig.  117),  roadside  ditches,  irrigation  water, 
rain  barrels,  and  similar  situations. 

The  genus  Culex  includes  a  large  number  of  species  placed  in  several  sub- 
genera.  Many  of  the  species  are  vectors  of  filariasis  (see  p.  562),  some  of  Japa- 
nese B  encephalitis  as  Culex  pipiens  fallens  and  C.  tritaeniorhynchus  (natural 
infection),  others  of  St.  Louis  encephalitis,  western  and  probably  eastern 
encephalomyelitis  of  horses,  and  encephalitis  of  man.  However,  most  of  the 
species  of  Culex  occur  in  the  tropical  and  subtropical  regions,  and  the  relation 
of  these  species  to  their  hosts,  in  most  cases,  is  not  known.  Edwards  (1932) 
listed  317  species,  and  since  then  over  100  new  species  have  been  described,  but 
comparatively  little  is  known  of  their  biology. 

THE  GENUS  AEDES:  This  genus  contains  a  large  number  of  species.  In 
1932  Edwards  listed  some  410  species,  and  since  then  over  100  new  species  have 
been  recognized.  The  species  are  frequently  abundant,  and  the  adult^may 
occur  in  vast  numbers,  especially  in  the  Arctic  regions,  the  subtropical  regions, 
and  the  north  temperate  zone.  They  are  distributed  from  the  polar  regions 
to  the  tropics  and  to  high  elevations  in  mountainous  areas.  Certain  species  as 
A.  sollicitans  and  A.  taeniorhynchus  (breeding  in  tidal  areas  along  seacoasts) ; 
A.  stimulans,  A.  excrucians,  A.  punctor,  A.  communis,  and  others  (in  north 
temperate  wooded  areas) ;  A.  vexans,  A.  sticticus,  and  A.  lateralis  (some  of  our 
flood-water  species);  A.  spcncerii,  A.  dorsalis,  A.  campestris  (on  the  open 
plains) ;  A.  nearcticus  and  A.  nigripes  (in  the  Arctic  regions) ;  and  A.  ventro- 
vittis  and  others  (in  high  mountainous  regions)  often  render  life  almost  un- 
endurable at  certain  seasons  of  the  year.  Not  only  do  Aedes  species  act  as  pests, 
but  a  goodly  number  serve  as  efficient  vectors  of  diseases  of  man  and  animals 
(see  Table  8). 

It  is  not  easy  to  briefly  summarize  the  biology  of  the  numerous  species  in- 
cluded in  this  genus.  Edwards  (1932)  has  given  a  general  summary  based  on 
the  various  subgenera  that  he  recognizes.  In  brief  we  may  say  the  eggs  are 
spindle-shaped  or  elliptical,  thick-shelled,  resistant  to  drying  to  a  marked 
degree,  and  id  singly  not  on  or  in  water  but  in  places  where  water  will  be 
either  by  rains,  melting  snows,  tidal  areas,  or  flood  waters,  in  tree  holes,  bamboo 


282 


MEDICAL  ENTOMOLOGY 


stumps,  etc.  As  the  eggs  are  very  resistant  they  may  ie  dormant  for  several 
years  (as  for  example  A.  vexans  and  A.  sticticus).  The  larvae  occur  in  various 
types  of  breeding  places,  and  such  places  can  be  largely  indicated  by  knowing 


Fig.  ii 8,  Upper:  A  deep  woodland  pool  in  which  Aedes  stimulans,  A.  fitchii, 
and  A.  cxcrucians  breed  in  immense  numbers.  Lower:  A  shallow  woodland 
pool  where  Aedes  stimulans,  A.  fitchii,  A.  excrucians,  A.  intruders,  A.  tri- 
churus,  and  A.  canadcnsis  breed. 

the  subgenus  to  which  the  species  belongs.  Most  of  the  larvae  are  bottom 
feeders  though  a  few  are  predaceous  (species  of  the  subgenus  Mucidus). 

The  species  of  the  subgenus  Ochlerotatus  are  world-wide  in  distribution,  and 
they  breed  in  temporary  ground  pools  formed  by  rains,  melting^  snows,  flood 


MOSQUITOES  283 

waters,  and  tidal  marshes;  a  few  in  tree  holes.  Examples:  A.  (0.)  taeniorhyn- 
chus  and  others  in  tidal  marshes  in  the  Americas;  A.  (O.)  vigilax,  coastal  areas 
of  Australia  and  nearby  islands;  A.  (0.)  mariac  in  sea-water  pools  along  the 
Mediterranean  coasts;  A.  (0.)  stimulant,  A.  (0.)  fitchii,  A.  (0.)  communis, 
A.  (O.)  trichurus,  and  others  in  snow-water  pools  in  northern  North  America 
(Fig.  118).  In  the  subgenus  Finlaya  practically  all  the  species  breed  in  tree 
holes  (Fig.  119),  bamboo  stems,  leaf  bases  of  various  plants,  potholes  in  stream 
beds,  coconut  husks,  banana  stumps,  pitcher  plants,  and  a  few  species  from 
grassy  pools.  Examples:  A.  (F.)  triseriatus,  A.  (F.)  alleni,  and  A.  (F.)  vari- 


Fig.  7/9.  Left:  A  sycamore  log  which  was  cut  for  the  honey;  now  filled  with  water. 
In  this  tree  hole  breed  Anopheles  barberi,  Aedcs  triseriatus,  Culex  apicalis,  and  C.  res- 
tuans.  Right:  A  tree  hole  in  which  Acdes  triseriatus  breed.  (Both  at  Ithaca,  New  York.) 

palpus  in  North  America,  and  many  species  in  practically  all  parts  of  the 
world.  The  subgenus  Stegomyia  is  practically  confined  to  the  tropical  and 
subtropical  regions  of  Africa,  the  Oriental  region,  and  the  Australasian  region, 
though  certain  species,  as  Aedes  (5.)  aegypti,  have  been  carried  by  commerce 
to  nearly  all  parts  of  the  world  where  they  can  find  satisfactory  breeding 
grounds.  This  subgenus  was  rather  extensively  studied  in  the  western  and 
southwestern  Pacific  regions  during  the  recent  war.  Many  new  species  have 
been  described  and  old  species  broken  down  into  a  number  of  distinct  species. 
Edwards  (1932)  lists  41  species  from  the  world,  and  some  20  new  species  have 
since  been  described.  This  is  an  important  group  of  mosquitoes.  The  principal 
breeding  places  are  tree  holes,  leaf  bases,  coconut  shells,  artificial  containers 
(as  in  A.  aegypti) ,  and  similar  situations.  The  adults  of  most  species  are  day 
.fliers.  Though  the  subgenus  Aedimorphus  has  over  50  species,  only  one  is  of 


284  MEDICAL  ENTOMOLOGY 

major  importance.  A.  (A.)  vexans  is  world-wide  in  distribution  and  a  pest 
wherever  it  occurs  in  abundance.  Most  of  the  species  breed  in  temporary  ground 
pools  or  flood  waters.  The  subgenus  Aedes  occurs  primarily  in  the  Oriental  and 
Australasian  regions.  Only  one  species,  A.  (A.)  cinereus  occurs  in  Europe  and 
America.  It  breeds  in  early  spring  pools.  The  other  subgenera  consist  of  few 
species  and  very  little  is  known  about  them. 

Aedes  (Stegomyia)  aegypti  Linn.  (Stegomyia  jasciata,  Aedes  argenteus, 
Aedes  calopus,  etc.)  :  The  yellow-fever  mosquito  (Fig.  120)  is  probably  the 
most  domesticated  of  any  species;  it  is  found  only  about  human  habitations 
and  primarily  lives  in  our  houses.  It  has  a  wide  distribution  in  the  tropical  and 
subtropical  regions.  It  is  found  in  most  countries  lying  between  latitudes  45° 
North  and  40°  South,  and  its  presence  in  temperate  regions  beyond  these 
limits  is  of  a  temporary  nature.  According  to  Howard,  Dyar,  and  Knab  (1912), 
"Its  permanent  distribution  is  determined  by  the  minimum  temperatures  and 
its  temporary  distribution  by  the  maximum  temperatures  of  any  given  region 
wherever  it  is  sufficiently  populated."  Carter  (1931)  agrees  with  this  view. 
The  minimum  temperatures  are  those  that  kill  the  hibernating  eggs  or  prevent 
their  development,  and  the  maximum  temperatures  are  those  that  permit  the 
larvae  to  develop  and  the  adults  to  flourish.  Carter  does  not  give  these  ranges  of 
temperatures,  though  it  is  generally  stated  that  in  those  areas  where  the  nights 
are  cool  (68°F.  and  below),  as  in  California,  the  mosquito  does  not  occur  even 
if  in  the  daytime  the  temperatures  are  sufficiently  high  to  be  subtropical.  Hindle 
gives  the  permanent  distribution  as  confined  between  the  two  isothermal 
lines  of  20°  C.  (68°  F.). 

The  species  can  be  recognized  easily  by  the  characteristic  curving  white  lines 
on  the  thorax  and  the  white  banding  of  the  tarsi.  Though  it  has  generally  been 
considered  an  American  species  that  has  spread  by  way  of  commerce  to  all 
parts  of  the  tropics,  many  workers  now  concede  that  it  was  originally  an 
Ethiopian  species  brought  to  the  Americas  by  the  early  navigators.  The  place 
of  origin  is  of  significance  with  regard  to  the  origin  and  spread  of  yellow  fever. 

LIFE  HISTORY:  The  eggs  (Fig.  me)  are  laid  singly  on  the  water,  just  at  the 
edge  of  the  water,  or  on  the  sides  of  the  container  above  the  surface  of  the 
water.  As  the  eggs  can  withstand  drying  for  a  long  time,  at  least  over  five 
months,  the  filling  of  the  receptacles  by  rain  or  otherwise  assures  the  young 
larvae  an  adequate  water  supply  for  their  short  larval  life.  The  eggs  hatch 
in  two  days  or  less,  if  the  temperatures  are  high,  but  hatching  may  be  prolonged 
when  the  weather  is  cool,  as  during  the  winter  months.  The  larval  life  is  com- 
paratively short,  occupying  six  to  ten  days,  or  it  may  be  greatly  prolonged  by 


Fig.  120.  The  yellow-fever  mosquito,  Aedcs  aegypti. 

cool  weather.  The  mature  larva  (Fig.  121)  is  robust,  rather  stout,  with  a  com- 
paratively short,  somewhat  pointed  siphon.  The  siphon  bears  a  pair  of  small 
hair  tufts  just  beyond  the  pecten.  The  scales  (8  to  12)  of  the  comb  are  rather 
distinctive — sole-shaped  with  a  long,  curving  apical  spine  and  several  sub- 
apical  spines  (Fig.  121  2).  The  larvae  are  very  responsive  to  disturbances  of 
any  kind,  darting  to  the  bottom  of  the  water  at  the  slightest  disturbance  or 
from  a  passing  shadow.  On  account  of  this  habit  their  presence  is  often  diffi- 


286 


MEDICAL  ENTOMOLOGY 


Fig.  121.  Larva  of  the  yellow-fever  mosquito,  Acdcs  aegypti.  (2)  One  of  the  teeth 
from  the  comb,  greatly  enlarged. 


MOSQUITOES  287 

cult  to  detect  unless  the  inspector  can  take  time  to  observe  them  as  they  quietly 
return  to  the  surface  or  unless  he  empties  out  the  container.  Even  then  they 
may  be  missed  as  the  larvae  press  themselves  close  to  the  bottom  and  are  not 
easily  dislodged.  This  burrowing  habit  frequently  enables  them  to  breed 
continuously  in  containers  of  drinking  water  which  are  frequently  emptied 
and  refilled,  since  many  of  them  escape  being  poured  out. 

The  pupal  period  is  very  short,  not  over  two  days  under  normal  conditions. 
The  entire  life  cycle  may  be  passed  in  ten  clays,  though  ordinarily  the  time 
required  varies  from  eleven  days  to  three  weeks.  Within  its  permanent  range 
it  breeds  throughout  the  year;  generation  succeeds  generation  with  great 
rapidity  when  water,  the  necessary  warmth,  and  a  blood  supply  are  available. 
During  the  colder  months  of  the  year  the  reproductive  rate  is  slowed  down  or 
the  eggs  may  remain  dormant  for  a  considerable  period;  the  dry  season  may 
be  passed  in  the  egg  stage. 

The  adults,  on  emerging,  mate  within  a  few  hours  or  a  few  days.  Mating 
takes  place  while  in  flight.  The  female  must  now  secure  a  blood  meal  in  order 
that  her  eggs  may  develop.  If  blood  cannot  be  obtained  the  eggs  remain  unde- 
veloped even  though  she  feeds  on  honey,  nectar,  etc.,  and  continues  to  live  for 
a  long  time.  The  obtaining  of  a  blood  meal  initiates  ovarian  development,  and 
a  steady  source  of  blood  enables  the  females  to  produce  the  maximum  number 
of  eggs.  Each  female  is  capable  of  laying  from  50  to  as  many  as  150  eggs  during 
her  lifetime.  The  females  actively  seek  blood.  They  are  primarily  diurnal  in 
their  feeding  habits  and  bite  in  bright  sunlight.  The  times  of  greatest  activity 
are  the  morning  and  evening  hours,  though  I  have  had  them  feed  on  me 
consistently  after  dark  in  a  lighted  office  where  we  were  breeding  them  in 
quantity.  The  song  of  the  yellow-fever  mosquito  is  very  feeble  and  it  prefers  to 
attack  under  cover,  as  about  the  ankles,  under  coat  sleeves,  at  the  back  of  the 
neck,  and  in  similar  places. 

The  adults  can  remain  alive  for  long  periods,  at  least  nearly  four  months  or 
even  more,  when  properly  fed  and  kept  under  conditions  ensuring  moisture 
and  warmth.  The  length  of  the  adult  life  is  of  great  importance  in  relation  to 
the  spread  of  yellow  fever.  In  the  open  the  adult  life  is  probably  not  so  pro- 
longed as  four  months,  but  on  this  point  we  have  no  very  exact  data.  The 
range  of  flight  is  another  important  problem.  It  has  generally  been  held  that 
they  do  not  fly  over  100  yards  from  their  breeding.  Dunn  (1927)  records  this 
species  as  breeding  in  water  containers  500  yards  from  any  habitation;  this 
would  indicate  a  flight  range  of  at  least  that  distance.  Shannon  and  Davis 
(1930),  in  a  series  of  well-planned  experiments,  obtained  a  flight  range  of  300 
io  350  meters  (13  mosquitoes  captured);  950-1000  meters  (7  mosquitoes 


288  MEDICAL  ENTOMOLOGY 

taken);  a  full  1000  meters  (i  mosquito  obtained).  In  these  experiments  some 
32,000  adults  were  employed  and  less  than  0.4  per  cent  were  recovered. 

BREEDING  PLACES  \  The  primary  breeding  place  is  in  water  held  in  artificial  con- 
tainers in  and  around  human  habitations.  These  mosquitoes  never  breed  in 
swamps,  pools,  or  temporary  puddles,  even  though  these  are  located  near 
houses.  The  more  common  types  of  water  containers  are  rain-water  barrels, 
wells,  cisterns,  tanks,  sagging  roof  gutters,  water-closet  tanks,  tin  cans,  vases 
with  flowers,  urns  in  cemeteries  (Fig.  122),  etc.,  in  fact,  in  any  type  of  artificial 
container  capable  of  holding  water;  they  also  breed  in  tree  holes  (probably 

their  original  breeding  ground), 
holes  in  stumps,  water  held  by 
bromeliads,    in    the    still-folded 
leaves  of  banana  plants,  and  in 
similar  situations.  Dunn  (1927) 
found    them    breeding   in    such 
numbers  in  tree  holes  (and  some 
of  the  tree  holes  were  at  least  300 
yards  from  houses)  that  he  con- 
sidered   this    type    of    breeding 
Fig.  ;_v.  View  of  a  UnKil  orouiul  in  the  south-   ground  of  importance  in  control 
ern  United  States.  In  each  niche  arc  one  or  two   wor]^    fje    ajso   founcl   that   the 
flower  vases,  and  Aedes  aegypti  breeds  in  them  ,  ,  .        .11. 

whenever  water  is  present.  e«Ss  could  remam  viable  in  tree 

holes  throughout  the  entire  dry 

season  in  West  Africa.  He  discovered  them  breeding  in  the  water  pockets  at 
the  bottom  of  crab  holes  about  lagoons.  It  is  said  that  the  females  prefer  clean 
water  for  oviposition  purposes,  but  the  larvae  have  been  found  in  nearly  all 
types  of  polluted  water.  It  would  seem  that  water  containing  leaves  is  very 
attractive  (Dunn).  Though  this  species  breeds  almost  exclusively  in  fresh 
water,  it  will  occasionally  breed  in  brackish  water.  Garnham  et  al.  (1946)  re- 
port finding  it  commonly  throughout  the  forests  in  parts  of  Kenya  breeding 
in  rock  holes  along  river  beds  in  dry  weather  and  in  holes  in  recently  felled 
trees.  They  further  state  that  it  is  not  common  about  human  habitations  in 
this  region. 

Aedes  (Stegomyia)  albopictus  (Skuse)  is  an  important  species  widely  dis- 
tributed in  India  west  to  the  Caspian  Sea,  east  throughout  Burma,  Indo-China, 
and  the  East  Indies  to  New  Guinea,  and  north  through  China  to  Manchuria; 
it  also  occurs  in  Japan,  the  Philippines,  the  Marianas,  Hawaii,  Madagascar,  and 
Mauritius.  Like  A,  (S.)  aegypti  it  is  being  rapidly  distributed  by  commerce. 
It  can  usually  be  recognized  by  the  narrow  median  silvery-white  stripe  extend- 


MOSQUITOES  289 

ing  nearly  the  whole  length  of  the  mesonotum,  the  white  flat  scales  on  the 
lobes  of  the  scutellum,  the  broad  white  rings  on  all  segments  of  the  hind  tarsi, 
and  the  white  scales  on  the  pleura  of  the  thorax  arranged  in  patches  rather 
than  in  lines  (Fig.  123).  This  species  is  largely  dominant  in  its  range  and  it  can 
usually  be  recognized  from  the  scutdlaris  group  by  the  white  scales  in  patches 
instead  of  in  broad  lines  on  the  pleura  of  the  thorax.5  A.  albopictus  is  largely 
found  about  human  habitations;  it  occurs  up  to  6000  feet  in  India  and  is  re- 
ported breeding  extensively  in  wooded  areas  in  the  lower  mountain  ranges  of 
Hawaii.  The  adults  are  strongly  anthropophilic  and  are  persistent  in  their 
attacks.  Though  they  usually  bite  outdoors  during  the  twilight  hours  or  in 
shady  places  during  the  day,  yet  the  females  readily  enter  buildings  for  a 
blood  meal.  This  species  breeds  primarily  in  bamboo  and  tree  stumps,  tree 


Fig.  123.  Left  and  center:  Lateral  and  Dorsal  views  of  the  thorax  of  Aedes  (Stegomyia) 
scutdlaris.  Right:  Lateral  view  of  Aedes  (S.)  albopictus. 

holes,  leaf  axils,  and  coconut  shells,  and  rarely  in  rock  pools  or  artificial  con- 
tainers. The  breeding  grounds  are  usually  about  human  dwellings.  Through- 
out its  range  it  is  an  effective  vector  of  dengue  and  it  has  been  shown  to  be 
experimentally  a  vector  of  yellow  fever. 

Aedes  (Stegomyia)  scutdlaris  (Walker)  [A.  (S.)  hebrideus  Edw.  is  the 
same  species]  occurs  in  New  Guinea,  New  Hebrides  and  probably  on  many 
other  Pacific  islands.  Its  breeding  grounds  are  quite  similar  to  those  of  albo- 
pictus though  it  also  uses  any  available  artificial  containers.  The  adults  are 
vicious  biters  and  seem  to  prefer  human  blood.  It  is  considered  to  be  a  vector 
of  dengue  (Daggy,  1944)  anc^  '**•  1S  reported  to  be  naturally  infected  with 
Wuchereria  bancrojti, 

Aedes  (Stegomyia)  simpsoni  Theobald  is  an  important  semidomestic  mos- 
quito. It  breeds  in  tree  holes,  bamboo  and  leaf  axils  in  banana  plantations,  and 


6  Unfortunately  there  are  a  number  of  species,  usually  not  very  abundant,  similarly 
nlarked.  These  can  only  be  identified  by  an  examination  of  the  male  genitalia. 


290  MEDICAL  ENTOMOLOGY 

similar  situations.  In  northern  Nigeria  it  was  found  to  pass  the  dry  season  as 
eggs  in  its  breeding  places.  In  Uganda  this  mosquito  is  very  common  and 
yellow-fever  virus  was  isolated  from  wild-caught  specimens  in  1941  (Smith- 
burn  and  Haddow,  1946);  it  is  known  to  be  an  important  vector.  This  mos- 
quito has  a  wide  distribution  in  Africa  from  Gambia  on  the  west  to  Abyssinia 
and  south  to  the  Transvaal  wherever  breeding  conditions  are  favorable.  Ac- 
cording to  Haddow  (1945),  the  female  is  almost  exclusively  diurnal  in  its 
biting  habits. 

Aedes  (Stegomyia)  ajricanus  Theobald  is  another  species  widely  distributed 
in  Africa  and  has  recently  been  incriminated  as  a  probable  vector  in  main- 
taining yellow-fever  virus  among  the  native  monkeys  and  possibly  other 
animals.  Smithburn  and  Haddow  (1946)  have  shown  this  species  to  be  the 
dominant  arboreal  form  in  Bwamba,  Uganda,  and  it  lives  and  feeds  in  the 
tree  canopy.  It  attacks  throughout  the  day,  though  the  biting  peak  is  during 
the  early  evening  hours. 

Aedes  sollicitans  Walker  is  our  famous  salt-marsh  or  "New  Jersey"  mos- 
quito. It  breeds  in  the  great  salt  marshes  from  Maine  to  Florida  and  west  to 
Texas  along  the  Gulf  shore,  in  the  Antilles,  Cuba,  and  Jamaica.  The  eggs  are 
deposited  in  the  moist  marshes  and  they  hatch  when  their  breeding  grounds 
are  flooded  by  high  tides  or  rains.  Under  favorable  conditions  the  life  cycle 
from  egg  to  adult  is  only  about  ten  days.  Where  conditions  are  favorable, 
breeding  is  continuous  throughout  the  year;  in  the  North  the  winter  is  passed 
in  the  egg  stage.  The  females  are  vicious  biters  and  frequently  render  life 
almost  unendurable  along  the  coastal  areas.  It  also  migrates  considerable  dis- 
tances; at  least  ^o-mile  migrations  are  on  record.  Along  the  west  coast  from 
San  Francisco  south  this  species  is  replaced  by  Aedes  squamiger,  another 
troublesome  salt-marsh  breeder.  In  the  interior  Aedes  dorsalis  breeds  in  the 
saline,  brackish,  or  alkaline  pools  found  in  the  great  plains.  It  also  occurs  in 
fresh  water.  It  is  one  of  the  dominant  species  of  the  western  plains  of  Canada 
and  the  United  States.  It  has  a  wide  distribution  in  North  America,  Europe, 
Asia,  China,  and  is  reported  from  North  Africa.  Aedes  taeniorhynchus  Wied. 
is  another  salt-marsh-breeding  mosquito  with  an  extensive  range.  It  is  reported 
as  breeding  along  the  coastal  areas  of  North  and  South  America,  on  the  east 
reaching  Connecticut  and  on  the  west  Santa  Barbara,  California.  It  often 
occurs  in  enormous  swarms,  particularly  in  the  southern  portion  of  its  range. 

In  our  northern  woodlands  we  have  a  number  of  species  that  breed  in  vast 
numbers  in  spring  pools  formed  by  melting  snows  and  spring  rains.  These 
species  hibernate  in  the  egg  stage,  and  there  is  usually  only  one  brood  a  year; 
the  adults  appear  in  early  spring  and  live  during  the  greater  part  of  the  sum- 


MOSQUITOES  291 

mer.  The  females  are  vicious  biters,  largely  confining  their  attacks  to  those 
who  invade  their  habitats,  the  woodlands.  Here  belong  Aedes  stimulant 
Walker,  A.  excrucians  Walker,  A.  punctor  Kirby,  A.  com  munis  de  Geer, 
A.  fitchii  F.  and  Y.,  and  others.  Aedes  vexans  Meig.  is  one  of  the  most  wide- 
spread and  annoying  species  of  the  genus.  Next  to  Culex  pipiens,  C.  fatigans, 
and  Aedes  aegypti,  it  is  the  most  widely  distributed  mosquito  species.  It  occurs 
practically  throughout  the  Palearctic,  Nearctic,  and  Oriental  regions.  It  breeds 
primarily  in  fresh- water  marshes,  swamps,  flooded  river  bottoms,  meadow 
pools,  etc.,  and  often  occurs  in  immense  swarms  after  spring  or  early  summer 
freshets.  It  is  capable  of  rather  extended  migrations  and  may  become  a  pest 
of  the  first  importance.  Normally  it  does  not  frequently  invade  houses  though 
it  may  do  so.  It  readily  attacks  man  and  other  animals.  There  may  be  several 
broods  a  season,  each  following  the  flooding  of  their  breeding  grounds.  (For 
further  information  on  the  species  of  this  genus,  consult  the  various  refer- 
ences at  the  end  of  this  chapter.) 

THE  GENUS  ERETMAPODITES:  This  genus  deserves  mention  since 
Bauer  (1928)  demonstrated  that  E.  chrysogaster  Graham  could  act  as  a  vector 
of  yellow  fever.  It  contains  18  species  and  6  subspecies  and  all  are  restricted  to 
Africa  south  of  the  Sahara  Desert.  One  species  occurs  also  in  Madagascar.  The 
larvae,  as  far  as  known,  are  predaceous  and  are  found  in  leaf  axils,  fallen 
leaves,  leafy  pools,  and  snail  shells  in  densely  wooded  or  heavy  vegetation 
areas  and  on  banana  plantations.  The  adults  are  active  biters  during  the  day 
in  areas  where  larvae  breed.  Haddow  (1946)  states  that  they  do  not  bite  in 
the  night  or  during  twilight.  As  Africa  is  a  reservoir  of  yellow  fever,  the 
importance  of  these  mosquitoes  in  maintaining  this  reservoir' among  animals 
may  be  of  more  importance  than  is  now  known.  Haddow  (1946)  reports  the 
isolation  of  a  virus  closely  related  to  Rift  Valley  fever  from  a  mixed  group  of 
these  species  collected  in  an  uninhabited  rain  forest. 

THE  GENUS  HAEMAGOGUS:  Haemagogus  is  close  allied  to  Aedes 
though  the  species  show  many  affinities  to  the  sabethines.  There  are  no  very 
good  characters  to  distinguish  the  genus,  but  their  day-flying  habits  (nor- 
mally at  high  elevations)  and  their  bright  metallic  blue  and  green  colora- 
tion will  aid  in  recognizing  them.  The  species  occur  from  Mexico  to  Argentina 
and  are  restricted  to  the  New  World.  The  species  are  very  difficult  to  identify 
and  as  yet  we  have  no  thorough  study  of  the  genus  as  a  whole.  However, 
Kumm  et  al.  (1946)  have  presented  a  detailed  study  of  the  species  they  found 
in  Colombia.  As  far  as  known  the  species  breed  in  tree  holes,  coconut  shells, 
rock  holes,  bamboo  joints,  artificial  containers,  or  similar  situations,  and  the 


292  MEDICAL  ENTOMOLOGY 

adults  are  normally  active  during  the  middle  of  the  day  and  usually  at  rela- 
tively high  elevations  in  the  tropical  forests. 

Haemogogus  spegazzinii  falco  Kumm  et  al.  is  the  most  widely  distributed 
species  in  Colombia,  is  regarded  as  an  important  vector  of  jungle  yellow  fever, 
has  been  found  repeatedly  naturally  infected,  and  occurs  abundantly  in  the 
jungle-fever  areas.  Furthermore  it  is  the  only  species  recorded  by  Kumm  et  al. 
(1946)  with  a  hairy  larva  in  Colombia.  They  further  consider  all  references 
to  H.  capricornii 6  Lutz  in  this  area  to  refer  to  the  above  species.  H.  janthinomys 
Dyar  is  also  a  synonym.  Bates  (1944)  in  an  intensive  study  of  H.  capricornii 
( ?  —  H.  spegazzinii  falco)  in  eastern  Colombia  confirmed  the  previous 
observations  of  Bugher  et  al.  (1944)  that  this  species  is  most  active  at  high 
elevations  (upper  tree  canopy)  during  midday  and  that  its  ground  activity  is 
increased  by  the  cutting  down  of  trees,  thus  increasing  the  light  intensity  of 
ground  levels.  This  may  explain  the  prevalence  of  jungle  yellow  fever  among 
woodcutters. 

ANOPHELINE  MOSQUITOES 

Anopheline  mosquitoes  are  placed  in  at  least  three  genera — Chagasia,  with 
three  or  possibly  four  species  known  only  from  South  America  and  Panama; 
Eironella,  with  some  six  to  eight  species  known  only  from  New  Guinea,  the 
Solomons,  and  nearby  islands;  and  Anopheles,  which  is  world-wide  in  distribu- 
tion with  nearly  400  species  and  varieties.  The  genus  Anopheles  has  been 
divided  into  numerous  genera,  at  least  38,  but  these  are  now  regarded  as 
synonyms  though  some  of  them  are  employed  to  indicate  subgenera  (Edwards, 
1932,  recognizes  only  four  subgenera). 

Anophelines  can  be  distinguished  from  the  culicines  in  all  stages  of  their 
development.  The  eggs  (Figs.  111,112)  in  all  species  are  deposited  singly  or  in 
small  groups  on  the  surface  of  the  water  and  possess,  in  practically  all  species, 
lateral  floats  or  air  cushions.  The  larva  (Fig.  106)  does  not  possess  a  respiratory 
siphon  and,  when  feeding,  rests  at  the  surface  of  the  water  and  parallel  to  it 
(Fig.  124).  The  pupae  can  be  recognized  by  the  lateral  spines  (Fig.  104) 
being  located  at  the  lateral  apical  angles  of  the  abdomen  and  normally  are 
peglike  except  the  last  pair.  The  adults,  both  males  and  females  in  practically 
all  species,  have  long  palpi,  usually  as  long  as  the  proboscis  (Fig.  125) ;  the 
wings  are  usually  spotted  (Fig.  126) ;  the  scutellum  is  smoothly  arcuate  behind 


6  As  all  Haemagogus  species  can  only  be  determined  by  the  male  genitalia  or  in  most 
cases  by  larvae,  it  is  interesting  to  note  that  no  males  of  this  species  have  ever  been  taken 
in  the  wild.  Males  were  obtained  by  rearing  from  eggs  obtained  from  captured  females. 


MOSQUITOES  293 

with  hairs  evenly  distributed,  never  distinctly  trilobed  with  hairs  and  scales 
on  the  lobes  except  in  the  genus  Chagasia.  Furthermore  the  adults,  when  at 
rest,  hold  their  bodies  at  a  distinct  angle,  30°  to  almost  90°,  while  the  culicines 
hold  their  bodies  nearly  parallel  to  the  substratum  (Fig.  127). 

The  structure  o£  the  eggs  of  anophelines  has  already  been  described.  How- 
ever, attention  should  be  called  to  the  recent  studies  of  anopheline  eggs  and 


Fig.  124.  Larva  of  Anopheles  sp.  resting  and  feeding  at  the  surface  of  the  water.  Note 
the  float  hairs  piercing  the  surface  film  and  the  thoracic  lobe  just  behind  the  head  attached 
to  the  surface  film. 


Fig.  725.  The  heads  of  mosquitoes,  (a)  Male  and  female  heads  of  a  culicine  mosquito. 
(b)  Male  and  female  heads  of  an  anopheline  mosquito.  Ant,  antennae;  MxPlp,  maxillary 
palpi;  P,  proboscises.  '  ' 

their  use  in  recognizing  species.  In  the  case  of  Anopheles  maculipennis  com- 
plex Bates  (1940)  recognizes  five  species  and  two  varieties  based  largely  on 
egg  characters,  though  minute  differences  can  be  found  in  the  adults,  their 
activities  (anthropophilic  or  zoophilic),  their  hibernation,  their  failure  to 
make  successful  crosses  in  certain  cases,  and  certain  minute  larval  and  male 
structures.  Yet  in  this  important  malaria-transmitting  complex  the  most  reli- 
able characters  for  separating  the  species  or  races  appear  to  be  in  the  eggs.  Cer- 
tain of  these  species  are  important  transmitters  of  malaria  (see  pp.  306,  343). 
In  Anopheles  walf{eri  the  development  of  two  egg  types  is  a  remarkable  phe- 


294 


MEDICAL  F.NTOMOLOGY 


Fig.  126.  Wings  of  American  Anopheles  spp.  (/)  A.  earlci.  (2) 
A.  quadrimaculatus.  (3)  A.  wal^eri.  (4)  A.  punctipennis.  (5)  A.  cru- 
cians. (6)  A.  barberi. 


MOSQUITOES  295 

nomenon — one  type  for  summer  breeding  (Fig.  128)  and  a  much  larger, 
frost-resisting  type  (Fig.  128)  for  hibernation  in  the  northern  portion  of  its 
range.  It  is  probable  that  some  tropical  species  produce  eggs  that  resist  desicca- 
tion during  the  dry  seasons  (estivation)  while  the  normal  type  is  produced 
in  the  wet  season.  This  seems  to  be  indicated  by  the  different  illustrations  of 
eggs  of  the  same  species  by  various  authors.  Unfortunately  very  little  work 
has  been  done  on  this  phase  of  mosquito  biology.  The  eggs  of  most  anophe- 
lines  studied  are  not  capable  of  withstanding  much  desiccation,  a  record  of 


Fig.  127,  The  resting  position  of  our  common  mosquitoes.  Left;  Culex  pipicns.  (All  our 
common  species  except  anophclines  normally  rest  in  this  position.)  Center:  Anopheles 
quadrimaculatus.  Right:  A.  crucians. 

about  15  days  being  the  maximum.  However,  the  study  of  the  eggs  for  identi- 
fication purposes  has  shown  interesting  results.  The  work  of  Causey,  Deane, 
and  Deanc  (1944)  on  the  eggs  of  30  South  American  species  shows  their  wide 
variety  and  the  variations  within  a  single  species. 

LARVAL  HABITATS:  It  is  not  possible  to  generalize  on  larval  habitats 
since  many  species  would  seem  to  have  certain  preferred  breeding  places 
though  others  readily  accept  any  available  aquatic  situation  suitable  for  larval 
development.  In  general,  it  may  be  said  that  anophelines  rarely  breed  in  open, 
wind-swept  bodies  of  fresh  water  that  are  free  of  vegetation,  along  shore  lines 
that  are  free  of  vegetation  or  debris,  or  in  swift-running  streams  with  clear 
margins,  and  not  commonly  in  forest  pools;  a  few  species  select  saline  pools 


296 


MEDICAL  ENTOMOLOGY 


or  marginal  areas  along  the  seashore,  and  some  species  select  tree  holes  or 
water  in  epiphytic  plants,  as  bromeliads.  Anophelines  occur  in  nearly  all  parts 
of  the  world  except  in  the  Arctic  regions  and  at  high  mountain  levels.  In 
general  it  may  be  said  that  breeding  occurs  between  the  summer  isotherm  of 
60°  North  and  between  60°  and  70°  of  the  southern  summer  isotherm.  The 
A.  maculipennis  complex  of  the  Old  World  has  probably  the  most  extensive 
distribution  of  any  anopheline  species.  It  occurs  from  Great  Britain  east 
through  central  Siberia  to  the  maritime  provinces  and  from  Sweden  and 
northern  Russia  south  to  North  Africa  and  east  along  the  northern  portion  of 
the  Mediterranean  through  an  extensive  area  of  southern  Russia  to  Mon- 
golia, Manchuria,  and  Japan.  If  the  North  American  varieties  (?)  arc  included, 


Fig.  128.  Upper:  The  summer  egg  of  Anopheles  walfyri.  Lower: 
Winter  egg  of  die  same  species. 

it  has  a  still  wider  distribution.  This  species  also  occurs  at  considerable  eleva- 
tions. Its  breeding  grounds  include  fresh  or  brackish  marshes,  swamps,  lagoons, 
rice  fields,  upland  streams,  cool  fresh-water  pools,  ponds,  and  similar  situations. 
The  more  common  breeding  places  and  distribution  of  the  anopheline  species 
which  are  known  to  be  vectors  of  malaria  are  indicated  in  Table  7. 

Most  anophelines  occur  in  the  lowlands.  However,  many  species  occur  up 
to  median  elevations  (1000  to  2000  feet)  and  some  at  considerable  heights.  In 
North  America  A,  quadrimaculatus  occurs  commonly  near  Ithaca  at  over  1200 
feet;  A.  earlei  has  been  taken  at  over  2000  feet;  A.  frecborni  has  been  taken 
breeding  at  7000  feet  in  Utah  (Rees,  1943) ;  6000  feet  in  southern  Idaho  (Gjul- 


MOSQUITOES  297 

lin).  In  Mexico  A.  parapunctipennis  and  A.  pseudopunctipennis  occur  com- 
monly from  3000  to  6500  feet.  In  the  Andean  region  Hackett  (1945)  reports  A. 
pseudopunctipennis  breeding  at  elevations  of  2773  meters  (about  8550  feet) ;  it 
is  the  primary  vector  of  malaria  throughout  the  mountain  region  at  elevations 
of  from  250  to  2500  meters.  A.  eiseni  has  been  taken  up  to  5000  feet.  A.  argyri- 
tarsis  occurs  from  the  lowlands  to  at  least  5000  feet,  and  in  Guatemala  it 
abounds  at  2000  feet.  In  Mexico  A.  albimanus  occurs  in  the  rainy  season  from 
the  lowlands  to  over  3000  feet.  In  Venezuela  Anduze  (1943)  reports  A.  strodei 
and  A.  oswaldoi  as  breeding  up  to  1600  feet,  and  A.  argyritarsis,  A.  eiseni,  A. 
neomaculipalpus,  and  A.  pseudopunctipennis  were  taken  up  to  3300  feet.  Be- 
tween 3300  and  8200  feet  A.  argyritarsis,  A.  pseudopunctipennis,  and  A.  boli- 
viensis  were  found  breeding.  In  Mexico  A.  pseudopunctipennis  occurs  from 
sea  level  to  7200  feet  or  more,  while  Shannon  reports  it  in  the  Andes  at  7800  feet. 

In  Africa  A.  garnhami  occurs  in  the  Kenya  mountains  to  as  high  as  n,ooo 
feet;  A.  implexus  occurs  from  3000  to  5000  feet,  breeding  in  deep  forest  shade 
in  swamps,  springs,  and  seepages;  A.  fyngi  is  reported  breeding  at  7000  feet; 
A.  gambiae  breeds  from  sea  level  to  7000  feet  in  Abyssinia,  at  5100  feet  in 
Arabia,  and  at  4000  feet  in  Uganda. 

In  India  a  long  scries  of  anophelines  are  reported  breeding  from  2000  to 
11,000  feet.  Christophers  (1933)  records  the  following  species:  A.  aitk^eni, 
A.  moghulensis,  and  A.  jeyporicnsis  are  found  from  the  plains  to  at  least 
6000  feet;  A.  hyrcanus  nigerrimus,  A.  turJjJiudi,  A.  annularis,  and  A.  annan- 
dalei  go  as  high  as  7000  feet;  A.  maculatiis  willmori  occurs  in  the  foothills  of 
the  Himalayas  from  2000  to  8000  feet;  A.  culicifacies  is  reported  even  as  high  as 
7500  feet;  A  gigas  gigas  usually  occurs  from  5000  to  6000  feet  in  southern  India, 
while  A.  gigas  bailey i  has  been  taken  at  11,000  feet  in  Tibet;  A.  barianensis, 
a  tree-hole  breeder,  occurs  from  5000  to  Hooo  feet  in  the  northwest  Himalaya 
region;  A.  minimus  breeds  abundantly  at  2000  feet  and  occurs  to  at  least  5000 
feet;  A.  fhwiatilis,  a  stream  breeding  species,  occurs  at  elevations  between 
1000  and  7500  feet.  Other  species  might  be  added  to  this  brief  list. 

In  the  Australasian  region  A.  minimus  occurs  from  sea  level  to  3000  feet; 
A.  farauti  has  been  reported  to  as  high  as  2000  feet;  and  A.  stigmaticus  occurs  to 
elevations  of  as  much  as  6000  feet. 

THE  ADULTS :  It  is  not  possible  to  give  a  general  summary  of  the  biology 
of  the  adults.  Instead  a  brief  summary  of  the  biology  of  a  few  of  the  more 
important  vectors  of  malaria  with  a  discussion  of  the  adults  must  suffice. 

Anopheles  quadrimaculatus  (Say)  (Fig.  129)  is  the  most  important  vector 
of  malaria  in  North  America.  Its  distribution  extends  from  New  Hampshire 


298  MEDICAL  ENTOMOLOGY 

and  Massachusetts  west  through  central  New  York  and  southern  Ontario  to 
Minnesota  and  Iowa,  south  throughout  the  southern  states,  and  west  to 
central  Texas,  Oklahoma,  and  eastern  Kansas.  It  also  occurs  in  eastern  Mexico 
south  to  Veracruz.  The  adults  are  active  during  the  evening,  night,  and 
morning  hours  and  readily  enter  houses  or  other  buildings  in  search  of  blood. 
They  readily  feed  on  man  and  wild  and  domestic  animals.  Normally  they  do 


Fig.  729.  Two  of  our  common  anophelincs.  Lcjt:  Anopheles  pttnctipcnnis.  Right: 
A.  quadrimaculatus. 

not  feed  during  the  daytime,  though  they  will  attack  in  houses  and  out  of 
doors  during  dark  and  cloudy  weather.  During  the  day  they  may  be  found 
resting  in  dark  corners  in  buildings,  underneath  all  kinds  of  houses,  in  stables 
and  hollow  trees,  under  bridges  and  culverts,  in  outdoor  privies  (one  of  the 
most  common  places),  and  in  any  shelter  that  provides  darkness  and  moisture. 
The  males  and  females  mate  shortly  after  emergence  either  after  or  before  a 
blood  meal.  Keener  (1945)  describes  the  mating  in  small  rearing  cages  as  tak- 
ing place  about  8  P.M.  They  mate  in  flight,  then  usually  fall  to  the  bottom  of  the 
cage  and  separate  after  about  10  to  15  seconds  (stenogamous  species).  A  single 


MOSQUITOES  299 

mating  is  sufficient  to  ensure  fertile  eggs  during  the  life  of  the  female.  If  blood 
meals  are  available  oviposition  takes  place  about  three  days  after  emergence. 
Keener  records  each  female  as  laying  9  to  12  batches  during  its  lifetime;  each 
batch  varied  from  194  to  263  eggs.  Three  hundred  females  deposited  200,000 
eggs  during  their  life  or  an  average  of  660  eggs  per  female.  Well-fed  females  ap- 
parently may  lay  from  2000  to  3000  eggs.  Oviposition  occurred  during  evening 
hours.  The  length  of  life  of  the  female  varied  from  7  to  62  days,  with  a  mean 
of  21  days;  the  males  varied  from  a  few  days  with  a  mean  of  7  days.  How  long 
they  may  live  in  nature  is  not  well  known. 

The  breeding  places  are  most  commonly  ponds,  pools,  grassy  and  weedy 
margins  of  lakes,  swamps,  and  collections  of  water  with  floating  debris  or 
emergent  or  floating  vegetation.  It  seems  to  prefer  open,  sunlit  waters  with 
debris  or  vegetation,  though  it  breeds  in  water  areas  densely  shaded  by  tall 
trees.  During  the  summer  season  the  larval  period  is  comparatively  short.  The 
eggs  hatch  in  from  2  to  3  days  and  the  larvae  complete  their  growth  in  from 
12  to  19  days,  depending  on  food  supply  and  water  temperature.  The  pupal 
period  varies  from  2  to  6  days.  Hurlbut  (1943)  found  the  average  period  from 
egg  to  adult  to  vary  from  18  to  23  days  at  an  outdoor  temperature  of  about 
74°  F.  The  number  of  generations  per  season  varies  according  to  the  region 
studied.  Boyd  (1930)  concluded  there  were  seven  to  eight  annual  generations 
in  North  Carolina,  and  in  southwestern  Georgia  eight  to  ten.  Hurlbut  (1943) 
records  nine  to  ten  generations  in  northern  Alabama.  Bradley  and  Fritz 
(1945)  present  an  interesting  account,  based  on  extensive  data,  of  the  duration 
of  the  significant  breeding  season  in  each  of  the  annual  isothermal  zones 
at  5°  F.  intervals  (50°  to  55°,  55°  to  60°,  60°  to  65°,  65°  to  70°,  and  70°  to 
75°  F.)  in  the  United  States,  and  within  each  zone  the  average  annual 
temperature  varies  only  within  5°  F.  In  the  70°  to  75°  isothermal  zone  breed- 
ing is  continuous  throughout  the  year,  but  in  the  50°  to  55°  isothermal  zone 
breeding  occurs  only  from  late  May  to  the  middle  of  October.  In  the  north- 
ern portion  of  its  range  and  at  high  elevations  the  females  (the  males  die 
off)  seek  hibernating  quarters  in  cool,  dark  places  such  as  cellars,  hollow 
trees,  caves,  and  r'tnilar  locations  where  there  is  a  certain  amount  of  mois- 
ture. In  the  warmer  portions  of  its  range  true  hibernation  is  regarded  as 
doubtful  since  breeding  n:ay  be  continuous,  and  larvae  have  been  taken  in 
practically  every  month  of  the  year.  It  is  probable  that  in  the  cool  season  larvae 
succeed  in  withstanding  considerable  cold  weather  and  that  the  larval  de- 
velopment period  is  greatly  lengthened,  thus  providing  for  rapid  production 
at  the  beginning  of  warmer  weather. 
'  Anopheles  jreeborni  Aitken  (A.  maculiiennis  jrceborni  Aitken)  is  widely 


300  MEDICAL  ENTOMOLOGY 

distributed  in  North  America  west  of  the  Rocky  Mountains  and  extends 
from  southern  British  Columbia  south  through  western  Montana,  Utah, 
Colorado,  and  New  Mexico  to  western  Texas.  Within  this  area  its  breeding 
grounds  are  restricted  by  more  or  less  local  conditions.  In  California  it  is 
widely  distributed  except  along  the  north  coast  and  is  very  abundant  in  the 
San  Joaquin  and  Sacramento  Valleys.  In  southern  California  it  reaches  the 
coast  at  San  Luis  Obispo.  It  is  abundant  in  the  Willamette  Valley,  Oregon, 
and  Stage  reports  it  breeding  in  abundance  in  irrigated  hayfields  in  the  arid 


Fig.  130.  Photograph  of  a  ro,ooo-acre  irrigated  hayfield  in  eastern  Oregon.  Note  the  low 
section  in  the  left-hand  corner  with  weeds  and  water.  Here  breed  Anopheles  jrecborni, 
Aedes  flavcscens,  A.  dorsalis,  and  Culex  tarsalis.  (Courtesy  Mr.  Stage,  U.S.  Bureau  of 
Entomology  and  Plant  Quarantine.) 

section  of  eastern  Oregon  (Fig.  130).  Rees  (1943)  indicates  a  wide  distribu- 
tion in  Utah.  He  reports  taking  this  species  at  an  elevation  of  7000  feet. 
According  to  Freeborn  (1943),  the  breeding  grounds  are  mainly  small,  in- 
significant fresh-water  pools  that  are  at  least  partially  CAposed  to  sunlight 
and  where  there  is  vegetative  protection  such  as  algae.  Such  places  include 
hoofprints  in  seepage  areas,  small  bays  in  streams,  cutofT  pools,  roadside 
pools,  and  semipermanent  pools  in  irrigation  areas.  It  rarely  breeds  in  foul 
water,  artificial  containers,  or  large  bodies  of  water  such  as  ponds  or  borrow 
pits  or  in  swamps  or  wooded  areas.  Hardman  (1947)  has  reared  this  species 
under  artificial  conditions  and  produced  seven  generations  in  seven  months. 


MOSQUITOES  301 

He  found  maximum  egg  production  in  a  wild-caught  female  to  be  1527 
whereas  laboratory-reared  females  averaged  751. 

The  adults  closely  resemble  A.  quadrimaculatus  but  they  can  usually  be 
separated  by  the  markings  of  the  mesonotum.  In  jreeborni  there  is  a  rather 
distinct  median,  longitudinal,  pruinose  stripe,  whereas  in  quadrimaculatus 
the  mesonotum  is  uniformly  dark  without  any  indication  of  a  median  stripe. 
The  larva  of  jreeborni  is  practically  identical  with  that  of  punctipennis. 
According  to  all  recent  workers,  jreeborni  is  the  prime  vector  of  malaria 
within  its  range.  It  is  known  to  seek  human  blood,  readily  invades  houses, 
and  is  a  vicious  indoor  biter. 

Anopheles  occidcntalis  Dyar  and  Knab  (A.  maculipennis  occidentalis  and 
A.  maculipennis  of  authors7)  is  apparently  restricted  to  a  coastal  area 
stretching  from  Ventura  Bay  north  to  Washington  and  British  Columbia. 
It  has  also  been  collected  in  Alaska  and  the  Yukon,  and  Aitken  reports  it 
from  Aklavik  on  the  Mackenzie  River  at  69°  North  latitude.  The  eastern 
form  listed  under  the  above  name  is  undoubtedly  a  distinct  species  and  is 
described  as  A.  earlei  Vargas.  Both  species  have  the  distinctive  coppery  or 
golden  spot  at  the  apex  of  the  wing.  Aitken  (1945)  does  not  give  much 
information  on  the  biology  of  this  species,  but  apparently  it  is  not  abundant 
in  its  range  and  plays  no  part  in  the  transmission  of  malaria.  He  does  not  re- 
port it  as  a  house  invader. 

Anopheles  earlei  Vargas  is  a  species  based  on  the  study  of  females  from 
Wisconsin;  the  type  male  came  from  Cayuta  Lake,  New  York.  Here  (eleva- 
tion 1272  feet)  it  usually  occurs  in  abundance,  though  its  larval  habitats  have 
not  been  studied  intensively.  However,  it  can  be  separated  in  all  stages  from 
A.  occidentalis  as  described  by  Aitken  (1945).  The  females  bite  readily  during 
the  daytime  but  attack  most  vigorously  during  the  twilight  hours  (till  9  P.M. 
at  least).  It  readily  invades  houses  and  the  females  enter  hibernation  in 
situations  similar  to  those  of  A.  quadrimaculatus.  Its  distribution  is  not  well 
known,  though  probably  it  is  the  species  that  extends  from  Maine  south  to 
New  York  and  west  along  the  United  States  and  Canadian  borders  to  the 
Rocky  Mountains.  It  is  definitely  known  from  New  York,  Michigan,  and 
Wisconsin.  Preliminary  experiments  by  Dr.  Boyd  indicate  that  this  anophe- 
line  may  be  a  vector  of  malaria. 

Anopheles  psettdopunctipennis  Theobald  is  apparently  a  variable  species 


7  Aitken  (1945)  gives  a  detailed  synonymic  statement  of  this  species,  but  his  references 
to  this  species  east  of  Wisconsin  and  Michigan  and  probably  cast  of  the  Rocky  Mountains 
do  not  refer  to  this  species.  See  A.  earlei  Vargas  below. 


302  MEDICAL  ENTOMOLOGY 

and  may  consist  of  several  species  or  subspecies.  The  adults  may  be  dis- 
tinguished from  closely  related  North  American  species  by  the  whitish  areas 
or  spots  (usually  2)  on  the  costal  margin  of  the  wing,  the  fringe  with  pale 
spots  at  tips  of  veins,  and  terminal  segment  of  the  female  palpus  white. 
A.  franciscanus,  regarded  by  Aitken  as  a  subspecies  or  variety,  may  be  sep- 
arated by  the  terminal  segment  of  the  female  palpus  not  being  entirely  white 
but  with  an  apical  black  ring.  In  the  larval  stage  the  presence  of  "tails"  on 
the  postspiracular  plates  of  the  respiratory  apparatus  is  diagnostic  through- 
out its  range  except  in  many  parts  of  California  where  the  "tails"  are  lacking. 
This  anopheline  (or  its  varieties)  is  probably  the  most  widely  distributed 
species  in  the  Americas  and  occurs  from  about  42°  North  latitude  in  the 
western  part  of  the  United  States  through  Mexico,  Central  America,  Panama, 
Colombia,  Venezuela,  and  south  to  northeastern  Argentina  (Cordoba,  31° 
South)  and  Chile  (Pica,  20°  30')  following  the  foothills  on  both  sides  of 
the  Andes.  It  also  occurs  in  Trinidad  and  Grenada.  According  to  Aitken 
(1945),  this  species  prefers  arid  canyons  and  valleys  where  the  larvae  occur 
in  the  small,  clear,  slow-moving  streams  and  side  pools  of  receding  rivers 
containing  a  rich  growth  of  algae  and  exposed  to  the  sun.  Barber  reports  it 
breeding  also  in  cool  pools  in  the  shade  in  New  Mexico.  In  Mexico  it  com- 
monly occurs  in  shaded  pools  with  algae.  Its  preference  seems  to  be  in  more 
or  less  exposed  waters  with  abundance  of  algal  growth.  According  to  Recs 
(1943)  the  females  hibernate,  and  he  found  them  commonly  in  outbuildings 
and  human  dwellings  in  southern  Utah.  The  relation  of  this  variable  species 
to  malaria  is  discussed  on  pages  341-343. 

Anopheles  punctipcnnis  (Say)  (Fig.  129)  is  the  most  widespread  anopheline 
in  North  America.  It  ranges  from  southern  Canada  south  to  the  Gulf  of  Mexico 
and  reaches  the  Mexican  plateau  (state  of  Hidalgo);  west  of  the  Rocky 
Mountains  it  ranges  from  British  Columbia  south  through  Washington  and 
Oregon  to  southern  California;  it  is  rare  or  not  found  in  most  of  the  moun- 
tain states.  In  the  east  its  breeding  places  are  varied — rain-water  barrels, 
roadside  puddles,  ruts  in  muddy  roads,  grassy  bogs,  swamps,  hog  wallows, 
spring  pools,  margins  of  streams,  lakes,  and  open  ponds.  The  writer  has  re- 
cently taken  it  in  deep  woodland  pools  (October,  1945).  The  adult  females 
hibernate  in  cellars,  houses,  outbuildings,  and  similar  situations.  Frequently 
during  the  winter  they  will  invade  sleeping  rooms  and  bite.  The  females 
usually  attack  during  the  twilight  hours  and  when  abundant  readily  enter 
houses  and  seek  blood. 

Anopheles  crucians  Wied.,  A.  bradleyi  King,  and  A,  georgianus  King  con- 
stitute a  complex  that  presents  many  difficulties.  A.  crucians  occurs  from 


MOSQUITOES  303 

Massachusetts  south  through  the  eastern  states  to  the  Gulf  of  Mexico  and 
west  to  western  Texas  and  north  to  Illinois  and  Kentucky.  It  breeds  almost 
exclusively  in  acid  waters.  A.  bradleyi  ranges  along  the  Atlantic  coast  from 
New  Jersey  to  Veracruz,  Mexico.  It  normally  breeds  in  saline  pools.  A. 
gcorgianus  has  been  taken  in  Georgia,  Alabama,  and  Louisiana  and  breeds 
in  fresh  water.  Though  these  species,  at  least  crucians,  readily  bite  humans, 
they  are  not  considered  of  any  importance  as  vectors  of  malaria.  Sabrosky 
et  al.  (1946)  report  3.38  per  cent  infection  in  November  with  Plasmodia  in 
South  Carolina,  and  these  species  may  play  a  more  important  role  than  is 
now  recognized. 

Anopheles  wal\eri  Theobald  is  widely  distributed  in  the  eastern  half  of 
the  United  States  west  to  Minnesota  and  western  Louisiana.  It  is  a  fierce  biter, 
attacking  principally  during  twilight  hours.  If  disturbed  it  will  attack  during 
the  day.  It  is  attracted  to  lights  and  is  frequently  taken  in  numbers  at  light 
traps.  It  is  the  only  known  anopheline  that  hibernates  in  the  egg  state  in  the 
northern  part  of  its  range. 

Anopheles  atropos  Dyar  and  Knab  is  a  salt-water  breeder  and  occurs  along 
the  Atlantic  coastal  area  from  New  Jersey  to  Texas  and  is  reported  from 
Cuba.  Anopheles  barberi  Coquillett  breeds  in  tree  holes  (Fig.  119)  and  is  our 
only  North  American  anopheline  that  hibernates  as  young  larvae  frozen  in 
the  water.  It  is  a  very  small  species.  It  is  widely  distributed  in  the  eastern 
half  of  the  United  States  north  to  Iowa  and  New  York.  It  has  been  shown 
capable  of  infection  with  Plasmodium  vivax  and  did  transmit  the  infection 
from  the  sick  to  the  well  (Stratman,  Thomas,  and  Baker,  1936). 

The  subgenus  Nyssorhynchus  is  restricted  to  a  region  extending  from 
Mexico,  through  Central  America,  to  South  America  and  most  of  the  West 
Indies.  Only  a  single  species,  A.  (N.)  albimanus  Wied.,  occurs  in  the  United 
States,  and  it  is  known  only  from  a  small  area  in  southeastern  Texas  around 
Brownsville  and  in  southern  Florida.  These  are  frequently  called  the  "white- 
footed"  anophelines  because  the  last  three  segments  of  the  hind  tarsi  are 
nearly  all  white.  Lane  (1939)  lists  17  species  in  this  subgenus  from  the  neo- 
tropical region  but  today  the  total  is  probably  greater.  Causey,  Deane,  and 
Deane  (1946)  recognize  IT  species  composing  the  tarsimaculatus  complex 
in  northeast  Brazil.  This  would  give  us  over  25  recognized  species.  In  this 
group  the  male  gcnitalia  is  characteristic — only  one  basal  spine  on  a  tubercle 
on  the  sidepiece  with  two  other  spines  inserted  near  the  middle.  The  larvae 
do  not  seem  to  be  characterized  as  a  group  or  easily  separated  from  the  sub- 
genus  Anopheles.  In  this  group  arc  many  important  vectors  of  malaria.  These 
include  A.  albimanus,  A.  darlingi,  A.  albitarsus,  and  A.  aquasalls. 


304  MEDICAL  ENTOMOLOGY 

Anopheles  (Nyssorhynchus)  albimanus  Wied.  has  a  wide  (distribution  in 
Mexico,  Central  America,  Panama,  the  West  Indies,  Colombia,  Ecuador,  and 
Venezuela  and  also  occurs  in  Texas  and  Florida.  The  adults  are  persistent  in- 
vaders of  dwellings  and  are  avid  feeders  on  man,  though  they  attack  horses 
and  other  animals.  They  are  primarily  nocturnal  and  definite  flights  are  re- 
corded in  Panama.  These  flights  occur  in  the  early  evening  hours  and  usually 
last  30  to  45  minutes.  During  the  night  the  mosquitoes  remain  in  houses  but 
leave  in  the  early  morning  hours  for  other  shelter  (the  writer  has  seen  adults 
1 7]  taken  in  a  native  Mexican  hut  full  of  blood  about  n  A.M'.).  Collection 
of  this  species  while  it  is  resting  during  the  day  in  native  huts  is  common  in 
the  state  of  Veracruz  (Mexico).  Extensive  migration  of  this  species  has  been 
recorded  and  flights  of  12  miles  or  more  have  been  noted  in  Panama.  The 
principal  requirements  for  breeding  places  are  sun,  vegetation,  and  little  or 
no  movement  of  water.  It  breeds  extensively  in  clear  pools,  slow  and  stagnant 
streams,  tracks  in  pastures,  open  ponds,  swamps,  seepage  areas,  potholes, 
ditches,  road  ruts,  and  lakes  with  surface  vegetation;  it  also  breeds  in  brackish 
pools  open  to  sunlight.  Normally  this  species  is  restricted  to  the  lowlands 
throughout  its  range,  though  in  the  rainy  reason  it  breeds  abundantly  at  over 
3000  feet  in  Veracruz.  It  is  one  of  the  important  vectors  of  malaria. 

Anopheles  (N.)  darlmgi  Root  was  described  from  the  state  of  Rio  de  Janeiro 
in  1926  and  is  known  as  an  excellent  vector  of  malaria.  Its  distribution  is 
from  Argentina  to  Venezuela;  it  also  occurs  in  British  Honduras  and  Guate- 
mala. Recently  (1943)  it  has  been  found  in  the  state  of  Chiapas,  Mexico,  and 
more  recently  (1946)  in  th_  state  of  Tabasco.  It  undoubtedly  will  spread  along 
the  coast  line  of  the  Gulf  of  Mexico  and  should  easily  gain  access  to  the 
southern  United  States.  Its  favorite  larval  habitats  are  among  mats  of  vege- 
tation in  shaded,  clear,  fresh  water  of  lagoons,  overflows,  and  floodwaters  as 
in  the  Amazon  Valley.  According  to  Shannon  (1933), tms  species  is  primarily 
a  lowland  breeder  and  is  associated  with  flood  water  conditions.  The  adults 
are  consistent  invaders  of  houses  and  prefer  human  blood.  Bates  (1947)  and 
Sigioli  (1947)  report  that  this  species  breeds  readily  under  artificial  conditions. 

Anopheles  (N.)  aqttasalis  was  described  by  Curry  (1923),  who  separated  it 
from  the  so-called  tarsimaculatus  complex.  It  is  a  brackish  water  breeder  and 
appears  to  be  quite  restricted  to  shaded  or  open  brackish  tidal  swamps, 
especially  along  tidal  river  areas,  on  the  Atlantic  side  of  Panama,  Nicaragua, 
Trinidad,  the  lesser  Antilles,  and  as  far  south  as  Pernambuco  and  Algoas  in 
Brazil.  It  is  also  recorded  breeding  inland  (TO  miles)  in  the  rice  fields  of 
Trinidad.  The  adults  feed  freely  on  animals  and  man  and  readily  enter 


MOSQUITOES  305 

houses.  However  they  leave  their  feeding  grounds  before  dawn  and  are  rarely 
found  in  buildings  during  the  day.  Throughout  its  range  it  is  an  important 
vector  of  malaria. 

Anopheles  (Kcrteszid)  bellator  Dyar  and  Knab  is  an  interesting  anophe- 
line  as  its  only  known  breeding  places  are  the  contained  water  in  epiphytic 
bromcliads.  It  occurs  in  Trinidad  and  Venezuela.  In  Trinidad  this  mosquito 
breeds  abundantly  in  the  water  collected  in  bromcliads  on  the  immortelle 
(Erythrina),  which  is  used  as  a  shade  in  the  cocoa  plantations,  and  on  other 
trees  on  the  highlands.  The  adults  are  anthropophilic,  attacking  humans  dur- 
ing the  evening  hours  (5  to  8  P.M.)  ;  they  seek  human  habitations  but  leave 
immediately  after  feeding;  they  also  feed  in  the  early  morning  hours.  The 
observations  of  de  Vertcuil  (1925-1937)  that  this  anopheline,  on  epidemio- 
logical  evidence,  is  an  important  vector  of  malaria  in  Trinidad  have  been 
abundantly  confirmed  by  Rozeboom  and  Laird  (1942)  and  Downs,  Gillette, 
and  Shannon  (1943). 

Anopheles  gambiac  Giles  is  probably  one  of  the  most  effective  transmitters 
of  malaria  in  regions  where  it  and  malaria  are  present.  It  occurs  over  most 
of  tropical  and  subtropical  Africa  where  breeding  conditions  are  favorable 
from  the  Sahara  Desert  south  to  Natal.  On  the  eastern  side  of  Africa  it  is 
abundant  in  Ethiopia  and  Eritrea  and  occurs  north  to  Khartoum  and  southern 
Egypt.  It  occurs  in  Arabia  and  the  islands  of  Mauritius,  Reunion,  and  Mada- 
gascar. This  anopheline  is  primarily  a  small  pool  breeder,  frequenting  such 
places  as  puddles,  shallow  ponds,  animal  footprints,  roadside  ditches,  irriga- 
tion furrows,  pools  in  beds  of  drying  streams,  and  similar  locations.  Sunlight 
appears  to  be  favorable  to  larval  development,  and  the  absence  of  vegetation 
and  open  shallow  water  are  preferred.  It  is  rarely  taken  in  artificial  containers. 
In  Brazil  where  it  gained  a  foothold  (now  exterminated)  in  1930  the  pre- 
ferred breeding  places  were  in  "small,  shallow,  sunlit  pools  of  fresh  water 
without  vegetation"  and  in  the  neighborhood  of  human  habitations.  Though 
the  above  statement  is  in  accord  with  investigations  in  many  parts  of  Africa 
and  Brazil,  yet  Haddow  et  at.  (1947)  report  this  species  as  the  most  abundant 
in  a  tropical  rain  forest  far  from  human  habitation  in  Bwamba  County, 
Uganda.  They  took  it  in  the  center  of  the  forest  and  at  all  elevations  from 
the  ground  to  the  tree  canopy  (82  feet)  during  both  the  dry  and  rainy  sea- 
sons. Out  of  a  total  of  32,315  mosquitoes  taken,  30,240  were  A.  gambiae. 
These  captures  represent  24  hours  of  collecting  at  all  levels  for  20  days  each 
during  1944  and  1945  in  both  dry  and  rainy  seasons.  (In  all  40  collections 
from  both  dry  and  rainy  seasons  were  made  in  these  two  years;  the  elevation 


3o6  MEDICAL  ENTOMOLOGY 

stations  were  at  o,  16,  31,  and  54  feet  during  the  rainy  season  of  1944  an^  tne 
dry  season  of  1945  at  Mongiro;  elevations  of  o,  22,  44,  58,  and  82  feet  were 
employed  during  the  rainy  season  of  1944  and  the  dry  season  of  1945  at 
Mamirimiri.) 

The  Anopheles  maculipennis  complex  of  Europe  and  Asia  has  been  studied 
more  intensively  than  any  other  anophcline  group.  Formerly  the  group  was 
considered  a  single  species  with  a  wide  distribution  extending  from  England 
and  Sweden  across  Russia  to  Japan  and  south  to  coastal  areas  of  northwest 
Africa  and  thence  cast  along  the  northern  Mediterranean  lands  east  through 
parts  of  Russia  to  Mongolia.  As  this  species  was  a  good  vector  of  malaria,  it 
became  apparent  that  malaria,  even  in  the  centers  where  it  should  occur, 


Hi  Hi  HJ         Bd  3       As        Md 


Pad  Pa 


Fig.  1^1.  Wing  of  Anopheles  gambiac,  illustrating  the  costal  wing  spots.  Pale  spofs: 
A,  apical  spot;  As,  accessory  sector  spot;  Hi,  H2,  II3,  humeral  spots;  Pa,  prcapical  spot; 
S,  sectoral  spot;  Sc,  subcostal  spot.  Dark,  spots:  Ad,  apical  dark  spot;  Bd,  basal  dark  spot; 
Md,  median  dark  spot;  Pad,  preapical  dark  spot;  Sq,  the  squama. 

was  absent  despite  the  abundance  of  this  species.  Furthermore,  it  was  demon- 
strated that  in  some  areas  the  females  avoided  man  and  preferred  animal 
hosts  (i.e.,  were  zoophilic).  The  differentiation  of  the  varieties  of  this  com- 
plex has  involved  prolonged  studies,  and  even  today  the  only  satisfactory 
characters  are  found  in  the  eggs.  As  a  result  this  complex  has  been  divided 
into  a  number  of  species  and  subspecies  which,  even  at  present,  are  not  well 
understood.  The  latest  summary  of  Bates  (1940)  lists  five  species  and  two 
subspecies.  These  are  A.  maculipennis  Meig.,  the  typical  form  widely  dis- 
tributed in  Europe  and  probably  Asia;  A.  messae  Falleroni,  closely  associated 
with  A.  maculipennis  and  with  a  similar  range;  A.  melanoon  melanoon 
Hackett,  said  to  be  restricted  to  the  Italian  peninsula;  A.  melanoon  subalpinus 
Hackett  and  Lewis,  occurs  in  Spain,  northern  Italy,  and  the  Balkans;  A. 
labranchiae  labranchiae  Falleroni,  said  to  be  restricted  to  Spain,  Italy,  certain 
Mediterranean  islands,  and  North  Africa;  A.  labranchiae  atroparvus  van 
Thiel,  which  is  widely  distributed  in  central  Europe  and  Asia;  and  A.  sacha- 


MOSQUITOES  307 

rovi  Favr,  which  is  widely  distributed  in  the  Mediterranean  area  east  to  cen- 
tral Russia  and  beyond.  The  biology  and  the  relation  of  these  forms  to  the 
transmission  of  malaria  have  been  fully  presented  by  Hackett  and  Missiroli 
(1935)  and  Hackett  (1937). 

The  subgenus  Myzomyia  Blanchard  is  known  only  from  the  Ethiopian, 
Oriental,  and  Australasian  regions.  The  main  differentiating  character  for 
this  group  is  in  the  male  genitaiia.  The  sidepicce  lacks  an  internal  spine  and 
the  basal  spines  number  four  to  six  and  are  not  set  on  tubercles.  The  wings 
arc  nearly  always  spotted  with  four  pale  spots  on  the  costal  margin.  In  the 
larvae  the  only  character  of  value  is  the  antennal  hair  ($rn);  it  is  always 
simple.  Here  belong  a  large  number  of  species  of  which  a  considerable  num- 
ber are  important  vectors  of  malaria.  These  include  A.  (M.)  [unestus  Giles 
(important  vector  in  tropical  Africa  and  Mauritius;  A.  (M.)  gambiae  Giles 
(see  above) ;  A.  (M.)  hargreavesi  Evans  (vector  in  Sierra  Leone,  Nigeria, 
Belgian  Congo,  etc.);  A.  (M.)  moitchete  Evans  (vector  in  central  Africa); 
A.  (M.)  pharoensis  Thco.  (vector  in  Africa  including  Egypt,  Palestine);  A. 
(M.)  nili  Thco.  (vector  in  many  parts  of  Africa) ;  A.  (M.)  pretoriensis  Theo. 
(probable  vector  when  abundant  in  Africa)  and  many  others  as  may  be  seen 
in  Table  7  (pp.  342-347). 

DISPERSION  AND  FLIGHT 

"Dispersion"  may  be  differentiated  from  general  "flight"  and  defined  as  the 
ordinary  distance  mosquitoes  travel  from  their  place  of  breeding  to  a  readily 
available  blood  source  within  a  comparatively  short  distance.  "Flight"  may 
be  assigned  to  the  conditions  when  mosquitoes  breeding  in  certain  areas  have 
to  search  for  blood  at  considerable  distances  such  as  nearly  a  mile  or  more. 
When  food  is  readily  available  there  may  be  no  need  for  extended  flight; 
when  food  is  scarce  and  maximum  production  of  adults  occurs,  then  the 
adults  must  go  far  afield. 

Dispersion  is  undoubtedly  the  most  important  question  from  the  standpoint 
of  the  epidemiology  of  the  diseases  transmitted  by  mosquitoes,  though  ex- 
tended flight  must  always  be  taken  into  account  when  mass  production  of 
any  species  occurs.  In  general,  it  has  been  fairly  well  established  that  a  mile 
zone  about  the  breeding  grounds  of  anophclines  is  their  normal  range. 
However,  many  factors  may  intervene  to  extend  this  zone,  and  then  we  may 
speak  of  the  "flight"  of  anophelincs  or  of  their  distribution.  Some  of  these 
factors  are:  (i)  mass  production  in  any  area  in  which  a  blood  source  is  not 
sufficient  to  meet  the  needs  of  the  adults;  (2)  favoring  winds  that  aid  in  a 


3o8  MEDICAL  ENTOMOLOGY 

wider  distribution;  and  (3)  artificial  means  of  distribution  that  may  carry 
them  far  beyond  any  normal  flight  range.  During  the  past  years  many  ex- 
periments have  been  conducted  by  mass  liberation  at  central  points  of 
anophelines  marked  by  means  of  aqueous  aniline  dyes  or  colored  powders 
such  as  bronzing,  gold,  or  aluminum  powders,  etc.  After  liberation  the  prob- 
lem of  capture  of  the  marked  specimens  involves  tedious  labors  and  requires 
a  large  number  of  collecting  points  around  the  periphery.  However,  many 
such  experiments  have  been  conducted.  Only  a  brief  summary  of  flight  range 
can  be  presented  here. 

FLIGHT  RANGE  OF  ANOPHELINES 

Anopheles  quadrimaculatus  Say  has  been  experimented  with  by  many 
workers.  It  seems  now  fairly  well  established  that  a  mile  zone  about  its  breed- 
ing places  is  the  normal,  effective  dispersal  area.  However,  adults  have  been 
taken  at  2  to  2.5  miles  (3200  to  4000  meters)  from  the  center  of  liberation 
(Eyles  and  Bishop,  1943).  Eyles  et  al.  (1945)  report  good  dispersal  at  2.7  miles 
and  further  flights  to  3.63  miles,  and  Gartrell  and  Orgain  (1946)  found  at 
Kentucky  Reservoir  a  good  3-mile  flight  during  mass  breeding.  HufTaker 
and  Back  (1945)  report  similar  conditions  in  Delaware,  where  mass  produc- 
tion occurred  over  an  extensive  area  (1500  acres  of  breeding  area)  and  despite 
abundance  of  blood  supply  the  females  easily  migrated  to  the  i-milc  (250 
9  9  per  shed)  and  to  the  i. 5-mile  (10  9  9  per  shed)  zones.  They  also 
report  taking  females  at  3  miles  from  the  breeding  zones.  Clarke  (1943) 
stained  masses  of  emerging  mosquitoes  and  recovered  this  species  8  miles 
distant  on  the  second  day  and  A.  pitnctipennis  10.5  miles  distant  on  the 
seventh  day.  These  studies  indicate  the  maximum  ranges  recorded  for  this 
species,  though  all  workers  agree  that  the  effective  flight  range  is  a  mile  or 
less. 

Anopheles  crucians  Wicd.  is  on  record  for  rather  long  sustained  flights. 
Metz  (1918)  noted  flights  of  nearly  2  miles.  Barber  et  al.  (1924)  records  ex- 
tensive flights  into  Gulfport,  Mississippi,  from  offshore  islands  where  breed- 
ing was  intensive  and  no  mosquitoes  could  be  found  breeding  on  the  coast; 
the  distance  varied  from  3  to  12  miles.  McCreary  and  Stearns  (1937)  cap- 
tured adults  at  lighthouses  in  Delaware  Bay  at  3.2  and  5.5  miles  distant  from 
the  nearest  shore  line. 

Anopheles  freeborni  Aitken  was  noted  by  Freeborn  (1921,  1932)  to  under- 
take long  migratory  flights  when  emerging  from  hibernation.  The  extent 
was  not  given  but  a  flight  of  nearly  4  miles  was  implied.  However  there 


MOSQUITOES  309 

does  not  seem  to  be  any  very  definite  data  on  the  ordinary  dispersal  flights 
during  summer  breeding. 

Anopheles  albimanus  Wied.  has  rather  extensive  flight  records.  Normally 
most  of  the  workers  stress  the  usual  flight  as  %  to  i  mile.  These  flights  occur 
at  dusk  and  dawn  and  usually  last  for  30  to  45  minutes,  the  dusk  flight  in 
search  of  food  and  the  dawn  flight  a  return  to  the  resting  places.  However, 
this  species  will  remain  in  houses  during  the  day.  When  mass  breeding 
occurs  as  on  Gatun  Lake  when  it  is  overgrown  with  Naja  and  other  aquatic 
vegetation,  flights  of  12  miles  are  noted  and  along  with  these  migrations  to 
the  sanitated  areas  a  rise  in  the  malaria  rates. 

Anopheles  gambiae  Giles  has  a  flight  range  of  normally  %  to  i  mile,  though 
experiments  in  various  parts  of  Africa  show  a  maximum  range  of  4.25  miles 
down  wind  and  1.5  miles  against  wind  (Adams,  1940).  Hacldow  et  al.  (1947) 
found  this  mosquito  the  most  abundant  species  in  a  forested  area  in  Uganda, 
and  it  was  taken  at  all  flight  stations  from  the  ground  up  to  82  feet  in  the 
forest  canopy.  This  would  certainly  indicate  that  tinder  favorable  conditions 
this  species  could  migrate  long  distances.  However,  in  the  eradication  of  this 
species  in  northeast  Brazil  every  indication  points  to  localized  spread:  distant 
points  become  infested  as  the  result  of  various  means  of  carriage.  Furthermore, 
it  was  found  to  be  almost  completely  restricted  to  places  surrounding  human 
habitation  and  never  reported  from  forested  areas.  In  other  words  it  was  a 
house-frequenting,  anthropophilic  mosquito. 

Anopheles  maciilipennis  complex  presents  a  more  complicated  problem  in 
determining  range  of  dispersion  or  flight.  Extensive  flight  studies  in  various 
parts  of  Europe  by  means  of  released,  stained  mosquitoes  clearly  show  a  flight 
range  of  several  miles  (^  to  4  miles),  but  which  species  of  this  complex  is  not 
clearly  indicated.  In  Holland  Swellengrebel  and  Nykamp  (1934)  found  a 
maximum  range  of  5.7  to  8.7  miles  of  marked  mosquitoes  (  3  and  ?  )  from 
their  breeding  grounds.  Shipova  (1936)  released  1253  stained  adults  in  October 
and  recovered  52  stained  individuals  in  hibernating  quarters  at  2,  6,  9,  and 
11.25  milcs  from  the  point  of  release.  Many  other  experiments  could  be  cited 
but  it  seems  fairly  well  established  that  the  normal  dispersion  is  usually 
within  the  i-  to  2-mile  etlective  range,  though  longer  flights  are  common  and 
must  be  taken  into  consideration  when  developing  effective  control  measures. 
A.  sacharovi  Favr,  a  closely  related  species,  has  a  recorded  range  of  2.8  miles 
(Kligler,  1924)  and  a  maximum  seasonal  flight  of  8.71  miles  (Kligler  and 
Mer,  1930). 

The  flight  range  of  a  considerable  number  of  anophelines,  particularly 
those  known  to  transmit  malaria,  has  been  investigated.  A.  maculatus  Theo., 


3io  MEDICAL  ENTOMOLOGY 

though  usually  given  as  rarely  dispersing  more  than  a  half-mile  in  Malaya, 
has  been  shown  by  Wallace  (1940)  and  Strahan  (1941)  to  exceed  even  a  mile 
flight  and  is  an  important  agent  in  maintaining  malaria  to  much  more  than 
the  half-mile  zone.  Anopheles  minimus  Theo.  seems  to  be  restricted  to  about 
a  half-mile  dispersion  though  longer  flights  have  been  recorded  (8  miles; 
Manson  and  Ramsay,  1933),  but  such  flights  do  not  seem  to  have  been  sub- 
stantiated by  other  workers.  A.  minimus  flavirostris  (Ludlow),  an  important 
vector  of  malaria  in  the  Philippines,  was  shown  by  Russell  and  Santiago 
(1934)  to  remain  rather  close  to  its  breeding  grounds,  rarely  exceeding  a 
mile,  though  previous  epidemiological  evidence  (Craig,  1909)  indicated  a 
much  greater  flight  range.  The  following  species  appear  to  be  largely  re- 
stricted to  the  half-mile  or  mite  zone :  A.  aconitus  Donitz,  A.  argyritarsis  R.-D., 
A.  culicifacies  Giles,  A.  fluviatilis  Giles;  the  following  to  a  range  of  over  i 
mile:  A.  junestus  Giles,  A.  multicolor  Camboulin  (max.  8  miles),  A.  sacha- 
rovi  Favr,  A.  pseudopunctipennis  Theo.,  A.  sergcnti  Thco.,  A.  stephensi 
Liston,  A.  sundaicus  (Rodenwalclt),  A.  siipcrpictus  Grassi,  and  A.  walf^eri 
Theo.  (1.5  to  2  miles). 

FLIGHT  RANGE  OF  CULICINES 

The  dispersion  of  culicines  has  not  received  the  same  attention  as  that  of 
anophelines.  The  following  brief  notes  may  be  of  interest. 

Culex  pipiens  Linn,  has  been  taken  at  least  14  miles  from  where  the  mos- 
quitoes were  dusted  with  aniline  dyes  (Clarke,  1943)  during  a  period  of  47 
days,  the  average  flight  range  being  9.2  miles.  McCreary  and  Stearns  (1937) 
captured  a  male  and  females  (12)  by  light  traps  8.2  and  8.4  miles  from  the 
nearest  shore  line.  Employing  marked  specimens  Afridi  et  al.  (1938)  reported 
Culex  fatigans  Wicd.  infiltrating  into  the  urban  areas  of  Delhi  for  at  least  3 
miles.  Culex  apicalis  Adams,  C.  salinarius  Coq.,  and  C.  restuans  Thco.  have 
been  taken  at  light  traps  at  8.2,  8.4,  and  3.2  miles  respectively  from  the  nearest 
shore  line  (McCreary  and  Stearns,  1937). 

Aedes  aegypti  (Linn.)  has  apparently  a  narrow  range  of  dispersal.  Shan- 
non and  Davis  (1930)  in  extensive  experiments  in  Brazil  demonstrated  a  sus- 
tained flight  over  open  water  of  1000  meters  by  employing  stained  specimens. 
Its  dispersal  on  land  is  known  to  exceed  500  yards,  but  in  general  its  move- 
ments are  rather  closely  restricted  to  human  habitations  where  it  migrates 
from  house  to  house  and  its  nearby  breeding  grounds  from  day  to  day. 

Aedes  albopictus  (Skuse),  like  A.  aegypti,  has  a  restricted  range  of  move- 
ment. Bonnet  and  Worcester  (1946)  in  a  series  of  well-planned  experiments  in 


MOSQUITOES  311 

Hawaii  with  marked  individuals  concluded  that  the  dispersal  range  rarely  ex- 
ceeds 200  yards  during  the  lifetime  of  the  adults.  Aedes  sollicitans  (Walker)  is 
known  to  migrate  considerable  distances  by  mass  flights,  at  least  30  to  40  miles. 
Curry  (1939)  recorded  an  invasion  of  a  ship  no  miles  distant  from  Cape 
Henry,  North  Carolina,  by  a  swarm  that  caused  considerable  annoyance  to  the 
passengers.  In  Delaware  McCreary  and  Stearns  (1937)  collected  large  num- 
bers of  males  and  females  at  light  traps  placed  8.2  and  8.4  miles  from  the 
shore  line.  In  the  same  traps  Aedes  cantator  (Coq.)  were  also  taken.  Though 
these  two  species  breed  primarily  along  our  tidal  marshes,  yet  they  have  been 
taken  in  many  of  the  salt  pools  located  inland  as  at  Ithaca  and  Syracuse,  New 
York,  and  at  various  points  inland  in  Alabama,  Florida,  Georgia,  North  and 
South  Carolina,  and  Mississippi.  Aedes  squamigcr  (Coq.)  a  salt-marsh 
breeder  along  the  southern  half  of  the  California  coast  line  is  stated  by  Herms 
and  Gray  to  migrate  as  much  as  50  miles.  Aedes  taeniorhynchus  (Wied.), 
another  salt-marsh  breeder,  is  known  to  migrate  considerable  distances, 
though  verified  flights  do  not  exceed  eight  or  nine  miles  (McCreary  and 
Stearns,  1937).  Like  A.  sollicitans  it  has  been  found  breeding  in  salt  pools  far 
inland  (30  to  240  miles)  but  this  is  certainly  not  an  invasion  by  sustained 
flight.  Probably  the  most  extended  flights  of  salt-marsh  breeders  are  by  Aedes 
vigilax  Skuse,  for  which  Hamlyn-Harris  (1933)  reports  6o-mile  migrations  in 
Australia,  and  Aedes  (Mucidus)  alternans  Westw.  8o-mile  migrations. 

Among  fresh-water-breeding  mosquitoes  there  are  a  number  of  interest. 
Aedes  vexans  Meig.  has  many  records  of  5-,  10-,  and  even  20-mile  migrations 
from  known  breeding  grounds,  and  in  many  cases  the  migratory  flights  have 
been  followed  day  by  day  from  breeding  grounds  for  at  least  5  miles.  Aedes 
latcralis  (Mcig.),  a  serious  pest  in  British  Columbia,  Washington,  and  Oregon, 
is  known  to  migrate  at  least  10  to  30  miles.  Stained  specimens  were  actually 
taken  5  miles  from  the  point  of  liberation,  and  the  species  was  abundant  15 
miles  from  its  breeding  grounds  but  gradually  diminished  at  the  25-mile 
limit:  one  was  taken  30  miles  from  breeding  grounds  (Stage,  1938).  Aedes 
dorsalis  (Meig.)  and  Aedes  spencerii  (Theo.)  are  reported  as  -migrating 
several  miles  but  no  experimental  data  are  available.  One  female  of  the  latter 
species  was  taken  at  Lake  Placid,  New  York,  on  July  26,  1945,  over  at  least 
500  miles  from  its  known  eastern  range. 

The  problem  of  mosquito  dispersion  by  air  currents  or  flight  to  the  upper 
reaches  of  the  atmosphere  presents  another  phase.  It  is  now  well  known  that 
a  number  of  mosquitoes  frequent  the  upper  canopy  in  many  tropical  forests. 
The  work  of  Glick  (1939)  demonstrated  that  mosquitoes  may  be  collected 
at  quite  high  levels  both  day  and  night  during  their  breeding  season.  In  all, 


3i2  MEDICAL  ENTOMOLOGY 

in  specimens  of  mosquitoes  were  taken  in  airplane  flights  throughout  the 
five  years,  representing  seven  genera  and  six  determined  species.  Of  these, 
44  were  taken  in  the  daytime  and  67  at  night.  The  night  flying  was  only 
10  per  cent  of  the  total  time  in  the  air.  Anopheles  quadrimaculatits  was  taken 
both  day  (3)  and  at  night  (8)  up  to  elevations  of  1000  feet;  five  Culex  species 
were  taken  at  elevations  of  200  and  5000  feet.  Aedes  vexans  was  taken  at  night 
at  500  feet  to  5000  feet. 

CLASSIFICATION  OF  THE  CULICIDAE 

KEYS  TO  THE  SUBFAMILIES,  TRIBES,  GENERA, 
AND  SUBGENERA 

The  Subfamilies 

ADULTS 

Mouth  parts  not  prolonged  into  a  proboscis,  extending  little  beyond  the 
clypeus;  scales,  when  present,  largely  confined  to  the  hind  margin  of 
the  wing Chaoborinae  8 

Mouth  parts  prolonged  into  a  proboscis,  extending  far  beyond  the  clypeus; 
scales  always  present  on  the  wing  veins  and  along  the  marginal  fringe; 
legs  with  scales;  body  usually  with  scales  or  they  may  be  almost  absent 
; .  .  Culicinae 

LARVAE  (4th  instar) 

Antennae  prehensile,  with  long  and  strong  apical  spines  (Fig.  94)   

Chaoborinae  8 

Antennae  not  prehensile  and  lacking  the  strong  apical  spines Culicinae 

PUPAE 

1.  Swimming  paddles  fused  basally,  not  movable;  with  apical  and  lateral 

articulated  spines  or  hairs  (Corethrella)  Chaoborinae  8 

Swimming  paddles  free,  movable;  without  long  hairs  or  spines 2 

2.  Respiratory  horn  either  almost  closed  apically  or  with  the  spiracular 

opening  near  the  middle;  surface  of  horn  with  hexagonal  reticulations 

Chaoborinae  8 

Respiratory  horn  open  at  tip,  spiracle  at  its  base Culicinae 

The  Tribes  of  the  Culicinae 
ADULTS 
i.  Proboscis  rigid;  basal  half  stout,  the  apical  half  more  slender  and  bent 

8  Not  further  treated  here;  adults  never  take  blood. 


MOSQUITOES  313 

sharply  backwards;  scutellum  evenly  rounded  with  marginal  hairs 

and  scales  well  distributed  Megarhinini 

Proboscis  not  rigid,  of  nearly  uniform  thickness  (though  the  apex  may 
be  swollen)  and  the  apical  half  not  bent  sharply  backwards 2 

2.  Scutellum  evenly  rounded,  crescent-shaped,  or  it  may  be  slightly  lobed 

(as  in  Chagasia),  without  or  with  few  scales  but  the  marginal  hairs 
evenly  distributed;  first  tcrgite  of  abdomen  always  without  scales; 
sternites  nearly  always  bare  of  scales;  palpi  of  males  and  females 
as  long  or  nearly  as  long  as  proboscis  (except  in  Bironella)  (Fig.  125) 

Anophelini 

Scutellum  trilobed  with  the  hairs  restricted  to  the  lobes;  scales  nearly  al- 
ways present  and  usually  in  patches;  abdomen  with  tergites  and 
sternites  clothed  with  scales;  palpi  in  the  females  short;  in  the  males 
long  and  bushy  (Fig.  125)  3 

3.  Base  of  hind  coxa  in  line  with  the  upper  margin  of  the  mcron;  (Fig. 

99,  #);  postnotum  with  a  group  of  bristles  (all  American  species); 
abdomen  almost  completely  free  of  hairs  and  usually  compressed 

Sabethini 

Base  of  hind  coxa  distinctly  below  upper  margin  of  meron;  postnotum 
lacking  bristles,  smooth  (except  in  some  oriental  species  of  Aedes)\ 
abdomen  with  hairs  on  hind  margins  of  segments Culicini 

LARVAE  (4th  instar) 

1.  Eighth  segment  without  an  elongated  siphon  or  respiratory  tube,  the 

spiracles  sessile Anophelini 

Eighth  segment  with  an  elongated  siphon  or  respiratory  tube  which 
is  at  least  as  long  as  broad 2 

2.  Mouth  brushes  prehensile,  each  composed  of  10  stout  rods  .  .  Megarhinini 
Mouth  brushes  not  or  rarely  prehensile,  each  composed  of  30  or  more 

hairs    3 

3.  Anal  segment  with  one  pair  of  ventral  hairs  or  tufts  instead  of  a  brush; 

siphon  usually  with  numerous  hairs  or  tufts Sabethini 

Anal  segment  with  a  ventral  brush,  usually  large  but  at  least  four 
separate  hairs  or  tufts;  siphon  usually  with  tufts  but  these  in  definite 
arrangement Culicini 

PUPAE 
i.  Lateral  apical  hairs  of  abdominal  segments,  except  the  last  pair,  are 

blunt  spines  and  placed  almost  exactly  at  the  corners Anophelini 

Lateral  apical  hairs  of  abdominal  segments  placed  well  before  the  apical 
corners  and  each  consists  of  a  branching  hair  or  a  single  hair 2 


3r4  MEDICAL  ENTOMOLOGY 

2.  Outer  part  of  paddle  produced  beyond  the  tip  of  midrib Megarhinim 

Outer  part  of  paddle  not  longer  than  midrib 3 

3.  Seventh  and  eighth  segments  with  large  posterolateral  tufts;  paddles 

smooth  and  lack  apical  hairs  Sabethini 

Abdomen  not  as  described  above;  paddles  with  apical  hairs Culicini 

Genera  and  Common  Sub  genera  of  Tribe  Anophelini 

ADULTS 

1.  Scutellum  slightly  trilobed  (South  American)   Chagasia  Cruz 

Scutellum  crescent-shaped,  evenly  rounded  2 

2.  Stem  of  second  fork  cell  wavy Bironella  Theobald 

Stem  of  second  fork  cell  straight Anopheles  Meigen  3 

3.  Thorax  blackish  with  a  broad  gray  line  from  neck  to  scutcllum  

Subgenus  Stethomyia  Theobald 

Thoracic  ornamentation  quite  otherwise 4 

4.  Wings  with  rarely  more  than  two  pale  spots  on  costa;  sidepiece  of  male 

genitalia  with  i  to  3  (usually  2)  strong  basal  spines  set  on  tubercles 

Subgenus  Anopheles  Meigen 

Wings  with  4  or  more  pale  costal  spots  (Fig.  131)  5 

5.  Sidepiece  of  male  genitalia  with  one  spine  at  base  and  two  beyond. 

(New  World  species)  Subgenus  Nyssorhynchits  Blanchard 

Sidepiece  of  male  genitalia  with  several  weak  spines  near  base  and 

not  set  on  tubercles.  (Old  World  species)  

Subgenus  Myzomyia  Blanchard 

LARVAE  (4th  Instar) 

1.  Body  of  larva  densely  clothed  with  short  hairs  in  addition  to  the  regu- 

lar hairs;  leaflets  of  palmate  tufts  greatly  expanded  apically  and  each 
ending  in  a  long  central  hair.  Anterior  flap  of  spiracular  apparatus 
produced  into  a  long,  stout,  bristlclike  structure Chagasia  Cruz 

Body  of  larva  not  densely  covered  with  fine  hairs;  leaflets  of  palmate 
tufts  not  as  described  above;  no  prolongation  of  anterior  flap  of 

.  spiracular  apparatus  2 

2.  Two  pairs  of  palmate  hairs  on  the  thorax Bironella  Theobald 

At  most  one  pair  of  palmate  hairs  on  thorax Anopheles  Meigen 

Key  to  Genera  of  the  Tribe  Culicini:  Adults 
(Modified  from  Edwards,  1932) 

i.  Squama  fringed  (fringe  usually  complete);  anal  vein  (6th)  reaching 
well  beyond  the  base  of  cubital  fork  (fork  of  5th  vein)  4 


MOSQUITOES  315 

Squama  bare  (Fig.  131)  or  with  i  to  4  short  hairs;  second  marginal  cell 
(R2)  shorter  than  its  stem;  anal  vein  (6th)  ends  about  opposite  of 
cubital  fork  (fork  of  5th  vein) 2 

2.  Wing  membrane  lacks  microtrichia;  second  marginal  cell  (R2)  shorter 

than  its  stem;  anal  vein  (6th)  ends  about  opposite  the  base  of  fork 

of  5th  vein Uranotaenia  Lyn.  Arrib. 

Wing  membrane  with  distinct  microtrichia  3 

3.  Second  marginal   (R2)   cell  shorter  than  its  stem;   several  posterior 

pronotal  bristles;  wing  scales  not  emarginate  at  tips.  (One  species, 

Malaya)  Zeugnomyia  Leicest. 

Second  marginal  cell  longer  than  its  stem;  2  posterior  pronotal  bristles; 

wing  scales  emarginate  at  tips.  (Africa,  India,  S.  Pacific)   

Hodgesia  Theobald 

4.  Pulvilli  present;  pleural  chaetotaxy  well  developed  but  spiracular  and 

postspiracular  bristles  absent  5 

Pulvilli  absent  or  rudimentary;  spiracular  and  postspiracular  bristles 
present  or  absent  or  one  set  may  be  present 6 

5.  Antennae  much  longer  than  the  proboscis;  first  flagellar  segment  of 

antenna  as  long  as  several  of  the  following  segments  taken  together; 
antennae  similar  in  both  sexes,  never  very  bushy.  (Sea  coasts  of  the 

Gulf,  Caribbean,  and  West  Indies)   Dcinoceriies  Theobald 

Antennae  not  much  longer  than  the  proboscis;  first  flagellar  segment 
not  as  long  as  several  of  the  following  segments  taken  together;  male 
antennae  very  bushy  and  different  from  the  female.  (World-wide  in 
distribution)  Culcx  Linnaeus 

6.  Postspiracular  bristles  absent;  claws  of  female  generally  simple  (except 

in  species  of  Haemagogus) 7 

Postspiracular  bristles  present  (at  times  only  i  or  2) ;  claws  of  female 
usually  toothed;  dorsocentrals  and  upper  sternopleurals  nearly  always 
well  developed 13 

7.  Spiracular  bristles  present  (at  times  only  i  or  2)  

Culiseta  Theobald 

Spiracular  bristles  absent 8 

8.  Pronotal  lobes  almost  touching  dorsally;  dorsocentral  and  prescutellar 

bristles  absent Haemagogus  Williston 

Pronotal  lobes  well  separated;  dorsocentral  and  prescutellar  bristles  well 
developed 9 

9.  Postspiracular  area  with  scales;  claws  of  female  usually  toothed;  palpi 

of  female  more  than  half  as  long  as  proboscis Armigeres  Theobald 


3i6  MEDICAL  ENTOMOLOGY 

Postspiracular  area  bare;  claws  of  female  simple;  palpi  of  female  not 
half  as  long  as  proboscis 10 

10.  All  segments  of  female  antennae  and  last  two  of  male  antennae  short 

and  thick;  middle  femur  with  a  scale  tuft Aedomyia  Theobald 

Antennae  slender;  middle  femur  without  a  scale  tuft  n 

11.  First  segment  of  front  tarsus  longer  than  the  last  four  taken  together; 

4th  segment  very  short,  only  as  long  as  wide;  mesonotum  usually 

with  narrow  longitudinal  lines  of  silvery- white  scales 

Orthopodomyia  Theobald 

First  segment  of  front  tarsus  not  so  long,  or  as  long,  as  the  last  four 
taken  together;  4th  segment  not  as  described  above 12 

12.  Proboscis  of  male  much  swollen  apically;  of  female  slightly  swollen 

or  else  cell  R2  (2nd  marginal)  shorter  than  its  stem  

Ficalbia  Theobald 

Proboscis  of  male  or  female  not  swollen  apically;  cell  Ro  (2nd  marginal) 
as  long  as  its  stem (in  part)  Mansonia  Blanchard 

13.  Spiracular  bristles  present,  at  times  only  i  or  2.  (The  Americas)  

Vsorophora  Rb.-Desvoidy 

Spiracular  bristles  absent 14 

14.  Eyes  widely  separated;  space  between  and  back  of  the  eyes  with  metal- 

lic silvery  scales  (African)   Eretmapodites  Theobald 

Eyes  not  so  widely  separated,  almost  touching;  space  between  and  back 
of  the  eyes  not  clothed  with  metallic  silvery  scales 15 

15.  Wing  scales  mostly  narrow  (when  broad  the  female  claws  are  toothed) 

16 

Wing  scales  all  very  broad;  female  claws  not  toothed 

(in  part)  Mansonia  Blanchard 

1 6.  Proboscis  slender,  not  recurved  at  tip  in  repose;  ornamentation  varied 

Aedes  Meigen 

Proboscis  stout,  recurved  at  tip  in  repose;  dark  species  with  flat  scales 
on  vertex  and  scute] lum Armigeres  Theobald 

LARVAE  (4thinstar) 

1.  Distal  half  of  air  tube  (siphon)  sharply  attenuated  and  apical  portion 

provided  with  sawlike  teeth  for  penetrating  plants 

Mansonia  Blanchard 

Air  tube  (siphon)  not  as  described  above 2 

2.  Head  longer  than  broad  or  as  long  as  broad  (appearing  more  or  less 

as  rounded);  8th  abdominal  segment  with  a  lateral  chitinous  plate 


MOSQUITOES  317 

with  one  row  of  comblike  teeth  on  its  posterior  margin;  antennae 

not  inflated  or  very  large Uranotaenia  Lyn.  Arrib. 

Head  always  broader  than  long;  8th  abdominal  segment  without  such 
a  plate  (except  at  times  in  certain  Psorophora  and  all  Aedomyia  spp. 
but  in  these  the  antennae  are  inflated  and  flattened)  3 

3.  Air  tube  with  pccten;  the  teeth  of  the  pectcn  nearly  always  denticu- 

late         4 

Air  tube  without  pecten  or  rarely  a  few  simple  teeth  and  these  not 
denticulate 9 

4.  Air  tube  with  several  pairs  of  ventral  hair  tufts  (never  less  than  2  pairs) 

and  occasionally  scattered  dorsal  hairs  or  the  air  tube  is  extremely  long 

and  slender  with  hair  tufts  apparently  lacking 5 

Air  tube  not  as  described  above;  with  never  more  than  a  single  pair  of 
hair  tufts  or  in  addition  there  may  be  a  median  ventral  line  of  hair 
tufts 7 

5.  Mouth  brushes  prehensile,  often  appearing  as  matted  tufts  or  as  rods 

(Subgenus  Lutzia)  Culex  Linnaeus 

Mouth  brushes  normal,  composed  of  long  hairs 6 

6.  Head  with  a  prominent  pouch  on  each  side  enclosing  the  mandible, 

which  has  a  hairy  base  Deinocerites  Theobald 

Head  not  as  described  above;  mandibles  without  a  hairy  base 

Culex  Linnaeus 

7.  Air  tube  with  a  pair  of  basal  hair  tufts  only  or  a  pair  of  basal  hairs 

(single)  Culiseta  Felt 

or 

Air  tube  with  a  pair  of  basal  hair  tufts  and  a  median  row  of  ventral 
tufts (Subgenus  Climactira)  Culiseta  Felt 

Air  tube  with  a  single  pair  of  ventral  tufts  placed  near  the  middle  of 
tube  or  beyond;  if  tufts  are  lacking  or  vestigial  the  anal  segment  is 
completely  ringed  by  the  dorsal  plate  or  saddle  and  pierced  by  some 
of  the  tufts  of  the  ventral  brush 8 

8.  Anal  segment  completely  ringed  by  the  saddle;  the  saddle  is  pierced  on 

the  mid-ventral  line  by  tufts  of  the  ventral  brush;  air  tube  often 

swollen  and  pecten  of  few  teeth Psorophora  Rb.-Desvoidy 

Anal  segment  not  completely  ringed  by  the  saddle,  but,  if  so,  the  ventral 
brush  is  confined  posterior  to  the  ring  (no  tufts  pierce  the  saddle) 

Aedes  Meigen 

Haemagogtts  Williston 


318  MEDICAL  ENTOMOLOGY 

9.  Antenna  short  with  a  simple  hair  on  shaft;  antenna  more  or  less  cylin- 
drical, never  inflated  10 

Antenna  longer  with  a  branched  hair  on  shaft;  antenna  may  be 
cylindrical  or  inflated  or  flattened  12 

10.  Ventral  tuft  of  air  tube  large n 

Ventral  tuft  small  and  simple.  (Only  i  species,  from  Malaya)  

Zeugnomyia  Leicester 

11.  Ventral  brush  of  anal  segment  well  developed  with  a  barred  area. 

(Oriental  and  Australasian)  Armigeres  Theobald 

Ventral  brush  of  anal  segment  with  never  more  than  four  pairs  of  single 
hairs,  usually  i  or  2  pairs  of  branched  hairs;  they  never  form  a  barred 
area.  (African)  Eretmapodites  Theobald 

12.  Antenna  very  large,  flattened,  not  cylindrical  in  cross  section.  (South 

and  Central  America,  Africa,  and  Oriental  region)    

Aedomyia  Theobald 

Antenna  never  very  large  and  flattened,  usually  cylindrical  in  cross 
section  13 

13.  Large  sclerotized  plates  present  on  dorsum  of  abdominal  segments  6  to 

8  or  rarely  absent Orthopodomyia  Theobald 

Sclerotized  plates  absent  on  abdominal  segments  6  to  8 14 

14.  Hair  tuft  of  antenna  well  removed  from  apex;  anal  segment  ringed 

by  saddle Ficalbia  Theobald 

Hair  tuft  of  antenna  close  to  apex;  anal  segment  ringed  by  saddle  . . . 

Hodgesia  Theobald 

Hair  tuft  of  antenna  before  the  middle;  anal  segment  not  ringed  by 

the  saddle  or  dorsal  plate Orthopodomyia  Theobald 

It  is  not  feasible  to  offer  keys  to  species  of  mosquitoes,  even  the  anophelines 
(except  those  of  North  America),  in  a  limited  textbook.  The  student  is  re- 
ferred to  the  bibliography  where  he  will  find  references  (and  references  with 
extended  bibliographies  are  double-starred)  which  will  enable  him  to  locate 
keys  to  the  species  of  nearly  any  region  of  the  world.  In  addition  to  keys  he 
must  have  detailed  descriptions  and  a  wealth  of  illustrations. 

KEY  TO  THE  ANOPHELINES  OF  NORTH  AMERICA 

Adults  (Males  and  Females) 

i.  Hind  tarsus  with  apical  portion  of  second  and  all  of  third  and  fourth 
segments  white;  fifth  segment  white  with  a  narrow,  basal,  black 
ring  (Subgenus,  Nyssorrhynchus)  albimanus  Wied. 


MOSQUITOES  319 

Tarsal  segments  of  all  legs  dark  or  black  without  white  markings 
(Subgenus,  Anopheles)  2 

2.  Scales  of  the  wings  entirely  dark  or  black;  apex  of  wing  may  have  a 

single  coppery  or  light  spot 3 

Wings  with  distinct  spots  or  areas  of  white  or  light-colored  scales  on 
the  veins  as  well  as  on  the  costal  margin  9 

3.  Scales  of  the  wings  not  grouped  in  spots  but  evenly  distributed  on  the 

veins;  legs  and  palpi  dark-scaled.  A  small  species  that  breeds  in  tree 

holes barberi  Coq. 

Scales  of  the  wings  grouped  in  darker  spots  which  are  usually  very  dis- 
tinct; palpi  may  be  dark-scaled  or  ringed  with  white 4 

4.  Segments  of  the  palpus  with  narrow  white  rings  at  their  apices;  terminal 

segment  with  white  apex;  white  or  yellowish  knee  spots  (apices  of 

femora)  present;  wing  spots  usually  distinct waU^eri  Thco. 

Palpi  entirely  dark-scaled,  rarely  any  pale  scales  present 5 

5.  Wing  spots  usually  not  very  distinct;   knee  spots  absent;  general 

coloration  very  dark atropos  D.  &  K. 

Wing  spots  very  distinct;  knee  spots  present;  general  coloration  not  so 
dark  6 

6.  Apex  of  wing  with  a  distinct  coppery  or  golden  patch  of  scales;  meso- 

notum  with  a  broad,  median,  longitudinal,  whitish  (pruinosc)  stripe 

7 

Apex  of  wing  without  such  a  spot,  uniformly  dark 8 

7.  Wing  5  to  6  mm.  in  length;  stem  vein  of  second  longitudinal  vein  be- 

yond dark  spot  with  outstanding  scales earlei  Vargas 

Wing  rarely  more  than  5  mm.  in  length,  frequently  less;  stem  vein  of 
second  longitudinal  vein  beyond  dark  spot  with  closely  appresscd 
scales,  none  outstanding occidentalis  D.  &  K. 

8.  Mesonotum  uniformly  colored,  no  distinct  stripe;  occurs  east  of  the 

Rocky  Mountains  and  is  widely  distributed  from  Canada  to  the 

Gulf  of  Mexico quadrimaculatus  Say 

Mesonotum  with  a  pale  pruinose  stripe,  fading  out  anteriorly;  occurs 
in  the  Rocky  Mountain  region  and  west  of  it;  the  dark  spots  of  the 
wings  are  usually  more  dense jreeborni  Aitken 

9.  Costal  margin  dark  except  a  white  or  yellowish-white  spot  at  extreme 

apex  of  wing;  vein  6  with  three  dark  spots  separated  by  white  scales. 

Stem  of  5th  vein  dark-scaled crucians  Wied. 

georgianus  King 

Stem  of  5th  vein  all  white-scaled bradleyi  King 


320  MEDICAL  ENTOMOLOGY 

Costal  margin  of  wing  with  2  white  spots,  one  near  apex  and  a  large  one 
at  outer  third  near  apex  of  subcostal  vein;  vein  6  with  only  i  or  2  dark 
spots  10 

10.  Veins  3  and  5  dark-scaled;  vein  6  with  short  basal  black  spot  separated 

by  a  light  area  from  the  dark  apical  half;  wing  fringe  without  pale 

spots  at  tips  of  veins;  palpus  black piinctipennis  Say 

Veins  3  and  5  with  central  areas  largely  pale-scaled;  vein  6  with  basal 
half  white,  apical  half  black;  wing  fringe  with  pale  spots  at  tips  of 
veins  n 

11.  Terminal  segment  of  palpus  entirely  white;  vein  4  pale  before  fork  . . 

pseudopunctipennis  Theo. 

Terminal  segment  of  palpus  white  at  base,  apical  half  black;  vein  4 
black  before  the  fork jranciscanus  McC. 

Males  (Based  on  the  Genitalia) 

1.  Sidepiece  with  4  stout  spines — i  basal,  2  accessory,  and  i  internal  (Sub- 

genus  Nyssorhynchus)  albimanus  Wicd. 

Sidepiece  with  3  stout  spines — 2  basal,  i  internal.  (Subgcnus  Anopheles) 

2 

2.  Mesosome  without  leaflets 3 

Mesosome  with  leaflets 4 

3.  Dorsal  lobe  of  claspette  nearly  cylindrical  in  shape  with  3  apical,  closely 

appressed,  overlapping  spines,  the  outer  2  sharply  curved  at  tips  and 
forming  a  kind  of  hood;  these  spines  nearly  twice  as  long  as  the 

lobe barberi  Coq. 

Dorsal  lobe  of  claspette  as  above  but  with  3  apical,  bladelike  spines,  all 

about  the  same  length  and  size;  spines  not  as  long  as  the  lobe 

jranciscanus  McC. 

4.  Leaflets  of  mesosome  deeply  serrate,  varying  from  2  to  4  pairs  and  dif- 

ficult to  see pseudopunctipennis  Theo. 

Leaflets  of  mesosome  not  serrate  5 

5.  Sidepiece  with  numerous  scales;  dorsal  and  ventral  lobes  of  each  clasp- 

ette fused  to  form  a  conical  lobe;  this  lobe  bears  5  spines,  rarely  less; 

lobes  of  ninth  tergite  very  long  and  pointed crucians  Wied. 

bradleyi  King 

georgianus  King 

Sidepiece  without  scales  or,  rarely,  a  few  present;  dorsal  and  ventral 
lobes  of  claspette  distinct;  lobes  of  ninth  tergite  usually  not  so  long 
or  so  pointed 6 


MOSQUITOES  321 

6.  Dorsal  lobe  of  claspette  with  bluntly  rounded  apical  spines,  sometimes 

expanded  at  apices  or  partially  fused 7 

Dorsal  lobes  of  claspette  with  pointed  spines 9 

7.  Lobes  of  ninth  tergite  short,  stout,  usually  expanded  at  apices;  spines 

of  dorsal  lobe  of  claspette  not  expanded  at  apices  but  generally  more 

'or  less  fused  and  rounded quadrimaculatus  Say 

Lobes  of  ninth  tergite  long  and  pointed  or  slightly  rounded;  spines  of 
dorsal  lobe  of  claspette  not  as  described  above 8 

8.  Dorsal  lobe  of  claspette  with  2  spines  fused  at  their  bases  and  each  ter- 

minating in  an  enlarged  and  rounded  knob;  ventral  lobe  with  only  2 
rather  large,  pointed  spines;  apical  leaflet  of  mcsosome  not  twice  as 

long  as  the  second  leaflet waU{cri  Theo. 

Dorsal  lobe  of  claspette  with  2  spines,  each  terminating  in  a  rounded 
knob  but  each  spine  arises  from  a  separate  tubercle  and  they  arc  not 
fused  at  their  bases;  apical  leaflet  of  mesosome  twice  as  long  as  the 
second  leaflet atropos  D.  &  K. 

9.  Dorsal  lobe  of  claspette  with  2  sharply  pointed,  apical  spines,  the  spines 

so  closely  associated  as  to  appear  as  only  one;  ventral  lobe  of  claspette 
with  a  large,  pointed  apical  spine,  a  smaller  internal  spine,  and  a 
minute  spine  between  them;  lobes  of  ninth  tergite  short,  stout,  and 
slightly  expanded  apically punctipcnnis  Say 

Lobes  of  claspette  not  as  described  above;  lobes  of  the  ninth  tergite  long 

or  short,  but  if  short,  pointed  apically  or  expanded 10 

10.  Dorsal  lobe  of  claspette  with  2  or  3  sharply  pointed  spines,  the  spines 
so  closely  associated  as  to  appear  almost  as  one;  lobes  of  the  ninth 
tergite  long,  narrow,  and  rounded  apically jreeborni  Aitken 

Dorsal  lobe  of  claspette  similar  to  that  described  above;  lobes  of  ninth 
tergite  short,  broad,  and  expanded  at  apex  earlei  Vargas 

Dorsal  lobe  of  claspette  similar  to  that  described  above;  lobes  of  ninth 

tergite  somewhat  longer,  narrow,  and  rarely  expanded  at  apex 

occidcntalis  D.  &  K. 

Larvae  (Fourth  Ins  far) 

1.  Abdomen  with  plumose,  lateral  hairs  on  the  first  six  segments;  all  head 

hairs  small,  single.  Larvae  occur  in  tree  holes barberi  Coq. 

Abdomen  with  plumose,  lateral  hairs  on  the  first  three  segments  only; 
frontal  hairs  (Nos.  5,  6,  and  7)  large  and  plumose 2 

2.  Palmate  hairs  well  developed  on  abdominal  segments  i  to  7;  both  inner 


322  MEDICAL  ENTOMOLOGY 

and  outer  clypeal  hairs  long  and  slender;  inner  clypeal  hairs  widely 
separated  and  feathered  on  outer  half;  outer  clypeal  hairs  with  minute 

branches  on  the  outer  half albimanus  Wied. 

Palmate  hairs  well  developed  on  abdominal  segments  2  or  3  to  7;  inner 
and  outer  clypeal  hairs  not  as  described  above 3 

3.  Outer  clypeal  hairs  not  densely  branched  dichotomously  4 

Outer  clypeal  hairs  densely  branched  dichotomously 6 

4.  Inner,  outer,  and  posterior  clypeal  hairs  long,  single,  subcqual,  and 

widely  separated  at  their  bases 5 

Inner  and  outer  clypeal  hairs  long,  usually  with  i  to  5  branches  near  the 
tips;  posterior  clypeal  hairs  short  and  may  be  branched;  inner  clypeal 
hairs  are  closely  approximated  at  their  bases atropos  D.  &  K. 

5.  Inner  angle  of  each  posterior  plate  of  respiratory  apparatus  produced  into 

a  long,  sclerotized  tail.  (In  living  larvae  these  tails  are  bent  upward 

at  right  angles  to  the  plate  and  project  through  the  water)  

psettdopunctipennis  Theo. 

Inner  angle  of  each  posterior  plate  rounded  and  not  produced  into  a 
tail '  franciscanus  McC. 

6.  Abdominal  segments  4  and  5  with  2  conspicuous  hair  tufts  (Nos.  2  and 

o)  anterior  to  the  palmate  tuft;  these  tufts  are  approximately  equal 

in  size  and  have  4  to  9  branches crucians  Wied. 

Abdominal  segments  4  and  5  with  only  i  hair  tuft  (No.  2)  anterior  to 
each  palmate  tuft;  hair  o  vestigial  or  lacking,  or,  if  present,  the  inner 
clypeal  hairs  are  sparsely  feathered  toward  the  tips 7 

7.  Inner  clypeal  hairs  divided  into  2  or  3  branches  or  feathered  toward  the 

tips 8 

Inner  clypeal  hairs  unbranched  (rarely  divided  into  2  branches  near  the 
middle)  9 

8.  Inner  clypeal  hairs  closely  approximate,  so  close  that  an  extra  tubercle 

of  the  same  size  cannot  be  placed  between  their  bases;  each  clypeal  hair 
is  sparsely  feathered  on  the  apical  half;  occipital  hairs  (Nos.  8  and  9) 

small,  each  with  2  to  4  branches wallferi  Theo. 

Inner  clypeal  hairs  not  so  closely  placed  that  an  extra  tubercle  of  the 
same  size  cannot  be  inserted  between  their  bases;  inner  clypeal  hairs 
with  2  or  3  branches  near  the  middle;  occipital  hairs  with  many 
branches  and  stout  shafts earlei  Vargas 

9.  Inner  clypeal  hairs  separated  at  their  bases  by  at  least  the  diameter  of  one 

tubercle;  palmate  tufts  well  developed  on  segments  3  to  7;  palmate 
tuft  on  segment  2  frequently  well  developed;  occipital  hairs  well 


MOSQUITOES  323 

developed  with  8  to  10  branches quadrimaculatus  Say 

occidentdis  D.  &  K. 

Inner  clypeal  hairs  so  closely  placed  that  an  extra  tubercle  cannot  be 

inserted  between  their  bases  10 

10.  Palmate  tufts  present  only  on  segments  4  to  6 gcorgianus  King 

Palmate  tufts  present  on  segments  3  to  7 n 

u.  Palmate  tufts  on  segments  3  and  7  smaller  than  the  others;  inner 

clypeal  hairs  normally  placed  close  together   bradleyi  King 

Palmate  tufts  on  segments  3  and  7  of  the  same  size  as  the  others 12 

12.  Hair  No.  2  on  abdominal  segments  4  and  5  multiple  (4-  to  5-branched) 

jrceborni  Aitken 

Hair  No.  2  on  segments  4  and  5  single punctipennis  Say 

REFERENCES  ° 
General  Worlds 

**American  Association  for  the  Advancement  of  Science.  A  symposium  on  hu- 
man malaria.  (Pub.  15.)  Washington,  D.C.,  1941. 

Rlanchard,  R.     Les  moustiques.     Paris,  1905. 

*Boyd,  M.  F.     An  introduction  to  malariology.     Cambridge,  Mass.,  1930. 

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*Edwards,  F.  W.  Diptera,  fain.  Culicidae.  In  P.  Wytsman,  Cenera  Insectorum, 
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Giles,  G.  M.  A  handbook  of  the  gnats  or  mosquitoes,  giving  the  anatomy  and 
life  history  of  the  Culicidae.  2nd  ed.  London,  1902. 

Click,  P.  A.  The  distribution  of  insects,  spiders  and  mites  in  the  air.  U.S.  Dept. 
Agr.,  Tech.  Bull.  673,  1939. 

Kumm,  H.  W.  The  distribution  of  malaria  carrying  mosquitoes.  Amer.  Jl.  Hyg., 
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.     The  distribution  of  yellow  fever  vectors.     Ibid.,  No.  12,  1931. 

**MacGregor,  M.  E.  Mosquito  surveys;  a  handbook  for  anti-malaria  and  anti- 
mosquito  workers.  London,  1937. 

**Marshall,  J.  H.    The  British  mosquitoes.     London,  1938. 

Martini,  E.  Ueber  Stechmikken.  Arch.  Schiff.  Trop.  Hyg.,  Beihft.,  24:  1-167, 
1920. 


0  Publications  on  the  morphology,  bionomics,  and  classification  of  mosquitoes  number 
many  thousands.  The  following  references  will  include,  as  far  as  possible,  a  fair  distribu- 
tion from  all  parts  of  the  world  so  that  any  student  will  find  some  article  that  will  aid 
him  in  his  work.  Many  of  die  articles  or  books  also  cover  the  field  of  malariology. 


324  MEDICAL  ENTOMOLOGY 

**Matheson,  R.    The  mosquitoes  of  North  America.    Ithaca,  N.Y.,  1944. 
*Russell,  P.  F.,  Rozeboom,  L.  E.,  and  Stone,  A.     Keys  to  anopheline  mosquitoes 

of   the   world.     Amer.   Ent.   Soc.   Philadelphia,    1943.     (Includes    adults   and 

larvae.) 
Theobald,  F.  V.     A  monograph  of  the  Culicidae  or  mosquitoes.     London  (British 

Museum),  1901-1910.  5  vols. 

Main  ly  Morph  ological 

Baisas,  F.  E.  Notes  on  Philippine  mosquitoes.  IV,  VI.  Philip.  Jl.  Sci.,  59:  65-84, 
1936;  61:  205-220,  1936. 

.    Notes  on  Philippine  mosquitoes.  VII.    Philip.  Bur.  Hlth.  Mon.  Bull.,  18: 

175-232,  1938.     (The  three  papers  by  Baisas  deal  largely  with  pupal  chaetotaxy.) 

Barraud,  P.  J.,  and  Covell,  G.  The  morphology  of  the  buccal  cavity  in  anopheline 
and  culicine  mosquitoes.  Ind.  Jl.  Med.  Res.,  15:  671-680,  1928. 

Christophers,  S.  R.  The  development  and  structure  of  the  terminal  segments 
and  hypopygium  of  the  mosquito,  with  observations  on  the  homologies  of  the 
terminal  segments  of  the  larva.  Ibid.,  10:  530-572,  1922. 

.    The  structure  and  development  of  the  female  genital  organs  and  hy- 
popygium of  the  mosquito.     Ibid.,  pp.  698-720,  1923. 
-,  and  Barraud,  P.  J.     Descriptive  terminology  of  male  genitalic  characters  of 


mosquitoes.    Ibid.,  pp.  827-835,  1923. 
Edwards,  F.  W.     The  nomenclature  of  the  parts  of  the  male  hypopygium  of 

Diptera,  Nematocera,  with  special  reference  to  mosquitoes.     Ann.  Trop.  Med. 

Hyg.,  14:  23-40,  1920. 
*Freeborn,  S.  B.     The  terminal  abdominal  structures  of  male  mosquitoes.     Amer. 

Jl.  Hyg.,  4:  188-212,  1924. 
*Hurlbut,  H.  S.     A  study  of  the  larval  chaetotaxy  of  Anopheles  wal^cn  Theobald. 

Ibid.,  28:  149-173,  1938. 
Macfie,  J.  W.  S.     The  chaetotaxy  of  the  pupa  of  Stegomyia  jasciata.     Bull.  Ent. 

Res.,  10:  161-169,  T920. 
Martini,  E.     Ueber  einige  fur  das  System  bedeutungsvollc  Merkmale  der  Stech- 

miicken.    Xool.  Jahrb.,  Abt.  Syst.,  46:  517-590,  1923. 
Nuttall,  G.  H.  F.,  and  Shipley,  A.    The  structure  and  biology  of  Anopheles.    Jl. 

Hyg.,  i:  45-77,  269-276,  451-482,  1901. 
Senevet,  G.    Contribution  a  1'etude  des  nymphes  des   Culicides.    Arch.   Inst. 

Pasteur  Algerie,  8:  297-382,  1930. 
.     Contribution  a  1'etude  des  nymphes  d'anophelines.     Ibid.,  9:  17-112,  1931; 

10 :  204-254,  1932;  12:  29-76,  1934. 

Mainly  Biological 

**Aitken,  T.  H.  G.     Studies  of  the  anopheline  complex  of  western  America. 

Univ.  Calif.  Pub.  Ent.,  7:  273-364,  1945. 
Atkin,  E.  E.,  and  Bacot,  A.    Stegomyia  jasciata.    Parasitology,  2:  482-536,  1917. 


MOSQUITOES  325 

Baker,  F.  C.    The  effect  of  photoperiodism  on  resting,  treehole  mosquito  larvae. 

Can.  Ent.,  67:  149-153,  1935. 
Balfour,  M.  C.     Studies  on  the  bionomics  of  North  American  anophelines.    Winter 

activities  of  anophelines  in  coastal  North  Carolina  (36°  N.  Lat.).    Amer.  Jl. 

Hyg.,  8:  68-76,  1928. 
Bang,  F.  B.,  Quinby,  G.  E.,  and  Simpson,  T.  W.    Anopheles  walferi  (Theo.); 

a  wild-caught  specimen  harboring  malaria  plasmodia.    U.S.  Pub.  Hlth.  Repts., 

55:  119-120,  1940. 
Barber,  M.  A.     The  food  of  anopheline  larvae — food  organisms  in  pure  culture. 

Ibid.,  42:  1494-1510,  1927. 
.    The  food  of  culicine  larvae — food  organisms  in  pure  culture.    Ibid.,  43: 

11-17,  I92$- 
,  and  Komp,  W.  H.  W.     Breeding  places  of  Anopheles  larvae  in  the  Yazoo- 

Mississippi  delta.    Ibid.,  44:  2457-2462,  1929. 
,  Komp,  W.  H.  W.,  and  Hayne,  T.  B.     Malaria  in  the  prairie  rice  regions 

of  Louisiana  and  Arkansas.     Ibid.,  41:  2527-2549,  1926. 
,  Komp,  W.  H.  W.,  and  Hayne,  T.  B.    Some  observations  on  the  winter 

activities  of  Anopheles  in  southern  United  States.    Ibid.,  39:  231-246,  1924. 
Bates,  M.    The  natural  history  of  mosquitoes.    New  York,  1949. 
.    Observations  on  the  distribution  of  diurnal  mosquitoes  in  a  tropical  forest. 

Ecology,  25:  159-170,  1944. 
.     Oviposition  experiments  with  anopheline  mosquitoes.    Amcr.  Jl.  Trop. 

Med.,  20:  569-583,  1940. 
Beattie,  M.  V.  F.    Physico-chemical  factors  in  relation  to  mosquito  breeding  in 

ponds.    Jl.  Ecol.,  18:  67-80,  1930. 
,  and  Howland,  L.  J.    The  bionomics  of  some  tree-hole  mosquitoes.    Bull. 

Ent.  Res.,  20:  45-58, 1929. 
Boyd,  M.  F.     Studies  on  the  bionomics  of  North  American  anophelines.     I.  The 

number  of  annual  generations  of  A.  quadrimaculatus .     II.  Physical  and  chemi- 
cal factors  in  their  relations  to  the  distribution  of  larvae  in  northeastern  North 

Carolina.    III.  Some  observations  on  imagines.    Amer.  Jl.  Hyg.,  7:  264-275, 

1927;  9:  346-370,  1929;  12:  449-466,  1930. 
,  and  Foot,  Helen.     Studies  on  the  bionomics  of  North  American  anophelines. 

The  alimentation  of  anopheline  larvae  and  its  relation  to  their  distribution  in 

nature.    Jl.  Prev.  Med.,  2:  219-242,  1928. 
,  and  Weatherbee,  A.  A.    Studies  on  the  bionomics  of  North  American 

anophelines.    V.  Winter  activities  of  Anopheles  imagines  in  coastal  North 

Carolina  (36°  N.  Lat.).    Amer.  Jl.  Hyg.,  9:  682-694,  1929. 
Bradley,  G.  H.    The  natural  breeding  places  of  Anopheles  mosquitoes  in  the 

vicinity  of  Mound,  Louisiana.    Amer.  Jl.  Trop.  Med.,  4:  199-223,  1924. 
.    Some  factors  associated  with  the  breeding  of  Anopheles  mosquitoes.    Jl. 

Agr.  Res.,  44:  381-399,  1932. 


326  MEDICAL  ENTOMOLOGY 

Bull,  C.  G.,  and  Reynolds,  B.  D.  Preferential  feeding  experiments  with  anopheline 
mosquitoes.  II.  Amer.  Jl.  Hyg.,  4:  109-118,  1924. 

,  and  Root,  F.  M.  Preferential  feeding  experiments  with  anopheline  mos- 
quitoes. I.  Ibid.,  3:  514-520,  1923. 

Buxton,  P.  A.  Further  studies  upon  the  chemical  factors  affecting  the  breeding 
of  Anopheles  in  Trinidad.  Bull.  Ent.  Res.,  25:  491-494,  1934. 

Davis,  N.  C.,  and  Shannon,  R.  C.  The  blood  feeding  habits  of  Anopheles  pseu- 
dopunctipennis  in  northern  Argentina.  Amer.  Jl.  Trop.  Med.,  8:  443-448, 
1928. 

Dozier,  H.  L.  Observations  on  breeding  places  and  winter  activities  of  mos- 
quitoes in  the  vicinity  of  New  Orleans,  Louisiana.  Proc.  Ent.  Soc.  Wash., 
38:  148-155,  1936. 

Dunn,  L.  H.  Observations  on  the  oviposition  of  Aedes  aegypti  Linn,  in  relation 
to  distance  from  habitation.  Bull.  Ent.  Res.,  18:  145-148,  1927. 

**Eyles,  D.  E.  A  critical  review  of  the  literature  relating  to  the  flight  and  dis- 
persion habits  of  anopheline  mosquitoes.  U.S.  Pub.  Hlth.  Bull.  287,  1944. 

,  and  Bishop,  L.  R.  An  experiment  on  the  range  of  dispersion  of  Anopheles 

quadrimaculatus.  Amer.  Jl.  Hyg.,  37:  239-245,  1943. 

Feng,  L.  C.  The  hibernation  mechanism  of  mosquitoes.  Arch.  SchirT.  Trop. 
Hyg.,  41 1331-337,  1937. 

Freeborn,  S.  B.  The  seasonal  life  history  of  Anopheles  maculipcnnis  with  reference 
to  humidity  requirements  and  "hibernation."  Amer.  Jl.  Hyg,,  16:  215-223, 
1932. 

Frohne,  W.  C.  Anopheline  breeding:  suggested  classification  of  ponds  based  on 
characteristic  desmids.  U.S.  Pub.  Hlth.  Repts.,  54:  1363-1387,  1939. 

Frost,  F.  M.,  Herms,  W.  B.,  and  Hoskins,  W.  M.  The  nutritional  requirements  of 
the  larva  of  the  mosquito,  Theobaldia  incident  Thorn.  Jl.  Exp.  Zool.,  73:  461- 
479,  1936. 

Griffitts,  T.  H.  D.  Winter  hibernation  of  Anopheles  larvae.  U.S.  Pub.  Hlth. 
Repts.,  33:  1996-1998,  1918. 

Haddow,  A.  J.  The  mosquitoes  of  Bwamba  County,  Uganda.  II.  Biting  activity 
with  special  reference  to  influence  of  microclimate.  Bull.  Ent.  Res.,  36:  33-73, 
1945.  III.  The  vertical  distribution  of  mosquitoes  in  a  banana  plantation  and 
the  biting  cycle  of  Aedes  simpsoni  Theo.  Ibid.,  pp.  297-304,  1945. 

,  et  al.  The  mosquitoes  of  Bwamba  County,  Uganda.  V.  The  vertical  distri- 
bution and  biting  cycle  of  mosquitoes  in  rain  forest  with  further  observations  on 
microclimate.  Ibid.,  37:  301-330,  1947. 

Hearle,  E.  The  life  history  of  Aedes  flavescens  Miiller.  Trans.  Roy.  Soc.  Canada, 
23:  85-102,  1929. 

Herms,  W.  B.,  and  Frost,  F.  M.  A  comparative  study  of  the  eggs  of  California 
anophelines.  Jl.  Parasit.,  18:  240-244,  1932. 

Hinman,  E.  H.  Biological  notes  on  Uranotaenia  spp.  in  Louisiana.  Ann.  Ent. 
Soc.  Amer.,  28:  404-407, 1935. 


MOSQUITOES  327 

.  Predators  of  the  Culicidae  (mosquitoes).  I.  The  predators  of  larvae  and 

pupae,  exclusive  of  fish.  II.  Predators  of  adult  mosquitoes.  Jl.  Trop.  Med. 
and  Hyg.,  37:  129-134,  145-150,  1934. 

.  A  study  of  the  food  of  mosquito  larvae  (Culicidae).  Amer.  Jl.  Hyg.,  12: 

238-270,  1930. 

.  The  winter  breeding  and  activity  of  culicine  mosquitoes  at  New  Orleans 

30°  N.  Lat.).  Amer.  Jl.  Trop.  Med.,  n:  459-467,  1931. 

,  and  Hurlbut,  H.  S.  A  study  of  winter  activities  and  hibernation  of  Anoph- 
eles quadrimaculatus  in  the  Tennessee  Valley.  Ibid.,  20:  431-446,  1940. 

Hurlbut,  H.  S.  Further  notes  on  the  overwintering  of  the  eggs  of  Anopheles 
wal\en  with  a  description  of  the  eggs.  Jl.  Parasit.,  24:  521-526,  1938. 

Jobling,  B.  The  efTect  of  light  and  darkness  on  oviposition  in  mosquitoes.  Trans. 
Roy.  Soc.  Trop.  Med.  Hyg.,  29:  157-166,  1935. 

King,  W.  V.  Notes  on  Culex  erraticus  and  related  species  in  the  United  States. 
Ann.  Ent.  Soc.  Amer.,  30:  345-357,  1937. 

,  and  Bull,  G.  The  blood  feeding  habits  of  malaria-carrying  mosquitoes. 

Amer.  Jl.  Hyg.,  3:  497~5I3>  T923- 

MacCreary,  D.  Comparative  density  of  mosquitoes  at  ground  level  and  at  an 
elevation  of  approximately  one  hundred  feet.  Jl.  Kcon.  Ent.,  34:  174—179,  1941. 

,  and  Stearns,  L.  A.  Mosquito  migration  across  Delaware  Bay.  N.  J.  Mosq. 

Exterm.  Assoc.  Proc.,  24:  188-197,  1937. 

McNeel,  T.  E.  Observations  on  the  biology  of  Mansonia  perttirbans  (Walk.). 
Ibid.,  19:  91-96,  1932. 

Matheson,  R.  The  efTect  of  Char  a  fragilis  on  mosquito  development,  with  a  note 
on  a  new  larviciclc.  Ibid.,  15:  77-86,  1928. 

.  The  utilization  of  aquatic  plants  as  aids  in  mosquito  control.  Amer. 

Natur.,  641,56-86,  1930. 

,  Brunett,  E.  L.,  and  Brody,  A.  L.  The  transmission  of  fowl  pox  by  mos- 
quitoes. Poultry  Sci.,  10:  211-223,  1931. 

,  and  Hinman,  E.  H.  Chara  frugilis  and  mosquito  development.  Amer.  Jl. 

Hyg.,  8:  279-296,  1928. 

,  and  Hurlbut,  H.  S.  Notes  on  Anopheles  wal^erl  Theobald.  Amer.  Jl. 

Trop.  Med.,  17:  237-242,  1937. 

New  Jersey  Mosquito  Extermination  Association.  Proceedings  .  .  .  ,  Vol.  I-. 
New  Brunswick,  N.J.,  1914-.  Annual  volumes  contain  a  wealth  of  informa- 
tion. 

Perez,  M.  An  anopheline  survey  of  the  state  of  Mississippi.  Amer.  Jl.  Hyg.,  u: 
696-710,  1930. 

Pinto,  C.  Disseminac.ao  da  malaria  pela  avic.ao;  biologia  do  Anopheles  gambiae 
e  autrous  anofelineos  do  Brasil.  Mem.  do  Instit.  Oswaldo  Cruz,  34:  293-430, 
1939. 

Rozeboom,  L.  E.  The  relation  of  bacteria  and  bacterial  filtrates  to  the  develop- 
ment of  mosquito  larvae.  Amer.  Jl.  Hyg.,  21:  167-179,  1935. 


328  MEDICAL  ENTOMOLOGY 

Rudolfs,  W.    The  composition  of  water  and  mosquito  breeding.    Ibid.,  9:  160- 

180,  1929. 
Shannon,  R.  C.    The  environment  and  behaviour  of  some  Brazilian  mosquitoes. 

Proc.  Ent.  Soc.  Wash.,  33:  1-27,  1931. 
Smith,  G.  E.,  Watson,  R.  B.,  and  Crowell,  R.  C.     Observations  on  the  flight  range 

of  Anopheles  quadrimaculatus  Say.     Atner.  Jl.  Hyg.,  34:  102-113,  1941. 
Smith,  J.  B.    Report  of  the  New  Jersey  Agricultural  Experiment  Station  upon 

the  mosquitoes  occurring  within  the  state,  their  habits,  life  history,  etc.    Trenton, 

N.J.,  1904. 

Soper,  F.  L.,  and  Wilson,  D.  B.     Anopheles  gambiae  in  Brazil.     New  York,  1943. 
Stage,  H.  H.    Some  examples  of  mosquito  ecology  in  the  Pacific  Northwest.    N.  J. 

Mosq.  Exterm.  Assoc.  Proc.,  29:  123-124,  1942. 
,  and  Yakes,  W.  W.     Some  observations  on  the  amount  of  blood  engorged 

by  mosquitoes.    Jl.  Parasit.,  22:  298-300,  1936. 
Trager,  W.    The  chemical  growth  factors  required  by  mosquito  larvae.     Biol. 

Bull.,  75:  75-84,  1938. 
.     On  the   nutritional   requirements   of  mosquito   larvae    (Aedes  aegypti). 

Amer.  Jl.  Hyg.,  22:  475-493,  1935. 
.     The  utilization  of  solutes  by  mosquito  larvae.     Biol.  Bull.,  71:  343-352, 

1936. 

Mainly  Taxonomic 

NEARCTIC  REGION 

Bradley,  G.  H.  On  the  identification  of  mosquito  larvae  of  the  genus  Anopheles 
in  the  United  States.  South.  Med.  JL,  29:  859-861,  1936. 

**Carpenter,  S.  J.,  Middlekaufl,  W.  W.,  and  Chamberlain,  R.  W.  The  mosquitoes 
of  the  southern  United  States  east  of  Oklahoma  and  Texas.  Amer.  Mid.  Nat., 
Monograph  3,  1946. 

*Dyar,  H.  G.  The  mosquitoes  of  the  Americas.  Carnegie  Inst.  Wash.,  Pub. 
No.  387,  1928. 

**Howard,  L.  O.,  Dyar,  H.  G.,  and  Knab,  F.  The  mosquitoes  of  North  and 
Central  America  and  the  West  Indies.  Ibid.,  No.  159,  1912-1917.  4  vols. 

*King,  W.  V.,  and  Bradley,  G.  H.  General  morphology  of  Anopheles  and  classi- 
fication of  the  Ncarctic  species.  Amer.  Assoc.  Adv.  Sci.,  Pub.  No.  15:  63-70, 
1941. 

** ,  Bradley,  G.  H.,  and  McNeel,  T.  E.  The  mosquitoes  of  the  southeastern 

United  States.  U.S.  Dept.  Agr.,  Misc.  Pub.  336,  1942. 

**Matheson,  R.  The  mosquitoes  of  North  America.  2nd  ed.  Ithaca,  N.Y., 
1944. 

Root,  F.  M.  The  larvae  of  American  Anopheles  mosquitoes  in  relation  to  classifica- 
tion and  identification.  Amer.  Jl.  Hyg.,  2:  379-393,  1922. 


MOSQUITOES  329 

Ross,  E.  S.,  and  Roberts,  H.  R.    Mosquito  atlas.    Part  I.  The  Nearctic  Anopheles. 

Part  II.  Old  World  Anophelines.  Amer.  Ent.  Soc.,  Philadelphia,  1943. 
**Simmons,  J.  S.,  and  Aitken,  T.  H.  G.    The  anopheline  mosquitoes  of  the 

northern  half  of  the  Western  hemisphere  and  of  the  Philippine  Islands.    U.S. 

Army,  Med.  Bull.  59,  1942. 

Many  of  the  states  of  the  United  States  have  issued  special  bulletins  either  by 
their  State  Agricultural  Colleges  or  their  health  departments  on  the  mosquitoes 
of  their  respective  areas. 

NEOTROPICAL  REGION 

Arribalzaga,  Lynch  F.    Diptcrologia  argentina.    Rev.  Mus.  de  La  Plata,  i:  457- 

477,  189052:  134-170,  1891. 

Bonne,  C.,  and  Bonne- Wcpster,  J.     Mosquitoes  of  Surinam.     Amsterdam,  1925. 
Deane,  L.  M.,  Causey,  O.  R.,  and  Deane,  M.  P.     Studies  on  Brazilian  anophelines 

from  the  northeast  and  Amazon  regions.  Amer.  Jl.  Hyg.,  Monograph  18,  1946. 
,  Causey,  O.  R.,  and  Deane,  M.  P.  Notas  sobre  a  distribute,  no  e  a  biologia  dos 

anofelinos  das  regidnes  nordestina  e  amazunica  do  Brasil.     Rev.  Serv.  cap.  Saude 

Pub.  Ano.  i  (4):  827-965,  1948. 
Dyar,  H.  G.     The  mosquitoes  of  the  Americas.     Carnegie  Inst.  Wash.,  Pub.  No. 

387,  1928. 

.     The  mosquitoes  of  Panama.     Ins.  Ins.  Mens.,  13:  101-195,  T93°- 

Galvas,  A.  G.     Biologia  y  distribution  geograhca  de  los  Anophelinos  en  Colombia. 

Rev.  Facult.  Medicina,  12,  1943. 
Howard,  L.  O.,  Dyar,  H.  G.,  and  Knab,  F.    The  mosquitoes  of  North  and  Central 

America  and  the  West  Indies.     Carnegie  Inst.  Wash.,  Pub.  No.   159,   1912- 

1917. 
Komp,  W.  H.  W.    The  anopheline  mosquitoes  of  the  Caribbean  region.    Nat. 

Inst.  Hlth.,  Bull.  No.  179,  1942. 

.     The  classification  and  identification  of  the  Anopheles  mosquitoes  of  Mex- 
ico, Central  America  and  the  West  Indies.     Amer.  Assoc.  Adv.  Sci.,  Pub.  No. 

15:  88-97,  i94i- 
.    The  species  of  the  subgenus  Kertcszia  of  Anopheles.    Ann.  Ent.  Soc.  Amer., 

30:  492~524»  !937- 
Kumm,  H.  W.,  Komp,  W.  H.  W.,  and  Ruiz,  H.    The  mosquitoes  of  Costa  Rica. 

Arner.  Jour.  Trop.  Med.,  20:  385-422,  1940. 

,  and  Zuniga,  H.    The  mosquitoes  of  El  Salvador.    Ibid.,  22:  399-415,  1942. 

Lane,  J.    Catalogo  dos  mosquitos  neotropicos.    S.  Paulo,  Brasil,  [  1939]. 

,  and  Cerqueira,  N.  L.    Os  Sabetinos   da   America   (Diptera,   Culicidae). 

Arquivos  Zool.  Estad.  Sao  Paulo,  7:  473-849,  1942. 
Martini,  E.    Los  mosquitos  de  Mexico.    Depart,  de  Salub.  Pub.  Mexico,  Bol., 

Tec.  Ser.  A,  No.  i,  1935. 

Peryassu,  A.  G.     Os  Anophelinos  do  Brasil.    Arch.  Mus.  Nac.,  23:  1-99,  1921. 
.     Os  Culicideos  do  Brasil.     Rio  de  Janeiro,  1908. 


330  MEDICAL  ENTOMOLOGY 

Root,  F.  M.    Studies  on  Brazilian  mosquitoes.  I-IV.    Amer.  Jl.  Hyg.,  6:  684- 

717,  1926;  7:  470-480,  574-598,  599-605,  1927. 
Senevet,  G.    Les  moustiques  de  la  Guyane  franchise  (Misson  1934).    Arch.  Inst. 

Pasteur  Algerie,  15:  352-382,  1937. 
,  and  Abonnenc,  E.    Les  moustiques  de  la  Guyane  franchise.    Le  genre  Culex. 

Ibid.,  17:  62-134,  1939. 
,  and  Abonnenc,  E.    Quelques  anophelines  de  la  Guyane  franchise.    Ibid., 

16:  486-512,  1938. 

PALEARCTIC  REGION 

Edwards,  F.  W.    A  revision  of  the  mosquitoes  of  the  palearctic  region.    Bull.  Ent. 

Res.,  12:  262-351,  1921. 
.     Una  revisione  delle  zanzare  delle  regioni  paleartiche.     Riv.  Malariologia, 

5:  393~466j  613-653,  1926. 
Hackett,  L.  W.,  and  Missiroli,  A.    The  varieties  of  Anopheles  maculipcnnis  and 

their  relation  to  the  distribution  of  malaria  in  Europe.     Ibid.,  14:  45-109,  1935. 
*Kirkpatrick,  T.  W.    The  mosquitoes  of  Egypt.    Cairo,  1925. 
Martini,    E.    Beitrage    zur    medizinischen    Entomologie    und    zur    Malaria- 

Epidemiologie  des  unteren  Wolgagebiets.     Abh.  Gebiete  Auslandsk.,  Hamburg 

Univ.,  29,  Ser.  D,  1928. 

.    Culicidae.    In  E.  Lindner,  Die  Fliegen  de  palaearktischen  Region.     Stutt- 
gart, 1929-1931. 
*Seguy,  E.     Histoire  naturelle  des  moustiques  de  France.     Paris,  1923. 

.    Les  moustiques  d'Afrique  Mineure,  de  I'Egypte  et  de  la  Syrie.    Paris,  1924. 

Stackelberg,  A.  A.    Faune  de  1'URSS,  insectes,  dipteres,  fam.  Culicidae  (subfam. 

Culicinae).    Inst.  Zool.  Acad.  Sci.  URSS  (Moscow)  3,  No.  4  (Nouv.  Ser.  No. 

JI)>  1937- 

ETHIOPIAN  REGION 

Bedford,  G.  A.  H.    South  African  mosquitoes.     S.  Afr.  Dept.  Agr.,  i3th  and 

i4th  Rept.  Vet.  Res.,  pp.  883-990,  1928. 
Bequaert,  J.    Medical  entomology  [Diptera].    In  R.  P.  Strong,  et  al.,  The  African 

republic  of  Liberia  and  the  Belgian  Congo,  pp.  825-846.     Cambridge,  Mass., 

'931- 
*Edwards,  F.  W.    Culicine  adults  and  pupae.     (Mosquitoes  of  the  Ethiopian 

region,  Vol.  III.)     London,  1941. 
*Evans,  A.  M.    Anophelini,  adults  and  early  stages.     (Mosquitoes  of  the  Ethiopian 

region,  Vol.  II.)     London,  1938. 
*Hopkins,  G.  H.  E.    Larval  bionomics  of  mosquitoes  and  taxonomy  of  culicine 

larvae.     (Mosquitoes  of  the  Ethiopian  region,  Vol.  I.)     London,  1936. 
**Meillon,  B.  de.    The  Anophelini  of  the  Ethiopian  geographical  region.    S.  Afr. 

Inst.  Med.  Res.,  Vol.  10  (No.  49),  1947. 


MOSQUITOES  331 

ORIENTAL  REGION 

*Barraud,  P.  J.  Family  Culicidae:  tribes  Megarhinini  and  Culicini.  (The  fauna 
of  British  India:  Diptera,  Vol.  V.)  London,  1934. 

.  A  revision  of  the  culicine  mosquitoes  of  India.  Parts  1-26.  Ind.  }1.  Med. 

Res.,  10-17,  1923-1929. 

*Christophers,  R.  S.  Family  Culicidae:  tribe  Anophelini.  (The  fauna  of  Brit- 
ish India:  Diptera,  Vol.  IV.)  London,  1933. 

Gater,  B.  A.  R.  Aids  to  the  identification  of  anopheline  larvae  in  Malaya.  Singa- 
pore, 1934. 

.    Aids  to  the  identification  of  anopheline  imagines  in  Malaya.    Singapore, 

'935- 
Li,  Feng-Swen,  and  Wu,  Shih-Cheng.    The  classification  of  mature  larvae  of 

Chinese  anopheline   mosquitoes.    Entom.   and   Phytopath.    (Hangchow),    2: 

3-14,  22-32,  43-52,  62-66,  82-93,  1934. 
,  and  Wu,  Shih-Cheng.    On  the  known  species  of  Chinese  Culicini  with  a 

few  species  of  other  tribes.    Ibid.,  3:  44-98,  1935. 
Marishita,  K.    Classification  of  the  Formosan  anophelines  with  a  key  to  species. 

Trans.  Nat.  Hist.  Soc.,  Formosa,  26:  347-355,  1936. 
*Puri,  I.  M.    Larvae  of  anopheline  mosquitoes  with  full  descriptions  of  those  of 

the  Indian  species.    Ind.  Med.  Res.  Mem.  No.  21:  1-227,  1931. 
Swellengrebel,  N.  H.,  and  Rodenwaldt,  E.    Die  Anophelen  von  Nicderlandisch- 

Ostindien.    3rd  eel.    lena,  1932. 
Toumanoff,  C.    L'anophelisme  en  Extreme-Orient.    Paris,  1936. 

AUSTRALIAN  REGION 

Edwards,  F.  W.    A  synopsis  of  the  adult  mosquitoes  of  the  Australian  region. 

Bull.  Ent.  Res.,  14:  351-399,  1924. 
Knight,  K.  L.,  Bohart,  R.  M.,  and  Bohart,  G.  E.    Keys  to  the  mosquitoes  of  the 

Australasian  region.    Nat.  Res.  Council,  Washington,  D.C.,   1944.     Mimeo- 
graphed. 
Lee,  D.  J.    An  atlas  of  the  mosquito  larvae  of  the  Australasian  region.  Tribes 

Megarhinini  and  Culicini.    Melbourne,  1944. 
,  and  Woodhill,  A.  R.    The  anopheline  mosquitoes  of  the  Australasian  region. 

Dept.  Zool.,  Univ.  Sydney,  Monograph  2,  1944. 
Mackerras,  I.  W.    Notes  on  Australian  mosquitoes.    Proc.  Linn.  Soc.  N.  South 

Wales,  52:  33-41,  284-298,  1927;  62:  259-262,  1937. 
Taylor,  F.  H.    The  Anopheles  of  the  Australian  region.    Trans.  Cong.  Far  East. 

Assoc.  Trop.  Med.  (7th  Cong.),  3:  143-164,  1930. 
.    A  check  list  of  the  Culicidae  of  the  Australian  region,    Univ.  Sydney,  Sch. 

Pub.  Hlth.  Trop.  Med.,  No.  i,  1934. 


332  MFDICAL  ENTOMOLOGY 

AREAS  IN  AND  ABOUT  THE  WESTERN  PACIFIC  OCEAN 

Bohart,   R.   M.     A   synopsis   of   the   Philippine   mosquitoes.     U.S.    Navy   Res., 

NAVMED  No.  580,  1945. 

* .    A  key  to  the  Chinese  culicine  mosquitoes.    Ibid.,  No.  961,  1946. 

* ,  and  Ingram,  R.  L.     Mosquitoes  of  Okinawa  and  the  islands  of  the  central 

Pacific.    Ibid.,  No.  1055,  1946. 
*Tsai-Yu,  H.,  and  Bohart,  R.  M.    The  mosquitoes  of  Japan  and  their  medical 

importance.    Ibid.,  1095,  1946. 
U.S.  Navy,  Bureau  of  Medicine  and  Surgery.     The  distribution  of  mosquitoes  of 

medical  importance  in  the  Pacific  area.    NAVMED  983,  1946. 


CHAPTER  XI 


Mosquitoes  in  Relation  to 
Human  Welfare 


MOSQUITOES  have  always  plagued  man  and  animals.  They  have 
limited  and  still  limit  man's  occupation  of  many  regions  of  the  globe. 
Always  considered  as  abominable  pests  about  which  he  knew  little  and 
cared  less,  he  was  suddenly  awakened  to  their  extreme  importance  by  the 
discovery  by  Ronald  Ross,  in  1898,  that  they  are  the  transmitters  of  malaria 
or  ague.  Long  before  this,  in  1878-1879,  Patrick  Manson  had  shown  that) 
mosquitoes  were  the  intermediate  hosts  of  Wuchcrcria  (Filaria)  bancrojti, 
a  roundworm  that  causes  serious  diseases  of  man.  This  discovery  had  not  at- 
tracted much  notice  as  the  diseases  caused  by  this  worm  were  not  known 
and  even  yet  are  not  well  understood.  The  incrimination  of  Aedes  aegypti 
(the  tiger  mosquito)  as  a  vector  of  yellow  fever  by  Dr.  Carlos  Finlay  (1881- 
1900)  and  the  final  proof  in  1900  by  Reed,  Carroll,  Lazear,  and  Agramonte 
aroused  the  greatest  interest  in  the  mosquito  problem.  At  present,  mos- 
quitoes are  regarded  as  probably  the  most  important  group  of  all  our  blood- 
sucking insects.  In  general,  mosquitoes  may  be  said  to  aflect  human  welfare 
in  the  following  ways: 

1.  Direct  irritation  caused  by  their  bites. 

2.  Diseases  of  man  which  are  transmitted  through  the  agency  of  mosquitoes. 

3.  Diseases  of  domestic  and  game  animals  which  are  transmitted  by  mos- 
quitoes. 

4.  Reduction  in  land,  real  estate,  and  other  property  values,  due  to  the 
excessive  abundance  of  mosquitoes. 

DIRECT  IRRITATION 

To  many  persons  the  bites  of  mosquitoes  are  only  a  temporary  annoyance; 
some  do  not  notice  their  bites;  but  many  people  suffer  greatly  even  from  a 


334  MEDICAL  ENTOMOLOGY 

few  bites.  The  number  of  people  who  appear  almost  immune  to  mosquito 
attacks  is  probably  not  large,  and  this  immunity  may  be  confined  to  the  bites 
of  mosquitoes  present  in  their  region.  Other  species  of  mosquitoes  may  cause 
them  great  annoyance.  As  this  phase  of  the  mosquito  problem  has  never  been 
sufficiently  stressed,  I  desire  to  call  particular  attention  to  it,  especially  at  this 
time  when  so  much  emphasis  is  placed  on  living  out  of  doors  to  conserve  our 
health(Mosquitoes  probably  affect  young  children,  particularly  babies,  more 
than  we  know.  To  many  people  the  bites  are  very  severe,  causing  swellings 
and  severe  itching,  followed  by  incessant  scratching  and  the  formation  of 
pustules.  This  is  followed  by  restlessness,  loss  of  sleep,  nervous  irritation,  and 
a  determination  to  avoid  mosquito  areas  at  all  costs.  In  many  persons  the 
lesions  caused  by  mosquito  bites  remain  for  months  and  retain  an  itching 
sensation.)Frequently  mosquito  outbreaks  may  assume  such  proportions  that 
all  outdoor  work  has  to  be  abandoned,  and  when  this  occurs  year  after  year 
the  development  of  the  district  is  greatly  retarded  if  not  entirely  abandoned. 
Bishopp  (1933)  reported  the  deaths  of  173  head  of  livestock  in  Florida  due  to 
attacks  of  Psorophora  confmnis,  and  the  milk  supply  of  the  area  was  reduced 
1000  gallons  per  day.  (When  mosquitoes  are  abundant,  domestic  animals 
sufifer,  especially  during  the  evening  and  night  hours.  In  housed  animals  such 
attacks  may  be  greatly  reduced  by  the  use  of  DDT  {see  pp.  389-391). 

DISEASES  TRANSMITTED  BY  MOSQUITOES 

At  least  thirteen  important  human  diseases  of  wide  distribution  are  trans- 
mitted by  mosquitoes  and  in  most  cases  only  by  mosquitoes.  If  the  transmit- 
ting mosquitoes  could  be  eliminated,  the  diseases  would  largely  disappear. 
These  are  malaria  (four  kinds),  yellow  fever,  dengue,  filariasis  (two),  en- 
cephalitis (at  least  four  different  diseases),  and  Rift  Valley  fever. 

MALARIA 

/Malaria,  according  to/Boyd  (1930),  is  the  worst  scourge  of  mankind.  The 
disease  is  caused  by-^minute  protozoan  that  invades  the  red  corpuscles  (Figs. 
132,133).  There  are  known  to  be  four  distinct  species  of  malarial  parasites, 
and  each  produce  a  distinct  type  of  disease.  The  parasites  are  known  as 
Plasmodium  vivax  (Fig.  132),  causative  agent  of  benign  tertian  or  vivax 
malaria;  Plasmodium  malariae,  causative  agent  of  quartan  malaria;  Plasmo- 
dium falciparum,  the  agent  of  malignant,-subtertian,  pernicious,  or  aestivo- 
autumnal  malaria;  and  P.  ovale,  the  causative  agent  of  ovale  malaria^  The 
common  and  most  prevalent  type  of  malaria  in  North  America  is  the  tertian. 


MOSQUITOES  AND  HUMAN  WELFARE  335 

Pernicious  or  aestivo-autumnal  malaria  occurs  in  the  states  bordering  on  the 
Gulf  of  Mexico.  According  to  Hoffman  (1916),  the  prevalence  of  the  various 
types  of  malaria  in  the  southern  states  is  about  65  per  cent  for  tertian,  13  per 
cent  for  quartan,  and  22  per  cent  for  aestivo-autumnaU  Malaria  is  one  of  the 
most  widely  distributed  of  human  diseases^  It  occurs  in  most  of  the  great 
fertile  regions  of  the  earth;  its  present  distribution  and  extent  of  endemicity  is 
shown  in  Fig.  134. 


Pig,  132,  Malaria  parasites  in  human  blood.  Upper  row:  Plasmodium  vivax  in  various 
stages  in  the  formation  of  merozoites.  Lower  row:  Plasmodium  jalciparum  in  placental 
blood,  showing  the  formation  of  merozoites  and  the  marked  dot  of  pigment.  Note  that 
in  P.  vivax  the  red  cells  are  greatly  enlarged  while  in  P.  jalciparum  there  is  no  apparent 
enlargement  of  the  red  cells.  (Photographs  by  the  author.)  . 

In  order  to  understand  the  essential  role  played  by  anopheline  mosquitoes 
in  the  transmission  of  malaria,  a  very  brief  outline  of  the  life  cycle  of  Plasmo- 
dium vivax  is  here  presented.  Plasmodium  vivax,  in  man,  lives  and  multiplies 
asexually  in  the  red  blood  corpuscles  (Fig.  132).  This  is  known  as  the  asexual 
cycle  (the  human  or  intrinsic  phase).  As  the  parasites  grow  (Fig.  133  1-3) 
they  cause  the  red  cells  to  become  enlarged  (not  true  of  Plasmodium  falci- 
parum)  and  absorb  the  cell  contents.  At  the  end  of  about  40  hours,  the 
trophozoite  is  mature  and  is  now  called  a  schizont  (5).  During  the  next  eight 


Fig.  733.  Diagrammatic  representation  of  the  life  cycle  of  the  benign  tertian  malaria 
parasite  (Plasmodium  vivax}  in  man  and  the  mosquito.  Nos.  I  to  4  show  the  growth  of 
the  parasite  in  the  red  blood  cells;  5  and  6,  the  mature  schizont  dividing  into  merozoites, 
and  their  escape  is  shown  in  7;  these  merozoites  invade  new  red  cells  and  the  cycle  con- 
tinues. Nos.  8,  9,  and  10  show  the  development  of  the  male  and  female  gametocytes.  The 
mosquito  is  shown  obtaining  these  sex  cells.  No.  u,  the  male  cells  (sperm)  being  dis- 
charged; 12,  the  sperm  cell  uniting  with  the  female  cell;  13,  the  fertilized  zygotc;  14,  the 
migrating  egg  or  ookinete;  15,  the  oocyst  outside  the  stomach  wall  of  the  mosquito;  16,  a 
nearly  mature  oocyst;  17,  the  stomach  of  a  mosquito  showing  oocysts;  18,  the  discharge  of 
the  sporozoites  by  the  breaking  of  the  oocyst;  19,  sporozoites  in  the  salivary  gland;  20,  the 
salivary  glands  of  a  mosquito;  21,  an  anophcline  is  seen  discharging  sporozoites  into  the 
blood  stream  of  a  new  host;  22  to  28  show  the  asexual  cycle  in  a  new  host.  (Modified  from 
James.) 


MOSQUITOES  AND  HUMAN  WELFARE  337 

hours  each  schizont  divides  into  a  number,  12  to  24,  merozoites  and  these  are 
discharged  into  the  blood  stream  by  the  rupturing  of  the  cell  wall  (6  and  7). 
Along  with  the  merozoites  are  liberated  the  wastes,  pigments,  and  probably  a 
toxin.  Each  merozoite  now  attacks  a  new  red  cell  and,  in  about  40  hours, 
becomes  a  schizont,  which  divides,  and  liberates  the  merozoites  at  the  end 
of  about  48  hours.  The  escape  of  so  many  merozoites  with  their  wastes  cor- 
responds with  the  onset  of  a  chill  followed  by  a  marked  rise  in  the  tempera- 
ture of  the  patient.  Hence  this  type  is  known  as  the  tertian  or  three-day 
fever,  the  chill  and  fever  appearing  on  the  third  day.  After  the  asexual  cycle 
has  continued  for  a  number  of  days,  there  appears  a  new  stage  in  the  cycle 
of  the  parasite.  Certain  merozoites  develop  into  male  and  female  gameto- 
cytes  or  sex  cells  (8,  9,  and  10).  Two  kinds  are  produced,  male  or  micro- 
gametocytes  and  female  or  macrogametocytes.  These  now  remain  in  the  red 
blood  cells  and  no  further  development  takes  place. 

At  this  point  the  anophcline  mosquito  becomes  essential  for  the  continuance 
of  the  life  of  the  parasite.  If  a  person  having  the  micro-  and  macrogametocytes 
in  his  blood  is  bitten  by  a  suitable  anopheline  mosquito  (as  Anopheles  qua- 
drimaculatus)  and  numbers  of  these  sex  cells  are  obtained,  a  further  remarkable 
development  takes  place  in  the  stomach  of  the  mosquito.  The  female  or 
macrogamctocyte  matures  into  what  is  called  a  macrogamete  and  is  then  ready 
for  fertilization.  The  male  cell  or  microgametocyte  gives  oil  a  number  of  small 
linear  bodies,  which  are  the  true  microgametes  or  male  elements  (n).  These 
lash  about  till  they  find  a  macrogamete  and  one  of  them  immediately  pene- 
trates it  (12)  and  completes  the  process  of  fertilization.  The  union  of  the  male 
and  female  produces  a  zygote  (13).  The  zygotes  are  produced  in  the  stomach 
of  the  mosquito.  The  zygote,  at  first  passive,  soon  elongates  and  begins  active 
movement;  hence  it  is  called  the  ookinetc  (14).  The  ookinete  penetrates  the 
wall  of  the  stomach  and  establishes  itself  between  the  epithelial  and  muscular 
layers  (15).  Here  it  becomes  spherical  and  grows  very  large  by  the  absorption 
of  food  from  the  surrounding  tissues.  It  is  now  called  an  oocyst  (16).  Within 
the  oocyst  remarkable  changes  (sporogony)  take  place  and,  at  the  end  of  four 
or  five  days,  the  oocyst  is  completely  filled  by  very  minute  organisms,  the 
sporozoites  (18).  The  sporozoites  escape  by  the  bursting  of  the  oocyst  and  are 
freed  in  the  body  cavity.  As  insects  have  no  closed  circulatory  system,  the 
blood  bathing  all  the  tissues,  the  sporozoites  are  now  free  to  wander  with  the 
blood.  They  are  said  to  bore  into  almost  all  the  tissues  and  organs  of  the  host, 
but  great  numbers  of  them  invade  the  salivary  glands  (19).  The  sporozoites 
are  now  ready  to  be  passed  with  the  salivary  secretion  into  a  new  host  when 
the  mosquito  bites  (21).  The  entire  cycle  (called  the  exogenous  or  extrinsic 


338  MEDICAL  ENTOMOLOGY 

phase)  within  the  mosquito  occupies  from  8  to  14  days  or  longer,  depending 
on  the  temperature  and  other  factors.  It  will  thus  be  seen  that  the  presence 
of  anopheline  mosquitoes  is  essential  for  the  beginning  of  a  new  infection  in 
man  and  furthermore  that  man  with  gametocytes  in  his  blood  is  essential 
before  mosquitoes  can  become  infected.  This  interdependence,  the  so-called 
etiological  chain  of  malaria,  is  well  shown  in  Fig.  133.  If  this  chain  can  be 
broken  at  any  one  point,  a  reduction  or  even  a  complete  elimination  of  the 
disease  can  be  accomplished. 

In  the  above  account  it  would  appear  that  the  sporozoites  discharged  by 
the  infected  mosquito  into  the  blood  stream  of  a  susceptible  person  invade 
the  red  cells  directly  and  start  the  malaria  cycle.  This  view  has  been  generally 
held  though  the  work  on  bird  malarias  has  shown  that  such  is  not  the  case  in 
those  species  causing  diseases  in  birds.  No  observer  has  ever  seen  the  direct  inva- 
sion of  red  cells  by  sporozoites  of  human  malarias.  Shortt  and  Garnharn  (1948) 
have  demonstrated  that  in  monkey  malaria  (Plasmodium  cynomolgi)  and 
human  malaria  (Plasmodium  vivax)  the  sporozoites  undergo  a  cyclical  de- 
velopment in  the  parenchymatous  cells  of  the  liver.  In  P.  vivax  the  sporozoites 
invade  the  liver  cells  and  each  sporozoite  grows  into  an  ovoid  mass,  forming 
a  cyst.1  Within  each  cyst  the  chromatic  material  (nucleus?)  divides  repeatedly 
and  by  the  fifth  to  seventh  day  a  fully  mature  schizont  is  formed,  containing 
from  800  to  1000  merozoites.  By  the  rupture  of  the  schizont  the  merozoites 
escape;  many  of  these  reach  the  blood  stream,  invade  the  red  blood  cells,  and 
start  the  blood  cycle.  Whether  the  developmental  cycle  of  the  sporozoites  may 
occur  in  other  tissues  has  not  been  determined.  The  sporozoite  cycles  for 
P.  jalciparurn  and  P.  malariac  are  still  unknown. 

The  blood  cycles  of  the  other  species  of  malarial  organisms  correspond  very 
closely  to  that  of  P.  vivax.  The  time  of  sporulation  differs — that  of  P.  malariac 
taking  place  at  the  end  of  three  days  and  the  rise  of  temperature  occurring 
on  the  following  day;  that  of  P.  jalciparurn  taking  place  irregularly  in  from 
24  to  48  hours  so  that  the  rise  in  temperature  of  the  patient  is  irregular;  that 
of  P.  ovale  is  about  the  same  as  for  P.  vivax.  Of  course,  people  suffering  from 
malaria  may  have  two  species  present  or  a  double  infection  of  any  one,  and 
this  complicates  the  clinical  picture  of  the  disease. 

In  order  that  the  exogenous  phase  of  the  malaria  parasites  may  be  com- 
pleted in  a  susceptible  mosquito  and  the  infected  mosquito  live  long  enough 
to  transmit  the  infection,  certain  climatic  conditions  appear  essential.  With 
P.  vivax  the  temperature  must  be  over  62°  F.  (16.6°  C.),  optimum  77°  F. 

1  New  names,  many  of  them,  have  been  used  to  designate  these  stages  but  no  uniformity 
has  been  reached. 


MOSQUITOES  AND  HUMAN  WELFARE 


339 


340  MEDICAL  ENTOMOLOGY 

(25°  C.),  and  the  relative  humidity  over  70  per  cent;  with  P.  jalciparum  the 
temperature  must  be  over  68°  F.  (20°  C.),  optimum  86°  F.  (30°  C.)  and  the 
relative  humidity  at  least  70  per  cent.  According  to  Gill  (1938),  vivax  malaria 
can  only  maintain  itself  in  temperate  zones  where  the  mean  temperature  dur- 
ing the  hottest  months  of  the  year  (July  or  August  in  the  Northern  hemisphere 
and  January  or  February  in  the  Southern  hemisphere)  lies  between  60.8°  F. 
(16°  C.)  and  68°  F.  (20°  C.)  or  higher  and  where  the  mean  monthly  relative 
humidity  does  not  fall  below  70  per  cent.  For  the  malignant  type  (P.  falci- 
parum)  the  temperature  must  be  about  or  over  68°  F.  (20°  C.),  optimum  86°  F. 
(30°  C.),  and  the  relative  humidity  near  70  per  cent.  Though  these  are  not 
absolute  values,  yet,  according  to  Gill  (1938),  they  largely  govern  the  distribu- 
tion of  malaria  though  not  the  distribution  of  anopheline  mosquitoes  capable 
of  transmitting  malaria.  Thus,  in  general,  the  global  area  where  malaria  may 
be  endemic  lies  south  of  the  summer  isotherm  of  60°  F.  in  the  Northern 
hemisphere  and  north  of  the  70°  F.  summer  isotherm  of  the  Southern  hemi- 
sphere (Fig.  134)  and  in  regions  where  temperature  and  relative  humidity  are 
such  as  to  furnish  suitable  conditions  for  the  completion  of  the  exogenous  cycle 
of  the  parasite  and  permit  the  mosquito  to  live  long  enough  to  infect  new 
hosts. 

SOURCES  OF  ANOPHELINE  INFECTIONS:  In  order  that  malaria 
may  occur  and  maintain  itself  in  any  given  region,  certain  conditions  are 
essential.  The  climatic  conditions  must  largely  correspond  to  those  outlined  in 
the  preceding  paragraph.  There  must  be  persons  who  have  in  their  blood  the 
micro-  and  macrogametocytes  of  one  or  more  of  the  malarial  parasites;  there 
must  also  be  present  a  species  of  Anopheles  that  feeds  on  man  and  can  act  as  a 
transmitter;  and,  finally,  this  anopheline  must  be  present  in  reasonable  num- 
bers to  ensure  adequate  infection.  The  only  known  source  of  the  gametocytes 
is  man;  no  animal,  either  in  the  wild  or  under  laboratory  conditions,  has  yet 
been  found  in  which  the  human  malarial  parasites  can  develop.  There  arc  at 
least  three  types  of  human  "carriers":  (i)  persons  who  have  had  the  disease, 
recovered,  and  carry  the  gametocytes  in  their  blood;  (2)  persons  who  have 
the  parasites  and  gametocytes  in  their  blood  but  have  never  sufTered  clinical 
symptoms  of  the  disease;  and  (3)  persons  who  have  the  disease  and  continue 
to  suffer  relapses  from  time  to  time.  The  first  two  types  are  known  as  "latent" 
carriers  and  are  a  constant  menace  to  the  general  population  in  any  malarious 
region.  The  last  type  is  probably  as  dangerous  because,  with  the  frequent 
recurrence  of  the  disease,  excessive  numbers  of  the  gametocytes  may  develop. 
Craig  and  Faust  (1940)  state  that  about  33  per  cent  of  those  having  malignant 
malaria  will  carry  gametocytes  and  hence  are  "carriers"  while  over  50  per  cent 


MOSQUITOES  AND  HUMAN  WELFARE  341 

of  those  with  vivax  malaria  will  normally  be  "carriers"  with  gametocytes  in 
their  blood.  However,  it  has  been  demonstrated  again  and  again  that  "carriers" 
with  gametocytes  in  their  blood  may  not  infect  susceptible  mosquitoes  while 
other  "carriers"  with  only  a  few  or  nondcmonstrable  gametocytes  may  infect 
anophelincs.  The  reason  for  this  is  not  easy  of  explanation. 

Given  a  source  of  the  parasites,  the  only  other  requirement  for  an  outbreak 
of  the  disease  is  adequate  numbers  of  a  species  of  Anopheles  which  readily 
bites  man  and  in  which  the  sexual  and  sporogenous  cycle  can  be  completed. 
Not  all  human  beings  are  good  "carriers";  neither  are  all  anophclines  good 
transmitters  of  malaria.  This  condition  is  certainly  fortunate,  for  if  all  our 
anophelines  were  good  transmitters  the  difficulties  in  the  reduction  and  control 
of  malaria  would  be  greatly  enhanced.  Unfortunately  we  do  not  know  all  the 
"good"  transmitters  or  all  the  "poor"  transmitters  among  the  anophelines. 
Furthermore,  it  is  well  known  that  the  same  species  of  Anopheles  may  be  a 
good  or  "dangerous"  transmitter  in  one  region  (A.  pseudopunctipennis  in 
parts  of  Argentina  and  Mexico;  A.  subpicttts  (rossi)  and  A.  hyrcanus  in  the 
Dutch  East  Indies)  and  a  poor  transmitter  of  the  disease  in  another  region 
(A.  pseudoptinctipennis  in  California;  A.  siibpicttis  (rossi)  and  A.  hyrcanus 
in  British  India).  Table  7  based  on  all  available  literature  gives  the  principal 
"good"  or  "dangerous"  transmitters  known  from  the  world  and  the  general 
region  where  they  are  known  to  transmit  malaria. 

In  Table  7  some  species  are  recorded  as  "good"  or  "dangerous"  transmitters 
of  malaria  either  from  known  surveys  or  based  on  epidemiological  grounds. 
About  another  score  could  be  added,  based  on  experimental  infections  under 
laboratory  conditions  or  the  finding  of  a  few  naturally  infected  forms  in  the 
wild.  In  North  America  the  principal  transmitters  are  A.  qitadrimaculatus  and 
A.  freeborni.  A.  crucians  is  readily  infected  under  laboratory  conditions  and 
undoubtedly  acts  as  a  transmitter  in  parts  of  its  range.  Though  A.  punctipennis, 
our  most  widely  distributed  species,  is  susceptible  to  infection,  yet  the  role 
it  plays  in  the  spread  of  the  disease  is  considered  unimportant.  A.  atropos  has 
recently  been  shown  susceptible  to  infection  and  it  probably  acts  as  a  transmitter 
within  its  range;  A.  waltyeri  has  been  found  infected  in  the  wild  and  is  readily 
infected  under  experimental  conditions. 

NATURAL  INFECTION  IN  ANOPHELINES:  Based  on  an  examina- 
tion of  all  available  literature,  nearly  sixty  different  species  or  varieties  of 
Anopheles  have  been  recorded  (from  dissections)  as  having  either  gut  or 
salivary  gland  infections  (natural) .  In  order  that  malaria  can  exist  in  any  region 
there  must  be  present  anopheline  mosquitoes  naturally  infected  with  the 
parasites.  If  no  such  infections  occur  and  if  there  are  no  human  "carriers," 


342 


MEDICAL  ENTOMOLOGY 


Table  7.  The  principal  vectors  of  malaria  throughout  the  world  (52  species). 


North  America  north  of  Mexico 


Species 

Range 

Larval  habitats 

A.  jreeborni  Aitken 

Southern  Oregon,  California 
in  drier  regions,  New  Mexico, 
western  Texas 

Fresh  seepages,  irrigation 
ditches,  rice  fields,  streams,  in 
open  sunlight 

A.  quadrimaculatus 
Say 

Massachusetts  west  through 
Ontario  to  Minnesota  south 
to  central  Texas,  Gulf  coast 
of  Mexico,  and  east  to  Atlan- 
tic coast 

Lakes,  ponds,  lime  sinks,  im- 
pounded waters,  fresh  marshes, 
swamps,  bayous,  grassy  pools, 
among  driftwood,  etc.  Vegeta- 
tion usually  abundant 

Mexico  and  Central  America 


A.  (N.)  albimanus 
Wied. 

Southeastern  Texas,  through 
Mexico,  Central  America,  to 
Colombia,  Ecuador,  and  Ven- 
ezuela; the  West  Indies 

Pools,  puddles,  hoof  prints, 
ponds,  marshes,  swamps,  fresh 
or  brackish  lagoons,  artificial 
containers,  almost  any  kind  of 
fresh  water  with  exposure  to 
sunlight 

A.  (N.)  aquasalis 
Curry 

Nicaragua,  Panama,  Trinidad, 
Lesser  Antilles,  northern  Bra- 
zil to  Alagoas 

Tidal  marshes  of  rivers,  brack- 
ish lagoons,  irrigation  waters 
(mostly  along  seacoasts  in  tidal 
areas) 

A.  (Kertcszia) 
bellator  D.  &  K. 
Important  vector  in 
Trinidad 

Trinidad,  Venezuela 

Breeds  only  in  water  in  epiphyt- 
ic bromeliads  (especially  "wild 
pineapples") 

A.  (N,)  darlingiRoot 

Mexico  (Tabasco),  Br.  Hon- 
duras, Guatemala,  Venezuela, 
south  along  Andean  foothills 
to  Argentina  &  Chile 

Fresh-water  marshes,  lagoons, 
seepages,  overflows  of  rivers, 
streams,  etc.,  with  vegetation 
and  exposed  to  sunlight 

A.  (A.}  pseudopunc- 
tipcnnis  pseudopuncti- 
pennis  Theo. 
Vector  in  parts  of 
range 

California  to  Utah,  east  to 
great  plains  and  south  through 
Mexico,  Central  America,  to 
Argentina  and  Chile 

Clean  seepages,  pools,  im- 
pounded water,  puddles,  streams 
with  algae;  more  or  less  open 
to  sunlight 

South  America 

A.  (N.)  albimanus 
Wied. 

See  above 

A.    (N.)   albitarsis 
Lyn.  Arrib. 
Vector  in  some  parts 
of  range 

Guatemala  south  through 
Central  America  to  Paraguay; 
Trinidad 

In  mats  of  aquatic  vegetation 
in  large  ponds,  marshes,  la- 
goons, bayous  of  flooding  riv- 
ers, and  not  too  much  shade 

MOSQUITOES  AND  HUMAN  WELFARE 


343 


Species 

Range 

Larval  habitats 

A.  (N.)  darlingi  Root 

See  above 

See  above 

A.   (M.)   gambiae 
Giles 

Established  in  northeast  Bra- 
zil; now  exterminated  (?) 

See  below 

A.  (A.)  pseudopunc- 
tipcnnis  pscudopuncti- 
pcnnis  Thco. 

See  above 

See  above 

A.  (N.)  pcssoai 
Galvao  &  Lane 
Vector  of  malaria  in 
the  Amazon  basin 

Colombia 
zil 

south  through  Bra- 

Open  shallow  pools  with 
and  algae 

grass 

Europe,  North  Africa,  and  the  Near  East 


(A.  (A.}  macitlipcn- 
nis  complex) 
i.  A.  lahranchiae  atro- 
parvus  van  Thiel 
Vector  in  England, 
Netherlands,  Spain, 
Portugal,  Germany  & 
Siberia 

Widely  distributed  in  Europe 
and  Asia  from  England  to 
Japan;  from  Sweden  and  mar- 
itime Siberia  south  to  Spain 
and  n.e.  Italy;  Mongolia 

Typically  in  brackish  water 
along  coastal  areas  but  also  oc- 
curs in  fresh  water  inland  as 
marshes,  swamps,  lagoons,  and 
any  suitable  water  more  or  less 
exposed  to  sunlight 

2.  A.  labranchiae  la- 
branchiae  Falleroni 
Vector  in  its  range 

S.  Spain,  Italy,  Dalmatian 
coast,  Sicily,  Sardinia,  Cor- 
sica, n.w.  coast  of  Africa 

Brackish  water  in  coastal 
marshes,  fresh  water  in  rice 
fields,  upland  streams,  and  in 
many  types  of  water 

3.  A.  (A.)  mcssae 
Falleroni 
Vector  in  Romania  & 
probably  elsewhere 

From  Norway  and  Sweden 
south  to  Italy  &  from  Britain 
east  to  Black  Sea  and  e.  Siberia 

Cool  fresh,  standing  bodies  of 
water  in  large  inland  river  val- 
leys, ponds,  lakes,  and  marshes 

A.  (A.)  clavigcr  Meig. 
(bijurcatus) 
Vector  in  Palestine 
and  Syria 

Europe,  Northern  Africa, 
Turkestan,  Asia  Minor 

Marshes,  rock  pools,  wells,  cis- 
terns 

A.  (M.)  multicolor 
Cambouliu 
Vector  on  epidemio- 
logical  grounds 

North  Africa  (desert  areas), 
Egypt,  Sudan,  Cyprus,  Ana- 
tolia, Palestine,  e.  Persia,  Ba- 
luchistan 

Pools,  stagnant  or  slow-flowing 
drains,  shallow  wells;  pools 
fresh  or  saline;  desert  pools  of 
high  salinity 

A.  (M.)  pharoensis 
Theobald 
Vector  in  Nile  prov- 
ince, Sudan 

Widespread  in  Africa,  Mada- 
gascar, Palestine 

Swamps  and  rice  fields  with 
vegetation 

A.  (A.}  sacharovi 
Favr  (elutus) 
Vector  in  Balkans, 
Palestine,  Near  East 

N.e.  and  central  Italy,  Sar- 
dinia, Corsica,  Balkans,  cen- 
tral Russia,  east  to  west  China, 
Iran,  Iraq 

Coastal  and  inland  marshes, 
fresh  or  brackish;  seems  to  pre- 
fer sunlight 

344 


MEDICAL  ENTOMOLOGY 
Table  7. — Continued. 


Species 

Range 

Larval  habitats 

A.  (M.)  serge  nti 
Theobald 
Vector  in  Egypt  & 
Palestine 

Canaries,  Algeria,  Tunisia, 
Egypt,  Syria,  Turkey,  Pales- 
tine, n.w.  India 

Rice  fields,  borrow  pits,  irriga- 
tion ditches,  drains,  seepages 

A.  (M.)  super  pictus 
Grassi 
Vector  in  S.  Europe, 
Mesopotamia,  Balu- 
chistan 

Spain  across  southern  Europe, 
Asia  Minor,  Syria,  Palestine, 
to  s.w.  India 

Pools  in  hilly  stream  beds,  riv- 
ers, irrigation  water,  seepages, 
all  more  or  less  open  to  the  sun 

Africa  mainly  south  of  the  Sahara  Desert 


A.  (M.)  junestus 
Giles 
Vector  throughout  its 
range 

Throughout  tropical  Africa 
north  into  Ethiopia  and  south 
to  Natal;  Mauritius 

Swamps,  weedy  margins  of 
streams  &  rivers,  furrows,  lakes, 
ponds,  ditches,  seepage  areas 

A.  (M.)  gambiae  Giles 
Vector  in  its  range 

var.  mclas  Theo. 

Tropical  Africa,  Sudan  north 
to  southern  Egypt,  Arabia, 
Madagascar,  Mauritius,  Re- 
union 

More  or  less  a  coastal  form 

Pools,  hoofprints,  puddles,  seep- 
age, water  holes,  drains,  pools 
in  stream  beds 

Both  fresh  and  saline  water 

A.  (M.)  hancoc^i  Edw. 
Vector  in  its  range,  es- 
pecially when  abundant 

Sierra  Leone,  Liberia,  Nigeria, 
Cameroons,  Belgian  Congo, 
Uganda 

Grassy  water  holes,  grassy 
ditches,  native  wells,  streams, 
swamps 

A.   (A/.)   hargreavesi 
Evans 
Vector  in  its  range,  es- 
pecially when  abundant 

Sierra  Leone,  Liberia,  Gold 
Coast,  s.  Nigeria,  Gaboon, 
Belgian  Congo 

Among  Pistia  in  open  and  jun- 
gle pools,  swamps,  stream  mar- 
gins 

A.   (M.)   moucheti 
Evans 
Vector  when  in 
numbers 
var.  nigeriensis  Evans 
Vector  when  abundant 

Cameroons,  central  &  eastern 
Belgian  Congo,  Uganda 

Southern  Nigeria 

Grassy  pools,  margins  of 
streams,  swamps;  vegetation 
usually  present 

Clear  water  with  Pistia,  swamps 
among  vegetation 

A.  (M.)  nili  Theobald 
Heavily  infected  in 
nature 

Sierra  Leone  east  to  Sudan 
and  south  to  Mozambique  & 
Zululand 

Margins  of  streams  in  deep 
shade  with  vegetation;  also  in 
clean  running  water  with  little 
shade;  swamps,  ditches 

A.  (M.)  pharoensis 

See  above 

A.  (M.)  pretoriensis 
Theobald 
Not  considered  im- 
portant 

Gold  Coast  across  Africa  to 
Somaliland  south  to  Trans- 
vaal &c  Natal;  Aden 

Rock  pools,  scmistagnant  pools 
in  streams  and  ditches,  shallow 
puddles,  hoofprints;  vegetation 
usually  absent 

MOSQUITOES  AND  HUMAN  WELFARE 


345 


Oriental  Region 

(India,  Ceylon,  Burma,  Malaya,  China,  Dutch  East  Indies,  Philippines, 
and  the  other  islands  in  this  region) 


Species 

Range 

Larval  habitats 

A.  (A/.)  aeon  it  us 
Doenitz 
(Feeds  mainly  on 
animals) 
Vector  in  Indo-CMna 

India,  Ceylon,  Burma,  s. 
China,  Malayan  region,  Neth. 
Indies,  Borneo,  Celebes,  Phil- 
ippines; widely  distributed 

Rice  fields,  streams,  pools, 
drains,  swamps,  irrigation 
ditches,  reservoirs,  and  similar 
situations 

A.  (M.)  cut  id  fades 
Giles 
Important  vector  in 
India,  Ceylon 

Baluchistan  to  Burma  south 
to  Ceylon;  also  reported  from 
Yunnan,  Siam,  Tonkin 

Pools,  pits,  wells,  rice  fields, 
pools  in  river  beds,  rock  quar- 
ries, irrigation  channels,  slow- 
flowing  streams;  fresh  water  but 
tolerates  brackish 

A.  (M.)  annularis  v. 
d.  Wulp 

India,  Ceylon,  Burma,  s. 
China,  Formosa,  Siam,  Indo- 
China,  Malayan  region,  Neth. 
Indies,  Philippines,  Borneo 

Every  type  of  water,  pure  or 
stagnant,  contaminated;  seep- 
ages, spring  pools,  flowing 
streams 

A.  (M.)  jhiviatilis 
James 
Vector  throughout  its 
range 

S.  China,  India,  Burma,  Siam, 
Turkestan,  Baluchistan.  Most- 
ly in  foothills  in  its  range 

Clean  hill  streams,  pools  in 
ravines,  stream  beds,  irrigation 
channels,  behind  boulders  in 
swift  water,  seepage  holes;  pre- 
fers sunlight 

//.  (A.}  hyrcanus 
sincnsis  Wied. 
Known  vector  in 
China,  s.  Japan,  Indo- 
China,  Ned.  Ind. 

N.  c.  India,  Burma,  China, 
Indo-China,  Korea,  Japan, 
Formosa 

Stagnant  water  of  rice  fields, 
pools,  swamps,  ponds,  lakes, 
slow  streams 

A,  (M.)  jcyporicnsis 
candidiensts  Koidzurni 
Vector  in  Tonkin 

A.  (A/.)  jeyporicnsis 
jcyporicnsis  James 
Not  important  vector 
in  India 

India,  China,  Burma,  For- 
mosa, Indo-China 

Eastern  India  and  probably 
Indo-China 

Flowing  water  in  ditches,  seep- 
age water 

Flowing  water  in  irrigation 
ditches,  marshy  edges  of  streams, 
lakes,  and  ponds 

A.  (M.)  Icucosphyrus 
Doenitz 
Vector  in  India,  Bur- 
ma, Borneo,  Neth.  In- 
dies 

India,  Ceylon,  Burma,  Ma- 
laya, Sumatra,  Java,  Borneo, 
Philippines,  Indo-China 

Heavily  shaded  pools  in  beds  of 
mountain  streams,  drains,  ele- 
phant foot  prints,  wells;  jungle 
breeder 

A.  (A/.)  maadatus 
Theobald 
Vector  in  Malaya, 
Netli.  Indies,  &  As- 
sam (?) 

India,  Ceylon,  Burma,  s. 
China,  Siam,  Malaya,  Neth. 
Indies,  Formosa,  Philippines, 
Indo-China 

Pools  in  swift  streams  ob- 
structed by  boulders,  pools,  rice 
fields,  lake  margins;  prefers 
sunlight 

346 


MEDICAL  ENTOMOLOGY 
Table  7. — Continued. 


Species 

Range 

Larval  habitats 

A.  (A/.)  minitnusTheo. 
Important  vector  in 
its  range  (Man  is  the 
preferred  host) 

E.  &  n.  India,  Ceylon,  Burma, 
Assam,  Siam,  Indo-China,  s. 
China,  Formosa 

Foothill  streams,  springs,  irri- 
gation ditches,  terraced  rice 
fields,  seepages;  breeds  in  sun- 
light waters 

A.  (M.)  minimus  fla- 
virostris  (Ludlow) 
Vector  in  the  Philip- 
pines 

Islands  of  the  Philippine 
group,  Celebes,  Java 

As  above  for  minimus 

A.  (M.)  mangy  anus 
(Banks) 
Vector  on  epidemio- 
logical  evidence 

Many  islands  of  the  Philip- 
pines 

Shallow,  slow-flowing  streams 
in  or  close  to  foothills,  irriga- 
tion ditches,  often  in  mats  of 
vegetation;  prefers  sunlight 

A.  (M.)  philippinensis 
Ludlow 
Vector  in  Bengal;  said 
not  to  be  in  the  Philip- 
pines 

India,  Burma,  Malaya,  Siam, 
Ncth.  Indies,  s.  China,  Philip- 
pines 

Tanks,  pools,  drains,  rice  fields, 
swamps,  ditches,  pits 

A.  (M.)  stephensi 
stephensi  Liston 
Important  vector  in 
urban  areas;  impor- 
tant in  its  range 

Eastern  Arabia,  s.  Iraq,  Iran, 
India,  Burma 

Wells,  cisterns,  flower  pots,  arti- 
ficial receptacles,  roof  gutters, 
temporary  water 

A.  (M.)  subpictus 
Grassi 
Known  vector  in 
Celebes 

India,  Malaya,  Yunnan,  Neth. 
Indies,  New  Guinea,  Indo- 
China 

Borrow  pits,  buffalo  wallows, 
brick  pits,  furrows  in  gardens, 
roof  gutters;  contaminated  wa- 
ter, even  brackish 

A.  (M.)  sundaicus 
(Rodenwaldt) 
Vector  throughout  its 
range 

India,  Burma,  Siam,  Malaya, 
Sumatra,  Java,  Borneo,  Les- 
ser Sunda  Isls.,  s.  Celebes 

Brackish  or  salt-water  lagoons 
and  swamps,  pools  of  brackish 
water  behind  coastal  embank- 
ments, tidal  drains,  and  similar 
places 

A.  (A/.)  superplctus 
Grassi 

See  above 

A.  (A/.)  umbrosus 
(Theobald) 
Vector  in  some  areas 
of  its  range 

East  India,  Tonkin,  Malaya, 
Coch  in-China,  Sumatra,  Java, 
Borneo,  Celebes 

Shaded  stagnant  pools  &  jungle 
morasses;  (brackish  water  in 
mangrove  swamps,  =^  A.  baezai 
Gater) 

A.  (A.)  barbirostris 
v.d.  Wulp 
Not  considered  an 
important  vector 

India,  Ceylon,  Burma,  Siam, 
China,  Malaya,  Borneo,  Su- 
matra, Java,  Lesser  Sundas, 
Celebes,  New  Guinea,  Philip- 
pine Isl. 

Deep  stagnant  water  with  vege- 
tation and  preferably  in  shade 
as  margins  of  rivers,  lakes, 
swamps,  pools  from  springs, 
canals,  rice  fields,  saline  swamps 

A.  (M.)  kpchi  Donitz 
Found  infected  in  In- 
dia &  Neth.  Indies 

India,  Burma,  Malaya,  s. 
China,  Sumatra,  Java,  Borneo, 
Lesser  Sundas,  Philippines, 
Moluccas 

Small  muddy  pools,  unplanted 
rice  fields,  streams,  irrigation 
ditches,  artificial  containers 

MOSQUITOES  AND  HUMAN  WELFARE 


347 


Australasian  Region 


(Australia,  Tasmania,  New  Zealand,  Islands  eastward  to  180°,  New  Guinea  and 
islands  north  to  equator  and  west  to  oriental  region) 


Species 

Range 

Larval  habitats 

//.  (A/.)  annulipesWlk. 
Only  on  epidemic- 
logical  evidence 

Coastal  and  inland  Australia, 
Tasmania,  New  Guinea. 
Breeds  at  elevations  of  5000  ft. 

Grassy  pools,  edges  of  marshes, 
slow-running  creeks,  hoofprints, 
rock  pools;  at  times  in  brackish 
water 

A.  (A.}  bancrojti  Giles 
Found  infected  in 
New  Guinea 

New  Guinea,  northern  Aus- 
tralia 

Shallow  water  overgrown  with 
vegetation  in  streams,  and  sim- 
ilar situations;  prefers  shade 

A.  (A/.)  jarauti  La- 
veran 
Dominant  vector  in 
its  range 

E.  New  Guinea,  New  Britain, 
Solomons,  New  Hebrides,  n. 
Australia 

River  &  stream  margins  with 
vegetation,  springs,  wells,  hog 
wallows,  ruts,  holes,  hoofprints, 
ditches,  and  artificial  receptacles 
as  boats,  tanks,  drums,  etc. 

A.  (A/.)  hmgae  Belkin 
&  Schlosser 
Vector  in  some  parts 
as  Guadalcanal  (?) 

Guadalcanal 

In  the  jungle  in  seepage  areas, 
potholes  in  streams,  rock  holes, 
dense  jungle  swamps,  &  tempo- 
rary pools 

A.  (A/.)  punctulatus 
Doenitz 
Vector  in  New  Guinea 

Moluccas,  New  Guinea,  New 
Ireland,  Solomons,  &  adjacent 
islands 

Rain  pools,  road  ruts,  footprints, 
potholes  in  drying  stream  beds; 
pools  may  be  muddy  and  free  of 
vegetation;  sunlight  loving 

malaria  will  be  absent  despite  the  abundance  of  "good"  or  "dangerous"  anophe- 
line  transmitters.  The  introduction  of  human  "carriers"  is  all  that  would  be 
necessary  for  an  outbreak  of  the  disease.  Boyd  (1930)  summarizes  many  of  the 
dissections  of  anophelines  made  in  order  to  determine  the  rate  of  natural 
infection.  The  results  show  a  rather  low  "rate"  of  natural  infection,  though 
the  rate  must  vary  widely  since  it  depends  on  many  factors.  In  the  United 
States,  as  summarized  by  Root,  Anopheles  quadrimaculatus  shows  a  percentage 
infection  of  1.47  (8864  dissections);  A.  punctipennis,  0.18  (543  dissections); 
and  A.  crucians,  0.25  (1203  dissections).  King  (1922,  1939)  reports  an  infec- 
tion rate  of  0.107  per  cent  (sporozoite)  in  9340  dissections  of  A.  quadrimacula- 
tus at  Mound,  Louisiana.  In  South  America  out  of  a  dissection  of  2666  A.  albi- 
tarsis only  25  were  found  infected  (all  from  Brazil).  Causey,  Deane,  and  Deane 
(1946)  report  a  10  per  cent  infection  in  A.  gambiae  found  in  houses  and  5.6 
per  cent  in  those  taken  in  the  wild,  but  Davis  (1931)  reports  62.8  per  cent 
natural  infections  in  172  mosquitoes  collected  in  houses  at  Natal,  Brazil.  In 
dissections  of  7486  A.  albimanus  53  were  reported  infected.  A.  darlingi  has 
a  high  rate  of  infection  from  a  maximum  of  88.8  per  cent  in  British  Guiana 


348  MEDICAL  ENTOMOLOGY 

(222  infected  out  of  250  dissected;  Kenney,  1946)  to  as  low  as  1.8  per  cent 
(1513  dissected;  Deane,  Causey  and  Deane,  1946).  A.  pseudopunctipennis 
showed  12  infected  out  of  435  dissected  in  Argentina  (Davis,  1927),  but  Patter- 
son (1911)  reported  1.03  per  cent  infection  in  1549  dissections.  Vargas  et  al. 
(1941)  record  12  gut  infections  out  of  526  dissections  and  4  gland  infections 
in  1246  dissections  in  Mexico.  Downs  et  al.  found  46  oocyst  infections  (3.3 
per  cent)  in  1383  A.  aquasalis  dissected  (collected  in  houses  in  Trinidad)  but 
out  of  1364  only  i  with  gland  infection;  in  A.  bdlator  they  record  10  stomach 
infections  (0.78  percent)  in  1263  dissections.  In  Africa  A.  jitnesttis  varies  in  its 
infection  rate  from  3  per  cent  (20,000  dissected  in  Kenya;  Garnham,  1938)  to 
12.5  per  cent  at  Freetown  (Gordon,  1932).  A.  gambiae  is  reported  by  Gordon 
et  al.  (1932)  to  have  an  infection  rate  of  over  n  per  cent  at  Freetown.  Barber 
and  Olinger  (1931)  found  1798  infected  out  of  14,904  dissections  (12.6  per  cent 
made  in  Southern  Nigeria.  (The  sporozoite  rate  varied  from  2.2  to  30.5  per 
cent,  according  to  the  place  where  the  mosquitoes  were  taken.)  In  Europe 
the  main  vector  is  A.  maculipennis  or  its  varieties.  Dissections  of  this  species 
show  a  low  infection  rate:  in  Macedonia  0.73  per  cent  in  14,713  dissections 
(Rice  and  Barber,  1935)  and  in  Greek  Macedonia  0.08  per  cent  (15,461  dis- 
sections) and  a  rate  of  0.30  per  cent  in  1311  dissections  of  mosquitoes  taken 
from  one  house  on  one  day  (Barber  and  Rice,  1937) .  Swellengrcbel  and  de  Buck 
(1938)  report  5.58  per  cent  infected  out  of  44,167  dissections  of  A.  nuicidi- 
pcnnis  atroparvus  (short  wings)  taken  in  houses  in  Holland  but  only  i  in- 
fected of  A.  macuhpennis  mcssae  (long  wings)  out  of  2880  dissected. 

DURATION  OF  INFECTION  IN  THE  MOSQUITO:  How  long  the 
malarial  parasites  can  survive  in  the  salivary  glands  of  mosquitoes  has  been 
partially  determined  in  a  number  of  instances.  The  ability  of  the  sporozoitcs 
to  survive  for  long  periods  and  infect  new  hosts  when  the  mosquito  bites  is  of 
great  importance.  Mayne  (1922),  using  Anopheles  punctipennis  infected  with 
Plasmodium  jalciparum,  recovered  the  sporozoitcs  (by  staining)  in  the  salivary 
glands  for  68,  70,  71,  83,  and  92  clays  after  infection.  He  produced  infection  in 
a  human  host  by  the  bite  of  a  mosquito  that  had  been  infected  55  days  pre- 
viously. This  same  mosquito  failed  to  infect  on  the  67th  clay  but  dissection 
on  the  68th  day  showed  living  sporozoites.  Boyd  et  al.  (1936)  report  that 
A.  quadrimaculatus  infected  experimentally  with  P.  jalciparum  could  transmit 
the  disease  for  at  least  40  days  after  the  extrinsic  developmental  cycle;  they 
proved  valueless  after  50  days. 

James  and  Shute  (1926)  kept  batches  of  A.  maculipennis  infected  with  P. 
vivax  at  temperatures  of  4°  C.  (37.4°  F.)  to  6°  C.  (42.8°  F.)  and  these  retained 
their  infectivity  for  two  and  one-half  months.  James  (1927)  reports  a  group  of 


MOSQUITOES  AND  HUMAN  WELFARE  349 

A.  maculipennis  that  retained  infectivity  for  nearly  six  months;  some  of  these 
were  later  reinfected  and  proved  capable  of  transmitting  malaria.  Some  of  the 
reinfected  specimens  lived  as  long  as  three  months  after  the  reinfection.  It  has 
generally  been  assumed  that  malaria  parasites  cannot  survive  in  the  anopheline 
mosquitoes  during  hibernation,  especially  in  the  colder  climates.  King  (1917) 
showed  that  P.  vivax  could  survive  in  A.  quadrimaculatus  at  a  temperature 
of  30°  F.  ( — 1°  C.)  for  at  least  two  days;  at  31°  F.  for  four  days;  and  at  a 
mean  temperature  of  46°  F.  (7.8°  C.)  for  seventeen  days.  He  also  found  that 
P.  falciparum  could  resist  temperatures  as  low  as  35°  F.  (1.7°  C.)  for  at  least 
one  day. 

James  (1927)  concludes  from  his  observations  on  specimens  of  A.  maculi- 
pennis that  were  infected  with  P.  vivax  and  that  remained  infective  for  six 
weeks  in  spite  of  refrigeration  at  3°  to  6°  C.  that  the  tertian  malaria  organism 
might  survive  the  winter  in  hibernating  anophelines  and  thus  produce  pri- 
mary attacks  of  malaria  in  winter  and  early  spring.  Inasmuch  as  many  anophe- 
line species  in  the  north  habitually  seek  out  human  habitations  for  the  purpose 
of  hibernation,  there  would  seem  to  be  no  question  that  such  individuals,  if 
infected  late  in  the  autumn  (natural  infections  are  recorded  from  dissections 
as  late  as  October  20  and  November  i,  at  Lenwil,  Louisiana;  October  4,  at 
Mound,  Louisiana;  and  October  25,  at  Edenton,  North  Carolina)  could  remain 
capable  of  infecting  human  hosts  during  the  winter  and  early  spring.  Swellen- 
grebel  and  de  Buck  (1938)  demonstrated  that  naturally  infected  A.  maculi- 
pennis atroparvus  in  Holland  lose  their  ability  to  transmit  vivax  malaria  after 
December,  for  at  that  time  the  sporozoites  are  dead  and  there  is  no  transmis- 
sion during  winter  and  early  spring,  though  this  mosquito  feeds  on  man  during 
winter  and  spring.  However,  the  temperature  is  below  that  required  for  the 
extrinsic  cycle  of  the  parasite.  All  the  spring  malaria  consists  of  relapses  (pri- 
mary) from  infection  received  the  preceding  autumn.  New  infections  occur 
only  late  in  July  to  October  when  the  temperature  and  relative  humidity  are 
right  for  the  extrinsic  development  of  the  parasite. 

CONTROL  OF  MALARIA:  The  problem  of  malaria  control  consists 
in  the  breaking  of  the  etiological  chain  at  some  vulnerable  point.  This  could 
be  done  by  any  one  of  the  following  methods  if  we  only  knew  some  effective 
procedure: 

i.  Elimination  of  the  human  "carriers."  No  very  useful  therapeutic  measures 
are  at  present  known  by  which  the  gametocytes  can  be  destroyed  in  the 
circulating  blood.  Atebrine  and  quinine  give  indications  of  value;  the  new 
drugs  paludrine,  aralen,  and  pentaquine  give  some  hope  of  success;  and 
other  drugs  may  yet  be  found,  but  it  seems  doubtful  if  such  a  beneficent  drug 


350  MEDICAL  ENTOMOLOGY 

can  be  discovered.  This  part  of  the  etiological  chain,  then,  remains  unbroken. 

2.  The  successful  treatment  of  malarial  patients  so  as  to  effect  a  cure  and 
prevent  the  formation  of  gametocytes.  Quinine  and  its  derivatives  have  been 
the  standard  treatments,  but  they  do  not  completely  cure  or  prevent  the  forma- 
tion of  gametocytes.  Atebrine,  aralen,  pentaquine,  and  paludrine  are  drugs  of 
great  value,  but  they  are  not  perfect  cures.  Furthermore,  if  a  successful  treat- 
ment were  known,  this  would  not  eliminate  the  first  type  of  "latent"  malarial 
carriers,  though  it  would  undoubtedly  in  time. 

3.  Elimination  of  the  anopheline  transmitters.  This  is  possible  when  we 
know  more  about  anopheline  biology  and  methods  of  control  that  are  finan- 
cially practicable.  This  procedure  would  seem,  at  present  at  least,  the  most  feasi- 
ble and,  from  experimental  work  so  far  carried  out,  the  most  efficient.  For 
methods  of  control  of  mosquitoes  see  Chapter  xn. 

Several  palliative  measures  can  be  employed.  These  consist  of  effective  screen- 
ing of  malarial  patients  against  anophelines  and  the  use  of  screens  and  bed- 
nets  by  the  general  population  in  malarious  regions.  These  measures,  when 
adequately  carried  out,  will  greatly  reduce  the  incidence  of  malaria.  At  the 
present  time  a  combination  of  all  these  measures,  however  ineffective  any  one 
of  them  may  be,  is  our  best  procedure  in  reducing  the  malarial  scourge. 

BLACKWATER  FEVER 

Blackwater  fever  is  a  severe  fever  of  unknown  etiology  accompanied  by 
prostrating  chills,  profuse  vomiting,  great  destruction  of  the  red  cells  (hemoly- 
sis),  and  the  passage  of  hemoglobin  in  the  urine  (the  urine  is  a  mahog- 
any color,  hence  the  name  of  the  disease).  At  present  it  is  apparently  quite  gen- 
erally accepted  that  blackwater  fever  is  probably  due  to  repeated  attack  or 
continuous  infection  with  malaria.  Apparently  many  cases  develop  during 
the  treatment  of  malaria  with  quinine,  and  the  administration  of  quinine 
may  play  some  part  in  the  genesis  of  the  attack.  The  disease  is  widely  distributed 
throughout  the  tropical  and  subtropical  regions  of  the  world  and  is  most 
prevalent  in  the  intensely  malarious  sections.  In  the  Americas  it  occurs  in 
the  northern  area  of  South  America,  the  Central  Americas,  the  West  Indies, 
and  parts  of  the  southern  states  of  the  United  States.  Recently  Stephens  made 
an  extended  study  of  the  incidence  of  this  disease  throughout  the  world  and 
he  shows  that  in  the  United  States  it  has  occurred  in  at  least  18  states  and 
as  far  north  as  New  York,  Illinois,  Colorado,  and  California.  Blackwater  fever 
is  a  very  severe  disease  with  a  high  mortality.  Apparently  it  can  only  be  pre- 
vented by  the  avoidance  of  long  and  continued  attacks  of  malaria.  It  has  many 


MOSQUITOES  AND  HUMAN  WELFARE  351 

complications  and  a  person  who  has  recovered  from  an  attack  should  not 
continue  to  live  in  a  highly  malarious  region.  In  order  to  reduce  the  incidence 
of  the  disease  in  any  area  the  most  logical  procedure,  based  on  our  present 
knowledge  of  the  disease,  would  be  the  destruction  of  malaria-carrying  anophe- 
lines. 

YELLOW  FEVER 

Yellow  fever  is  one  of  the  most  virulent  of  human  diseases.  Until  recently 
it  was  believed  that  the  disease  was  of  American  origin  and  its  transmitter, 
Aedes  aegypti,  an  American  species  of  mosquito.  Accumulating  evidence  has 
definitely  established  the  original  home  both  of  the  disease  and  the  mosquito 
to  have  been  Central  West  Africa,  whence  they  have  been  carried  to  the 
Americas.  Though  the  mosquito  has  been  carried  by  commerce  to  practically 
all  regions  of  the  globe  where  it  can  maintain  itself,  it  does  appear  rather  curious 
that  the  Americas  became  a  permanent  home  of  yellow  fever.  Carter  in  1922 
gave  the  Caribbean  littoral  as  the  probable  original  home  of  the  disease,  but  the 
same  author  in  1930  reached  the  conclusion,  based  both  on  historical  and 
biological  (very  strong  evidence)  grounds,  that  Africa  was  the  original  home. 

DISTRIBUTION:  At  present  yellow  fever  is  widely  distributed.  It  is 
known  to  be  endemic  in  Brazil,  the  Amazon  basin,  Colombia,  Venezuela, 
Peru,  Bolivia,  and  probably  other  South  American  areas,  and  in  Africa  it 
extends  from  the  west  coast  south  of  the  Sahara  into  the  Anglo-Egyptian  Sudan, 
Uganda,  Tanganyika,  Ethiopia  (?),  and  the  great  valley  of  the  Niger. 

Formerly  yellow  fever  was  rather  widespread  around  the  Caribbean  Sea 
and  was  introduced  from  time  to  time  to  northern  cities,  where  numerous 
epidemics  occurred  during  the  summer.  This  disease,  so  highly  fatal  to  non- 
immunes,  remained  a  mystery  till  Reed,  Carroll,  Lazear,  and  Agramonte 
finally  established,  in  1900,  that  it  could  be  transmitted  from  the  sick  to  the 
well  only  by  a  mosquito,  the  tiger  mosquito  (Aedes  jasciatus,  Aedes  argenteus, 
Stegomyia  ]asciata,  or  Aedes  aegypti;  unfortunately  this  mosquito  has  a  long 
list  of  synonyms).  Their  conclusions  have  been  well  established  and  the 
etiological  chain  in  this  disease  is  again  the  parasite  (a  virus),  the  man 
with  the  parasite  (the  patient),  the  mosquito,  and  finally  a  new  patient. 
Noguchi  isolated  an  organism,  Leptospira  icteroides,  which  he  claimed  was 
the  etiological  agent,  but  recent  work  has  clearly  shown  that  it  is  not — that  it 
is  only  Leptospira  icterohaemorrhagiae  (—  interrogans),  the  causative  agent 
of  infectious  jaundice  (Weil's  disease).  The  causative  agent  is  a  virus. 


352  MEDICAL  ENTOMOLOGY 

Yellow  fever  is  an  acute,  febrile,  noncontagious  disease,  characterized  by 
profound  prostration,  jaundice,  hemorrhages,  and  albuminuria.  The  death 
rate  is  very  high.  A  single  attack  confers  immunity.  The  incubation  period  in 
man  is  generally  three  to  seven  days,  though  it  may  be  shorter  (two  days) 
or  somewhat  prolonged  (very  rarely).  However,  the  causative  agent  is  nor- 
mally present  in  the  blood  stream  of  man  only  during  the  first  three  or  four 
days  after  the  onset  of  the  disease.  Whether  it  is  present  before  the  initial 
attack  is  still  undetermined,  though  work  with  monkeys  would  indicate  that 
it  probably  is.  The  period  during  which  the  parasite  is  present  in  the  blood 
stream  is  of  great  significance  when  the  infection  of  the  mosquito  carrier  is 
considered.  The  importance  of  the  mosquito  in  the  spread  of  the  disease  may  be 
stated  very  briefly.  In  order  to  obtain  the  parasite  the  mosquito  (Aedes  aegypti) 
must  bite  a  patient  during  the  first  three  or  rarely  four  days  after  the  initial 
attack.  Within  the  mosquito  the  parasite  undergoes  a  developmental  cycle, 
for  it  is  not  till  9  (at  temperatures  of  28°  C.)  to  14  days  later  that  the  mosquito 
is  capable  of  infecting  a  susceptible  person.  Once  infected  the  mosquito  re- 
mains capable  of  transmitting  the  disease  to  nonimmimes  as  long  as  it  lives. 
How  long  an  infected  mosquito  can  live  in  nature  is  not  easy  to  determine,  but 
under  experimental  conditions  infection  has  been  transferred  59  days  (one 
case),  and  118  days  (Hinclle,  1931)  after  the  infecting  meal.  Bauer  (1940) 
reports  keeping  an  infected  A.  aegypti  alive  for  200  days.  A  single  bite  of  an 
infected  mosquito  may  bring  about  an  attack  of  the  disease. 

Until  the  year  1928  it  was  generally  accepted  jjiat^the  yellow-fever  chain 
consisted  of  the  human  patient  (no  other  animals  were  known  to  be  sus- 
ceptible), the  yellow-fever  mosquito  (Aecles  aegypti),  and  susceptible  or  non- 
immune  human  individuals.  As  there  is  no  known  specific  treatment  for  the 
disease,  all  efforts  were  concentrated  on  the  reduction  or  elimination  of  the 
mosquito  in  attempts  to  control  yellow  fever.  So  successful  has  this  procedure 
been  that  practically  the  entire  yellow-fever  areas  in  the  Americas  have  been 
rendered  free  from  the  disease.  However,  sporadic  outbreaks,  and  these  widely 
separated,  have  occurred  and  still  occur  in  certain  sections  of  South  America. 
The  endemic  center  in  West  Africa  presented  a  problem  and  a  serious  menace 
as  a  possible  focus  for  the  continued  spread  of  the  disease.  The  investigations 
carried  on  at  Lagos  and  at  other  African  points  have  resulted  in  the  re- 
examination  of  the  entire  yellow-fever  problem.  Stokes,  Bauer,  and  Hudson 
(1928)  for  the  first  time  demonstrated  that  monkeys  (Macacus  rhesus)  were 
susceptible  to  the  disease,  producing  fatal  infections  in  two  monkeys  by  the 
bites  of  Aedes  aegypti  85  and  91  days  after  the  mosquito  obtained  its  infective 


MOSQUITOES  AND  HUMAN  WELFARE  353 

blood  meal.  Since  then  a  long  list  of  different  species  of  monkeys  has  been 
shown  to  be  susceptible.  In  1928  Bauer  showed  that  other  species  of  mosquitoes, 
Aedes  stolen  Evans  (apicoannulatus  Edw.),  Aedes  luteocephalus  Newst.,  and 
Eretmapodites  chrysogaster  Graham,  could  act  as  transmitters  of  yellow  fever. 
The  results  of  Bauer's  work  have  been  fully  confirmed  and  numerous  investi- 
gations have  since  added  other  species  of  mosquitoes  from  various  parts  of  the 
world. 

Yellow  fever  demonstrated  its  versatility  when  in  1933  Sopcr  reported  a 
jungle  outbreak  far  from  the  presence  of  Aedes  aegypti  or  any  other  known 
vector  of  the  disease.  Known  now  as  "jungle  yellow  fever,"  it  shows  the  same 
characteristics  as  the  classical  type  (urban)  but  its  source  and  all  its  vectors  have 
yet  to  be  determined.  Those  known  at  present  arc  listed  below  and  the  sus- 
pected animal  reservoirs  are  indicated.  The  existence  of  jungle  yellow  fever 
will  always  be  a  menace,  for  an  infected  person  or  persons  may  visit  the  more 
distant  urban  centers  (as  by  airplane)  and  form  a  focus  for  the  infection  of 
Acdcs  aegypti  (provided  it  is  present  in  numbers).  Jungle  yellow  fever  is 
widespread  in  Africa.  Recently  Smithtuirn  and  Haddow  (1946)  reported  the 
presence  of  yellow  fever  in  mosquitoes  taken  from  an  uninhabited  forest  in 
Bwamba  (Africa),  indicating  a  cycle  of  yellow  fever  without  the  human 
factor.  The  development  of  a  yellow-fever  vaccine  has  been  of  inestimable  value, 
for  millions  of  people  in  yellow-fever  areas  can  be  readily  vaccinated  and 
immunity  is  of  considerable  permanence. 

These  recent  results  show  that  the  yellow-fever  etiological  chain  is  much 
more  complicated  than  at  first  thought.  There  is  an  animal  reservoir  other  than 
man  and  its  extent  is  still  unknown.  Probably  not  all  the  mosquitoes  capable 
of  transmitting  the  disease  have  yet  been  discovered.  In  man  it  is  generally 
stated  that  the  virus  occurs  in  the  blood  stream  only  during  the  first  three  or 
four  clays  after  the  initial  attack.  In  susceptible  monkeys  it  has  been  shown 
that  the  virus  is  present  in  the  blood  stream  from  the  initial  infection  till  their 
death  and  also  in  their  tissues  after  death.  By  analogy  it  might  be  assumed  that 
man  has  the  virus  in  his  blood  shortly  after  the  initial  infection,  that  is,  several 
days  before  the  febrile  attack.  If  true,  the  period  during  which  mosquitoes  can 
obtain  the  virus  is  increased.  Again  the  old  question  as  to  whether  there  are 
"carriers"  has  been  raised  but  it  has  not  been  finally  answered. 

The  following  list  presents  data  on  the  known  mosquitoes  that  have  been 
found  capable  of  transmitting  the  disease  from  monkey  to  monkey  or  other 
experimental  animals  either  by  their  bites  or  by  a  suspension  of  the  ground-up 
bodies  or  that  have  been  found  infected  in  the  wild: 


354  MEDICAL  ENTOMOLOGY 

Table  8.  Mosquitoes  capable  of  transmitting  yellow  fever  (excluding  A.  aegypti). 

*By  bites,  naturally.         fExperimental  transmission      JFound  infected  in  the  wild. 
§Efficient  transmitters.         by  bites. 

1 1 Experimental  transmission 
by  crushed  bodies. 


Africa  (Ethiopian  Region) 


Species 


General  distribution 


Larval  habitat 


}'Aedes  aegypti 
queenslandensis 
(Theo.) 

%\Aedes  afrlcanus 
(Theo.) 


^Aedes  albopicttis  Eastern  Ethiopian, 

(Skusc) 

\\Acdcs  initans 
(Theo.) 

*Aedes  luteocephalus      Widely  distributed 
(Newst.) 

-\Aedes  metallicus  Widely  distributed 

(Edw.) 

\\Aedes  nigricephahts     West  African  region 
(Theo.) 

\\Acdes  punctocostalis     West  African  region 
(Theo.) 


Eastern  Ethiopian,  Domestic,   largely   artificial   con- 

northern  Australia  tamers 

Widespread  Tree  holes,  banana  stumps;  oc- 

casionally in  artificial  containers. 
Adults  tree-canopy-loving,  crepus- 
cular 

Tree     holes,     rock     holes,     con- 
Oriental,  northern  Australia    tainers;  domestic 

Widely  distributed  Crab  holes,  brackish   surface 

pools 

Tree  holes,  bamboo  stumps 


*-\%Aedes  slmpsoni 
(Theo.) 

* \Acdcs  stol{esi 
Evans 

•\Acdes  taylorl 
Edw. 

•\Aedes  vittatus 
(Bigot) 

^Culex  jatigans 
Wied. 

\\Culcx  thalass'ms 
Theo. 

*-\-+Eretmapodites 
chrysogaster 
Graham 


Widely  distributed 

West  Africa,  Uganda 
Nigeria,  East  Africa 


Tree  holes,  coconut  shells 
Crab  holes 

Not  known.  Probably  ground 
forest  pools  (Hopkins,  1936) 

Leaf  axils  of  banana,  etc.,  pine- 
apple tops,  tree  holes,  coconut 
shells.  Adults  diurnal 

Tree  holes,  banana  and  bamboo 
stumps 

Tree  holes 


Widespread;  also  in  Oriental    Rock  pools,  drains,  gutters,  wells, 
and  Australian  regions  and    artificial  containers 
about  Mediterranean 

Widespread  in  tropics  and        Breeds    in    all    sorts    of    pools, 
subtropics  Domestic. 

Widespread  Water   holes,    crab    holes,   earth 

drains,  old  pots 

Widely  distributed  Tree  holes,  fallen  leaves,  banana 

stumps,  artificial  containers 


MOSQUITOES  AND  HUMAN  WELFARE  355 


Species 

General  distribution 

Larval  habitat 

*  \Mansonia 
ajricanus 
(Theo.) 

^Mansonia 
unijormis 
(Theo.) 

Widely  distributed  and  com- 
mon in  tropical  Africa 

Ethiopia,  Orient,  north 
Australia,  n.  &  s.  China, 
Formosa,  Japan 

Larvae  attached  to  aquatic  plants 
Larvae  attached  to  aquatic  plants 

Neotropical  and  Nearctic  Regions 
South  America,  Central  America,  West  Indies,  U.S.A. 


*^Acdes  fluviatilis  Brazil,  Guianas  Rock    pools    along    rivers,    ant 

(Lutz)  rings,  clay  rings 

\\Acdcs  ]ulvilhorax        Trinidad,  Surinam,  Tree  holes 

(Lutz)  Venezuela,  Brazil 

*\\Acdcs  leucocelaenus     Widely  distributed  Tree  holes 

D.  &  S. 

\\Aedcsnubilns  West  Indies,  Central  and          Temporary  ground  pools 

(Theo.)  S.  America 

\\Aedesscapularis  Widespread  Temporary  rain  pools 

(Rond.) 

\\Aedcsserratus  Widespread  Temporary  rain  pools 

(Theo.) 

\\Aedestaeniorhynchus  Coastal   areas,   N.,   S.,  &        Brackish  pools  or  at  times 
(Wied.)  Central  America,  Mexico;        fresh-water  pools 

also  inland  marshes 

\\Acdcstcrrens  Mexico,  Central  America,       Tree-hole  breeder 

Walk.  to  Argentina 

•\Acdcs  triseriatus  North  America  Tree  holes 

Say 

* \\Haemagogus  Panama  to  Argentina  Tree  holes,  bamboo  stumps 

capricornii 
(Lutz) 

^Haemagogus  Mexico  to  Argentina  Tree  holes 

cquinus  Theo. 

*^$Haemagogus  Colombia  Tree  holes,  etc. 

spcgazzinii  var. 
jalco  Kum  et  al. 
(syn.  janthinomys} 

^Haemagogus  Colombia,  Guianas,  Tree  holes 

splendent  Will.  Brazil 

\\Mansonia  Brazil  Attached  to  aquatic  plants 

albicosta 
Pcry, 


356 


MEDICAL  ENTOMOLOGY 
Table  8—  Continued. 


Species 


General  distribution 


Larval  habitat 


\\Mansonia 
chrysonotum 
(Pery.) 

\\Mansonia 
jasciolata 
Lyn.  Arrib. 

\\Mansonia 
justamansonia 
(Chagas) 

\\Mansonia 
titillans 
Walk. 

\\Psorophora  cingulata 
Fabr. 

\\Psorophora  jerox 
Hum. 

||Sabethines  (pooled 

group) 

Sabcthoidcs 

Limatus 
£  Wyeomyia 

Gocldia 

Trichoprosopon 

\Acdes  geniculatus 
(Oliv.) 


Brazil 


Attached  to  aquatic  plants 


Mexico  to  Argentina  Attached  to  aquatic  plants 


Brazil,  Colombia 


Neotropical 


Central  America 
to  Brazil 

Southern  Canada  to 
Argentina 


South  American 


Attached  to  aquatic  plants 

Attached  to  floating 
water  plants 

Temporary  rain  pools 
Temporary  rain  pools 


Forest  breeders 


Europe,  Asia  Minor  Tree  holes 


At  present  the  number  of  known  mosquitoes  in  which  the  parasite  under- 
goes a  cyclical  development  and  can  be  transferred  to  susceptible  animals  is  17 
for  Africa,  21  for  South  America,  i  for  the  Far  East  and  i  (Aedes  aegypti)  of 
general  distribution,  a  total  of  40  species.  In  addition  other  species  have  been 
somewhat  incriminated  by  the  inoculation  of  the  infected  macerated  bodies 
into  monkeys.  Though  this  list  is  large,  the  importance  of  many  of  the  species 
as  transmitters  of  yellow  fever  to  man  is  probably  not  great.  Their  chief  sig- 
nificance lies  in  the  fact  that  all  of  them  are  potential  transmitters  to  monkeys 
or  other  susceptible  animals  that  may  become  reservoirs  of  the  virus. 

In  addition  to  the  above  list  of  mosquitoes  the  following  arthropods  are 
capable  of  transmitting  yellow  fever,  mechanically,  through  interrupted  feed- 
ings: Stomoxys  calcitrant,  Ctenocephalides  canis,  Cimex  lectularius  and  C. 
hemipterus  (feces  of  these  two  also  infective),  Triatoma  megista,  Ornithodoros 
moubata,  O.  rostrata,  Amblyomma  cajennense,  and  other  blood-feeding  in- 
sects that  attack  man. 


MOSQUITOES  AND  HUMAN  WELFARE  357 

ANIMAL  RESERVOIRS:  Man,  suffering  from  yellow  fever,  was  long 
assumed  to  be  the  only  source  for  mosquito  infection  and  the  consequent 
spread  of  the  disease.  Since  the  discovery  of  Stokes  and  his  co-workers  (1928) 
that  monkeys  are  susceptible  to  yellow  fever,  a  rather  long  list  of  the  monkeys 
of  the  Old  and  New  World  have  been  found  susceptible.  What  this  animal 
reservoir  may  mean  in  the  future  spread  of  the  disease  can  only  be  conjectured. 
It  clearly  points  to  a  serious  condition  should  the  disease  reach  India  and  the 
Far  East. 

In  the  Old  World  many  monkeys  have  been  found  susceptible:  Macacus 
rhesus,  M.  cynomologus,  M.  sinicus,  M.  innus,  M.  nemestrinus,  Cercopithecus 
tantalus,  C.  nicitans  inpangae,  Cercocebus  torquatus,  Erthrocebus  patas,  and 
many  others;  New  World:  Alonatta  seniculus,  Pithecia  monacha,  Cebus  vane- 
gatus,  C.  versutus,  C.  flavus,  Callithrix  albicollis,  C.  penidllata  (found  infected 
in  the  wild),  Leontoccbus  ur stilus,  Cebus  macrocephala,  Lagothrix  lagotricha, 
Ateleus  ater,  Saimiri  scireits,  Pseiidoccbus  azarae,  and  others. 

POSSIBLE  SPREAD  OF  YELLOW  FEVER:  At  present  the  transmitter 
par  excellence,  Acdcs  aegypti,  continues  to  breed  almost  unmolested  in  its 
range  within  the  United  States  and  probably  also  in  many  parts  of  Central 
and  South  America  and  the  rest  of  the  world.  That  yellow  fever  may  spread 
again  into  regions  where  it  has  apparently  been  eliminated  is  not  only  a  pos- 
sibility but  a  probability.  With  the  development  of  airplane  transportation,  the 
most  distant  parts  of  the  Americas  are  brought  close  to  our  doors.  The  intro- 
duction of  a  single  incipient  case  or  "carrier"  (?)  of  yellow  fever  might  be 
sufficient  to  start  a  small  focus  from  which  the  disease  could  spread  with  great 
rapidity.  Because  of  these  possibilities,  the  elimination  or  reduction  of  Aedes 
acgypti  should  be  attempted  in  all  places  where  it  now  occurs. 

In  1932  the  Rockefeller  Foundation  for  Medical  Research  developed  a  vac- 
cine (a  living,  modified  virus)  that  has  proved  of  immense  value  in  reducing 
outbreaks  of  yellow  fever  and  bringing  outbreaks  under  control.  Since  that 
year  millions  of  people  in  yellow-fever  areas  and  those  going  to  such  areas 
have  been  vaccinated.  A  single  vaccination  confers  a  longstanding  immu- 
nity. 

DENGUE 

Dengue  is  a  noncontagious  infectious  disease  of  low  mortality.  It  is  fre- 
quently known  as  "breakbone  fever."  Its  onset  is  characterized  by  headache, 
aching  eyes,  and  severe  body  and  limb  pains.  The  causative  agent  is  unknown, 
but  it  is  a  filter-passing  organism  and  is  transmitted  by  mosquitoes.  The  disease 
is  widespread  throughout  many  tropical  and  subtropical  regions  of  the  world. 


358  MEDICAL  ENTOMOLOGY 

It  frequently  occurs  in  epidemic  or  pandemic  waves  when  the  great  majority 
of  the  population  may  suffer.  Chandler  and  Rice  (1923)  state  that  the  1922 
epidemic  in  the  United  States  was  preceded  by  an  excessive  abundance  of 
mosquitoes,  especially  Aedes  aegypti.  In  Galveston  and  Houston  there  were 
over  60,000  cases,  and  some  500,000  to  600,000  cases  were  indicated  from  Texas 
alone.  In  Northern  localities  the  disease  appears  in  the  summer  or  autumn 
when  the  mosquito  host  is  prevalent,  but  it  always  dies  out  when  cold  weather 
intervenes,  killing  or?  the  mosquito.  In  North  America  dengue  is  confined 
largely  south  of  38°  North  latitude. 

Investigations  of  Siler  and  his  co-workers  (1926)  and  Simmons  and  his 
associates  (1930  and  1931)  prove  that  at  least  two  species  of  mosquitoes,  Aedes 
aegypti  Linn,  and  Aedes  albopictus  Skuse,  arc  effective  transmitters.  Cleland, 
Bradley,  and  MacDonald  (1906)  had  already  proved  that  Aedes  aegypti  was 
an  effective  transmitter  of  dengue  in  Australia.  The  yellow-fever  mosquito  was 
undoubtedly  first  incriminated  by  Bancroft  (1906).  Culex  jatigans  (quinque- 
fasciatus),  long  considered  an  important  transmitter,  is  now  known  not  to 
play  any  significant  part  in  its  spread.  Simmons  (1931)  confirmed  the  findings 
of  Ashburn  and  Craig  (1907)  that  by  interrupted  feedings  Culex  jatigans  can, 
mechanically,  transmit  the  disease  and  in  epidemics  may  play  a  part  in  its 
spread.  Furthermore,  in  Formosa,  Armigeres  obturbans  has  been  shown  capa- 
ble of  transmitting  the  disease  under  experimental  conditions.  Recently  Aedes 
scutellaris  Walk,  has  been  shown  to  be  an  important  vector  in  New  Guinea 
and  New  Hebrides. 

The  virus  of  the  disease  appears  to  be  present  in  the  blood  stream  from  the 
day  before  and  during  the  first  three  or  four  days  of  the  febrile  attack.  In  order 
to  become  infected,  the  mosquito  must  bite  a  dengue  patient  during  these  first 
three  to  five  days.  It  requires  at  least  eleven  (eight  according  to  some  workers) 
days  before  the  mosquito  is  capable  of  transmitting  the  virus  to  a  susceptible 
person.  Once  infected  the  mosquito  remains  infected  throughout  its  life  (70 
days  experimentally  for  Aedes  aegypti  and  54  days  for  Aedes  albopictus) . 

As  in  yellow  fever,  no  experimental  animals  were  formerly  known  to  be 
susceptible  to  the  disease.  Recently  Simmons  and  his  associates  (1931)  have 
demonstrated  that  monkeys,  Macacus  fuscatus  and  M.  philippinensis,  are  sus- 
ceptible, though  they  show  no  clinical  symptoms.  They  proved  the  infection 
by  transfers  back  by  mosquitoes  to  human  volunteers  and  other  monkeys. 
They  found  that  monkeys  from  nonendemic  centers  were  more  susceptible 
than  those  from  regions  where  the  disease  is  prevalent.  It  would  thus  appear 
that  monkeys  may  be  of  considerable  importance  in  the  epidemiology  of  the 
disease. 


MOSQUITOES  AND  HUMAN  WELFARE  359 

As  many  people  suffering  from  this  disease  may  have  it  in  mild  form,  they 
remain  at  their  daily  tasks  and  are  excellent  subjects  from  which  large  num- 
bers of  mosquitoes  become  infected.  The  yellow-fever  mosquito  is  the  most 
domesticated  of  all  our  species  and  it  is  present  in  large  numbers  in  houses.  It 
bites  at  all  times  during  the  day  and  even  at  night.  It  will  thus  be  seen  that 
a  small  outbreak  may  soon  become  epidemic  and  spread  with  great  rapidity. 
The  most  efficient  method  of  controlling  the  disease  is  by  the  elimination  of 
the  mosquito  carriers.  Aedes  aegypti  occurs  throughout  the  tropical  and  sub- 
tropical regions,  while  Aedes  albopictus,  having  about  the  same  habits,  is  re- 
stricted at  present  to  the  Oriental  region.  It  has  been  recently  established  in 
Hawaii. 

F1LARIASIS 

Filariasis  is  due  to  an  infection  with  Wuchereria  (Filaria)  bancrofti  Cobbold 
or  W.  malayi  (Brug),  rounclworms  found  in  the  adult  stage  in  man.  Filariasis 
is  indigenous  throughout  a  large  part  of  the  world  and  may  be  said  to  occur 
from  about  41°  North  to  about  30°  South  latitude  in  the  Eastern  hemisphere 
and  from  about  30°  North  to  nearly  30°  South  latitude  in  the  Western  hemi- 
sphere. In  the  United  States  filariasis  occurs  only  in  a  small  area  about  Charles- 
ton, South  Carolina,  though  at  present  it  is  practically  extinct. 

WUCHERERIA  BANCROFTI:  The  adult  worms  live  together,  often 
coiled  up  in  tangles,  in  various  parts  of  the  lymphatic  system.  The  females  dis- 
charge their  embryos  in  the  lymph  channels,  whence  they  gain  access  to  the 
blood  stream.  The  embryos  are  generally  known  as  micro filariae  as  they  appear 
in  the  blood.  Manson  (1878)  discovered  that  there  was  a  marked  periodicity 
in  the  appearance  of  the  microfilariae  in  the  peripheral  blood,  the  maximum 
nocturnal  abundance  occurring  between  10  P.M.  and  2  A.M.,  while  during  the 
day  they  concentrated  in  the  pulmonary  vessels,  capillaries  of  the  heart,  and 
parts  of  the  kidney.  This  periodicity  led  Manson. to  make  his  remarkable 
experiment  with  the  house  mosquito  (Culex  fatigans)  and  to  discover  the 
developmental  cycle  in  the  intermediate  host,  the  first  instance  of  an  insect 
serving  as  an  intermediate  host  of  any  parasite. 

Since  the  work  of  Manson,  extensive  studies  in  the  Pacific  area  have  shown 
there  is  also  a  nonperiodic  strain  of  this  filaria,  the  microfilariae  being  present 
in  the  blood  stream  of  infected  persons  at  all  times  during  the  day  as  well  as  at 
night.  This  condition  occurs  in  the  Philippines,  Fiji,  Samoa  (where  first  dis- 
covered), Tahiti,  and  other  islands  in  this  region.  However  the  filariae  are 
identical  with  the  periodic  form  known  from  the  rest  of  the  world. 


36o 


MEDICAL  ENTOMOLOGY 


Fig.  135.  (A}  Microfilaria  of  Wuchcreria  bancrojti  in  human  blood.  Nos.  i,  3-6, 
8-12  illustrate  the  development  of  Wuchercria  bancrojti  by  days  in  the  mosquito.  The 
last  4  days  (13-16)  are  not  shown  because  the  worm  becomes  very  large.  (All  photo- 
graphs from  living  specimens  by  R.  J.  Schlooser;  all  at  the  same  magnification.) 


MOSQUITOES  AND  HUMAN  WELFARE  361 

LIFE  CYCLE  IN  THE  MOSQUITO:  When  blood  containing  microfilariae  (Fig, 
135  A)  is  obtained  by  a  susceptible  mosquito,  the  embryos  escape  from  their 
sheaths  and  bore  through  the  intestinal  wall.  In  about  24  hours  they  have  all 
migrated  to  the  thoracic  muscles.  Here  each  worm  undergoes  further  develop- 
ment (molting  twice),  but  there  is  no  increase  in  numbers.  In  from  n  to  20  days 
the  larval  development  is  complete  and  the  parasites  migrate  forward  to  the  pro- 
boscis. Finally  they  come  to  lie,  generally  in  pairs,  in  the  hemocele  of  the  la- 


Fig.  136  (/<?//).  Infective  stage  of  Wuchcrerla  bancrojti  emerging  h 
of  a  mosquito.  (Photograph  by  R.  J.  Schlooser.) 
Fig.  137  (right}.  Elephantiasis.  Photograph  of  a  case  in  Manilla. 

bium.  They  are  now  ready  to  pass  to  a  new  host.  At  the  time  of  taking  blood, 
the  worms  escape  from  the  labium  (Fig.  136)  and  are  said  to  bore  directly 
through  the  skin.  In  due  time  these  larvae  reach  the  lymphatics  where  they 
become  sexually  mature;  eventually  new  generations  of  microfilariae  reach 
the  blood  stream.  The  mosquito  is  an  essential  link  in  the  chain  in  the  develop- 
ment and  transfer  of  this  parasite. 

The  presence  of  mature  filarial  worms  in  man  does  not  necessarily  mean  a 
diseased  condition.  It  is  frequently  associated  with  marked  changes  in  the 
lymphatic  system,  however,  and  is  believed  to  be  responsible  for  a  great  variety 


362 


MEDICAL  ENTOMOLOGY 


of  organic  disturbances,  as  lymphangitis,  adenitis,  elephantiasis  (Fig.  137),  and 
other  complications. 

Since  Manson's  experiments  a  large  number  of  mosquitoes  have  been  dis- 
covered to  act  as  intermediate  hosts  in  the  developmental  cycle  of  this  round- 
worm.  Most  of  these  discoveries  have  been  made  within  recent  years.  The 
following  list,  though  probably  not  complete,  will  give  some  idea  of  their 
numbers  and  distribution : 


Species 

Culex  annulirostris  Skuse 
Culex  jatigans  Wied. 

Culex  juscanus  Wied. 
Culex  pipiens  Linn. 

Culex  pipiens  pallens  Coq. 
Culex  tars ali s  Coq. 
Culex  ivhitmorei  Giles 
Culex  habilitator  D.  &  K. 
Culex  sinensis  Theo. 
Culex  tritaeniorhynchus  Giles 
Culex  salinarius  Coq. 
Culex  erraticus  D.  &  K. 
Culex  pallidothorax  Theo. 
Culex  vishnui  Theo. 
Aedes  aegypti  Linn. 

Aedes  pseudosci4tellaris  Theo. 
Aedes  scutellaris  Walk. 
Aedes  taeniorhynchus  Wied. 
Aedes  thibaulti  D.  &  K. 
Aedes  togoi  Theo. 
Anopheles  aconitus  Donitz 


General  distribution  (as  vectors) 
Dutch  East  Indies,  Celebes 

Widespread  in  tropical  and  subtropical 
regions.  Good  vector 

China  (Shanghai  area) 

Widespread  in  temperate  regions.  (Vec- 
tor in  China,  Japan,  Egypt;  readily  in- 
fected  in  U.S.A.) 

Central  China,  Japan 

Exp.  in  the  United  States 

East  Indies  and  Pacific  Islands 

West  Indies 

Poor  host  in  Australia 

Japan 

Exp.  in  the  United  States 

Exp.  in  the  United  States 

China,  India,  Ceylon,  Siam,  Indo-China 

India 

A  good  vector  in  some  areas  (West 
Africa,  Dutch  Guiana);  not  in  others; 
not  in  the  Pacific  area 

Polynesia  (Samoa  area) 

New  Guinea,  New  Hebrides,  etc. 

West  Indies  (N.,  S.,  and  C.  America) 

Exp.  in  U.S.A. 

Japan 

Dutch  East  Indies 


MOSQUITOES  AND 
Species 

Anopheles  albimanus  Wied. 
Anopheles  albltarsis  Lyn.  Arrib. 
Anopheles  algeriensis  Theo. 
Anopheles  am  ictus  Edw. 
Anopheles  aquasalis  Curry 
Anopheles  bancrojtl  Giles 
Anopheles  barbirostris  v.d.W. 
Anopheles  constant  Lav. 
Anopheles  crucians  Wied. 
Anopheles  darlingi  Root 
Anopheles  jarautl  Lav. 
Anopheles  fuliginosus  Giles 
Anopheles  junestus  Giles 
Anopheles  gambiae  Giles 
Anopheles  hyrcanus  nigerrimus  Giles 
Anopheles  hyrcanus  sinensis  Wied. 
Anopheles  jeyporicnsis  James 
Anopheles  maculatus  Theo. 
Anopheles  maculipalpus  Giles 
Anopheles  minimus  Theo. 
Anopheles  pallid  us  Theo. 
Anopheles  philippinensis  Lud. 
Anopheles  ramsayi  Covell 
(pseudojamesi) 

Anopheles  punctulatus  Donitz 
Anopheles  rhodesiensis  Theo. 
Anopheles  s pi  en  did  us  Koid. 
Anopheles  squamosus  Theo. 
Anopheles  stephensi  Listow. 
Anopheles  subpictus  Grassi 

(—  rossi  Giles) 
Anopheles  sundaicus  Roden. 


HUMAN  WELFARE  363 

General  distribution  (as  vectors) 
Caribbean  area 
Brazil 

Tunis  (Africa) 
N.  Queensland 
Brazil 

New  Guinea  (?) 
India,  Celebes 
Mauritius 

America  (poor  vector) 
British  Guiana 

Solomon  Isls.,  New  Hebrides 
India 
Africa 
Africa 
India 

China,  Siam 
Hong  Kong 
Hong  Kong 
Mauritius 
Hong  Kong 
India 
India 

India 

Solomon  Isls.,  New  Guinea 

Africa 

Hong  Kong 

Sierra  Leone 

India 

India 
India 


364  MEDICAL  ENTOMOLOGY 

Species  General  distribution  (as  vectors) 

Anopheles  varuna  lyen.  India 

Psorophora  confinnis  Lyn.  Arrib.  Exp.  in  U.S.A. 

Psorophora  discolor  Coq.  Exp.  in  U.S.A. 

Mansonia  ajricanus  Theo.  Africa 

Mansonia  indianus  Edw.  Tonkin 

Mansonia  juxtamansonius  Chagas  Brazil 

Mansonia  pseudotitillans  Theo.  Malaya 

Mansonia  unijormis  Theo.  Africa 

The  above  list  (60  species)  is  rather  long  but  it  is  not  complete.  In  addition, 
some  45  species  have  been  found  refractory  or  not  easily  infected.  Furthermore, 
many  of  the  attempted  infection  experiments  may  have  failed  owing  to  the 
conditions  under  which  they  were  performed.  Basu  and  Rao  (1939)  demon- 
strated practically  100  per  cent  infection  of  Culex  fatigans  at  temperatures  of 
80°  F.  and  relative  humidity  of  90  to  100  per  cent;  at  temperatures  of  60°  F. 
or  below  and  low  humidity  infection  rarely  occurred,  or  if  it  did  the  develop- 
mental period  in  the  mosquito  was  greatly  prolonged. 

No  known  drug  has  much  efTect  on  this  parasitic  worm.  Various  operative 
measures  are  advocated  but  without  great  success.  The  only  cilective  method  is 
the  control  of  the  mosquito  transmitters  in  the  various  regions  where  filariasis 
is  prevalent.  Individuals  in  endemic  areas  should  exercise  great  care  to  protect 
themselves  from  the  bites  of  mosquitoes.  Along  with  this  should  be  considered 
the  human  carriers  in  order  to  reduce  mosquito  infection. 

Recently  Brug  (1927)  described  a  new  species  of  filaria,  Wuchcreria  malayi, 
from  Sumatra.  He  has  shown  that  nearly  50  per  cent  of  the  people  are  infected 
with  this  filarial  worm  and  that  it  is  transmitted  by  mosquitoes,  Mansonia 
annulipes  and  M.  annulata.  He  obtained  83  and  93  per  cent  infection  in  the 
mosquitoes  in  his  experiments,  while  in  nature  he  found  i  to  2  per  cent  infec- 
tion. Other  known  mosquito  vectors  include  Mansonia  annulifera,  M.  indianus, 
M.  longipalpis  (=  annulipcs),  M.  unijormis,  Anopheles  barbirostris,  and  A. 
hyrcanus  var.  sinensis.  At  present  this  filaria  is  also  known  from  other  parts  of 
the  East  Indies,  New  Guinea,  Celebes,  India,  Indo-China,  parts  of  China,  and 
nearby  regions.  In  Sumatra  infection  by  this  filarial  worm  results  in  a  high 
percentage  of  elephantiasis.  The  life  cycle  of  this  worm  in  the  mosquito  is 
practically  identical  with  that  of  W.  bancrofti. 

Filariasis  is  not  uncommon  in  many  animals.  Dogs  suffer  from  a  peculiar 
filariasis  due  to  Diro filaria  immitis.  The  adult  worms  are  extremely  long  and 


MOSQUITOES  AND  HUMAN  WELFARE  365 

slender  and  are  found  in  the  right  heart  or  occasionally  in  the  lungs.  A  number 
of  mosquitoes  serve  as  the  intermediate  host.  The  microfilariae  do  not  undergo 
their  development  in  the  thoracic  muscles  but  in  the  Malpighian  tubules  (Fig. 
63)  of  the  mosquitoes.  Hu  (1931)  lists  seven  Anopheles  spp.,  seven  Aedes  spp., 
and  three  Culex  spp.  as  known  hosts  in  which  development  is  completed.  The 
North  American  species  are  Anopheles  punctipennis,  Aedes  aegypti,  A.  cana- 
densis,  A.  sollicitans,  A.  taeniorhynchus,  A.  vexans,  Culex  pipiens,  C.  jatigans, 
C.  restuans,  and  probably  C.  salinarius. 

Diroflaria  magalhaesi  is  reported  from  man,  one  case  in  the  left  ventricle  of 
a  Brazilian  child.  Nothing  is  known  of  its  development  though,  in  all  proba- 
bility, mosquitoes  serve  as  intermediate  hosts.  Faust  et  al.  (1939)  report  finding 
a  Dirofilaria  (a  male)  from  a  native  of  New  Orleans,  naming  it  D.  lorn- 
sianensis. 

ENCEPHALITIDES 

A  number  of  virus  diseases  have  been  generally  grouped  under  this  title. 
Of  these  virus  diseases  mosquitoes  have  been  definitely  proved  as  vectors  of 
equine  cncephalomyelitis  (eastern  and  western  strains  in  the  United  States  and 
Canada  and  Venezuelan  strain  in  Trinidad  and  northern  S.  America),  St. 
Louis  encephalitis  (in  middle  and  western  United  States),  Japanese  B  en- 
cephalitis (Japan,  Formosa,  maritime  area  of  China,  and  probably  Siberia). 

EQUINE  ENCEPHALOMYELITIS:  This  disease  has  long  been  known, 
under  various  names,  as  a  highly  fatal  disease  in  horses.  Meyer  et  al.  (1931) 
first  isolated  the  virus  from  sick  horses  in  the  San  Joaquin  Valley,  California. 
In  recent  years  thousands  of  horses  in  the  United  States  have  suffered  from 
this  disease  (nearly  400,000  in  the  years  1935  to  1939)  and  many  also  in  western 
Canada;  the  death  rate  varied  from  30  to  90  per  cent.  In  1938  during  an  out- 
break of  equine  encephalomyelitis  in  Massachusetts  human  cases  developed 
and  were  definitely  established  as  caused  by  the  virus  of  equine  encephalomye- 
litis. In  the  same  year  human  cases  were  also  diagnosed  in  California.  It  is  now 
established  that  in  North  America  there  are  two  strains,  the  western  strain 
(occurs  west  of  the  Appalachian  Mountain  ranges)  and  the  eastern  strain 
(east  of  those  mountains).  Sporadic  human  cases  were  reported  from  various 
sections  of  the  United  States  from  1938  till  the  great  epidemic  of  1941,  when 
over  3000  human  cases  occurred  in  North  and  South  Dakota,  Minnesota,  and 
the  Canadian  provinces  of  Manitoba  and  Saskatchewan  (545  cases  in  this  last 
province  alone).  From  the  beginning  mosquitoes  were  suspected  as  vectors 
owing  to  their  abundance  and  prevalence  at  the  times  and  places  of  the  out- 


366 


MEDICAL  ENTOMOLOGY 


breaks.  Experimentally  Aedes  aegypti  was  shown  by  Kelser  (1933)  to  be  easily 
infected  by  the  western  strain  if  fed  on  guinea  pigs  within  two  to  three  days 
after  inoculation;  there  was  an  incubation  period  in  the  mosquito  of  at  least 
six  days.  Soon  a  considerable  number  of  mosquito  species  were  shown  experi- 
mentally to  be  capable  of  transmitting  the  disease,  and  the  virus  was  shown  to 
multiply  in  the  mosquitoes.  During  the  great  human  outbreak  (1941)  Culex 
tarsalis  Coq.  was  found  naturally  infected  in  the  Yakima  Valley,  Washington, 
by  Hammon  et  al.  (1941).  Since  then  the  following  mosquito  species  have  been 
found  naturally  infected : 


Species 
Culex  tarsalis  Coq. 


Culex  pipiens  Linn. 
Culiseta  inornata  Will. 


Disease 

Western  strain 
(many  times);  St. 
Louis  encephalitis 

Western  and  St. 
Louis  encephalitis 

Western  strain 


Anopheles  jreeborni  Aitken       Western  strain 
Aedes  dor  sails  (Meig.)  Western  strain 

Mansonia  perturbans  (Walk.)  Eastern  strain 


Distribution  and  habits 
West  of  the  Appalachian 
Mountains;  breeds  in  all  sorts 
of   ground    pools,    containers; 
feeds  on  birds,  man,  etc. 

Widespread;  breeds  as  above; 
feeds  readily  on  birds,  man. 

Widespread;  breeds  in  more  or 
less  permanent  woodland 
pools;  bites  man. 

Western    N.    America,    west 
of  the  Rocky  Mts. 
Widespread  in  northern  U.S.; 
pool  breeder,  fresh  or  saline; 
bites  man. 

Widely  distributed,  bites  man. 
Found  infected  in  Alabama. 
(Personal  communication) 


At  the  present  time  no  species  of  mosquito  has  been  found  naturally  in- 
fected with  the  eastern  strain.  Experimentally  the  following  species  have  been 
shown  capable  of  transmitting  either  the  western  or  eastern  strain:  Aedes 
aegypti  (both  strains),  A.  sollicitans  (both  strains),  A.  nigromaculis  (western), 
A.  dorsalis  (western),  A.  taeniorhynchus  (both  strains),  A.  vexans  (both 
strains),  A.  cantator  (eastern),  A.  triseriatus  (eastern),  A.  atropalpus  (eastern). 
In  addition  the  tick,-Dermacentor  andersoni  (western  strain,  transmission  and 
transovarial  transmission),  the  mite,  Liponyssus  sylviarum  (western  strain, 
natural  infection  in  California),  the  chicken  mite,  Dermanyssus  gallinae 
(western  strain,  natural  infection),  and  the  bug,  Triatoma  sanguisuga  (strain  ?, 
in  Kansas)  can  transmit  one  of  the  strains. 


MOSQUITOES  AND  HUMAN  WELFARE  367 

Venezuelan  equine  encephalomyelitis  appears  to  be  quite  similar  to  the 
eastern  strain  of  North  America.  Recently  human  cases  have  been  reported 
from  Trinidad.  Gilyard  (1944)  reports  the  mosquitoes  Aedes  taeniorhynchus, 
Anopheles  neomaculipalpis,  and  Mansonia  titillans  to  be  natural  vectors. 

St.  Louis  encephalitis  appears  to  be  a  strictly  neurotropic  virus.  In  1933  and 
1937  extensive  outbreaks  occurred  in  St.  Louis  and  the  surrounding  county. 
The  virus  was  isolated  in  1933  and  proved  to  be  a  new  virus.  The  outbreak 
of  1933  involved  over  1000  human  cases.  The  disease  has  now  been  reported 
from  various  parts  of  the  western  half  of  the  United  States.  Hammon  et  al. 
(1941)  isolated  the  virus  from  wild  Culex  tarsalis  (captured  in  the  Yakima 
Valley,  Washington).  This  mosquito  is  known  to  be  a  definite  vector.  Culex 
pipiens  has  also  been  shown  to  be  a  vector.  Smith  et  al.  (1944,  1945,  1946, 
1948)  have  proved  that  Dermanyssus  gallinae  (the  common  chicken  mite)  is  a 
natural  vector  among  poultry  and  that  there  is  transovarial  transmission 
through  generation  after  generation.  This  mite  seems  to  be  the  natural  reser- 
voir of  the  virus,  infecting  poultry  and  maintaining  the  disease.  From  infected 
birds  mosquitoes  obtain  the  virus  and  transmit  it  to  other  birds  and  ani- 
mals, including  man.  In  addition,  the  dog  tick,  Derrnacentor  variabdis,  can 
transmit  the  virus  in  all  stages  and  also  through  the  egg.  Hence  this  tick  may 
also  prove  a  good  reservoir.  The  following  mosquitoes  have  been  shown 
capable  of  transmitting  the  virus  of  St.  Louis  encephalitis  under  experimental 
conditions  or  they  have  been  found  infected  in  nature:  Culex  pipiens,  C. 
quinquejasciatus,  C.  tarsalis,  Aedes  aegypti,  A.  dorsalis,  A.  lateralis,  A.  nigro- 
maculis,  A.  taeniorhynchus,  A.  triseriatus,  A.  vexans,  Anopheles  jreeborni, 
A.  punctipcnnis,  Culiseta  incident,  and  C.  inornata. 

Japanese  B  encephalitis  has  been  known  from  about  1871.  In  1924  an  exten- 
sive outbreak  occurred  in  Japan  and  since  then  numerous  cases  have  been 
recorded  from  those  islands.  Hsiao  and  Bohart  (1946)  report  12,341  cases 
between  1924  to  1933  with  a  death  rate  of  64.8  per  cent.  The  disease  has  also 
been  reported  from  Okinawa,  where  cases  occurred  among  American  troops 
as  well  as  natives.  From  all  available  evidence  mosquitoes  are  the  vectors,  and 
experimental  transmission  has  been  accomplished  with  Culex  pipiens  pallens, 
Culex  tritaeniorhynchus,  and  Aedes  to  got.  In  Culex  pipiens  pallens  there  was 
successful  transovarial  transmission.  The  last  species  and  C.  tritaeniorhynchus 
were  found  infected  in  nature. 

RESERVOIRS  OF  ENCEPHALITIDES :  It  has  been  well  established  that 
the  reservoirs  of  the  eastern  and  western  strains  of  equine  encephalomyelitis  and 
St.  Louis  encephalitis  are  primarily  birds,  especially  domestic  poultry.  It  will  be 
noted  that  the  mosquitoes  concerned  in  the  transmission  of  these  diseases  are 


368  MEDICAL  ENTOMOLOGY 

well-known  feeders  on  birds  and  also  on  man.  Among  birds  the  disease  is 
undoubtedly  transmitted  by  these  mosquitoes,  though  the  chicken  mite, 
Dermanyssus  gallinae,  has  been  shown  to  be  a  most  efficient  transmitter  among 
domestic  fowls.  The  reservoir  of  the  other  one  does  not  seem  to  be  known. 

Rift  Valley  fever  is  a  disease  apparently  restricted  to  parts  of  East  Africa, 
particularly  Kenya  and  Uganda.  The  virus  of  the  disease  was  isolated  in  1931, 
and  in  1933  Daubney  and  Hudson  demonstrated  that  mosquitoes  (Mansonia 
spp.)  were  capable  of  transmitting  the  virus  by  inoculation  (experimental). 
The  disease  occurs  principally  among  sheep  and  cattle  though  goats,  mice, 
and  rats  are  susceptible.  Monkeys  are  also  known  to  be  susceptible.  During  an 
outbreak  in  Kenya  in  1944  humans,  principally  shepherds,  became  infected  and 
laboratory  personnel  are  reported  to  have  contracted  the  disease.  Smithburn 
et  al.  (1948)  recovered  the  virus  from  a  number  of  mosquitoes  caught  in  the 
wild  in  Uganda.  They  report  Acdcs  tarsalis  Newstead,  A.  albocephalus  Edw., 
and  A.  dcndrophilus  Edw.  to  be  naturally  infected.  However  the  females  of 
the  first  two  species  are  not  easily  differentiated  with  certainty.  Erctmapodites 
spp.  were  recovered  infected  in  the  wild  several  times,  and  E.  chrysogaster 
Graham  was  shown  to  transmit  the  disease  experimentally. 

MYIASIS  (See  Chapter  xvn) 

Certain  species  of  mosquitoes  act  as  mechanical  carriers  of  a  human-  and 
animal-myiasis-producing  fly,  Dermatobia  hominis.  For  a  full  account  see 
pages  517-521. 

BIRD  MALARIA 

Species  of  the  genus  Culex  are  responsible  for  the  transmission  of  bird 
malarias,  rather  common  and  widespread  diseases  of  birds. 

FOWL  POX 

Fowl  pox,  a  common  and  widespread  disease  of  poultry,  has  been  shown 
(1928-1931)  by  several  workers  to  be  transmitted  by  a  number  of  different 
species  of  mosquitoes. 

REDUCTION  IN  LAND  VALUES 

It  is  common  knowledge  that  an  abundance  of  mosquitoes  causes  a  marked 
reduction  in  land  values.  This  is  particularly  true  in  summer,  seaside,  and  lake 
resorts  and  in  urban  areas  subject  to  mosquito  invasion.  Manufacturing  and 
industrial  districts  often  feel  the  effects  of  mosquito  abundance.  Some  of  our 


MOSQUITOES  AND  HUMAN  WELFARE  369 

most  valuable  lands  as  in  New  Jersey  and  the  bottom  lands  of  Mississippi  have 
had  and  continue  to  have  their  development  retarded  owing  to  hordes  of 
mosquitoes,  which  frequently  render  life,  except  to  the  most  hardened,  unen- 
durable. When  this  is  accompanied  by  diseases,  the  development  is  almost 
stopped.  Furthermore,  outbreaks  of  malaria  and  dengue  throw  another  heavy 
burden  on  such  communities  due  to  sickness,  the  consequent  loss  of  income, 
and  the  expense  attendant  thereto.  The  remarkable  results  following  mosquito 
control  and  the  consequent  increase  in  real  estate  values  and  the  health  and 
vigor  of  the  peoples  have  been  noteworthy  in  many  places  but  only  a  few 
can  be  cited,  as  Havana,  Panama,  the  Canal  Zone,  Port  Said,  and  Singapore. 
Where  diseases  are  not  present,  but  only  noxious  mosquitoes,  the  reduction 
of  the  latter  brings  about  a  marked  increase  in  land  values.  No  finer  example 
can  be  cited  than  the  work  clone  in  New  Jersey.  Headlee  (1926)  after  present- 
ing a  detailed  summary  of  the  tax  valuations  of  the  Atlantic  and  Bay  Coast 
area  of  New  Jersey  for  the  past  twenty-five  years  concludes  with  this  remarka- 
ble statement,  "Thus  it  appears,  under  New  Jersey  conditions,  that,  where 
salt-marsh  mosquitoes  are  naturally  absent,  there  has  occurred  an  average 
increase  in  taxable  values  during  the  past  ten  years  of  55  per  cent  more  than 
where  they  are  still  present  or  only  recently  reduced;  and  that,  where  salt- 
marsh  mosquitoes  have  been  largely  eliminated  during  the  last  ten  years, 
there  has  occurred  an  average  annual  increase  of  75  per  cent  more  than  where 
they  are  still  present  or  very  recently  reduced." 

REFERENCES  2 
MALARIA 

Barber,  M.  A.,  and  Olinger,  M.  T.     Studies  on  malaria  in  southern  Nigeria.     Ann. 

Trop.  Med.  Parasit.,  25:  361-501,  1931. 
Boyd,  M.  F.    Studies  of  the  epidemiology  of  malaria  in  the  coastal  lowlands  of 

Brazil.    Amer.  Jl.  Hyg.,  Monograph  5,  1926. 

* .     An  introduction  to  nialariology.     Cambridge,  Mass.,  1930. 

Carter,  H.  R.    Report  on  malaria  and  anopheline  mosquitoes  in  Ceylon.    Colombo, 

Ceylon,  1927.    Ceylon  Sessional  Paper,  vn. 

Celli,  A.    A  history  of  malaria  in  the  Roman  Campagna.    London,  1933. 
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292,  1939. 
*Covell,  G.    A  critical  review  of  the  data  recorded  regarding  the  transmission  of 

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and  breeding  places.    Ind.  Med.  Res.  Mem.  No.  7,  1927. 

2  The  literature  on  malaria  is  overwhelming;  only  a  few  references  can  be  listed  here; 
most  references  have  long  bibliographies  and  these  should  be  consulted. 


370  MEDICAL  ENTOMOLOGY 

**Covell,  G.  The  present  state  of  our  knowledge  regarding  the  transmission  of 
malaria  by  the  different  species  of  anopheline  mosquitoes.  Rec.  Mai.  Surv.  Ind., 
2:  1-48,  1931. 

** .    Malaria  control  by  anti-mosquito  measures.    London,  1931. 

*Craig,  C.  F.     A  manual  of  the  parasitic  Protozoa  of  man.     New  York,  1926. 

** ,  and  Faust,  E.  C.     Clinical  parasitology.     3rd  ed.     Philadelphia,  1943. 

*Gill,  C.  A.     The  seasonal  periodicity  of  malaria.     London,  1938. 

**Hackett,  L.  W.  The  varieties  of  Anopheles  maculipennis  and  their  relation  to 
the  distribution  of  malaria  in  Europe.  Kiv.  di  Malario.,  14:  3-67,  1935. 

.    Malaria  in  Europe.    London,  1937. 

,  and  Missiroli,  A.  The  natural  disappearance  of  malaria  in  certain  regions 

of  Europe.  Amer.  Jl.  Hyg.,  13:  57-78,  1931. 

Hoffman,  F.  L.     The  malarial  problem  in  peace  and  war.     Newark,  N.J.,  1918. 

James,  S.  P.    Malaria  at  home  and  abroad.    London,  1920. 

.  Epidemiological  results  of  a  laboratory  study  of  malaria  in  England.  Trans. 

Roy.  Soc.  Trop.  Med.  Hyg.,  20:  143-165,  1926. 

.  Report  on  the  first  results  of  laboratory  work  on  malaria  in  England.  Pub. 

League  of  Nations,  iii,  Health.  (Review,  Brit.  Med.  Jl.,  p.  79,  July  10,  1926.) 

.  History  of  a  group  of  Anopheles  mosquitoes  infected  with  Plasmodium 

vivax  (Grassi  &  Feletti).  Abh.  Gebiete  Auslandsk.,  Hamburg  Univ.,  26,  Ser. 
D  (Med.):  220-222,  1927. 

.  Problems  of  malaria  prophylaxis.  Conclusions  of  the  Malaria  Commis- 
sion of  the  League  of  Nations.  Brit.  Med.  JL,  ii,  pp.  340-343,  1927. 

Jones,  W.  H.  S.  Malaria:  a  neglected  factor  in  the  history  of  Greece  and  Rome. 
Cambridge,  Eng.,  1907. 

.     Malaria  and  Greek  history.     Manchester,  1909. 

King,  W.  V.  The  effect  of  cold  upon  malaria  parasites  in  the  mosquito  host. 
Jl.  Exp.  Med.,  25:  495-498,  1917. 

.  On  the  development  of  malaria  parasites  in  the  mosquito.  Amer.  Jl.  Hyg., 

10:  560-579,  1929. 

Kligler,  I.  J.  The  epidemiology  and  control  of  malaria  in  Palestine.  Chicago, 
1930. 

*Knowles,  R.,  and  Senior- White,  R.  Malaria,  its  investigation  and  control.  Cal- 
cutta, 1927. 

*Kumm,  H.  W.  The  geographical  distribution  of  the  malaria  carrying  mos- 
quitoes. Amer.  Jl.  Hyg.,  Monograph  10,  1929. 

*MacGregor,  M.  E.  Mosquito  surveys:  a  handbook  for  anti-malarial  and  anti- 
mosquito  field  workers.  London,  1928. 

Malaria.  Collected  memoranda  on  the  subject  of  malaria.  Rec.  Mai.  Surv.  Ind., 
i  (2),  1930.  (Reprints  of  selected  papers  from  1847  to  1924.) 

Pinto,  C.  Disseminac.ao  da  malaria  pela  avia^ao;  biologia  do  Anopheles  gamblae 
e  outros  anofelineos  do  Brasil.  Mem.  do  Instit.  Oswaldo  Cruz,  34:  293-430,  1939. 

Ross,  Ronald.    The  prevention  of  malaria.    London,  1910. 


MOSQUITOES  AND  HUMAN  WELFARE  371 

.    Studies  on  malaria.    London,  1928. 

Russell,  P.  F.    Lessons  in  malariology  from  World  War  II.    Amer.  Jl.  Trop.  Med., 

26:  5-13,  1946. 
** ,  West,  L.  S.,  and  Manwell,  R.  D.    Practical  malariology.    Philadelphia, 

1946. 
Shortt,  H.  E.,  and  Garnham,  P.  C.  C.     The  pre-crythrocytic  cycle  of  Plasmodium 

cynomolgi  and  Plasmodium  vivax.    Trans.  Roy.  Soc.  Trop.  Med.  Hyg.,  41:  785- 

795,  1948. 

.  Demonstration  of  a  persisting  exo-erythrocytic  cycle  in  Plasmodium  cy- 
nomolgi and  its  bearing  on  the  production  of  relapses.  Brit.  Med.  Jl.,  i,  pp.  1225- 

1228,  1948. 

Simmons,  J.  S.,  et  al.    Malaria  in  Panama.     Amer.  Jl.  Hyg.,  Monograph  13,  1939. 
**Soper,  F.  L.,  and  Wilson,  D.  B.     Anopheles  gambiae  in  Brazil,  1930-1940.     The 

Rockefeller  Foundation,  N.Y.,  1943. 
Swellengrebel,  N.  H.,  and  de  Buck,  A.     Malaria  in  the  Netherlands.     Amsterdam, 

1938. 
Watson,  Malcolm.     Prevention  of  malaria  in  the  Federated  Malay  States.    London, 

1921. 

YELLOW  FEVER 

Bacot,  A.  W.  Report  of  the  Yellow  Fever  Commission  (West  Africa).  Vol.  3 
(Suppl.).  London,  1916. 

**Bates,  M.,  and  Roca-Garcia,  M.  Experiments  with  various  Colombian  mar- 
supials and  primates  in  laboratory  cycles  of  yellow  fever.  Amer.  Jl.  Trop.  Med., 

26:  437~453»  I946- 
,  and  Roca-Garcia,  M.    The  development  of  the  virus  of  yellow  fever  in 

Hacmogogus  mosquitoes.    Ibid.,  pp.  585-605,  1946. 
Bauer,  J.  H.     The  transmission  of  yellow  fever  by  mosquitoes  other  than  Aedes 

acgypti.     Ibid.,  8:  261-282,  1928. 
,  and  Hudson,  N.  P.    The  incubation  period  of  yellow  fever  in  the  mosquito. 

Jl.  Exp.  Med.,  48:  147-153,  1928. 
Beeukes,  H.,  Bauer,  J.  H.,  and  Mahaffy,  A.  F.     Yellow  fever  endemicity  in  West 

Africa.    Amer.  Jl.  Trop.  Med.,  10:  305-333,  1930. 
Bugher,  J.  C.,  et  al.    Epidemiology  of  jungle  yellow  fever  in  eastern  Colombia. 

Amer.  Jl.  Hyg.,  39:  16-51,  1944. 
Carter,  H.  R.     Immunity  to  yellow  fever.     Ann.  Trop.  Med.  Parasit.,  10:   153- 

164,  1916. 
* .     Yellow  fever.  An  epidemiological  and  historical  study  of  its  place  of  origin. 

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Davis,  N.  C.    Susceptibility  of  capuchin  (Cebus)  monkeys  to  yellow  fever.    Amer. 

Jl.Hyg.,  11:321-334,  1930. 
.     The  transmission  of  yellow  fever.     Further  experiments  with  monkeys 

of  the  New  World.    Amer.  Jl.  Trop.  Med.,  u:  113-125,  1931. 


372  MEDICAL  ENTOMOLOGY 

Davis,  N.  C.,  and  Shannon,  R.  C.    Further  attempts  to  transmit  yellow  fever  with 

mosquitoes  of  South  America.    Ibid.,  14:  715-722,  1931. 
Finlay,  Carlos  E.     Carlos  Finlay  and  yellow  fever.     New  York,  1940. 
Fosdick,  R.  B.    Unraveling  the  yellow  fever  mystery.    Rockefeller  Foundation, 

a  review  for  1940,  pp.  27-31. 
Garnham,  P.  C.  C.,  ct  al.     The  mosquitoes  of  the  Kaimosi  Forest,  Kenya  Colony, 

with  special  reference  to  yellow  fever.    Bull.  Ent.  Res.,  36:  473-496,  1946. 
Gilmore,  R.  M.    Mammalogy  in  an  epidemiological  study  of  jungle  yellow  fever  in 

Brazil.     Jl.  Mammalogy,  24:  144-162,  1943. 
Kirk,  R.    An  epidemic  of  yellow  fever  in  the  Nuba  Mountains,  Anglo-Egyptian 

Sudan.    Ann.  Trop.  Med.  Parasit.,  35:  67-112,  1941. 
Kumm,  H.  W.    The  geographical  distribution  of  the  yellow  fever  vectors.     Amer. 

Jl.  Hyg.,  Monograph  12,  1931. 
,  et  al.    Studies  on  mosquitoes  of  the  genus  Haemagogus  in  Colombia.     Amer. 

Jl.Hyg.,43:  13-28,  1946. 

Lewis,  D.  J.     Mosquitoes  in  relation  to  yellow  fever  in  the  Nuba  Mountains,  Anglo- 
Egyptian  Sudan.     Ann.  Trop.  Med.  Parasit.,  37:  65-76,  1943. 
** .    General  observations  on  mosquitoes  in  relation  to  yellow  fever  in  the 

Anglo-Egyptian  Sudan.     Bull.  Ent.  Res.,  37:  543-565,  1947. 
,  Hughes,  T.  P.,  and  Mahafify,  A.  F.     Experimental  transmission  of  yellow 

fever  by  three  common  species  of  mosquitoes  from  the  Anglo-Egyptian  Sudan. 

Ann.  Trop.  Med.  Parasit.,  36:  34-38,  1942. 
MahafTy,  A.  F.,  et  al.     Yellow  fever  in  western  Uganda.     Trans.  Roy.  Soc.  Trop. 

Med.  Hyg.,  36:  9-20,  1942. 

Philip,  C.  B.     Studies  on  the  transmission  of  experimental  yellow  fever  by  mos- 
quitoes other  than  Aedes.     Amer.  Jl.  Trop.  Med.,  10:  1-16,  1930. 
Reed,  W.    The  etiology  of  yellow  fever.     Phila.  Med.  Jl.,  6:  790-796,  1900. 
Shannon,  R.  C.,  et  al.    Yellow  fever  virus  in  jungle  mosquitoes.     Science,  88: 

iio-in,  1938. 
Smithburn,  K.  C.,  and  Haddow,  A.  J.     Isolation  of  yellow  fever  virus  from  African 

mosquitoes.    Amer.  Jl.  Trop.  Med.,  26:  261-271,  1946. 
*Soper,  F.  L.    Jungle  yellow  fever.    A  new  epidemiological  entity  in   South 

America.     Rev.  Hyg.  e  Saude  Publica,  TO:  107-144,  1936. 
* .    The  newer  epidemiology  of  yellow  fever.     Amer.  Jl.  Pub.  Hlth.  27:  1-14, 

1937- 
Stokes,  A.,  Bauer,  J.  H.,  and  Hudson,  N.  P.    The  transmission  of  yellow  fever  to 

Macacus  rhesus:  preliminary  note.     Jl.  Amer.  Med.  Assoc.,  90:  253-254,  1928. 
,  Bauer,  J.  H.,  and  Hudson,  N.  P.    Experimental  transmission  of  yellow  fever 

to  animals.    Amer.  Jl.  Trop.  Med.,  8:  103-164,  1928. 
**Taylor,  R.  M.,  and  Cunha,  J.  F.  da.     An  epidemiological  study  of  jungle  yellow 

fever  in  an  endemic  area  in  Brazil.  I,  II.    Amer.  Jl.  Trop.  Med.,  Suppl.,  26, 

1946. 
Wadell,  M.  B.,  and  Taylor,  R.  M.    Studies  on  the  cyclic  passage  of  yellow  fever 


MOSQUITOES  AND  HUMAN  WELFARE  373 

virus  in  South  American  mammals  and  mosquitoes.    Amer.  Jl.  Trop.  Med.,  25: 
225-230,  1945. 

Yellow  Fever.  Results  of  the  work  of  Maj.  Walter  Reed,  Medical  Corps,  United 
States  Army,  and  the  yellow  fever  Commission.  .  .  .  U.S.  6ist  Congress,  3d 
Session,  Senate  Document  822.  Washington,  D.C.,  1911. 

DENGUE 

Ashburn,  P.  M.,  and  Craig,  C.  F.     Experimental  investigations  regarding  the 

etiology  of  dengue  fever.     Philip.  Jl.  Sci.,  B,  2:  93—147,  1907. 
*Blanc,  G.,  and  Caminopetros,  J.    Recherches  experimentales  sur  la  dengue.    Ann. 

Inst.  Pasteur,  44:  367-436,  1930. 
Chandler,  A.  C.,  and  Rice,  Lee.     Observations  on  the  etiology  of  dengue  fever. 

Amer.  Jl.  Trop.  Med.,  3:  233-262,  1923. 
Cleland,  J.  B.,  Bradley,  B.,  and  MacDonald,  W.    Dengue  fever  in  Australia. 

Jl.  Hyg.,  16:  317-418,  1918;  18:  217-254,  1919. 
Mackerras,  I.  M.     Transmission  of  dengue  fever  by  Aedes  (Stegomyia)  scutellans 

Walk,  in  New  Guinea.     Trans.  Roy.  Soc.  Trop.  Med.  Hyg.,  40:  295-312,  1946. 
Perry,  W.  J.     The  dengue  vector  on  New  Caledonia,  the  New  Hebrides,  and  the 

Solomon  Islands.     Amer.  Jl.  Trop.  Med.,  28:  253-259,  1948. 
Schule,  P.  A.     Dengue  fever.     Ibid.,  8:  203-213,  1928. 
*Siler,  J.  F.,  Hall,  M.  W.,  and  Hitchens,  A.  P.     Dengue;  its  history,  epidemiology, 

mechanism  of  transmission,  etiology,   clinical  manifestations,   immunity,   and 

prevention.     Philip.  Bur.  Sci.,  Monograph  20,  1926. 
Simmons,  J.  S.     Dengue  fever.     Amer.  Jl.  Trop.  Med.,  n:  77-102,  1931. 
* ,  St.  John,  J.  H.,  and  Reynolds,  F.  H.     Experimental  studies  of  dengue, 

Philip.  Jl.  Sci.,  44:  1-251,  1931. 
,  et  al.    Transmission  of  dengue  fever  by  Aedes  albopictus  Skuse.    Philip. 

Jl.  Sci.,  41:  215-231,  1930. 
Usinger,  R.  L.     Entomological  phases  of  the  recent  dengue  epidemic  in  Honolulu. 

U.S.  Pub.  Hlth.  Repts.,  59:  423-430,  1944. 

FILARIASIS 

Bahr,  P.  H.    Filariasis  and  elephantiasis  in  Fiji.    Jl.  London  Sch.  Trop.  Med., 

Suppl.  i,  1912. 
Basu,  B.  C.,  and  Rao,  R.  S.     Studies  on  iilariasis.     Ind.  Jl.  Med.  Res.,  27:  233-249, 

J939- 
Brug,  S.  L.,  and  Rook,  H.  de.    Filariasis  in  Ned.-Ind.    Geneesk.  Tijd.  Ned.-Ind., 

70:451-474,1930. 
*Buxton,  P.  A.     Researches  in  Polynesia  and  Melanesia.    London  Sch.  Hyg.  Trop. 

Med.,  Mem.  2, 1928. 
,  and  Hopkins,  G.  H.  E.     Researches  in  Polynesia  and  Melanesia.    Ibid.,  Mem. 

i,  1927.     (Both  reports  beautifully  illustrated.) 


374  MEDICAL  ENTOMOLOGY 

Byrd,  E.  E.,  et  al.    Studies  on  filariasis  in  the  Samoan  area.    U.S.  Nav.  Med.  Bull., 

44:  1-20,  1945. 
Causey,  O.  R.,  et  al.    Studies  on   the   incidence   and   transmission   of  filaria, 

Wuchererla  bancrojti,  in  Belem,  Brazil.    Amer.  Jl.  Hyg.,  41:  143-149,  1945. 
Coggeshall,  L.  T.     Filariasis  in  servicemen:  retrospect  and  prospect.    Jl.  Amer. 

Med.  Assoc.,  131:  8-12,  1946. 
Edwards,  F.  W.    The  carriers  of  Filaria  bancrojti.    Jl.  Trop.  Med.  and  Hyg., 

25:  168-170,  1922. 
Francis,  E.    Filariasis  in  southern  United  States.     U.S.  Pub.  Hlth.  Serv.,  Hyg. 

Lab.,  Bull.  117,  1919. 
*Feng,  L.    Anopheles  hyrcanus  var.  sinensis  Wied.,  transmitter  of  Wuchereria 

(Filaria)  bancrojti  in  Woosung  district  Shanghai,  China.     Amer.  Jl.  Hyg.,  14: 

502-514,  1931. 
Flu,  P.  C.     Report  on  investigations  in  Surinam   (South  America),  Sept.   1927 

to  Dec.  1927.    Acta  Leidemsia,  3:  1-188,  1928. 
Giglioli,  G.     The  transmission  of  Wuchereria  bancrojti  by  Anopheles  darlingi  in 

the  American  tropics.    Amer.  Jl.  Trop.  Med.,  28:  71-85,  1948. 
Heydon,  G.  M.    Some  common  Queensland  mosquitoes  as  intermediate  hosts  of 

Wuchereria  bancrojti  (Filaria  bancrojti}.     Parasitology,  23:  415-427,  1931. 
Hu,  S.  M.  K.     Studies  on  host  relationships  of  Diro filaria  immitis  Leidy  and  its  culi- 

cine  intermediate  hosts.    Amer.  Jl.  Hyg.,  14:  614-629,  1931. 
.    Preliminary  observations  on  the  longevity  of  infective  larvae  of  Wuchereria 

bancrojti  in  Culex  pipiens  var.  pallens  Coq.     Chinese  Med.  JL,  49:  529-536, 

1935- 

.  Experiments  on  repeated  infections  of  filarial  larvae  in  Culex  pipiens  var. 

pallens  Coq.  Ibid.,  12:  13-18,  1937. 

.  Studies  on  the  susceptibility  of  Shanghai  mosquitoes  to  experimental  in- 
fection with  Wuchereria  bancrojti  Cobbold.  Peking  Nat.  Hist.  Bull.,  9:  249- 
260,  1935;  13:  39-52,  1938;  14:  15-22,  1939. 

Manson,  Patrick.  The  filaria  sanguinis  hominis  and  certain  new  forms  of  parasitic 
diseases  in  India,  China  and  warm  countries.  London,  1883. 

Menon,  T.  B.,  and  Ramamurti,  B.  The  behaviour  of  the  infective  larvae  of 
Wuchereria  bancrojti  with  special  reference  to  their  mode  of  escape  and  penetra- 
tion of  the  skin.  Ind.  Jl.  Med.  Res.,  29:  393-401,  1941. 

Newton,  W.  L.,  and  Pratt,  I.  Experiments  to  determine  potential  vectors  of 
Wuchereria  bancrojti  in  the  continental  United  States.  Amer.  Jl.  Trop.  Med., 
26:  699-706,  1946. 

,  Wright,  W.  H.,  and  Pratt,  I.  Experiments  to  determine  potential  vectors 

of  Wuchereria  bancrojti  in  the  continental  United  States.  Ibid.,  25:  253-261, 
1945. 

Taylor,  A.  W.  The  domestic  mosquitoes  of  Gadau,  Northern  Nigeria,  and  their 
relation  to  malaria  and  filariasis.  Ann.  Trop.  Med.  Parasit.,  24:  425-435,  1930. 


MOSQUITOES  AND  HUMAN  WELFARE  375 

*Yamada,  S.  An  experimental  study  on  twenty-four  species  of  Japanese  mos- 
quitoes regarding  their  suitability  as  intermediate  hosts  of  Filaria  bancrojti 
Cobbold.  Sci.  Kept.  Govt.  Inst.  Inf.  Dis.,  6:  559-622,  1928. 

ENCEPHALITIDES 

*Bishopp,  F.  C.    Mosquito  transmission  of  encephalomyelitis  or  brain  fever  of 

horses.    Jl.  Wash.  Acad.  Sci.,  29:  495-501,  1939. 
Davis,  W.  E.    A  study  of  birds  and  mosquitoes  as  hosts  for  the  virus  of  eastern 

equine  encephalomyelitis.     Amer.  JL  Hyg.,  32:  45-59,  1940. 
Getting,  V.  A.    Equine  encephalomyelitis  in  Massachusetts.    New  Eng.  Jl.  Med., 

224:  999-1006,  1941. 
**Hammon,   W.   McD.     The  arthropod-borne   virus   encephalitides.     Amer.   Jl. 

Trop.  Med.,  28:  515-525,  1948, 

,  and  Reeves,  W.  C.     Culex  tar  satis  Coq.,  a  proven  vector  of  St.  Louis  en- 
cephalitis.   Proc.  Soc.  Exp.  Biol.  Med.,  51:  142,  1942. 
,  and  Reeves,  W.  C.    Laboratory  transmission  of  St.  Louis  encephalitis.     Jl. 

Exp.  Med.,  78:  241,  1943. 
,  et  al.     Isolation  of  the  viruses  of  western  equine  and  St.  Louis  encephalitis 

from  Culcx  tarsalis.    Science,  94:  328-330,  1941. 
** ,  et  al.     Mosquito  vectors  and  inapparent  animal  reservoirs  of  St.  Louis 

and  western  equine  encephalitis  viruses.     Amer.  Jl.  Pub.  Hlth.,  33:  201-207, 

1943. 
Leake,  J.  P.    Epidemic  of  infectious  encephalitis.    U.S.  Pub.  Hlth.  Repts.,  56: 

1902-1905,  1941. 
Reeves,  W.  C.,  et  al.    Recovery  of  western  equine  encephalomyelitis  virus  from 

wild  bird  mites  (Liponyssus  sylvlarum)  in  Kern  County,  California.    Science, 

105:  411-412,  1947. 
Rempel,  J.  G.,  et  al.    Multiple  feeding  habits  of  Saskatchewan  mosquitoes.    Canacl. 

Jl.  Res.,  24:  71-78,  1946. 
Smith,  Margaret  M.,  et  al.    St.  Louis  encephalitis  infection  of  chicken  mites, 

Dermanyssus  gallinae,  by  feeding  on  chickens  with  viremia;  transovarian  pas- 
sage of  virus  into  the  second  generation.    Jl.  Exp.  Med.,  84:  1-6,  1946. 
* ,  et  al.    Experiments  on  the  role  of  the  chicken  mite,  Dermanyssus  gallinae, 

and  the  mosquito  in  the  epidemiology  of  St.  Louis  encephalitis.    Ibid.,  87:  119- 

138,  1948. 

RIFT  VALLEY  FEVER 

Daubney,  R.,  and  Hudson,  J.  R.    Rift  Valley  fever.    East  Afr.  Med.  JL,  10:  2-19, 

1933- 

Smithburn,  K.  C.,  Haddow,  A.  J.,  and  Gillett,  J.  D.  Rift  Valley  fever.  Isola- 
tion of  the  virus  from  wild  mosquitoes.  Brit.  Jl.  Exp.  Path.,  29:  107-121,  1948. 


CHAPTER  XII 


The  Problem  of 
Mosquito  Control 


E  preceding  chapter  has  outlined  briefly  the  important  relations  of 
JL  mosquitoes  to  human  welfare.  Though  these  have  been  known  for  many 
years,  only  recently  have  somewhat  adequate  measures  been  taken  to  reduce 
mosquito  abundance  and  then  mainly  in  the  control  of  disease-transmitting 
species.  This  is  exemplified  in  the  great  antimosquito  campaigns  where  special 
diseases  had  to  be  controlled  in  order  that  certain  national  developments  could 
be  undertaken  or  that  wars  could  be  prosecuted.  The  results  of  such  under- 
takings have  been  of  unprecedented  success.  Witness  the  work  in  the  Malay 
Peninsula,  Cuba,  the  Panama  Canal  Zone,  New  Jersey,  parts  of  California, 
Italy,  parts  of  Greece,  Palestine,  Singapore,  the  Tennessee  Valley,  and  recently 
in  the  conduct  of  the  Second  World  War  and  in  the  proposed  extermination  of 
malaria  in  the  United  States.  All  of  these  vast  control  operations  have  been 
organized  by  able  men  supported  by  governments  or  private  capital  in  order 
that  epidemic  diseases  might  be  brought  under  control  so  as  to  permit  certain 
national  developments.  Yet  despite  this,  vast  areas  of  the  most  fertile  regions 
of  the  world  suiTer  from  mosquito-borne  diseases  which  retard  and,  in  some 
cases,  prevent  their  agricultural  and  industrial  development.  Hoffman  (1916) 
made  a  plea  and  presented  a  tentative  plan  for  the  eradication  of  malaria 
throughout  the  Western  hemisphere.  His  plea  was  based  on  the  knowledge 
"that  malaria  is  perhaps  the  most  important  of  human  diseases,  and  though  it 
is  not  often  directly  fatal,  its  wide  prevalence  in  almost  all  warm  climates 
produces  an  enormous  amount  of  sickness  and  mortality."  Boyd  (1930)  desig- 
nates malaria  as  "the  worst  of  human  scourges";  Russell  (1943)  estimates  that 
even  today  there  are  3,000,000  deaths  each  year  from  malaria  and  at  least 
300,000,000  cases  of  malarial  fevers  annually  throughout  the  world. 

The  problem  of  mosquito  control  may  be  considered  from  two  viewpoints. 
First  is  the  reduction  and  control  of  species  known  to  be  good  vectors  of 


PROBLEM  OF  MOSQUITO  CONTROL  377 

disease — that  is,  species  control  or  eradication.  This  is  well  illustrated  by  the 
work  on  yellow  fever  (urban)  where  the  adequate  control  of  Aedes  aegypti 
will  bring  about  the  reduction  and  elimination  of  the  disease.  This,  however, 
does  not  apply  to  jungle  yellow  fever,  as  we  do  not  yet  know  all  the  complexes 
involved  in  control  of  this  disease  in  jungle  areas.  Species  control  is  also  practical 
for  dengue,  for  when  A.  aegypti,  A.  albopictus,  and  A.  scutellaris  are  brought 
under  control  the  disease  usually  disappears.  This  same  procedure  frequently 
applies  to  malaria.  In  our  own  country  the  control  of  Anopheles  quadrimacu* 
latus  would  mean  the  elimination  of  malaria  in  our  eastern  and  southern  states 
provided  no  new  vector  reached  our  shores.  An  adequate  demonstration  of  this 
procedure  is  well  illustrated  by  the  great  reduction  of  malaria  in  parts  of  north- 
eastern Brazil  by  the  control  and  eradication  of  the  introduced  vector  Anophe- 
les gambiae.  Many  more  examples  could  be  given  of  the  effectiveness  of  this 
procedure  in  controlling  human  disease  by  controlling  the  vector,  or  by  what 
is  called  "breaking  the  chain"  in  the  life  cycle  of  the  parasite  or  virus.  How- 
ever, in  the  case  of  encephalitides,  as  St.  Lou's  encephalitis,  eastern  and  western 
encephalitis,  etc.  the  control  of  specific  vectors  is  not  easily  possible,  not  only 
because  we  do  not  know  all  of  them,  but  because  it  would  be  difficult  to  conduct 
a  campaign  directly  against  those  we  do  know.  So  another  procedure  should 
be  considered.  In  planning  the  control  of  a  vector  of  a  disease  it  should  be 
decided  whether  all  pest  mosquitoes  ought  not  also  to  be  taken  into  account. 
When  an  insect-borne  disease  is  prevalent,  it  is  usually  not  difficult  to  arouse 
public  opinion  and  obtain  funds  for  adequate  control  work.  When  the  epi- 
demic subsides  the  control  operations  are  generally  discontinued  and  mos- 
quitoes breed  in  abundance  to  plague  the  inhabitants.  If  full  information  in 
such  a  campaign  is  given  that  all  mosquitoes  should  be  controlled  in  order 
that  the  inhabitants  may  enjoy  freedom  from  mosquitoes  as  well  as  the  dis- 
ease, the  good  work  can  continue.  This  would  increase  the  well-being  of  all 
and  adequately  provide  against  a  future  epidemic  of  the  disease. 

In  many  sections,  not  only  of  our  own  country  but  in  various  parts  of  the 
world,  a  wise,  well-organized,  well-directed  plan  of  mosquito  (and  of  flies 
and  other  pest)  control  by  cities,  towns,  counties,  or  other  units  would  bring 
about  a  gradual  reduction  of  these  noxious  insects,  prevent  the  outbreak  of 
disease,  reduce  or  eliminate  malaria,  permit  people  to  enjoy  their  gardens, 
playgrounds,  parks,  or  other  recreation  facilities  and  so  increase  land  and  real 
estate  values  that  the  actual  cost  would  be  more  than  repaid  by  the  increase 
in  taxable  values.  In  planning  such  work  several  fundamental  facts  must  be 
borne  in  mind.  In  the  first  place,  water  should  be  considered  one  of  the  first 
essentials  in  any  community  and  the  proper  handling  of  such  a  valuable  and 


378  MEDICAL  ENTOMOLOGY 

essential  natural  resource  must  be  given  first  consideration.  It  is  easy  to  elim- 
inate mosquito  breeding  if  we  eliminate  all  standing  water,  but  such  effective 
drainage  might  do  more  harm  than  good.  How  then  shall  such  a  problem  be 
solved?  In  planning  a  control  problem  the  area  in  which  operations  are  to  be 
conducted  should  be  thoroughly  studied  and  the  following  basic  knowledge 
obtained : 

1.  The  mosquitoes  breeding  in  the  control  area  should  be  determined  and 
all  breeding  places  definitely  located. 

2.  The  mosquitoes  breeding  outside  the  control  area  and  that  are  liable  to 
migrate  should  be  investigated.  This  need  not  be  an  intensive  survey  but 
it  should  be  careful  enough  to  avoid  sad  experiences  later  when  control  activi- 
ties are  under  way. 

3.  Topographical  or  aerial  maps  of  the  area  should  be  obtained,  and  all 
mosquito-breeding  places  as  well  as  all  water  areas  such  as  ponds,  wells, 
streams,  lakes,  and  swimming  pools  should  be  carefully  located  on  such 
maps. 

The  three  steps  stated  above  are  essential  lo  the  outlining  of  control  activi- 
ties. How  can  they  be  carried  out?  Successful  control  depends  on  scientific 
knowledge.  Mosquitoes,  either  in  the  adult  or  larval  stages,  can  be  identified 
only  by  those  who  know  them — not  by  those  who  think  they  know  them 
or  believe  that  all  mosquitoes  have  the  same  habits.  In  carrying  out  the  first 
step  much  data  may  be  obtained  on  breeding  areas  that  can  be  located  on 
the  topographical  map.  But  omitting  all  factors  but  the  first  one  for  the 
present,  let  us  see  the  problem  in  its  true  relation  to  control.  The  species  that 
is  mainly  responsible  can  usually  be  collected  during  an  outbreak.  If  it 
proves  to  be  the  common  house  mosquito,  Culex  pipiens,  the  types  of  breed- 
ing grounds  are  well  known,  and  certain  control  measures  are  indicated.  If 
it  proves  to  be  Aedes  vexans,  a  different  breeding  ground  is  assured,  and 
other  control  measures  must  be  applied.  If  the  main  outbreaks  are  due  to 
the  early  spring  species,  as  Aedes  stimulant,  A.  excrucians,  and  A.  fitchii, 
another  type  or  types  of  breeding  places  must  occur  in  or  near  the  area.  If 
anophelines  are  present  in  numbers,  then  still  other  types  of  breeding 
grounds  prevail  and  other  methods  of  control  are  indicated.  If  the  main 
outbreaks  are  due  to  such  migratory  forms  as  Mansonia  perturbans,  Aedes 
vexans,  A.  sollicitans,  A.  cantator,  or  A.  taeniorhynchus,  the  problem  be- 
comes more  complicated. 

The  second  step  is  necessary  in  order  that  the  species  breeding  in  the  area 
surrounding  the  district  under  control  may  be  known.  If  migratory  species 


PROBLEM  OF  MOSQUITO  CONTROL  379 

breed  here,  steps  will  have  to  be  taken  to  reduce  the  breeding  areas  as  much 
as  possible. 

The  third  step  may  be  combined  to  a  great  degree  with  the  first  if  deter- 
minations are  made  from  the  larvae.  Every  part  of  the  area  should  be  care- 
fully mapped;  all  standing  water,  streams,  ponds,  cisterns,  wells,  catch 
basins,  marshes,  or  lakes  should  be  accurately  located  on  a  large-scale  map.1 
All  such  places,  particularly  the  ponds,  streams,  bayous,  swamps,  etc.,  should 
be  carefully  described  so  that  changes  of  personnel  will  not  delay  the  work. 

When  the  above  information  is  at  hand,  a  definite  plan  for  the  ultimate 
reduction  and  elimination  of  breeding  grounds  may  be  undertaken.  Any 
plan  will  depend  largely  on  local  conditions,  the  extent  and  character  of  the 
breeding  grounds,  and  the  species  of  mosquitoes  involved.  The  only  known 
methods  now  available  are  drainage  operations,  filling  and  grading,  keeping 
the  banks  of  streams  and  large  ponds  clear  of  marginal  and  floating  vegetation, 
employment  of  surface-feeding  fishes,  oiling  operations,  and  the  use  of 
poisons  or  the  new  remarkable  insecticide,  DDT.  Any  plans  evolved  should 
be  in  co-operation  with  all  the  other  agencies  which  have  to  do  with  sanita- 
tion, city  or  rural  planning  commissions,  departments  of  public  works,  etc., 
and  such  work  should  be  under  the  immediate  direction  of  the  agency 
dealing  with  public  health.  It  is  too  early  yet  to  hope  for  states  or  provinces 
to  undertake  large-scale  operations  unless  it  is  in  particularly  malarious 
regions  and  then  only  in  co-operation  with  national  governments.  When 
the  co-operation  of  all  public  bodies  and  the  citizens  of  a  given  area  can 
be  obtained,  plans  should  be  carefully  prepared  and  continuity  of  activity 
is  essential  from  year  to  year. 

TYPES  OF  CONTROL  OPERATIONS 

When  a  plan  for  mosquito  reduction  suitable  for  the  area  under  con- 
sideration has  been  evolved,  particular  attention  should  be  paid  to  the  various 
methods  of  control.  A  few  of  these  may  be  briefly  outlined  here. 

DRAINAGE 

When  the  known  breeding  areas  are  fairly  well  determined  in  a  given 
district,  those  that  can  be  drained  or  greatly  reduced  by  drainage  should 
receive  the  most  careful  consideration.  Plans  for  drainage  should  be  made  by 

1  Such  maps  can  be  obtained  by  enlarging  the  topographical  maps  of  the  Geological 
Survey  or  aerial  maps. 


380  MEDICAL  ENTOMOLOGY 

expert  sanitary  or  drainage  engineers.  Careful  attention  should  be  paid  to 
the  type  of  drainage,  as  open  or  closed  drains,  the  grade  of  drainage,  and 
the  discharge  of  the  flow.  Where  water  has  to  be  discharged  from  a  diked 
tidal  area,  gates  must  be  provided  to  prevent  all  backflow.  This  is  true  only 
if  the  land  is  to  be  reclaimed  for  agricultural  or  other  developmental  pur- 
poses. Otherwise  open  ditches  with  clean  margins  will  permit  the  flushing 


Fig.  138.  Vicksburg,  Mississippi.  Upper:  Before  malaria  control  drainage. 
Lower:  After  construction  of  reinforced  concrete  invert  with  sodded  banks. 
(Courtesy  Mr.  Rector  and  Mississippi  State  Board  of  Health.) 

of  these  areas  at  each  high  tide.  If  the  drainage  is  well  done,  all  water  will 
be  carried  away  within  a  few  days  and  thus  prevent  a  brood  of  mosquitoes 
reaching  maturity.  Furthermore,  the  inflow  of  the  tides  will  bring  an  abun- 
dance of  fishes,  which  will  aid  in  devouring  any  mosquito  larvae  present 
along  the  drains  or  that  hatch  with  the  presence  of  water.  The  problems  of 
salt-marsh  drainage,  diking,  pumping,  and  the  maintenance  of  ditches,  are 
all  very  difficult,  but  exceptional  progress  has  been  made  in  New  Jersey 
and  California.  In  the  interior,  where  discharge  into  rivers,  bayous,  or  lakes 


PROBLEM  OF  MOSQUITO  CONTROL  381 

subject  to  rise  in  levels  takes  place,  drainage  gates  should  be  installed.  Various 
types  are  on  the  market,  and  full  information  can  be  obtained  from  engineer- 
ing firms. 

Drainage  should  be  carried  out  only  by  experts.  If  well  and  carefully  done 
(Fig.  138),  the  value  of  reclaimed  lands,  either  for  agricultural,  develop- 
mental, or  industrial  purposes,  will  often  more  than  repay  the  original  cost. 
All  drainage  work  must  be  carefully  inspected  from  time  to  time  in  order 
that  it  be  kept  functioning  properly. 

FILLING  AND  GRADING 

Filling  and  grading  operations  should  be  devej^ped  as  a  continuous  pro- 
cedure. Plans  for  this  work  can  be  made  only  when  the  mosquito-breeding 
areas  are  rdther  definitely  located,  and  the  work  should  be  done  in  co- 
operation with  whatever  organizations  have  supervision  of  public  works — 
park  commissions,  town-  or  city-planning  commissions,  building  commis- 
sions, etc.  In  this  way  all  temporary  pools;  stagnant  and  unsightly  ponds; 
borrow  pits;  pools  formed  along  railway  embankments,  by  road  or  street 
construction,  by  building  operations  of  all  kinds,  and  by  the  impounding 
of  water  for  city  water  supplies;  and  all  operations  of  whatever  kind  that 
may  bring  about  standing  or  stagnant  water  will  be  brought  under  the 
supervision  of  those  in  charge  of  mosquito-control  work.  By  careful  co- 
ordination of  these  various  activities  new  ponds  or  pools  may  be  avoided, 
and  many  old  ones  can  be  filled  with  the  minimum  amount  of  labor  and 
cost.  This  feature  of  mosquito-control  operations  is  one  of  the  most  impor- 
tant in  cities,  villages,  and  towns.  Full  authority  by  law  should  be  provided 
for  carrying  out  effectively  the  sanitary  regulations  involved  in  any  or  all 
such  operations. 

STREAMS  AND  PERMANENT  PONDS 

Local  streams,  rivers,  and  permanent  and  impounded  bodies  of  water 
present  many  difficulties.  Where  the  streams  are  sluggish  and  the  banks 
have  marginal  vegetation,  with  little  side  pools,  bayous,  bottom  lands  sub- 
ject to  overflow,  etc.,  the  problem  becomes  complicated.  As  far  as  possible, 
the  stream  should  be  diverted  in  a  direct  course  with  the  maximum  amount 
of  fall.  The  vegetation  and  shrubbery  should  be  removed  but  not  so  as  to 
give  an  unsightly  appearance.  All  rocks  and  debris  that  prevent  a  free  flow 
or  may  provide  stagnant  pools  during  drought  should  be  removed.  Bot- 
tom lands  subject  to  flood  may  be  drained  by  subsoil  drains.  The  control 


382  MEDICAL  ENTOMOLOGY 

work  along  streams  and  rivers  should  be  made  as  permanent  as  possible. 
In  the  case  of  large  ponds  or  reservoirs  that  must  not  be  drained,  it  is 
possible  to  reduce  and  even  prevent  mosquito  breeding.  Such  bodies  of  water 
should  have  clear  margins;  the  trees  and  shrubbery  should  be  removed  for 
some  distance  from  the  banks;  flotage  and  the  growth  of  all  types  of  floating 


Fig.  739.  Upper:  A  clean  shore  line  where  breeding  of  anophelines  is  practically  elimi- 
nated. Lower:  An  area  where  it  is  practically  impossible  to  obtain  a  clean  shore  line  and 
breeding  is  abundant.  (Wheeler  Lake,  Tennessee  River.) 

vegetation  should  be  prevented  (Fig.  139).  This  will  allow  free  wind  action, 
which  will  largely  prevent  oviposition;  the  removal  of  the  shrubbery  de- 
stroys the  resting  and  hiding  places  for  the  adults.  This  method  of  procedure 
has  been  found  quite  successful  in  some  sections  of  Louisiana  where  stagnant 
water  in  bayous  has  been  impounded  by  damming,  raising  the  water  level, 
clearing  out  debris,  and  removing  the  shrubbery.  Here  it  was  not  possible 
to  drain  as  the  river  level  was  higher  than  that  of  the  bayous  and  pumping 


PROBLEM  OF  MOSQUITO  CONTROL  383 

was  not  advisable,  so  the  experiment  of  impounding  these  waters  was  tried 
and  proved  successful.  This  type  of  water  storage  should  be  attempted  in 
other  sections  of  the  country. 

Local  conditions  create  special  problems,  but  as  our  knowledge  of  mos- 
quito biology  increases,  methods  may  be  devised  to  prevent  or  control  breed- 
ing. In  many  parts  of  the  tropics  the  most  hopeless  situations  have  been 
valiantly  attacked,  and  the  results  have  been  successful  beyond  the  fondest 
hopes.  It  would  therefore  appear  that  even  the  most  difficult  situation  in 
America  can  be  successfully  attacked  if  we  have  the  courage  and  perseverance 
to  push  on  to  the  end. 

IMPOUNDED  WATERS 

The  problem  of  mosquito  control,  particularly  of  anophelines  that  are  ac- 
tive vectors  of  malaria,  in  areas  where  there  has  been  extensive  impoundage 
of  water  for  power,  flood  or  erosion  control,  or  fish  ponds  has  become  a 
major  one  in  many  parts  of  the  world  as  well  as  in  our  own  country.  Here  the 
problem  of  water  management  is"  *t>T  great  importance.  Kiker  and  Strom- 
quist  (1939)  have  laid  down  the  essential  requirements  in  the  preparation 
of  a  reservoir  for  impoundage:  "That  the  reservoir  be  cleared  so  as  to  present 
a  clean  water's  surface  after  impoundage  between  maximum  and  minimum 
water  levels;  and  that  all  depressions  between  maximum  and  minimum  water 
levels  be  drained  so  as  to  provide  water  level  fluctuation  with  the  reservoir." 
When  water  is  impounded  in  this  manner,  the  problem  of  anopheiine  control 
is  greatly  simplified.  In  addition  to  the  usual  control  measures,  outlined  in 
the  next  few  pages,  a  system  of  fluctuating  water  levels  will  show  marked 
results  in  the  reduction  of  mosquito  breeding.  During  the  breeding  season 
the  water  level  is  lowered  at  regular  intervals  and  then  raised  to  within  an 
inch  or  more  of  the  previous  level.  The  period  of  each  fluctuation  is  usually 
about  a  week.  This  procedure  may  be  called  "cyclical  fluctuation  with  water- 
level  recession."  By  this  method  shore-line  debris  is  stranded  and  marginal 
vegetation  is  largely  prevented  from  gaining  a  foothold.  The  problems  of 
marginal  vegetation  and  debris  are  most  important  since  such  protected  areas 
are  ideal  places  for  mosquito  breeding.  Until  more  is  learned  of  the  biology 
of  shore-line  aquatic  and  semiaquatic  plants  not  much  further  progress  can 
be  made  in  the  management  of  shore-line  problems.  The  only  thing  that  can 
be  done  on  the  basis  of  our  present  knowledge  is  to  maintain  clean  shore 
lines  (Fig.  139)  by  every  available  means  as  well  as  by  water-level  fluctuation 
and  recession. 

When  feasible  it  has  been  found  advantageous  to  maintain  high  water 


384  MEDICAL  ENTOMOLOGY 

levels,  above  the  maximum  "mosquito  control"  elevation,  at  the  beginning 
of  the  growing  season  in  order  to  delay  the  development  of  marginal  vege- 
tation. This  constant-level  phase  should  be  maintained  until  significant 
anopheline  production  begins.  Such  a  procedure  will  prevent  the  seeds  of 
some  objectionable  plants  from  gaining  a  foothold  in  the  marginal  areas 
and  thus  give  a  cleaner  shore  line  later  in  the  season  when  anopheline  pro- 
duction is  at  its  maximum. 

OILS  AND  OILING  OPERATIONS 

Kerosene  oil  was  one  of  the  first  oils  suggested  and  used  for  the  killing 
of  mosquito  larvae.  It  is  still  used  and  is  very  effective,  but  the  film  formed 
on  the  water  surface  is  soon  broken  down,  especially  in  warm  climates.  At 
present  various  grades  of  petroleum  oils  are  extensively  used  throughout 
the  world.  In  order  to  act  effectively  an  oil  should  have  the  following  quali- 
fications: (a)  it  should  be  highly  toxic  to  larvae  and  pupae;  (b)  it  should 
spread  evenly  and  rapidly  on  all  kinds  of  water;  (c)  it  should  penetrate 
through  debris  and  vegetation;  (cl)  it  should  form  a  fairly  stable  and  lasting 
film;  (e)  it  should  be  noninjurious  to  man  and  not  kill  fish,  waterfowl,  or 
plant  life;  and  (f)  its  cost  should  be  reasonable.  Such  an  oil  is  not  easily 
obtainable,  and  various  types  are  employed  to  meet  the  conditions  under 
which  they  are  used. 

How  oils  kill  mosquito  larvae  is  not  very  well  understood.  It  is  generally 
stated  that  the  oil  film  is  drawn  into  the  tracheal  system,  and  if  the  oil  is  of 
high  volatility,  the  toxic  action  is  very  rapid  owing  to  the  penetration  of  the 
tissues.  If  the  oil  is  of  low  volatility  and  viscosity,  the  death  of  the  larvae  and 
pupae  is  probably  due  to  suffocation. 

After  extensive  investigations  and  field  trials  the  New  Jersey  Experiment 
Station  recommends  an  oil  with  the  following  qualities:  type — distillate  fuel 
oil;  gravity  (A.P.I.)— 27-33;  flash— 130°  F.  or  higher;  viscosity  S.U.  at  100° 
F. — 35  to  40;  distillation — 10  per  cent  at  43o°-45o°  F.,  50  per  cent  at  5io°-55o° 
F.,  90  per  cent  at  630°  F.  and  higher.  This  oil  spreads  well,  will  give  a  prac- 
tically perfect  kill  of  larvae  and  pupae  within  a  few  hours  after  application, 
and  leaves  a  fairly  stable  film.  Under  normal  conditions  the  film  will  not  last 
more  than  ten  days  to  two  weeks.  This  requires  that  fresh  applications  be 
made  whenever  breeding  is  observed.  The  amount  of  oil  required  varies  ac- 
cording to  the  breeding  area  and  the  vegetation  present.  Twenty-five  to  sixty 
gallons  will  usually  cover  any  given  acre  of  water  surface. 

Fuel  oil  as  described  above  is  rather  objectionable  on  small  ponds  in  pri- 
vate grounds,  on  fish  ponds,  on  ponds  containing  aquatic  ornamental  plants, 


PROBLEM  OF  MOSQUITO  CONTROL  385 

on  ponds  frequented  by  waterfowl,  or  in  similar  aquatic  situations.  To  meet 
this  objection  the  New  Jersey  Experiment  Station  devised  a  mixture  of 
pyrethrum  and  oil  known  as  the  New  Jersey  Pyrethrum  Mosquito  Larvicide. 
It  is  composed  of  66  per  cent  kerosene  or  similar  light  petroleum  distillate; 
0.07  per  cent  pyrethrins;  33.5  per  cent  water;  and  0.5  per  cent  sodium  lauryl 
sulfate.  This  is  a  stock  solution  and  is  diluted  i  part  to  10  parts  of  water 
before  using.  It  kills  larvae  and  pupae  promptly,  is  not  injurious  to  fish,  plants, 
or  waterfowl,  but  does  not  give  any  lasting  film. 


Fig.  140.  A  shoulder  spray  tank  used  in  spraying  small  ponds.  (Courtesy 
Connecticut  Agriculture  Experiment  Station.) 

In  the  Panama  Canal  Zone  Curry  (1943)  reports  most  effective  control  of 
larvae  and  pupae  by  the  use  of  ordinary  bunker  fuel  oil  as  furnished  by  the 
United  States  Navy.  The  oil  spreads  well  and  kills  promptly;  the  film  is 
effective  for  about  two  weeks  under  the  hot  tropical  sun.  In  general  any  good 
fuel  oil  is  highly  toxic  to  mosquito  larvae.  However,  practically  all  these 
oils  are  not  very  effective  on  water  heavily  charged  with  sewage. 

The  time  of  applying  oil  is  of  great  importance.  In  many  sections  of  the 
country  where  the  early  spring  species  are  the  chief  menace  the  oil  must  be 
applied  before  the  adults  have  emerged.  Many  of  these  species  have  only  a 
single  brood  each  season;  hence  the  control  measures  must  be  carried  out  at 
the  proper  time.  In  sections  of  the  country  where  there  are  several  to  many 
annual  broods  or  where  different  species  breed  at  different  times  the  timing 


386  MEDICAL  ENTOMOLOGY 

of  the  oiling  operations  is  very  important.  Oil  films  break  down  in  a  short 
time,  rarely  lasting  more  than  ten  days  to  two  weeks.  In  cooler  climates  the 
oil  film  is  effective  longer  than  in  hot  climates.  Severe  rainstorms  may  also 
affect  the  oil  film.  Careful  inspection  is  essential  to  determine  the  timing  and 
effectiveness  of  the  oiling  operations. 

The  method  of  applying  the  oils  will  depend  largely  on  the  area  to  be 
covered,  its  accessibility  to  roadways,  and  the  difficulties  of  actually  reaching 
the  water.  On  small  ponds  and  streams,  in  wooded  areas,  in  marshes,  swamps, 
and  similar  places,  the  ordinary  shoulder  spray  tank  is  most  satisfactory 
(Fig.  140).  Here  the  pressure  is  obtained  by  compressed  air,  and  any  size 


Fig.  141.  A  power  sprayer  used  in  oiling  large  areas  accessible  to 
roadways.  (Courtesy  Bergen  County,  New  Jersey,  Mosquito  Commis- 
sion.) 

of  nozzle  may  be  used  but  preferably  one  that  gives  a  fine  mistlike  spray. 
In  areas  accessible  to  trucks,  as  along  roadways,  extensive  narrow  marshes, 
or  swamps,  the  oil  may  be  applied  from  an  auto  truck  having  a  tank  and  a 
pump  driven  by  the  engine  of  the  truck  (Fig.  141).  Such  power-driven  spray 
outfits  are  in  extensive  use  in  orchards,  parks,  and  woodland  areas  to  control 
insect  pests.  They  can  easily  be  employed  in  antimosquito  campaigns.  By 
the  use  of  several  leads  of  hose,  and  lengthening  them,  extensive  areas  can 
be  covered  in  a  minimum  time.  Their  use  will  depend  entirely  on  local 
conditions  and  their  availability. 

Many  other  methods  of  applying  oil  have  been  tried  and  some  are  in  use. 
Streams,  ditches,  and  ponds  have  been  treated  by  placing  barrels  filled  with 
oil  above  them,  the  barrels  being  so  constructed  that  a  constant  drip  reaches 


PROBLEM  OF  MOSQUITO  CONTROL  387 

the  surface  of  the  water.  The  oil  is  gradually  carried  onward  by  the  stream 
or  spreads  slowly  over  the  surface.  This  is  not  very  satisfactory  owing  to  the 
failure  of  the  oil  film  to  penetrate  the  grassy  margins,  drift,  or  flotage.  Waste 
soaked  in  oil  and  anchored  in  ponds  has  the  same  drawbacks.  Fine  sand 
soaked  in  oil  and  sowed  broadcast  over  ponds  has  given  satisfactory  results. 
As  the  sand  falls  on  the  water  or  sinks  through  the  vegetation  to  the  water 
surface,  the  oil  is  given  off  and  leaves  a  good  film. 

In  large  lakes,  ponds,  and  reservoirs,  where  the  margin  and  flotage  is  not 
easily  accessible  except  by  small  boats,  a  tank  placed  in  a  boat  and  fitted  with 
a  pump  to  give  the  necessary  pressure  may  be  employed  (Fig.  142).  The  pump 


Fig.  142.  Spraying  a  shore  line  with  a  petroleum  oil  mixture  for  mosquito  control  from 
a  power  boat.  (Courtesy  Tennessee  Valley  Authority,  Division  of  Health.) 

may  be  used  to  force  the  oil  out  directly  or  it  may  be  used  to  compress  the 
air.  If  air  compression  is  employed,  pumping  is  not  continuous  and  in  gen- 
eral a  better  and  more  even  spray  may  be  obtained. 

In  all  oiling  work  the  most  essential  points  are  the  use  of  a  good,  free- 
running,  toxic  oil,  good  equipment,  and  extreme  care  in  covering  all  the 
water  surface  with  a  film  of  oil.  The  laborers  should  be  carefully  trained 
and  their  work  constantly  supervised  by  reliable  inspectors. 

POISONS 

In  recent  years  poisons  have  been  used  extensively  for  the  control  of  anophe- 
lines.  As  the  larvae  are  surface  feeders,  any  poison  that  will  remain  at  the 
surface  or  on  the  surface  film  for  a  short  time  will  be  eaten  by  them.  In  this 
work  Paris  green  has  been  found  most  efficient  and  has  been  employed  ex- 


388  MEDICAL  ENTOMOLOGY 

tensively  in  areas  where  malaria  is  endemic.  The  Paris  greeri  is  diluted  with  a 
diluent  such  as  soapstone,  hydrated  lime,  or  road  dust  and  dusted  on  the 
surface  by  various  means.  When  well  done,  the  results  are  almost  perfect, 
destroying  practically  100  per  cent  of  the  anopheline  larvae.  More  recently 
airplanes  have  been  employed,  which,  carrying  specially  designed  apparatus, 
have  dusted  large  areas  of  marshes,  swamps,  densely  wooded  areas,  lakes, 
and  reservoirs  with  the  greatest  success.  Only  a  pound  to  a  pound  and  a  half 
of  Paris  green  need  be  used  per  acre.  The  most  important  problems  in  this 
work  are  to  determine  the  correct  diluent  and  the  particle  size  of  the  Paris 
green  in  order  that  the  dust  may  settle  promptly  and  remain  for  some  time 
on  the  surface  film.  In  dusting  either  by  hand  or  by  airplane  the  work  must 


Fig.  143.  Airplane  dusting  with  Paris  green  for  the  control  of  Anopheles  larvae. 
(Courtesy  Tennessee  Valley  Authority,  Division  of  Health.) 

be  done  when  there  is  no  wind,  usually  in  the  early  morning  hours,  or  much 
of  the  material  will  be  lost.  Furthermore  the  pilots  must  be  trained  for  low 
flying,  20  to  50  feet  above  the  water  surface  (Fig.  143).  As  yet  no  successful 
way  has  been  found  to  destroy  the  larvae  of  culicines  by  poisons,  though  much 
experimental  work  has  been  directed  to  this  end. 

Recently  it  has  been  shown  that  borax,  in  concentrations  of  two  to  two  and 
a  half  ounces  per  gallon  of  water,  is  effective  in  preventing  mosquito  breeding 
in  rain-water  barrels,  cisterns,  and  similar  containers.  Borax-treated  water 
should  not  be  used  for  drinking  purposes.  It  is  excellent  for  washing  purposes. 
The  advantage  of  borax  over  oil  is  that  it  is  permanent  and  needs  only  to  be 
renewed  when  the  cisterns,  etc.,  are  refilled  by  fresh  water.  Water  barrels  so 
treated  have  remained  all  summer  without  further  treatment.  It  is  only  neces- 
sary to  add  more  borax  when  the  barrels  are  refilled  by  fresh  rain  water. 

Many  other  substances  are  under  investigation,  such  as  derris,  pyrethrum 


PROBLEM  OF  MOSQUITO  CONTROL  389 

powder,  and  other  arsemcals,  and  methods  of  employing  them  against  the 
non-surface-feeding  culicines  will  undoubtedly  develop. 

DDT  AS  A  LARVICIDE 

During  the  Second  World  War  a  new  insecticide  appeared  and  received  de- 
served attention.  This  is  DDT  or  dichloro-diphenyl-trichloroethane  or  as  2,2-bis 
(/7-chlorophenyl)  -i-i,  i-trichloroethane.  It  is  a  white  crystalline  solid  and  was 
first  produced  in  1874  by  Zeidler,  a  German  chemist.  Its  melting  point  is  108° 
to  109°  C  (226.4°  to  228.2°  F.).  It  is  practically  insoluble  in  water  but  dis- 
solves in  many  organic  solvents  as  the  following: 

Solvent  Grams  DDT  in  100  cc.  solvent 

Cyclohexanone  100  to  120 

Benzene  77  to  83 

Xylene  56  to  62 

Acetone  50  to  55 

Diesel  oil  No.  2  10  (approx.) 

Kerosene,  crude  8 

Kerosene,  refined  4 

Velsicol  20  --)- 

ir 
DDT  has  been  experimented  with  in  various  forms  by  many  workers  in 

the  United  States,  in  war  areas,  and  in  other  parts  of  the  world.  At  present  the 
following  methods  may  be  employed: 

1.  A  0.5  per  cent  DDT  in  refined  kerosene  (water  white)  or  Diesel  oil  No. 
2  at  the  rate  of  0.05  pound  per  acre  gave  good  control  of  larvae  in  Tennessee 
Valley  Authority  experiments.  This  would  mean  the  application  of  about 
1.3  gallons  of  the  mixture  per  acre.  This  preparation  would  require  4  pounds 
of  DDT   (pure)   or  20  pounds   (20  per  cent  DDT)   to  each   100  gallons 
of  kerosene  oil  and  it  should  be  applied  at  the  rate  stated  above.  A  5  per  cent 
petroleum  oil  solution  may  be  prepared  by  dissolving  21/s  pounds  of  DDT  in 
5  gallons  of  No.  2  fuel  oil  or  kerosene  oil.  For  treatment  use  only  at  the  rate 
of  2  quarts  per  acre  of  water  surface.  The  spray  must  be  applied  as  a  fine  mist 
with  slow  delivery. 

2.  A  wettable  DDT  powder  containing  50  per  cent  DDT  could  be  used 
in  the  same  proportions  in  ordinary  water.  This  would  require  8  pounds  of 
the  powder  to  each  100  gallons  of  water,  but  it  should  probably  be  applied 
at  a  higher  rate  as  2  to  5  gallons  per  acre.  For  culicine  larvae  these  dosages 
should  be  increased  about  2  times  or  slightly  more.  This  form  of  DDT  is 
usually  referred  to  as  a  suspension. 

3.  Water  emulsions  are  prepared  by  dissolving  DDT  in  one  of  the  solvents 


39o  MEDICAL  ENTOMOLOGY 

and  adding  a  wetting  agent  or  emulsifier  to  form  a  concentrate.  One  of  the 
concentrates  recommended  is  25  pounds  of  DDT  and  4  pounds  of  Triton 
X-ioo  in  71  pounds  of  xylene.  Dilutions  are  made  by  adding  the  required 
amount  of  the  concentrate  to  water  slowly,  with  continuous  stirring.  A  5 
per  cent  emulsion  of  DDT  is  prepared  by  adding  i  volume  of  the  concentrate 
to  4  volumes  of  water  or  i  volume  of  concentrate  to  24  volumes  of  water  for 
a  i  per  cent  emulsion  and  so  on.  As  emulsions  mix  promptly  with  water, 
the  effect  of  DDT  on  other  aquatic  organisms  as  Crustacea,  fish,  and  aquatic 
insects  other  than  mosquito  larvae  may  be  detrimental.  At  present  the  al- 
lowable amount  of  DDT  to  prevent  damage  is  about  o.i  pound  per  acre  of 
water  surface.  This  would  mean  using  about  2  gallons  or  less  of  a  i  per  cent 
emulsion  per  acre  so  as  not  to  exceed  0.05  p.p.m.  of  DDT  in  the  water.  In 
cisterns,  wells,  urns,  or  otiier  containers  the  water  of  which  is  not  used  for 
drinking  purposes  the  dosages  should  be  increased  to  double  or  more  and 
thus  give  more  lasting  control. 

4.  DDT  as  an  aerosol  is  handled  by  airplanes  adapted  for  atomizing  an  oil 
solution  of  DDT.  The  solution  (20  per  cent  DDT  in  Velsicol  NR-70  as  em- 
ployed by  the  Tennessee  Valley  Authority)  is  carried  in  the  plane  (Stearman 
17),  and  by  means  of  pumps  it  is  forced  into  a  pipeline  from  the  engine  exhaust 
line  (4-inch  pipe)  just  in  front  of  a  standardized  venturi  so  as  to  give  a 
mistlike  spray  with  droplets  of  25  to  50  microns  in  size.  By  using  such  stand- 
ardized equipment  an  effective  swath  of  200  feet  wide  could  be  covered  each 
trip  by  the  plane,  and  this  would  give  eflective  control  (about  90  per  cent 
larval  kill).  The  amount  applied  at  each  treatment  was  o.i  pound  per  acre 
of  water  surface.  Sixteen  routine  treatments  in  a  single  season  over  the  same 
area  gave  excellent  control  of  mosquito  larvae  and  had  no  appreciable  effect 
on  fish  food  organisms  (though  most  surface  Hemiptera  were  destroyed). 
However,  good  results  have  been  obtained  by  applying  as  little  as  0.05  pound 
per  acre  of  water  surface. 

5.  Many  successful  attachments  for  spraying  DDT  have  been  developed 
for  various  types  of  planes.  For  ordinary  routine  work  involving  considerable 
areas  the  Stearman  17  and  various  types  of  Army  and  Navy  planes  have 
proved  very  effective.  The  spray  is  delivered  under  pressure  of  about  100 
pounds  per  square  inch  by  means  of  a  pump  and  is  delivered  through  a 
breaker  bar  placed  on  the  underside  of  the  lower  wing  on  each  side.  Along 
each  breaker  bar  are  located  a  varying  number  of  spray  nozzles  of  the  proper 
type  to  give  the  desired  spray  coverage.2  Using  such  a  plane  a  large  area  can 

2  The  breaker  bar  has  recently  been  largely  replaced  by  a  system  of  atomizing  nozzles 
located  along  the  trailing  edge  of  the  wings,  or  at  outer  corners  of  wings  and  tail. 


PROBLEM  OF  MOSQUITO  CONTROL  391 

be  covered  with  a  highly  concentrated  DDT  solution  in  very  small  amounts. 
The  amounts  applied  per  acre  varies,  but  good  results  have  been  obtained  by 
applying  as  little  as  o.i  pound  of  DDT  per  acre  as  sprays  (0.2  quarts  of  a  20 
per  cent  DDT  solution). 

DDT  AS  AN  ADULTICIDE 

The  application  of  DDT  solutions  to  the  surface  of  buildings,  both  within 
and  vvithout,  have  given  good  results  in  killing  adult  mosquitoes  and  other 
insects.  As  a  result  of  numerous  experiments  the  desired  deposit  (residual) 
to  give  adequate  kill  is  about  200  milligrams  of  DDT  per  square  foot.  This 
is  obtained  by  using  a  5  per  cent  DDT  solution  in  kerosene  oil  (5  pounds  of 
DDT  in  i2/{>  gallons  of  kerosene  oil).  To  obtain  r  residue  of  200  milligrams 
per  square  foot  requires  about  i  gallon  of  the  5  per  cent  mixture  per  1000 
square  feet.  In  applying  the  material  a  fine,  not  a  mist,  spray  is  required,  and 
it  should  be  under  a  pressure  of  40  to  50  pounds  so  as  to  cover  the  surface 
without  any  runoff.  Such  a  deposit  when  well  applied  will  give  adequate  kill 
for  over  a  month  or  longer.  Such  deposits  can  be  obtained  by  the  use  of  hand 
sprayers,  knapsack  sprayers,  or  power  sprayers  so  long  as  adjustments  are 
made  to  leave  the  proper  amounts.  This  type  of  anopheline  control  has  shown 
good  reduction  of  malarial  incidence  in  areas  where  extensive  spraying  of 
all  buildings  (on  the  inside)  has  been  undertaken.  More  recently  the  wettable 
DDT  suspensions  have  also  given  good  kill  of  adults  (mosquitoes  and  flies). 
The  50  per  cent  wettable  DDT  is  usually  employed  only  outside  on  gardens, 
shrubbery,  trees,  about  bases  of  houses,  and  inside  barns,  chicken  houses,  and 
similar  buildings.  The  wettable  DDT  gives  good  results  when  applied  in- 
doors at  concentrations  of  5  to  12  pounds  in  50  gallons  of  water,  but  usually 
leaves  undesirable  deposits  in  private  homes. 

Aerosol  bombs  have  been  employed  for  some  time  for  the  killing  of  adult 
mosquitoes  and  flies.  These  bombs,  in  various  sizes,  are  on  the  market  and 
full  directions  for  their  use  are  stamped  on  each  bomb. 

DDT  FOR  THE  DESTRUCTION  OF  HIBERNATING  ADULTS  : 

Not  much  work  has  been  done  in  this  field  owing  to  the  difficulty  of  de- 
termining the  main  places  of  hibernation.  However,  Aitken  (1946)  describes 
such  a  treatment  in  an  area  of  some  93  square  miles  in  Italy.  All  the  houses, 
barns,  outbuildings,  and  places  of  shelter  were  thoroughly  treated  so  as  to 
give  about  83  milligrams  of  DDT  per  square  foot.  The  results  indicated  a 
marked  decrease  in  anopheline  breeding  the  year  following  treatment.  There 
was  also  a  recession  of  malaria  from  a  splenic  index  of  43  per  cent  to  25 
per  cent  and  a  parasitemia  from  21  per  cent  to  i  per  cent.  In  an  area  where 


392  MEDICAL  ENTOMOLOGY 

no  such  treatment  was  given  the  malaria  index  showed  a  marked  increase. 
Soper  et  al.  (1947)  indicates  somewhat  similar  results  from  the  treatment 
of  all  buildings,  etc.,  in  an  area  of  120  square  miles  in  the  Tiber  Delta,  Italy. 
They  used  6.5  per  cent  DDT  in  kerosene  so  as  to  leave  about  200  milligrams 
of  DDT  per  square  foot  of  surface.  This  method  should  prove  of  value  in 
areas  where  the  main  hibernating  places  of  the  anopheline  carriers  are  mainly 
buildings  of  the  local  inhabitants. 

NATURAL  ENEMIES  AS  CONTROLS 

Mosquitoes  have  many  natural  enemies,  both  as  predators  and  parasites. 
Certain  species  of  birds,  bats,  and  insects  prey  upon  them,  but  their  effec- 
tiveness in  reducing  the  mosquito  population  does  not  appear  very  marked. 
Many  species  of  fish  feed  on  the  larvae  and  certain  top-feeding  fishes  (min- 
nows, gold  fishes,  etc.)  have  been  employed  in  attempts  to  reduce  mosquito 
abundance.  Gambusia  affinis  is  probably  one  of  the  most  valuable  of  top 
minnows  as  it  is  hardy,  breeds  rapidly,  and  normally  frequents  shallow  water 
suitable  for  mosquito  breeding.  Gambusia  holbroohj,  a  close  relative  of  G. 
affinis,  has  been  carefully  studied  by  Hildebrand  (1925)  and  his  conclusions 
warrant  the  utilization  of  this  species  wherever  it  can  be  employed.  His  ex- 
periments covered  a  considerable  range  of  aquatic  environments,  especially 
those  with  dense  growths  of  water  plants,  and  he  found  that  Gambusia  hol- 
broolft  brought  about  a  very  marked  decrease  in  mosquito  breeding.  In  no 
single  instance  was  the  control  perfect,  but  in  certain  experiments  the  results 
almost  approached  complete  control.  Gambusia  affinis  is  a  native  minnow  of 
the  great  Mississippi  Valley;  G.  holbroofy,  native  to  the  Atlantic  watershed; 
yet,  despite  their  present  wide  distribution  and  abundance,  reliance  on  mos- 
quito control  by  these  fishes  depends  largely  on  introducing  them  into 
mosquito-breeding  ponds,  lakes,  streams,  etc.,  frequently  each  year.  Further- 
more, in  order  that  the  fishes  may  do  effective  work,  dense  growths  of  aquatic 
vegetation  must  be  prevented.  The  maintenance  of  top-minnow  hatcheries  is 
not  difficult  so  that  the  costs  of  fish  control  are  not  high.  Though  G.  affinis 
has  been  introduced  into  many  parts  of  the  world  and  striking  successes  have 
attended  its  introduction,  yet  too  much  hope  must  not  be  placed  on  fish  as 
effective  agents  in  mosquito  control.  As  a  natural  aid  they  are  extremely  valu- 
able. Connor  (1921)  used,  with  remarkable  effectiveness,  the  chalaco  (Dormi- 
tator  latifrons,  family  Gobiidae)  in  the  campaign  against  yellow-fever  mos- 
quito in  Guayaquil,  Ecuador.  Here  the  city  had  no  adequate  water  supply, 
the  water  being  distributed  daily  to  the  householders  and  stored  in  tanks, 


PROBLEM  OF  MOSQUITO  CONTROL  393 

cans,  and  other  receptacles.  As  there  were  over  7000  tanks  and  30,000  other 
types  of  water  receptacles,  the  breeding  of  Aedes  aegypti  continued  in  great 
volume.  As  a  modern  water  service  could  not  be  installed  at  once,  Connor 
conceived  the  idea  of  using  fish.  After  many  trials  he  selected  the  chalaco  and 
distributed  at  least  one  fish  for  every  container.  The  fish,  a  local  species,  was 
obtained  from  fishermen  and  stored  in  a  specially  prepared  well  where  con- 
ditions approximated  those  of  the  streams  from  which  the  fish  came.  In  a 
few  days  the  fish  were  transferred  to  a  second  well  containing  water  similar 
to  that  used  in  the  city.  From  the  second  well  the  fish  were  distributed  to  all 
water  containers  throughout  the  city.  The  results  were  remarkable,  for 
mosquito  breeding  was  reduced  to  a  minimum. 

Many  other  species  of  top-feeding  fishes  have  been  employed  and  with 
considerable  success.  Though  undoubtedly  fishes  play  an  important  role  in 
mosquito  reduction  and  the  utilization  of  certain  species  is  highly  to  be  com- 
mended, yet  adequate  control  cannot  be  obtained  by  them  alone  unless  the 
conditions  are  more  or  less  ideal  from  the  standpoint  of  the  fishes  employed. 
In  any  plan  to  use  fishes  in  a  control  area,  the  best  possible  scientific  advice 
should  be  obtained.  The  effectiveness  of  the  fishes  depends  on  conditions 
which  bring  about  their  rapid  breeding  and  maintenance  and  furnish  them  a 
continuing  food  supply. 

OTHER  METHODS  OF  MOSQUITO  REDUCTION 

In  recent  years  much  attention  has  been  devoted  to  the  study  of  the  aquatic 
conditions  that  favor  or  reduce  mosquito  breeding.  It  is  a  common  observation 
that  certain  ponds,  etc.,  are  favorite  breeding  grounds  while  in  other  similar 
ponds  or  marshes  no  breeding  occurs.  Though  much  work  has  been  done, 
no  definite  conclusions  seem  warranted.  Certain  aquatic  plants  as  Cham  and 
Phyllotria  species  appear  to  have  a  deterrent  effect  both  on  egg  deposition 
and  larval  development.  Other  plants,  as  Utricularia  spp.  (Fig.  144,  bladder- 
worts)  destroy  large  numbers  of  larvae  (Matheson,  1931)  though  Hildebrandt 
(1925)  concluded  that  U.  macrorhiza  (=  vulgarii)  and  U.  radiata  had  very 
little  effect  in  reducing  larval  abundance  in  ponds  that  he  observed  in  the 
southeastern  states;  surface-loving  plants  as  species  of  Lemna,  Wollfia  (Fig. 
144),  and  Azolla  form  dense  mats  on  the  water  surface  and  prevent  egg  de- 
position or  interfere  with  larval  development;  and  other  plants  may  play 
important  roles  in  the  prevention  of  breeding  or  encourage  excessive  abun- 
dance of  larvae.  In  general  it  may  be  said  that  the  presence  or  absence  of  the 
necessary  larval  food  appears  to  be  the  deciding  factor.  But  what  is  the 


394  MEDICAL  ENTOMOLOGY 

necessary  larval  food?  Many  examinations  of  the  larval  gut  contents  have 
been  made;  some  studies  of  the  plankton  in  typical  breeding  pools  versus 
nonbreeding  pools  have  been  carried  out;  from  these,  however,  no  conclusions 
can  yet  be  drawn.  As  the  larvae  sweep  all  available  material  into  their  intesti- 
nal tracts,  there  is  no  means  of  deciding  what  is  actually  digested  and  what 
is  passed  out  in  the  wastes.  Hinman  (1930)  has  shown  that  a  large  proportion 
of  the  material  ingested  by  the  larvae  passes  through  the  alimentary  canal 


Fig.  144.  Left:  Portion  of  stem  of  bladderwort  (Utricularia)  with  mosquito  larvae  in 
four  bladders.  Right:  Surface  of  water  completely  covered  by  Wollfia  punctata  and  a 
few  plants  of  Lemna  minor. 

unchanged  and  thus  cannot  be  regarded  as  food.  He  further  demonstrated 
that  larvae  of  Aedes  aegypti  can  be  reared  under  sterile  conditions.  Eggs, 
sterilized  externally,  were  introduced  into  Berkefeld-filtered  water,  and  nor- 
mal adults  emerged  in  eight  to  nine  days  (the  usual  time  under  the  most 
favorable  conditions).  The  only  food  available  for  these  larvae  was  the 
solutes  and  colloids  that  could  pass  through  the  finest  filters.  Matheson  and 
Hinman  (1931)  also  demonstrated  that  larvae  of  several  other  species  of 
mosquitoes  grew  vigorously  in  Berkefeld-filtered  water.  It  would  seem  clear, 
then,  that  probably  the  most  important  sources  of  foods  for  mosquito  larvae 
are  the  substances  in  solution  and  colloids  present  in  the  water.  If  we  could 


PROBLEM  OF  MOSQUITO  CONTROL  395 

determine  what  are  the  essential  solutes,  considerable  progress  might  be  made 
in  simplifying  the  problem  of  mosquito  control.  If  by  the  use  of  certain 
aquatic  plants,  by  the  chemical  treatment  of  water  areas,  etc.,  the  necessary 
larval  food  can  be  destroyed,  mosquito  control  operations  may  be  greatly 
simplified  and  rendered  less  expensive. 

PROTECTION  FROM  MOSQUITOES 
SCREENING 

Though  actual  control  measures  against  both  larvae  and  adults  of  mos- 
quitoes may  be  carried  on  in  any  locality,  probably  the  most  effective  measure 
to  ensure  comfort  in  homes  is  by  screening.  Screening  not  only  effectively  bars 
mosquitoes  but  also  eliminates  many  other  noxious  insects  as  houseflies, 
black  flies,  and  others.  In  all  populated  areas  where  financial  means  are  ade- 
quate screening  should  be  practiced.  In  areas  where  housing  is  poor,  financial 
means  are  not  available,  and  the  population  is  indifferent,  every  effort  should 
be  made  to  aid  such  communities.  It  has  been  definitely  proved  that  adequate 
screening,  even  in  highly  malarious  rural  areas  with  inadequate  housing, 
will  reduce  malaria  to  a  minimum.  Screening  should  be  well  done  so  that 
no  entrances  are  left,  such  as  through  open  fireplaces  or  openings  in  flooring 
or  walls.  Porches  should  also  be  screened.  Such  screening  combined  with 
DDT  treatments  (residual  sprays)  of  the  interior  and  screens  will  ensure 
comfort  in  homes.  The  type  of  screening  wire  will  depend  largely  on  the 
locality  and  the  availability  of  material.  In  general  the  i6-mesh  screen  (16 
meshes  to  the  inch)  will  prove  most  useful.  Copper,  bronze,  or  galvanized 
screens  are  available  and  recently  plastic  screens  -have  been  developed.  Cop- 
per or  bronze  screens  are  long  lasting,  even  in  areas  near  the  sea,  while 
galvanized  screens  may  give  only  a  few  years'  service  and  then  must  be 
repaired  or  renewed.  Full  details  of  methods  of  screening  will  be  found  in 
the  references. 

PERSONAL  PROTECTION 

When  traveling  or  living  in  areas  where  there  are  dangerous  insect-borne 
diseases  (malaria,  yellow  fever,  filariasis,  dengue,  etc.)  bed  nets  should  be  a 
part  of  the  equipment.  These  are  available  or  may  be  made.  In  entering  a  bed 
net  great  care  should  be  exercised  to  see  that  all  mosquitoes  or  other  insects 
are  absent  or  are  killed.  The  bed  net  should  be  carefuly  tucked  about  the  bed 
or  sleeping  place  so  as  to  leave  no  opening,  and  the  net  should  be  so  arranged 
that  the  sleeper's  body  does  not  touch  the  net  at  any  point. 


396  MEDICAL  ENTOMOLOGY 

During  World  War  II  excellent  mosquito  repellents  were  developed  and 
tested.  These  consist  of  Rutgers  612  (2-ethylhexanediol-i-3),  dimethyl  phthal- 
ate,  and  indalone.  They  are  available  and  give  a  fair  degree  of  protection 
against  mosquitoes  and  black  flies.  For  general  protection  against  insects  a 
combination  of  the  three  is  recommended,  i.e.,  6  parts  of  dimethyl  phthalate, 
2  parts  of  Rutgers  612,  and  2  parts  of  indalone  (the  so-called  "6-2-2"  formula). 
These  materials  should  be  applied  according  to  the  directions  of  the  manufac- 
turer. They  are  not  injurious  to  the  skin  and  should  be  rubbed  over  all  ex- 
posed surfaces,  but  avoid  getting  them  into  the  eyes.  Alone  or  in  combination 
they  will  give  fairly  good  protection  for  two  to  four  hours.  They  can  also  be 
rubbed  or  spread  over  the  clothing  with  impunity  and  thus  give  added 
protection. 

SPECIAL  CONTROL  PROBLEMS 

The  general  methods  of  mosquito  control  have  been  outlined  above. 
Several  special  phases  need  to  be  emphasized.  These  concern  the  control  of 
yellow  fever,  malaria,  and  dengue.  Though  yellow  fever  is  now  known  to 
be  transmitted  (at  least  from  monkey  to  monkey  and  probably  from  man  to 
man,  or  monkey  to  man)  by  many  species  of  mosquitoes  in  addition  to  the 
yellow-fever  mosquito  (Aedes  aegyptt),  the  transmitter  that  must  be  con- 
sidered of  prime  importance  is  the  last  one.  Furthermore,  an  animal  reservoir 
of  at  least  vast  possibilities  has  been  discovered  in  a  large  number  of  different 
species  of  monkeys.  At  present  the  disease  is  restricted  to  extensive  areas  in 
South  America  and  a  large  area  in  West  Africa  extending  deep  into  the 
continent.  Formerly  it  was  thought  that  if  the  disease  in  man  could  be 
stamped  out,  either  by  the  death  of  the  infected  or  their  recovery  (immunes), 
no  further  centers  of  infection  would  exist  so  that  the  presence  of  the  yellow- 
fever  mosquito  would  no  longer  be  a  menace  unless  new  human  cases  were 
brought  in  from  other  centers  of  infection.  Also  the  mosquito  transmitter 
(Aedes  aegypti)  was  looked  upon  as  an  urban  mosquito,  not  common  or 
abundant  in  rural  areas.  Whether  this  conclusion  can  be  accepted  as  fully 
proved  is  doubtful.  That  this  mosquito  does  not  occur  far  from  human  habita- 
tion appears  well  authenticated,  and  there  seems  no  reason  to  doubt  that  it 
could  become  established  about  every  human  abode  where  it  can  survive. 
Given  these  conditions  and  the  presence  of  monkey  reservoirs,  it  would  seem 
that  the  possibility  of  permanent  yellow-fever  centers  is  assured.  Though 
an  excellent  vaccine  is  now  available  and  most  effective,  it  would  be  an  en- 
tirely justified  procedure  for  all  cities,  villages,  towns,  and  other  centers  of 
population  seriously  to  plan  a  strict  control  over  this  mosquito.  If  not,  an 


PROBLEM  OF  MOSQUITO  CONTROL  397 

outbreak  of  yellow  fever  involves  almost  a  military  supervision  (as  in  the 
outbreaks  in  New  Orleans,  Rio  de  Janeiro,  etc.).  As  this  mosquito  breeds 
practically  only  in  artificial  water  containers,  the  consistent  and  continued 
elimination  of  these  breeding  places  would  result  in  such  a  permanent  reduc- 
tion of  the  numbers  of  this  mosquito  that  the  introduction  of  a  few  yellow- 
fever  cases  would  not  result  in  an  outbreak  of  the  disease.  Though  the  disease 
has  not  reached  the  populous  centers  of  northern,  eastern,  or  southern  Africa 
and  India,  yet  the  possibilities  of  modern  transportation  are  constant  sources 
of  danger.  Unless  reduction  of  the  yellow-fever  mosquito  is  brought  about, 
the  appearance  of  the  disease  in  any  of  these  populous  regions  might  mean  a 
disaster  of  serious  proportions,  despite  the  use  of  the  vaccine  (as  witness  the 
outbreak  in  1940  in  the  Anglo-Egyptian  Sudan).  Furthermore,  new  endemic 
centers  would  be  established  and  the  continued  spread  of  the  disease  would 
be  assured.  In  recent  years  (1933)  the  discovery  of  jungle  yellow  fever  in 
South  America  has  added  a  new  problem  to  yellow-fever  control.  This  should 
emphasize  more  strongly  the  need  for  urban  control  of  Aedes  aegypti  and 
the  more  extensive  use  of  the  vaccine  in  suspected  areas. 

Though  dengue  is  a  disease  of  low  mortality,  yet  the  lowered  vitality  of 
its  victims  and  the  rapidity  of  its  spread  warrant  special  consideration.  As 
Aedes  aegypti  is  the  only  known  transmitter  in  America,  we  must  assume 
that  it  breeds  in  vast  numbers  in  many  southern  states,  as  witness  some 
500,000  to  600,000  cases  of  dengue  in  Texas  in  1922.  The  control  of  the  mos- 
quito is  apparently  not  very  effective  in  the  United  States.  Here  again  the 
elimination  of  the  breeding  places  of  the  yellow-fever  mosquito  should  be  a 
major  consideration  in  every  city  and  village  where  it  occurs. 

Malaria,  unlike  yellow  fever  and  dengue,  is  primarily  a  disease  of  rural 
districts,  small  cities,  and  villages.  The  anopheline  transmitters  do  not  breed 
to  any  extent  in  artificial  water  containers  but  are  primarily  restricted  to  more 
or  less  permanent  bodies  of  protected  fresh  water,  slow-running  streams, 
marshes,  swamps,  and,  with  certain  species,  to  brackish  water  along  coastal 
areas.  Fortunately  all  anophelines  are  not  "good"  or  "dangerous"  transmitters 
of  malaria.  In  recent  years  consistent  efforts  have  been  made  to  determine 
these  "dangerous"  transmitters,  discover  their  specific  breeding  grounds, 
their  bionomics,  etc.,  and  then  concentrate  all  efforts,  at  first,  to  the  control  of 
such  species.  The  results  of  such  directed  endeavors  have  been  very  gratifying 
in  certain  countries  as  the  Federated  Malay  States,  the  Canal  Zone,  Palestine, 
etc.  Whether  such  principles  can  always  be  applied  remains  for  the  future 
to  decide.  The  reduction  and  control  of  anopheline  vectors  of  malaria  are 
highly  specialized  procedures.  Such  work  should  be  guided  by  well-trained 


398  MEDICAL  ENTOMOLOGY 

malariologists  and  entomologists,  and  the  procedure  to  be  followed  must  be 
based  on  a  sound  knowledge  of  the  bionomics  of  anopheline  vectors  in  any 
particular  region  (witness  the  problem  of  A.  gambiae  in  Brazil). 

PLAN  OF  ORGANIZATION 

In  order  to  plan  and  carry  out  mosquito  control,  a  well-organized  unit  is 
essential.  Such  an  organized  division  should  be  in  close  association  with  or 
directly  under  the  officer  in  charge  of  public  health  work.  This  work  may  be 
done  under  local  regulations  or,  where  several  communities  unite,  under  a 
specific  state  or  provincial  law  3  empowering  townships,  districts,  or  counties 
to  organize  mosquito  abatement  districts.  In  any  such  organized  district  the 
work  of  mosquito  control  should  be  under  a  responsible,  well-trained  en- 
tomologist, or  one  familiar  with  the  problems  of  mosquito  biology.  The  suc- 
cess or  failure  will  largely  depend  on  his  ability  and  freedom  to  plan  and 
carry  out  effective  measures.  The  budget  for  the  proposed  work  should  be 
independent  and  appropriated  specifically  for  mosquito-control  work.  The 
officer  in  charge  should  be  granted  wide  discretionary  powers,  and  he  should 
have  authority  to  carry  out  well-planned  schemes  that  may  involve  either 
private  or  public  rights. 

Such  an  officer  should  have  authority  to  secure  the  co-operation  of  all 
public  and  private  planning  commissions,  and  all  private  or  public  bodies 
engaged  in  any  operations  that  involve  or  may  involve  the  formation  of  ponds, 
reservoirs,  or  impounded  water,  or  that  deal  with  building,  street,  road,  and 
real  estate  developments,  drainage  schemes,  etc.  Only  in  this  way  will  the 
officer  have  an  opportunity  to  inspect  all  plans  that  might  compel  him  to 
modify  his  scheme  of  mosquito  control.  The  organized  unit  should  include 
trained  inspectors  and  laborers.  The  numbers  and  their  equipment  will  be 
dependent  on  the  extent  of  the  abatement  district  and  the  difficulties  involved. 
Furthermore,  the  officer  should  have  authority  to  engage  sanitary  engineers 
and  other  experts  when  highly  technical  plans  have  to  be  prepared  and  car- 
ried out.  In  this  way,  one  person  will  be  held  responsible  and  his  success 
or  failure  can  easily  be  judged  by  the  mosquito  density  in  his  district. 

Another  important  duty  will  be  to  aid  the  health  authorities,  public  works 
departments,  etc.,  in  drawing  up  careful  sanitary,  drainage,  and  water  storage 
regulations  involving  all  conditions  that  may  increase  or  decrease  mosquito 
breeding.  The  expense  of  such  an  organization  will  depend  on  many  factors. 
There  is  one  consideration,  however,  that  should  outweigh  the  cost:  any 

3  Such  laws  are  in  effect  in  New  Jersey,  California,  Illinois,  and  probably  many  other 
places.  The  New  Jersey  law  seems  the  most  far-reaching  and  adequate  in  our  country. 


PROBLEM  OF  MOSQUITO  CONTROL  399 

work  done  should  be  well  done,  a  long-time  plan  of  operations  should  be 
obtained,  and  a  continuing  policy  should  be  assured.  Furthermore,  the  cost 
of  the  improvements  to  public  and  private  property  may  largely  be  charged 
to  such  properties  and  the  general  increase  in  taxable  values  should  far  ex- 
ceed the  costs. 

REFERENCES  4 

*Aitken,  T.  H.  G.     A  study  of  winter  DDT  house  spraying  and  its  concomitant 

cflects  on  anophelines  and  malaria  in  an  endemic  area.    Jl.  Nat.  Mai.  Soc.,  5: 

168-187,  1946. 
American  Mosquito  Control  Association.     The  use  of  aircraft  in  the  control  of 

mosquitoes.     Amcr.  Mosq.  Con.  Assoc.,  Bull.  I,  1948. 
Clapp,  J.  M.,  Fay,  R.  W.,  and  Simmons,  S.  W.    The  comparative  residual  toxicity 

of  DDT  to  Anopheles  quadrimaculatus  when  applied  on  different  surfaces.     U.S. 

Pub.  Illth.  Rcpts.,  62:  158-170,  1947. 

Connor,  M.  E.     Fish  as  mosquito  destroyers.     Nat.  Hist.,  21:  279-281,  1921. 
**Covcll,  G.     Malaria  control  by  anti-mosquito  measures.     London,  1931. 
Crawford,  }.  A.     Mosquito  reduction  and  malaria  prevention.     London,  1926. 
*Hall,  T.  F.,  Pciifound,  W.  T.,  and  Hess,  A.  D.     Water  level  relationships  of 

plants  in  the  Tennessee  Valley  with  particular  reference  to  malaria  control.    Jl. 

Tenn.  Acad.  Sci.,  21:  18-59,  1946. 

Hardenhurg,  W.  E.     Mosquito  eradication.     New  York,  1922. 
*Hcrms,  W.  R.,  and  Gray,  H.  F.     Mosquito  control.     New  York,  1944. 
Hewitt,  R.,  and  Kotcher,  E.     Observations  on  household  anophelism  in  a  selected 

group  of  mosquito-proofed  and  non-mosquito-proofed  homes.     U.S.  Pub.  Hlth. 

Repts.,  56:  1055-1061,  1941. 

Hildebrand,  S.  F.     A  study  of  the  top  minnow,  Gambusia  holbroofy,  in  its  rela- 
tion to  mosquito  control.     U.S.  Pub.  Hlth.  Serv.,  Bull.  153,  1925. 
*Hinman,  E.  H.     A  study  of  the  food  of  mosquito  larvae.     Amer.  Jl.  Hyg.,  12: 

238-270,  1930. 
*Kligler,  I.  }.     The  epidemiology  and  control  of  malaria  in  Palestine.     Chicago, 

1930. 
*Knipling,  E.  F.,  ct  aL    Evaluation  ot:  selected  insecticides  and  drugs  as  chemo- 

therapeutic  agents  against  external  bloodsucking  parasites.     Jl.  Parasit.,  34:  55-70, 

1948. 
Kruse,  C.  W.,  and  Metcalf,  R.  L.     An  analysis  of  the  design  and  performance  of 

airplane  exhaust  generators  for  the  production  of  DDT  aerosols  for  the  control 

of  Anopheles  quadrimaculatus.     U.S.  Pub.  Hlth.  Repts.,  61:  1171-1184,  1946. 

4  The  literature  on  mosquito  control  is  very  great.  Fortunately  several  extensive  ac- 
counts have  recently  been  published  and  most  of  these  contain  bibliographies.  Only  a 
few  references  can  be  included  here  and  the  reader  is  referred  to  them  for  further  in- 
formation. 


400  MEDICAL  ENTOMOLOGY 

*LePrince,  J.  A.,  and  Orenstein,  A.  }.  Mosquito  control  in  Panama.  New  York, 
1916. 

*Matheson,  R.  The  utilization  of  aquatic  plants  as  aids  in  mosquito  control. 
Amer.  Natur.,  64:  56-86,  1930. 

New  Jersey  Mosquito  Extermination  Association.  Proceedings  .  .  .  Vols.  I-. 
New  Brunswick,  N.J.,  1914-.  Valuable  papers  each  year  on  mosquito  prob- 
lems. 

Penfound,  W.  T.  The  relation  of  plants  to  malaria  control  with  special  reference 
to  impounded  waters.  U.S.  Pub.  Hlth.  Repts.,  57:  261-268,  1942. 

* ,  et  al.  The  spring  phenology  of  plants  in  and  around  the  reservoirs  in  north 

Alabama  with  particular  reference  to  malaria  control.  Ecology,  26:  332-352, 
1945. 

Senior-White,  R.  Progress  towards  the  realization  of  biological  control  of  mos- 
quito breeding.  Trans.  Cong.  Far  East  Assoc.  Trop.  Med.  (yth  Cong.),  2:  718- 
722, 1929. 

Soper,  F.  L.,  and  Wilson,  D.  B.     Anopheles  gambiae  in  Brazil.     New  York,  1943. 

,  et  al.  The  organization  of  permanent  nation-wide  anti-Aedes  aegypti  meas- 
ures in  Brazil.  New  York,  1943. 

* ,  et  al.  Reduction  of  anopheles  density  by  the  pre-season  spraying  of  build- 
ing interiors  with  DDT  in  kerosene,  at  Castel  Volturno,  Italy  in  1944-1945  and 
in  the  Tiber  Delta  in  1945.  Amer.  Jl.  Trop.  Med.,  27:  177-200,  1947. 

Speer,  A.  }.  Compendium  of  the  parasites  of  mosquitoes.  U.S.  Pub.  Hlth.  Serv., 
Hyg.  Lab.,  Bull.  146,  1927. 

Stromquist,  W.  G.    Engineering  aspects  of  mosquito  control.    Civil  Eng.,   14: 

43i-434>  J944- 

U.S.  Public  Health  Service  and  the  Tennessee  Valley  Authority.  Malaria  control 
on  impounded  waters.  Washington,  1947.  (A  most  valuable  work  by  many 
authorities  on  impounded  water  and  the  problems  of  malaria  control  by  anti- 
mosquito  measures.) 

Upholt,  W.  M.,  et  al.  The  experimental  use  of  DDT  in  the  control  of  the  yellow 
fever  mosquito,  Aedcs  aegypti.  U.S.  Pub.  Hlth.  Repts.,  Suppl.,  186:  90-96, 
1945. 

Watson,  M.    The  prevention  of  malaria.    London,  1921. 

.  Twenty-five  years  of  malaria  control  in  the  Malay  Peninsula,  1901-1926.  Jl. 

Trop.  Med.  Hyg.,  32:  337-340,  1929. 

Watson,  R.  B.,  and  Rice,  M.  E.  Further  observations  on  mosquito-proofing  for 
malaria  control.  Amer.  Jl.  Hyg.,  34:  150-159,  1941. 


CHAPTER  XIII 


Other  Bloodsucking 
Nemocerous  Flies: 

Simuliidae  and 
Ceratopogonidae  or  Heleidae 


IN  ADDITION  to  the  mosquitoes  (Culicidae)  and  the  moth  flies  (Psy- 
chodidae)  two  other  families  of  Nemocera  contain  bloodsucking  species. 
These  flies  are  all  very  small,  some  of  them  extremely  minute,  but  many  of 
them  are  vicious  biters  and  extremely  annoying  to  man  and  animals.  Re- 
cently certain  species  have  been  proved  or  incriminated  as  transmitters  of 
important  diseases.  As  these  flies  are  world-wide  in  distribution,  often  ex- 
tremely abundant  in  individuals,  attack  man  and  animals  with  terrible 
severity,  and  are  now  known  to  transmit  certain  diseases,  the  study  of  them 
has  attracted  considerable  attention  in  recent  years.  Owing  to  their  minute 
size  and  the  difficulties  involved  in  the  study  of  their  life  histories,  not  as 
much  progress  has  been  attained  as  could  be  desired. 

FAMILY  SIMULIIDAE 

The  Black  Flies,  the  Buffalo  Gnats 

The  Simuliidae  may  be  recognized  by  their  small  size  (i  to  6  millimeters 
in  length),  stout  bodies,  short  legs,  and  characteristic  "humped"  appearance 
due  to  an  arching  of  the  thorax  (Fig.  145).  The  wings  (Fig.  145)  are  broad 
with  the  anterior  veins  well  developed,  the  others  indistinct.  The  antennae 
are  nine,  ten,  or  eleven  jointed  and  usually  not  as  long  as  the  head;  the  seg- 
ments are  short,  closely  pressed  together,  and  bear  numerous  short  hairs.  In 
the  males  the  eyes  are  contiguous  (holoptic),  while  in  the  females  the  eyes 


402 


MEDICAL  ENTOMOLOGY 


are  rather  widely  separated  (dichoptic).  The  mouth  parts  are  formed  for 
piercing  and  sucking.  Only  the  females  are  known  to  take  blood. 

The  family  includes  at  present  a  rather  large  number  of  species.  Williston 
(1908)  reported  only  about  75  species  in  all  the  world,  but  Bequaert  (1931) 


Fig.  145.  The  black  fly,  Simulium  arcticum  Malloch.  Male  above,  female 
below.  Veins  are  labeled  according  to  the  Comstock  system.  (From  Cameron.) 

records  some  330  species,  distributed  as  follows:  125  for  the  Palearctic  region, 
53  for  the  Nearctic,  80  for  the  Neotropical,  24  for  the  Ethiopian,  26  for  the 
Oriental,  and  24  for  the  Australasian.  Dyar  and  Shannon  (1927)  report  47 
species  for  North  America  and  Greenland,  and  Bequaert  (1926)  indicates 
70  species  for  South  and  Central  Americas.  Smart  (1945)  lists  623  world 


OTHER  BLOODSUCKING  NEMOCEROUS  FLIES  403 

species;  Vargus  (1946)  adds  23  species  to  this  list.  The  family  is  world- wide 
in  distribution,  extending  from  the  tropics  to  the  Arctic  Circle  and  to  eleva- 
tions of  at  least  9000  feet. 

STRUCTURE  OF  THE  MOUTH  PARTS:  The  mouth  parts  constitute 
a  short  proboscis  composed  of  the  following  parts:  The  labrum.  This  is  an 
elongated  unpaired  structure  (in  cross  section  like  a  three-sided  pyramid) 


Fig.  146  (If ft).  Lateral  view  of  the  mouth  parts  of  a  black  fly  (Eusimulium  lascivum} 
to  show  the  relationship  of  the  various  parts  and  their  muscles.  Comp  Ibr-ep,  compressor 
muscles  of  the  labrum;  Dil  ant  oes,  dilator  muscle  of  the  anterior  esophagcal  pump; 
Dil  ph,  dilator  muscle  of  the  pharyngeal  pump;  Dil  p  oes,  dilator  muscle  of  the  posterior 
csophageal  pump;  Dil  sal  pmp,  dilator  muscle  of  salivary  pump;  Fr  cl,  frontoclypeus; 
Hyp,  hypopharynx;  Lbr-ep,  labrum;  Lev  Ibr  ep,  Icvator  muscle  of  labrum;  Oes  pmp, 
esophageal  pump;  Ph  pmp,  pharyngeal  pump;  Ret  ph,  retractor  of  the  pharyngeal  pump; 
Sal  ch,  salivary  channel;  Sal  d,  salivary  duct;  Sal  g,  salivary  gland;  Sal  pmp,  salivary 
pump;  Tens  fr  cl,  tensor  of  the  frontal  clypcus.  (After  Krafchick.) 

Fig.  747  (right).  Mouth  parts  of  Prosimulium  hirtipes.  Left:  Mandible.  Right:  Left  max- 
illa, dorsal  view.  C,  cardo;  D,  depression  in  mandible  with  elevation  on  opposite  side;  G, 
galca;  P,  palpus;  S,  stipes;  SP,  sensory  organ.  (Maxilla  drawn  at  twice  the  scale  of  man- 
dible.) 

movably  attached  to  the  membrane  suspended  from  the  frontoclypeus.  It  is 
continued  directly  forward  from  the  head  as  a  strong  convex  plate  strength- 
ened medially  and  laterally  by  sclerotizecl  bars  that  meet  at  the  distal  ex- 
tremity. The  base  of  each  labral  bar  is  more  or  less  Y-shaped,  the  arms  of  the 
Y  forming  the  bases  of  the  lateral  walls.  These  arms  meet  extensions  from 
the  head  and  the  lower  anterior  walls  of  the  pharyngeal  pump.  These  points 
of  contact  form  the  fulcra  for  the  levation  and  depression  of  the  labrum.  The 
arrangement  of  these  parts  and  their  muscles  are  shown  in  Fig.  146.  The  tip 


4o4  MEDICAL  ENTOMOLOGY 

of  the  labrum  is  provided  with  denticles  on  each  side  of  the  median  line. 
The  mandibles  (Fig.  147)  consist  of  a  pair  of  broad  spatulate  structures, 
sharply  pointed  distally  and  provided  with  numerous  small  recurved  teeth 
along  the  apical  margin.  Each  mandible  has,  near  its  middle,  a  small  area  with 
a  depression  on  one  side  and  an  elevation  opposite.  In  the  position  of  rest  the 
mandibles  are  closed  scissorlike  and  lie  between  the  labrum  and  hypopharynx. 
They  are  locked  together  by  means  of  the  device  just  mentioned,  the  elevation 
on  one  fitting  into  the  depression  of  the  other  as  first  observed  by  Jobling  (1928) 
for  Culicoides.  The  maxillae  (Fig.  147)  are  paired  structures,  arising  just  be- 
low the  mandibles.  Each  maxilla  has  the  usual  parts:  cardo,  stipes  (these 
two  usually  united),  galea,  and  palpus.  The  galea  has  a  curved,  basal,  sclero- 
tized  arm,  which  terminates  in  a  vicious-looking,  swordlike  cutting  structure 
(Fig.  147).  The  margins  of  the  blade  are  recurved  ventrally  and  bear  rctrorse 
teeth.  The  palpus  consists  of  four  segments  (the  basal  one  subdivided) ;  the 
second  segment  has  a  deep  pit  in  which  is  probably  located  a  sensory  organ. 
The  hypopharynx  is  an  unpaired  organ  lying  below,  and  in  close  union  at 
the  base  with,  the  labrum.  It  arises  from  the  floor  of  the  pharynx,  with  which 
it  is  joined  by  a  hingelike  arrangement.  It  is  deeply  concave  on  its  dorsal  side 
and  its  sclerotized  margins  receive,  in  V-like  notches,  the  extensions  of  the 
lateral  bars  of  the  labrum.  The  salivary  pump  is  attached  near  the  base  of 
the  hypopharynx,  and  the  salivary  duct  perforates  the  base  of  the  hypopharynx 
and  extends  along  its  middle  to  near  the  apex.  Back  of  the  pharynx  lies  the 
pharyngeal  pump.  The  labium  consists  of  two  lobes,  each  of  which  is  con- 
cave anteriorly  so  that  the  mouth  parts  are  concealed  within  when  at  rest. 
Each  lobe  is  composed  of  three  segments.  The  proximal  parts  are  fused  along 
the  posterior  mid-line  while  the  other  segments  are  free.  The  fused  basal 
segments  probably  represent  the  theca  and  the  free  segments  the  labellae. 

The  action  of  the  mouth  parts  in  obtaining  blood  has  not  been  observed 
or  carefully  described.  In  all  probability  they  function  as  in  Culicoides  as  de- 
scribed by  Jobling  (1928).  He  says,  in  describing  their  action, 

It  was  noted  that  the  labrum-epipharynx,  the  hypopharynx,  and  the  mandibles 
interposed  between  these  two  parts,  compose  together  a  piercing  stylet  which  per- 
forms forward  and  backward  movements  during  biting.  When  these  mouthparts 
have  penetrated  a  little  more  than  half  their  length  into  the  skin,  the  protraction 
and  retraction  cease.  During  the  sucking  of  blood  the  mandibles  are  not  withdrawn 
to  the  sides,  but  by  the  structure  of  their  middle  parts  they  are  maintained 
between  the  labrum-epipharynx  and  hypopharynx.  Thus  the  food  canal  is  formed 
by  them  and  the  labrum-epipharynx  as  has  already  been  indicated  by  Leon  (1924), 


OTHER  BLOODSUCKING  NEMOCEROUS  FLIES  405 

The  labium  functions  as  a  guide,  holding  the  mouth  parts  in  position  while 
making  the  puncture.  The  action  of  the  maxillae  could  not  be  observed  by 
Jobling,  but  he  thinks  the  galea  moves  forward  and  backward,  thus  having 
a  tearing  action. 

BIOLOGY:  The  larval  stage  of  all  known  species  is  passed  in  running 
water.  The  larvae  are  found  in  swift  currents,  at  the  edge  of  waterfalls,  on 
rocks  where  the  water  sweeps  by  (Fig.  148),  in  shallow  mountain  streams, 


;.:/.:  .....  :::.. 


Fig.  148.  Note  the  large  stone  sticking  above  the  swift-running  water.  Near 
the  water's  edge  and  on  the  rock  are  large  numbers  of  males  of  Eusimulium 
muttatttm  waiting  for  the  emergence  of  the  females.  Below  are  large  masses  of 
larvae  and  pupae'of  this  species. 

in  roadside  ditches,  and  in  similar  situations.  They  attach  themselves  by  means 
of  an  anal  disc  (see  below)  and  retain  their  position  even  in  very  swift  water. 
They  are  usually  found  in  the  shallower  parts  of  the  streams,  especially 
where  the  water  breaks  over  some  obstruction,  or  attached  to  floating  grasses 
or  other  pendulous  plants. 

The  eggs  are  laid  at  the  level  of  the  water,  or  just  below,  on  any  convenient 
surface  as  bare  rocks,  debris,  or  other  smooth  objects  (Simulium  pictipes) ;  on 
blades  of  grass  trailing  at  the  surface  of  the  water  (S.  vittatum,  S.  venustum, 
S.  bracteatum) ;  or  under  the  water  to  a  depth  of  a  few  inches  to  a  foot. 
Bradley  (1935)  states  that  Cnephia  pecuarum  drops  its  eggs  directly  in  the 


4o6  MEDICAL  ENTOMOLOGY 

flowing  water;  the  eggs  are  heavier  than  the  water  and  they  settle  to  the 
bottom.  The  total  number  of  eggs  a  single  female  may  lay  is  not  known, 
though  Pomeroy  (1916)  records  349  eggs  laid  by  one  female,  under  experi- 
mental conditions,  in  twelve  minutes.  Other  records  indicate  a  female  may 
lay  as  many  as  500  or  more  eggs  at  one  oviposition.  According  to  most 
observations,  oviposition  takes  place  during  the  evening  hours — from  four  to 
about  eight  o'clock.  The  eggs  are  minute,  about  0.25  mm.  in  length  and  some- 
what triangular  in  shape.  They  hatch  in  from  4  to  12  days  or  more,  depending 
largely  on  temperature  and  aquatic  conditions,  or  they  may  remain  dormant 
for  a  long  time. 

The  larvae  (Fig.  149)  of  the  Simuliidae  can  usually  be  recognized  from 
their  habitats.  The  more  common,  easily  observed  characters  are  the  form  of 
the  body — generally  subcylindrical,  usually  enlarged  at  each  end,  and  at- 
tenuated in  the  middle;  the  possession  of  two  large  fan-shaped  organs  on  the 
head;  a  short  median  leg  armed  with  hooks  on  the  ventral  surface  of  the 
segment  back  of  the  head;  a  disc  provided  with  rows  of  hooks  arranged  in 
circles  on  the  posterior  end  of  the  body;  and  the  presence  of  characteristic 
anal  gills  (blood  gills).  The  larval  stages  of  comparatively  few  species  have 
been  fully  described.  Edwards  (1920)  has  summarized  his  work  on  the 
British  species;  Pomeroy  (1916)  has  carefully  described  five  American 
species;  Friedcricks  (1920)  many  of  the  more  common  species  of  Germany; 
Puri  (19^2-19^)  the  Indian  species;  Gibbins  (1933-1937)  aac^  Bequaert 
(1938)  certain  African  species;  Bequaert,  HofTman,  and  Vargas  a  number 
of  species  from  Central  America  and  Mexico;  and  Twinn  (1936)  many 
Canadian  species. 

The  larva,  on  escaping  from  the  egg,  attaches  to  the  nearest  object  by 
means  of  the  thoracic  proleg.  The  body  is  then  moved  about  till  the  sucker- 
like  anal  disc  can  be  brought  into  contact  and  more  or  less  permanent  attach- 
ment follows.  According  to  Wu  (1931),  the  anal  disc  is  not  a  true  sucker 
but  attachment  is  brought  about  by  glutinous  material  placed  on  the  disc 
by  the  mouth.  The  larvae  are  capable  of  movement,  looping  from  place  to 
place  by  means  of  the  proleg  and  anal  disc.  According  to  Puri  (1925),  this  is 
accomplished  as  follows:  the  larva  places  some  saliva  on  a  selected  spot  and 
fixes  the  proleg  to  this  spot;  it  then  places  saliva  in  front  of  the  previous  spot 
and,  withdrawing  the  anal  disc,  attaches  it  to  the  new  saliva.  In  this  manner 
the  larva  can  move  slowly  about.  It  also  spins  a  silken  thread  from  the  salivary 
glands  and  can  use  this  as  a  means  of  dropping  down  stream  and  then  crawl 
back  on  the  thread  to  the  place  of  attachment. 

The  larva  undergoes  six  molts,  pupation  occurring  at  the  last  molt.  The 


OTHER  BLOODSUCKING  NEMOCEROUS  FLIES 


407 


duration  of  the  larval  period  varies  widely.  Puri  records  four  to  six  weeks 
(S.  aureum  and  S.  erythrocephalum)  during  the  summer;  Pomeroy  notes 
full  larval  development  in  South  Carolina  in  17  days  (S.  venustum,  S.  brae- 


Fig.  149.  (/)  Dorsal  view  of  larva  of  Simulium  arcticum.  (2)  Pupa  in  its  pupal  case. 
(^)  Pupa  removed  from  pupal  case.  (4)  Pupa,  ventral  view.  (5)  Lateral  view  of  larva 
of  Simulium  pictipes.  (6)  Pupa  in  its  case,  lateral  view.  (7)  Lateral  view  of  pupa. 
F,  mouth  fans;  G,  blood  gills;  P,  median  prothoracic  leg;  S,  posterior  sucker;  Tg,  tracheal 
gills.  (/  to  4  from  Cameron;  5  to  7  from  Johannsen.) 

teatum,  S.  vittatum,  and  S.  pictipes)',  Cameron  (1922)  states  that  S.  arcticum 
(simile)  requires  three  to  four  weeks  in  western  Canada;  Wu  (1931)  records 
13  to  17  days  for  S.  vittatum  in  Michigan. 
Pupation  takes  place  in  the  larval  habitat.  The  larva  spins  a  silken  cocoon 


408  MEDICAL  ENTOMOLOGY 

(Fig.  149)  within  which  the  pupal  period  is  passed.  The  pupal  stage  varies 
from  two  to  seven  days,  or  longer  in  cooler  weather.  The  adults,  on  emer- 
gence, rise  to  the  surface  of  the  water  and  take  to  wing. 

The  number  of  annual  generations  varies  greatly  in  different  parts  of  the 
world.  Pomeroy  thinks  that  there  are  five  or  six  generations  in  South  Carolina; 
Cameron  records  four  generations  for  S.  arcticum  (simile) ;  Edwards  thinks 
there  is  but  one  generation  of  S.  venustum  and  S.  reptans,  two  generations  of 
S.  latipes,  three  of  S.  equinum  and  S.  ornatum,  and  four  generations  of  S. 
argyreatum  in  England.  Smart  (1934)  states  there  are  four  or  five  annual 
generations  of  S.  pictipes  in  central  New  York;  Prosimuliitm  magnum  has 
only  one  generation  in  the  same  area;  P.  hirtipes  has  frequently  two  genera- 
tions in  the  Adirondack  region  of  New  York  state  and  this  is  also  true  for 
Simulium  venustum;  Twinn  (1936)  records  two  or  three  generations  of  S. 
vittatum  Zett.  in  Ontario  and  Quebec.  Bradley  (1935)  records  only  a  single 
generation  a  year  for  Cnephia  pecuarurn. 

The  adults  are  vigorous  fliers  and  have  been  recorded  four  or  more  miles 
from  their  breeding  grounds.  Cameron  (1922)  records  a  1 2-mile  flight  for 
S.  arcticum.  It  is  believed  that  their  migratory  habits  are  induced  by  their 
desire  for  blood,  blood  being  the  principal  food  of  the  adults  (females).  Most, 
if  not  all,  the  species  are  bloodsucking  in  habit  (S.  aureum  is  not  known  to 
take  blood;  S.  pictipes  is  also  thought  to  be  an  exception  but  it  has  been  re- 
corded as  feeding  on  mules).  Certain  species  seem  to  prefer  the  blood  of 
particular  animals  though  other  species  are  more  catholic  in  their  tastes. 
Thus  Pomeroy  states  that  S.  venustum  seldom  attacks  man  or  cattle  but  is  a 
severe  pest  of  horses  and  mules,  feeding  within  the  ears.  Dyar  and  Shannon 
(1927)  report  the  same  species  as  very  annoying  to  man,  and  this  agrees  with 
the  writer's  experience.  Bequaert  (1938)  summarizes  the  data  on  the  feeding 
habits  of  black  flies.  Some  feed  largely  on  birds  as  S.  bracteatum  Coq. 
(  —  aureum  Fries),  S.  venustum  Say  (important  pest  of  ducks),  S.  atratum 
de  Meij.  (on  birds  in  Java),  S.  virgatum  Coq.,  and  S.  mexicunum  Bellardi 
(on  horses  but  not  man  in  Guatemala);  only  5  of  the  57  species  of  the 
Ethiopian  region  attack  man  (S.  damnosum  Theo.,  S.  naevei  Roub.,  S.  adersi 
Pom.,  S.  willmani  Roub.,  and  S.  griseicole  Beck.).  In  addition  we  may  add  S. 
venustum  Say  and  S.  hirtipes  Fries  as  severe  pests  of  man  in  their  ranges. 
Twinn  (1936)  reports  S.  vittatum  Zett.  as  feeding  on  horses;  S.  arcticum  Mai. 
is  a  severe  pest  of  cattle,  horses,  and  sheep;  and  in  Mexico  S.  metallicum  Bel- 
lardi, S.  ochraceum  Walk,  and  S.  callidum  D.  &  S.  are  known  to  bite  man. 
Other  species  are  known  to  be  very  destructive  to  animals  including  man,  as 
Cnephia  pecuarum  (Riley)  and  S.  columbaschensis  Fabr. 


OTHER  BLOODSUCKING  NEMOCEROUS  FLIES  409 

CLASSIFICATION:  The  family  Simuliidae  has  been  rudely  treated  by 
the  taxonomists.  It  has  been  divided  into  six  or  more  subfamilies  with  nu- 
merous genera  and  subgenera  (Enderlein,  1921).  Edwards  (1931),  however, 
recognized  but  a  single  genus,  Simulium,  and  seven  subgenera.  Vargas  (1945) 
recognized  but  one  genus,  Simulium,  for  the  New  World  species.  Smart 

(1945)  recognized  two  subfamilies  and  six  genera  from  the  world.  Vargas 

(1946)  adopts  the  classification  by  Smart  but  in  addition  adopts  nine  sub- 
genera  in  the  genus  Simulium  (restricted).  The  following  key  (adapted  from 
Smart)  will  serve  to  separate  the  genera : 

T.  R,  of  the  radius  joining  the  costa  about  the  middle  of  the  front  margin 

of  the  wing;  radial  sector  (Rs)  forked,  (i  sp.,  California)  

Parasimulium 

Rt  of  the  radius  joining  the  costa  well  beyond  the  middle  of  the  front 
wing  (Fig.  145) ;  radial  sector  forked  or  not 2 

2.  Radial  sector  (Rs)  forked;  pedisulcus  and  calcipala  lacking.  (28  spp.) 

Prosimulium 

Radial  sector  (Rs)  not  forked  (Fig.  145);  pedisulcus  and  calcipala  (Fig. 
150)  may  be  present  or  absent 3 

3.  Vein  Cu2  straight;  anal  vein  straight;  pedisulcus  absent;  calcipala  well 

developed.  (Neotropical;  13  spp.)    Gigantodax 

Vein  Clio  sinuous  (Fig.  145) ;  anal  vein  sinuous 4 

4.  Antennae  with  10  segments  or  less  (mainly  Australian  and  Andean  re- 

gion of  S.  America)  Austrosimulium 

Antennae  with  n  segments;  rarely  10 5 

5.  Pedisulcus  absent  or  very  indistinct;  calcipala  minute  or  absent;  basal 

section  of  radius  lacks  macrotrochia  above;  distal  section  of  radial  sector 
with  a  single  row  of  macrotrichia  above.  (World-wide;  36  spp.)   .... 

Cnephia 

Pedisulcus  present;  calcipala  present  (Fig.  150);  basal  section  of  radius 
and  distal  section  of  radial  sector  with  or  without  macrotrichia.  (World- 
wide; over  500  spp.)  Simulium 

It  is  not  feasible  to  give  keys  to  species  as  many  characters  are  based  on  the 
male  or  female  genitalia.  Keys  will  be  found  in  some  of  the  references  cited 
and  these  are  indicated. 

RELATION  TO  DISEASE 

The  black  flies  or  buffalo  gnats  affect  man  and  animals  in  at  least  two  ways, 
by  their  bites  and  as  intermediate  hosts  of  parasites. 


4io  MEDICAL  ENTOMOLOGY 

BITES :  The  bites  of  black  flies  are  extremely  annoying.  The  flies  commonly 
appear  in  swarms  and  attack  with  great  avidity.  Various  species  have  been 
recorded  from  the  tropics  to  the  polar  circles  as  inflicting  severe  damage  to 
stock  and  causing  a  peculiar  fever  in  man.  Probably  the  most  famous  species 
is  the  Golubatz  fly  (S.  columbaschensis  Fabr.),  which  frequently  occurs  in 
countless  numbers  in  parts  of  Romania,  Yugoslavia,  and  Hungary.  Ciurea 
and  Dinuflescu  (1924)  paint  a  gloomy  picture  of  an  invasion  of  this  fly  in 
certain  parts  of  Romania  during  the  season  of  1923.  Domestic  animals  suffered 
severely  and  the  authors  record  the  death  of  16,474;  large  numbers  of  wild 
animals,  as  foxes,  deer,  and  hares,  were  also  killed.  Though  man  was  also 
severely  attacked  and  suffered  from  their  bites,  no  deaths  are  on  record. 
Riley  (1887)  gives  an  extended  account  of  outbreaks  of  Cnephia  pecuarum, 
the  buffalo  or  turkey  gnat,  in  the  lower  Mississippi  Valley.  Mules,  horses, 
cattle,  sheep,  sitting  turkeys  and  hens,  hogs,  dogs,  and  cats  suffered  in  the 
order  named.  Large  numbers  of  these  animals  were  killed,  especially  mules, 
horses,  turkeys,  hens,  and  hogs.  Cattle  also  succumbed  if  weakened  from 
poor  food  and  exposure.  There  also  appear  reports  of  deaths  of  human  beings 
but  most  of  them  seem  doubtful.  Webster  (1904)  gives  a  striking  account 
of  the  plagues  of  this  fly  in  the  same  region.  Bradley  (1935)  reports  heavy 
losses  of  mules  in  Mississippi  and  eastern  Arkansas  in  1927,  1931,  and  1934. 
A  total  of  over  1600  were  killed  during  these  years.  Rempel  and  Arnason 
(1947)  describe  the  mass  attack  of  Simttliitm  arcticum  Mai.  on  horses,  cattle, 
and  sheep.  The  animals  began  dying  within  6  to  24  hours  after  the  attack. 
If  cold  weather  intervened,  the  flies  disappeared,  and  this  happened  in  some 
of  the  worst  outbreaks.  In  all,  over  800  cattle,  horses,  and  sheep  were  killed 
during  the  years  1944,  1945?  and  1946.  Various  travelers  and  explorers  give 
weird  accounts  of  the  abundance  of  black  flies  and  the  suffering  caused  by 
their  bites.  Wilhelmi  (1920)  presents  an  excellent  summary  of  black-fly 
plagues  (die  Kriebelmticl^enplagc). 

Stokes  (1914)  carefully  investigated  the  effects  of  the  bites  of  Simulium 
vennstum.  The  typical  bite  in  a  susceptible  individual  appears  to  run  the 
following  course:  bite  painless,  followed  by  hemorrhagic  spots  or  red  patches; 
a  papular  lesion  develops  in  3  to  24  hours,  and  later  a  vesicular  lesion  which 
may  last  for  a  few  days  to  several  weeks.  The  lesions  from  several  nearby 
bites  may  become  confluent  presenting  a  large  vesicopapular  lesion  with 
considerable  exudate  followed  by  extensive  edema,  and  the  formation  of 
oozing  and  crusted  plaques.  Pruritus  (intense  itching)  begins  shortly  after 
the  bites  and  may  become  diffuse  with  considerable  heat  and  burning  sensa- 
tion; the  pruritus  may  return  periodically  even  after  the  lesions  have  ap- 


OTHER  BLOODSUCKING  NEMOCEROUS  FLIES  411 

patently  healed.  Frequently  the  intense  itching,  followed  by  scratching,  may 
cause  secondary  infection  with  more  serious  results.  As  the  flies  frequently 
attack  back  of  the  ears,  over  the  eyes,  cheeks,  and  neck,  inflammation  and 
edema  at  these  sites  may  be  marked.  In  addition  to  the  lesions,  pruritus,  etc., 
produced  by  the  bites,  most  people  suffer  from  swelling  of  the  lymphatic 
glands  (lymphangitis),  which  become  tender  and  painful  on  pressure.  These 
swellings  usually  subside  without  further  trouble  if  the  patient  is  not  sub- 
jected to  further  black-fly  attacks.  Stokes  records  no  constitutional  effects 
from  the  bites  though  such  have  been  noted  by  other  workers. 

There  appears  to  be  considerable  immunity  to  the  bites  of  black  flies.  Many 
persons  reared  in  black-fly  areas  seem  to  acquire  a  certain  immunity.  The 
writer  has  suffered  agonies  from  their  bites,  while  native  companions  re- 
mained unattractive  to  the  flies  and  unbitten.  I  have  seen  fishermen  come 
from  the  woods  with  their  faces  streaming  with  blood  due  to  black-fly  bites 
but  they  suffered  no  apparent  harm;  others  show  distinct  feverishncss,  irrita- 
tion, and  intestinal  disturbances;  in  one  case  a  lineman  was  brought  in  almost 
unconscious  from  continued  exposure  but  he  recovered  in  a  few  days. 

The  presence  of  these  flies  renders  many  attractive  areas  almost  unhabitable 
during  certain  seasons  of  the  year.  Though  attempts  have  been  made  to 
immunize  man  against  their  bites,  no  great  success  has  been  achieved.  The 
activating  agent  in  the  causation  of  the  vesicular  papules,  pruritus,  etc.,  is 
believed  to  be  in  the  secretions  of  the  salivary  glands  but  what  it  is  remains 
as  yet  unknown. 

DISEASE:  Though  black  flies  have  been  accused  of  transmitting  diseases, 
it  is  only  within  the  past  few  years  that  definite  experimental  work  has  proved 
them  to  be  intermediate  hosts  of  human  parasites. 

Onchocerciasis  is  an  infection  due  to  species  of  Onchocerca  (family  Filari- 
idae  of  the  Nemathelminthes).  Onchocerca  volvulus  Leuck.  causes  subcuta- 
neous tumors  that  vary  from  small,  smooth  nodules  to  swellings  as  large 
as  a  walnut  (Fig.  151).  In  many  cases  no  nodular  swellings  may  occur,  though 
the  microfilariae  can  be  recovered  from  the  skin,  the  subcutaneous  lymph 
channels,  and  the  peripheral  blood.  This  parasite  was  first  found  in  a  native 
of  the  Gold  Coast,  Africa,  in  1893.  Since  then  it  has  been  found  widely  dis- 
tributed along  the  west  coast  of  Africa  and  from  Sierra  Leone  to  the  Congo 
basin,  east  to  southern  Sudan,  Uganda,  Nyasaland,  Kenya,  and  other  parts 
of  Africa.  Blacklock  (1926)  reports  that  40  to  50  per  cent  of  the  natives  ex- 
amined in  Sierra  Leone  had  the  microfilariae  of  0.  volvulus  in  their  skins. 
In  the  same  year  he  elucidated  the  further  development  of  this  worm  in  its 
insect  vector.  He  discovered  that  a  black  fly,  Eusimulium  damnosum  Theo., 


4i2  MEDICAL  ENTOMOLOGY 

ingests  these  microfilariae;  the  ingested  microfilariae  show  great  activity  in 
the  gut  of  the  fly  and  on  the  second  day  after  feeding  they  are  found  in  the 
posterior  thoracic  muscles;  here  development  proceeds  and  molting  ap- 
parently occurs.  At  the  end  of  a  minimum  of  six  or  seven  days  mature 
larvae  are  found  in  the  labium  of  the  proboscis  and  are  ready  to  infect  new 
hosts  when  the  fly  bites.  Only  man  has  been  found  naturally  infected  with 


Fig.  150  (left).  Hind  leg  of  Simulium  vittatum.  Cal,  calcipala;  F,  femur;  Peel,  pedisul- 
cus;  Tb,  tibia. 

Fig.  757  (right).  Onchocerciasis.  Note  nodules  on  elbow  and  hip.  (After  Blacklock, 
Annals  of  Tropical  Medicine  and  Parasitology.) 

O.  volvulus.  Though  no  transmission  experiments  by  means  of  experimen- 
tally infected  flies  have  been  attempted  on  man,  it  is  believed  that  Simulium 
damnosum  is  the  vector.  Experiments  with  monkeys  were  negative.  Though 
S.  damnosum  is  widely  distributed  in  tropical  Africa,  its  early  stages  and 
breeding  habits  are  apparently  unknown. 

Onchocerca  caecutiens  Brumpt  was  first  found  by  Robles  in  1915  in  nodules 
on  the  scalp  of  about  95  per  cent  of  the  population  of  the  Pacific  slope  of 
Guatemala  at  elevations  between  600  and  2000  meters.  The  infection,  in  a 
certain  proportion  of  cases,  shows  no  clinical  symptoms,  but  many  have 


OTHER  BLOODSUCKING  NEMOCEROUS  FLIES  413 

painful  erysipelaslike  swellings;  hence  it  is  called  "coastal  erysipelas."  Recent 
workers  seem  to  consider  O.  caecutiens  identical  with  O.  volvulus.  Hoffman 
(1930)  reports  that  all  the  people  in  certain  parts  of  Chiapas,  Mexico,  have 
the  microfilariae  in  the  lymph  and  86  per  cent  show  nodular  swellings.  The 
nodular  swellings  occur,  not  only  on  the  head,  but  on  the  iliac  crests,  ribs, 
shoulder  blades,  and  other  parts  of  the  body.  Ochoterena  (1930)  demonstrated 
the  microfilariae  in  the  excised  eye  of  a  blind  man,  the  "embryos  congregating 
in  the  outer  third,  in  the  corneal  epithelium."  Strong  (1931)  confirmed  these 
results  and  states  that  the  continued  passage  of  these  microfilariae  through 
the  lymphatics  of  the  eye  for  long  periods  may  cause  conjunctivitis,  keratitis, 
and  iritis.  It  would  thus  seem  that  this  parasite  in  Africa,  Central  America, 
and  Mexico  may  be  the  causative  agent  of  certain  types  of  blindness. 

Hoffman  (1930)  first  traced  the  development  of  this  microfilaria  in  a  black 
fly,  Simulium  callidum  D.  &  S.  (  —  mooscri).  He  showed  that  the  micro- 
filariae, after  being  ingested  by  the  black  fly,  pass  from  the  intestine  to  the 
thoracic  muscles  where  further  development  takes  place.  The  develop- 
mental period  in  the  fly  is  six  or  more  days,  and  the  infective  stage  passes  to 
the  mouth  parts  where  the  microfilariae  are  ready  to  infect  new  individuals 
when  the  fly  bites.  Hoffman,  Strong,  et  al.  and  others  have  amply  demon- 
strated complete  development  of  this  parasite  in  the  following  black  flies  in 
Mexico:  Simulium  metallicum  Bellardi  (  —  avidttm  HofTman),  S.  ochraceum 
Walk.,  and  S.  callidum  D.  &  S.  (  ~  mooseri  Dampf). 

In  addition  to  the  human  diseases  transmitted  by  black  flies,  O'Roke  has 
shown  that  Simulium  venustum  Say  transmits  a  malarialike  disease  of  ducks 
caused  by  a  protozoan,  Leucocytozoon  anatis  Wickware.  This  disease  is  said 
to  be  very  deadly  to  young  ducklings.  Johnson  (1942)  reports  a  Leucocytozoon 
of  turkeys  transmitted  by  S.  nigroparvum  Twinn.  Steward  (1937)  has  demon- 
strated the  life  cycle  of  Onchocerca  gutterosa  Neum.  (a  parasite  of  cattle)  in 
the  black  fly,  Simulium  ornatum  Meig.  in  England. 

PROTECTION  FROM  BITES:  Though  certain  persons  claim  immunity 
to  black-fly  bites,  the  effect  on  the  average  person  is  usually  severe,  even 
causing  clinical  symptoms  of  disease.  Recently  the  United  States  Bureau  of 
Entomology  and  other  agencies  during  World  War  II  have  developed  ex- 
cellent repellents  for  mosquitoes,  and  some  of  these  are  effective  against 
black  flies.  These  are  dimethyl  phthalate  and  indalone.  Everready  or  612, 
developed  at  Rutgers  University,  is  also  an  excellent  repellent.  Dimethyl 
phthalate  and  612  are  effective  for  about  a  maximum  of  four  to  six  hours. 
Apply  these  repellents  to  all  exposed  parts  but  avoid  getting  them  into  the 


4T4  MEDICAL  ENTOMOLOGY 

eyes;  they  may  also  be  applied  to  stockings  or  other  clothing  through  which 
the  flies  may  bite.  These  repellents  are  pleasant,  noninjurious  to  the  skin, 
and  can  be  applied  as  often  as  necessary. 

CONTROL  OF  BLACK  FLIES :  The  control  of  black  flies  is  very  difficult. 
As  their  breeding  grounds  are  mainly  swift  or  slow-flowing  streams  of  all 
sizes,  it  does  not  seem  possible  to  destroy  the  larvae  except  by  the  use  of 
chemicals  that  may  kill  nearly  all  animal  and  plant  life.  The  amount  of  such 
chemicals  needed  would  be  very  great  in  some  rivers  where  these  flies  often 
breed  in  vast  numbers.  In  the  smaller  streams,  however,  breeding  can  be 
reduced  by  the  removal  of  debris,  such  as  logs,  branches,  stumps,  stones, 
floating  weeds  or  grasses,  or  other  obstructions.  The  cost  is  usually  excessive. 
Attempts  have  been  made  to  reduce  breeding  by  the  application  of  DDT 
either  as  an  oil  emulsion  or  water  suspension.  The  results  are  not  very  en- 
couraging as  the  amount  of  DDT  required  kills  so  much  of  the  other  valuable 
animal  life.  It  may  be  possible  to  devise  methods  and  ascertain  amounts  that 
are  effective  against  black-fly  larvae  but  not  injurious  to  other  life  in  the 
streams.1 

The  adults,  when  abundant,  may  be  killed  by  DDT  as  aerosols,  mist  sprays, 
etc.,  applied  by  airplanes,  helicopters,  or  special  ground  equipment.  Such 
methods  have  been  applied  extensively  against  hordes  of  mosquitoes  and  have 
proved  satisfactory  to  those  who  pay  for  the  expenditures. 

FAMILY  CERATOPOGONIDAE  (Heleidae) 
The  Punkies,  No-scc-ums 

The  Ceratopogonidac  contains  a  small  number  of  known  species,  usually 
referred  to  as  "punkics."  This  family  may  be  distinguished  by  the  long  an- 
tenna (13  to  15  segments) ;  the  short  proboscis  (Fig.  154) ;  and  the  membrane 
of  the  wings  which  bears  micro-  and  macrotrichia  and  is  commonly  orna- 
mented, in  some  genera,  with  dark  spots  and  pale  areas  (Fig.  153).  The 
family  contains  a  considerable  number  of  genera  but  only  about  four  have 
species  that  are  bloodsucking  in  habit.  These  are  Leptoconops,  Lasiohelca, 
Holoconops,  and  Culicoides.  The  most  important  genus  is  undoubtedly 
Culicoides. 


1  Recent  reports  indicate  that  black-fly  larvae  can  be  destroyed,  even  in  large  streams, 
by  airplane  spraying  some  distance  above  their  breeding  grounds.  How  effective  these 
measures  are  and  the  correct  amounts  of  DDT  to  use  have  not  been  adequately  determined. 
The  destruction  of  other  aquatic  life  in  these  streams  is  a  problem  that  has  not  been 
solved  satisfactorily. 


OTHER  BLOODSUCKING  NEMOCEROUS  FLIES  415 

KEY  TO  THE  GENERA  2 

(Adults  bite  man  or  animals) 

1.  Racliomedial  cross  vein  absent;  antennae  of  females  with  13  to  14  seg- 

ments (including  pedicel  and  minute  scape)  2 

Radiomedial  cross  vein  present;  media  with  two  branches;  antennae  of 
females  with  15  segments  (including  pedicel  and  minute  scape)  ....  3 

2.  Antenna  of  female  with  14  segments  Leptoconops 

Antenna  of  female  with  13  segments Holoconops 

3.  Empodium  well  developed,  nearly  as  long  as  the  claws.  First  radial  cell 

small  and  narrow;  second  cell  long  and  narrow.  (Severe  bloodsuckers; 

S.  American)    Lasiohelea 

Empodium  small  or  vestigial;  claws  small  and  simple;  two  radial  cells 
usually  present  and  second  branch  of  radius  ends  beyond  middle  of 
wing;  wings  usually  spotted.  (A  large  genus)  Cttlicoides 

THE  GENUS  CULICOIDES 

The  flies  belonging  to  this  genus  are  all  bloodsucking  and  arc  usually 
known  as  "punkics."  (The  term  "sand  flies"  is  frequently  used  but  this  should 
be  restricted  to  the  bloodsucking  species  of  Psychoclidae.)  They  are  extremely 
annoying  and  on  account  of  their  small  size  (only  i  to  nearly  3  mm.  in  length) 
can  easily  pass  through  the  openings  of  the  ordinary  mosquito  screens.  In 
some  parts  of  the  tropics  and  subtropics  they  are  so  abundant  as  to  interfere 
seriously  with  the  development  of  certain  regions.  Their  mouth  parts  (Fig. 
152)  are  admirably  adapted  for  taking  blood  and  closely  resemble,  in  structure, 
the  mouth  parts  of  the  Simuliidae.  The  males  are  not  known  to  take  blood. 

LIFE  HISTORY:  Oviposition  has  apparently  been  observed  in  only  one 
species,  C.  tyefferi  Patton.  This  species  lays  its  eggs  in  a  mass  in  the  vicinity 
of  water,  on  some  algae  or  green  plant  growth.  Other  species  undoubtedly 
lay  their  eggs  in  a  similar  manner.  The  larvae  arc  found  only  in  water  or  in 
water-saturated  sand  or  soil,  both  brackish  and  fresh,  where  there  is  decaying 
vegetation.  They  like  water  holes  in  stumps,  tree  holes,  and  manure  heaps 
and  water-holding  plants;  a  few  may  be  found  in  slime-covered  bark  of  trees 
and  under  bark  and  rotting  vegetation.  The  larvae  (Fig.  154)  are  minute, 

2  The  number  of  genera  in  this  family  varies  widely  depending  on  the  author; 
Johannsen  (1943)  recognizes  45  genera  in  the  Americas.  Those  indicated  above  are  the 
only  genera  in  which  the  species  are  bloodsucking  in  habit.  For  keys  to  genera  and 
species,  consult  the  bibliography. 


416  MEDICAL  ENTOMOLOGY 

elongate,  cylindrical,  nearly  colorless,  and  difficult  to  find.  The  easiest  method 
of  obtaining  the  larvae  is  to  collect  water  with  the  bottom  debris  and  soil 
from  suspected  breeding  places,  place  it  in  small  jars,  and  allow  the  debris 
to  settle.  The  larvae,  if  present,  can  then  be  seen  performing  their  peculiar 
movements.  They  swim  about  eellike  with  a  side-to-side  movement  of  the 
anterior  part  of  the  body,  followed,  each  time,  by  a  similar  motion  of  the 
posterior  part.  The  length  of  the  larval  life  does  not  seem  to  be  known. 


Fig.  752  (left).  Head  and  mouth  parts  of  Culicoidcs  pulicatis  L.  fc,  frontoclypeus; 
ga,galea;  h,  hypopharynx;  1,  labium;  Ire,  labrum-epipharynx;  m,  mentum;  md,  mandible; 
p,  palpus;  ph,  pharynx;  s,  stipes.  (After  Jobling,  Bulletin  oj  Entomological  Research.) 

Fig.  153  (right).  Wings  of  Culicoides  spp.  (/)  C.  coc^erelli  Coq.  (2)  C.  diabolicus  Hoff. 
(3)  C.  stellijcr  Coq.  (After  Hoffman,  American  Journal  oj  Hygiene.) 

Pupation  takes  place  in  the  water,  on  the  surface  of  wet  mud,  at  the  water 
edge,  or  among  algae.  The  pupa  is  elongate  with  conspicuous  breathing  trum- 
pets arising  from  the  thorax  (Fig.  154).  The  breeding  habits  and  bionomics 
of  this  group  are  imperfectly  known. 

Culicoides  canithorax,  C.  melens,  and  C.  dovei  (Fig.  154)  are  serious  pests 
in  many  places  along  the  Atlantic  seaboard.  In  the  West  Leptoconops  torrens 
is  an  abundant  species  in  the  Sacramento  and  San  Joaquin  Valleys.  Culicoides 
guttipennis  and  C.  obsoletus  (sanguisuga  Coq.)  are  widely  distributed  in 
North  America  and  are  annoying  pests.  C.  furens  Poey  is  widely  distributed 
along  the  southern,  western,  and  northern  shores  of  the  Gulf  of  Mexico, 


OTHER  BLOODSUCKING  NEMOCEROUS  FLIES  417 

southeastern  Florida,  the  West  Indies,  Bahamas,  and  down  the  Atlantic  coast 
to  Brazil. 

The  habits  of  the  various  species  of  Culicoides  are  not  well  known.  Root 
and  Hoffman  (1937)  record  33  species  from  North  America  and  the  Mexican 
highlands.  They  give  very  little  information  regarding  their  habits  or  bionom- 
ics. Johannsen  (1943)  lists  52  species  from  North  America,  Mexico,  and 
the  West  Indies. 


Fig.  154.  Life  stages  of  the  salt-marsh  punkie,  Culicoides  dovei.  (A}  Adult.  (#)  Two 
of  the  eggs.  (C)  Full-grown  larva.  (D)  Pupa.  (All  enlarged;  after  Dove  and  Hall.) 

OTHER  GENERA 

The  species  of  Leptoconops  and  iMsiohdea  are  less  well  known.  The 
adults,  so  far  as  observed,  are  known  to  suck  blood  and  are  said  to  be  very 
annoying. 

DISEASE 

The  punkies  affect  man  and  animals  by  their  bites  and  by  acting  as  inter- 
mediate hosts  of  parasitic  worms.  To  most  people  the  bite  is  very  annoying. 
It  is  usually  accompanied  by  a  prickling  sensation;  later  a  reddened  area 


418  MEDICAL  ENTOMOLOGY 

appears  about  the  point  of  puncture,  which  usually  swells,  and  is  followed 
by  an  intolerable  itching  that  may  last  for  days.  No  serious  effects  follow  if 
scratching  is  avoided. 

FILARIASIS:  Sharp  (1928),  in  the  Cameroons,  demonstrated  that  Culi- 
coides  austeni  serves  as  the  intermediate  host  of  Acanthocheilonema  perstans. 
This  filarial  worm  is  widely  distributed  throughout  tropical  Africa  and 
coastal  parts  of  South  America  from  Venezuela  to  Argentina.  It  is  not  known 
to  cause  any  specific  human  disease.  The  microfilariac  are  found  in  the 
peripheral  blood  of  man,  gorilla,  and  chimpanzee.  These  are  obtained  when 
the  fly  takes  blood.  Within  the  gut  of  Culicoides  austeni  the  rnicrofilariae  are 
very  active  penetrating  the  gut  wall  within  a  few  hours  (six).  About  24  hours 
later  they  are  found  in  the  thoracic  muscles,  where  development  proceeds. 
Six  days  later  they  migrate  to  the  head  and  neck,  and  within  a  day  or  so  more 
they  are  ready  to  emerge  by  way  of  the  fly's  proboscis.  Though  no  actual 
passage  of  the  larvae  from  the  fly's  proboscis  through  the  human  skin  was 
observed  by  Sharp,  it  is  believed  that  this  species  serves  as  an  actual  trans- 
mitter of  this  worm.  Culicoides  grahami  has  also  been  incriminated  as  a 
transmitter.  Furthermore,  in  a  dissection  of  227  specimens  of  C.  austeni  caught 
in  the  wild,  7  per  cent  were  found  infected  with  the  larvae  of  A.  perstans. 

Buckley  (1934)  demonstrated  the  developmental  cycle  of  Mansonella  oz- 
zardi  (Manson)  in  Culicoides  jurens  Poey.  This  filarial  worm  of  man  occurs 
in  parts  of  South  and  Central  America,  Mexico,  and  certain  parts  of  the  West 
Indies. 

CONTROL  OF  SAND  FLIES 

No  successful  methods  have  yet  been  devised  for  satisfactorily  controlling 
these  pests.  Hull  et  al.  (1939)  attempted  control  of  breeding  in  marshes  and 
mangrove  swamps  by  diking  and  pumping  the  areas  dry.  When  successful, 
good  control  was  obtained.  The  application  of  insecticides  has  not  been  ef- 
fective. The  use  of  DDT  in  breeding  areas  might  prove  valuable.  The  treat- 
ment of  screens,  doors,  and  other  woodwork  about  homes  with  a  5  per  cent 
DDT  in  kerosene  or  other  solvent  has  given  some  success  in  preventing 
these  minute  flies  from  entering  homes.  The  use  of  repellents  for  personal 
protection  is  valuable.  (See  pp.  395-396.) 


OTHER  BLOODSUCKING  NEMOCEROUS  FLIES  419 

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Monograph  i,  1945. 
* ,  Palacios,  A.  M.,  and  Najera,  A.  D.    Simulidos  de  Mexico.    Rev.  Inst.  Salub. 

y  Enferm.  Trop.,  7:  101-192,  1946. 
**Wilhelmi,  J.    Die  Kriebelmuckenplage.    Jena,  1920. 
*Wu,  Y.  Fang.    A  contribution  to  the  biology  of  Simulium  (Diptera).    Mich. 

Acad.  Sci.  Arts  Let.,  13:  543-599,  1931. 


OTHER  BLOODSUCKING  NEMOCEROUS  FLIES  421 

CERATOPOGONIDAE  (HELEIDAE) 

Bequacrt,  J.    Report  of  an  entomological  trip  to  the  Truxillo  Division,  Honduras, 

to  investigate  the  sand-fly  problem.     i3th  Ann.  Kept.,  United  Fruit  Co.,  Med. 

Dept.,  pp.  193-206,  1925. 
Carter,  H.  F.    A  revision  of  the  genus  Leptoconops  Skuse.    Bull.  Ent.  Res.,  12: 

1-28,  1921. 
,  Ingram,  A.,  and  MacFie,  J.  W.  S.     Observations  on  the  Ceratopogonine 

midges  of  the  Gold  Coast,  with  descriptions  of  new  species.    Ann.  Trop.  Med. 

Parasit.,  14:  187-210,  211-274,  309-331,  1920;  15:  177-212,  1921. 
Dove,  W.  E.,  and  Hall,  D.  G.    Dikes  and  automatic  tide  gates  in  control  of  sand- 
flies  and  salt  marsh  mosquitoes.     J.  Parasit.,  20:  337-338,  1934. 
Edwards,  F.  W.    On   the   British   biting  midges    (Diptera,   Ceratopogonidae). 

Trans.  Ent.  Soc.  Lond.,  74:  389-426,  1926. 
Fiilleborn,   F.    The   "blinding   filaria"   of   Guatemala    (Onchocerca   caecutiens 

Brumpt,  1919).     Proc.  Internal.  Conf.  on  Health  Problems  in  Trop.  Amer., 

pp.  241-256,  1924. 
Goetghebuer,  M.    Ceratopogoninae  de  Belgique.    Mem.  Mus.  R.  Hist.  Nat.  Belg. 

8  (3):  1-116, 1920. 
.    Heleidae  (Ceratopogonidae).    In  E.  Lindner,  Die  Fliegen,  Lieferung  77, 

78:  1-133,  Stuttgart,  1933-1934. 
Hoffman,  W.  A.     A  review  of  the  species  of  Culicoides  of  North  and  Central 

America  and  the  West  Indies.     Amer.  }1.  Hyg.,  5:  274-301,  1925. 
Hull,  J.  B.,  Dove,  W.  E.,  and  Platts,  N.  G.    Experimental  diking  for  control  of 

sandfly  and  mosquito  breeding  in  Florida  salt-water  marshes.    Jl.  Econ.  Ent., 

32:  309-312,  1939. 
Ingram,  A.,  and  MacFie,  J.  W.  S.    Notes  on  some  African  Ceratopogoninae — 

species  of  the  genus  Lasiohelea.     Ann.  Trop.  Med.  Parasit.,  18:  377-392,  1924. 
,  and  MacFie,  J.  W.  S.    Diptera  of  Patagonia  and  south  Chile.    II.  Fasc.  4. 

Ceratopogonidae,  pp.  155-232,  1931. 
Jobling,  B.    The  structure  of  the  head  and  mouth  parts  of  Culicoides  pulicaris  L. 

Bull.  Ent.  Res.,  18:  211-236,  1928. 
*Johannsen,  O.  A.    A  generic  synopsis  of  the  Ceratopogonidae  (Heleidae)  of  the 

Americas,  a  bibliography,  and  a  list  of  the  North  American  species.    Ann.  Ent. 

Soc.  Amer.,  36:  763-791,  1943. 
Kieffer,  J.  J.    Chironomidae.    In  P.  Wytsman,  Genera  Insectorum,  Fasc.  42. 

Brussels,  1906. 
.    Faune  de  France,     n.  Dipteres  (Nematoceres  piqueurs);  Chironomidae, 

Ceratopogoninae.    Paris,  1925. 
Lutz,  A.    Contribu^a  para  o  estudion  das  "Ceratopogonias"  haematofagas  encon- 

tradas  no  Brazil.    MIL    Mem.  do  Instit.  Oswaldo  Cruz,  4:  1-33,  1912;  5:  45- 

73, 1913;  6:  81-99, 1914. 


422  MEDICAL  ENTOMOLOGY 

Macfie,  J.  W.  S.    The  genera  of  Ceratopogonidae.    Ann.  Trop.  Med.  Parasit., 

34:  13-30,  1940. 
Malloch,  J.  R.     The  Chironomidae,  or  midges,  of  Illinois,  with  particular  reference 

to  the  species  occurring  in  the  Illinois  River.     Bull.  State  Lab.  Nat.  Hist.,  10, 

art.  VI:  1915;  u,  art.  IV:  305-363,  1915. 
Painter,  R.  H.    The  biology,  immature  stages,  and  control  of  the  sandflies  (biting 

Ceratopogoninae)  at  Puerto  Castilla,  Honduras.     i5th  Ann.  Rept.,  United  Fruit 

Co.,  Med.  Dept.,  pp.  245-262,  1927. 
Robles,  R.     Onchocercose  humaine  au  Guatemala  produsiant  la  cecite  et  "1'erysipele 

du  littoral"  (Erisipela  de  la  costa).    Bull.  Soc.  Path.  Exot.,  12:  442-463,  1919. 
*Root,  R.  M.,  and  Hoffman,  W.  A.    The  North  American  species  of  Culicoides. 

Amer.  Jl.  Hyg.,  25:  150-176,  1937. 
Sharp,  N.  A.  D.     Development  of  Microfilaria  perstans  in  Culicoides  grahami; 

a  preliminary  note.    Trans.  Roy.  Soc.  Trop.  Med.  Hyg.,  21:  70,  1927. 
* .    Filaria  perstans;  its  development  in  Culicoides  austeni.    Ibid.,  pp.  371— 

396,  1928. 
*Thomsen,  Lillian  C.     Aquatic  Diptera.     V.  Ceratopogonidae.     Cornell   Univ. 

Agr.  Exp.  Sta.,  Mem.  210:  57-80,  1937. 


CHAPTER  XIV 


The  Tabanidae  and  Rhagionidae: 

Horseflies,  Deer  Flies,  Clegs, 
Green-headed  Flies;  Snipe  Flies 


THE  family  Tabanidae  is  a  very  large  one.  Between  two  thousand  and 
twenty-five  hundred  species  have  been  described  from  the  world;  over 
three  hundred  species  are  recorded  from  North  America.  The  adults  are  of  stout 
build  (Fig.  155) ;  bristles  practically  absent;  eyes  large  and  prominent  (contigu- 


7 


Fig.  755.  Tabanus  atratus  Fabr,  Female  at  left;  male  at  right. 

ous  in  nearly  all  the  males)  and  usually  brilliantly  colored  (the  colors  disappear 
after  death) ;  antenna  with  the  third  joint  annulated  (Fig.  51  5)  but  never  with 
a  style;  proboscis  well  developed,  short  (Tabanus,  Haemafopota) ,  rather  long 


424  MEDICAL  ENTOMOLOGY 

.^Chrysops),  or  very  long  (certain  Pangonia  spp.);  mouth  parts  adapted  for 
piercing  (Fig.  156) ;  venation  (Fig.  56)  rather  characteristic,  the  costal  vein 
extending  all  around  the  wing.  The  squamae  are  large  and  the  pulvilli  and 
empodia  are  padlike. 

In  general  the  adults  are  robust,  rather  compact-looking  flies;  the  powerful 
wings,  stout  depressed  abdomens,  and  large,  rounded  heads  give  them  the 
appearance  of  vigor  and  activity.  They  range  in  size  from  about  that  of  the 
housefly  (some  Chrysops  species)  to  the  large  Tabanus  species  with  a  wing 
expanse  of  over  two  and  one-half  inches.  The  females  of  the  great  majority  of 
the  species  are  bloodsucking  in  habit,  while  the  males  peacefully  take  only 
plant  juices,  nectar,  excreta  of  some  other  insects,  or  any  available  liquids  con- 
taining nutritive  material.  The  females  have  a  wide  range  of  hosts,  the  larger 
mammals,  especially  our  domestic  animals,  being  most  frequently  attacked. 
Certain  species  are  known  to  attack  crocodiles  and  others  obtain  blood  from 
sea  turtles,  biting  between  the  plates  on  the  back.  In  many  parts  of  the  world 
they  are  serious  pests  of  livestock,  and  cattlemen  frequently  suffer  serious 
losses  from  outbreaks  of  these  flies.  Webb  and  Wells  (1924)  state  that  a 
medium-sized  tabanid  requires  8  to  TO  minutes  to  feed  and  takes  about  0.125 
cubic  centimeters  of  blood;  Stone  (1930)  estimates  that  such  a  fly  takes  nearly 
0.2  cubic  centimeters  for  a  meal.  It  will  thus  be  seen  that  when  these  flies  are 
very  abundant  the  daily  loss  of  blood  must  be  a  serious  drain. 

The  flies  are  lovers  of  sunlight,  warmth,  and  moisture.  They  are  attracted 
to  moving  objects,  and  species  of  Tabanus  and  Chrysops  consistently  attack 
man.  During  dark,  cloudy  days,  or  cool,  rainy  weather  they  remain  inactive, 
resting  quietly  in  secluded  places.  Their  range  of  flight  must  be  considerable, 
though  no  one  has  apparently  investigated  this  phase  of  their  activities.  Mac- 
Creary  (1940)  reports  the  collection  of  adults  at  light  traps  located  3  to  8 
miles  offshore.  They  are  much  more  abundant  near  their  breeding  grounds — 
swamps,  marshes,  irrigated  land,  river  bottoms,  along  the  margins  of  rivers 
and  lakes,  and  in  similar  places — than  in  the  open,  drier  country.  The  length 
of  the  adult  life  is  apparently  not  very  long,  probably  not  over  four  weeks  to 
two  months  as  shown  by  Stone  (1930)  from  his  consistent  weekly  collecting 
data.  In  Louisiana  Jones  and  Bradley  (1916  and  1917)  present  somewhat  similar 
data,  which  indicate  a  longer  season  for  the  activity  of  the  adults  of  certain 
species  (Tabanus  vicarius,  T.  lineola,  Chrysops  flavidus).  In  the  region  of 
central  New  York  and  no  doubt  elsewhere  (as  indicated  by  Jones  and  Bradley 
in  Louisiana),  the  emergence  and  flight  activity  of  the  different  species  take 
place  at  rather  definite  periods  of  the  year.  As  a  result,  the  maximum  abun- 
dance of  any  one  species  may  be  concentrated  in  a  rather  short  period  (as 


THE  TABANIDAE  AND  RHAGIONIDAE 


425 


Tabanus  pumilus  in  midsummer)  or  somewhat  prolonged  in  the  case  of  those 
species  that  normally  emerge  later  in  the  season. 

THE  MOUTH  PARTS  OF  A  HORSEFLY  (Chrysops  sp.) :  In  the  horsefly 
the  mouth  parts  project  downward  and  look  like  a  cylindrical  sac  with  a  pair 


-Hphy 


Lm 


Fig.  156.  Frontal  view  of  the  head  and  mouth  parts  of  a  horsefly  (Chiysops  univitta- 
tus).  The  mouth  parts  are  withdrawn  from  the  labium  in  order  to  show  them  separately. 
Ant,  antenna;  Clp,  clypeus;  Hphy,  hypopharynx;  Lb,  labrum;  Lm,  labium  (the  dotted 
line  points  to  the  tip,  usually  called  the  labella);  rnd,  mandible;  MX,  maxilla;  MxPlp, 
maxillary  palpus. 

of  palpi  overlapping  it  (Fig.  156).  The  saclike  appearance  is  due  to  the  en- 
largement of  the  labium,  which  is  hollowed  out  on  its  anterior  face  and 
terminates  in  two  lobes,  the  labella.  Within  this  hollow  lie  the  mouth  parts 
for  piercing.  These  consist  of  a  long  dagger-shaped  labrum,  a  pair  of  saber- 
shaped  mandibles,  a  pair  of  bladelike  maxillae  with  their  palpi,  and  a  long 


426  MEDICAL  ENTOMOLOGY 

tapering  stylet,  the  hypopharynx.  The  details  of  these  structures  and  their 
muscles  are  shown  and  explained  in  Fig.  157.  The  labium  is  a  large,  thick 
organ,  deeply  grooved  along  its  anterior  face,  and  terminates  in  the  two  broad 
lobes  called  the  "labella."  In  the  normal  position  the  labella  are  closed,  but 


Fig.  757.  Mouth  parts  of  a  horsefly  (Chrysops  univittatus] .  Left:  Labrum  and  hypo- 
pharynx  showing  their  relationship  and  their  connection  to  the  head  and  some  of  the 
muscles  (the  hypopharynx  is  slightly  withdrawn  in  order  to  show  it  more  clearly). 
Center:  The  right  mandible  with  muscles  in  place.  Right:  The  left  maxilla  with  its 
muscles.  C,  cardo;  Clp,  clypeus;  Dm,  dilator  muscle  of  the  food  pump;  DSp,  dilator 
muscle  of  the  salivary  syringe;  Em,  extensor  muscle  of  the  maxilla;  Fp,  food  pump  or 
pharyngeal  pump;  Hphy,  hypopharynx;  Lm,  labrum;  LmM,  labral  muscle;  Mi,  Ms,  Ms, 
muscles  that  move  the  mandible;  md,  mandible;  Mt.  mouth;  MX,  maxilla;  MxPlp, 
maxillary  palpus;  Rm,  retractor  muscle  of  maxilla;  Sg,  common  salivary  duct  leading  to 
salivary  syringe  (note  the  two  valves,  one  at  entrance  to  syringe  and  one  at  exit);  Sp, 
salivary  syringe;  St,  stipes. 

they  can  be  spread  apart  like  broad,  soft  pads.  The  posterior  portions  of  the 
labella  are  firmly  united,  but  the  anterior  halves  are  separated  by  a  deep 
median  cleft.  The  undersurface  of  each  lobe  is  traversed  by  close-set  channels 
called  "pseudotracheae." 
The  action  of  these  mouth  parts  is  difficult  to  determine.  The  probable 


THE  TABANIDAE  AND  RHAGIONIDAE  427 

action  is  as  follows :  the  fly  spreads  its  soft,  padlike  labella  on  the  skin,  drives 
the  mandibles  into  the  skin,  and  by  means  of  the  powerful  mandibular  muscles 
rips  it.  By  continuing  such  action  the  mouth  parts,  except  the  labium,  are 
driven  deeper  and  deeper  into  the  flesh.  The  barbed  ends  of  the  maxillae  prob- 
ably act  as  holdfasts,  and  the  mandibles  by  muscular  action  can  be  twisted 
in  the  wound.  By  this  means  blood  soon  flows  rapidly  and  is  pumped  by 
the  food  pump  up  the  channel  made  by  the  labrum  and  hypopharynx.  The 


Fig.  158.  Egg  masses  of  horseflies.  (A)  Egg  mass  of  Chrysops  sp. 
(B)  Egg  mass  of  Tabanus  phaenops.  (B  after  Dotcn.) 

salivary  secretion  is  forced  into  the  wound  by  the  salivary  pump.  This  secre- 
tion is  said  to  possess  an  anticoagulin  and  an  irritant  to  facilitate  and  increase 
blood  flow. 

LIFE  HISTORY:  As  the  larval  life  of  practically  all  our  common  species 
is  passed  in  water,  wet  soil,  or  semiaquatic  conditions,  the  eggs  are  laid  in  the 
vicinity  of  such  situations.  The  places  of  oviposition  may  be  classified  as  fol- 
lows (according  to  Stone,  1930)  : 

i.  Foliage  or  other  objects  over  shallow,  quiet  water,  edge  of  shallow 
pools,  lakes. 


428  MEDICAL  ENTOMOLOGY 

2.  Foliage  or  other  objects  in  relatively  deep  water  at  some  distance  from 
shore,  or  on  ledges,  or  rocks,  over  deep  water. 

3.  Stones  or  other  objects  projecting  over  flowing  streams. 

4.  Vegetation,  as  leaves  or  trunks  of  trees,  over  either  moist  or  even  quite 
dry  soil. 

The  eggs  are  deposited  in  masses  (Fig.  158),  varying  in  number  from  100 
to  800  eggs.  The  species  of  Chrysops  usually  place  their  eggs  in  a  single  layer 
(Fig.  158  A),  though  C.  celer  and  C.  piJ(ei  place  theirs  in  double  tiers;  those  of 
Tabanus  are  generally  laid  in  several  layers  (Fig.  158  B).  The  egg  masses  are 
protected  by  a  gluey,  waterproof  covering,  placed  on  them  by  the  female  when 


Fig-  159-  A  sagittal  sectional  view  of  the  head  of  a  tabanid  larva  to  show  the  relation 
of  the  mouth  parts  to  the  pharynx.  C,  canal  through  the  mandible;  CB,  cephalic  brush 
of  spines;  DM,  dilator  muscle  of  the  salivary  pump;  DPh,  dilator  muscles  of  the  pumping 
pharynx;  E,  esophagus;  Lm,  levator  muscle  of  the  mandible  and  maxilla  and  the  cephalic 
brush;  LbPlp,  labial  palpus;  Md,  mandible;  MX,  maxilla;  Ph,  pharynx;  Pip,  maxillary 
palpus;  S,  common  salivary  duct;  Sm,  salivary  duct  from  pump  to  labium;  Sp,  salivary 
syringe;  T,  anterior  extension  of  the  tentorium;  Ten,  tentorium;  V,  valves  of  the  salivary 
pump.  (Redrawn  and  modified  from  Cameron.) 

in  the  act  of  oviposition.  The  egg  stage,  normally,  lasts  but  a  short  time, 
usually  not  more  than  5  to  7  days,  though  it  may  be  prolonged  by  cool,  un- 
favorable weather.  All  of  the  eggs  of  a  mass  hatch  at  about  the  same  time,  and 
the  larvae  immediately  drop  to  the  water  or  the  ground  beneath. 

The  larvae  are  primarily  carnivorous  and  cannibalistic;  some  species  are  un- 
doubtedly saprophagous  (many  Chrysops  spp.).  The  larval  mouth  parts  are 
adapted  for  piercing  and  extracting  the  contents  of  their  victims  (Fig.  159). 
The  length  of  the  larval  life  varies  considerably.  In  most  of  our  North  Ameri- 
can species  the  larval  stage  requires  from  9  to  n  months  though,  undoubtedly, 
the  amount  and  availability  of  food  determines,  to  a  large  extent,  the  time  of 
pupation.  Under  laboratory  conditions  Webb  and  Wells  reared  Tabanus 
punctifer  from  the  egg  to  the  adult  stage  in  less  than  two  years.  The  rearing 


THE  TABANIDAE  AND  RHAGIONIDAE 


429 


conditions  were  abnormal  and,  in  nature,  the  larval  growth  is  completed 
probably  in  less  than  a  year.  Stone  (1930),  Schwardt  (1936),  Logothetis  (un- 
published thesis),  and  others  have  reared  considerable  numbers  of  Tabanidae. 
The  average  larval  life  of  those  reared  was  about  n  to  a  little  over  12  months, 
while  the  pupal  period  varied  from  five  days  to  two  or  three  weeks.  However, 
certain  larvae  of  the  species  required  nearly  two  years  (as  Tabanus  vicarius 
in  its  northern  range). 


Fig.  160.  Larvae  of  Tabanidae.  (/)  Chrysops  discalis  Will.  (2)  C.  excitans 
Walk.  (3)  C.  julvaster  OS.  (4)  Siphon  of  C.  excitans.  (5)  Tabanus  rcinwardtii 
Wied.  (6)  T.  septcntrionalis  L.  (From  Cameron,  Bulletin  of  Entomological 
Research.) 

The  larvae  of  Tabanidae  possess  n  body  segments  exclusive  of  the  small 
retractile  head  (Fig.  160).  The  body  is  cylindrical,  tapering  toward  both  ends, 
usually  striated  longitudinally,  and  with  a  single  posterior  siphon.  The  siphon 
is  borne  on  the  dorsal  portion  of  the  anal  segment.  It  can  be  telescoped  within 
the  anal  segment  and  bears  on  its  tip  the  openings  of  the  respiratory  system 
(metapneustic).  In  addition,  the  presence  of  Graber's  organ  within  the  tenth 
and  eleventh  segments  (readily  seen  in  most  tabanid  larvae)  will  distinguish 
these  larvae  from  all  others.  The  organ  consists  of  a  scries  of  capsules,  each 


430  MEDICAL  ENTOMOLOGY 

containing  a  pair  of  minute,  black  pyriform  bodies,  lying  in  a  pyriform  sac 
directly  beneath  the  integument  of  the  tenth  and  eleventh  segments.  In  the 
case  of  Goniops  chrysocoma,  the  larva  has  a  club-shaped  body,  swollen  pos- 
teriorly, and  the  striations  are  overshadowed  by  the  mammillated  parts  of  the 
integument;  Graber's  organ  is  not  easily  seen  and  no  distinct  siphon  is  visible. 
When  the  larvae  are  mature  they  migrate  to  drier,  rather  compact  soil  where 
they  pupate.  The  pupal  period  is  rather  short,  ranging  usually  from  one  to 
three  weeks. 

CLASSIFICATION 

The  family  Tabanidae  contains  a  large  number  of  genera,  at  least  over  sixty.1 
Surcouf  (1921)  presents  a  key  to  the  genera  of  the  world;  Krober  and  Bequaert 
give  us  a  review  of  most  of  the  African  species;  Hine  (1903)  treats  of  the 
North  American  species;  and  other  workers  give  incomplete  accounts  of  the 
species  from  different  parts  of  the  world.  Bequaert  (1924)  states  that  in  Amer- 
ica, north  of  Panama,  there  are  over  334  species  distributed  among  21  genera; 
of  this  number  71  belong  to  the  genus  Chrysops  and  206  to  the  genus  Tabanus; 
the  other  genera  contain  from  i  to  18  species.  Brennan  (1935)  gives  an  excellent 
account  of  the  subfamily  Pangoniinac  and  Stone  (1938)  that  of  the  subfamily 
Tabaninae  for  North  America.  Philip  (1947)  attempts  a  rather  new  classifica- 
tion of  the  Tabanidae,  dividing  the  family  into  the  normal  subfamilies  and 
these  into  tribes  (3  tribes  in  the  Pangoniinae;  4  tribes  in  the  Tabaninae)  and 
recognizes  27  genera  with  474  species  for  North  America  north  of  Mexico. 
However,  the  following  brief  key  will  aid  in  placing  the  more  common  species 
in  their  correct  genera.  For  the  identification  of  the  larvae,  Stone  (1930)  gives 
preliminary  keys  to  the  immature  stages  of  the  North  American  species 
(Chrysops,  Tabanus,  and  Goniops  spp.)  which  he  knew. 

KEY  TO  SOME  OF  THE  NORTH  AMERICAN  GENERA 

1.  Hind  tibiae  with  spurs  at  the  tips;  ocelli  usually  present 

Subfamily  Pangoniinae  2 

Hind  tibiae  without  spurs  at  their  tips;  ocelli  absent 

Subfamily  Tabaninae  7 

2.  Third  segment  (the  flagellum)  of  antenna  with  5  distinct  annuli 3 

Third  segment  of  antenna  with  8  distinct  annuli 4 

3.  Pedicel  (2nd  segment)  of  antenna  about  one-half  as  long  as  the  first  seg- 

ment (the  scape)  Silvius 

1Enderlein  (1922,  1923)  recognizes  over  150  genera  from  the  world,  many  of  them 
with  but  one  or  two  species. 


THE  TABANIDAE  AND  RHAGIONIDAE  431 

Pedicel  more  than  one-half  as  long  as  the  scape,  often  nearly  as  long; 
wings  usually  infuscated,  picturelike Chrysops 

4.  Eyes  of  females  acutely  angulate  above;  basal  portion  of  wing  infuscated 

Goniops 

Eyes  of  female  not  angulate  above;  wings  of  uniform  color 5 

5.  Maxillary  palpi  short,  stubby,  about  equal  in  length  to  the  proboscis 

Apatolestes 

Maxillary  palpi  slender,  shorter  than  proboscis 6 

6.  Cell  R5  petiolate EsenbecJ^ia 

Cell  R5  open,  not  petiolate Stonemyia 

7.  Third  antennal  segment  with  4  annuli;  wings  gray,  with  small  white 

spots     Haematopota 

Third  antennal  segment  with  5  annuli;  wing  pattern,  if  any,  not  as 
above 8 

8.  Basal  part  of  third  antennal  segment  without  a  dorsal  projecting  tooth; 

eyes  bare;  wing  with  at  least  a  subapical  brown  spot Diachlorus 

Basal  part  of  third  antennal  segment  with  or  without  a  dorsal  projecting 
angle;  if  angle  is  present  eyes  are  bare  (not  pilose)  9 

9.  Eyes  distinctly  pilose;  ocellar  tubercle  absent;  eyes  of  female  with  a  single 

diagonal,  purple  line  (usually  present  even  in  dried  specimens).  Palpi 

not  black  and  abdomen  without  a  dorsal  stripe Atylotus 

Eyes  pilose  or  bare  but  without  the  diagonal  line;  either  the  palpus  black 

or  the  abdomen  with  a  narrow,  dorsal  stripe Tabanus 

Stcnotabanus 

NOTES  ON  SOME  OF  THE  GENERA:  The  genus  Tabanus  contains  a 
vast  assemblage  of  species,  over  a  thousand  being  listed  from  the  world;  Be- 
quaert  (1924)  reports  over  two  hundred  from  North  America  north  of  Pa- 
nama, while  Stone  (1938)  recognizes  124  species  in  North  America  north  of 
Mexico.  Most  of  the  species  are  large  (Fig.  155),  stout,  vigorous  fliers  and 
readily  attack  man  and  animals. 

Chrysops  is  the  next  largest  genus,  the  species  being  world-wide  in  distribu- 
tion; over  eighty  species  are  recorded  from  North  America.  They  are  com- 
monly called  "deer  flies."  The  species  are  rather  small  (Fig.  161).  The  wings 
are  clear  except  for  a  broad,  dark  area  along  the  anterior  margin  of  the  wing 
and  a  broad,  dark  band  across  the  wing  at  the  level  of  the  discal  cell  or  just 
beyond  it;  the  apex  may  be  clear  or  infuscated.  They  readily  attack  man  and 
are  often  extremely  annoying.  Most  of  the  species  are  partial  to  low-lying 
marshy  or  swampy  woods. 

Silvius  is  a  small  genus  of  which  we  have  six  species  in  North  America. 


432  MEDICAL  ENTOMOLOGY 

Representatives  of  this  genus  occur  abundantly  in  the  Australian  region. 

The  species  of  the  genus  Haematopota  are  most  abundant  in  the  Ethiopian 
and  Oriental  regions,  though  they  occur  in  all  parts  of  the  world.  Only  two 
species  are  recorded  by  Stone  (1938)  as  occurring  in  North  America. 

In  the  genus  Pangonia  the  eyes  are  more  or  less  broadly  separated  in  the 
female,  whereas  in  the  male  they  may  be  contiguous  or  separated.  Ocelli  are 
usually  present  though  they  may  be  absent.  The  proboscis  is  of  variable  length, 
but  it  is  generally  longer  than  the  head  and  frequently  very  long.  The  sixth 
longitudinal  vein  is  straight.  This  genus  has  been  broken  up  into  a  number 
of  genera  of  rather  doubtful  validity. 

The  genus  Diachloms  is  practically  restricted  to  South  America.  One  species, 
£>.  jerrugatus  Fabr.,  is  known  from  North  America  (Delaware  to  Florida 
and  Mexico  to  Brazil). 

RELATION  TO  DISEASE 

In  addition  to  the  effects  of  their  bites  and  the  loss  of  blood,  man  and  animals 
suffer  from  certain  diseases  that  are  distributed  by  tabanids  either  mechanically 
or  as  intermediate  hosts. 

FILARIASIS 

Loa  loa  Cobbold  is  a  filarial  worm  that  has  been  recovered  at  various  times 
from  man  for  over  a  hundred  years.  The  earliest  observations  (1770-1825) 
were  on  Negroes  recently  imported  into  the  West  Indies.  Later  this  worm  was 
found  in  its  indigenous  territory  in  West  Africa.  At  present  it  is  widespread 
along  the  west  coast  from  Nigeria  and  the  Cameroons  down  to  Angola  and 
inland  to  central  tropical  Africa  and  possibly  to  Uganda.  The  mature  female 
worm  measures  from  50  to  70  mm.  in  length  and  about  0.5  mm.  in  maximum 
width;  the  male  from  30  to  34  mm.  in  length  to  about  0.4  mm.  in  width.  They 
are  found  in  the  subcutaneous  tissues  of  man  where  they  migrate  back  and 
forth.  They  have  been  found  in  various  parts  of  the  body  but  seem  to  have  a 
predilection  for  the  head,  especially  the  eye  (hence  often  called  the  "eye 
worm").  Frequently  these  worms  appear  to  produce  swellings,  the  so-called 
"Calabar  swellings,"  which  may  become  as  large  as  half  a  goose  egg.  These 
swellings  are  generally  painless,  hot,  and  disappear  in  a  few  days.  What 
relation  the  worm  bears  to  the  swellings  has  not,  apparently,  been  deter- 
mined. 

The  females  discharge  microfilariae  in  the  passages  made  during  their  migra- 
tions. These  reach  the  peripheral  blood  vessels,  where  they  are  found  during 


THE  TABANIDAE  AND  RHAGIONIDAE  433 

certain  parts  of  the  day  (9  A.M.  to  2  P.M.),  hence  were  called  Micro filaria  diurna 
by  Manson.  On  epidemiological  grounds  Manson  (1895)  suggested  that  a  spe- 
cies of  mangrove  fly  (Chrysops  dimidiata  v.  d.  Wulp)  was  the  intermediate 
host.  Leiper  (1912,  1913)  and  Kleine  (1915)  added  certain  experimental  evi- 
dence in  support  of  this  view.  However,  the  Connals  (1921  and  1922)  com- 
pletely elucidated  the  entire  life  cycle  of  this  worm.  From  dissections  of  wild 
specimens  (2283)  of  Chrysops  dimidiata  and  C.  silacea  they  found  0.96  per 
cent  infected  with  filariae.  Experimentally  they  showed  that  these  flies  take 
up  the  microfilariae  while  feeding;  the  microfilariae  then  bore  their  way  out 
of  the  gut  and  lodge  in  the  thoracic  and  abdominal  muscles;  here  further  de- 
velopment takes  place  and  in  10  to  12  days  after  the  infective  meal  mature 
larvae  appear  in  the  proboscis.  The  fly  is  now  ready  to  infect  new  hosts.  Most 
of  the  larvae  leave  the  fly  at  its  first  meal,  though  it  may  remain  capable  of 
infecting  new  hosts  for  at  least  five  days.  The  Connals  were  able  to  infect, 
experimentally,  guinea  pigs,  rabbits,  and  a  monkey.  The  two  tabanids,  C.  dimi- 
diata  and  C.  silacea,  are  strictly  diurnal  in  their  feeding  habits  and  feed  com- 
monly on  man.  In  all  probability  other  species  of  bloodsucking  flies  will  be 
found  capable  of  transmitting  this  filarial  worm. 

TULAREMIA 

Tularemia  is  an  infectious  disease  caused  by  Bacterium  tularensc  (Pasteu- 
rella  tularensii) .  Primarily  it  occurs  in  nature  as  a  plaguelike  disease  of  rodents, 
especially  rabbits  and  hares.  It  is  transmitted  to  man  by  various  bloodsucking 
insects  (see  Chapter  in).  It  is  of  interest  here  because  Francis  (1919,  1920)  first 
recognized  the  identity  of  "deer-fly  fever"  and  the  "plague-like  disease  of 
rodents."  By  careful  experiments  Francis  and  Mayne  (1921)  were  able  to 
demonstrate  the  agency  of  Chrysops  discalis  (Fig.  161)  in  disseminating  the 
disease  from  infected  to  healthy  guinea  pigs  and  rabbits.  They  found  the 
method  of  transmission  was  purely  mechanical,  though  the  fly  could  remain 
infective  as  long  as  14  days.  They  found  that  practically  all  the  flies  did  remain 
infective  at  least  as  long  as  eight  days  after  their  infecting  meals.  They  also 
demonstrated  that  numerous  human  cases  of  tularemia  were  due  to  the  bite  of 
this  fly,  the  fly  obtaining  the  bacterium  from  jack  rabbits  and  transmitting  it 
to  man.  Cases  due  to  the  bite  of  Chrysops  discalis  have  been  reported  from 
Utah,  Idaho,  Wyoming,  Colorado,  Nevada,  Oregon,  and  Montana. 

ANIMAL  DISEASES 

The  species  of  Tabanidae  are  extremely  annoying  and  injurious  to  live- 
stock and  many  of  the  larger  game  animals.  Not  only  do  these  animals  suffer 


434  MEDICAL  ENTOMOLOGY 

from  their  bites  and  consequent  loss  of  blood,  but  the  flies  frequently  dis- 
tribute pathogenic  organisms  from  one  animal  to  another.  This  is  due  to  the 
fact  that  frequently  the  flies,  not  being  allowed  to  complete  their  blood  meal 
on  one  host,  immediately  attack  another.  In  this  way  they  may  transmit, 
mechanically,  any  organism  on  the  proboscis  obtained  from  the  previous  host. 
The  principal  types  of  disease  transmitted  in  this  manner  are  those  in  which 
the  virulent  organisms  are  present,  in  large  numbers,  in  the  peripheral  blood 
and  somewhat  resistant  to  short  exposures. to  the  air.  Here  are  found  such 
diseases  as  anthrax,  trypanosomiasis,  hemorrhagic  septicemia,  etc. 


Fig.  161.  Chrysops  discalis  Will.  (After  Francis.) 

ANTHRAX:  A  few  investigators  have  demonstrated  the  possibility  of  the 
mechanical  transmission  of  this  disease  from  animal  to  animal  by  biting  flies, 
principally  Tabanidae.  Mitzmain  (1914)  proved  in  a  number  of  controlled 
experiments  that  Tabanus  striatus  could  transmit  anthrax  from  infected  to 
healthy  animals.  This  was  accomplished  by  the  method  of  interrupted  feed- 
ing, the  fly  feeding  on  a  heavily  infected  guinea  pig  and  then  transferring 
within  a  short  time  to  a  healthy  one.  If  flies  were  allowed  to  feed  on  infected 
guinea  pigs  a  short  time  after  their  death  and  were  then  transferred  to  healthy 
pigs,  no  infection  resulted.  Though  his  experiments  were  few  in  number,  he 
demonstrated  the  possibility  of  species  of  Tabanidae  distributing  the  disease 
in  nature.  Morris  (1918)  obtained  a  high  percentage  of  infection  by  feeding 


THE  TABANIDAE  AND  RHAGION1DAE  435 

a  Tabanus  sp.  on  dying  guinea  pigs  (from  four  hours  before  death  till  20 
minutes  after  death)  and  then  immediately  feeding  them  on  healthy  pigs. 
Herms  states  that  physicians  have  told  him  of  the  infection  of  man  (malig- 
nant pustule)  by  the  bites  of  horseflies. 

TRYPANOSOMIASIS:  Various  species  of  trypanosomes  have  been  shown 
to  be  transmitted  mechanically  on  the  proboscis  of  different  species  of  horseflies. 
It  would  be  entirely  possible  for  almost  any  bloodsucking  tabanid  to  do 
this  provided  it  could  feed  for  a  brief  period  on  an  infected  animal  and  then 
be  immediately  transferred  to  a  susceptible  host.  The  trypanosomes  are  in- 
jected, provided  they  are  present  within  or  on  the  proboscis  in  a  viable  condi- 
tion, into  the  new  host  at  the  time  of  biting.  Some  of  the  important  trypano- 
somes that  have  been  shown  capable  of  being  transmitted  in  this  manner  are 
T.  evansi  (causative  agent  of  surra),  principally  by  species  of  Tabanidae  and 
also  by  Stomoxys  calcitrant  and  S.  nigra  (as  this  trypanosomc  has  no  known 
intermediate  host  in  which  a  cyclical  development  takes  place,  the  only  known 
method  of  transfer  is  by  biting  flics) ;  T.  soudanense  (believed  to  be  only  a 
variety  of  T.  evansi) ,  which  causes  a  chronic  disease,  eldcbab,  of  camels  and 
is  transmitted  by  horseflies;  and  T.  hippicum,  which  causes  a  trypanosomiasis 
of  mules  and  horses  in  South  America  and  parts  of  Central  America  and  is 
transmitted  by  Tabanus  importunus  (Colombia  and  Venezuela).  In  Panama, 
Dunn  (1932)  and  Clark  and  Dunn  (19^)  demonstrated  that  the  vampire 
bat  (Desmodits  rotund  its  miirinits)  is  the  important  vector.  T.  annamense, 
another  horse-infecting  trypanosome  in  Annam  and  Tonkin,  is  transmitted 
by  tabanid  species;  T.  cquiperditm,  the  causative  agent  of  dourine  in  horses, 
has  been  shown  to  be  capable  of  transmission  by  bloodsucking  flics,  Tabanus 
nemoralis  and  Stomoxys  calcitrans  (this  trypanosome  is  normally  transmitted 
by  direct  contact  of  mucous  surfaces  as  in  coitus;  it  has  no  known  intermediate 
host) . 

CONTROL 

No  successful  methods  of  controlling  horseflies  have  as  yet  been  devised. 
The  reduction  of  possible  breeding  areas  by  drainage  is  suggested,  and  Webb 
and  Wells  (1924)  point  out  that  no  breeding  took  place  in  well-drained 
areas.  Recently  Logothetis  and  Schwardt  (1948)  found  numerous  larvae  of 
Tabanus  vicarius  (costalis),  one  of  our  most  abundant  horseflies,  in  dry 
upland  soil  such  as  pasture  land,  cornfields,  and  cabbage  fields.  As  many 
tabanids  have  the  habit  of  flying  over  pools,  dipping  their  bodies  into  the 
surface  of  the  water,  Portchinsky  suggested  the  application  of  kerosene  oil 


436  MEDICAL  ENTOMOLOGY 

to  the  surface  of  pools  favored  by  the  flies.  He  tried  several  experiments  with 
most  gratifying  results.  The  oil  would  have  to  be  applied  when  the  flies  are 
abundant  and  at  various  periods  to  meet  the  time  of  emergence  of  the  dif- 
ferent species.  Webb  and  Wells  record  an  egg  parasite,  Prophanurus  emersoni 
Girault,  as  an  effective  check  on  the  breeding  of  Tabanus  punctijer. 


Pig,  162.  Symphoromyia  atripes.  (After  Ross,  Annals  of  the  Entomological  Society  of 
America.) 

THE  RHAGIONIDAE  (LEPTIDAE) 
The  Snipe  Flies 

The  Rhagionidae  consists  of  rather  small,  or  medium-sized,  dark  flies,  found 
commonly  in  woodlands,  especially  near  moist  places.  Unlike  the  horseflies, 
they  are  rather  sluggish  and  easily  captured.  Both  adults  and  larvae  are  preda- 
ceous.  However  only  two  genera  are  known  to  be  bloodsucking  in  habit, 
Symphoromyia  in  North  America  and  Spaniopsis  in  Australia.  The  species 
of  Symphoromyia  can  be  recognized  by  the  kidney-shaped  third  antennal  seg- 


THE  TABANIDAE  AND  RHAGIONIDAE  437 

ment.  About  25  species  of  Symphoromyia  are  known  from  North  America 
and  most  of  these  species  are  from  the  mountainous  regions  of  the  West.  Prac- 
tically none  of  these  have  been  taken  in  lowlands  or  valleys. 

S.  hirta  Johnson  is  a  large  species  (7.5  mm.  in  length)  and  is  widely  distrib- 
uted in  North  America.  Its  flight  habits  resemble  those  of  Chrysops  spp.  and 
its  bite  is  rather  severe.  Mills  (1943)  describes  an  outbreak  of  this  fly  in  the 
mountains  of  southwest  Montana,  the  flies  attacking  viciously  and  being 
very  troublesome  to  game  animals.  S.  atripes  Bigot  (Fig.  162)  is  prevalent  in 
parts  of  the  mountains  of  western  America  and  it  is  recorded  as  causing  as 
much  or  more  annoyance  than  mosquitoes.  It  attacks  quietly  and  Ross  (1940) 
records  it  as  extremely  annoying  in  the  mountains  (above  5000  ft.)  in  British 
Columbia.  S.  pachyceras  Will,  and  S.  kjncaidi  Aid.  are  also  reported  as  blood- 
sucking in  habit  in  parts  of  the  Pacific  coast  area. 

As  far  as  known,  the  biology  or  breeding  habits  of  none  of  our  blood- 
sucking species  are  known.  Other  species  of  rhagionids  are  known  to  breed 
in  moist  soil  where  there  is  decaying  vegetation 

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,  and  Connal,  S.  The  development  of  Loa  loa  (Guyot)  in  Chrysops  silacea 

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*Francis,  E.  Arthropods  in  the  transmission  of  tularaemia.  Trans.  4th  Internat. 
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438  MEDICAL  ENTOMOLOGY 

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Lutz,  Ad.     Tabaniden  Brasiliens  und  einiger  Nachbarstaaten.     Mem.  do  Instit. 

Oswaldo  Cruz,  5:  142-191,  1913;  7:  51-119,  1915. 
McAtee,  W.  L.    Facts  in  the  life-history  of  Goniops  chrysocoma.    Proc.  Ent.  Soc. 

Wash.,  13:  21-29,  1911. 
*MacCreary,  D.     Report  on  the  Tabanidae  of  Delaware.     Univ.  Del.,  Agr.  Exp. 

Sta.,  Bull.  226,  1940. 
*Marchand,  W.    The  early  stages  of  Tabanidae  (horse-flics).     Rockefeller  Inst. 

Med.  Res.,  Monograph  13,  1920. 


THE  TABANIDAE  AND  RHAGIONIDAE  439 

Mitzmain,  M.  B.    The  biology  of  Tabanus  striatus  Fabr.,  the  horse-fly  of  the 

Philippines.     Philip.  }1.  Sci.,  8:  197-218,  1913. 
.    The  mechanical  transmission  of  surra  by  Tabanus  striatus  Fabr.    Ibid.,  pp. 

223-229,  1913. 
.     Collected  studies  on  the  insect  transmission  of  Trypanosoma  evansi,  and  a 

summary  of  experiments  in  the  transmission  of  anthrax  by  biting  flies.     U.S. 

Pub.  Hlth.  Serv.,  Hyg.  Lab.,  Bull.  94,  1914. 
Philip,  C.  B.     Methods  of  collecting  and  rearing  the  immature  stages  of  Tabanidae 

(Diptera).     Jl.  Parasit.,  14:  243-253,  1928. 
* .     The  Tabanidae  of  Minnesota.     Minn.  Agr.  Exp.  Sta.,  Tech.  Bull.  80, 

W- 
.     A  catalog  of  the  blood-sucking  fly  family  Tabanidae  of  the  Nearctic  region 

north  of  Mexico.     Amer.  Mid.  Natural,  37:  257-324,  1947. 
*Schwardt,  H.  H.    Horseflies  of  Arkansas.    Univ.  Arkansas,  Agr.  Exp.  Sta.,  Bull. 

332>  I936- 
Stammer,  H.  J.     Die  Larvcn  der  Tabanidcn.     Zeit.  Wiss.  Biol.,  Abt.  A.,  Zcit. 

Morph.  Okol.  Ticre,  i:  121-170,  1924. 
Stekhoven,  J.  H.  S.     The  blood-sucking  arthropods  of  the  Dutch  East  Indian 

Archipelago.     VI f.     The  Tabanidae  of  the  Dutch  East  Indian  Archipelago. 

Treubia,  6  (Suppl.),  1926. 
*Stone,  Alan.     The  bionomics  of  some  Tabanidae  (Diplera).     Ann.  Ent.  Soc. 

Arner.,  23:  261-304,  1930. 
* .     The  horseflies  of  the  subfamily  Tabaninae  of  the  Nearctic  region.     U.S. 

Dept.  Agr.,  Misc.  Pub.  305,  1938. 
Surcouf,  J.  M.  R.     Diptera.     Family  Tabanidae.     Genera  Insectorum,  Fasc.  175, 

1921. 
Webb,  J.  L.,  and  Wells,  R.  W.    Horse-flies;  Biologies  and  relation  to  western 

agriculture.     U.S.  Dept.  Agr.,  Bull.  1218,  1924. 

RHAGIONIDAE 

Aldrich,  J.  M.     The  dipterous  genus  Symphoromyia  in  North  America.     Proc. 

U.S.  Nat.  Mus.,  49:  113-142,  1915. 
Ross,  H.  H.    The  Rocky  Mountain  "black-fly,"  Symphoromyia  atripes.    Ann. 

Ent.  Soc.  Amer.,  33:  254-257,  1940. 


CHAPTER  XV 


The  Bloodsucking 

Muscoidean  Flies:  Muscidae, 

Subfamily  Stomoxyidinae 


THOUGH  the  great  majority  of  flies  belonging  to  the  family  Muscidae  are 
nonbloodsucking  in  habit  (see  Chapter  xvi),  a  small,  closely  related 
group,  the  Stomoxyidinae,  are  bloodsucking  and  are  of  great  importance  to 
the  medical  man  and  the  veterinarian.  These  flies  belong  to  the  genera 
Stomoxys,  Haematobia  (Siphona),  Glossina,  Stygeromyia,  Haematobosca, 
Bdellolarynx,  and  possibly  a  few  others.  The  species  of  Stomoxys  and  Haema- 
tobia are  widely  distributed  throughout  the  world;  those  of  Glossina  are 
restricted  practically  to  the  African  continent;  the  other  genera  have  repre- 
sentatives in  the  Oriental  and  Ethiopian  regions.  In  the  Americas  we  have 
practically  only  two  species,  Stomoxys  calcitrans  and  Haematobia  irritans, 
which  are  widely  distributed  and  of  considerable  importance.  None  of  these 
bloodsucking  species  except  Glossina  spp.  and  Stomxys  spp.  have,  as  yet,  been 
incriminated  as  intermediate  hosts  of  pathogenic  organisms. 

THE  BITING  STABLE  FLY 
Stomoxys  calcitrans  Linn. 

The  biting  stable  fly  is  a  close  relative  of  the  housefly  but  can  be  distin- 
guished by  the  sharp,  piercing,  nonretractile  proboscis,  the  distinct  rounded 
spots  on  the  abdomen  (Fig.  163),  and  the  wing  venation.  This  bloodsucking 
fly  is  widely  distributed  throughout  the  world  and  may  be  found  wherever 
man  and  his  domestic  animals  occur.  It  has  been  called  the  stable  fly  because 
of  its  common  occurrence  in  and  around  stables,  though  it  also  frequents 
houses  (particularly  in  late  summer  and  autumn)  and  is  often  known  as  the 
"biting  housefly"  or  "dogfly."  It  is  a  lover  of  the  open  and  often  occurs  in 


BLOODSUCKING  MUSCOIDEAN  FLIES  441 

immense  swarms  about  cattle,  especially  throughout  our  central  states  from 
Texas  to  Canada  and  in  the  Argentine  Republic.  This  fly  is  a  vicious  biter 
and  attacks  a  great  variety  of  animals  as  well  as  man.  Bishopp  (1931)  reports 
that  mules,  horses,  cattle,  hogs,  dogs,  cats,  sheep,  and  goats  are  subject  to 
attack  in  about  the  order  named.  The  loss  of  blood  due  to  these  flies  when 
they  are  abundant  is  a  serious  drain,  and  in  severe  outbreaks  many  animals 
may  die  or  be  so  weakened  that  other  diseases  develop  and  cause  death.  Further- 
more, both  Bishopp  and  Freeborn  have  recorded  a  marked  reduction  of  milk 
flow  and  beef  production  when  these  flies  are  plentiful. 

The  bloodsucking  habit  of  this  species  caused  it  early  to  be  suspected  and 
later  incriminated  as  a  mechanical  distributor  of  numerous  animal  and  human 


Fig.  163.  Biting  flies.  Left:  Stomoxys  calcitrans.  Center:  Glossina  palpalis.  Rig/it: 
Ghssina  fly  in  resting  position. 

diseases.  It  has  been  shown  to  be  the  intermediate  host  of  at  least  one  nematode, 
Habronema  microstoma,  and  a  cestode,  Hymenolepis  carioca. 

The  mouth  parts  (Figs.  164,168)  are  admirably  adapted  for  piercing  and 
taking  blood.  Unlike  the  mosquito,  the  stable  fly  uses  the  entire  proboscis  in 
making  the  wound  and  both  males  and  females  suck  blood.  The  parts  consist 
of  those  found  in  the  housefly  (see  pp.  134-139),  but  greatly  modified  to  meet 
the  needs  of  piercing.  The  rostrum  (Fig.  164  a)  is  much  smaller  and  the 
pharyngeal  skeleton  or  fulcrum  is  not  so  well  developed  or  heavily  sclerotized. 
Owing  to  the  acute  flexure  of  the  proboscis  between  the  rostrum  and  the 
haustellum,  there  is  a  marked  difference  in  the  structure  of  the  buccal  cavity. 
The  prepharynx  appears  as  a  large  cylindrical  duct,  and  the  outer  wall  is  com- 
posed of  thick  rings  forming  a  supporting  framework  for  the  food  channel. 
Haustellum:  The  labium  is  strongly  sclerotized,  enlarged,  and  bulbous  at  the 


442  MEDICAL  ENTOMOLOGY 

base  tapering  to  the  apex;  it  appears  like  a  club.  Its  upper  surface  is  grooved 
to  form  a  deep  labial  gutter  in  which  lie  the  labrum  and  hypopharynx.  Both 
of  these  are  shorter  than  the  haustellum  and  do  not  reach  the  base  of  the 
labella,  attaining  only  the  labellar  sclerites  (f urea) .  The  food  channel  is  formed 


Fig.  164.  Mouth  parts  of  the  stable  fly  (Stomoxys  calcitrant),  (a)  Side  view  of  the 
proboscis,  (b)  The  labella  of  the  proboscis  with  the  prestomal  teeth  exposed,  (c)  Cross 
section  of  the  labrum  and  hypopharynx  near  the  middle  of  the  proboscis.  B,  swollen  base 
of  the  labium;  F,  fulcrum;  Fc,  food  channel;  H,  haustellum;  Hphy,  hypopharynx;  La, 
labellum;  Lb,  labium;  Lg,  labial  gutter;  Lm,  labrum;  MxPlp,  maxillary  palpus;  P, 
pharynx;  PP,  prepharynx;  Pt,  prestomal  teeth;  R,  rostrum;  Sd,  salivary  duct;  Sg,  salivary 
duct  in  hypopharynx;  St,  stipes;  W,  chitinous  membrane. 

by  the  juncture  of  the  margins  oi  the  labrum  and  the  hypopharynx  and  opens 
directly  into  the  pharynx  (Fig.  164).  Labella:  The  labella  are  small,  oval  lobes, 
much  reduced  as  compared  with  those  of  the  housefly  (Fig.  164  b) .  When  at 
rest  the  lobes  are  closely  appressed  along  their  inner  face,  concealing  com- 
pletely the  cutting  and  tearing  apparatus.  When  the  lobes  are  expanded  two 


BLOODSUCKING  MUSCOIDEAN  FLIES  443 

series  of  teeth  are  exposed,  five  on  each  side  attached  to  the  discal  sclerite.  Be- 
tween the  teeth  may  be  observed  a  number  o£  leaflike  blades  that  aid  in  the 
tearing  of  tissues.  The  labellar  sclerite  is  not  so  prominent  as  that  of  the  house- 
fly. In  biting,  the  stable  fly  brings  the  rostrum  and  haustellum  into  line,  the 
labella  are  everted,  and  by  means  of  the  labellar  teeth  and  leaflike  structures 
the  skin  is  punctured.  The  labella  are  sunk  into  the  wound  so  that  the  blood 
may  be  drawn  up  the  food  channel  into  the  pharynx. 

LIFE  HISTORY 

The  most  common  breeding  grounds  are  horse  manure  and  straw  stacks.  It 
has  been  found  breeding  in  cow,  sheep,  and  other  manures  when  mixed  with 
considerable  amounts  of  straw.  Other  common  breeding  grounds  are  the  left- 


Fig.  165  (left).  Eggs  of  Sfomoxys  calcitrans  attached  to  straw.  (After  Bishopp.) 
Fig.  166  (right).  Stomoxys  calcitrans.  Female  engorged  with  blood.  (After 
Bishopp.) 

over  grains  and  straw  about  dairies,  piggeries,  etc.  It  has  also  been  found 
breeding  in  fermenting  piles  of  grass,  weeds,  peanut  wastes,  and  other  vege- 
table rubbish.  Intensive  breeding  is  reported  in  fermenting  seaweed  piled  up  by 
the  sea  along  the  northern  shores  of  parts  of  the  Gulf  of  Mexico.  Moisture  is 
essential  for  the  development  of  the  larva.  Wet,  soggy  manures,  edges  of  rotting 
straw  stacks,  and  fermenting  grass  piles  are  frequently  found  swarming  with 
the  larvae  during  warm,  damp  weather.  This  species  has  never  been  found 
breeding  in  human  excrement. 

The  newly  emerged  female  requires  a  number  of  blood  meals  (Bishopp 
thinks  at  least  three)  for  the  production  of  eggs.  She  lays  her  eggs  in  irregular 
masses,  usually  a  few  to  as  many  as  25  in  a  single  group  (Fig.  165).  A  female 
may  lay  several  batches  (as  many  as  122  eggs)  before  seeking  another  blood 
meal.  A  single  fly  may  lay  eggs  at  least  three  times,  taking  several  blood  meals 
between  ovipositions.  Bishopp  (1931)  records  a  maximum  production  of  632 
eggs  by  a  single  female. 


444  MEDICAL  ENTOMOLOGY 

The  egg  is  elongate-ovoid,  of  a  creamy- white  color,  and  measures  about  i  mm. 
in  length.  The  incubation  period  varies  from  two  to  five  days,  usually  three 
days  (at  a  temperature  of  70°  F.).  The  young  larvae  immediately  bury  them- 
selves in  their  food  and  development  is  quite  rapid.  With  an  abundance  of 
food,  moisture,  and  summer  temperatures  (75°  to  85°  F.)  the  larvae  reach 
maturity  in  about  two  to  three  weeks;  at  higher  temperatures  maturity  may 
be  reached  in  n  days  but,  in  cool  weather,  larval  development  may  require  a 
month  or  more.  The  full-grown  larva  measures  about  20  mm.  in  length,  is 
white  to  creamy  white  in  color,  and  resembles  very  closely  the  larva  of  the 
housefly.  It  may  be  distinguished,  however,  by  the  narrower,  more  pointed 
anterior  end  and  by  the  posterior  spiracles  (Fig.  195  5).  In  the  biting  stable 
fly  the  posterior  spiracles  are  widely  separated,  rather  triangular  in  shape,  and 
heavily  sclerotized;  in  the  housefly  they  are  close  together  and  nearly  D-shaped. 

Pupation  takes  place  usually  in  the  drier  parts  of  the  breeding  grounds, 
either  toward  the  margins  or  near  the  underlying  soil.  The  chestnut-colored 
puparia  measure  from  5  to  7  mm.  in  length  and  may  be  distinguished  by  the 
posterior  spiracles  (the  spiracles  are  those  of  the  last  larval  instar,  Fig.  195). 
The  pupal  period  varies  greatly  and  is  dependent  largely  on  temperature, 
varying  from  6  to  20  or  more  days.  The  entire  life  cycle  from  the  egg  to  adult 
may  be  completed  in  as  few  as  14  days,  though  the  normal  period  is  usually 
three  to  four  weeks.  Under  unfavorable  conditions  the  life  cycle  may  be  greatly 
prolonged — seven  or  more  weeks. 

HABITS  OF  THE  ADULT 

These  flies  are  lovers  of  the  open  and  commonly  congregate  on  sunny  walls, 
fences,  and  other  exposed  situations.  During  storms,  dark  days,  and  at  nightfall 
they  seek  shelter,  invading  barns,  houses,  or  any  available  shelter.  On  the  open 
prairies  they  often  occur  in  immense  swarms  and  render  life  almost  unendura- 
ble not  only  for  cattle  but  also  for  man.  However,  their  most  common  habitat 
is  about  stables  and  farmyards  where  a  constant  blood  supply  is  available. 
Both  the  males  and  females  are  vicious  bloodsuckers.  The  bite  is  painful,  but 
once  the  beak  is  inserted  and  the  flow  of  blood  starts,  little,  if  any,  pain  is 
felt.  The  fly  requires  from  two  to  five  minutes  to  obtain  a  full  blood  meal. 
When  fully  gorged  (Fig.  166)  it  flies  away  rather  sluggishly,  settling  on  some 
nearby  object  to  digest  its  meal.  During  warm  weather  digestion  is  very  rapid 
and  the  flies  require  two  meals  a  day.  In  cool  weather  they  usually  require  a 
full  day  to  digest  a  single  blood  meal. 

They  are  vigorous  fliers  and  will  follow  their  food  supply  for  considerable 
distances.  How  far  they  can  travel  docs  not  seem  to  be  known.  However, 


BLOODSUCKING  MUSCOIDEAN  FLIES  445 

considerable  distances  may  be  traversed  along  roadways,  the  flies  taking  a 
blood  meal,  settling  down  to  digest  it,  and  then  following  another  passing 
host.  In  this  way  the  adults  may  be  found  long  distances  from  their  breeding 
grounds.  They  have  been  observed  in  trains,  automobiles,  etc.  The  life  of  the 
adult  is  rather  long,  varying  from  a  few  days  to  as  many  as  72  days  for  the 
female  and  94  for  the  male  (Mitzmain).  As  a  rule  the  probable  length  of 
adult  life  is  not  over  three  or  four  weeks. 

In  warm  climates,  breeding  is  continuous  throughout  the  year.  In  the  south- 
ern United  States  breeding  is  intermittent  during  the  winter  months  and  the 
larval  life  is  greatly  prolonged.  In  the  colder  parts  of  North  America  the  winter 
months  are  passed  normally  in  the  larval  and  pupal  stages. 

RELATION  TO  DISEASE 

Though  the  biting  stable  fly  has  been  accused  and,  in  some  cases,  apparently 
incriminated  as  a  vector  of  pathogenic  organisms,  most  of  the  recent  work 
indicates  that  this  fly  plays  but  a  small  part  in  the  spread  of  diseases. 

POLIOMYELITIS:  A  very  considerable  amount  of  work  has  been  done 
on  the  part  it  may  play  in  the  transmission  of  poliomyelitis;  though  at  first 
incriminated  all  later  researches  tend  to  prove  that  it  has  no  part  in  the  spread 
of  the  disease.  Furthermore,  the  advances  made  in  the  study  of  the  disease 
point  to  the  improbability  that  any  bloodsucking  insect  could  act  as  a  vector. 
It  would  seem  more  probable  that  flies  that  prefer  fecal  wastes  and  nasal 
discharges  would  be  incriminated  as  vectors.  As  a  matter  of  fact,  recent  work 
has  incriminated  such  flies  (see  p.  476). 

TRYPANOSOMIASIS:  This  fly  has  been  shown  to  act  as  a  mechanical 
vector  of  a  number  of  species  of  trypanosomes.  Trypanosoma  evansi,  the  causa- 
tive agent  of  surra  (see  Chapter  xiv)  of  horses  and  mules,  is  known  to  be 
distributed  by  it.  This  is  especially  true  when  flies  are  abundant  and  blood 
meals  are  interrupted,  the  fly  passing  directly  from  one  animal  to  another.  The 
trypanosomes  are  transported  on  the  proboscis  and  can  withstand  at  least  ten 
minutes'  exposure  to  the  air.  In  some  parts  of  the  world  species  of  Stomoxys 
are  regarded  as  important  agents  in  the  spread  of  surra. 

Under  experimental  conditions  Stomoxys  calcitrans  has  been  shown  capable 
of  infecting  susceptible  animals  with  the  following  species  of  trypanosomes 
(there  is  no  development  or  multiplication  of  the  trypanosomes  in  the  fly) : 

Trypanosoma  brucei  (causative  agent  of  nagana) 

Trypanosoma  rhodesiense  (causative  agent  of  Rhodesian  sleeping  sickness) 


446  MEDICAL  ENTOMOLOGY 

Trypanosoma  gambiense  (causative  agent  of  Gambian  sleeping  sickness) 
Trypanosoma  cazalboui,  T.  dimorphon,  and  some  others 
In  order  to  bring  about  the  transfer  by  the  fly  it  must  obtain  the  trypanosomes 
from  an  infected  animal  and  then  feed,  usually  within  ten  minutes,  on  a 
susceptible  animal.  Infection  takes  place  through  the  living  trypanosomes  in 
or  on  the  proboscis  of  the  fly. 

INFECTIOUS  ANEMIA  OF  HORSES:  A  virus  disease  of  horses,  in- 
fectious anemia,  is  widespread  in  North  America,  Europe,  and  Japan,  and 
probably  other  countries.  In  recent  years  this  disease  has  been  shown  to  be 
transmitted  by  the  interrupted  feedings  of  Stomoxys  calcitrant  from  the  sick 
to  the  well  by  Scott  (1922)  and  by  Stein  et  al.  (1942).  The  latter  authors  have 
also  demonstrated  sufficient  virus  in  the  mouth  parts  of  certain  tabanids  as 
well  as  Stomoxys  calcitrant  that  have  fed  on  sick  animals  to  infect  susceptible 
animals. 

The  genus  Stomoxys  contains  a  considerable  number  of  species,  probably 
twenty  or  more  depending  on  the  authority  consulted.  Zumpt  (1938)  lists  some 
27  species,  all  of  which  except  the  one  described  above  occur  in  the  African 
or  Oriental  regions.  None  of  these  appear  to  be  of  much  medical  importance. 

CONTROL 

The  control  of  the  biting  stable  fly  consists  essentially  in  the  elimination  or 
reduction  of  their  breeding  grounds.  The  treatment  and  handling  of  manure 
for  the  prevention  of  the  breeding  of  the  housefly  (see  Chapter  xvi)  is  also  effec- 
tive against  this  species.  Cleanliness  in  the  handling  of  feeds  in  and  around  pig- 
geries, stables,  etc.,  will  eliminate  many  breeding  places.  However,  the  most 
important  breeding  ground  of  this  fly  is  in  strawstacks,  especially  when  they 
become  wet  and  rotting  and  heating  take  place.  In  order  to  reduce  breeding, 
strawstacks  should  be  built  with  vertical  sides  and  the  top  so  arranged  as  to 
shed  as  much  water  as  possible.  The  base  of  the  stack  should  be  cleaned  up 
so  that  no  rotting  and  heating  straw  accumulates.  All  straw  not  intended  for 
the  feeding  of  animals  or  other  use  should  be  spread  over  the  fields  and 
ploughed  under  or  it  should  be  piled  and  burned.  Old  strawstacks  should 
not  be  allowed  to  stand,  for  they  usually  become  centers  for  the  breeding  of 
enormous  numbers  of  flies.  Such  stacks  should  be  distributed  over  the  land  or 
burned.  Intensive  breeding  also  occurs  in  fermenting  vegetable  rubbish,  such 
as  stacked  peanut  wastes,  fermenting  seaweed  piled  along  shore  lines,  and  any 
fermenting  plant  wastes.  The  employment  of  DDT  sprays  gives  excellent 
promise  for  the  control  of  the  adults.  In  using  DDT  follow  the  directions  on 
the  containers. 


BLOODSUCKING  MUSCOIDEAN  FLIES 
THE  HORN  FLY 


447 


The  horn  fly  (Haematobia  irritans  Linn.)  is  rather  small,  only  about  one- 
half  as  large  as  the  biting  stable  fly.  It  is  primarily  a  pest  of  cattle  and  acquires 
its  name  from  its  habit  of  clustering  at  the  base  of  the  horns.  It  rarely,  if  ever, 
attacks  man.  The  species  breeds  exclusively  in  fresh  cow  dung.  Though  the 
fly  is  a  serious  pest  of  cattle,  it  is  not  known  to  be  of  any  great  importance  in  the 
transmission  of  diseases.  It  is  not  of  any  medical  importance. 


GLOSSINA  PALPALIS 

GLOSSINA  TACHINOIDES          • 

GLOSSINA  SUB-MORSITANS    • 

GLOSSINA  MORSITANS  A 


Fig.  767.  Distribution  of  the  important  Glossina  flies  in  Africa.  (Adapted  from  the 
latest  map  showing  this  distribution.) 

^THE  GLOSSINA  OR  TSETSE  FLIES 

The  Glossina  or  tsetse  flies  are  primarily  inhabitants  of  tropical  and  sub- 
tropical Africa,  various  species  occupying  different  or  overlapping  areas  of 
the  continent.  The  only  record  of  any  species  having  been  found  outside 
Africa  is  from  southeast  Arabia  and  this  record  is  doubtful.  Their  distribution 
in  Africa  lies  between  a  line  drawn  from  the  mouth  of  the  Senegal  River  east 


448  MEDICAL  ENTOMOLOGY 

through  Lake  Chad  to  the  Nile  and  thence  to  the  coast  at  about  4°  North  lati- 
tude south  to  a  line  drawn  from  the  mouth  of  the  Cunene  River  east  through 
the  southern  boundary  of  Angola  to  the  northeastern  extremity  of  St.  Lucia 
Lake  in  Zululand  (Austen).  Within  this  area  Newstead  (1924)  recognizes 
20  species,  i  subspecies,  and  5  varieties.  The  various  species  are  not  widely 
distributed  throughout  this  vast  region  but  occupy  certain  areas,  some  closely 
restricted  to  districts  suitable  for  their  development,  as  G.  swynnertoni  Austen, 
or  widely  distributed  over  a  vast  area,  as  G.  palpalis  and  G.  morsitans  and 
their  varieties  (Fig.  167).  This  genus  is  probably  one  of  the  most  important 


Ant _ 


Fig.  168.  Heads  of  bloodsucking  flies.  Left:  Stomoxys  calcitrant.  Right:  Glossina  sp.  a, 
arista  (note  the  difference);  Ant,  antenna;  G,  the  gena;  Lb,  labium;  MxPlp,  maxillary 
palpi  (within  these  lie  die  labium  and  piercing  mouth  parts) ;  V,  vibrissa. 

among  insects.  The  flies  are  the  transmitters  of  many  species  of  trypanosomes, 
especially  the  important  pathogenic  species — those  causing  sleeping  sickness  of 
man  and  nagana  of  cattle,  horses,  and  a  wide  variety  of  game  animals. 

In  structure  these  flies  closely  resemble  Stomoxys  but  they  differ  rather 
markedly  in  certain  features.  Their  life  histories  more  nearly  approach  some 
of  those  of  the  Pupipara  rather  than  those  of  the  typical  muscids.  The  more 
important  external  characteristics  can  be  summarized  here  but  very  briefly. 
The  adults,  when  at  rest,  hold  their  wings  crossed  scissorlike  (see  Fig.  163) 
over  the  abdomen.  The  wing  venation  is  also  quite  distinctive.  The  proboscis 
is  held  in  front  of  the  head  and  appears  large  and  stout  owing  to  the  develop- 


BLOODSUCKING  MUSCOIDEAN  FLIES  449 

ment  of  the  maxillary  palpi.  The  palpi  are  thick,  porrect  structures.  Each  palpus 
has  a  broad,  flat  channel  on  its  inner  face.  The  proboscis  lies  within  the  channel 
formed  by  the  apposition  of  the  palpi  (Fig.  168). 

The  proboscis  consists  of  the  rostrum,  haustellum,  and  labella.  The  rostrum 
is  very  short,  pyramidal  in  shape,  and  compact.  Extending  at  right  angles 
from  its  distal  end  lies  the  haustellum.  The  haustellum  resembles  that  of 
Stomoxys.  At  its  base  is  a  large,  bulbous  structure  usually  known  as  the  "bulb." 
The  labium  extends  to  the  labella  as  an  elongated  sclerotized  structure  and 
grooved  along  its  upper  surface  (the  labial  gutter).  Within  the  labial  gutter 
lie  the  labrum  and  hypopharynx.  The  labella  are  not  well  marked  off  from 
the  labium  proper.  On  the  inner  face  of  the  labella  are  rasps,  prestomal  teeth, 
and  certain  accessory  structures  that  serve  to  penetrate  when  the  fly  seeks  blood. 
Both  males  and  females  are  bloodsucking  in  habit. 

BIOLOGY  OF  GLOSS1NA  SPECIES 

Though  the  Glossina  flies  are  distributed  over  an  extensive  area  in  Africa, 
they  are  not  found  everywhere  but  are  restricted  to  particular  tracts,  known  as 
"fly  belts."  These  "belts"  may  be  very  limited  owing  to  the  conditions  neces- 
sary for  the  species  to  obtain  food,  shelter,  and  an  opportunity  to  reproduce.  As 
the  knowledge  of  these  flies  is  far  from  complete,  the  biology  of  the  two  most 
important  species  is  here  briefly  considered. 

GLOSSINA  PALPALIS  ROBINEAU-DES VOIDY :  This  species  (Fig. 
163),  the  transmitter  of  Gambian  sleeping  sickness  of  man,  is  distributed 
throughout  central  Africa  (Fig.  167),  in  an  area  bounded  by  a  line  drawn  from 
the  mouth  of  the  Senegal  River  east  to  southern  Ethiopia,  thence  south  to  the 
southern  end  of  Lake  Tanganyika,  and  west  to  central  Angola  (here  reaching 
the  Atlantic  Ocean).  Within  this  extensive  area  the  fly  occurs  primarily  along 
watercourses,  rivers,  and  lakes  bordered  with  forests  having  undergrowths. 
The  flies  do  not  wander  far  from  water,  generally  not  over  a  few  hundred 
yards.  Shade  is  essential,  but  it  may  vary  from  dense  vegetation  to  more  or 
less  open  forest  or  even  the  tall  grass  and  sedges  along  rivers  or  lakes.  The  flies 
are  most  active  during  the  hours  of  sunshine  and  are  attracted  to  moving 
objects.  They  seem  to  prefer  dark  skins  and  clothes  to  light-colored  skins  or 
clothes.  The  preferred  food  of  this  species  seems  to  be  the  blood  of  man, 
though  they  attack  various  domestic  and  game  animals  such  as  pigs,  goats, 
monkeys,  hippopotamuses,  crocodiles,  bushbucks,  waterbucks,  mongeese,  etc. 
The  adults  are  long  lived,  the  average  length  of  life  varying  from  about  100  to 
over  250  days. 


450  MEDICAL  ENTOMOLOGY 

LIFE  HISTORY:  Unlike  most  of  the  muscoidean  flies,  the  Glossina  species  do 
not  lay  eggs.  Though  the  eggs  are  formed  they  pass  singly  into  a  uterine  pouch 
where  they  hatch.  Only  a  single  egg  is  received  by  the  uterine  pouch  at  a  time. 
Here  the  egg  hatches  and  the  larva  completes  its  growth  within  this  peculiar 
uterus,  The  food  for  growth  is  supplied  by  special  glands,  the  so-called  "milk 
glands."  Roubaud  found  that  the  period  of  gestation  of  the  first  larva  produced 
by  a  female  was  22  days  and  the  intervals  between  subsequent  larvae  varied 
from  9  to  10  days.  The  mature  larvae  are  deposited  in  dry  soil  situated  in  close 
proximity  to  water  and  in  the  shade.  The  pupal  period  varies  from  25  to  55  days. 

GLOSSINA  MORSITANS  WESTWOOD  AND  G.  SUB-MORSI- 
TANS:  These  species  occupy  extensive  areas  in  central,  western,  and  eastern 
Africa  (Fig.  167).  The  "fly  belts"  of  these  species  are  not  so  restricted  as  of 
G.  palpalis.  They  have  a  widespread  distribution  during  the  wet  season.  Shade 
and  moisture  do  not  appear  so  essential,  for  these  flies  may  be  found  long 
distances  from  water.  During  the  dry  season  they  concentrate  in  certain  areas 
where  there  is  some  shade,  as  among  the  nondcciduous  trees  or  fresh  green 
grass  in  the  extensive,  open,  low-lying  country.  This  green  grass  is  supported 
by  subsoil  water  and  affords  excellent  grazing  for  game  animals,  which,  in 
turn,  furnish  an  abundant  food  supply  for  the  flies.  The  flies  travel  considera- 
ble distances,  especially  when  following  animals.  There  seems  no  doubt  that 
they  can  migrate  from  five  to  ten  miles.  Many  observers  state  that  the  flies 
are  most  active  during  the  cool  of  the  day,  morning  and  evening  hours, 
though  others  record  them  as  biting  in  the  brightest  sunshine  in  the  heat 
of  the  day. 

LIFE  HISTORY  (G.  morsituns] :  Unlike  G.  palpalis,  G.  morsitans  is  not  de- 
pendent on  the  proximity  of  water  for  its  breeding  grounds.  The  females 
deposit  mature  larvae  in  loose,  dry  soil;  the  pupae  have  also  been  found  in 
hard  soil,  in  wood  ash  from  forest  fires,  and  in  other  situations.  Some  kind  of 
shade  seems  essential  though  this  may  be  furnished  by  shrubbery,  fallen  trees, 
overhanging  rocks,  tree  hollows,  or  burrows  in  the  ground.  In  general  the 
breeding  grounds  of  this  species  appear  to  be  widely  scattered  over  its  entire 
range.  The  pupal  period  varies  from  about  21  to  60  or  more  days,  dependent 
largely  on  temperature. 

RELATION  TO  DISEASE 

The  Glossina  flies  are  the  transmitters  of  various  species  of  trypanosomes, 
the  most  important  affecting  man  being  Trypanosoma  gambiense  (the  causa- 
tive agent  of  Gambian  sleeping  sickness),  T.  rhodesiense  (causative  agent  of 


BLOODSUCKING  MUSCOIDEAN  FLIES  451 

Rhodesian  sleeping  sickness  and  believed  to  be  a  variety  of  the  following  spe- 
cies), and  T.  brucei  (causative  agent  of  nagana  or  tsetse-fly  disease  of  horses, 
dogs,  cattle,  and  game  animals).  Trypanosomiasis  is  the  general  term  applied  to 
infection  with  any  species  of  Trypanosoma.  Trypanosoma  species  are  Protozoa, 
belonging  to  the  class  Mastigophora,  subclass  Zoomastigina,  family  Trypano- 
somatidae.  The  trypanosomes  are  found  as  parasites  in  the  blood  stream,  occa- 
sionally in  the  tissues,  of  vertebrates.  A  great  number  of  species  has  been 
described,  and  many  of  them,  if  not  all  (with  the  exception  of  T.  equiperdum 
and  T.  evans'i)  require  an  invertebrate  host  for  the  completion  of  their  life 
cycle  and  transmission  to  new  hosts.  The  body  of  a  typical  trypanosome  (Fig. 


Fig.  169.  Trypanosoma  rhodesiense  in  blood  of  guinea  pig. 

169)  appears  as  a  curved,  narrow  leaf  or  flattened  blade.  The  ends  are  tapering, 
one  end  usually  being  blunter  than  the  other.  The  nucleus  is  generally  central 
and  the  blepharoblast  lies  near  the  blunt  or  posterior  end.  From  the  kineto- 
nucleus  arises  the  flagellum,  which  passes  out  of  the  body  and  forms  the  outer 
border  of  the  undulating  membrane  and  may  be  continued  as  a  free  flagellum 
beyond  the  body.  Reproduction  is  by  binary  fission. 

Though  there  are  numerous  species  of  trypanosomes,  only  a  comparatively 
few  are  known  to  be  pathogenic.  The  species  known  to  be  pathogenic  to  man 
are  T.  gambiense,  T.  rhodesiense  (Fig.  169),  and  T.  cruzi.  The  first  two  are 
restricted  to  tropical  Africa  and  are  transmitted  by  Glossina  flies;  the  last  one 
occurs  in  South  America  and  is  transmitted  by  bugs  of  the  family  Reduviidae 
(see  pp.  184-187). 


452  MEDICAL  ENTOMOLOGY 

Trypanosoma  gambiensc  has  a  distribution  in  Africa  that  closely  approxi- 
mates that  of  Glossina  palpalis.  Sleeping  sickness  has  been  known  for  nearly 
two  hundred  years,  and  various  accounts  of  its  peculiar  manifestations  were 
written  in  the  early  part  of  the  nineteenth  century,  particularly  by  those  en- 
gaged in  the  slave  trade.  The  disease  was  brought  over  to  the  West  Indian 
Islands  but  never  became  established  nor  did  it  spread  among  the  population 
for  reasons  now  well  known.  Though  restricted  at  first  to  an  extensive  area  in 
West  Africa,  its  distribution  throughout  that  continent  began  with  the  com- 
mercial development  in  the  eighties  of  the  last  century.  It  is  believed  that 
Stanley,  the  African  explorer,  brought  the  disease  into  the  heart  of  the  con- 
tinent and  to  the  Uganda  and  Great  Lakes  region  during  his  trip  across  from 
the  Congo  to  the  Nile  (1887-1889).  In  1901  an  epidemic  of  the  disease  broke 
out  in  Uganda,  and  since  that  time  intensive  investigations  have  been  con- 
ducted by  numerous  workers  in  various  parts  of  Africa. 

Sleeping  sickness  manifests  itself  in  two  rather  distinct  phases — an  inter- 
mittent fever  phase  that  may  last  for  months  or  years  and  the  so-called  true 
"sleeping  sickness."  The  first  stage  is  characterized f)y  irregular  fever,  debility, 
languor,  vague  pains,  enlargement  of  the  glands  of  the  neck,  edematous  swell- 
ings, and  generally  an  erythematous  rash.  This  condition  may  continue  for 
months  or  years  (now  called  "trypanosomiasis"  stage)  and  is  practically  always 
followed  by  the  second  phase,  the  "sleeping  sickness"  stage  (due  to  the  invasion 
of  the  nervous  system).  The  drowsiness  and  languor  become  pronounced,  no 
interest  is  taken  in  the  surroundings,  and  no  attempt  is  made  to  obtain  food 
though  the  patient  will  eat  if  food  is  offered.  The  fever  continues,  wasting 
becomes  pronounced,  and  the  patient  passes  into  a  state  of  coma  till  death 
intervenes  (Fig.  170). 

Although  the  disease  was  long  known,  it  was  not  till  Forde  observed  an 
organism  (which  he  thought  at  first  was  a  filaria)  in  the  blood  of  a  European 
patient  in  Gambia  suffering  from  a  peculiar  fever  known  as  "Gambian 
fever"  that  led  to  the  discovery  of  the  causative  agent.  Button  (1902)  saw 
Forde's  preparations  and  pronounced  the  organism  a  Trypanosoma,  which  he 
later  described  as  Trypanosoma  gambiense.  Castellani  (1903),  working  in 
Uganda,  discovered  a  trypanosome  in  the  cerebrospinal  fluid  of  natives  suffer- 
ing from  sleeping  sickness,  described  it  as  T.  ugandense,  and  asserted  it  to  be 
the  etiological  agent  of  the  disease.  Bruce  and  Nabarro  (1903)  confirmed 
Castellani's  work  and  also  recovered  the  parasite  from  the  blood  in  the  early 
and  later  stages  of  the  disease.  It  was  soon  determined  that  T.  ugandense 
was  identical  with  T.  gambiense,  so  that  the  etiological  agents  of  West  Coast 
and  central  African  sleeping  sickness  are  the  same.  Since  then  numerous 


BLOODSUCKING  MUSCOIDEAN  FLIES  453 

investigators  have  fully  confirmed  and  extended  these  results.  Bruce  and 
Nabarro  (1903),  by  means  of  a  study  of  the  distribution  of  the  disease  and  the 
species  of  tsetse  fly  (Glossina  palpalis)  present  in  the  area,  concluded  that  this 
fly  was  the  agent  responsible  for  its  spread.  This  they  confirmed  by  feeding  ex- 
periments, transmitting  trypanosomes  by  the  fly  from  patients  to  healthy 
monkeys  and  also  infecting  monkeys  by  flies  caught  in  the  wild. 

Though  Glossina  flies  had  now  been  shown  to  transmit  (in  practically  all 
experiments  probably  mechanically  though  some  workers  thought  there  must 
be  a  cyclical  development  in  the  fly)  two  species  of  trypanosomes  (T.  brucei 
by  G.  morsitans  and  T.  gambiense  by  G.  palpalis),  it  was  not  known  what 


Fig.  170.  Sleeping  sickness.  A  group  of  natives  in  differ- 
ent stages  of  the  disease.  (From  Byan  and  Archibald,  The 
Practice  of  Medicine  in  the  Tropics.) 

relation  these  parasites  bore  to  the  flies.  Kleine  (1909)  demonstrated  that  the 
trypanosomes  undergo  a  cyclical  development  in  the  flies  and  that  once  a  fly 
is  infected  it  may  remain  infected  for  a  considerable  period.  These  results  have 
been  fully  confirmed,  adding  another  link  in  the  etiological  chain  of  this 
disease.  Finally  Bruce  and  his  co-workers  (1910,  1911)  showed  the  possibility 
of  domestic  cattle  and  wild  game  acting  as  reservoirs  of  T.  gambiense.  Since 
then,  owing  to  the  extreme  difficulty  of  identifying  the  different  species  of 
trypanosomes,  many  confusing  reports  on  this  phase  of  the  parasite's  host  have 
been  published.  It  would  seem,  according  to  Wenyon  (1926),  that  "occa- 
sionally domestic  animals  Jiving  in  association  with  human  beings  amongst 
whom  this  disease  occurs  may  acquire  the  infection,  but  there  is  little  or  no 
evidence  to  incriminate  the  wild  game  as  reservoirs  of  this  trypanosome." 


454  MEDICAL  ENTOMOLOGY 

The  cyclical  development  of  T.  gambiense  in  Glossina  pulpalis  has  been  most 
carefully  investigated  by  Robertson  (1913).  When  the  fly  ingests  blood  con- 
taining trypanosomes,  one  of  several  alternatives  may  occur: 

1.  All  the  trypanosomes  may  be  digested  in  50  to  72  hours  and  disappear 
from  the  gut. 

2.  Some  of  the  trypanosomes  may  persist  in  the  crop  and  gut  but  disappear 
with  the  next  feeding. 

3.  They  may  survive  in  the  gut  and  multiply  in  the  first  blood  meal  even 
though  a  second  feeding  has  taken  place.  These  may  be  swept  out  when  the 
original  meal  is  digested. 

4.  Some  may  persist  and  develop  in  the  crop  with  successive  feedings,  but 
no  infection  will  occur  as  there  is  never  a  permanent  crop  infection. 

5.  Some  will  persist  in  the  gut  after  the  first  meal  has  been  entirely  replaced 
by  the  second  blood  meal. 

This  last  condition  brings  about  a  permanent  infection  of  the  fly.  The 
trypanosomes  multiply  rapidly  and  from  the  tenth  to  the  fifteenth  day  distinct, 
slenderer  forms  arise  and  almost  completely  fill  the  posterior  part  of  the  mid- 
gut.  These  push  forward  to  the  proventriculus,  thence  up  into  the  hypo- 
pharynx  and  along  the  salivary  ducts  into  the  salivary  glands.  Arriving  in 
the  salivary  glands  they  gradually  change  to  broad  crithiclial  forms,  multiply, 
and  fill  up  the  glandular  cavity.  Here  soon  appear  stumpy  forms,  closely 
resembling  the  blood  type,  and  these  arc  the  infective  forms.  The  entire 
cyclical  development,  from  the  time  of  the  ingestion  of  blood  trypanosomes 
to  the  appearance  of  the  infective  salivary  forms,  requires  from  20  to  ^o  days. 
During  this  period  the  fly  must  have  access  to  blood  meals  when  needed. 
Once  a  fly  becomes  infected  it  remains  so  for  probably  the  rest  of  its  life. 

In  addition  to  G.  palpalis  the  following  species  have  been  shown,  experi- 
mentally, to  be  capable  of  transmitting  T.  gambiense:  G.  morsituns,  G.  palli- 
dipes,  G.  jusca,  and  G.  tachinoides. 

Rhodcsian  sleeping  sickness  is  caUsSed  by  T.  rhodesiense  (Fig.  169)  which 
was  recognized  and  described  by  Stephens  and  Fantham  in  1910.  The  disease 
runs  a  more  rapid  course  and  brings  about  death  in  a  few  months  (three  or 
four),  death  usually  intervening  before  the  "sleeping  stage"  develops.  The 
parasite  is  more  pathogenic  to  laboratory  animals,  monkeys  dying  in  from 
8  to  14  days  after  infection,  whereas  with  T.  gambiense  death  may  occur  in  from 
27  to  159  days;  in  rats,  T.  rhodcsiense  is  extremely  virulent,  whereas  T.  gam- 
biense produces  a  chronic  infection.  Many  investigators  believe  that  T.  rho- 
desiense is  but  a  strain  of  T.  brucei  which  has  become  capable  of  infecting  man. 

This  type  of  sleeping  sickness  is  rather  restricted  in  its  distribution,  occurring 


BLOODSUCKING  MUSCOIDEAN  FLIES  455 

in  parts  of  Rhodesia,  about  Lake  Nyasa,  in  the  northeast  part  of  Mozambique, 
and  in.  the  southeastern  corner  of  Tanganyika.  This  disease  was  shown  by 
Kinghorn  and  Yorkc  (1912)  to  be  distributed  by  G.  morsitans  and  confirmed 
by  Bruce  and  his  co-workers  (1914).  The  latter  also  incriminated  G.  brevipalpis. 
The  developmental  cycle  of  the  parasite  in  the  fly  is  similar  to  that  of  T.  gam- 
biensc  in  G.  palpalis. 

Nagana  or  tsetse-fly  disease  of  cattle  is  caused  by  T.  bntcci.  This  parasite 
was  discovered  by  Bruce  in  1895,  who  also  showed  (1897)  that  it  was  trans- 
mitted by  Glossina  morsitans.  The  disease  is  widespread  in  Africa,  extending 
from  Zululand  to  the  Sudan.  T.  brucei  is  probably  the  most  virulent  of  all 
known  pathogenic  trypanosomes.  It  is  inoculable  into  practically  all  mammals. 
Horses,  mules,  donkeys,  and  camels  usually  die  within  a  fortnight  to  tbrce 
weeks;  cattle  are  not  killed  so  rapidly  but  very  few  recover;  pigs  succumb 
quickly  and  dogs  die  in  about  two  weeks  after  inoculation;  rats  and  mice  are 
very  susceptible,  while  cats  are  more  tolerant;  monkeys,  with  the  exception 
of  baboons,  die  usually  in  three  or  four  weeks;  many  other  domestic  animals 
are  susceptible,  and  the  disease  runs  a  rather  rapid  course  (Wenyon).  Bruce 
(1^95)  found  what  he  considered  this  species  in  many  kinds  of  wild  game 
and  later  demonstrated  that  in  Nyasaland  nearly  32  per  cent  of  the  wild  game 
harbored  T.  brucei  or  other  species  pathogenic  to  domestic  animals.  This  work 
has  been  confirmed  by  other  workers  and  the  reservoir  of  this  trypanosome 
definitely  established. 

Though  this  trypanosome  is  primarily  a  parasite  of  numerous  species  of 
mammals,  man  has  long  been  considered  immune.  Since  the  discovery  of  T. 
rhodesiense  by  Stephens  and  Fantham,  many  investigators  consider  this  human 
species  as  but  a  strain  of  T.  brucei  that  has  become  adapted  to  man  (Wenyon, 
1926).  Kleine  (192$)  maintains  that  T.  rhodesicnse  is  a  distinct  species  and  that 
its  animal  reservoir  has  not  yet  been  ascertained. 

The  species  of  Glossina  flies  that  are  known  to  transmit  T.  brucei  are  G. 
morsitans,  G.  brevipalpis,  G.  pallidipes,  G.  palpalis,  and  G.  tachinoides. 

CONTROL  OF  GLOSSINA  FLIES 

As  no  very  effective  treatment  for  sleeping  sickness  of  man  (except  the 
use  of  certain  drugs,  and  these  do  not  prevent  reinfection  or  guarantee  a  cure), 
nagana  of  horses,  mules,  cattle,  etc.,  and  other  trypanosomiascs  has  yet  been 
devised,  the  problem  of  the  control  of  Glossina  flies  is  a  major  one  in  many 
parts  of  Africa.  Sleeping  sickness  has  devastated  many  populous  districts 
(Uganda)  of  Africa,  rendered  much  agricultural  land  unfit  for  habitation, 
and  threatens  the  future  development  of  some  of  the  most  fertile  regions  of  the 


456  MEDICAL  ENTOMOLOGY 

world.  Though  extensive  investigations  have  been  and  are  now  being  carried 
on,  the  problem  of  tsetse-fly  control  is  a  baffling  one.  At  the  present  time  much 
progress  has  been  made  in  the  reduction  of  Glossina  flies  by  some  or  all  of 
the  following  methods:  (i)  by  clearing  the  jungle  along  the  "fly  belts,"  by 
using  the  same  methods  about  native  villages,  and  by  removing  forested  areas 
along  water  courses  (it  is  only  necessary  to  clear  some  50  to  100  yards  in  these 
areas  as  the  flies  rarely  move  very  far  from  protected  growths) ;  (2)  by  trapping 
the  flies  in  those  areas  where  they  are  numerous,  especially  near  populated 
districts;  (3)  by  avoiding  "fly  belts"  so  as  not  to  introduce  the  disease  into 
free  areas;  (4)  by  wearing  white  clothing  (the  flies  prefer  dark  surfaces  on 
which  to  alight)  and  by  wearing  head  nets,  gloves,  and  protective  clothing; 
no  satisfactory  repellent  has  yet  been  developed;  (5)  by  constructing  better 
housing,  using  screens,  and  improving  sanitation;  and  (6)  by  destroying  game 
animals.  The  latter  method,  though  practiced  in  some  districts,  does  not  seem 
worth  while  as  domestic  animals  may  also  serve  as  reservoirs.  However  their 
reduction  in  populous  areas  may  serve  a  useful  purpose.  More  recently  the  use 
of  various  DDT  formulations  in  certain  areas  shows  promise. 

REFERENCES 

*Austen,  E.  E.,  and  Hegh,  E.     Tsetse-flies.     London,  1922. 

Bcquacrt,  }.     Tsetse-flies — past  and  present  (Diptera,  Muscoidea).     Em.  News, 

41:  158-164,  202-203,  227~233>  I93°- 

Bishopp,  F.  C.     The  stable-fly;  how  to  prevent  its  annoyance  and  its  losses  to  live- 
stock.    U.S.  Dept.  Agr.,  Farmers'  Bull.  1097,  1931. 
Bruce,  D.     Preliminary  report  on  the  tsetse-fly  disease  or  nagana  in  Zululand. 

Umbobo,  1895. 
.     Further  report  on  the  tsetse-fly  disease  or  nagana  in  Zululand.     London, 

1897. 
,  and  Nabarro,  D.    Progress  report  on  sleeping  sickness  in  Uganda.    Repts. 

Sleep.  Sick.  Comm.,  Roy.  Soc.,  No.  i,  1903. 
Buxton,  P.  A.     Studies  on  Soils  in  Relation  to  the  Biology  of  Glossina  submorsitans 

and  tachinoides  in  the  north  of  Nigeria.     With  An  Appendix  by  K.  Mellanby. 

Bull.  Ent.  Res.,  27:  281-287,  1936. 
,  and  Lewis,  D.  J.     Climate  and  tsetse-flies;  laboratory  studies  upon  Glossina 

submorsitans  and  tachinoides.    Phil.  Trans.  Roy.  Soc.,  B  224:  175-240,  1934. 
Carpenter,  G.  D.  H.    A  naturalist  on  Lake  Victoria,  with  an  account  of  sleeping 

sickness  and  the  tsetse-fly.    London,  1920. 

Castellani,  A.  Trypanosoma  in  sleeping  sickness.  Brit.  Med.  Jl.,  i:  1218,  1903. 
Dicke,  B.  H.  The  tsetse-fly's  influence  on  South  African  history.  S.  Afr.  Jl.  Sci., 

29:  792-796,  1932. 


BLOODSUCKING  MUSCOIDEAN  FLIES  457 

Duke,  H.  L.    Some  observations  on  the  bionomics  of  Clossina  palpalis  on  the 

islands  of  Victoria  Nyanza.     Bull.  Ent.  Res.,  9:  263-270,  1919. 
Dutton,  }.  E.     Trypanosoma  in  man.     Brit.  Med.  Jl.,  Jan.  4,  p.  42;  Sept.  20,  p.  88 1, 

1902. 
*Enderlein,  G.     Ucber  die  ^Classification  der  Stomoxinae  (blutsaugende  Musciden) 

und  neue  Arten  aus  Europa  und  Afrika.    Zcit.  Angew.  Ent.,  14:  356-368,  1928. 
*Fiske,  W.  W.    Investigations  into  the  bionomics  of  Glossina  palpalis.    Bull.  Ent. 

Res.,  10:  347-463,  1920. 
Forde,  R.  M.     Some  clinical  notes  on  a  European  patient  in  whose  blood  a  try- 

panosome  was  observed.    JL  Trop.  Med.  and  Hyg.,  5:  261-263,  1902. 
Griinberg,  Karl.    Die  blutsaugenden  Dipteren.    Jena,  1907. 
Harris,  R.  H.  T.  P.     Some  facts  and  figures  regarding  the  attempted  control 

of  Glossina  pallidipcs  in  Zululand.     S.  Afr.  Jl.  Sci.,  29:  495-507,  1932. 
*Hegh,  Emile.    Les  tse-tses.    Brussels,  1929. 
*Hindle,  E.    Plies  in  relation  to  disease.    Blood-sucking  flies.     Cambridge  Pub. 

Health  Series,  Cambridge,  Eng.,  1914. 
Jackson,  C.  H.  N.     Some  new  methods  in  the  study  of  Glossina  morsitans.     Proc. 

Zool.  Soc.  Lond.,  Part  4:  811-896,  1936. 
Jobling,  B.     A  revision  of  the  structure  of  the  head,  mouth-parts  and  salivary 

glands  of  Glossina  palpalis  Rob.-Desv.     Parasitology,  24:  449-490,  1933. 
*Kinghorn,  A.,  and  Yorke,  W.     On  the  transmission  of  human  trypanosomes  by 

Glossina  morsitans  Westw.;  and  on  the  occurrence  of  human  trypanosomes  in 

game.     Ann.  Trop.  Med.  Parasit.,  6:  1-23,  269-285,  1912. 

Kleine,  F.  K.    Positive  Infektionsversuche  mit  Trypanosoma  bruccl  durch  Glos- 
sina palpalis.    Deutsch.  Med.  Woch.  35:  469,  1909. 
.     Zur  Flpidemiologie  der  Schlafkrankheit.     Deutsch.  Med.  Woch.,  49:  505- 

506,  1923. 
Mcllanby,  Helen.    Experimental  work  on  reproduction  in  the  tsetse-fly,  Glossina 

palpalis.    Parasitology,  29:  131-141,  1937. 
Melvin,  R.     Notes  on  the  biology  of  the  stable-fly,  Stomoxys  calcitrant.     Ann.  Ent. 

Soc.  Amer.,  24:  436-438,  1938. 
Mitzmain,  M.  B.    The  role  of  Stomoxys  calcitrans  in  the  transmission  of  Trypano- 

soma  evansi.    Philip.  Jl.  Sci.,  B,  7:  475-518,  1912. 
.    The  bionomics  of  Stomoxys  calcitrans  Linnaeus;  a  preliminary  account. 

Ibid.,  8:  29-48,  1913. 
.    Collected  studies  on  the  insect  transmission  of  Trypanosoma  evansi,  and 

summary  of  experiments  in  the  transmission  of  anthrax  by  biting  flies.     U.S.  Pub. 

Health  Serv,,  Hyg.  Lab.,  Bull.  94, 1914. 
Moggridge,  J.  Y.    Experiments  on  the  crossing  of  open  spaces  by  Glossina  swynner- 

toni.     Bull.  Ent.  Res.,  27:  435-448,  1936. 
*Nash,  T.  A.  M.    The  ecology  of  Glossina  morsitans  Westw.,  and  two  possible 

methods  for  its  destruction.    Ibid.,  24:  107-157,  163-195,  1933. 


458  MEDICAL  ENTOMOLOGY 

Nash,  T.  A.  M.    Climate,  the  vital  factor  in  the  ecology  of  Glossina.    Ibid.,  28: 

75-127,  1937. 
Nettles,  W.  C.     An  unusual  outbreak  of  stable  fly  and  its  control.     Jl.  Econ.  Ent., 

27:  1197-1198,1934. 
Newstead,  R.     On  the  life-history  of  Stomoxys  calcitrant  Linn.     Jl.  Econ.  Biology, 

i :  157-166,  1906. 

** ,  Evans,  A.  M.,  and  Potts,  W.  H.     Guide  to  the  study  of  tsetse-flies.     Liver- 
pool School  Trop.  Med.,  Mem.,  n.s.,  i,  1924. 
Patton,  W.  S.     Studies  on  the  higher  Diptera.     II.  The  genus  Stomoxys  GeofTroy 

(Sens.  lat.).     Ann.  Trop.  Med.  Parasit.,  27:  501-537,  1933. 
Robertson,  M.    Notes  on  certain  aspects  of  the  development  of  Trypanosoma- 

gambiense  in  Glossina  palpalis.     Proc.  Roy.  Soc.,  B,  85:  241-248,  1912. 
.     Notes  on  the  life-history  of  Trypanosoma  gambicnsc,  with  a  brief  reference 

to  the  cycles  of  Trypanosoma  nanum  and  Trypanosoma  pecorum  in  Glossina 

palpalis.     Phil.  Trans.  Roy.  Soc.,  B,  203:  161-184,  1913. 
*Scguy,  E.     Etude  sur  les  Stomoxyclincs  et  particulieremcnt  dcs  mouches  Char- 

bonneuses  du  genre  Stomoxys.     Encycl.  Ent.,  B.,  II  Dipt.,  8:  15-58,  1935. 
Simmons,  S.  W.,  and  Dove,  W.  E.     Breeding  places  of  the  stable  fly  or  "dog  fly," 

Stomoxys  calcitrans  (L),  in  northwestern  Florida.     J.  Econ.  Ent.,  34:  457-462, 

1941. 
Stephens,  J.  W.  W.,  and  Eantham,  H.   B.     On  the  peculiar  morphology  of  a 

trypanosome  from  a  case  of  sleeping  sickness  and  the  possibility  of  its  being  a 

new  species  (T.  rhodesiensc).     Ann.  Trop.  Med.  Parasit.,  4:  343-350,  1910. 
Swynncrton,  C.  F.  M.     The  tsetse-flies  of  East  Africa.  A  first  study  of  their  ecology, 

with  a  view  to  their  control.     Trans.  Ent.  Soc.  Lond.,  Vol.  84,  1936. 
Symes,  C.  B.,  and  Vane,  R.  T.     The  eradication  of  G.  palpalis  from  river  areas 

by  the  "block"  method.     Nairobi,  Kenya,  1957. 
*Wilhelmi,  J.     Die  gemeine  Stechfliege  (Wadcnstccher);  Untenmchungen  liber 

die  Biologic  der  Stomoxys  calcitrans  L.     Zeit.  Angew.  Ent.,  Monograph  2,  1917. 
*Zumpt,    F.     Die    Tsetsefliegcn.    Ihre    Erkennungsmerkmale,    Lebensweise    und 

Bckarnpfung.     Jena,  1936. 


CHAPTER  XVI 


The  Housefly  and  Its  Allies1 


THE  housefly  (Mtisca  domcstica  Linn.),  or  the  "typhoid-fly"  as  it  is  desig- 
nated by  some  writers,  is  the  most  common  and  abundant  fly  in  and  about 
homes  throughout  the  world;  it  is  the  animal  most  commonly  associated  with 
man;  it  is  distributed  from  the  subpolar  regions  to  the  tropics,  where  it  occurs 
in  enormous  numbers. 

DESCRIPTION:  The  housefly  (Fig.  171)  is  mouse-gray  in  general  color. 
The  thorax  is  gray,  marked  by  four  equally  broad,  dark,  longitudinal  stripes, 
most  clearly  defined  in  front.  The  abdomen  has  the  sides  of  the  basal  half 
yellowish  and  somewhat  transparent;  the  posterior  segment  is  brownish  black 
and  a  dark  longitudinal  line  extends  along  the  middle  of  the  dorsum.  The  legs 
are  blackish  brown.  The  wings  are  clear  though  somewhat  yellowish  at  the 
base.  The  venation  is  rather  distinctive  (Fig.  172);  the  fourth  longitudinal 
vein  is  sharply  bent  upwards  so  as  nearly  to  meet  the  vein  in  front.  The 
squamae  (calypteres)  are  large,  opaque,  yellowish.  The  adult  measures  6  to 
7  mm.  in  length  with  a  wing  expanse  of  13  to  15  mm. 

LIFE  HISTORY:  The  housefly  undergoes  a  complete  metamorphosis. 
Mating  takes  place  in  from  2  to  12  days  after  the  adults  emerge.  Oviposition 
may  begin  within  2  to  3  days  after  copulation.  The  female  deposits  its  eggs 
singly,  laying  from  too  to  150  eggs  at  a  time  in  a  batch  (Fig.  173).  Each  female 
lays  several  batches,  four  or  more,  during  her  lifetime,  that  is,  from  400  to  600 
eggs.  Dunn  (1923)  records  remarkable  fertility  for  the  housefly  in  Panama, 
a  single  female  laying  2^87  eggs  during  a  period  of  31  clays. 

The  egg  is  white,  oval  in  shape,  and  measures  about  i  mm:  in  length.  Along 
the  dorsal  surface  of  the  egg  are  two  distinct  riblike  thickenings.  The  eggs 
hatch  in  from  12  to  24  hous  (at  temperatures  of  from  68°  to  80°  F.),  though 


1  For  the  identification  of  the  families  in  this  group  of  flies,  consult  the  key  on  pp. 
228-231,  beginning  at  No.  11. 


460  MEDICAL  ENTOMOLOGY 

hatching  may  be  delayed  by  lower,  or  somewhat  hastened  by  higher,  tempera- 


tures. 


The  larva  (Fig.  173)  develops  very  rapidly  when  food  supply  and  tempera- 
ture are  favorable.  There  are  three  larval  stages  or  instars.  The  last  stage  is 
reached  in  from  four  to  eight  days.  The  mature  larva  measures  about  12  mm. 
in  length.  It  is  white  in  color  and  conically-cylindrical  in  shape.  The  body  tapers 


Fig.  777.  The  housefly,  Musca  domestica.  (Courtesy  Department  of  Agricul- 
ture, Division  of  Entomology,  Canada.) 

off  gradually  from  the  middle  region  to  the  anterior  or  head  end.  The  posterior 
is  cylindrical  but  the  last  segment  is  larger  and  obliquely  truncate.  The  body 
is  composed  of  twelve  visible  segments  and  is  legless.  Near  the  middle  of  the 
dejUyjjL^  of  the  last  segment  are  the  posterior  spiracles— MynD-shaped 
sclerotizcd  rings  placed  rather  close  together  (Fig.  195  4).  Each  spiracle  con- 
sists of  a  ring  that  encloses  three  sinuous  slits  through  which  the  air  passes 
to  the  tracheal  system.  On  the  inner  flat  side  of  the  ring  is  a  heavy  sclerotized 
area,  the  so-called  "button."  The  anterior  spiracles  are  situated  laterally  at  the 


THE  HOUSEFLY  AND  ITS  ALLIES  461 

posterior  border  of  the  third  body  segment.  Each  spiracle  consists  of  a  fan- 
shaped  body  bearing  six  to  eight  small  papilliform  processes. 

The  larva  of  the  housefly,  like  all  muscid  larvae,  lacks  a  true  head :  the  first 
segment  (usually  termed  the  "pseudocephalon")  is  nearly  all  retracted  within 
the  body.  At  the  anterior  end  of  the  larva  is  seen  a  heavily  sclerotized  structure 
withdrawn  within  the  anterior  segments.  This  structure  is  the  cephalo- 
pharyngeal  skeleton.  It  is  a  part  of  the  head  and  mouth  parts  that  has  become 
invaginated  within  the  thoracic  segments.  This  structure  occurs  in  all  mus- 
coidean  larvae  and  shows  numerous  modifications.  As  it  is  used  extensively 
for  identification  purposes,  a  detailed  description  is  here  presented  (see  Chap- 


Pig.  772.  Wing  of  housefly;  veins  and  a 
C,  costa. 


labeled,  a,  anal  cell;  AV,  auxiliary  vein; 


ter  xvn  for  those  of  other  species).  Anteriorly  may  be  recognized  a  pair  of  oral 
lobes,  each  of  which  bears  a  pair  of  sensory  papillae  (Fig.  174).  Between  and 
below  the  sensory  lobes  is  the  mouth  opening.  On  the  lateral  and  ventral 
surface  of  these  lobes  may  be  noted  a  series  of  delicate  parallel  channels  that 
converge  toward  the  mouth;  these  have  been  called  "food  channels"  (Fig. 
174  FC).  Behind  and  lying  within  the  thoracic  segments  is  the  cephalo- 
pharyngeal  skeleton.  This  structure  consists  of  a  number  of  heavily  sclerotized 
sclerites  as  follows:  Mandibular  Sclerite  (MS) — This  sclerite  has  a  broad  base 
and  bears  a  pair  of  mouth  hooks.  Each  mouth  hook  is  shaped  like  a  claw, 
directed  forward  and  downward;  the  left  hook  is  much  smaller  than  the 
right  and  may  be  overlooked  (the  small  left  hook  is  found  in  all  species  be- 
longing to  the  genus  Mused).  The  larva  takes  only  liquid  food  and  the  mouth 
hooks  are  employed  in  tearing  and  loosening  the  debris  and  as  an  aid  in 
forward  movements.  Dental  Sclerite  (DS) — At  each  side  of  the  base  of  the 


462  MEDICAL  ENTOMOLOGY 

mandihulate  sclerite  is  a  small  dental  sclcrite;  each  affords  attachment  for 
powerful  muscles  which  depress  the  mouth  hooks.  Hypostomal  Sclerite 
(HS) — Posteriorly  the  mandibular  sclerite  articulates  with  the  hypostomal 
sclerite.  This  consists  of  two  irregularly  shaped  lateral  plates  connected  by  a 
ventral  sclerotized  bar.  The  Pharyngeal  Sclerites  (PhS) — The  hypostomal 
sclerite  articulates  with  the  anterior  portion  of  the  pharyngcal  sclcrites.  The 
pharyngeal  sclerites  consist  of  two  lateral,  irregular  plates  united  at  their 


Fig.  775.  Metamorphosis  of  insects.  The  housefly,  Mt4sca  domcstica.  (a)  Eggs  as  laid 
in  horse  manure.  (/>)  The  full-grown  larva  (head  of  larva  to  right),  (c}  The  puparium. 
(d)  The  adult  fly.  S,  anterior  and  posterior  spiracles. 

dorsoanterior  ends  by  a  transverse  sclerite — the  dorsopharyngeal  sclerite;  ven- 
trally  the  lateral  plates  are  continuous  with  the  floor  of  the  pharynx  (Ph). 
The  floor  of  the  pharynx  is  distinctly  grooved  longitudinally. 

When  the  larva  is  mature  it  ceases  feeding  and  proceeds  to  contract.  The 
anterior  end  is  drawn  in  and  within  a  few  hours  (6  to  12)  a  cylindrical  case, 
the  puparium,  is  formed  (Fig.  173).  Within  the  puparium  the  true  pupa  de- 
velops. At  first  the  puparium  is  creamy  yellow  in  color  but  it  soon  changes  to 
a  rich,  dark  brown.  Externally  nearly  all  the  larval  structures,  except  the 
cephalopharyngeal  skeleton,  which  is  withdrawn  within  the  puparium,  may 
be  observed.  The  pupa  develops  a  new  opening  to  the  respiratory  system,  a 
pair  of  small,  spinelike  projections  between  the  fifth  and  sixth  segments.  The 


THE  HOUSEFLY  AND  ITS  ALLIES  463 

puparium  averages  about  6.5  mm.  in  length.  The  pupal  period  occupies  from 
four  to  five  days,  though  it  may  be  shortened  by  high  temperatures  (90°  to 
95°  F.)  or  prolonged  by  cool  weather.  When  ready  to  emerge  the  imprisoned 
fly  breaks  open  the  anterior  end  of  the  puparium  by  means  of  the  ptilinum  or 
frontal  sac^JThe  puparium  splits  in  a  circular  fashion  in  the  fifth  segment  and 
two  lateral  slits  pass  forward  from  it.  The  fly  works  its  way  out  and  if  the 
puparium  has  been  formed  beneath  the  soil  the  fly  pushes  its  way  upward  by 
alternately  inflating  and  deflating  the  frontal  sac  (ptilinum).  The  external 


Ph  S 


HS 


MS 


SD 


Pig.  174.  The  anterior  end  of  the  larva  of  the  housefly  showing  the  structure 
of  the  cephalopharyngeal  skeleton.  DC,  dorsal  cornua;  DS,  dental  sclerite; 
FC,  food  channels;  IIS,  hypostomal  sclerite;  MS,  mandibular  sclerite;  OH,  oral 
hook;  Ph,  pharynx;  PhS,  pharyngeal  sclerite;  SD,  salivary  duct;  SP,  sensory 
papilla;  VC,  ventral  cornua. 

skeleton  soon  hardens,  the  wings  become  firm,  and  the  fly  starts  out  as  a 
mature  insect. 

The  entire  life  cycle  from  the  deposition  of  the  eggs  till  the  emergence  of 
the  adults  varies  widely,  due  to  temperature,  food  and  other  factors.  Nor- 
mally it  requires  from  8  to  20  days.  In  the  warm  summer  months  the  average 
time  is  from  10  to  16  days.  Where  conditions  are  favorable,  as  in  the  tropics 
and  subtropics,  breeding  is  continuous  throughout  the  year.  Where  con- 
tinuous breeding  occurs  the  number  of  flies  is  appalling  and  they  invade  every 
conceivable  place  seeking  food  and  shelter.  Even  in  the  United  States  and 
countries  generally  outside  the  subtropics  where  breeding  is  interrupted  by 


464  MEDICAL  ENTOMOLOGY 

the  cold  winters,  the  abundance  of  houseflies  at  the  end  of  the  summer  season 
makes  them  a  terrible  scourge.  The  excessive  numbers  are  due  to  its  high 
reproductive  capacity  and  the  number  of  broods.  In  the  region  of  Washing- 
ton, D.C.,  Howard  (1917)  estimates  that  there  are  10  to  12  generations  a  sea- 
son. As  each  female  fly  lays  from  200  to  600  eggs  (a  much  higher  number  is 
recorded  by  Dunn),  the  progeny  of  one  female  has  been  estimated  to  be 
1,875,000,000,000  adults  at  the  end  of  the  eighth  generation. 

HIBERNATION:  In  the  cooler  climates  the  continuous  breeding  of  this 
fly  is  interrupted  by  the  winter  season.  How  it  passes  the  winter  has  been 
investigated  by  numerous  workers.  The  results  are  far  from  uniform.  Hewitt 
(1914)  thought  the  adults  hibernated,  seeking  out  sheltered  places  in  which 
to  pass  the  winter.  The  same  author  (1915)  states  that  the  adults  do  actually 
hibernate  in  the  region  of  Ottawa,  Canada.  He  did  not  succeed  in  carrying 
living  larvae  or  puparia  through  the  winter  under  experimental  conditions. 
Hutchison  (1918)  concludes  from  a  long  series  of  experiments  that,  in  the 
region  of  Washington,  D.C.,  hibernation  takes  place  in  the  larval  and  pupal 
stages  in  or  under  large  manure  heaps,  or  the  species  is  maintained  over  the 
winter  by  continued  breeding  in  warm  places  where  food  (both  larval  and 
adult)  and  shelter  are  available.  He  finds  no  evidence  to  support  the  thesis 
that  the  adults  hibernate  from  November  to  April  "either  outdoors,  in  pro- 
tected stables,  or  in  attics  or  heated  buildings."  Herms  (1923)  states,  "In  hiber- 
nation flies  may  live  over  winter,  i.e.,  from  October  to  April,  which  is  the  case 
in  our  Eastern  and  Central  States."  No  experimental  or  observational  data 
appear  to  support  the  statement  of  Herms  except  those  of  Hewitt.  In  northern 
New  York  (Lake  Champlain  region)  Matthysse  found  excessive  breeding  of 
houseflies  in  box  stalls  housing  horses  during  the  middle  of  the  winter  season. 
The  author  made  similar  observations  in  box  stalls  in  Nova  Scotia  years  ago. 
It  is  probable  that  breeding  continues  in  many  such  places  throughout  the  cold 
weather.  The  author  has  frequently  found  freshly. emerged  houseflies  in  cafe- 
terias and  similar  eating  places  in  winter,  indicating  local  breeding  in  garbage 
cans  or  other  refuse. 

BREEDING  PLACES:  The  results  of  numerous  investigations  clearly 
demonstrate  that  horse  manure  is  the  favorite  breeding  ground  of  the  housefly. 
When  horse  manure  mixed  with  straw  or  other  refuse  is  piled  in  the  open,  it 
soon  becomes  heavily  infested  with  maggots  (Fig.  175).  The  number  of  flies 
that  may  develop  in  a  small  manure  heap  is  almost  beyond  belief  ./Herms 
counted  685  maggots  per  pound  and  estimated  that  900,000  were  present  in  a 
ton  of  manure  that  had  been  exposed  only  four  days.  Howard  counted  160 


THE  HOUSEFLY  AND  ITS  ALLIES  465 

maggots  and  146  puparia  in  four  ounces  of  manure — in  other  words,  a  pound 
of  manure  could  produce  1200  flies  and  a  ton  of  manure,  if  heavily  infested, 
could  yield  nearly  2,400,000  flies  every  two  weeks  during  the  summer  months. 
When  it  is  remembered  that  manure  piles  are  always  present  and  that  the 
housefly  ranges  widely,  it  is  not  to  be  wondered  that  the  pest  occurs  in  countless 
numbers.  Not  only  does  the  housefly  breed  in  open  piles  of  horse  manure  but 
the  writer  has  found  them  in  box  stalls  where  the  manure  mixed  with  straw 
had  been  allowed  to  accumulate.  In  such  places,  especially  near  the  margins 
where  the  manure  is  not  so  thoroughly  packed,  the  maggots  may  be  found  in 
countless  numbers.  In  fact,  horse  manure  wherever  found,  if  moist,  serves  as 
an  ideal  breeding  ground. 


Fig.  775.  View  of  barnyard,  showing  an  ideal  place  for  the  breeding  of  houseflies. 

The  second  most  favored  breeding  place  is  human  excrement  wherever 
exposed,  as  in  open  privies,  in  wooded  dell,  hillsides,  back  alleys,  and  yards. 
Such  exposed  human  feces  are  very  dangerous  breeding  grounds  as  will  be 
shown  later.  Other  breeding  grounds  are  cow  manure,  especially  when  mixed 
with  straw  and  horse  manure,  manure  and  wastes  about  piggeries,  decaying 
animal  and  vegetable  wastes  where  fermentation  occurs,  piled  decaying  vege- 
tables, so-called  "septic  tanks"  (the  cracks  between  the  covering  boards  fur- 
nishing the  entrances  and  exits  for  the  flies),  and,  most  fruitful  of  all  breeding 
grounds,  the  garbage  dumps  of  many  of  our  cities  and  larger  villages.  A  visit  to 
a  garbage  dump  will  soon  convince  any  intelligent  citizen  that  he  is  paying 
out  money  to  provide  breeding  places  for  flies  that  invade  his  home,  defile  its 
cleanliness,  contaminate  his  food,  and  distribute  diseases.  Other  extensive 
breeding  places  are  found  wherever  feed  grain  or  other  foods  are  scattered 


466  MEDICAL  ENTOMOLOGY 

such  as  beside  or  under  slatted  walks,  at  loading  and  unloading  platforms, 
and  in  similar  places  where  rain  soon  produces  ideal  conditions  for  the  larvae. 
Urine-soaked  soil  and  places  about  homes  where  greasy  wastes  arc  dumped 
about  buildings  are  other  favorite  spots.  In  conclusion  it  may  be  said  with 
fair  accuracy  that  the  housefly  will  breed  in  practically  all  decaying  and  fer- 
menting animal  and  plant  wastes. 

HABITS  OF  THE  ADULTS 

The  housefly  is,  above  all  things,  a  lover  of  human  and  animal  habitations. 
The  identification  of  all  flics  captured  in  households  (over  200,000  have  been 
identified)  shows  that  about  90  per  cent  of  them  consist  of  the  housefly.  The 
maximum  abundance  of  flies  in  homes  occurs  toward  the  end  oi:  the  summer 
season  when  they  seek  warmth  and  shelter  as  well  as  food.  They  are  constantly 
on  the  move,  exploring  every  surface,  seeking  food  in  every  conceivable  place, 
and  leaving  their  wastes  on  every  object. 

FOOD  AND  FEEDING:  Its  principal  foods  are  liquids  such  as  syrups, 
milk,  water  containing  proteins,  sugars,  moisture  on  decaying  fruits,  sputum, 
fecal  wastes — in  fact,  any  substance  however  vile  if  it  is  moist  or  can  be  dis- 
solved. It  also  seeks  food  on  moistened  surfaces  as  about  the  mouth,  nostrils, 
eyes,  sores,  and  wounds  of  man  or  animals  or  exposed  meat,  cheese,  or  other 
foods.  The  method  of  feeding  needs  to  be  well  understood  as  it  is  of  great 
significance  in  the  carriage  of  pathogenic  bacteria  and  parasites.  The  mouth 
parts  are  fully  explained  and  illustrated  in  Chapter  v,  and  the  method  of 
feeding  is  described.  The  fly,  undisturbed,  can  fully  engorge  in  less  than  hall 
a  minute.  On  a  substance  such  as  dry  sugar,  sweetened  cakes,  dry  blood, 
sputum,  etc.,  the  fly  dissolves  it  first  by  secretions  from  the  lingual  salivary 
glands  and,  frequently,  by  regurgitating  a  part  of  the  liquid  present  in  the 
crop.  This  habit  of  regurgitating  is  especially  noticeable  after  the  fly  has  fed 
on  liquids  (Fig.  50).  Furthermore  this  habit  of  regurgitation  is  commonly 
employed  on  nearly  every  surface  the  fly  tests  with  its  proboscis,  leaving  as 
a  result  light-colored  opaque  spots — the  so-called  "vomit  spots."  Such  spots 
are  frequently  more  common  on  windows,  ceilings,  etc.,  than  the  fecal  spots. 
The  regurgitation  from  the  crop  does  undoubtedly  serve  in  the  spread  of 
pathogenic  as  well  as  nonpathogenic  organisms.  These  methods  of  feeding 
make  the  housefly  a  serious  menace,  for  it  may  quickly  pass  from  fecal  wastes, 
vomits,  exposed  sores,  and  wounds  directly  to  the  daintiest  foods  and  liquids 
of  all  kinds  and  pass  on  either  by  its  vomit  spots  or  fecal  wastes  a  part  of 
whatever  has  been  engorged. 


THE  HOUSEFLY  AND  ITS  ALLIES  467 

In  addition  to  its  feeding  habits  the  housefly  possesses  an  ideal  hairy  body 
and  legs  to  which  all  sorts  of  germs  may  adhere  as  it  wallows  over  the  most 
filthy  of  animal  fecal  wastes,  garbage,  soiled  food,  etc.  Furthermore,  its  feet 
(six  of  them)  are  each  provided  with  two  flattened  pads  (Fig.  54).  These  pads 
(pulvilli)  are  thickly  beset  with  tiny  hairs  from  which  a  sticky  substance 
exudes  enabling  the  fly  to  walk  on  glass,  on  ceilings,  and  similar  places,  and 
to  gather  up  or  leave  behind  any  filth  that  it  may  have  garnered  in  its  travels. 
Such  (lies  frequently  fall  into  our  milk,  drinks  of  all  kinds,  jams,  etc.,  and 
distribute  what  they  have  collected. 

FLIGHT:  The  housefly  is  a  vigorous  flier  and  can  travel  considerable 
distances.  From  the  standpoint  of  fly  control  and  the  dispersion  of  fly-borne 
diseases  the  flight  range  is  very  important.  In  other  words,  can  a  small  area 
such  as  a  village  or  city  conduct  intensive  campaigns  for  the  destruction  of 
breeding  grounds  and  thereby  hope  to  remain  free  from  flies?  Or,  in  rural 
communities,  can  individual  farmers  or  small  communities  control  flies  and 
remain  free  from  migratory  hordes  coming  from  not  far  distant  breeding 
grounds?  Furthermore,  if  the  housefly  is  a  wide-ranging  species  its  possibili- 
ties of  distributing  disease-producing  organisms  are  greatly  increased.  Until 
H)i6  the  maximum  flight  range  was  considered  not  over  a  mile,  and  this 
conclusion  was  based  on  experiments  conducted  in  England.  In  that  year 
Parker  in  Montana  demonstrated,  largely  under  city  conditions,  that  the  fly 
travels  nearly  two  miles  and  in  considerable  numbers.  Recently  Bishopp  and 
Laake  (1921)  carried  out  an  extensive  series  of  flight  experiments  in  Texas. 
The  flies  were  captured,  dusted  with  finely  powdered  red  chalk  or  paint,  and 
then  liberated  in  the  open  fields.  In  all,  some  234,000  flies  were  used  in  these 
experiments.  The  results  are  very  significant.  Within  24  hours  after  liberation 
the  housefly  was  captured  six  miles  distant  from  the  point  of  release,  and  the 
maximum  distance  traveled  was  1 3.14  miles  by  one  female.  Considerable  num- 
bers of  the  flies  were  recaptured  at  the  traps  at  ranges  of  five,  six,  and  eight 
miles,  showing  conclusively  that  the  housefly  migrates  long  distances  within 
comparatively  short  periods  of  time.  From  the  point  of  release  the  flies  tended 
to  migrate  with  the  prevailing  winds,  but  they  also  spread  at  right  angles  to, 
and  even  against,  the  wind.  These  investigators  concluded  that  moderate 
winds  have  little  influence  in  directing  the  spread  of  flies. 

RESTING  PLACES:  As  the  control  of  houseflies  by  DDT  seems  very  effec- 
tive, it  is  of  some  importance  to  recognize  their  selective  resting  places  at  night 
or  on  dark  days  so  that  treatment  may  be  directed  to  those  particular  places. 
In  barns  and  buildings  of  all  kinds,  including  our  homes,  flies  seem  to  seek 


468  MEDICAL  ENTOMOLOGY 

out  cracks  and  crevices  (Fig.  176)  such  as  those  behind  moldings  and  in  wall- 
paper, boards,  and  plaster  for  resting.  This  is  shown  by  the  dense  fecal  wastes  in 
those  places.  Adequate  treatment  of  such  areas  may  be  just  as,  or  more,  effec- 
tive than  a  general  over-all  treatment  with  DDT. 

LONGEVITY:  That  the  housefly  can  survive  long  periods  if  food  and 
shelter  are  adequate  has  been  demonstrated  many  times.  Flies  reared  experi- 
mentally in  the  autumn  or  winter  have  been  kept  alive  for  many  weeks— over 


Fig.  776  (left).  Resting  place  of  housefly.  Note  the  dense  fecal  wastes  along  the  cracks. 
(Courtesy  Federal  Research  Administration,  H.  I.  Scudder.) 

Fig,  777  (right).  Conical  hoop  fly  trap,  side  view.  A,  hoops  forming  frame  at  bottom; 
B,  hoops  forming  frame  at  top;  C,  top  of  trap  made  of  barrel  head;  D,  strips  around  door; 
E,  door  frame;  F,  screen  on  door;  G,  buttons  holding  door;  H,  screen  on  outside  of  trap; 
I,  strips  on  side  of  trap  between  hoops;  J,  tips  of  these  strips  projecting  to  form  legs; 
K,  cone  made  of  tin  or  screen  wire;  L,  united  edges  of  screen  forming  the  cone;  M, 
aperture  at  top  of  cone.  (From  Bishopp.) 

eleven  by  Jepson  (1909).  Hewitt  was  unable  to  keep  them  alive  longer  than 
seven  weeks.  Herms  in  California  records  an  average  life  period  of  30  days, 
with  a  maximum  of  60  days  in  the  summer.  Under  experimental  conditions 
during  the  summer  at  Ithaca,  New  York,  individual  flies  have  been  fed  and 
kept  alive  for  from  30  to  70  days.  It  is  evident,  therefore,  that  the  housefly  lives, 
on  the  average,  at  least  a  month  during  the  summer  and  rather  longer  during 
the  cool  months  if  food  and  shelter  are  provided. 


THE  HOUSEFLY  AND  ITS  ALLIES  469 

"    THE  HOUSEFLY  AND  DISEASE 

That  the  housefly  is  an  active  and  important  carrier  of  bacteria,  certain 
Protozoa,  and  the  eggs  of  helminths  (round-  and  flatworms)  has  been  dem- 
onstrated by  extensive  experimental  work  by  numerous  investigators.  Further- 
more it  serves  as  an  intermediate  host  in  the  developmental  cycle  of  certain 
parasitic  worms.  In  general  houseflies  affect  the  health  of  man  and  animals 
in  the  following  ways: 

1.  By  their  annoying  habits  and  excessive  numbers  they  irritate  and  reduce 
the  vitality  of  man  and  animals.  This  is  especially  true  for  children,  old  people, 
persons  suffering  from  nervous  disorders,  or  those  sickly  and  delicate.  In  the 
case  of  domestic  animals,  Freeborn  and  Bishopp  have  also  shown  that  an  exces- 
sive number  of  flies  causes  a  marked  reduction  in  milk  flow  in  cows. 

2.  By  means  of  their  hairy  bodies,  their  feet  well  provided  with  sticky  pads, 
and  their  feeding  and  egg-laying  habits,  they  serve  as  ideal  mechanical  distrib- 
utors of  filth  containing  bacteria,  protozoan  cysts,  and  helminth  eggs  to  man's 
food  and  directly  to  his  person?  especially  about  his  mouth  and  eyes  where 
they  constantly  seek  moisture. 

3.  As  the  housefly  feeds  on  all  kinds  of  fecal  material,  especially  human; 
decaying  animal  and  plant  substances;  infected  liquids,  as  milk  and  water, 
it  can  take  into  its  intestinal  tract  all  sorts  of  bacteria,  protozoan  cysts,  and  cer- 
tain helminth  eggs,  and  distribute  them  in  its  feces  or  by  way  of  the  vomit 
spots.  It  has  been  shown  by  many  workers  that  certain  of  these  organisms 
pass  through  the  fly's  intestine  in  a  viable  condition.  It  has  also  been  shown 
that  the  maggots  feeding  on  infected  fecal  material  take  in  certain  bacteria  and 
pass  them  on  through  the  pupal  stage  to  the  adults.  Experimental  evidence 
indicates  that  this  method  of  transfer  of  pathogenic  organisms  is  rather  un- 
common. 

4.  The  housefly  serves  as  an  intermediate  host  in  the  life  cycle  of  certain 
parasitic  helminths. 

ORGANISMS  DISTRIBUTED  BY  THE  HOUSEFLY 

As  a  mechanical  distributor  of  germs  the  housefly  probably  has  no  equal. 
Cox,  Lewis,  and  Glynn  (1912)  showed, that  flies  from  sanitary  areas  carried 
externally  much  smaller  numbers  (21,000  to  100,000)  of  bacteria  per  fly  than 
flies  from  unsanitary  areas  (800,000  to  500,000,000  per  fly).  Torrey  (1912)  ob- 
tained similar  results.  In  the  fly's  intestinal  tract  the  abundance  of  bacteria  is 
astounding,  owing,  no  doubt,  to  its  varied  feeding  habits.  Torrey  states  that 
the  bacteria  of  the  intestinal  tract  are  816  times  as  numerous  as  those  upon 


470  MEDICAL  ENTOMOLOGY 

the  external  surface  of  the  fly.  Cox,  Lewis,  and  Glynn  report  numbers  of 
bacteria  in  the  intestinal  tract  varying  from  10,000  to  333,000,000  per  fly  from 
unsanitary  areas  and  only  100  to  10,000  per  fly  caught  in  sanitary  districts.  Scott 
(1917),  working  in  the  District  of  Columbia,  reports  much  fewer  bacteria 
carried  externally  per  fly  and  confirms  the  previous  workers'  results  that 
flies  from  sanitary  areas  carry  fewer  organisms  than  those  from  unsanitary 
areas. 

The  danger  from  flies  is  their  habit:  of  wallowing  and  feeding  in  all  sorts 
of  fecal  matter,  decaying  wastes,  etc.,  and  then  flying  directly,  or  within  a  short 
period,  to  human  food,  depositing  thereon  their  fecal  wastes  and  vomit  spots, 
or  contaminating  it  by  germs  carried  externally.  Though  much  work  has  been 
done  in  an  effort  to  determine  the  organisms  distributed  by  flies,  the  results  are 
not  as  extensive  as  is  frequently  believed.  The  problem  is  an  extremely  dif- 
ficult one.  However,  the  following  known  pathogenic  bacteria  (the  list  is  not 
intended  to  be  complete)  have  been  isolated  from  the  housefly. 

Bacillus  typ/wsus  ~  by  Hamilton  (1905),  Fielder  ( 1905),  Faichne  ( 1909),  Hrterelli 
(1910),  Graham-Smith  (1910),  Cochrane  (1912). 

Bacillus  paratyphosus  "A"  by  Torrcy  (1912). 

Bacillus  paratyphosus  "B"  by  Nichol  (1911). 

Bacillus  dysentenae  (Morgan's  organism)  by  Morgan  and  Ledingham.  (1908- 
1909). 

Bacillus  dyscntcriac  (Flexncr  type)  by  Graham-Smith  (1909),  Manson-Bahr 
(1910),  and  others. 

Bacillus  coll  (and  its  many  varieties)  by  various  investigators. 

Bacillus  enteritidis  ( ? )  by  Torrey  (1912). 

Bacillus  tuberculosis  by  Spillman  and  Haushaller  (1887),  Hoffman  (1888),  Hay- 
ward  (1894),  Lord  (1904),  Graham-Smith  (1910),  and  others. 

Bacillus  pestis  by  Yersin  (1894),  Nuttall  (1897). 

Bacillus  cuniculicida  by  Scott  ( 1917). 

Bacillus  anthracis  by  Graham-Smith  (1910,  1911,  1912). 

Bacterium  tularcnse  by  Way  son  (1914). 

Brucella  abortus  by  Nishirnote  (1931,  unpublished). 

Staphylococcus  spp.  by  many  workers. 

Streptococcus  spp.  by  various  workers. 

Spirillum  cholcrae  (Vibrio  comma)  by  Tizzoni  and  Cattani  (1886),  Simmonds 
(1892),  Graham-Smith  (1910). 

Though  many  other  species  of  bacteria  have  been  reported  from  the  house- 
fly, it  would  seem  that  this  entire  field  should  be  carefully  rcstudiecl,  using  the 

-The  names  of  bacteria  employed  here  are  those  that  appeared  in  the  original  papers. 
The  present  names  can  be  found  in  any  modern  textbook  of  bacteriology. 


THE  HOUSEFLY  AND  ITS  ALLIES  471 

newer  and  more  exacting  technique  of  present-day  bacteriologists  and  giving 
more  attention  to  the  specific  types  of  bacteria. 

Cysts  of  the  following  human  intestinal  Protozoa  have  also  been  reported 
taken  up  by  the  housefly  and  passed  in  its  feccs  in  a  viable  condition:  Enda- 
moeba  histolytica,  Endarnoeba  coli,  Giardia  intestinalis  (by  Wcnyon  and 
O'Connor,  1917;  Roubaud,  1918;  and  Root,  1921),  and  Chilomastix  mcsnili 
(Root,  1921).  These  cysts  do  not  persist  alive  within  the  fly's  intestinal  tract 
for  any  great  length  of  time,  usually  not  longer  than  two  or  three  days.  How- 
ever, they  are  passed  in  a  viable  condition  during  this  time  and  may  be 
deposited  in  milk,  on  moist  foods,  or  in  water.  Furthermore,  Wenyon  and 
O'Connor  recovered  the  cysts  of  E.  histolytica,  E.  coli,  and  Giardia  intestinalis 
in  the  feccs  of  flies  caught  in  the  wild.  What  importance  can  be  assigned 
the  housefly  as  a  distributor  of  Protozoa  is  still  unsettled  and  further  work 
along  this  line  is  needed.  Frye  and  Melaney  (^2)  report  finding  the  cysts 
of  Endtinwcba  coli,  E.  histolytica,  E.  nana,  and  Giardia  in  flies  caught  in  houses 
where  carriers  were  present.  None  were  found  in  flies  taken  out  of  doors. 

As  an  intermediate  host  in  the  developmental  cycle  of  helminths  the 
housefly  plays  no  mean  part.  As  yet  our  data  are  far  from  complete  but  the 
following  species  are  known  to  pass  certain  stages  in  the  fly:  Choanotaenia  in- 
jiindt buhim,  Davainca  tctragona,  Davauiea  cesticillits,  Habroncma  micro- 
stoma,  Habronema  megastoma,  and  Habroncma  nuiscae.  As  a  result  of  his 
experimental  work  Nicoll  (1911)  found  the  fly  capable  of  ingesting  and  passing 
in  a  viable  condition  the  eggs  oi  the  following  species:  Tacnia  solittm,  Taenia 
serrata,  Taenia  margmata,  Hvmenolcpis  nana,  Dipvlnliiim  caninnm,  Oxyitns 
vcrmiciilaris,  and  Triclntris  trichiura.  Externally  the  fly  may  distribute  from 
fecal  wastes  any  eggs  that  may  adhere  to  its  hairy  body  or  feet.  These  can  be 
deposited  in  liquids,  foods,  or  other  material  eaten  or  handled  by  man. 

SPECIFIC  DISEASES 

TYPHOID  FEVER :  As  already  pointed  out,  the  housefly  acts  as  an  efficient 
carrier  of  many  of  the  colon-typhoid  bacilli.  Typhoid  and  the  paratyphoid 
fevers  are  caused  by  Ebcrt/iclla  typhosa,  Salmonella  paratyphi  (B.  paratypliosus 
A),  and  S.  schottmi'dleri  (Bacillus  paratyphostis  B).  These  organisms  are  pri- 
marily parasitic  and  according  to  Jordan  (1929)  are  found  outside  the  human 
body  "only  in  those  situations  where  it  could  be  more  or  less  directly  traced 
to  an  origin  in  the  discharges  of  a  typhoid  patient  or  convalescent."  In  pure 
water  the  life  of  typhoid  bacteria  appears  to  be  rather  short,  probably  not  over 
a  month,  and  there  is  no  multiplication  but,  on  the  contrary,  a  steady  decline 
in  their  numbers  as  time  goes  on/Human  infection  from  water  is  to  be  feared 


472  MEDICAL  ENTOMOLOGY 

chiefly  when  there  is  fresh  sewage  contamination;  undoubtedly  the  principal 
typhoid  epidemics  have  been  traced  to  polluted  drinking  water.  In  the  human 
b6dy  the  typhoid  organisms  are  present  principally  in  the  intestine,  urinary 
bladder  (at  least  25  per  cent  of  all  cases;  Jordan,  1929),  kidneys,  and  the  blood 
stream.  In  the  kidneys  the  infection  may  be  intense  (100,000,000  to  500,000,000 
bacteria  in  a  single  cubic  centimeter  of  urine)  and  be  prolonged  for  weeks  and 
months  after  recovery.  The  same  holds  true  for  the  gall  bladder  infections. 
In  addition,  a  small  percentage  (0.5  to  n.6  per  cent  or  even  as  high  as  25  per 
cent)  of  those  who  recover  from  typhoid  fever  became  "chronic  carriers"  or 
"permanent  carriers,"  that  is,  they  continue  to  pass  the  bacilli  in  their  feces  or 
urine  for  considerable  periods — six  months  (chronic  carriers)  or  during  their 
lifetime  (permanent  carriers).  From  this  hasty  survey  it  will  be  seen  that  the 
typhoid  bacilli  arc  discharged  from  the  human  patient  and  "carriers"  in  the 
urine  and  feccs  so  that  the  ground  about  open  privies,  soil  or  water  polluted 
with  sewage,  etc.,  may  and  do  serve  as  foci  for  the  further  spread  of  the  dis- 
ease. Here  we  are  only  interested  in  the  part  played  by  the  housefly  in  the 
spread  of  the  disease.  Houseflies  are  constant  visitors  to  sewage  wastes  and  to 
exposed  human  feces,  on  which  they  feed  and  oviposit;  they  also  are  attracted 
to  urine  and  frequently  breed  in  soil  saturated  with  urine.  From  such  filth 
they  pass  directly  to  our  food,  deposit  their  feces  and  vomit  spots  thereon,  or 
fall  into  milk,  sweetened  liquids,  jams,  etc.,  and  may  leave  behind  large  num- 
bers of  the  typhoid  bacilli.  )That  flies  carry  these  bacilli  has  been  proved  a 
number  of  times,  and  Hamilton  (1903)  has  shown  experimentally  that  living 
bacilli  may  remain  in  or  on  the  body  of  the  fly  for  at  least  23  days  after  con- 
tamination. Reed  and  his  associates  (1900)  present  the  most  extended  in- 
vestigations of  fly  carnage  of  typhoid  in  their  study  of  the  severe  outbreaks 
of  the  disease  among  American  troops  during  the  Spanish-American  war. 
Jordan  (1929)  states  that  "cases  formerly  attributed  to  air-carriage  may  per- 
haps be  more  reasonably  ascribed  to  the  agency  of  flies."  Sweet  (1922)  states 
that  flies  are  in  part  responsible  for  the  spread  of  typhoid  fever.  "In  the  United 
States  alone  during  1920  over  8000  persons  died  from  typhoid  fever,  and  ten 
times  that  number  suffered  from  the  infection,  the  rate  being  several  times 
higher  than  that  of  many  civilized  countries."  From  these  and  numerous  other 
investigations  it  is  safe  to  conclude  that  flies  are  an  important  agency  in  the 
dissemination  of  typhoid  fevers.  (As  most  of  the  positive  findings  of  flies 
harboring  typhoid  baccilli  were  made  before  our  present  fuller  knowledge  of 
the  disease,  it  would  seem  that  the  earlier  work  ought  to  be  confirmed  or 
disproved  by  modern  techniques.) 


THE  HOUSEFLY  AND  ITS  ALLIES  473 

DYSENTERY:  Two  distinct  diseases  are  indicated  under  this  term:  bacil- 
lary  dysentery  caused  by  Shigclla  (Bacillus)  dysenteriae  and  S.  paradysenteriae 
and  amoebic  dysentery  caused  by  Endamocba  histolytica.  These  organisms 
have  been  shown  to  be  carried  by  flies  and  distributed  either  by  way  of  their 
fcces  or  vomit  spots. 

Bacillary  dysentery  is  frequently  a  scourge  in  armies,  prisons,  camps,  and 
military  barracks.  Not  infrequently  epidemics  occur  in  the  Tropic,  Temperate, 
and  even  in  the  Arctic  zones.  The  spread  of  the  disease  is  due  to  direct  or 
indirect  contact  with  the  fecal  wastes  of  those  afflicted.  Furthermore,  about 
3  per  cent  of  those  recovered  may  continue  to  pass  the  bacillus  in  their  stools 
and  are  thus  dangerous  individuals  in  the  community.  Flies  play  an  impor- 
tant part  as  indirect  distributors  of  the  bacilli,  feeding  on  infected  fecal 
wastes  and  then  contaminating  human  food.  The  bacilli  have  been  shown 
to  survive  for  at  least  five  days  in  the  intestinal  tract  of  flies.  Manson-Bahr 
(1924)  states  that  "the  seasonal  incidence  of  bacillary  dysentery  corresponds  in 
a  remarkable  manner  with  the  maximum  prevalence  of  these  pests  (house- 
flies)." 

•In  amoebic  dysentery  the  organism  Endamoeba  histolytica  is  discharged  in 
the  stools  in  the  precystic  or  cystic  stage.  As  Endamoeba  histolytica  may  not, 
in  many  people,  produce  clinical  symptoms  of  disease,  we  have  what  are 
called  "contact"  and  "convalescent"  carriers.  As  normally  5  to  10  per  cent  of 
the  average  population  may  be  infected,  there  are  large  numbers  of  contact 
carriers.  Persons  who  have  had  the  disease  and  have  recovered  are  known  as 
"convalescent  carriers."  Such  carriers,  unless  effectively  treated,  may  continue 
to  pass  the  cysts  for  many  years.  From  these  two  sources  fecal-feeding  flies 
may  easily  obtain  the  cysts  from  exposed  excrement,  untreated  sewage  wastes, 
etc.,  and  distribute  them  to  our  food,  water,  or  milk. 

In  addition,  a  disease  of  infants,  known  as  "summer  diarrhea,"  is  frequently 
all  too  prevalent.  The  inciting  agent  is  apparently  Shtgella  spp.  Shigetta  dysten- 
teriae  has  been  found  associated  with  numerous  cases  but  is  not  invariably 
present;  other  intestinal  bacteria  undoubtedly  play  a  part  in  the  causation  of 
the  disease.  Flies  are  generally  accused  of  acting  as  important  distributors  of 
the  causative  agents  of  the  disease  and  should  be  regarded  with  suspicion  until 
shown  otherwise.  All  stools,  vomits,  and  wastes  from  infants  suffering  from 
the  disease  should  be  disinfected  and  at  all  times  protected  from  flies.  In  pre- 
venting the  spread  of  the  disease  the  protection  of  infants  and  their  food  from 
flies  is  of  extreme  importance.  Martin  (1913),  after  analyzing  all  the  factors 
involved  in  the  spread  of  summer  diarrhea,  concludes  that  the  carnage  by 


474  MEDICAL  ENTOMOLOGY 

flies  may  not  be  the  dominant  one  but  probably  is  one  of  the  most  important. 
Armstrong  (1914)  clearly  shows  an  increase  of  the  disease  among  infants  in 
an  unprotected,  congested,  unsanitary  area  in  New  York  City  as  compared 
with  a  fly-protected,  more  sanitary  area  in  another  congested  district  of  the 
same  city.  Recent  experimental  work  by  Watt  and  Lindsay  (1948)  indicates 
that  diarrheal  diseases  can  be  reduced  in  high  morbidity  areas  by  the  efficient 
use  of  DDT.  However  the  authors  conclude  that  the  cost  of  eliminating  the 
worst  fly-breeding  places  is  less  and  the  results  more  effective  than  the  use  of 
DDT.  In  other  words,  good  sanitary  measures  cost  less  in  the  long  run  and 
are  permanent,  whereas  the  use  of  DDT  is  a  temporary  expedient. 

CHOLERA:  Cholera  is  an  acute  disease  caused  by  Spirillum  cholerae  (Vib- 
rio commit).  The  organism  is  discharged  in  the  stools  of  the  patientsjimd 
infection  takes  place  only  through  the  contamination  of  food  or  water  or  by 
direct  contact.  In  the  dejecta  of  cholera  patients  the  vibrios  may  live  for  days 
in  soiled,  damp  linen,  for  months  in  water  or  damp  soil.  Again  a  certain  per- 
centage of  recovered  cases  harbor  the  germ  in  their  intestines  and  act  as  carriers. 
From  such  sources  fecal-feeding  flies  can  obtam  the  vibrios  and  pass  them 
on  through  their  feces  or  vomit  spots  directly  to  food  or  drink.  The  vibrios 
of  cholera  were  early  shown  to  be  carried  by  flics. jSirnmonds  (1X92)  captured 
flies  in  a  cholera  post-mortem  room  and  obtained  colonies  of  the  vibrios  from 
them.  Graham-Smith  (1910)  experimented  with  flies  and  obtained  the  vibrios 
from  the  legs  up  to  30  hours  after  contamination,  from  the  intestine  and  crop 
for  48  hours  after  infection.  These  findings  have  been  confirmed  by  other 
workers  and  various  observers  have  recorded  their  belief  that  flics  arc  active 
agents  in  the  spread  of  cholera  epidemics.  Patton  (1930)  doubts  that  flics  play 
any  active  part  in  the  spread  of  cholera.  Recently  Gill  and  Lai  ( 1931)  presented 
a  new  and  rather  startling  hypothesis  of  fly  carriage  of  cholera.  The  vibrios 
were  found  capable  of  surviving  in  the  fly  for  at  least  five  days;  in  other  cases 
the  vibrios  apparently  disappeared  from  the  gut  after  24  hours  or  so  and  re- 
appeared on  or  about  the  fifth  day,  at  which  lime  the  flies  are  capable  of 
infecting  food  or  drink  by  their  feces  (the  authors  tentatively  suggest  a 
definite  host-parasite  relationship  in  this  case).  They  also  showed  that  infection 
of  milk  by  the  proboscis  can  take  place  up  to  24  hours  after  infection,  but  they 
have  no  evidence  that  proboscis  infection  may  occur  on  and  after  the  fifth  day. 

ANTHRAX:  Anthrax  is  primarily  a  disease  of  cattle  and  sheep  caused  by 
Bacillus  anthracis.  Man  becomes  infected  mainly  through  abrasions  of  the 
skin  (malignant  pustule),  the  organism  coming  from  various  sources  as 
infected  cattle,  sheep,  or  their  products.  That  flies  may  act  as  carriers  has  been 


THE  HOUSEFLY  AND  ITS  ALLIES  475 

demonstrated  by  Ballinger,  Buchanan,  Graham-Smith,  and  others.  As  Bacillus 
anthracis  is  a  sporcforming  bacillus,  it  can  be  easily  distributed.  Graham-Smith 
has  shown  that  flies  fed  on  the  spores  may  contain  living  spores  in  their  in- 
testinal tract  for  at  least  14  days  and  on  their  bodies  for  20  days.  Dried  feces 
and  vomit  spots  contained  viable  spores  for  20  days.  He  also  showed  that  when 
larvae  were  fed  on  the  spores  a  large  proportion  of  the  adults  from  these  larvae 
were  infectcd^As  the  spores  of  anthrax  remain  viable  in  the  soil  for  many  years 
(at  least  30),  flies  may  obtain  them  in  various  ways  while  feeding  on  fecal 
wastes,  polluted  water,  etc.  Man  may  become  infected  through  the  deposition 
of  such  spores  on  his  food,  or,  more  probably,  on  exposed  sores,  wounds,  etc) 
What  actual  part  flies  (nonbloodsucking  flies)  may  play  in  the  spread  of  this 
disease  among  domestic  animals  is  not  known. 

YAWS  (Frambocsia,  Tropical  Ulcer) :  This  disease,  caused  by  Treponema 
pertenite,  is  widely  distributed  throughout  the  tropical  and  subtropical  regions. 
It  is  .very  prevalent  in  many  of  the  West  Indian  islands  and  parts  of  South 
America  and  has  been  reported  from  the  southern  United  States.  The  disease 
is  characterized  by  ulcerous  papules  which  form  funguslike,  encrusted,  granu- 
lomatous  eruptions-jwhich  may  extend  all  over  the  body.  The  spread  of  the 
disease  is  mainJylJy  direct  contact  from  person  to  person.  However,  flies  have 
been  incriminated,  and  Castcllani  and  Chalmers  state  that  flies  eagerly  crowd 
upon  the  open  sores,  even  in  the  hospitals,  when  the  dressings  are  removed. 
Castellani  has  recovered  the  spirochete  from  houseflics  allowed  to  feed  on  the 
scrapings  from  the  sores,  and  he  was  able  to  infect  monkeys  by  placing  flies 
on  the  scarified  areas  on  the  eyebrows.  When  the  excessive  abundance  of 
flies  in  tropical  countries  is  taken  into  consideration,  it  would  seem  that  house- 
flies,  flesh  flies,  and  other  flies  (as  Hippdates  spp.,  family  Chloropidae)  must 
play  a  part  in  its  distribution. 

CONJUNCTIVITIS  (Ophthalmia) :  There  are  many..^ye  diseases,  caused 
by  various  agencies.  In  the  spread  of  some  of  thesef  flies  are  undoubtedly 
concerned.  In  many  parts  of  the  tropics  as  China,  India,  Egypt,  sections  of 
South'  America,  and  Porto  Rico  trachoma  of  the  eyes  is  very  prevalent.  The 
housefly  is  a  constant  menace  on  account  of  its  abundance  and  its  persistent 
efforts  to  obtain  moisture  and  secretions,  purulent  or  otherwise,  from  about 
the  eyes.  Elliott  (1923)  states  that  swarms  of  flies  may  be  seen  alighting  on 
the  eyes  of  people  suffering  from  ophthalmia  and  they  readily  pass  on  the 
infection  to  the  next  healthy  conjunctiva  on  which  they  alight.  "Flies  are  a  great 
danger  as  they  carry  discharges  from  morbid  to  healthy  eyes"  (Elliott) .  Similar 
cpnclusions  are  stated  by  Castellani  and  Chalmers.  As  early  as  1888  Howe  stated 


476  MEDICAL  ENTOMOLOGY 

that  the  number  of  cases  of  conjunctivitis  in  Egypt  increased  in  proportion 
to  the  increase  of  flies>)  As  far  as  the  writer  is  aware  there  are  no  specific 
investigations  dealing  with  muscid  flies  as  agencies  in  the  spread  of  eye  dis- 
eases in  temperate  climates.  When  one  witnesses  the  abundance  of  flies  about 
exposed  babies,  persons  with  eye  diseases,  etc.,  it  would  seem  that  such  insects 
must  play  a  part  not  as  yet  well  known. 

POLIOMYELITIS :  In  recent  years  because  of  the  accumulated  knowledge 
oT  this  disease  the  common  house-frequenting  flies  rather  than  the  blood- 
sucking flies  have  been  incriminated  as  possible  vectors. /Paul  et  al.  (1941) 
report  transmission  to  monkeys  from  flies  (1000  to  1200  collected  at  a  camp 
kitchen  in  Connecticut,  where  cases  in  children  were  present)  macerated  and 
injected  into  a  cynomologous  monkey.  Similar  results  were  obtained  from 
flies  caught  near  a  privy  in  Alabama  where  cases  of  polio  had  recently  occurred. 
Sabin  and  Ward  (1941)  also  demonstrated  the  virus  in  flies  taken  from  urban 
places  in  Cleveland  and  Atlanta  where  human  cases  were  present.  These  data 
were  based  on  infections  of  cynomologous  monkeys  injected  intraperitoneally 
with  macerated  flies.  Unfortunately  in  all  these  experiments  a  variety  of  flies 
were  employed  so  that  it  is  not  possible  to  say  which  species  carried  the  virus. 
However,  all  of  them  normally  occur  about  houses;  most  will  feed  on  fecal 
wastes,  sewage  wastes,  and  human  food;  and  the  results  demonstrate  that 
flies  do  carry  the  virus7£Toomey  et  al.  (1941)  report  obtaining  the  virus  from 
flies  taken  at  the  outlet  of  raw  sewage  near  where  the  disease  was  present. 
Ward  et  al.  (1945)  demonstrated  that  food  such  as  bananas  exposed  to  flies  in 
and  about  homes  where  polio  was  present  became  infected  and  produced 
subclinical  cases  of  polio  when  fed  to  chimpanzees.  Furthermore,  the  feces  of 
these  test  monkeys  showed  the  presence  of  the  virus  for  one  or  two  months  after 
the  last  feeding.  According  to  Bang  and  Glaser  (1943),  the  housefly  (Musca 
domes tied)  retained  Theiler's  mouse  "poliomyelitis"  as  long  as  12  days  after 
being  infected  by  feeding  but  the  mouse-adapted  human  strain  survived  only 
two  days. 

OTHER  DISEASES :  Flies  have  been  reported  as  spreading  other  diseases 
(plague,  tuberculosis,  smallpox,  leprosy,  etc.),  but  the  importance  of  this 
means  of  distribution  is  probably  not  great  or  has  not  been  fully  investigated. 
This  may  be  said  especially  of  tuberculosis.  Though  the  tubercle  bacillus  is 
taken  up  from  sputum,  intestinal  wastes,  exudates  from  tubercular  sores,  etc., 
and  is  known  to  pass  through  the  fly's  intestine  in  a  viable  condition  for  at 
least  a  week,  we  know  practically  nothing  of  the  part  played  by  flies  in  the 
spread  of  the  disease.  Their  role  may  be  of  more  significance  than  is  generally 


THE  HOUSEFLY  AND  ITS  ALLIES  477 

conceded,  especially  when  some  of  the  recent  work  on  the  presence  and  via- 
bility of  B.  tuberculosis  is  considered.  Brown  and  his  co-workers  (1916)  re- 
covered viable  bacilli  in  a  sewage-contaminated  stream  three  and  one-half  miles 
below  the  outfall;  Conroy,  Conroy,  and  Laird  (1921)  demonstrated  living 
bacilli  in  the  effluent  from  an  Imhoff  tank  at  a  sanitarium;  Cummins  and  Ack- 
land  (1929)  found  them  in  a  thin  coating  over  stones  at  the  point  of  escape 
of  the  effluent  from  a  septic  tank;  Williams  and  Hay  (1930)  demonstrated 
living  and  virulent  B.  tuberculosis  (bovinus)  in  cow  manure  exposed  in  the 
south  of  England  for  five  months  in  winter,  two  months  in  spring,  two  months 
in  summer,  and  four  months  in  autumn.  In  manure  protected  from  sunlight 
the  organism  lives  at  least  four  months  in  summer;  in  liquid  cow  manure  the 
bacillus  lived  for  at  least  four  months.  The  recovery  of  viable  tuberculosis 
bacilli  in  such  situations  clearly  indicates  ideal  sources  where  flies  may  obtain 
them  either  by  feeding  or  during  larval  development. 

OTHER  COMMON  HOUSE-FREQUENTING  FLIES 

{^Besides  the  housefly  (Musca  domestica)  other  species  of  Musca  flies  are 
found  frequenting  the  home.  Musca  nebula  and  M,  vicina  are  the  most  com- 
mon bazaar-  and  house-frequenting  flies  in  Indues  M.  sorbens  is  a  house  visitor 
throughout  the  Netherlands  Indies;  other  species  occur  in  the  Ethiopian  and 
oriental  regions  but  do  not  appear  to  be  serious  pests  about  homes.  Other 
important  flies  arc  the  lesser  housefly  (Fannia  canicularis,  Fig.  196),  the 
latrine  fly  (Fannia  scalaris),  the  nonbiting  stable  fly  (Muscina  stabulans,  Fig. 
192),  the  biting  stable  fly  (Stomoxys  calcitrant,  Fig.  166),  the  "blowflies" 
(Calliphora  spp.),  the  green-bottle  flies  (Lucilia  spp.),  and  the  cluster  fly  (Pol- 
lenia  rudis).  The  species  of  "blowflies"  and  green-bottle  flies  (Calliphora  spp. 
and  Lucilia  spp.)  may  also  act  as  mechanical  vectors  of  many  of  the  disease- 
producing  organisms  in  the  same  manner  as  the  housefly.  They  are  not,  how- 
ever, such  invaders  of  our  houses,  but  in  slum  districts  and  badly  sanitated 
areas  they  may  prove  important  vectors,  as  shown  by  Yao  ct  al.  (1929)  in 
Peiping,  China,  and  by  other  investigators  in  different  areas.  Most  of  these 
flies  except  the  last  one  are  discussed  in  Chapter  xvu,  to  which  the  reader  is 
referred. 

Though  the  larvae  of  these  flies  (except  the  species  Pollenia  rudis)  occa- 
sionally cause  myiasis,  they  are  also  of  some  importance  as  nuisances  about 
the  home  and  as  mechanical  carriers  of  pathogenic  organisms.  In  general,  how- 
ever, it  may  be  said  with  certainty  that  in  nearly  all  cases  the  common  house- 
fly constitutes  over  90  per  cent  of  the  fly  population  in  houses.  The  cluster  fly 
(Pollenia  rudis)  is  found  invading  houses  only  in  the  autumn.  In  many  places 


478  MEDICAL  ENTOMOLOGY 

it  is  veritable  pest.  The  adult  closely  resembles  the  housefly  in  size  but  is  more 
sluggish.  The  thorax  lacks  the  light  and  dark  lines  and  bears  many  short, 
golden  hairs.  In  the  larval  stage  it  is  parasitic  on  certain  species  of  earthworms. 
The  abundance  of  the  adults  largely  depends  on  the  availability  of  the  larval 
host.  As  no  very  effective  method  of  reducing  the  numbers  of  earthworms  is 
known,  we  cannot  control  the  fly  in  the  larval  stage.  As  the  adults  enter  our 
houses  in  order  to  hibernate,  their  presence  is  only  noted  in  the  autumn  and 
again  in  the  spring  when  they  leave  their  hiding  places.  In  the  fall  they  invade 
every  corner  and  darkened  retreat,  where  they  gather  together,  often  in  im- 
mense clusters.  They  may  be  found  in  every  crack  and  crevice,  crawling  slug- 
gishly about.  The  most  effective  control  is  to  "swat"  them,  to  spray  with  Flit, 
or,  better,  to  use  DDT  as  for  houscflies,  carefully  spraying  all  their  resting 
places. 

THE  CONTROL  OF  FLIES 

As  the  housefly  constitutes  the  major  part  of  the  fly  population  of  our  homes 
and  is  a  constant  menace  to  our  health  and  happiness,  any  sanitary  measures 
required  for  its  reduction  ought  to  be  welcomed  and  carried  out  with  alacrity. 
Furthermore,  it  is  the  most  abundant  species  in  our  food  and  bakery  shops,  in 
city  markets,  in  candy  and  delicatessen  stores,  in  meat  markets  and  packing 
establishments,  in  and  about  dairy  buildings  and  milk  establishments  of  all 
kinds,  in  public  and  private  toilets,  in  open  privies  (especially  about  rural 
homes  and  camp  sites),  and  in  our  public  parks  and  playgrounds  where  thou- 
sands and  tens  of  thousands  of  our  people  congregate. 

In  order  to  realize  the  problem  of  the  control  of  the  housefly  it  is  necessary 
once  again  to  indicate  its  breeding  places.  It  breeds  most  abundantly  in  horse 
manure  (Fig.  175),  in  human  excrement,  decay  ing  vegetable  and  animal  matter 
of  all  kinds  where  fermentation  is  taking  place,  in  garbage  cans  and  waste,  in 
city  dumps  and  cesspools,  in  ground  saturated  with  urine  and  fecal  wastes,  in 
poultry  wastes,  hog  pens,  dairy  wastes,  and  cow  manure  mixed  with  straw  or 
horse  manure,  in  wastes  from  slaughter  houses — in  fact,  in  nearly  all  places 
where  animal  or  plant  substances  decay  and  fermentation  takes  place.  It  is 
thus  clear  that  the  prevention  of  fly  breeding  is  primarily  a  problem  of  sanita- 
tion and  cleanliness.  As  the  housefly  has  an  extended  range  of  flight,  at  least 
10  or  12  miles,  the  prevention  of  fly  breeding  is  a  community  problem. 

The  main  essentials  in  fly  control  may  be  briefly  summarized: 

i.  By  suitable  sanitary  measures  eliminate  as  many  of  the  breeding  grounds 
'is  possible  at  a  minimum  expenditure  of  time  and  money. 


THE  HOUSEFLY  AND  ITS  ALLIES  479 

2.  Destroy  the  eggs  and  larvae  in  the  breeding  grounds  that  cannot  be 
eliminated.   ^^ 

.x-i 

3.  Where  the  previous  methods  cannot  be  effectively  carried  out,  the  fol- 
lowing palliatives  should  be  employed  in  order  to  reduce  the  number  of  adults: 
(a)  The  effective  use  of  screens  on  all  doors,  windows,  or  other  openings 
through  which  flies  may  enter,  (b)  The  use  of  DDT  as  a  residual  spray.  This 
is,  at  present,  the  most  satisfactory  treatment,  (c)  The  employment  of  fly 
and  larval  traps,  (d)  The  use  of  fly  papers,  poison,  and  "swatting." 

SANITARY  MEASURES 

With  the  rapid  development  of  city,  town,  and  county  public  health  activi- 
ties, the  education  of  the  general  public  to  adopt  effective  sanitary  measures 
ought  not  to  be  too  long  delayed.  Yet  despite  educational  propaganda  by 
means  of  health  units,  the  public  schools,  the  radio,  etc.,  we  find  some  of  the 
worst  sanitary  conditions  in  our  largest  cities,  in  public  and  private  institutions, 
in  our  schools,  colleges,  and  universities,  in  our  great  public  parks,  and  even 
in  our  homes.  Cleanliness  and  the  love  of  cleanliness  may  be  on  the  increase 
but  the  appearance  of  great  filthy  "dumps"  near  cities  and  villages,  great  rivers 
polluted  with  sewage  wastes,  harbor  fronts  reeking  with  rotting  garbage,  wide- 
spread carelessness  in  the  disposal  of  wastes,  etc.,  make  one  dubious.  In  cities 
and  villages  the  problem  of  effective  control  of  flies  is  comparatively  simple 
as  compared  with  the  rural  one.  The  following  should  reduce  fly  abundance 
in  cities: 

\^sK\\  efficient  sewage-disposal  system — meaning  by  that  a  system  providing 
for  the  receival,  treatment,  and  discharge  of  all  sewage  wastes  in  such  a  manner 
that  no  opportunity  for  fly  breeding  can  occur. 

2.  A  garbage  collection  system  that  compels  the  individual  householder  to 
sterilize  the  cans  thoroughly  each  week  or  to  dry  all  wastes  and  place  them 
in  the  cans  securely  wrapped  in  paper.  Only  tightly  closing  cans  of  heavy  con- 
struction should  be  used.  Collections  should  be  made  once  or  twice  a  week  in 
the  North  and,  if  possible,  five  or  six  times  a  week  in  the  South  (referring  to 
the  Northern  hemisphere).  Garbage  cans  should  be  handled  with  care  and 
not  thrown  about  as  if  they  were  only  intended  for  destruction.  A  well-trained 
collection  crew  is  essential  so  that  garbage  is  not  spilled  about  private  homes  or 
scattered  indiscriminately  about  the  streets  and  alleys. 

3.  The  effective  disposal  of  such  garbage  collections,  preferably  by  incinera- 
tion. Where  incineration  cannot  be  employed  then  a  sanitary  "dump"  may 
be  devised.  A  sanitary  dump  is  feasible  and  can  be  seen  in  certain  cities.  In  such 


480  MEDICAL  ENTOMOLOGY 

cities  the  ashes  are  collected  separately;  they  must  be  free  from  all  garbage. 
During  the  winter  the  ashes  may  be  piled  in  large  heaps  on  the  dump.  The 
garbage  is  then  disposed  each  day  along  the  front  of  the  dump,  covered  with 
ashes,  and  treated  with  an  effective  disinfectant  and  deodorant.  (These  are 
now  obtainable  and  at  reasonable  prices.)  In  warm  climates  the  problem  is 
more  difficult  but  it  is  not  unsolvable.Clhe  daily  application  of  a  5  per  cent 
DDT  spray  on  the  dump  will  prove  very  eff  ectiveT) 

4.  Proper  treatment  of  the  garbage-collecting  wagons.  They  should  be  thor- 
oughly cleaned,  washed,  and  treated  with  disinfectants  and  deodorants  each 
day  after  the  close  of  work.  An  up-to-date  storage  and  rest  room  with  bathing 
and  cleaning  facilities  should  be  provided  for  the  collection  crews.  And,  most 
essential  of  all,  the  person  in  charge  of  such  work  should  be  thoroughly  im- 
bued with  one  ideal,  cleanliness. 

5.  An  alert  and  well-trained  sanitary  corps  to  deal  promptly  and  effectively 
with  all  problems  arising  from  the  disposal  of  wastes  and  the  maintenance 
of  conditions  inimical  to  the  public  health. 

6.  The  effective  disposal  of  all  manure  from  horses,  cattle,  and  other  ani- 
.  mals  kept  in  cities  (see  below) . 

7.  Spraying  with  DDT  during  World  War  II  for  the  control  of  mosquitoes, 
lice,  bedbugs,  and  other  insects  has  shown  DDT  to  be  the  most  effective  agent 
in  the  control  of  the  adults  of  the  housefly.  It  is  not  of  any  value  in  destroying 
the  larvae.  To  control  the  housefly  it  is  employed  as  a  residual  spray.  It  should 
be  applied  as  a  5  per  cent  (by  weight)  spray  (kerosene  solution  or  xylene 
emulsion)  to  all  indoor  surfaces  so  as  not  to  "run-off"  but  leave  a  residue  of 
at  least  200  mgm.  per  square  foot,  that  is  at  least  i  gallon  of  the  mixture  to 
1000  square  feet.  Also  all  screens,  the  framework  of  doorways  and  cellar  en- 
trances, and  other  exposed  place  where  flies  congregate  should  be  treated. 
In  barns,  privies,  and  outbuildings  of  all  kinds  where  it  is  not  so  necessary  to 
leave  no  visible  deposit,  an  emulsion  or  wettable  powder  suspended  in  water 
may  be  employed.  In  using  this  material  either  employ  a  professional  operator 
or  be  careful  to  follow  the  directions  of  the  manufacturer  or  the  advice  given 
by  your  health  department,  experiment  station,  or  the  national  health  agencies. 

Under  rural  conditions  the  problem  of  fly  control  and  the  adoption  of  sani- 
tary measures  for  the  prevention  of  fly  breeding  are  more  difficult.  The  farmer 
must  maintain  domestic  animals  and  conserve  the  manure  supply  for  the 
growing  of  crops.  Cleanliness  and  effective  screening  are  the  most  available 
means  together  with  the  effective  use  of  DDT.  However,  the  individual 
farmer,  though  clean  and  most  exacting  in  carrying  out  sanitary  measures, 
may  suffer  from  the  carelessness  of  his  neighbors.  Under  farm  conditions 


THE  HOUSEFLY  AND  ITS  ALLIES  481 

the  most  effective  measures  may  be  summed  up  as  follows.  (The  efficient  and 
careful  use  of  DDT  may  render  some  of  these  measures  unnecessary.) 

4.  An  efficient  disposal  system  for  all  manure,  especially  human  excrement. 
Indoor  toilets  with  septic  tanks  are  well  known  and  full  instructions  for  their 
installation  can  easily  be  obtained  from  health  departments  or  frequently  from 
the  state  agricultural  colleges.  Where  these  cannot  be  installed,  sanitary  out- 
door privies  can  be  constructed  or  the  "chemical"  treatment  of  fecal  wastes 
may  be  employed. 

2.  Manure  of  domestic  animals  should  be  disposed  of  daily  where  possible, 
the  manure  being  distributed  on  the  fields,  preferably  with  a  manure  spreader. 
When  this  can  be  practised,  cleanliness  is  essential — no  left-overs  in  stables, 
drains,  corners,  carriers,  dump  carts,  or  other  vehicles  used  in  the  disposal. 
Such  a  procedure  is  costly  on  the  average  farm,  where  manure  is  usually  piled 
either  directly  outside  the  barns  (Fig.  175)  or  placed  in  concrete  pits  to  await 
future  disposal.  In  such  cases(?ly  breeding  may  be  prevented  by  one  of  the 
following  treatments)  recommended  by  the  United  States  Department  of 
Agriculture: 

Hellebore  may  be  used  at  the  rate  of  0.5  pound  to  10  gallons  of  water.(§tir 
the  powdere^Thellebore  in  the  water  and  allow  to  stand  for  24  houj3>.  This 
mixture  is  sufficient  to  treat  10  cubic  feet  or  8  bushels  of  manure,  (pie  solu- 
tion may  be  sprayed  on  the  manure  with  a  hand  pump.  The  hellebore  has  no 
injurious  efTect  on  the  manure. 

Powdered  borax  used  at  the  rate  of  i  pound  to  16  cubic  feet  of  manure  is 
very  effective,  ^he  powder  may  be  distributed  over  the  manure  and  wet  down 
by  sprinkling  with  water.  Care  should  be  taken  not  to  treat  the  same  manure 
more  than  once.  When  borax  is  applied  at  the  above  rate  there  is  no  deleterious 
effects  on  the  fertilizer  value  of  the  manure  unless  the  manure  is  applied  to  the 
land  in  excess  of  15  tons  to  the  acre. 

Foreman  and  Graham-Smith  (1917)  recommend  the  treatment  of  manure 
with  coal-tar  oil,  especially  creosote  oil.  This  should  be  sprinkled  on  the  heap 
each  day  after  the  fresh  manure  is  added.  One  hundred  cubic  centimeters 
should  be  used  for  each  horse  per  day.  By  such  a  daily  increment  fly  breeding 
may  be  prevented.  They  also  recommend  the  spraying  of  carcasses  with  a 
cresote  solution  that  destroys  the  odors,  prevents  the  development  of  maggots, 
and  stops  the  putrefactive  processes.  This  method  should  be  of  value  where 
it  is  impossible  to  burn  or  bury  deeply  animals  that  have  recently  died.  It  was 
used  with  some  success  during  the  World  War  I  when  flies  and  putrefying 
bodies  made  conditions  almost  unbearable.  The  creosote  recommended  is  a 
coal-tar  creosote  oil  containing  14  to  1 8  per  cent  tar  acids. 


482  MEDICAL  ENTOMOLOGY 

In  addition  to  cleanliness  and  the  treatment  of  manure,  various  types  of 
traps  for  the  adults  (Fig.  177)  and  larvae  are  highly  recommended  about  the 
milk  houses  and  stables.  Screens  should  be  employed  on  the  home  and  the 
milk  house,  and  all  utensils  used  in  handling  milk  should  be  screened  from 
flies.  From  the  standpoint  of  disease  it  is  extremely  important  that  farmers 
should  control  flies. 

Larval  traps  are  based  on  the  fact  that  the  mature  maggots  migrate  from 
the  manure  heap  toward  the  margins  or  bottom.  This  is  especially  true  if  the 
manure  is  well  packed  and  "heating"  takes  place.  Under  such  conditions 
the  maggots  do  not  penetrate  more  than  one  to  three  inches  below  the  surface, 
thus  preventing  excessive  breeding.  Several  types  of  larval  traps  have  been  de- 
vised and  are  used  where  conditions  make  them  desirable  as  at  army  posts  and 
residences  near  which  horses  are  stabled.  The  most  elaborate  trap  in  that 
devised  by  Baber  (1918  and  1925).  This  was  modified  by  Allmett  (1926). 
Hutchison  (1915)  devised  a  somewhat  simpler  type  that  is  said  to  be  effective. 
As  Baber's  trap  is  rather  expensive  to  construct  and  chiefly  suitable  for  per- 
manent army  and  cavalry  posts,  the  reader  is  referred  to  the  original  publica- 
tions. Hutchinson's  trap  is  simple  and  easily  installed.  It  consists  of  a  concrete 
pit  4  inches  deep  and  of  varying  size,  depending  on  the  amount  of  manure 
to  be  stored.  A  pit  22  feet  long  and  12  feet  wide  will  serve  for  holding  the 
manure  from  three  horses  for  about  four  months.  A  drainage  outlet  should 
be  provided  at  ont  end  of  the  pit.  This  opening  can  be  plugged  when  the 
pit  is  in  use.  The  manure  is  not  stored  in  the  pit  but  is  placed  on  a  lattice  frame- 
work supported  on  legs  within  the  pit.  The  lattice  tops  should  be  about  6 
inches  above  the  top  of  the  pit  and  the  margins  at  least  i  foot  from  the  inner 
margins  of  the  concrete  walls.  When  in  use  the  bottom  of  the  pit  is  covered 
with  at  least  i  inch  of  water.  The  horse  manure  is  piled  carefully  on  the  top 
of  the  lattice  platform  each  clay  and  moistened.  In  this  way  large  numbers 
of  flies  will  be  attracted  for  egg-laying  purposes.  The  mature  larvae  will 
migrate  downward  or  to  the  margins  and  drop  into  the  pit  where  they  will  be 
drowned.  If  the  water  in  the  pit  is  kept  covered  with  a  layer  of  fuel  oil,  the 
maggots  will  be  killed  more  quickly  and  at  the  same  time  mosquitoes  will  be 
kept  from  breeding.  By  this  procedure  the  adults  are  attracted  to  the  trap  for 
oviposition,  but  rarely  will  any  of  the  larvae  succeed  in  reaching  the  adult  state. 

The  problem  of  fly  control  is  an  ever-present  one.  Fly-control  campaigns 
have  been  organized  and  carried  on  with  great  vigor  in  many  parts  of  the 
world.  The  effects  of  such  campaigns  usually  wear  oflf  in  a  few  years  and 
conditions  gradually  become  as  bad  as  ever.  The  "swat  the  fly"  campaigns  are 
usually  futile  for  our  efforts  are  directed  away  from  the  essential  basis  of  fly 


THE  HOUSEFLY  AND  ITS  ALLIES  483 

control,  the  prevention  of  fly  breeding.  It  is  highly  desirable  to  kill  flies,  but 
do  not  let  such  eiTorts  obscure  the  fundamental  necessity,  if  we  are  to  reduce 
the  fly  population  to  any  marked  degree,  of  directing  our  endeavors  to  the 
bettering  of  sanitary  conditionsQ/he  effective  educational  work  carried  out 
along  sane  and  sensible  lines  will  produce  better  results  than  short,  intensive 
campaigns.) If  our  health  officers  are  adequately  supported  by  an  intelligent 
public  opinion,  they  can  gradually  develop  the  desire  for  cleanliness  of  person, 
of  home,  of  private  and  public  buildings,  of  all  operations  concerned  with  the 
disposal  of  garbage  and  wastes,  and  of  farming  operations.  Until  we  can  instill 
into  the  great  body  of  our  citizens  the  desire  for  cleanliness  in  all  things,  we  can 
hope  for  very  little  progress  by  the  passage  of-  drastic  sanitary  laws  which, 
difficult  to  enforce,  ofttime  defeat  the  ends  they  were  intended  to  serve. 

THE  FAMILY  CHLOROPIDAE  (OSCINIDAE) 

This  is  a  family  of  very  small  flies,  rarely  exceeding  3  mnj.  in  length.  The 
family  may  be  recognized  by  the  absence  or  great  reduction  of  the  squamae,  the 


Fig.  178  (^70-  Wing  of  Hippelatcs  sp.  Note  the  absence  of  the  sixth  vein  and  only  i 
fracture  (f)  on  costa. 

Fig.  779  (right}.  The  eye  gnat,  Hippchitcs  pusio,  showing  the  "vomit  spot"  (VS). 
(Sketched  from  a  photograph  by  Kumm.) 

lack  of  a  longitudinal  suture  on  the  second  antennal  segment,  the  subcosta 
vestigial,  the  presence  of  only  one  fracture  on  the  costa,  and  the  absence  of  the 
sixth  longitudinal  and  anal  veins  (Fig.  178).  The  most  important  genera,  from 
a  medical  standpoint,  are  Hippelatcs  and  Siphttnculina.  The  Litter  genus  con- 
tains what  has  been  called  the  "eye  fly"  (S.  jimicola  de  Meyere)  of  India,  Cey- 


484  MEDICAL  ENTOMOLOGY 

Ion,  Java,  and  other  Eastern  countries.  Roy  (1928)  presents  evidence  that  the 
prevalence  o£  this  fly  in  Assam  corresponds  closely  to  epidemics  of  naga  sore 
and  conjunctivitis.  Though  these  flies  are  incapable  of  piercing  the  skin  and 
taking  blood,  their  mouth  parts  are  so  constructed  (somewhat  like  those  of 
the  housefly)  that  each  labellum  has  the  tips  of  the  six  pseudotracheae  up- 
turned and  sharp,  so  they  can  abraid  the  edges  of  sores  and  the  conjunctival 
epithelium  about  the  eyes  or  make  small  multiple  lesions  about  wounds. 

HIPPELATES  FLIES:  EYE  GNATS 

Species  of  the  genus  Hippdates  have  long  been  suspected  of  being  involved 
in  the  transmission  of  pinkeye  or  "sore  eye"  in  various  parts  of  the  southern 
United  States.  Herms  (1928)  pointed  out  that  Hippdates  push  Loew  (as 
flavipes  Loew)  was  probably  responsible  for  the  epidemics  of  pinkeye  in  the 
Coachella  Valley,  California.  Bengston  (1933)  reported  similar  conditions  in 
Florida  and  incriminated  the  same  species  as  the  vector.  It  appears  well 
established  that  this  fly  acts  as  a  mechanical  vector  of  this  type  of  conjunctivi- 
tis in  various  parts  of  the  southern  United  States,  especially  in  southern  Cali- 
fornia. Flies  of  this  genus  have  also  been  regarded  as  playing  some  part  in  the 
spread  of  yaws. 

Hippelates  pusio  Loew  (Fig.  180)  is  a  small  (2  mm.)  blackish  fly  with 
yellowish  legs,  the  femora  being  usually  brownish  or  black  on  the  basal  half. 
The  eyes  are  prominent  and  appear  yellowish  in  mounted  specimens.  An- 
tennae are  bright  yellow,  the  last  segment  bearing  a  long,  hairlike  arista.  The 
thorax  is  shining  black,  with  numerous  short,  fine  hairs  arranged  in  rows.  The 
wings  are  hyaline  (Fig.  178)  and  are  held  crossed,  scissorlike  when  at  rest. 
Each  hind  tibia  has  a  very  long,  thin  spine  near  its  distal  end. 

This  fly  frequently  occurs  in  immense  numbers,  as  in  the  Coachella  Valley, 
California.  Hall  (1932)  describes  in  detail  its  biology  and  habits.  The  adults 
are  not  attracted  to  lights  at  night  but  favor  the  bright  sunlight  during  the 
day.  They  are  attracted  to  wounds,  pus,  sebaceous  material,  and  especially  to 
secretions  about  the  eyes.  They  swarm  about  in  immense  numbers  and  are  very 
annoying.  In  California  they  are  most  abundant  during  the  spring  (March 
to  May)  and  autumn  (August  to  October),  though  they  breed  throughout  the 
year  where  conditions  are  favorable. 

The  females  lay  their  minute,  curved,  fluted  eggs  in  loose  soil  heavily 
charged  with  organic  material.  They  also  breed  in  human  and  other  animal 
excrement,  especially  when  mixed  loosely  with  soil.  The  adults  are  not  long- 
lived  but  the  life  cycle  from  egg  to  adult  is  short,  varying  from  two  to  four 
weeks  (longer  in  cool  weather),  so  that  a  dense  population  of  adults  is  main- 


THE  HOUSEFLY  AND  ITS  ALLIES  485 

tainecl  during  favorable  breeding  conditions.  The  larva  is  legless,  short  (3.3 
mm.),  cylindrical,  white,  and  possesses  a  single  mouth  hook  with  which  it 
feeds  and  propels  itself.  The  larval  period  varies  from  a  few  days  to  much 
longer  in  cool  weather.  Pupation  takes  place  in  the  medium  in  which  the 
larvae  live. 

Hippelates  pallipes  Loew  is  an  abundant  species  in  Jamaica,  throughout  most 
of  the  West  Indies,  and  in  other  parts  of  tropical  America.  Kumm  (1935, 1936) 
has  studied  this  species  extensively  in  Jamaica  but  did  not  succeed  in  finding 
its  natural  breeding  places.  He  reared  it  under  artificial  conditions,  and  its 


Fig.  180.  The  eye  gnat,  Hippelates  puslo.  (A)  The  egg.  (B)  The  larva.  (C)  The  pu- 
parium.  (D)  The  adult.  (All  after  Hall.) 

life  cycle  is  quite  similar  to  that  of  H.  pusio.  As  this  is  the  most  abundant 
Hippelates  species  in  Jamaica,  studies  were  confined  largely  to  its  importance 
as  a  vector  of  yaws.  Kumm  et  al.  (1935)  records  this  fly  as  feeding  in  enormous 
numbers  on  yaws  lesions,  especially  those  on  the  lower  extremities.  They  found 
large  numbers  of  the  spirochete,  Treponema  pertenue,  in  the  esophageal  diver- 
ticulum,  and  these  remain  alive  for  at  least  seven  hours  and  some  of  them  may 
be  regurgitated  in  the  vomit  spot  (Fig.  179)  when  they  feed  on  a  susceptible 
person.  Spirochetes  that  pass  into  the  digestive  tract  are  all  digested.  Any 
transmission  of  yaws  is  purely  mechanical,  no  developmental  cycle  occurring 
in  the  fly. 

CONTROL:  Various  methods  have  been  tried  to  control  these  pests  but  with- 
-out  great  success.  Traps,  general  sanitation  methods,  and  improved  agricul- 


486  MEDICAL  ENTOMOLOGY 

tural  practices  have  given  some  relief.  When  more  is  known  of  the  larval 
breeding  places,  it  may  be  possible  to  clean  up  bad  areas  by  the  use  of  DDT  or 
some  of  the  newer  insecticides  by  directly  treating  the  soil.  The  use  of  repel- 
lents employed  against  mosquitoes  and  blackflies  may  be  of  some  value. 

IDENTIFICATION  OF  OUR  COMMON  MUSCID  FLIES 3 

Flies  About  the  Home;  Flies  That  ,Cause  Myiasis;  Flies  That 
Are  Bloodsucking  in  Habit 

Hypopleural  bristles  absent i 

Hypopleural  bristles  present  (Fig.  85)  n 

1.  Sixth  vein  very  short;  seventh  vein  tends  to  curve  under  the  sixth; 

fourth  vein  straight Fannia  (Homalomyid) 

Sixth  vein  fairly  long;  seventh  vein  straight;  fourth  vein  bowed  or 
angled  near  its  distal  end  (Fig.  172)  2 

2.  Proboscis  long,  directed  forward,  and  fitted  for  piercing 3 

Proboscis  not  elongate;  the  labella  fleshy  and  not  adapted  for  piercing  .  .     5 

3.  Rays  of  arista  plumose  (Fig.  168).  (African  species)  Glossina 

Rays  of  arista  simple,  not  plumose 4 

4.  Palpi  much  shorter  than  the  proboscis Stomoxys 

Palpi  nearly  as  long  as  the  proboscis Haematobia 

5.  Arista  bare    Synthcsiomyia 

Arista  pectinate  (plumose  on  the  upper  side)  Hemichlora 

Arista  plumose   6 

6.  Large  species  (about  the  size  of  worker  bumblebee)  with  conspicuous 

black  and  yellow  pile Hypodermodes 

Smaller  species  (about  the  size  of  the  housefly)  without  dense  black  and 
yellow  pile 7 

7.  Color  metallic  bluish  black  or  green;  stripes  evident  on  anterior  margin 

of  thorax  8 

Color  opaque  gray  or  black 9 

8.  Middle  tibia  with  a  prominent  bristle  on  its  surface  beyond  the  middle 

Pyrdlia 

Middle  tibia  without  such  a  prominent  bristle Morellia 

9.  The  last  section  of  fourth  vein  distinctly  angled  (Fig.  172);  sterno- 

pleural  bristles  i  :2;  eyes  bare Musca 

The  last  section  of  the  fourth  vein  gently  bowed  (Fig.  192)  10 


3  For  the  identification  of  flies  to  families  consult  the  key  on  pages  228-231. 


THE  HOUSEFLY  AND  ITS  ALLIES  487 

10.  Eyes  hairy;  sternopleural  bristles  2:2 Myiospila 

Eyes  bare;  sternopleural  bristles  1:2 Muscina 

11.  Body  color  opaque  gray  or  black,  never  sbining  metallic;  arista  bare  or 

pubescent  12 

Metallic  blue  or  blue-green  species,  or  the  abdomen,  at  least,  shining 
metallic  bluish  black 13 

12.  Thorax  with  deciduous  yellow,  curly  pile  among  the  macrochaetae 

against  a  shining  black  background Pollenia  rudis 

Thorax  without:  deciduous  yellow,  curly  pile  but  with  four  distinct  gray- 
ish lines  Wohljahrtia  vigil 

13.  Basal  section  of  first  vein  (the  part  preceding  the  humeral  cross  vein) 

ciliated  (bearing  fine  hairs)    14 

Basal  section  of  first  vein  bare • 17 

14.  Bucca  and  face,  yellow  with  yellow  pile;  one  posthumeral  bristle 

(Formerly  Chrysomya  or  Cochliomyia)  Callitroga 

Bucca  black  with  black  hairs;  usually  two  posthumeral  bristles 15 

15.  Squamae  white;  anterior  acrostichals  well  distinguished  from  the  sur- 

rounding hairs  16 

Squamae  darkened;  anterior  acrostichals  not  distinct  from  the  surround- 
ing hairs;  prothoracic  spiracle  black Protophormia 

1 6.  Four  intra-alar  bristles;  six  or  more  marginal  scutcllar  bristles;  meso- 

thoracic  spiracle  dark  orange  to  black Protocalliphora 

Two  intra-alar  bristles;  four  marginal  scutellar  bristles;  mesothoracic 
spiracle  distinctly  light-orange-colored Phormia 

17.  Upper  surface  of  lower  squamae  (calypter)  bare  (Fig.  85)  Lucilia 

Upper  surface  of  lower  squamae  distinctly  pilose 18 

18.  Two  bristles  near  middle  on  exterior  surface  of  front  tibia;  one  sub- 

lateral  bristle  (posthumeral)  (Cynomyia)  Cynomyopsis 

One,  rarely  two,  bristles  near  middle  on  exterior  surface  of  front  tibia; 
three  sublateral  bristles Calliphora 

SPECIES  NOTES 

Funnia:  Two  species  are  not  infrequently  the  cause  of  intestinal  myiasis  and 
are  commonly  found  in  houses.  They  are  F.  canicularis  and  F.  scalaris. 

Stomoxys:  There  is  only  one  species  in  the  United  States,  S.  calcitrans.  Other 
species  occur  in  different  parts  of  the  world. 

Musca:  Only  one  common  species,  M.  domes  fica.  Other  species  occur  in  the 
Orient,  the  Ethiopian  region,  and  Europe. 


488  MEDICAL  ENTOMOLOGY 

Muscina:  There  are  two  common  species  in  America,  though  a  third  (pas- 
cuorurn)  has  recently  been  introduced: 

1.  Legs  entirely  black;  palpi  reddish  yellow M.  pascuorum 

Legs  not  entirely  black,  usually  some  yellow  present;  if  black,  palpi  black 

2 

2.  Palpi  black;  tibiae  usually  mostly  black  though  a  yellowish  tinge  may  be 

present M.  assimilis 

Palpi  yellow;  tibiae  and  distal  portion  of  femora  yellow M.  stabulans 

Pollenia:  Only  one  common  species,  P.  ritdis. 
Calliphora:  We  have  three  common  species: 

1.  Three  intra-alar  bristles  C.  (yiridescens)  livida  4 

2.  Two  intra-alar  bristles 

B.  Bucca  black;  beard  reddish  C.  vomitoria 

BB.  Bucca  brownish  or  reddish;  beard  black  C.  (erythrocephala)  vicina  5 
Lucilia:  We  have  three  common  species: 

1.  Two  postacrostichals  (Fig.  85) L.  illustris 

2.  Three  postacrostichals   

B.  Palpi  black L.  silvarum  ° 

BB.  Palpi  yellow  L.  sericata  1 

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THE  CHLOROPIDAE 

Bengston,  I.  A.     Seasonal  acute  conjunctivitis  in  the  southern  states.     U.S.  Pub. 

Hlth.  Repts.,  48:  917-926,  1933. 
*Bigham,  J.  T.     Hippelatcs  (eye  gnat)  investigations  in  the  southeastern  states. 

Jl.  Econ.  Ent.,  34:  439-444,  1941. 
Burgess,  R.  W.    The  eye  gnat  in  the  Coachella  Valley,  California.    U.S.  Bur.  Ent. 

and  PI.  Quar.,  £-35,  1935. 
Castellani,  A.    Experimental  investigations  on  framboesia  tropica.    Jl.  Hyg.,  7: 

558-569,  1907. 
Graham-Smith,  G.  S.    The  Oscinidae  (=Chloropidae)  as  vectors  of  conjunctivitis 

and  anatomy  of  the  mouthparts.    Parasitology,  22:  457-467,  1930. 
Hall,  D.  G.    Some  studies  on  the  breeding  media,  development,  and  stages  of 

the  eye  gnat,  Hippelates  push  Loew.     Amer.  Jl.  Hyg.,  16:  854-864,  1932. 
Herms,  W.  B.,  and  Burgess,  R.  W.    A  description  of  the  immature  stages  of 

Hippelates  pusio  Loew  and  a  brief  account  of  its  life  history.    Jl.  Econ.  Ent., 

23:  600-603,  1930. 
Kumm,  H.  W.    The  digestive  mechanism  of  one  of  the  West  Indian  eye  gnats, 

Hippelates  pallipes  Loew.    Ann.  Trop.  Med.  Parasit.,  29:  283-298,  1935. 


THE  HOUSEFLY  AND  ITS  ALLIES  493 

.    The  natural  infection  of  Hippelates  pallipes  Loew  with  the  spirochaetes 

of  yaws.    Trans.  Roy.  Soc.  Trop.  Med.  Hyg.,  29:  265-272,  1935. 
* .    The  Jamaica  species  of  Hippelates  and  Osdnella  (Diptera,  Chloropidae). 

Bull.  Ent.  Res.,  27:  307-329,  1936. 
* ,  and  Turner,  T.  B.    The  transmission  of  yaws  from  man  to  rabbit  by  an 

insect  vector,  Hippelates  pallipes  Loew.    Amer.  Jl.  Trop.  Med.   16:  245-271, 

1936. 
,  et  al.    The  duration  of  motility  of  the  spirochaetes  of  yaws  in  a  small  West 

Indian  fly,  Hippelates  pallipes  Loew.    Ibid.,  15:  209-223,  1935. 
Roy,  D.  N.    A  note  on  the  breeding  and  habits  of  the  eye-fly,  Siphonella  junicola 

Meij.    Ind.  Med.  Gaz.,  63:  369-370,  1928. 
Saunders,  G.  M.,  et  al.    The  relationship  of  certain  environmental  factors  to  the 

distribution  of  yaws  in  Jamaica.     Amer.  Jl.  Hyg.,  23:  558-579,  1936. 


CHAPTER  XVII 


Myiasis  of  Man 
and  Allied  Conditions 


THE  infection  of  man  by  insects  has  been  known  from  ancient  times. 
Though  there  is  a  number  of  scattered  references  from  which  almost 
definite  identification  of  the  invading  insect  can  be  determined,  it  was  not 
till  early  in  the  nineteenth  century  that  observations  became  somewhat  specific. 
Hope  (1840)  brought  together  all  the  more  definite  references  to  insect  larvae 
invading  man  and  evolved  a  terminology  that  is  in  use  at  the  present  time. 
The  invasion  of  man  and  animals  by  dipterous  larvae  he  termed  myiasis;  by 
coleopterous  larvae,  canthariasis;  by  lepidopterous  larvae,  scoleciasis  (a  term 
first  used  by  Kirby  and  Spence  in  1815  to  include  all  infestations  of  man  and 
animals  by  insects  and  their  larvae).  Hope  records  63  cases  of  myiasis,  35  of 
canthariasis,  and  7  of  scoleciasis.  Since  that  time  there  have  been  almost  in- 
numerable references  to  insect  invasions  of  man  and  animals,  but  most  of 
them  are  brief;  no  specific  determinations  are  given  or  are  possible.  Even  at 
the  present  time  our  knowledge  of  these  infections  is  rather  meager.  The  fol- 
lowing account  is  largely  restricted  to  conditions  found  in  the  Americas. 

CThe  term  myiasis  is  restricted  to  the  infections  of  man  and  animals  caused 
by  the  invas'ion  of  dipterous  larvae.  The  various  types  of  myiasis  are  usually 
designated  by  the  localization  of  the  invading  larvae:  cutaneous  or  dermal  (in 
the  skin  or  subcutaneous  tissues),  gastric  (in  the  stomach),  intestinal  (in  the 
intestines),  urogenital  (in  the  urogenital  tract),  aural  (in  the  ear),  nasal  or 
rriinal  (in  the, nose),  ocular  (in  the  eye),  etc.  From  the  standpoint  of  the  en- 
tomologist, this  classification  is  rather  unsatisfactory,  but  it  meets  the  needs 
of  the  pathologist  and  the  physician.  Patton  (1921)  has  proposed  another 
grouping  based  on  the  habits  of  the  flies  and,  though  not  a  zoological  arrange- 
ment, it  gives  us  a  much  better  conception  of  the  relation  of  these  flies  to  their 
hosts.  This  arrangement  is  briefly  outlined  at  the  end  of  the  chapter.  For  our 
purposes  it  will  be  more  satisfactory  to  discuss  these  myiasis-producing  flies 


MYIASIS  OF  MAN  AND  ALLIED  CONDITIONS  495 

according  to  the  families  they  represent.  (For  a  classification  of  flies  see  pp. 
486-488).  / 

THE  FAMILY  SARCOPHAGIDAE  (Mctopiidae) 

The  family  Sarcophagidae  (flesh  flies)  contains  comparatively  few  genera, 
but  the  species  are  numerous  and  very  abundant.  These  flies  are  rather  large 
(Fig.  85)  and  the  coloration  is  generally  quite  uniform.  As  a  group  they  are 
dull-colored,  the  thorax  striped  longitudinally  with  gray  and  the  abdomen 
marmorate.  The  arista  is  plumose  or  strongly  pubescent  to  the  middle,  bare 
beyond  (this  is  one  of  the  most  distinctive  characters  of  the  family).  The  ab- 
domen is  not  strongly  bristled  and  the  bristles  are  restricted  to  the  apical 
portion.  The  larvae  are  typically  muscoidean  (Fig.  173)  but  may  be  dis- 
tinguished by  the  presence  of  a  girdle 'of  minute  spines  on  the  abdominal  seg- 
ments. The  mouth  hooks  are  well  developed,  curved,  and  provide  good 
weapons  for  the  tearing  of  tissues.  The  larvae  are  amphipneustic.  The  posterior 
stigmal  plates  (Fig.  182)  are  situated  in  a  deep  cavity;  the  slits  are  three  in 
number  for  each  spiracle  and  are  arranged  nearly  vertical  and  parallel. 

The  adults  are  everywhere  abundant,  especially  about  decaying  vegetation, 
fruit,  excrement,  decomposing  animal  matter,  and  similar  conditions.  As  far 
as  is  known  all  the  species  are  larviparous,  depositing,  not  eggs,  but  living 
larvae.  The  larval  habits  are  extremely  varied:  some  are  parasitic  on  warm- 
blooded animals,  on  insects  (Orthoptera),  on  snails,  etc.;  many  are  scavengers; 
and  others  occur  in  wounds,  sores,  ulcers,  or  cavities  from  which  foul-smelling 
material  is  being  discharged.  Both  the  adults  and  larvae  are  very  difficult  to 
identify.  As  yet  it  is  scarcely  more  than  possible  to  place  the  larvae  in  the 
family,  though  some  generic  distinctions  have  been  attempted  (Root,  1923). 
The  adults  can  only  be  determined  by  experts,  though  the  work  of  Aldrich 
(1916)  lessens  the  labors  of  beginners.  Wherever  the  larvae  of  the  flesh  flies 
are  found,  every  effort  should  be  made  to  rear  the  adult  so  that  positive  records 
may  be  obtained.  The  following  notes  are  mainly  restricted  to  American 
species. 

THE  GENUS  WOHLFAHRTIA 

Wohlfahrtia  vigil  Walker  is  a  large,  grayish  fly  (Fig.  181)  measuring  7.5  to 
14  mm.  in  length.  It  is  widely  distributed  in  eastern  North  America.  Walker 
(1920, 1922)  first  recorded  its  attacking  man;  he  reared  the  adults  from  larvae 
obtained  from  an  infection  of  a  young  child  at  Toronto,  Ontario.  The  lesions 
occurred  on  the  left  side  of  the  neck  under  the  jaw  (Fig.  183).  On  the  removal 


496  MEDICAL  ENTOMOLOGY 

of  the  maggots  the  wounds  healed  rapidly.  Unlike  other  myiasis-producing 
Sarcophagidae,  this  species  attacks  the  healthy  skin,  not  entering  through  one 
of  the  nautral  orifices  as  the  nose,  ear,  or  open  sores.  Walker  (1931)  gives  a 
resume  of  eight  cases  reported  from  man.  Felt  (1924)  reports  what  he  believes 
is  a  case  of  ocular  infection.  Several  first-stage  larvae  were  removed  from  the 
conjunctiva  of  a  man  in  Cattaraugus  County,  New  York.  The  larvae  were 
found  in  a  small  cyst.  Sanders  (1928)  records  a  case  of  infection  in  a  child  three 
months  old.  The  larvae  were  present  in  superficial  pustules  on  the  neck.  Two 
additional  cases  can  be  reported  from  New  York  state.  The  first  was  in  a  young 
child  at  Utica.  The  attending  physician  removed  several  maggots  from  pus- 


Fig.  181  (left).  W  ohlfahrtia  vigil.  (After  Walker,  Journal  of  Parasitology.) 
Fig.  182  (right).  Posterior  spiracles  of  larva  of  Wohljahrtia  vigil.  Note  their  location 
in  a  deep  pit  at  posterior  of  body  (SP). 

tules  on  the  neck.  The  larvae  were  sent  to  the  writer  and  definitely  identified. 
The  second  case  occurred  in  young  puppies  about  four  weeks  old.  Four  mature 
larvae  were  removed  from  deep  cutaneous  lesions  and  identified  by  the  writer. 
Shannon  (1923)  records  the  rearing  of  this  species  at  Ithaca  from  larvae  found 
deeply  embedded  in  the  shoulder  muscles  of  rabbits.  Gerston  et  al.  (1933)  re- 
ported two  cases  in  babies  in  North  Dakota.  At  the  present  time  this  species 
has  been  recorded  from  children,  rabbits,  cats,  foxes,  mink,  ferrets,  and  puppies. 
Undoubtedly  it  has  many  more  hosts.  Ford  (1936)  gives  an  extended  account 
of  this  species.  The  adults  are  not  attracted  to  exposed  meat  nor  do  they  oviposit 
on  it.  They  were  found  in  nature  in  warm  areas  as  along  railroad  tracks  (or 
on  hot  sidewalks,  by  the  writer)  and  fed  apparently  on  the  nectar  of  such 
flowers  as  wild  caraway,  milkweed,  sweet  clover,  early  golden  rod,  and  probably 
other  plants.  The  females,  when  ready  to  oviposit,  dart  suddenly  at  their  host, 
usually  alighting  on  the  head  beside  the  eyes  or  mouth,  and  deposit  a  number 


MYIASIS  OF  MAN  AND  ALLIED  CONDITIONS  497 

of  larvae.  The  larvae  immediately  penetrate  the  tenderest  skin  and  grow 
rapidly,  producing  a  distinctive  lesion.  The  larval  period  varies  from  7  to  9 
or  more  days  and  the  pupal  period  is  about  10  to  12  days.  The  females  are  ready 
to  larviposit  in  about  13  to  17  days  after  emergence. 

The  mature  larva  l  measures  16  to  18  mm.  in  length.  The  ccphalopharyngeal 
apparatus  (Fig.  184)  is  very  characteristic  and  is  fully  explained  in  the  figure. 
One  of  the  most  distinguishing  characteristics  of  the  larva  is  a  band,  more  or 
less  interrupted,  of  minute  spinules  present  on  each  of  the  body  segments. 
These  bands  of  spinules  are  more  pronounced  in  the  first  and  second  larval 
stages.  The  posterior  spiracles  are  located  in  a  deep  pit  (Fig.  182).  Each  spiracle 
has  three  slits  arranged  as  shown  in  Fig.  194  _j;  the  peritreme  is  well  developed 


mh 


Fig.  18 j  (left}.  Male  infant  infected  with  larvae  of  Wohljahrtia  vigil.  The  arrow  points 
to  the  seat  of  infection.  (After  Walker,  Journal  of  Parasitology.) 

Fig.  184  (right}.  Cephalopharyngeal  skeleton  of  the  mature  larva  of  Wohljahrtia  vigil. 
ac,  rod! ike  process  of  pharyngeal  sclerite;  dc,  dorsal  cornua;  ds,  dental  sclerite;  hs, 
hypostomal  sclerite;  i,  incision  of  dorsal  cornua;  mh,  mouth  hooks;  p,  pharyngeal  sclerite; 
vc,  ventral  cornua. 

but  does  not  completely  surround  the  spiracle.  The  button  is  not  well  de- 
veloped. Each  anterior  spiracle  consists  of  9  to  10  stout,  fingerlike  processes. 

Wohljahrtia  opaca  Coq.  (meigenii  of  authors)  is  a  closely  allied  species 
found  in  the  western  United  States  but  nothing  is  known  of  its  biology. 

Wohljahrtia  magnified  Schiner  is  an  Old  World  species  widely  distributed  in 
southern  Europe,  Asia,  and  Africa.  It  deposits  living  larvae  in  all  sorts  of 
wounds,  sores,  diseased  eyes,  nose,  ear,  vagina,  soiled  wool,  etc.,  and  is  a  serious 
pest  of  domestic  animals  as  well  as  man.  In  its  habits  it  closely  resembles  the 
screw  worm  (Callitroga  amerieana)  of  America. 

THE  GENUS  SARCOPHAGA 

Sarcophaga  haemorrhoidalis  Fall,  is  a  large  grayish  fly,  10  to  14  mm.  in 
length.  It  has  a  wide  distribution  in  America,  Europe,  Africa,  and  Asia.  Aldrich 

xThe  mature  larvae  of  myiasis-producing  flies  can  generally  be  recognized  by  the 
cephalopharyngeal  structure  and  the  posterior  spiracles  (see  figures). 


498  MEDICAL  ENTOMOLOGY 

(1916)  reports  that  a  Mr.  J.  B.  Gill  of  Monticello,  Florida,  evacuated  numbers 
of  nearly  mature  larvae  in  his  stools;  from  these  eight  adults  were  reared.  He 
also  records  the  rearing  of  adults  by  Haseman  from  larvae  passed  in  human 
feces.  The  larvae  came  from  a  young  girl,  the  members  of  whose  family  had 
been  troubled  for  several  years  by  intestinal  myiasis.  It  is  believed  that  most  of 
the  records  of  Sarcophaga  species  causing  intestinal  myiasis  refer  to  this  fly. 
The  species  normally  breeds  in  carrion,  decomposing  animal  matter,  etc.  In 
the  cases  of  human  infection  the  females  probably  deposit  their  larvae  on  soiled 
food  or  other  substances  eaten  by  man. 

OTHER  SARCOPHAGID  INFECTIONS:  Higgins  (1890)  records  large  numbers  of 
sarcophagid  larvae  vomited  by  a  child  only  18  months  old.  Riley  (1906)  reports 
the  infestation  of  a  tumor  on  the  back  of  an  elderly  woman  by  10  or  12  maggots. 
Patton  (1923)  figures  a  cutaneous  myiasis  of  the  cheek  caused  by  the  larvae  of 
Sarcophaga  fuscicauda.  Keilin  (1924)  reports  a  case  of  intestinal  myiasis  by  a 
sarcophagine  fly.  Wohl  (1913)  gives  an  account  of  a  young  man  relieved  after 
the  expulsion  of  sarcophagid  larvae;  these  were  reared  and  identified  as  Sar- 
cophaga  sarrace niac  (?)  Riley. 

THE  FAMILY  CALLIPHORIDAE 

In  this  family  the  species  are  usually  quite  large  and  the  body,  especially  the 
abdomen,  is  metallic  blue,  green,  or  varying  shades  of  these  colors.  Here  be- 
long the  blowflies,  the  bluebottle  flies,  the  green-bottle  flies,  and  some  others. 
Many  of  the  species  are  very  serious  pests  to  domestic  and  game  animals  and 
some  occasionally  attack  man.  In  general  their  larvae  develop  in  fresh  or  de- 
caying flesh,  destroying  the  carcasses  of  dead  animals  (scavengers);  some 
consistently  are  found  in  wounds  and  sores  of  all  kinds;  other  attack  the  young 
of  nesting  birds  (bloodsucking  larvae) ;  some  breed  in  dung;  and  one  species, 
Pollenia  rudis,  (the  cluster  fly)  is  parasitic  on  species  of  earthworms.  Only  the 
more  important  species  are  treated  here. 

THE  GENUS  CALL1TROGA 

Callitroga  americana  (Gushing  and  Patton),  the  screwworm  fly,  is  the  most 
important  American  species.  The  adult  varies  from  8  to  10  mm.  in  length  and 
is  metallic  green  in  color,  with  three  distinct  longitudinal  dark  stripes  on  the 
thorax  (Fig.  185) ;  the  head  is  bright  yellow  and  the  eyes  reddish  yellow.  It  is 
widely  distributed  in  the  Americas,  extending  from  the  southern  part  of  the 
United  States  southward  to  southern  Brazil  and  northern  Chile  (Hall,  1948). 
In  the  United  States  it  is  most  prevalent  and  injurious  in  the  South  and  South- 


MYIASIS  OF  MAN  AND  ALLIED  CONDITIONS  499 

west.  Its  range  frequently  extends  northward  to  central  California  in  the  West 
and  northern  Iowa  and  Indiana  in  the  East.  The  species  cannot  survive  tem- 
peratures below  20°  F.  for  the  adults  or  15°  F.  for  larvae  or  pupae.  It  breeds 
throughout  the  year  in  the  extreme  southern  part  of  the  United  States.  The 
adults  do  not  hibernate.  It  is  also  a  serious  pest  in  parts  of  Central  America, 
Panama,  and  South  America.  This  species  was  confused  with  Callitroga  macel- 
laria  (Fabr.)  until  Gushing  and  Patton  (1933)  definitely  demonstrated  that 
the  true  "screwworm"  fly  was  an  undescribed  species.  As  a  result,  most  of  the 


Fig.  185  (lejt).  Adult  female  of  Callitroga  americana,  the  American  screwworm  fly. 
Fig.  186  (right).  Effects  of  an  attack  of  the  American  screwworm  fly  on  a  patient. 
(Courtesy  of  U.S.  Department  of  Agriculture,  Bureau  of  Entomology.) 

references  in  our  literature  refer  either  to  one  or  the  other  or  a  mixture  of  the 
two.  The  following  account  is  based  on  the  detailed  studies  made  of  this  species 
by  various  members  of  the  United  States  Bureau  of  Entomology. 

BIOLOGY  AND  HABITS:  This  species  is  an  obligatory  parasite,  the  females  ovi- 
positing only  in  fresh  wounds  of  man  and  other  animals.  It  is  not  saprophagous. 
It  probably  is  the  chief  cause  of  myiasis  throughout  its  range.  The  adults  are 
said  not  to  be  active  but  remain  resting,  though  they  can  range  long  distances, 
ii  miles  as  reported  by  Parrish  (1937).  They  have  been  observed  in  nature 
feeding  upon  wounds,  fresh  meat,  and  fresh  manure.  Brody  (1939)  fed  the 
flies  on  a  wide  variety  of  foods.  When  oranges,  grapefruit,  tomatoes,  or  canta- 
loupes were  supplied  daily,  the  flies  survived  the  preoviposition  period  (9  days) 


5oo  MEDICAL  ENTOMOLOGY 

and  laid  viable  eggs.  On  meat  or  its  products  eggs  were  never  obtained.  The 
gravid  females  appear  to  select  wounds  2  to  10  days  old.  Each  female  lays  from 

10  to  nearly  400  eggs  in  a  shinglelike  mass  tightly  glued  to  the  edge  or  surface  of 
the  wound,  near  the  dry  scab,  or  on  dried  blood  clots.  The  eggs  hatch  in  from 

11  to  about  21  hours  and  the  young  larvae  immediately  penetrate  and  feed  on 
the  tissues  of  the  wound.  As  they  penetrate  deeply  the  posterior  spiracles  are 
directed  upward  to  keep  in  contact  with  the  air.  Growth  is  rapid.  The  larvae 
feed  gregariously  and  produce  a  deep,  pocketlike  injury  (Fig.  186).  The  larvae 
mature  in  from  4  to  about  8  days  depending  on  conditions  of  the  wound. 
Dropping  to  the  ground  they  pupate  in  the  soil.  The  pupal  period  varies  from 
7  clays  in  the  hot  summer  to  54  days  in  winter  (Texas). 


Fig.  187.  Left:  Posterior  end  of  larva  of  Callitroga  amcricana.  Right: 
Same  of  Callitroga  macellaria,  the  false  screwworm  fly.  Note  the  ap- 
pearance of  the  tracheae,  heavy  and  dark  in  C.  americana. 

The  mature  larva  is  typically  muscoid  in  appearance.  It  is  nearly  17  mm.  in 
length  and  each  segment  is  banded  with  rather  stout  spines.  The  tracheal 
trunks  leading  from  the  posterior  spiracles  are  pigmented  through  the  last 
three  or  four  segments  (Fig.  187).  The  pigmented  tracheal  trunks  and  the 
presence  of  spines  on  the  dorsal  and  lateral  margins  of  the  two  segments  next 
to  the  last  one  will  distinguish  the  larva  of  C.  amcricana  from  that  of  C.  macel- 
laria. 

RELATION  TO  DISEASE:  As  this  species  has  been  confused  for  a  long  time  with 
C.  macellaria  (Fabr.),  the  numerous  references  to  myiasis  of  man  and  other 
animals  are  difficult  to  interpret.  However,  the  data  all  indicate  that  the  latter 
species  is  only  a  secondary  invader  and  is  primarily  a  scavenger.  All  primary 
infestations  of  nonputrid  wounds  are  by  C.  americana  (Gushing  and  Patton). 
This  fly  may  deposit  its  eggs  on  any  wound,  however  small,  such  as  a  scratch  or 
injured  toenail,  and  numerous  cases  of  human  infection  by  this  species  have 
been  recorded  since  the  status  of  this  species  was  recognized  (1933).  It  is  a  very 
dangerous  pest  of  cattle,  sheep,  goats,  and  other  animals.  In  1934  during  a  severe 
outbreak  of  this  species  in  the  southeastern  United  States  over  1,300,000  cases 
were  reported,  while  in  1935,  1,200,000  cases  were  recognized  in  Texas  alone. 


MYIASIS  OF  MAN  AND  ALLIED  CONDITIONS  501 

The  attacks  were  so  severe  that  thousands  of  animals  died,  and  James  (1947) 
reports  a  mortality  rate  of  nearly  20  per  cent  in  uncontrolled  cases.  The  wound 
made  by  these  larvae  is  deep-seated  (Fig.  186),  and  when  heavy  infection  of 


Fig.  y<V(V.  Cullitrogii  americana  infestation.  (A}  Of  the  navel  of  a  young  calf.  (#)  Of  a 
sheep.  (C)  Of  head  of  goat,  a  severe  case.  (Courtesy  of  the  U.S.  Bureau  of  Entomology 
and  Plant  Quarantine.) 

the  nasal  and  frontal  regions,  of  the  eyes,  ears,  and  mouth,  occurs,  death  usually 
results  if  it  is  not  treated  promptly.  The  navel  and  vaginal  regions  are  often  in- 
vaded by  the  maggots  and  serious  conditions  ensue  (Fig.  188). 
During  these  outbreaks  Dove  (1937)  listed  55  human  cases  for  1935  (and 


502  MEDICAL  ENTOMOLOGY 

estimated  over  100  cases)  but  only  8  cases  for  1936.  This  great  reduction  in 
human  infestation  was  undoubtedly  due  to  the  excellent  results  obtained  by 
the  development  of  control  measures  and  the  widespread  use  of  Smear  62,  de- 
veloped by  the  United  States  Bureau  of  Entomology.  In  the  human  cases  in- 
festation occurred  in  the  nose,  eyes,  vagina,  sarcomas,  small  wounds,  scratches, 
bruises,  blood  clots,  and  similar  places.  There  were  no  deaths  where  medical 
treatment  was  obtained,  but  several  deaths  occurred  in  untreated  cases.  Nasal 
infestations  are  usually  extremely  painful,  the  patient  frequently  becoming 
delirious.  In  one  case  of  nasal  infection  in  Texas  Dove  reports  the  physician 
removing  385  larvae  during  a  nine-day  period. 

CONTROL:  The  most  effective  control  methods  involve  the  prevention  of 
wounds  in  animals  due  to  barbed  wire,  righting,  dehorning,  or  other  agencies. 
If  wounds  become  infested  the, use  of  Smear  62  2  is  most  effective.  It  is  prepared 
as  follows  (United  States  Bureau  of  Entomology)  : 

1.  Diphenylamine  (Tech.  grade)  3%  parts  by  weight 

2.  Benzol  (P.P.)  3%     "      "       " 

3.  Turkey  red  oil  (pH  10  or  neutral)  i  part     " 

4.  Lamp  black  -  2  parts    "        " 

Dissolve  i  in  2  and  allow  to  stand  for  about  a  day.  Add  3  and  mix  thoroughly; 
4  is  added  gradually  and  the  mixture  stirred  till  it  reaches  the  consistency  of 
molasses.  This  mixture  should  be  stored  in  a  tight  container  in  a  cool  place.  As 
benzol  is  highly  inflammable,  no  fire  or  other  hazard  such  as  lighted  cigarettes 
or  cigars  should  be  near  when  making  or  using  the  mixture.  If  it  becomes  too 
thick  the  addition  of  benzol  will  bring  it  back  to  the  necessary  consistency.  On 
animals  apply  with  a  small  paintbrush  (about  i-inch  size).  Clean  each  wound 
and  apply  carefully.  Avoid  getting  it  into  the  eyes.  This  treatment  should  be 
repeated  every  few  days  till  the  wounds  heal. 

In  human  infestations  the  physician  should  be  consulted  immediately  as  de- 
lay may  be  serious.  The  maggots  develop  so  rapidly  that  failure  to  obtain  treat- 
ment may  result  in  serious  complications.  When  these  flies  are  abundant  certain 
precautions  should  be  observed.  Avoid  sleeping  in  exposed  places,  such  as 
porches  and  open  rooms,  or  out  of  doors  unless  nets  are  employed.  Small 
wounds,  exudates  from  the  eyes,  nostrils,  or  other  regions,  exposed  blood  clots, 
or  abrasions  should  be  carefully  treated  so  that  healing  may  be  prompt.  The 
maggots  cannot  penetrate  the  unbroken  human  skin  though  they  can  that  of 
rabbits  and  guinea  pigs. 

Callitroga  macdlaria  (Fabr.)  is  usually  referred  to  as  the  secondary  screw- 

2  At  the  present  time  several  other  effective  smears  are  on  the  market. 


MYIASIS  OF  MAN  AND  ALLIED  CONDITIONS  503 

worm  fly.  The  adult  closely  resembles  the  primary  screwworm  fly  in  coloration. 
It  is  more  bluish  metallic  but  otherwise  similarly  colored.  About  the  only 
obvious  difference  is  that  the  short  hairs  of  the  parafrontals  are  white  to  yellow- 
ish, whereas  in  C.  americana  these  hairs  on  the  upper  half  are  black  (to  base  of 
antennae)  and  golden  on  the  lower  portion.  The  most  distinguishing  characters 
are  found  in  the  male  genitalia.  The  length  is  6  to  9  mm. 

This  species  is  widely  distributed  in  the  Nearctic  and  Neotropical  regions, 
extending  from  central  Canada  south  through  the  United  States,  Mexico, 
Central  America,  the  West  Indies,  and  South  America  to  Patagonia. 

The  adults  are  active  fliers  and  swarm  about  carrion,  especially  in  warm, 
humid  weather.  They  are  wide-ranging  as  Bishop  and  Laake  (1921)  report 
migrations  of  8  miles  in  24  hours,  10  miles  in  less  than  48  hours,  with  a  maxi- 
mum of  over  15  miles.  Though  they  primarily,  lay  their  eggs  on  carrion,  yet 
they  oviposit  about  festering  wounds  or  wounds  infested  with  C.  americana 
where  the  larvae  feed  on  the  necrotic  tissues  and  wastes.  On  carrion  the  females 
deposit  thousands  of  eggs,  sometimes  in  immense  masses.  The  eggs  hatch  in 
from  6  hours  to  much  longer  in  cool  weather.  Growth  is  rapid,  the  larvae  be- 
coming mature  in  6  to  20  days.  The  larvae  enter  the  soil  to  pupate  and  the 
adults  emerge  in  3  or  more  days.  The  entire  life  cycle  from  egg  to  adult  varies 
from  6  to  39  days  (Bishopp,  1915).  After  emergence,  mating  takes  place  and 
the  females  begin  laying  eggs  in  3  to  18  days.  Each  female  may  lay  several 
batches  of  eggs,  but  her  life  is  short — only  two  to  six  weeks.  In  southern  Texas 
Bishopp  (1915)  reports  from  10  to  14  broods  annually.  In  the  North  breeding 
ceases  at  temperatures  below  40°  F.,  in  fact  Bishopp  states  that  50°  to  60°  F.  is 
the  minimum  temperature  for  fly  activity. 

The  larva  closely  resembles  that  of  C.  americana  but  can  be  recognized  by  the 
absence  of  dorsal  and  lateral  spines  on  the  two  abdominal  segments  preceding 
the  last  one  and  the  lack  of  pigmentation  on  the  tracheal  trunks  (Fig.  187). 

Though  this  species  attacks  carrion  primarily,  it  will  oviposit  on  sheep  with 
wool  dirtied  by  urine  or  fecal  wastes,  on  festering  sores,  or  on  any  animal  with 
contaminated  wounds.  Though  it  has  frequently  been  reported  from  man,  it  is 
believed  most  of  such  infestations  were  due  to  C.  americana. 

THE  GENUS  CHRYSOMYA 

Chrysomya  bezziana  is  a  species  closely  related  to  our  screwworm  fly.  It  is 
a  common  fly  of  Africa,  Asia,  and  the  Philippine  Islands.  Though  it  mainly 
infests  wounds,  sores,  ulcers,  etc.,  of  animals,  Patton  reports  it  as  a  serious 
invader  of  man  (in  India)  and  records  the  larvae  from  all  sorts  of  wounds — 
sores,  ulcers,  the  nose,  eye,  ear,  vagina,  and  gums.  There  are  a  few  human 


504  MEDICAL  ENTOMOLOGY 

records  from  Africa  and  none  from  the  Philippines.  In  Africa  Cuthbertson 
(1933)  states  that  "next  to  the  Tsetse  fly  (G.  morsitans)  this  blowfly  is  the 
most  important  pest  of  cattle,  sheep,  horses,  dogs  and  other  domestic  animals 
in  Rhodesia."  He  notes  that  the  complete  life  cycle  occupies  14  to  18  days  and 
that  there  are  eight  generations  a  year.  The  females  are  very  prolific,  each  fe- 
male laying  from  500  to  600  eggs.  The  spread  of  this  fly  to  the  Americas  would 
add  another  serious  pest  of  our  domestic  animals  and  probably  also  man. 

Other  species  of  Chrysomya  that  attack,  domestic  animals  and  occasionally 
man  are  C.  marginal}*  (Wied.),  common  in  Africa  (mainly  a  scavenger);  C. 
albiceps  (Wied.),  widespread  in  Europe,  the  Middle  East,  India,  and  Africa 
(one  of  the  important  sheep  maggots  in  South  Africa);  C.  chloropyga 
(Wied.),  important  sheep  pest  in  South  Africa;  and  C.  rufifacies  (Macq.),  a 
pest  of  sheep  in  Australia.  Some  of  these  have  been  reported  from  man. 

THE  GENUS  CALLIPHORA 

The  genus  Calliphora  (Fig.  189)  contains  a  number  of  species  of  which 
three  are  our  common  blowflies  or  bluebottle  flies — C.  vomitoria  (Linn.), 
C.  vicina  R.-D.  (erythrocephala  Meig.),  and  C.  livida  Hall  (=  viridescens 
R.-D.)  (See  table  for  identification  of  these  three  flies  on  pp.  486-488).  The 
first  two  species  are  the  most  common  and  abundant.  The  three  species  re- 
semble each  other  very  closely  in  size,  coloring,  and  habits.  Each  varies  from 
7  to  12  mm.  in  length,  with  a  wing  expanse  of  about  25  mm.  The  eyes  are  red, 
the  thorax  is  bluish  gray  with  indistinct,  longitudinal,  darker  blue  stripes,  and 
the  abdomen  is  somewhat  paler  blue  with  whitish  pubescence  on  the  anterior 
half  of  each  segment.  They  are  stout,  active  flies  and  produce  a  rather  charac- 
teristic loud  buzzing  sound  during  flight.  They  frequent  places  where  meat  or 
decaying  animal  and  vegetable  matter  are  exposed  and  are  always  abundant 
about  slaughter  houses,  piggeries,  and  unclean  places  of  all  kinds.  They  oviposit 
on  exposed  flesh.  The  developmental  cycle  is  very  rapid.  The  eggs  hatch  in 
from  8  to  24  hours,  and  the  larval  growth  is  completed  in  from  4  to  9  days; 
pupation  takes  place  in  the  soil  and  the  adults  emerge  in  from  10  to  17  days. 
The  entire  life  cycle  requires  from  two  to  four  weeks.  C.  vicina  and  C.  vomi- 
toria are  Holarctic  in  distribution;  C.  livida,  Nearctic.  The  larvae  can  usually 
be  identified  by  the  cephalopharyngeal  structure  and  posterior  spiracles  (Figs. 
190,194,195). 

Though  development  normally  takes  place  on  dead  flesh,  the  flies  frequently 
oviposit  on  wounds,  sores,  ulcers,  or  other  festering  places  of  animals  and, 
rarely,  man.  Courtis  (1927)  removed  three  nearly  mature  larvae  from  a  pus 


MYIASIS  OF  MAN  AND  ALLIED  CONDITIONS  505 

pocket  in  the  left  lachrymal  sac  of  a  patient.  These  larvae  pupated  and  the 
adults  proved  to  be  C.  vomitoria.  Oronato  (1922)  reports  a  long  series  of  in- 
festations by  various  species  of  muscoidean  flies  in  Tripoli.  Calliphora  vicina 
R.-D.  (erythrocephala)  is  recorded  from  two  human  cases,  and  numerous 


Fig.  189.  The  bluebottle  fly,  Calliphora  vomitoria,  enlarged.  (Courtesy  Department  of 
Agriculture,  Division  of  Entomology,  Canada.) 

infestations  of  various  animals  by  different  species  are  listed.  Harvey  (1934) 
lists  the  above  species  from  a  human  case  in  England.  There  are  also  many 
records  of  the  larvae  of  these  flies  causing  intestinal  and,  occasionally,  nasal 
myiasis. 


506 


MEDICAL  ENTOMOLOGY 


VC 


SPP 


Fig.  790.  Cephalopharyngeal  structures  of  mature  larvae.  (/)  Stomoxys  calcitrant. 
(2)  Phormiaregina.  (3)  Callitrogamacellaria.  (4)  Lucilia  sericata.  (5)  Muscina  stabulans. 
Ac,  rodlike  prolongation  of  pharyngeai  sclerite;  DC,  dorsal  cornua;  DS,  dental  sclerite; 
HS,  hypostomal  sclerite;  OH,  oral  or  mouth  hooks;  PH,  pharynx;  PHS,  pharyngeai 
sclerite;  SD,  salivary  duct;  SPP,  salivary  pump;  VC,  ventral  cornua.  (All  drawn  to  same 
scale.) 


MYIASIS  OF  MAN  AND  ALLIED  CONDITIONS  507 

THE  GENUS  LUCILIA 

The  green-bottle  flies.  This  genus  contains  a  considerable  number  of  species 
about  which  very  little  is  known.  Unfortunately  the  genus  has  been  split  into 
a  number  of  genera  of  doubtful  validity.  At  least  the  following  species  are  of 
some  importance:  L.  caesar  (Linn.),  L.  sericata  Meig.  (placed  by  some  in 
Phaenicia),  L.  illustris  (Meig.),  and  L.  cuprina  (Wied.).  Lucilia  (Bujolucilia) 
siharum  (Meig.)  is  a  known  parasite  of  toads  in  Europe  and  possibly  in  North 
America.  L.  caesar  of  American  authors  is  regarded  now  as  L.  illustris  (Meig.), 
and  all  our  references  are  to  this  species  since  L.  caesar  is  believed  not  to  occur 
in  North  America.  In  America  L.  illustris  is  primarily  a  carrion  feeder  and  is 
the  most  common  green-bottle  fly  on  freshly  exposed  meat  or  about  recently 
killed  animals.  Kingscote  (1932)  reports  it  as  causing  myiasis  in  foxes  in 
Canada,  and  James  (1947)  lists  two  human  cases.  Lucilia  (Phaenicia)  sericata 
(Meig.)  is  widely  distributed  in  North  America,  Mexico,  Central  America, 
parts  of  South  America,  Europe,  Asia,  Africa,  Australia,  and  many  islands.  It 
is  the  chief  species  causing  myiasis  in  sheep  in  the  United  States,  the  British 
Isles,  and  South  Africa;  it  is  common  in  New  Zealand,  and  it  is  reported  from 
Australia.  The  species  is  mostly  a  breeder  in  carrion  but  causes  "sheep-strike" 
in  soiled  wool,  festering  wounds,  or  sores.  The  females  deposit  their  eggs  in 
masses  in  such  places,  and  the  larvae  feed  on  the  diseased  tissues,  frequently 
causing  severe  injury.  The  life  cycle  is  short — egg  to  adult  in  from  9  to  14  days. 
Many  generations  occur  each  season,  especially  in  the  warmer  parts  of  its  range. 
Human  cases  of  myiasis  by  this  species  have  been  reported  but  these  must  be 
regarded  as  doubtful.  This  is  the  species  formerly  used  extensively  by  Baer 
(1931)  and  others  for  the  clearing  of  deep-seated  wounds  after  surgical  opera- 
tions. It  is  probably  not  used  now  because  of  the  discovery  of  better  treatments. 
L.  caesar  (Linn.)  is  a  Palearctic  species  and  has  been  reported  from  other  areas 
but  these  were  probably  mistaken  identifications  (probable  species  L.  illustris). 
Its  importance  as  a  cause  of  myiasis  cannot  be  stated  as  the  correct  identification 
of  such  infestations  is  questionable.  L.  (Phaenicia)  cuprina  (Wied.)  is  dis- 
tributed throughout  parts  of  the  Ethiopian,  Oriental,  and  Australian  regions 
and  over  many  islands  in  the  Indian  and  Pacific  oceans.  In  Australia  this 
species  is  the  principal  cause  of  "sheep-strike"  and  severe  losses  to  sheep  owners 
are  reported.  Though  reported  from  North  America,  Hall  (1948)  regards  our 
species  as  distinct  (L.  pallescens) .  Human  cases  are  said  to  occur  but  identifica- 
tions are  doubtful.  The  species  L.  sericata,  L.  cuprina,  and  L.  pallescens  are 
almost  identical  and  it  is  doubtful  if  they  are  good  and  distinct  species.  The 
change  of  habit  from  carrion  feeding  to  attacking  festering  wounds  or  soiled 


5<>8  MEDICAL  ENTOMOLOGY 

wool  would  not  appear  to  be  of  much  importance  where  the  latter  conditions 
are  more  common  than  dead  carcasses. 

OTHER  GENERA 

Phormia  regina  (Meig.),  known  as  the  "black  blowfly"  (Fig.  191),  is  a  com- 
mon and  widely  distributed  species  in  North  America,  Europe,  parts  of  Asia, 
Australia,  and  some  islands  in  the  Pacific  Ocean.  It  is  known  to  oviposit  in  old 
suppurating  sores,  particularly  in  sheep  and  goats.  It  is  primarily  a  carrion 
feeder  and  is  very  abundant  where  dead  carcasses  lie  exposed.  The  life  cycle 
from  egg  to  adult  varies  from  10  to  25  days.  There  are  a  few  records  of  its  in- 


Fig.  /p/.  Phormia  regina.  Female.  Fig.  792.  Muscina  stabulans.  Female. 

vading  human  tissues.  Stewart  (1929)  reports  an  interesting  case  of  a  woman 
suffering  from  scalp  sores  with  heavy  pus  exudate.  After  admission  to  the 
hospital  and  preliminary  treatment,  numerous  dipterous  maggots  were  ob- 
served crawling  out  of  the  sores.  The  maggots  were  very  numerous,  particularly 
back  of  the  ears.  The  larvae  were  reared  and  a  definite  record  of  this  species 
infesting  man  established. 

Cordylobia  anthropophaga  Grunberg,  the  tumbu  fly,  is  widely  distributed 
in  tropical  Africa,  south  to  the  Transvaal  and  Natal.  Blacklock  and  Thompson 
(1923)  have  rather  fully  elucidated  the  bionomics  of  this  species.  The  females 
oviposit  in  sand  contaminated  with  fecal  wastes.  The  female  digs  a  small  cavity 
for  the  placement  of  her  eggs  and  lays,  usually  in  two  batches,  some  300  to 
400  eggs.  At  37°  C.  the  eggs  hatch  in  from  24  to  48  hours;  at  ordinary  room 
temperature  they  hatch  in  three  days,  The  young  larvae  are  stimulated  to 


MYIASIS  OF  MAN  AND  ALLIED  CONDITIONS  509 

activity  by  heat,  pressure,  or  movement  and  come  to  the  surface  to  infest  their 
hosts.  They  attack  and  penetrate  the  skin,  completing  their  larval  development 
in  about  9  or  10  days.  Leaving  their  hosts  the  larvae  pupate  in  the  soil.  The 
pupal  period  occupies  from  22  to  24  days.  The  principal  hosts  are  rats  and  dogs; 
the  feet  of  children  are  frequently  severely  infested. 

Auchmeromyia  luteola  (Fabr.),  the  "Congo  floor  maggot,"  is  a  common 
species  in  tropical  Africa.  The  females  lay  their  eggs  in  the  soiled  dirt  floors 
of  the  native  huts.  The  larvae  are  bloodsuckers,  attacking  humans  to  obtain 
food  and  usually  feeding  at  night.  After  feeding  they  bury  themselves  in  the 
soil  and  come  out  again  when  hungry. 

The  cluster  fly,  Pollenia  rudis  (Fabr.),  should  be  mentioned  here  not  because 
it  causes  myiasis  but  because  it  is  a  veritable  pest  in  our  homes.  The  species  is 
parasitic  on  several  species  of  earthworms  and  there  are  two  or  three  genera- 
tions a  year.  In  the  cold  days  of  autumn  the  adults  seek  shelter  in  buildings, 
and  attics  are  frequently  found  swarming  with  them,  not  hundreds  but 
thousands,  and  they  leave  behind  them  their  filth  and  many  dead  bodies.  Here 
they  pass  the  winter  in  the  North,  and  these  large,  cumbersome  flies  (easily 
recognized  by  the  abundance  of  short,  golden-yellow,  curly  pile  among  the 
hairs  of  the  thorax  and  by  their  size — they  are  larger  than  the  housefly)  come 
out  from  time  to  time  and  fly  with  a  buzzing  sound  through  the  rooms.  The 
author  has  seen  homes,  hospitals,  and  other  buildings  just  swarming  with  them 
despite  the  owners'  efforts  to  prevent  their  entrance.  They  may  easily  be 
eliminated  by  spraying  attics  or  other  resting  places  with  a  5  per  cent  DDT  in 
kerosene  or  other  solvent  so  as  to  leave  a  good  residue. 

Several  species  of  the  Calliphoridae  live,  during  the  larval  stage,  in  the  nests 
of  birds  and  suck  the  blood  of  the  nestlings.  Here  belong  Protocalliphora 
avium,  P.  hirudo,  and  other  species. 

THE  FAMILY  MUSCIDAE 

To  this  family  belong  many  nonbloodsucking  flies  in  which  the  arista  is 
plumose  to  the  tip  (Fig.  171),  the  first  posterior  cell  is  narrowed  or  closed 
toward  the  margin  of  the  wing  (Fig.  172),  and  the  hypopleural  bristles  are 
absent.  The  flies  are  nonmetallic  in  coloring,  usually  grayish  or  dark-colored. 
Comparatively  few  species  of  this  group  have  been  associated  with  myiasis. 

Musca  domestica  Linn.,  the  common  housefly  (see  Chapter  xvi  for  a  full 
account),  or  rather  its  larva,  has  been  reported  many  times  as  causing  human 
intestinal  myiasis.  As  the  housefly  normally  breeds  in  a  great  variety  of  decay- 
ing vegetable  matter,  manure  of  nearly  all  kinds,  etc.,  human  infection  must 
take  place  through  drinking  or  eating  contaminated  liquids  or  foods  or  the 


5io  MEDICAL  ENTOMOLOGY 

flies  actually  oviposit  on  the  soiled  anus  (as  in  the  case  of  ill-kept  infants). 
The  eggs  or  young  larvae  are  swallowed  or  pass  into  the  rectum,  and  ap- 
parently development  can  continue  in  the  human  intestine.  The  actual  dis- 
turbance caused  by  the  presence  of  the  larvae  is  probably  not  very  great  but 
we  have  no  well-defined  infection  fully  recorded.  The  great  majority  of  cases 
have  been  reported  from  infants.  Jones  (1913)  removed  about  thirty  living 
larvae  from  the  stomach  of  a  patient  suffering  from  a  hepatic  abscess.  Recently 
Rennie  (1927)  has  described  a  case  of  intestinal  myiasis  in  a  breast-fed  baby 
in  Scotland.  Leon  (1921)  reports  a  peculiar  case  of  urinary  myiasis  in  a  young 
man  (22  years  of  age)  in  Romania.  The  patient,  suffering  from  blennorrhagia, 
had  evidently  been  infected  by  the  housefly  ovipositing  in  the  discharge  during 
his  sleeping  hours.  In  all,  17  larvae  of  M.  domestica  were  passed  in  his  urine. 
Mumford  (1926)  describes  two  cases  of  urinary  myiasis  in  infants,  one  in  a 
male  and  the  other  in  a  female.  In  the  first  case  the  infection  was  prolonged,  the 
child  suffered  from  convulsions  and  severe  pain  at  micturition  and,  in  all, 
passed  several  hundred  larvae.  Treatment  with  urotropine  resulted  in  the  pas- 
sage of  only  dead  larvae  and  the  apparent  recovery  of  the  child.  The  second 
case  is  not  so  clear  as  the  larvae  and  well-developed  eggs  were  found  on  the 
diaper  soiled  with  urine.  No  adult  flies  were  reared  and  the  sickly  child  died. 
At  Ithaca  about  100  living  larvae  of  the  housefly  were  removed  at  autopsy  from 
the  small  intestine  of  a  pig  (August  1944). 

Muscina  stabulans  (Fallen),  the  nonbiting  stable  fly  (Fig.  192),  is  one  of  the 
common  flies  about  barns  and  it  also  occurs  in  houses.  The  species  is  widely  dis- 
tributed throughout  the  world.  It  is  slightly  more  robust  than  the  housefly,  dark 
gray  in  color,  with  two  rather  distinct  medium  dark  lines  and  two  lateral  in- 
distinct lines  on  the  thorax  (quite  similar  to  the  housefly) ;  the  abdomen  is  dark 
gray  with  lighter  markings.  The  venation  (Fig.  193)  is  quite  distinct  and  will 
aid  in  its  identification.  This  species  breeds  in  decaying  fruit  and  vegetables, 
manure,  human  excrement,  raw  and  cooked  meats,  decaying  carcasses,  dead 
insects,  and  similar  substances.  The  larva  looks  like  a  typical  housefly  maggot 
but  can  be  distinguished  by  the  posterior  spiracles.  Each  spiracular  plate  (Fig. 
194  4)  is  round,  small,  with  a  wide  peritreme,  and  the  three  short  slits  are 
directed  toward  the  median  line.  The  larvae  of  this  species  are  known  to  cause 
human  intestinal  myiasis.  Portchinsky  (1913)  records  severe  abdominal  pains, 
bloody  stools,  nausea,  and  vomiting  associated  with  an  invasion  of  this  larva. 
The  patient  continued  to  suffer  for  about  five  months.  After  treatment  50  living 
larvae  were  expelled.  The  patient  recovered  but  was  later  troubled  with  in- 
testinal catarrh.  Brand  (1931)  reports  an  interesting  case  in  a  child  only  15 
months  old.  When  brought  to  the  doctor  for  treatment  the  child  was  suffering 


MYIASIS  OF  MAN  AND  ALLIED  CONDITIONS  511 

from  convulsions  and  general  debility.  After  five  weeks'  treatment  with  ultra- 
violet irradiations  and  increased  diet  it  was  discovered  that  the  child  was 
passing  "worms."  The  mother,  during  the  sixth  week,  brought  in  a  fresh  stool 
and  it  was  found  alive  with  maggots  and  numerous  pupal  cases.  The  larvae 
proved  to  be  Musca  domestica  but  the  pupal  cases  all  gave  forth  Muscina  stabu- 
lans  (wrongly  recorded  in  Brand's  article  as  Stomoxys  stabulans).  No  specific 
treatment  seems  to  have  been  given.  On  October  12,  about  ten  weeks  after  the 
first  maggots  were  observed,  the 
family  moved  into  another  home 
and  the  infection  suddenly  ceased. 
Three  months  later  the  child  had 
apparently  almost  completely  re- 
covered. How  the  child  became 
infected  and  continued  to  pass 
maggots  for  such  a  long  time  is 
not  explained.  The  sudden  spon-  f ig 

taneous  cure  could  be  explained 
by  the  season  of  the  year;  these  flies  do  not  breed  after  the  first  of  October  in 
central  New  York.  Franchini  (1927)  records  a  case  in  a  man  25  years  of  age. 
At  intervals  during  two  years  the  patient  suffered  from  pruritus  ani  and 
abdominal  pains,  and  passed  loose,  mucoid,  and  at  times  bloodstained  stools. 
Treatment  with  stovarsol  resulted  in  the  discharge  of  larvae  of  Muscina 
stabulans  and  the  patient  recovered. 

THE  FAMILY  ANTHOMYIIDAE 

The  anthomyids  are  common  and  abundant  flies.  The  larval  habits  are 
extremely  varied,  many  developing  in  decaying  vegetable  matter,  others  in 
living  plant  tissues,  and  some  in  animal  excrement;  a  few  are  parasitic.  The 
larvae  of  certain  species  attack  onions,  radishes,  and  turnips  or  mine  in  the 
leaves  of  spinach,  lettuce,  swiss  chard,  and  other  greens,  and  these  may  be 
eaten.  Several  species  are  known  to  cause  intestinal  myiasis  when  taken  into 
the  alimentary  tract  with  food  or  by  accident. 

Fannia  canicularis  (Linn.)  is  the  so-called  "lesser  housefly"  (Fig.  196)  and 
may  be  seen  commonly  hovering  in  mid-air  or  flying  hither  and  thither  in 
our  homes.  It  is  a  grayish  fly,  measuring  from  5  to  6  mm.  in  length.  It  breeds 
in  all  kinds  of  decaying  vegetable  and  animal  matter  and  in  the  excrement 
of  horses,  cows,  and  man.  It  is  frequently  found  in  decaying  grass  piled  up 
on  lawns.  The  ^ggs  hatch  in  about  25  hours,  and  the  larvae  complete  their 
growth  in  about  a  week  if  food,  moisture,  and  temperature  are  favorable. 


512 


MEDICAL  ENTOMOLOGY 


Fig.  194.  Posterior  spiracular  plates  of  mature  larvae.  (/)  Sarcophaga  bullata.  (2) 
Callitroga  maccllaria.  (3)  Wohlfahrtia  vigil.  (4)  Muscina  stabulans.  (All  drawn  to  the 
same  scale  showing  the  relative  size  and  distance  apart  on  the  larvae.) 


MYIASIS  OF  MAN  AND  ALLIED  CONDITIONS 


513 


Fig.  795.  Posterior  spiracular  plates  of  mature  larvae.  (/)  Cattiphora  vonritoria.  (2) 
Phormia  regina.  (3)  Lucilia  sencata.  (4)  Musca  domestica.  (5)  Stomoxys  calcitrant.  (All 
drawn  to  the  same  scale  showing  the  relative  size  and  distance  apart  on  the  larvae.) 


5i4  MEDICAL  ENTOMOLOGY 

Otherwise  the  larval  life  may  be  prolonged  to  three  or  four  weeks.  The  larva 
(Fig.  197)  is  very  characteristic  and  may  be  recognized  by  its  flattened  ap- 
pearance and  spinclike  appendages.  It  measures  from  5  to  6  mm.  in  length. 
The  pupal  period  occupies  about  a  week.  The  species  is  widely  distributed 
throughout  the  world. 

Fannia  sedans  Fabr.  has  been  called  the  "latrine  fly"  on  account  of  its  most 
common  breeding  habitat.  In  appearance  the  adult  is  almost  identical  with  that 
of  the  lesser  housefly.  It  can  be  distinguished  from  it  by  the  middle  tibia,  which 
possesses  a  distinct  tubercle.  The  females  select  excrement  of  man  and  animals 


Fig.  196  (left).  Fannia  canicularis  L.,  the  lesser  housefly.  Female. 

Fig.  797  (center).  Larva  of  Fannia  canicularis.  (From  Hewitt,  The  Housefly, 
by  permission  of  the  Cambridge  University  Press.) 

Fig.  198  (right).  Larva  of  Fannia  scalaris.  (From  Hewitt,  The  Housefly,  by 
permission  of  the  Cambridge  University  Press.) 

for  the  placement  of  their  eggs.  The  eggs  hatch  in  about  24  hours  and  the  larval 
growth  is  completed  in  6  to  12  days.  The  larva  (Fig.  198)  is  very  distinctive. 
It  is  flattened  dorsoventrally  and  bears  spiny  processes  that  are  somewhat 
feathered.  Viewed  from  above  the  larva  appears  to  be  surrounded  by  a  fringe 
of  featherlike  appendages.  The  pupal  period  occupies  about  nine  days. 

INTESTINAL  AND  GASTRIC  MYiASis:  There  are  numerous  records  of  the  larvae 
of  both  these  species  causing  gastric  and  intestinal  myiasis  of  man.  Hewitt 
(1912)  gives  a  brief  summary  of  the  known  cases.  He  states,  "The  presence  of 
these  larvae  in  the  stomach  is  usually  indicated  by  nausea,  vertigo,  and  violent 
pains;  the  larvae  in  many  cases  are  expelled  by  vomiting.  If  they  occur  in  the 
intestine,  they  are  expelled  with  the  feces  and  their  presence  is  signalised  by 


MYIASIS  OF  MAN  AND  ALLIED  CONDITIONS  515 

diarrheal  symptoms,  abdominal  pains,  or  hemorrhage  caused  by  the  traumatic 
lesions  of  the  mucous  membrane  of  the  intestine  which  the  larvae  affect." 

In  addition  to  invading  the  intestines,  the  larvae  of  F.  canicularis  have  been 
recorded  from  the  urethra  of  both  males  and  females.  Chevril  (1909)  sum- 
marized all  known  cases  (20)  and  concluded  that  six  were  genuine,  ten  were 
probable,  and  four  doubtful.  He  also  gave  an  additional  case  of  a  woman  who 
suffered  from  albuminuria  and  urinated  with  difficulty.  Later  she  discharged 
30  to  40  larvae  of  F.  canicularis  in  her  urine  and  apparently  recovered.  King 
(1914)  reports  a  case  of  urethral  myiasis  in  a  young  man  in  Virginia  due  to  the 
larvae  of  F.  scalaris.  Three  larvae  were  passed  at  different  times.  Mumford 
1926)  gives  an  account  of  a  severe  case  of  urinary  myiasis  in  a  young  male 
baby  in  England  due  to  the  larvae  of  Fannia  canicularis  and  Musca  domestica. 
The  infection  was  prolonged  and  several  hundred  larvae  were  passed.  Detwiler 
(1929)  reports  a  case  of  urinary  myiasis  in  western  Ontario  due  to  the  larvae  of 
F.  canicularis. 

MODE  OF  INFECTION  :  All  the  larvae  of  anthomyids  so  far  reported  as  causing 
gastric,  intestinal,  and  urogenital  myiasis  belong  to  the  two  species  described 
above.  These  species  normally  breed  in  animal  excrement  and  decaying  vege- 
table and  animal  matter.  Such  larvae  can  apparently  continue  their  growth  in 
the  alimentary  canal  of  man.  Man  probably  becomes  infected  from  eating  de- 
caying fruit,  food  soiled  with  excrement,  or  other  contaminated  matter  on 
which  the  eggs  had  been  laid  or  in  which  very  young  larvae  were  present. 
Hewitt  suggests  that  in  open  privies  the  flies  are  attracted  to  unclean  persons 
and  deposit  their  eggs  about  the  anus  or  the  external  genital  orifice  (especially 
of  females) ;  the  eggs  hatch  and  the  larvae  migrate  into  the  intestines  or  up 
the  urethra.  In  young  children  infection  may  occur  by  direct  oviposition  about 
the  anal  opening,  especially  on  those  that  are  unclean  and  left  exposed.  In  adults 
such  infection  may  take  place  during  sleep  or  a  drunken  stupor  or  while  lying 
in  the  open  uncovered  and  unclean.  These  are  common  flies  in  sleeping  rooms 
during  the  warm  season  and  direct  infection  can  easily  take  place  under  certain 
conditions. 

THE  FAMILY  OESTRIDAE  , 

In  recent  years  the  family  Oestridae  has  been  restricted  to  a  small  group  of 
flies,  the  larvae  of  which  are  parasitic  in  the  nasal  region  and  frontal  or  maxil- 
lary sinuses  of  sheep,  goats,  horses,  antelopes,  and  other  hoofed  mammals. 
Rarely  the  first-stage  larvae  are  reported  from  man,  entering  the  eye,  nose,  or 
mouth.  The  groups  separated  from  the  original  family  include  the  Cutere- 


516  MEDICAL  ENTOMOLOGY 

bridac,  warble-producing  larvae  in  a  variety  of  mammals  as  rabbits,  rodents 
generally,  domestic  and  wild  mammals,  and  man  and  the  Hypodermatidae, 
the  well-known  warble  flies  of  domestic  cattle  and  deer.  The  adults  of  these 
three  families  may  be  recognized  by  the  following  brief  key: 

1.  Postscutellum  well  developed;  squamae  large;  apical  cell  greatly  narrowed 

or  closed  at  margin  of  wing 2 

Postscutellum  not  developed;  squamae  large  and  apical  cell  narrowed  at 
margin ' Cuterebridae 

2.  Apical  cell  closed  and  petiolate  (Fig.  199) Oestridae 

Apical  cell  open,  though  narrowed  at  the  margin  (Fig.  204) 

Hypodermatidae 

The  larvae  of  these  three  families  are  usually  easily  recognizable  and  the 
separating  characters  are  given  on  pages  531-533. 

The  Oestridae  possess  two  genera  that  are  of  some  importance  in  medical 
entomology,  Oestrus  and  Rhinoestrus.  Oestrus  ovis  Linn,  is  the  sheep  nasal 
botfly.  The  adult  (Fig.  199)  measures  from  10  to  12  mm.  in  length.  The  head 
is  large,  more  or  less  yellowish;  the  thorax  is  dark  with  numerous  deep,  black 
pits  and  overlaid  by  a  grayish  bloom;  the  abdomen  is  almost  black  and  the 
legs  are  yellow.  The  species  is  widespread  through  the  world  and  is  a  serious 
pest  in  sheep-producing  countries.  The  adults  do  not  feed.  The  females  in 
flight  dash  at  their  hosts  (principally  sheep  and  goats)  and  deposit  living  larvae 
in  or  near  the  nostrils.  These  pass  up  the  nostrils  and  enter  the  sinuses.  Here 
the  larvae  complete  their  development  and  when  mature  drop  or  are  sneezed 
out.  Entering  the  ground  to  pupate,  the  adults  emerge  in  three  or  four  weeks. 
The  growth  of  the  larvae  in  the  sinuses  may  be  very  rapid,  as  short  as  2/4 
months  or  less  in  warm  climates  or  may  be  prolonged  throughout  the  winter  in 
colder  climates.  In  Europe  there  is  said  to  be  but  one  annual  generation,  but  in 
North  America  there  are  evidences  of  two  annual  generations. 

Though  primarily  a  pest  of  sheep  and  goats,  these  flies  have  caused  many 
human  infections,  especially  among  sheep  and  goat  herders  about  the  Mediter- 
ranean Basin  and  parts  of  Russia.  The  fly  discharges  its  living  larvae  into  or 
near  the  eye.  The  maggots  penetrate  the  conjunctiva  and  produce  a  painful 
conjunctivitis.  As  these  larvae  cannot  develop  in  man  beyond  the  first  stage, 
the  finding  and  removal  of  the  maggots  results  in  immediate  cessation  of  pain 
and  cure.  The  larvae  have  also  been  reported  as  causing  myiasis  of  the  nose  and 
throat,  the  flies  discharging  their  larvae  into  the  nose  or  mouth.  These  infec- 
tions are  painful  but  as  the  larvae  cannot  complete  their  development  the  cause 
of  trouble,  often  very  severe,  disappears  in  a  week  or  two  unless  secondary 


MYIAS1S  OF  MAN  AND  ALLIED  CONDITIONS  517 

infections  develop.  Dupuy  d'Uby  (1931)  gives  detailed  accounts  of  case  his- 
tories of  man. 

Rhinoestrus  purpureus  (Brauer)  is  normally  a  parasite  of  horses,  mules, 
zebras,  and  other  Equidae.  It  is  widespread  in  Africa,  southern  Europe,  the 
Near  East,  India,  extensive  areas  in  Russia,  Mongolia,  Manchuria,  and  parts 
of  China.  Human  cases  of  eye  infection  have  been  reported  by  Portchinsky 


Fig.  799  (left).  The  sheep  nose  fly,  Oestrus  ovis.  (Courtesy  Department  of  Agriculture, 
Division  of  Entomology,  Canada.) 
Fig.  200  (right).  An  anthomyiid  fly  carrying  a  mass  of  eggs  of  Dcrmatolna  hominis. 

THE  FAMILY  CUTEREBRIDAE 

The  Cuterebridae  (the  warble  flies  of  rodents,  man,  and  deer)  is  a  compara- 
tively small  family  of  very  important  flies.  The  adults  (Fig.  201)  are  rather 
large  and  appear  like  bees,  some  like  bumblebees.  The  mouth  opening  is 
small  and  the  mouth  parts  are  usually  vestigial.  The  adults  of  many  of  the 
species  are  not  commonly  observed  except  by  those  who  seek  them.  All  the 
species  are  parasitic  on  mammals  during  their  larval  stage.  Parasitism  occurs  in 
tumors  or  warbles  under  the  skin  (hence  the  name)  or  in  the  nasal  and  pharyn- 
geal  cavities. 

Dermatobia  hominis  Linn.,  Jr.  (D.  noxialis  Goudot,  D.  cyaniventris  Macq.), 
the  human  warble  fly  (Fig.  201),  is  widely  distributed  and  abundant  in  Cen- 
tral and  South  America  and  Mexico.  The  adult  is  12  to  18  mm.  in  length;  the 
head  is  mainly  yellow,  the  thorax  dark  bluish  gray,  and  the  abdomen  a  bril- 
liant dark  blue.  These  flies  are  apparently  rarely  seen  in  nature.  They  occur 
most  commonly  in  forested  regions  or  along  the  margins  of  forests. 


5i8  MEDICAL  ENTOMOLOGY 

LIFE  CYCLE:  Sambon  (1922)  carefully  describes  the  method  of  oviposition. 
The  females  select  other  species  of  arthropods,  usually  mosquitoes,  various  flies 
(Fig.  200),  or  even  ticks  as  carriers  of  their  eggs.  They  apparently  seek  out 
some  shady,  mosquito-ridden  pool  and  await  the  emergence  of  the  adult  mos- 
quitoes or  capture  a  fly  in  the  shade.  When  the  mosquitoes  fly  away  from  their 
pupal  cases,  some  of  them  are  seized  by  the  botflies.  Each  botfly  quickly  de- 
posits 14  to  25  eggs  and  glues  them  to  the  abdomen  of  the  mosquito  or  fly. 
(Fig.  200).  The  eggs  are  so  placed  that  the  ends  through  which  the  young 
maggots  emerge  are  directed  away  from  the  mosquito  host.  Each  egg  contains 
a  fully  developed  first-stage  maggot  ready  for  hatching.  The  mosquito  most 


Fig.  201.  The  human  botfly,  Dermatobia  hominis.  Female. 

commonly  used  is  Psorophora  (Janthinosoma)  lutzii  Theo.,  a  fierce,  biting 
species  and  abundant  in  woodlands.  Psorophora  posticata  Say  is  also  said  to  be 
employed  for  oviposition  purposes.  Patton  and  Evans  (1929)  figure  an  antho- 
myid  with  a  mass  of  Dermatobia  eggs  attached  to  her  abdomen.  Dunn  (1918) 
records  five  separate  infections  of  one  individual  with  D.  hominis  through 
the  probable  agency  of  a  tick  (?Amblyomma  cajennense).  He  also  found  the 
mature  eggs  on  a  species  of  Limnophora  (Anthomyiidae)  from  which  he 
infected  himself.  In  addition  to  these,  Neiva  records  Musca  domestica,  Sto- 
moxys  calcitrans,  a  tabanid,  and  sylvan  muscids  as  carriers  in  Brazil. 

When  a  mosquito  or  other  insect  bearing  the  eggs  of  Dermatobia  hominis 
bites  or  visits  man,  the  warmth  evidently  induces  the  maggots  to  burst  open 
the  eggshell.  The  young  maggot  bores  directly  into  the  skin,  usually  taking 
advantage  of  the  puncture  made  by  the  mosquito  or,  as  in  the  report  of  Dunn, 


MYIASIS  OF  MAN  AND  ALLIED  CONDITIONS  519 

the  sites  of  tick  bites.  Busck  (1913)  reared  the  maggot  on  himself.  He  noted 
the  infection  on  May  29  and  on  September  9,  just  103  days  later,  the  maggot 
left  his  arm  fully  grown.  The  maggot  was  placed  in  moist  sand,  pupation  took 
place  and  the  adult  emerged  on  October  23.  Busck  states  that  the  larva  caused 
him  little  pain  though  the  exuding  wastes  and  serum  were  annoying  and 


c 


Fig.  202.  Dennatobia  hominis*  (A)  Full-grown  larva  after  emergence.  (6)  Second-stage 
larva.  (C)  First-stage  larva,  greatly  enlarged.  M,  mouth  hooks.  (A  and  B  not  to  the  same 
scale;  C  redrawn  after  Newstead  and  Potts.) 

necessitated  bandaging.  At  times  the  grub  would  rotate  on  its  own  axis  and 
cause  severe  pain.  During  the  infection  Busck  states  that  he  required  at  least 
three  to  five  hours  more  sleep  each  day;  after  the  grub  emerged  his  sleep  re- 
quirements returned  to  normal.  Dunn  (1930)  reports  rearing  six  larvae  on 
himself — two  experimental  infections  on  his  left  forearm  (Fig.  203)  and  four 
natural  infections  at  about  the  same  time.  All  these  infections  were  from  eggs 
carried  by  an  anthomyid  fly,  JJmnophora  species.  Penetration  of  the  unbroken 
skin  took  place  in  42  minutes  in  one  case  and  one  hour  and  35  minutes  in  the 


520  MEDICAL  ENTOMOLOGY 

other.  Dunn  experienced  considerable  discomfort  from  occasional  severe  pains 
at  the  points  of  infection  and  muscular  soreness  and  stiffness,  while  the  ex- 
uding wastes  required  bandaging.  The  time  required  from  the  penetration  of 
the  skin  till  the  emergence  of  the  mature  larva  was  46  days  and  15  hours  in  one 
case,  46  days  and  21  hours  in  another,  whereas  two  others  required  50  days 
and  15  hours  and  54  days  and  18  hours  respectively.  After  the  larval  emergence 
the  lesions  (Fig.  203)  soon  healed,  leaving  slight  scars.  The  pupal  period  varied 
from  22  to  24  days. 


Fig.  203  (left).  Lesions  caused  by  the  larvae  of  Dcrmatohia  Iwnunis  reared  on  a  man's 
arm.  Upper  lesion  shown  8  hours  after  the  larva  had  emerged,  lower  lesion  2  days  before 
larva  emerged.  (Courtesy  Mr.  Dunn.) 

Fig.  204  (right).  The  heel  fly,  Hypoderma  lineatum.  (Courtesy  Department  of  Agri- 
culture, Division  of  Entomology,  Canada.) 

The  full-grown  grub  (Fig.  202  A)  measures  from  18  to  over  24  mm.  in 
length  and  is  rather  characteristically  bottle-shaped — the  narrow  and  tubular 
end  (the  neck  of  the  bottle)  constituting  the  posterior  part;  as  the  prepupal 
stage  approaches,  the  maggot  becomes  more  grublike  (Fig.  202  A).  The  larval 
mouth  hooks  are  very  powerful  and  large.  The  body  is  well  supplied  with  stout, 
short,  backward-projecting  hooks,  very  efficient  for  maintaining  or  shifting 
position  in  the  flesh  of  the  host.  These  hooks  or  spines  are  arranged  as  follows: 
on  the  segment  back  of  the  anterior  spiracles  there  is  a  more  or  less  double 
row  of  spines  on  the  dorsum;  the  next  segment  bears  a  double  row  all  around 
its  anterior  margin;  the  next  (presumably  the  first  abdominal  segment)  bears 


MYIASIS  OF  MAN  AND  ALLIED  CONDITIONS  521 

two  belts  of  spines — a  double  row  along  the  anterior  margin  and  a  dorsal  row 
just  back  of  the  middle,  which  reaches  the  latero ventral  angles;  the  next  two 
segments  are  similarly  armed;  the  next  segment  (4th  abdominal)  has  an 
anterior  row  of  small  spines,  double  on  the  venter  and  several  rows  on  the 
posterior  margin  on  the  dorsal  side;  the  remaining  segments  are  unarmed 
except  the  last  two,  which  bear  numerous  small  spines  all  over  them.  These 
small  spines  are  directed  backward  and  undoubtedly  enable  the  larva  to  keep 
the  skin  of  the  host  broken.  The  spiracles  are  located  on  rather  weakly  chi- 
tinized  areas  and  each  possesses  three  slits,  directed  ventrally  and  slightly 
toward  the  median  line. 

THE  LESION  :  The  lesion  (Fig.  203)  appears  as  a  typical  boil  or  warble.  Within 
the  boil  the  larva  lives  with  the  constricted  end  toward  the  surface — the 
spiracles  being  located  on  the  tip.  Usually  a  small  scab  forms  over  the  apex  of 
the  boil  but  serum  exuclate  and  wastes  are  constantly  discharged.  The  lesion 
is  of  long  duration,  from  two  to  four  months.  If  located  near  a  joint  or  if  it 
becomes  secondarily  infected,  serious  conditions  may  arise.  The  native  treat- 
ment usually  consists  of  opening  the  tip  of  the  boil,  applying  tobacco  juice,  and 
then  squeezing  out  the  larva.  Busck  found  that  the  larva  could  be  removed 
easily  by  softening  the  boil,  widening  the  aperture,  and  then  carefully  applying 
pressure  well  below  the  boil.  In  this  way  the  larva  can  be  forced  out  without  the 
use  of  the  surgeon's  knife.  It  would  seem  that  local  freezing  before  squeezing 
out  the  grub  would  be  the  most  effective  treatment.  After  removal  of  the  grub, 
the  wound  should  be  thoroughly  washed  and  treated  with  antiseptics. 

HOSTS:  The  principal  hosts  are  domestic  animals  as  cattle,  dogs,  cats,  mules, 
pigs,  donkeys,  etc.,  and  man. 

PROPHYLAXIS:  As  this  botfly  attacks  mammals  primarily,  efforts  should  be 
made  to  reduce  their  abundance  in  domestic  animals.  Navarro  (1927)  reports 
that  in  the  eucalyptus  forest  regions  near  Sao  Paulo,  Brazil,  the  infestation  is 
very  severe.  He  gives  the  following  infestation  rates:  man,  44  per  cent  (819 
persons  examined) ;  cattle,  100  per  cent;  mules,  17  per  cent;  pigs,  12.3  per  cent; 
horses,  9.3  per  cent;  and  donkeys,  5  per  cent.  In  parts  of  Mexico,  Central 
America,  and  Panama  severe  infestation  of  cattle  frequently  occurs  and  human 
cases  are  not  uncommon.  In  order  to  escape  infection  in  regions  where  this 
fly  is  prevalent  avoidance  of  mosquitoes,  ticks,  and  bloodsucking  and  other 
flies  is  essential.  Houses  should  be  carefully  screened  and  bed  nets  should 
be  used.  All  small  and  persistent  pimples  should  be  carefully  watched  and 
treated. 


522  MEDICAL  ENTOMOLOGY 

THE  GENUS  CUTEREBRA 

The  adults  look  much  like  bumblebees.  They  are  parasitic  in  their  larval 
stages  on  rabbits  and  rodents  (such  as  squirrels,  chipmunks,  field  mice) .  The 
mature  larvae  are  large,  ovoid,  and  thickly  set  with  spines  or  scales.  They  are 
known  only  from  North  America.  Only  two  human  cases  of  infection  are 
apparently  recorded.  Beachley  and  Bishopp  (1942)  report  a  nasal  infection  in 
a  woman  in  Virginia.  A  single  first-stage  larva  of  a  Cuterebra  species  was 
squeezed  out  after  causing  severe  pain.  Bequaert  (1945)  describes  an  infestation 
of  a  man  at  Ware,  Massachusetts.  The  maggot,  16  mm.  in  length,  was  removed 
alive  from  a  boillike  swelling  below  the  right  nipple.  It  proved  to  be  C.  buc- 
cata  (F.),  the  rabbit  warble  (Fig.  213). 

THE  FAMILY  HYPODERMATIDAE 

Hypoderma  bovis  Linn,  and  Hypoderma  lineatum  (Villers)  are  the  com- 
mon ox  warble  flies  of  Europe,  America,  and  other  parts  of  the  world.  In 
northern  climates  the  grubs  may  be  found  in  swellings  or  warbles  on  the  backs 
of  cattle  from  early  January  to  late  April.  When  mature  the  grubs  are  very 
large  and  work  themselves  out  of  the  swellings,  dropping  to  the  ground  where 
they  pupate.  The  adults  (Fig.  204)  are  active  during  the  summer  months, 
depositing  their  large  eggs  on  the  hairs  from  the  hocks  to  the  knees  and  along 
the  sides  of  the  belly.  The  maggots  enter  the  skin,  where  they  hatch  and  pro- 
ceed to  migrate  through  various  parts  of  the  body  and  usually  reach  the  wall  of 
the  esophagus  during  September,  October,  and  November.  From  here  they 
migrate  through  the  connective  tissue  by  various  routes  and  eventually  appear 
on  the  backs  of  the  cattle  in  early  January  or  later.  Though  these  maggots  are 
primarily  parasites  of  cattle,  there  are  numerous  records  of  human  infection 
both  in  Europe  and  America.  Miller  (1910)  reported  an  interesting  case  in 
an  eleven-year-old  boy  from  Roanoke,  Virginia.  The  boy  was  admitted  to  the 
Johns  Hopkins  Hospital  on  March  13,  1908,  with  a  swelling  under  the  chin. 
The  excision  of  the  swelling  uncovered  a  second-stage  larva  of  Hypoderma 
lineatum.  The  boy  had  noticed  a  lump  below  his  left  knee  in  December.  This 
"lump"  had  migrated  up  his  leg  and  abdomen,  under  the  axilla,  up  the  right 
side  of  the  neck,  and  irregularly  about  the  scalp,  passing  back  of  the  ear  to  the 
submental  region,  which  it  reached  in  about  two  months.  Here  it  remained 
stationary  till  excised.  A  second  lump  appeared  on  his  groin  in  January,  and 
this  migrated  upward  till  it  reached  the  occipital  region  where  it  came  to  a 
head.  The  boy  broke  the  scab  and  pulled  out  an  active  grub  about  one  inch 
long.  Style  (1924)  records  a  similar  migrating  infection  in  a  four-year-old  boy 


MYIASIS  OF  MAN  AND  ALLIED  CONDITIONS  523 

in  England.  In  all  he  removed  three  grubs  from  swellings  on  various  parts  of 
the  scalp.  One  of  the  grubs  was  definitely  identified  as  the  penultimate  stage 
of  H.  lineatum.  Of  interest  here  is  that  the  boy  suffered  severe  pain  as  the 
swellings  appeared  and  disappeared  about  the  head.  Lanford  and  Warner 
(1925)  describe  an  infection  of  the  testicle  of  a  22-month-old  child.  They  re- 
moved three  larvae  from  the  tunica  vaginalis.  There  is  apparently  no  record 


Fig.  205.  Posterior  spiracles  of  larvae.  Left':  Hypoderma  bovis.  Center:  Hypoderma 
lineatum.  Right:  Oestrus  ovis. 

of  migration  in  this  case.  Herms  (1925)  reports  infection  due  to  H.  bovis  in  a 
cowboy.  The  grub  migrated  from  the  groin  over  the  body  and  became  localized 
on  the  shoulder,  where  the  grub  was  squeezed  out.  Six  months  later  a  second 
grub  emerged  from  a  swelling  on  the  thigh.  Another  case  of  infection  is  re- 
ported by  Andre  (1925)  in  a  young  child  in  Upper  Savoy.  The  grub  was 
removed  from  a  swelling  behind  the  ear.  Toomey,  Topsent,  Wegelin,  and 
Condorelli  report  other  cases  from  Europe.  These  grubs  can  only  be  identified 
by  a  close  study  of  the  posterior  spiracles  (Fig.  205). 

THE  FAMILY  GASTEROPHILIDAE 

The  adults  of  the  botflies  of  horses  (Figs.  206-208)  can  be  easily  recognized 
by  their  general  likeness  to  honeybees  and  their  persistent  flight  about  horses 
during  the  summer  months.  The  larvae  of  at  least  three  species  of  world-wide 


Figs.  206,  207,  208.  Adults  of  Gasterophilus  species.  Left  to  right:  G.  intestinalis, 
G.  haemorrhoidalis,  G.  nasalis.  (Courtesy  Department  of  Agriculture,  Division  of  En- 
tomology, Canada. 


524  MEDICAL  ENTOMOLOGY 

distribution  have  been  reported  as  causing  myiasis  in  man  under  such  terms 
as  "creeping  eruption,"  "larva  migrans,"  subcutaneous  myiasis,  or  other 
terms.  In  all  known  cases  the  infection  was  due  to  invasion  by  the  first-stage 
larvae.  The  three  species  involved  are  Gastcrophilus  intestinalis  (de  Geer), 
G.  nasalis  (Linn.),  and  G.  haemorrhoidalis  (Linn.). 

The  botflies  lay  their  eggs  on  the  hairs  (Fig.  209) ;  G.  intestinalis  on  various 
parts  of  the  body,  usually  inside  the  knees;  G.  haemorrhoidalis  about  the  lips 

-FT  and  mouth;  and  G.  nasalis  under 
the  jaw.  By  accident  they  may  be 
deposited  on  the  hairs  of  man. 
Tamura  (1921)  summarizes  43 
reports  from  literature  and  of 
these  the  causative  agent  was  de- 
termined in  only  six  cases.  Four 
cases  of  "creeping  eruption"  due 
to  the  larvae  of  G.  intestinalis 
and  one  caused  by  the  larva  of 
G.  haemorrhoidalis  have  been  re- 
ported from  America.  Of  these, 
four  were  from  Manitoba  and 
Saskatchewan  and  one  from  Ne- 

Fig.  209.  Eggs  of  botflies  as  laid  on  hairs,  (a)   braska.  Austmann    (1926)    gives 
Gasterophilns   nasalis.    (b)    G.   intestinalis.    (c)   an  interesting  account  of  his  case. 


G.  haemorrhoidalis.   (After  Hadwen  and  Cam 
eron.) 


The  larva  was  located  in  the  fore- 


arm and  the  physician  saw  the 
case  about  four  weeks  after  the  beginning  of  the  infection.  The  larva  migrated 
at  about  the  rate  of  1.5  cm.  per  day.  Iodine  treatment  for  two  weeks  failed. 
Then  the  physician  cleared  the  skin  with  light  machine  oil,  observed  the  active 
larva  in  the  skin,  and  removed  it  with  a  needle.  The  larva  proved  to  be  the  first 
instar  of  G.  intestinalis.  Montgomery  (1930)  describes  a  Gasterophilus  infec- 
tion in  an  elderly  farmer  in  Minnesota  and  gives  an  extended  account  of  the 
lesion  and  the  pathology  of  the  infection.  Several  cases  of  "creeping  eruption" 
due  to  Gasterophilus  larvae  have  also  been  reported  from  Russia.  In  order  that 
physicians  may  recognize  these  larvae,  illustrations  of  the  three  common 
species  are  given  (Fig.  210)  and  the  typical  posterior  spiracles  (Fig.  212). 

THE  FAMILY  SYRPHIDAE 

The  Syrphidae  constitute  one  of  the  largest  families  of  flies.  The  great 
majority  are  brightly  colored  flies  and  love  the  sunshine.  On  account  of  their 


MYIASIS  OF  MAN  AND  ALLIED  CONDITIONS 


525 


flight  habit — remaining  continuously  on  the  wing  and  hovering  near  ^e 
same  spot — they  have  been  called  "hover  flies."  Some  species  closely  reser?ene 
bees,  especially  the  drone  bees,  wasps,  or  hornets.  The  most  distinguishing  char- 
acter of  the  adults  is  the  presence  of  the  spurious  vein  (Fig.  211,  Sp.)  in  the 
wing.  In  this  family  practically  only  two  genera,  Tubijera  (Eristalis)  and 
Syrphus,  need  be  considered. 

Tubijera  (Eristalis)  tenax  (Linn.),  the  drone  fly,  is  a  rather  large  fly  (Fig. 
2r T)  resembling  the  drone  bee.  The  adults  may  be  seen  flying  over  open  cess- 


Fig.  210.  Larvae  of  Gasterophilus  species.  Left:  G.  haemorrhoidalis.  Center:  G.  intesti- 
nal is.  Right:  G.  nasal  is. 

pools,  water  heavily  charged  with  rotting  animal  matter,  and  liquid  manure 
and  about  open  privies,  the  effluent  from  septic  tanks,  etc.,  near  or  on  which  they 
deposit  their  eggs.  The  larvae  are  very  distinctive  (Fig.  211)  and  are  known 
as  "rat-tailed  maggots."  Though  their  larval  habitat  should  mitigate  against 
human  infection,  a  rather  large  number  of  cases  of  intestinal  myiasis  of  man 
caused  by  the  larvae  of  this  or  related  species  is  on  record.  Hall  and  Muir 
(1913)  carefully  investigated  all  known  cases  and  listed  13,  12  intestinal  and 
i  nasal.  In  1918  Hall  recorded  another  case  in  a  boy  18  years  of  age.  This 
patient  passed  a  rat-tailed  maggot  in  his  stool.  The  symptoms  were  intense 
irritation  of  the  rectum.  At  this  time  a  total  of  20  cases  were  listed — 18  in  man 


5a6  MEDICAL  ENTOMOLOGY 

(fo-  intestinal,  i  nasal)  and  2  (vaginal)  in  cows.  Since  then  Pumpelly  has  re- 
x  as  ed  a  case  in  a  man  30  years  of  age,  residing  in  Virginia.  The  patient,  suf- 
fering from  constipation,  had  passed  worms  in  his  stools.  Treatment  with 
carbon  tetrachloride  resulted  in  the  evacuation  of  six  larvae,  all  Tubijera 
tenax  (?).  Another  case  has  been  reported  from  Argentina,  a  i5-month-old 
child  evacuating  larvae  after  treatment,  and  one  from  the  Federated  Malay 


Fig.  211.  The  rat-tailed  maggot,  Tubijer  tenax.  Upper:  The  adult.  Lower: 
The  larva.  Note  the  long  telescoped  breathing  tube.  Sp,  spurious  vein. 

States.  Bruce  has  also  reported  a  case  of  vaginal  myiasis  in  a  cow  in  British 
Columbia.  The  vagina  was  diseased  and  the  author  thinks  the  fly  deposited 
her  eggs  directly  on  the  exudate.  In  all,  12  maggots  were  recovered.  Swartz- 
welder  (1942)  reports  removing  7  maggots  after  treatment  of  a  six-year-old 
child  in  Louisiana. 

Infection  with  Tubijera  larvae  would  seem  only  possible  from  drinking 
fouled  water  containing  young  larvae  or  eggs,  from  soiling  the  hands  with 
wastes  on  which  young  larvae  or  eggs  were  present,  from  eating  unwashed 
water  cress  obtained  from  filthy  water,  or  in  some  cases  from  eating  rotting 


MYIASIS  OF  MAN  AND  ALLIED  CONDITIONS  527 

fruit.  Though  T.  tenax  is  the  most  commonly  reported  species  whose  larva 
causes  myiasis,  other  species,  T.  arbustorum  and  T.  dimidiatus,  have  also  been 
incriminated.  It  may  be  pointed  out  here  that  species  identification  of  Tubi- 
fcra  larvae  is  probably  impossible  at  present.  All  specific  references,  except 
where  the  adult  has  been  reared,  should  be  regarded  as  doubtf v/b  T.  tenax  is, 
however,  our  most  common  species,  world-wide  in  distribution,^ _.d  numerous 
cases  of  infestation  have  been  reported. 

Syrphus  larvae  have  also  been  reported  as  causing  intestinal  myiasis  by 
Austen,  Patton,  and  Mumford.  As  the  larvae  of  Syrphus  are  practically  all 
predacious,  feeding  largely  on  plant  lice,  infection  must  have  taken  place  from 
eating  unwashed  greens  or  vegetables  as  lettuce,  spinach,  celery,  cabbage,  etc., 
the  larvae  being  swallowed  along  with  the  lice.  In  all  human  infections  so 
far  reported  the  Syrphus  larvae  were  dead  when  evacuated. 

OTHER  CASES  OF  MYIASIS 

Patton  and  Evans  (1929)  describe  a  urinary  myiasis  due  to  the  larvae  of 
Psychoda  albipennis  (family  Psychodidae)  in  a  young  boy.  One  of  the  larvae 
was  obtained  directly  from  the  bladder  with  the  aid  of  the  cystoscope.  How 
infection  took  place  is  not  clear,  the  authors  conjecturing  invasion  through 
eating  of  infested  soil  and  the  passage  of  the  larvae  from  the  rectum  to  the 
bladder.  Okada  (1927)  reports  a  gastric  myiasis  caused  by  the  larvae  of  Psy- 
choda b.  punctata  Curt.  The  patient,  a  girl  of  seventeen,  vomited  living  larvae. 
Austen  (1912)  records  an  intestinal  infection  by  the  larvae  of  Megaselia 
(Apiochaeta)  scalaris3  (Phoridae).  A  European,  resident  in  Burma,  passed 
the  larvae  in  his  stools  for  about  a  year.  The  infection  was  supposed  to  have 
originated  from  infested  candied  bael  fruit  that  he  had  eaten.  Despite  all 
precautions  the  patent  continued  to  pass  not  only  larvae  every  few  months  but 
puparia  and,  on  one  occasion,  8  to  12  flies.  It  is  believed  that  the  fly  bred  con- 
tinuously in  the  intestine — the  adults  mating,  eggs  being  deposited,  and  the 
cycle  continuing.  The  fly  is  widespread  in  its  distribution,  breeds  readily  in 
decaying  meat,  animal  matter  of  all  kinds,  various  foodstuffs,  dead  insects, 
and  similar  substances.  Patton  records  breeding  generation  after  generation 
of  the  fly  in  small,  corked  glass  tubes.  He  believes  that  this  fly  commonly 
causes  intestinal  myiasis  but  is  overlooked  because  of  its  small  size.  Wright 
(1927)  reports  an  interesting  case  of  ophthalmomyiasis  due  to  this  fly  in  a 
patient  in  a  hospital  at  Madras.  The  crusted  keratitis  of  the  cornea  was  thor- 
oughly washed  with  sterilized  saline  solution  and  the  crust  then  removed. 
It  was  broken  up,  cultures  made  on  blood-smeared  agar,  and  later  subcultured. 

8  Also  called  repicta,  xanthina,  jerruginca,  circumsetosa. 


528  MEDICAL  ENTOMOLOGY 

In  a  week  Wright  found  all  his  cultures  infested  with  maggots.  These  were 
reared  and  the  adults  proved  to  be  Megaselia  (Apiochaeta)  scalaris.  Van  Slyke 
(1932)  found  live  eggs  in  stools  of  natives  of  the  Belgian  Congo  and  reared 
adults. 

The  larvae  of  the  cheese  skipper  (Piophila  casei,  family  Piophilidae)  have 
been  reported  many  times  as  causing  a  mild  intestinal  myiasis.  The  larvae 
normally  live  in  cheese,  hams,  bacon,  beef,  smoked  fish,  and  similar  foods. 
The  larva  has  the  marked  ability  of  coiling  on  itself,  placing  its  mouth  parts 
in  the  hollow  just  behind  the  posterior  spiracles  and  then,  by  a  sudden  release, 
to  jump  considerable  distances  (6  inches  vertically  or  10  inches  horizontally), 
hence  the  name  "cheese  skipper."  As  cheese  is  one  of  its  favorite  breeding 
grounds,  man  becomes  infected  by  eating  "maggoty"  cheese,  a  dish  considered 
a  delicacy  by  some  people.  It  also  may  be  ingested  from  infected  meat  of  all 
kinds.  The  larva  is  muscoid  in  shape,  6  to  8  mm.  in  length  when  mature,  with 
a  rather  powerful,  cephalopharyngeal  skeleton.  The  posterior  spiracles  are 
situated  at  the  ends  of  two  processes  on  the  dorsal  surface  of  the  eighth  seg- 
ment and  appear  as  two  separate  brownish  structures.  Each  spiracle  is  rounded 
with  three  straight  slits  that  are  directed  inwards  and  backwards.  Though 
this  larva  rarely  causes  much  disturbance  in  the  human  intestinal  tract,  Ales- 
sandrini  reports  that  it  is  very  resistant  to  drugs  and  chemicals,  that  in  many 
cases  lesions  and  slight  hemorrhages  may  occur  owing  to  the  abrasive  action 
of  the  mouth  hooks,  and  patients  may  suffer  from  colicky  pains  and  head- 
aches. Simmons  (1927)  states  the  larvae  pass  through  the  intestines  of  dogs 
alive  and  cause  lesions.  It  is  said  to  be  common  among  soldiers  in  military 
camps. 

Recently  Shrewsbury  (1930)  reports  a  case  of  intestinal  myiasis  in  a  child 
due  to  the  larvae  of  Rhyphtts  fenestralis  Scop.  The  enteritis  cleared  up  after 
the  child  passed  some  four  larvae  during  a  period  of  three  weeks.  Meleney 
and  Harwood  (1935)  investigated  a  case  of  intestinal  myiasis  caused  by  Her- 
metia  illucens  Linn,  (family  Stratiomyidae)  in  a  ten-year-old  boy  at  Nash- 
ville, Tennessee.  They  reared  the  maggots  that  had  caused  irritation  in  stomach 
and  intestine  with  fainting  spells.  Infestation  probably  came  from  eating  raw 
fruit  or  vegetables.  Canavan  (1936)  reports  a  similar  case  by  this  fly  in  a  six- 
year-old  boy.  Irritation  was  severe  with  fever  of  104°  F.,  vomiting,  diarrhea, 
and  pains.  With  discharge  of  maggots  the  child  recovered. 

SCOLECIASIS 

Infection  by  lepidopterous  larvae  is  rather  rare  and  the  reported  human 
cases  are  of  doubtful  validity.  Hope  (1840)  designated  this  type  of  parasitism 


MYIASIS  OF  MAN  AND  ALLIED  CONDITIONS  529 

as  scoleciasis  and  records  some  seven  cases.  The  only  seemingly  reliable  case 
is  that  of  a  boy  who  repeatedly  ate  raw  cabbage  and  later  vomited  larvae  of 
the  cabbage  butterfly,  Pieris  brassicae.  As  far  as  the  writer  is  aware,  no  authen- 
tic cases  are  reported  in  recent  literature. 

CANTHARIASIS 

Accidental  myiasis  by  Coleoptera  (beetles)  has  been  designated  canthariasis 
by  Hope.  He  tabulated  all  known  cases  at  that  time.  Instances  of  such  in- 
vasions are  not  rare  but  most  of  them  are  of  doubtful  validity.  Reported  cases 
relate  to  the  larvae  of  the  Dermestidae  (the  larder  beetles)  or  the  Teneb- 
rionidae  (the  food-infesting  species).  Infection  probably  occurs  through  the 
eating  of  cereals,  breakfast  foods,  and  so  forth  containing  the  eggs  or  very 
young  larvae.  Most  of  the  cases  refer  to  Tenebrio  molitor,  the  common  meal 
worm.  This  worm  is  one  of  the  important  hosts  of  the  cysticercoid  of  the 
tapeworm,  Hymenolepis  diminuta,  a  parasite  of  rats,  mice,  and  occasionally 
man.  Hinman  and  Faust  (1932)  summarize  the  known  cases  in  America — in 
all,  44  infections  of  this  tapeworm  in  man.  They  also  list  the  recorded  cases 
of  this  meal  worm  from  humans,  some  18  cases,  and  report  two  new  cases; 
one  a  woman  who  vomited  a  mature  larva  and  the  second  a  patient  under- 
going a  tonsilectomy  in  whose  tonsil  a  larvae  was  found.  Palmer  (1946)  re- 
ports an  infection  in  a  four-month-old  baby,  never  breast-fed.  The  infection 
lasted  for  over  four  months,  the  baby  passing  living  larvae  of  this  beetle  at  inter- 
vals. Infection  is  assumed  from  the  feeding  of  infested  precooked  cereals.  Lig- 
gett (1931)  reports  a  peculiar  rhinal  myiasis  in  a  young  girl  due  to  the  in- 
vasion of  larvae  of  Attagenus  piccus  Oliv.  (the  black  carpet  beetle).  Several 
workers  in  India,  South  Africa,  and  Ceylon  have  reported  a  peculiar  type 
of  intestinal  myiasis  caused  by  the  presence  of  scarabaeid  beetles.  The  beetles 
(Onthophagus  bijasciatus,  O  unijasciatus,  and  Caccobius  mutans)  were  passed 
alive  in  the  stools.  The  infections  occurred  only  in  young  (three-  to  eight- 
year-old)  children  and  the  method  of  invasion  may  be  surmised.  Sharpe  (1947) 
lists  an  unusual  intestinal  myiasis  by  Ptinus  *«*#/(Ptinidae). 

GROUPING  OF  MYIASIS-PRODUCING  FLIES  4 

The  following  outline  according  to  Patton  (1921)  presents  more  accurately 
our  present  knowledge  of  myiasis-producing  flies.  Such  flies  may  be  placed 
in  three  groups:  (i)  specific  myiasis-producing  flies,  (2)  semispecific  myiasis- 
producing  flies,  and  (3)  accidental  myiasis-producing  flies. 

4  For  a  complete  list  consult  James  (1947). 


530  MEDICAL  ENTOMOLOGY 

SPECIFIC  MYIASIS-PRODUCING  FLIES:  In  this  group  belong  those 
flies  that  are  obligatory  parasites.  They  may  cause  various  types  of  myiasis 
such  as  cutaneous,  aural,  nasal,  and  intestinal.  The  following  list  includes 
practically  all  the  known  flies  that  are  obligatory  parasites  causing  myiasis. 

Cordylobia  anthropophaga  (Africa),  Chrysomya  bezziana  (Africa,  India, 
the  Philippine  Islands),  Wohljahrtia  magnified  (Europe,  Asia,  Africa),  Wohl- 
fahrtia  vigil,  Callitroga  americana  (North  America),  and  all  species  of  the 
family  Oestridae  (including  also  the  recently  separated  familes  Gasterophilidae, 
Cuterebridae,  and  Hypodermatidae). 

SEMISPECIFIC  MYIASIS-PRODUCING  FLIES:  This  group  includes 
those  flies,  the  females  of  which  normally  oviposit  or  larviposit  on  fresh  or 
decaying  animal  or  vegetable  matter  but  may  lay  their  eggs  or  larvae  in  sores, 
wounds,  skin  abrasions,  diseased  organs  emitting  foul  discharges  (as  the  nose, 
ears,  genital,  or  other  organs),  etc.  The  females  of  such  flies  are  apparently 
attracted  by  foul  odors  to  their  places  of  oviposition  and  hence  any  suppurat- 
ing wound  or  foul  discharge  on  a  living  animal  may  serve  as  the  attractant. 
The  following  list  includes  the  more  important  species  of  flies  that  have  been 
found  invading  human  tissues : 

CALLIPHORIDAE — Callitroga  (Chrysomya)  macellaria,  Chrysomya  bezziana, 
Calliphora  vomitoria,  Calliphora  vicina  (erythrocephala),  Lucilia  sericata, 
Lucilia  caesar  (?),  L.  ittustris,  Phormia  regina;  MUSCIDAE — Musca  domestica, 
Muscina  stabulans.  SARCOPHAGIDAE — Sarcophaga  haemorrhoidalis,  Sarcophaga 
juscicauda,  Sarcophaga  chrysostoma,  Sarcophaga  spp.  ANTHOMYIIDAE — Fannia 
canicularis,Fanniascalaris.  PHORIDAE — Megaselia  (Apiochaeta)  scalaris. 

ACCIDENTAL  MYIASIS-PRODUCING  FLIES:  In  this  group  belong 
those  flies  whose  eggs  or  larvae  are,  in  some  way,  taken  accidentally  into  the 
alimentary  tract  of  man ;  or,  in  some  cases,  the  flies  may  oviposit  on  the  fouled 
anal  region  or  urinary  organs  and  the  larvae  thus  gain  entrance.  The  following 
list  gives  the  more  important  species  of  flies  reported  from  the  alimentary 
tract  or  urinary  organs: 

MUSCIDAE— Musca  domestica  (intestinal  and  urinary  myiasis),  Muscina 
stabulans,  Stomoxys  calcitrans  (intestinal  myiasis).  ANTHOMYIIDAE — Fannia 
canicularis  and  Fannia  scalaris  (intestinal  and  urinary  myiasis).  SARCOPHAGI- 
DAB — Sarcophaga  haemorrhoidalis t  S.  juscicauda,  Sarcophaga  spp.  (all  intes- 
tinal myiasis).  SYRPHIDAE— T#£/7e*ra  tenax,  T.  dimidiatus,  T.  arbustorum, 
Syrphus  spp.  (all  intestinal  myiasis).  PHORIDAE— Megaselia  (Apiochaeta)  sca- 
laris (intestinal  myiasis).  PiopmuDiE—Piophila  casei  (intestinal  myiasis). 
RHYPHIDAE— Rhyphus  fenestralis  (intestinal). 


MYIASIS  OF  MAN  AND  ALLIED  CONDITIONS  531 

In  conclusion  it  should  be  pointed  out  that  many  records  of  gastro-intestinal 
infections  by  fly  larvae  are  certainly  doubtful.  Causey  (1938)  fed  larvae  of  six 
different  species  of  flies  to  dogs  and  in  all  cases  the  larvae  were  found  either 
dead  or  partially  digested  in  the  stomach  and  intestines.  None  passed  through 
the  fecal  wastes  alive. 

FLY  (BLOWFLY)  LARVAE  AS  SURGICAL  AIDS 

Recently,  in  fact  since  World  War  I,  the  late  Dr.  William  S.  Baer  of  Balti- 
more has  employed  maggots  (blowfly  larvae)  for  the  treatment  of  chronic 
osteomyelitis.  This  treatment  was  the  result  of  observations  made  during  the 
war.  He  noted  that  deep  wounds,  caused  by  various  missiles,  yielded  more 
readily  to  treatment  when  infected  with  maggots.  The  maggots  devoured  the 
dead  and  dying  tissues  and,  probably  at  the  same  time,  destroyed  the  invading 
bacteria.  Thus  the  wounds  became  rather  thoroughly  cleansed  and  healing 
took  place.  The  work  with  fly  maggots  for  deep-seated  wounds  was  developed 
and  proved  highly  successful.  More  recently,  other  and  equally  effective 
methods  have  been  devised  and  maggot  treatment  is,  apparently,  not  practiced. 

KEY  TO  THE  THIRD-STAGE  LARVAE  OF  THE  MORE 
COMMON  FLIES  THAT  CAUSE  MYIASIS 5 

1.  Larva  typically  resembling  that  of  the  housefly  (Fig.  173);  the  body 

slender,  cylindrical,  tapering  anteriorly  and  more  or  less  truncate 

posteriorly    2 

Larva  large,  stout,  resembling  that  of  the  cattle  warble,  Hypoderma  spp.; 
cylindrical  or  more  or  less  flattened,  depressed  or  pear-shaped  (Fig. 

202    ,9 

Larva  with  spiny  or  fleshy  lateral,  dorsal  or  terminal  processes  (Figs. 

W^8)    l6 

2.  Last  apparent  segment  (anal)   with  a  deep  concavity  in  which  are 

located  the  spiracles  (Fig.  182);  each  dorsal  cornua  of  pharyngeal 

sclerite  with  a  deep,  posterior  incision  (Fig.  184) 

Sarcophagidae  (  Wohljahrtia  spp.,  Sarcophaga  spp.) 

Last  apparent  segment  (anal)  without  such  a  deep  concavity;  spiracles 
more  or  less  flush  with  the  posterior  face  of  the  anal  segment;  dorsal 
cornua  of  pharyngeal  sclerite  without  an  incision 3 


5  Keys  to  the  first-  and  second-stage  larvae  are  omitted  because  they  are  not  of  suffi- 
cient accuracy  to  warrant  their  use.  Such  larvae  should  be  submitted  to  specialists.  For 
more  detailed  keys  to  species  consult  James  (1947). 


532  MEDICAL  ENTOMOLOGY 

3.  Slits  of  posterior  spiracles  sinuous,  short  or  rather  long,  with  the  button 

area  usually  deep  in  the  peritreme  (Fig.  195, 4,5)  . .  Muscidae  (in  part)  4 
Slits  of  posterior  spiracles  long,  slender,  and  nearly  parallel  to  each  other 
(Figs.  194,195)  and  directed  to  button  area Calliphoridae  (in  part)  6 

4.  Posterior  spiracles  D-shaped;  three  sinuous  slits  in  each  spiracle  plate 

(Fig.  195,  4)  Musca  domestica 

Posterior  spiracles  not  D-shaped;  rounded  or  somewhat  irregular 5 

5.  Spiracular  slits  slightly  curved  and  surrounded  by  a  large,  dense  peri- 

treme (Fig.  194,  4)  ." Muscina  stabulans;  M.  spp. 

Spiracular  slits  S-shaped  with  a  dense  peritreme;  button  in  the  center 
(Fig.  195, 5)  Stomoxys  calcitrant 

6.  Peritreme  of  posterior  spiracles  complete  and  with  a  distinct  button 

(Fig.  195,  /,  3)  Calliphora,  Lucilia,  Cynomyopsis,  spp. 

Peritreme  not  complete  and  button  weak,  scarcely  discernible  or  in  a 
thinner  area  of  peritreme 7 

7.  Posterior  spiracles  with  button  located  in  a  thinner  area  of  the  peritreme 

(Fig.  195,  2)   Phormia  regina 

Posterior  spiracles  lacking  a  button,  not  indicated 8 

8.  Tracheal  trunks  extending  from  posterior  spiracles  not  pigmented  (Fig. 

187)    Callitroga  macellaria 

Tracheal  trunks  extending  from  posterior  spiracles  deeply  pigmented 
for  some  distance  (Fig.  187).  The  true  screwworm  of  America 
Callitroga  americana 

9.  Each  posterior  spiracle  with  three  distinct  slits  (Fig.  194  /,  2,  3)  10 

Each  posterior  spiracle  with  numerous  small  openings  but  without  well- 
defined  slits  (Fig.  205)  13 

10.  Larva  pear-shaped  (Fig.  202)  and  heavily  spined;  spiracular  slits  straight 

and  sunk  in  a  deep  cavity Dermatobia  hominis 

Larva  ovate;  spiracular  slits  bent  at  the  middle  and  at  most  in  a  shallow 
cavity  (Fig.  212)  Gasterophilidae  n 

11.  Spines  on  the  anterior  margins  of  the  segments  stout  and  in  a  single  row 

(Fig.  210)  G.  nasalis 

Spines  on  the  anterior  margins  of  the  segments  arranged  in  a  double  row  12 

12.  Spines  small,  tapering  to  a  fine  point;  spines  absent  on  dorsum  of  seg- 

ment ii  and  middle  portion  of  segment  10  (Fig.  210)  

G.  haemorrhoidalis 

Anterior  row  of  spines  stout,  blunter,  larger;  spines  present  on  dorsum  of 
segment  10  and  a  few  each  side  of  dorsum  of  segment  n  (Fig.  210) 
G.  intestinalis 


MYIASIS  OF  MAN  AND  ALLIED  CONDITIONS  533 

13.  Mouth  hooks  poorly  developed Hypodermatidae  14 

Mouth  hooks  well  developed 15 

14.  Posterior  spiracles  with  the  stigmatal  plate  deeply  cleft,  funnellike  toward 

the  button  (Fig.  205)  Hypoderma  bovis 

Posterior  spiracle  with  the  stigmatal  plate  more  shallowly  cleft  toward 
the  button  (Fig.  205)  Hypoderma  lineatum 

15.  Mouth  hooks  hornlike;  body  with  weak  spines;  posterior  spiracles 

heavily  sclerotized  with  button  in  the  center  and  part  of  the  plate  (Fig. 

205)    Oestrus  ovis 

Mouth  hooks  not  so  stout;  body  thickly  set  with  spines  or  stout  scales 


Fig.  212  (/<?//).  The  posterior  spiracles  of  a  larva  of  Gasterophilus  intestinalis. 
Fig.  2/3  (right) .  Second-stage  larva  of  Cuterebra  buccata. 

(Fig.  213) ;  posterior  spiracles  divided  into  plates Cuterebra  spp. 

1 6.  Larva  cylindrical,  stout,  with  a  long,  posterior  tubular  extensible  process. 

(Fig.  21 1 )   Tubijera  spp. 

Larva  not  cylindrical;  posterior  extensible  process  lacking;  with  lateral 
and  dorsal  fleshy  processes  or  spines 17 

17.  The  fleshy  processes  more  or  less  feathered  (Fig.  198)  ....  Fannia  scalaris 
The  fleshy  processes  simple,  more  spinelike  (Fig.  197) 

Fannia  canicularis 

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60:  235-237, 1945. 
King,  E.  F.    Myiasis  of  the  urinary  passages.    Jl.  Amer.  Med.  Assoc.,  63:  2285- 

2286,  1914. 
*Knipling,  E.  F.    A  key  for  the  blowfly  larvae  concerned  in  wound  and  cutaneous 

myiasis.    Ann.  Ent.  Soc.  Amer.,  32:  376-383,  1939. 
Lanford,  }.  A.,  and  Warner,  C.  M.    Human  myiasis  due  to  ox  bot-fly  larvae 

(Hypoderma  llneatd).    New  Orleans  Med.  and  Surg.  Jl.,  77:  473-474,  1925. 
Larrousse,  F.    La  myiase  oculaire  a  OestruS  ovis  L.  dans  la  region  parisienne. 

Bull.  Soc.  Path.  Exot.,  14:  595-601,  1921. 
.    Nouveau  cas  de  myiase  oculaire  a  Oestrus  ovis  L.  en  France.    Ann.  Parasit. 

Hum.  comp.,  2:  274,  1924. 

Lawson,  G.  B.    Myiasis.    South.  Med.  Jl.,  22:  1003-1004,  1929. 
Leon,  N.    A  case  of  urethral  myiasis.    Jl.  Parasit.,  7:  184-185,  1921. 
Liggett,  H.    Parasitic  invasion  of  the  nose.    Jl.  Amer.  Med.  Assoc.,  96:  1571- 

1572,  1931. 
MacGregor,  M.  E.    The  posterior  stigmata  of  dipterous  larvae  as  a  diagnostic 

character.    Parasitology,  7:  176-188,  1914. 
Meillon,  B.  de.    A  note  on  two  beetles  of  medical  interest  in  Natal.    S.  Afr.  Med. 

Jl.,  1937:  479,  1937. 
Meleney,  Henry  E.,  and  Harwood,  Paul  D.    Human  intestinal  myiasis  due  to  the 

larvae  of  the  soldier  fly,  Hermetia  illucens  Linne.    Amer.  Jl.  Trop.  Med.,  15: 

45~49>  J935- 
Miller,  R.  T.    Myiasis  dermatosa  due  to  the  ox-warble  flies.    Jl.  Amer.  Med. 

Assoc.,  55:  1978-1979,  1910. 
Montgomery,  H.    Larva  migrans   (creeping  eruption).     Arch.  Dermat.   Syph., 

22:  813-821,  1930. 
Mumford,  E.  P.    Three  new  cases  of  myiasis  in  man  in  the  north  of  England, 

with  a  survey  of  earlier  observations  by  other  authors.     Parasitology,  18:  375- 

383,  1926. 
Neiva,  A.,  and  Gomes,  J.  T.    Biologia  da  Mosca  do  Berne  (Dermatobia  hominis) 

observada  em  todas  as  suas  phases.    Ann.  Paul.  Med.  Cir.,  S.  Paulo,  8:  197-209, 

1917. 
Okada,  J.  K.     Un  cas  nouveau  de  myiase  du  tube  digestif  cause  par  la  larve  de 

Psychoda  b.  punctata  Curt.    Ann.  Parasit.  Hum.  Comp.,  5:  105-106,  1927. 
Palmer,  E.  D.    Intestinal  canthariasis  due  to  Tenebrio  molitor.    Jl.  Parasit.,  32: 

54-55,  1946. 
Patton,  W.  S.    Notes  on  the  myiasis-producing  Diptera  of  man  and  animals.    Bull. 

Ent.  Res.,  12:  239-261,  1921. 
* .    Some  notes  on  Indian  Calliphorinae.    Ind.  Jl.  Med.  Res.,  8:  17-29,  1920; 

9:  548-574,  635-691,  1921-1922.    (See  also  other  articles  by  the  author  in  this 

journal.) 


MYIASIS  OF  MAN  AND  ALLIED  CONDITIONS  537 

*Portchinsky,  J.  A.    Oestrus  ovis  L.;  its  life-history  and  habits,  the  methods  of 

combatting,  and  its  relation  to  human  beings.    Mem.  Bur.  Ent.  Sci.  Commit., 

Central  Bd.  Land  Admin,  and  Agr.,  St.  Petersburg,  10,  No.  3,  1913.    (Extensive 

account.    Translation  in  the  Cornell  Univ.  Library.) 
.     Wohljahrtia  magnified  Schin.  and  allied  Russian  species.  The  biology  of 

this  fly  and  its  importance  to  man  and  domestic  animals.    Mem.  Bur.  Ent.  Sci. 

Com.,  Min.  Agr.  Petrograd,  9,  1916.    (In  Russian.) 
Pumpelly,  W.  C.    Case  of  human  infestation  by  larvae  of  the  fly  Eristalis  tenax. 

Jl.  Amer.  Med.  Assoc.,  84:  37,  1925. 
Rennie,  J.    A  case  of  intestinal  myiasis  in  a  breast-fed  infant.    Parasitology,  19: 

139-140,  1927. 
Sambon,  L.  W.    Observations  on  the  life-history  of  Dermatobia  hominis  (Linn.). 

Rept.  Adv.  Committee,  Trop.  Dis.  Res.  Fund  for  1914.    Appendix  vn:  119-150, 

London,  1915. 
.    Tropical  and  subtropical  diseases.    Jl.  Trop.  Med.  and  Hyg.,  25:   170- 

185,  1922. 

Sharpe,  D.  S.    An  unusual  case  of  intestinal  myiasis.    Brit.  Med.  Jl.,  i:  54,  1947. 
Shrewsbury,  J.  F.  D.    A  case  of  human  intestinal  myiasis.    Brit.  Med.  Jl.,  2: 

I043>  ^3°' 
Simmons,  P.    The  cheese  skipper  as  a  pest  in  cured  meats.    U.S.  Dept.  Agr., 

Bull.,  1453,  1927. 
Stark,  H.  H.    Ophthalmia  myiasis  externa,  due  to  the  larva  of  Oestrus  ovis. 

Jl.  Amer.  Med.  Assoc.,  81:   1684-1685,  1923. 
Stewart,  M.  A.    A  case  of  dermal  myiasis  caused  by  Phormia  regina  Meig.    Ibid., 

92:  798-799,  1929. 
Stroud,  R.  J.    Myiasis  in  the  southwest  with  particular  reference  to  the  species 

Chrysomyia  macdlaria.    Southwest.  Med.,  u,  313-316,  1927. 
Toomey,  N.    Hypodermiasis  (ox-warble  disease).    Brit.  Jl.  Dermat.  Syph.,  34: 

31-42, 1922. 
Walker,  E.  M.     Wohljahrtia  vigil  (Walker)  as  a  human  parasite.    Jl.  Parasit.,  7: 

1-7,  1920. 
.    Some  cases  of  cutaneous  myiasis  with  notes  on  the  larva  of  Wohljahrtia 

vigil  (Walker).    Ibid.,  9:  1-5,  1922. 
Wells,  R.  W.,  and  Knipling,  E.  F.    A  report  on  some  recent  studies  on  species 

of  Gasterophilus  occurring  in  horses  in  the  United  States.    Iowa  State  Coll.  Jl. 

Sci.,  12:  181-203,  1938. 

Wright,  R.  E.    Myiasis  with  chronic  degeneration  of  cornea.    Amer.  Jl.  Ophthal- 
mology, 10 :  411-412,  1927. 
Young,  J.  W.    Dermal  myiasis.    Report  of  three  cases.    Arch.  Dermat.  Syph., 

49:309-311,1944. 


CHAPTER  XVIII 


The  Siphonaptera:  Fleas 


FLEAS  are  small  wingless  insects  (Figs.  217,221)  in  which  the  body  is 
strongly  compressed  so  that  the  vertical  diameter  is  great,  the  transverse 
smalpThe  mouth  parts  are  formed  for  piercing  and  sucking;  the  meta- 
morphosis is  complete. 

Fleas  are  all,  in  the  adult  stage,  ectoparasites  of  warm-blooded  animals — 
mammals  and  birds  (one  species  has  been  recorded  from  a  snake).  They  live 
among  the  hairs  and  feathers  and  in  the  nests  of  their  hosts.  Their  compressed 
bodies,  their  long  legs,  and  their  hard,  smooth  exoskeleton  give  them  unique 
advantages  for  life  as  external  parasites.  Fleas  visit  their  hosts  primarily  for 
food,  both  males  and  females  being  bloodsuckers.  The  larval  life  is  spent  in 
the  nests,  burrows,  or  other  habitats  of  their  hosts.  Usually  each  animal  species 
or  group  of  related  species  has  its  own  particular  fleas;  though  fleas,  unlike 
many  parasites,  may  pass  from  host  to  host  with  considerable  indifference — 
as,  for  example,  cat  and  dog  fleas  readily  attack  man;  rat  fleas  will  readily  pass 
to  other  animals  and  to  man  in  the  absence  of  their  own  hosts.' 

EXTERNAL  ANATOMY 

/The  body  of  a  flea  is  composed  of  the  usual  insect  parts — a  head,  a  thorax  of 
three  segments,  and  a  ten-segmented  abdomen.  The  last  three  segments  of 
the  abdomen  are  modified  for  sexual  purposesTpig.  214  outlines,  somewhat 
diagrammatically,  the  main  features  of  the  external  structures  of  a  flea. 

(The  head  in  most  species  is  roughly  triangular  in  lateral  outline  (Fig.  214). 
The  posterior  border  articulates  with  the  thorax.  The  ventral  border  (Cteno- 
cephalides  cants)  is  armed  with  stout,  backward-projecting  spines,  the  cteni- 
dium  or  genal  comb  (Fig.  222  b).  The  antennal  groove,  situated  just  behind 
the  eye,  divides  the  head  into  two  regions — the  anterior  called  the  frons,  the 
posterior  the  occiput/The  antennal  grooves,  in  this  species,  do  not  unite  on 
the  middorsal  line. (Within  the  groove  lies  the  antenna  (Fig.  214  Ant).  The 
antenna  is  composed  of  three  segments,  the  last  one  of  which  is  larger  and 


THE  SIPHONAPTERA:  FLEAS 

Thorax 


539 


Fig.  214.  A  somewhat  diagrammatic  lateral  view  of  a  male  flea  showing  the  main 
structures  used  in  identification.  Ant,  antenna  in  antennal  groove  (G);  Cla,  claw;  Clsp, 
clasper  with  its  movable  finger  (Mp)  and  the  immovable  process  (Ps) ;  Cx,  the  coxae; 
E,  eye;  Ep,  epipharynx;  Epm.i,  epimeron  of  the  third  thoracic  segment;  Epsi  and  Epss, 
episterna  of  the  first  and  third  thoracic  segments;  F,  the  femur;  Fc,  frontal  notch;  Fr, 
the  frons;  G,  groove  for  the  antenna;  ge,  gena  on  which  the  genal  comb  is  located  when 
present;  LbPlp,  labial  palpi;  LSp,  lateral  spines  on  the  last  tarsal  joint  (also  called  plantar 
spines);  M,  maxillary  plate;  Mb,  manubrium  of  the  clasper;  Mp,  movable  process  of  the 
clasper;  MX,  maxillae  (lacinia  of  the  maxillae);  MxPlp,  maxillary  palpi;  n,  a  portion  of 
the  tergum  of  the  third  thoracic  segment;  O,  upper  bristle  is  the  occular,  lower  the  oral; 
Oc,  occiput;  PC,  prothoracic  comb  or  ctenidium;  Pe,  penis  plate;  Pen,  penis  with  the  coil 
of  springs;  Pg,  pygidium;  PI,  pleuron  of  the  second  thoracic  segment;  Ps,  immovable 
process  of  the  clasper;  Psp,  antepygidial  bristles  or  spines;  Sp,  spiracles  of  the  meso-  and 
metathoracic  segments;  2Sp-8Sp,  spiracles  of  the  abdomen;  Tar,  tarsus,  each  with  five 
segments  (1-5);  Tb,  tibia;  Tr,  trochanter.  (The  numerals  indicate  the  terga,  1-3,  i-io, 
and  the  sterna,  2-9,  of  the  thorax  and  abdomen.) 

longer  than  the  others  and  is  called  the  club  (Fig.  51),, The  club  is  divided 
into  a  number  of  pseudo-joints  by  posterior  indentations.  In  some  species  the 
club  is  divided  into  distinct  subsegments\In  front  of  the  antenna  is  the  eye,  a 
dark,  pigmented  spot.  In  fleas  there  are  no  compound  eyes  and  frequently 
eyes  are  entirely  lacking.  In  some  fleas  the  antennal  grooves  are  connected  by 
a  deep  constriction  that  renders  the  frons  capable  of  independent  movement— 


54o  MEDICAL  ENTOMOLOGY 

such  fleas  are  known  as  the  broken-headed  fleas;  the  great  majority  of  fleas  do 
not  possess  this  constriction  and  the  frons  is  not  capable  of  independent  move- 
ment. Frequently  the  constriction  is  represented  by  a  thickening  of  the  in- 
tegument, the  falx,  but  in  many  even  this  is  absent,  s  V 
'f  The  mouth  parts  (Fig.  215)  are  formed  for  piercing  and  are  located  at  the 
anterior  ventral  margin  of  the  head.  These  consist  of:  (i)  the  epipharynx 
(EP),  a  long,  slender  stylet,  deeply  concave  on  its  posterior  surface  and  lying 


Fig.  2/5.  Mouth  parts  of  the  flea.  Left:  Frontal  view  of  head  of  flea  with  the  mouth 
parts  drawn  out.  Right:  Cross  section  of  the  mouth  parts.  Ep,  epipharynx;  PC,  food 
channel;  LbPlp,  labial  palpi;  M,  maxillary  plate;  MX,  lacinia  of  the  maxilla;  MxPlp, 
maxillary  palpi;  Sga,  salivary  duct. 

in  close  approximation  to  the  lacinia  of  the  maxillae  (the  labrum  is  represented 
by  a  minute  structure  at  the  base  of  the  epipharynx).  (The  mandibles  are 
lacking.)  (2)  The  maxillae,  prominent  structures  consisting  of  a  pair  of  palpi 
(MxPlp),  a  triangular  plate  (the  maxillary  plate,  M),  and  a  pair  of  elongated 
stylets  (formerly  called  the  mandibles)  now  known  to  be  the  laciniae  of  the 
maxillae  (Mx).  Each  lacinia  is  a  long,  broad  blade,  convex  on  its  outer  surface, 
concave  on  the  inner,  and  traversed  by  a  strong  midribC.The  distal  two-thirds 
of  the  outer  wall  is  armed  with  rows  of  denticles  directed  toward  its  base.  The 


THE  SIPHON  AFTER  A:  FLEAS  541 

margins  of  the  laciniae  are  thin  and  fit  closely  together  and  to  the  epipharynx, 
forming  the  food  channel  up  which  the  blood  is  pumped.  (3)  The  labium 
consists  of  two  lateral  portions,  the  labial  palpi  (LbPlp),  united  at  their  bases 
forming  the  rostrum  or  proboscis.  Each  palpus  is  divided  into  segments, 
strongly  concave  internally,  and  so  placed  that  the  two  palpi  form  a  sheath  or 
tube  within  which  the  epipharynx  and  the  laciniae  of  the  maxillae  lie  (Fig. 
215).  (4)  Salivary  glands  are  present  with  a  distinct  salivary  pump.  The 
secretion  from  the  glands  is  injected  into  the  wound  down  a  canal  formed 
between  the  laciniae  (Fig.  215  Sga). 

The  action  of  the  mouth  parts  has  been  differently  interpreted  by  different 
workers.  According  to  Patton  and  Cragg,  the  wound  is  made  by  the  protrac- 
tion and  retraction  of  the  bladelike  laciniae.  The  maxillae  (laciniae)  and 
epipharynx  are  then  driven  into  the  wound  thus  made.  The  saliva  is  forced 
down  the  maxillary  channel  and  the  blood  is  pumped  by  the  pharynx  through 
the  tube  made  by  the  laciniae  and  epipharynx,  which  are  in  close  apposition. 
•fc^The  thorax  consists  of  three  well-defined  segments,  each  segment  bearing 
a  pair  of  legs.  A  pair  of  spiracles  is  located  just^  behind  the  pronotum  and  an- 
other pair  between  the  meso-  and  meta-thorax^In  the  dog  flea  the  posterior 
margin  of  the  pronotum  bears  a  row  of  large,  black  spines,  the  pronotal  comb 
or  pronotal  ctenidium.  ^The  legs  are  well  developed  and  adapted  for  leaping 
and  rapid  movement  among  the  hairs  or  feathers  of  their  hosts.  Each  leg  (Fig. 
214)  consists  of  a  coxa,  trochanter,  femur,  tibia,  and  tarsus,  the  latter  com- 
posed of  five  segments.  The  last  pair  of  legs  is  usually  larger  than  the  others 
and  functions  extremely  well  in  the  act  of  jumping. 

(  The  abdomen  consists  of  at  least  ten  segments,  of  which  nine  can  be  readily 
recognized.  The  last  three  segments  arc  greatly  modified  for  sexual  purposes 
and,  in  the  male,  present  the  most  striking  and  bizarre  structures  (Fig.  214). 
In  the  female  the  abdomen  appears  ovoid  in  shape  and  ends  rather  bluntly. 
Within  the  abdomen  of  the  female  can  be  seen  the  spermatheca,  a  rather  strik- 
ing, somewhat  pigmented  organ  (Fig.  223).  This  organ  varies  greatly  in  shape 
in  different  species  and  is  used  extensively  for  taxonomic  purposes.  The  terga 
and  sterna  of  the  various  segments  can  be  easily  recognized.  On  the  posterior 
marginofjhejeventh  segment  is  located  the  antcpyg^aj_bristle  or.  iiLmany 
spccieffibristlcsXFig.  214,  Psp).  In  the  figure  it  consists  of  three  macrochaetae, 
one  on  each  side  of  the  middle  one  that  projects  backwards.^ack  of  the  eighth 
segment  is  located  a  small,  more_or  jless  heart-shaped  area,  the  pygidium  (Pg)> 
part  of  the  tergum  of  the  tenth  segment.  Its  function  is  not  known.  It  bears 
many  setae  arising  from  clear,  circular  areas.  It  probably  is  sensory  in  function. 
Below  the  pygidium,  arising  from  a  slight  elevation,  is  a  group  of  rather  stout 


542  MEDICAL  ENTOMOLOGY 

setae,  the  anal  stylets.  The  spiracles  normally  number  ten,  two  on  the  thorax 
and  eight  on  the  abdomenj) 

BIONOMICS  OF  FLEAS 

LIFE  HISTORY :  The  eggs  are  ovoid  in  shape  and  white  or  creamy  white  in 
color.  They  are  deposited  either  in  the  nest,  burrow,  or  similar  abode  of  the 
host  or  laid  on  the  host  while  the  females  are  feeding.  They  are  not  glued  to 
the  host  but  are  laid  among  the  hairs  or  feathers,  whence  they  fall  off  com- 
monly in  the  sleeping  places  or  in  the  haunts  most  frequented  by  their  hosts. 
Pulex  irritans,  the  human  flea,  is  said  to  lay  most  of  its  eggs  when  free  from 
its  host.  As  a  result  the  haunts,  resting  places,  burrows,  and  iiesMnDecome 
heavily  infested  with  the  eggs  and  larvae,  and  the  newly  emerging  adults  find 
ready  access  to  their  favorite  hosts, 


Fig.  2/6  (left) .  The  common  rat  flea,  Nosopsyllus  jasciatus.  Larva  above  and 
pupa  below.  (After  Bishopp.) 

Fig.  2/7  (right).  Adult  female  of  Nosopsyllus  jasciatus.  (After  Bishopp.) 

The  eggs  hatch,  depending  on  moisture  and  temperature,  in  from  2  to  12 
days.  The  young  larvae  are  minute,  active,  elongated,  legless,  and  eyeless  crea- 
tures. They  move  about  actively  in  the  dust  and  debris  in  or  near  the  nest  of 
the  host.  Development  is  very  rapid  provided  there  is  an  abundance  of  food 
and  the  temperature  and  moisture  conditions  are  favorable.  In  the  human  flea 
the  larval  period  may  be  as  short  as  nine  days  or  greatly  prolonged;  in  the  dog. 
flea  as  short  as  seven  days;  and  in  other  fleas  the  larval  period  varies  widely 
(see  Table  9).  The  larvae,  when  mature  (Fig.  216),  are  usually  less  than  one- 
fifth  of  an  inch  in  length.  They  are  slender  and  each  segment  is  provided  with 
a  number  of  bristles  that  assist  in  crawling.  The  head  is  distinct,  the  mouth 

1  For  a  full  and  detailed  discussion  of  the  external  anatomy  of  fleas,  consult  Snodgrass 
(1946). 


THE  SIPHONAPTERA:  FLEAS  543 

parts  are  of  the  biting  type,  and  a  pair  of  slender  antennae  are  present.  The 
tip  of  the  abdomen  is  provided  with  a  pair  of  fleshy  fingers,  which  aid  in  larval 
movements. 

The  larval  food  consists  of  particles  of  organic  matter  present  in  the  dust 
and  dirt  in  which  they  live.  Probably  the  most  important  source  of  food  is  the 
dried  particles  of  blood  voided  by  the  adult  fleas,  which  frequently  fall  where 
the  larvae  are  feeding. 

When  mature  the  larvae  spin  silken  cocoons  to  which  particles  of  dirt  usually 
adhere  (Fig.  216).  Within  the  cocoon  molting  takes  place  to  form  the  pupal 
stage.  The  pupal  period  varies  widely,  from  a  few  days  (7)  to  nearly  a  year, 
depending  on  a  variety  of  circumstances.  The  length  of  the  life  cycles  of 
various  species  of  fleas,  especially  of  those  of  importance  to  man,  is  shown  in 
Table  9  (from  Bishopp,  1915). 

Table  9.  Life  cycle  of  fleas  in  different  countries. 

Length  of    Length  of      Length  of      Complete 

Country  and  species  egg  larval  cocoon  life 

stage  stage  stage  cycle 


days 

days 

days 

WCC'J^S 

UNITED  STATES 

Atlantic  coast 

Ctenocephalides  cams  (dog  flea)   . 

2-4 

8-24 

5-7 

2-4 

NosopsyHus  jasciatus  *  (rat  flea)  . 

6 

13 

18 

37  days 

Pacific  coast 

Pulex  irritant  (human  flea)  

7-9 

28-32 

30-34 

9-1  r 

NosopsyHus  fasciatus    

5-6 

24-27 

24-26 

7-8 

Xcnopsylla  cheopis   (Oriental   rat 

flea)    

Q-I3 

32-34 

25—30 

Q—  II 

Oropsylla  montana  (ground  squir- 

.^     j 

j    j^ 

y     A 

rel  flea)    

7-8 

26-28 

24—27 

8-0 

EUROPE 

~T     ~  / 

1  j 
days 

Pulex  irritans  

4-12 

8-100 

6-220 

19-264 

Ctenocephalides  canis  

8-14 

12-142 

io-354 

35-366 

NosopsyHus  fasciatus   

5-14 

1  2-  1  14 

3-450 

20-467 

Xcnopsylla  cheopis   

10  or  less 

14-84 

9-191 

31-256 

INDIA 

Xenopsylla  cheopis   

2 

7 

7-14 

21-22 

AUSTRALIA 

weeks 

Pulex  irritans  

6 

12 

14 

4-6 

T    v 

'  At  Ithaca,  New  York  (unpublished  thesis  by  Stanford). 

BREEDING  PLACES:  Fleas  breed  in  a  great  variety  of  places  when  the 
conditions  of  moisture  and  temperature  are  right  and  food  is  available.  In 


544  MEDICAL  ENTOMOLOGY 

houses  they  are  found  in  the  cracks  and  crevices  of  the  flooring,  under  matting 
and  carpets,  and  very  frequently  in  the  dust  and  dehris  in  cellars,  especially  if 
cats  and  dogs  are  kept  as  pets  and  allowed  to  sleep  in  the  cellar.  Rat  fleas  breed 
in  granaries,  barns,  warehouses,  basements,  chicken  houses,  and  sheds.  The 
young  fleas  may  be  found  among  the  straw,  sacking,  rubbish,  and  other  waste 
about  and  in  buildings  frequented  by  rats.  Fleas  have  been  found  breeding 
in  abundance  under  corncribs  and  other  buildings  where  cats,  dogs,  chickens, 
and  other  animals  rest  during  the  heat  of  the  day.  Out  of  doors  both  the  human 
flea  and  cat  and  dog  fleas  have  been  found  breeding  in  lawns,  particularly  near 
buildings  or  under  the  shade  of  shrubbery  where  animal  or  vegetable  matter 
is  present  in  considerable  amounts.  The  writer  has  seen  lawns  at  Ithaca  heavily 
infested  with  the  cat  flea  and  also  garbage  dumps  where  fleas  were  present 
in  large  numbers. 

HABITS  OF  THE  ADULTS 

(.The  adults  are  only  periodic  parasites  on  their  hosts,  coming  to  them  pri- 
marily for  food.  Fleas  feed  at  frequent  intervals,  usually  at  least  once  a  clay  and 
sometimes  much  oftener.  The  frequent  biting  is  due  to  the  constant  dis- 
turbanceyttie  fleas  not  being  allowed  to  complete  their  meal  at  one  biting.  Also 
fleas  will  feed  to  repletion  and  still  continue  to  feed,  passing  almost  unaltered 
blood  per  anumXBlood  appears  to  be  essential  for  the  production  of  eggs. 
Fleas  readily  pass  from  host  to  host  but  the  principal  means  of  spread  is  by 
their  hosts  and  through  the  scattering  of  their  eggs  as  their  hosts  migrate  from 
place  to  placeyFleas  are  famous  for  their  powers  of  jumping  but  such  powers 
are  greatly  exaggerated  in  the  minds  of  people.  Mitzmain  found  that  the 
human  flea  could  make  a  horizontal  jump  of  at  most  13  inches;  the  maximum 
vertical  jump  did  not  reach  8  inches;  with  other  species  of  fleas  the  jumping 
powers  are  apparently  much  less. 

(Jleas  are  comparatively  long-lived.  In  rather  cool,  humid  climates  the  length 
of  life  is  much  longer  than  in  dry,  hot  climates. J3acot  (1914),  in  a  most  elabo- 
rate series  of  experiments,  showed  that  the  maximum  length  of  life  in  various 
species  was  as  follows: 

Fed  Unfed 

Pulex  irritans  (the  human  fleas) 513  days  125  days 

Nosopsyllus  fasciatus  (the  rat  flea) 106  days  95  days 

Xenopsylla  cheopis  (Indian  rat  flea)    100  days  38  days 

Ctenocephalides  cams  (dog  flea)  234  days  58  days 

Ceratophyllus  gallinae  (hen  flea)   354  days  127  days 


THE  SIPHONAPTERA:  FLEAS  545 

In  California,  Mitzmain  records  that  the  common  rat  flea  lived  for  160  days, 
the  Oriental  rat  flea  for  49  clays,  and  the  common  ground  squirrel  flea,  Orop- 
sylla  (Diamanus)  montana  for  64  days  when  fed  frequently.  In  warm  cli- 
mates the  longevity  of  unfed  fleas  is  comparatively  short.  On  the  basis  of  his  ex- 
periments, Bacot  (1914)  concludes  that  active  adults  in  favorable  situations, 
and  when  no  hosts  are  available  for  considerable  periods,  can  survive  for  the 
following  periods: 

Nosopsyllus  jasciatus   22  months 

Pulcx  irrltans  19  months 

Xcnopsylla  cheopis   10  months 

Ctenocephalides  cam's 18  months 

These  long  periods  of  survival  may  account  for  the  presence  of  fleas  in  houses, 
camps,  resorts,  and  similar  places  that  have  been  unoccupied  for  months  or 
even  a  year  or  more. 

The  reproductive  capacity  of  fleas  varies  widely,  though  comparatively  few 
exact  observations  have  been  made  on  this  point.  Bacot  records  the  maximum 
number  of  eggs  laid  by  a  single  female  of  Pitlex  irritans  over  a  period  of  196 
days  as  448,  of  which  115  were  fertile. 

CLASSIFICATION  OF  FLEAS 

The  order  Siphonaptera  contains  probably  over  1200  species  from  the  world, 
and  new  species  are  being  described  every  year.  The  order  is  divided  into  five 
or  six  families  and  far  too  many  subfamilies  and  genera.  The  following  ab- 
breviated key  will  be  of  aid  in  placing  the  species  that  are  of  importance  to 
man.  (For  more  complete  keys  consult  Ewing  and  Fox,  1943;  Fox,  1940;  Hub- 
bard,  1947;  and  the  extensive  works  of  Jordan  and  Rothschild.) 

KEYS  TO  THE  FAMILIES  OF  SIPHONAPTERA 
(And  the  More  Important  North  American  Species  Associated  with  Man)  2 

i.  Thorax  greatly  reduced;  the  thoracic  terga  taken  together  shorter  than 
the  first  abdominal  tergum;  gravid  females  greatly  distended  (Fig. 

218)  Hectopsyllidae  2 

Thorax  not  greatly  reduced;  the  thoracic  terga  taken  together  normally 
much  longer  than  the  first  abdominal  tergum  (Fig.  221)  3 


2  This  key  will  place  species  in  their  families.  Under  each  family  only  those  species 
associated  with  man  in  North  America  and  with  plague  transmission  are  given.  The 
identification  of  fleas  is  difficult  and  specialists  should  be  consulted  for  most  identifications. 


546  MEDICAL  ENTOMOLOGY 

2.  Coxa  of  third  leg  with  a  patch  of  spinelets  on  inner  surface;  abdominal 

segments  2  and  3  with  spiracles.  The  sticktight  flea  (Fig.  220) 

Echidnophaga  gallinacea  (Westwood) 

Coxa  of  third  leg  without  such  a  patch  of  spinelets;  abdominal  segments 
2  and  3  of  female  without  spiracles.  Mainly  restricted  to  warmer  re- 
gions of  world.  The  jigger  or  chigoe  (Fig.  218)  . .  Tunga  penetrans  Linn. 
3.  The  terga  of  abdomen  typically  with  only  one  transverse  row  of  setae 
(Fig.  214) ;  groove  between  frons  and  occiput  usually  absent  (the  old 

suborder  Integricipita,  in  part) ;  eyes  usually  present Pulicidae  4 

The  terga  of  abdomen  typically  with  more  than  one  transverse  row  of 
setae;  groove  between  frons  and  occiput  frequently  present.  (The  old 
suborder  Fracticipita,  in  part) 9 

4.  Genal  comb  (ctenidium)  absent  (Fig.  222  c)   5 

Genal  comb  present;  pronotal  comb  present  (Fig.  222  a)  7 

5.  Pronotal  comb  (ctenidium)  absent  (Fig.  222  c)  6 

Pronotal  comb  present.  A  typical  ground  squirrel  flea  (Fig.  222  g) 

Hoplopsyllus  anomalus  Baker 

•6.  Pleuron  of  second  thoracic  segment  (mesosternite  of  authors,  Fig.  214 
PI)  divided  by  a  stout,  vertical,  rodlike  thickening.  The  oriental  rat 

flea Xenopsylla  cheopis  (Roth.) 

Pleuron  not  so  divided.  The  human  flea Pulex  irritans  Linn. 

7.  Teeth  of  the  genal  comb  straight,  blunt,  black  spines  and  arranged 

nearly  vertically  (Fig.  222 ;').  Hosts  rabbits  and  hares  of  North  America 

Cediopsylla  simplex  (Baker) 

Teeth  of  genal  comb  curved,  sharp  spines  (7  to  8)  and  arranged  nearly 
parallel  to  long  axis  of  flea  (Fig.  222  a)  Ctenocephalides  8 

8.  Frons  high  and  well  rounded;  first  two  spines  of  genal  comb  shorter 

than  the  others  (Fig.  222  b).  The  dog  flea C.  cants  (Curtis) 

Frons  low,  flat,  and  somewhat  pointed,  all  spines  of  genal  comb  of  about 
the  same  length  (Fig.  222  a).  The  cat  flea C.  felis  (Bouche) 

9.  Head  somewhat  elongated,  ventral  flaps  present  (2  or  3)  on  each  side 

near  to  fronto-genal  angle  (Fig.  222  /).  Parasitic  on  bats 

Ischnopsyllidae 

Head  not  elongated;  ventral  flaps  absent;  not  parasitic  on  bats 10 

10.  Genal  comb  absent;  combs  on  the  abdominal  terga  frequently  present. 

Includes  the  family  Ceratophyllidae  of  authors  ....  Dolichopsyllidae  11 
Genal  comb  present;  combs  on  the  abdominal  terga  frequently  present 

, Hystrichopsyllidae  12 


THE  SIPHONAPTERA:  FLEAS  547 

11.  Pronotal  comb  of  12  or  more  spines  on  each  side.  The  chicken  flea 

Ceratophyllus  gallinae  (Schrank) 

Pronotal  comb  of  less  than  12  spines  on  each  side  (Fig.  222  d) ;  movable 
finger  of  clasper  of  male  short,  broad,  flattened,  and  without  black 

spinifrons,  only  spines.  The  common  rat  flea 

Nosopsylltts  jasciatus  (Bosc.) 

As  above  except  the  movable  finger  of  clasper  is  elongate,  sword-shaped. 
Hosts  restricted  to  species  of  ground  squirrels  (Citellus  spp.)  of  the 
western  United  States  east  to  Idaho.  Considered  an  important  vector 

of  plague  among  its  hosts  (Fig.  222  e)  

Oropsylla  (Diamanus)  montana  (Baker) 

12.  Genal  comb  consists  of  three  sharp  teeth  directed  backward.  A  common 

species  on  rabbits,  mice,  moles  and  other  small  mammals  in  the  eastern 

United  States Ctenophthalmus  pseudargyrtes  Baker 

Genal  comb  of  four  teeth  directed  backwards,  blunt  (Fig.  222  h).  A 
common  species  on  mice  and  rats Leptopsylla  segnis  (Schon.) 

IMPORTANT  SPECIES 

The  classification  of  fleas  into  families  has  not  been  accomplished  in  a  very 
satisfactory  manner,  as  illustrated  by  the  preceding  key.  In  the  following  brief 
account  the  species  are  placed,  as  far  as  possible,  in  the  families  generally  ac- 
cepted by  taxonomists. 

THE  FAMILY  HECTOPSYLLIDAE 

The  most  important  flea  belonging  to  this  family  is  Tunga  penetrans  Linn., 
the  jigger  or  sand  flea  (the  true  chigger  is  a  mite,  Eutrombicula  spp.,  see  pp. 
106-111).  It  is  one  of  the  most  annoying  pests  of  tropical  and  subtropical  coun- 
tries, where  it  frequently  occurs  in  immense  numbers.  It  is  native  to  the  New 
World  and  was  introduced  into  the  continent  of  Africa  late  in  the  nineteenth 
century.  Since  then  it  has  spread  to  India  and  parts  of  the  Far  East.  In  America 
it  occurs  in  Florida,  the  West  Indies,  Mexico,  and  Central  and  South  America. 

The  jigger  is  the  smallest  flea  known,  measuring  only  about  i  mm.  in 
length.  The  adults  are  fond  of  warmth  and  drought  and  may  be  found  in 
immense  numbers  in  dry  dust  in  and  about  human  habitations.  The  males 
and  virgin  females  attack  a  wide  range  of  hosts,  practically  all  warm-blooded 
animals.  Man  and  pigs  appear  to  be  favored  hosts,  though  cats,  dogs,  and  rats 
are  readily  attacked.  When  the  female  is  fertilized,  she  remains  on  the  host 


548  MEDICAL  ENTOMOLOGY 

and  burrows  into  the  skin.  Her  favorite  points  of  attack  are  between  the  toes, 
under  the  toenails,  in  tender  parts  of  the  feet,  and  in  similar  places.  Here, 
nourished  by  the  host's  blood,  the  eggs  begin  to  develop.  The  abdomen  now 
swells  up  almost  to  the  size  of  a  pea  (Fig.  218),  the  posterior  end  barely  reach- 
ing beyond  the  swelling  of  the  host's  skin  and  forming  a  plug  for  the  hole. 
The  eggs  mature  and  are  expelled  through  the  tip  of  the  abdomen.  When  all 
her  eggs  are  laid,  the  female  shrivels  up  and  drops  out  or  is  expelled  by  ulcera- 
tion.  The  eggs  drop  to  the  ground  and,  if  they  fall  in  suitable  situations,  hatch 
and  the  larvae  mature.  Hicks  (1930)  states  that,  under  experimental  con- 
ditions, the  eggs  hatch  in  from  three  to  four  days.  He  reared  the  larvae  on 


Fig.  218  (lejt).  The  jigger  flea,  Tunga  penetrans.  Gravid  female.  (From  Ewing.) 
Fig.  2/9  (right).  Lesions  of  hands  and  feet  due  to  the  jigger  flea,  Tunga  penetrans. 

(Photograph  by  Daniels,  from  Manson-Bahr,  Tropical  Diseases,  by  permission  of  Wm. 

Wood  and  Company.) 

dried  insects'  tissues  saturated  with  blood.  He  found  the  entire  life  cycle  took 
about  17  days.  Faust  and  Maxwell  (1930)  report  an  interesting  case  of  a  patient 
in  New  Orleans  who  became  infected  from  sitting  on  sisal  hemp  that  had  just 
been  imported  from  Yucatan.  The  infection  occurred  about  the  pubic  and 
inguinal  regions  and  the  lower  right  quadrant  of  the  abdomen.  They  found 
large  numbers  (several  hundreds)  of  the  larvae,  in  all  stages  of  development, 
in  scrapings  from  the  infested  skin.  This  finding  is  unique  as  it  is  probably 
the  first  authentic  record  of  larval  development  in  the  skin  of  a  host. 

The  wounds  made  by  the  burrowing  females  cause  itchiness  and  inflam- 
mation and  become  very  painful.  As  the  females  develop  in  size,  the  swellings 
grow  larger  and  ulceration  may  follow,  especially  after  the  females  have  dis- 
charged all  their  eggs.  These  sores,  especially  on  the  feet  (Fig.  219),  may 
become  secondarily  infected,  resulting  in  gangrene,  tetanus,  and  other  diseases. 


THE  SIPHONAPTERA:  FLEAS  549 

Children  playing  barefooted  near  piggeries  or  on  roadways  or  streets-  over 
which  pigs  arc  driven  become  heavily  infected  and  frequently  die  from  gas 
gangrene  and  tetanus.  When  the  feet  are  badly  infected,  walking  is  impossible 
and  Patton  points  out  that  in  the  East  African  campaign  during  World  War  I 
the  troops  suffered  severely  from  this  terrible  pest. 

The  treatment  for  this  flea  when  embedded  in  the  tissues  is  not  very  satis- 
factory. Each  flea  can  be  removed  under  aseptic  conditions  by  enlarging  the 
entrance  hole  with  a  clean  needle  and  carefully  removing  the  entire  flea.  The 
wound  should  then  be  thoroughly  sterilized  and  dressed.  Tt^  proper  prophy- 
laxis is  the  wearing  of  boots  or  shoes  with  close-fitting  leggings  in  regions 


Fig.  220.  Echidnophaga  gallinacca.  Left:  The  adult  female.  Right:  The  head  of  a 
rooster  infested  with  this  flea.  (After  Bishopp.) 

where  the  flea  is  abundant;  the  housing  of  domestic  animals  as  pigs  and  fowls 
away  from  human  dwellings;  the  cleaning  of  yards  and  dwellings  of  dust, 
debris,  and  other  refuse  so  as  to  reduce  the  breeding  grounds;  and  forbidding 
the  driving  of  infected  animals  over  roads,  streets,  and  other  places  frequented 
by  barefooted  children.  Several  other  species  of  this  genus  are  known:  one, 
from  China,  in  the  ears  of  rats;  one  from  Peru,  and  a  few  more  from  different 
parts  of  the  world.  They  are  not  reported  as  attacking  man. 

The  "sticktight"  flea,  Echidnophaga  gallinacea  (Fig.  220),  ii'-an  important 
pest  of  poultry  in  most  tropical  and  subtropical  countries.  It  is  very  prevalent 
in  the  southern  and  southwestern  parts  of  the  United  States  and  occurs  as  far 
north  as  New  York,  Minnesota,  and  Oregon.  It  is  a  small,  dark-colored  flea 
and,  unlike  its  relatives,  does  not  move  about  after  it  once  has  obtained  a 
feeding  ground  but  remains  attached,  with  its  mouth  parts  deeply  embedded, 


550  MEDICAL  ENTOMOLOGY 

for  days  or  weeks.  It  is  also  gregarious  and  localizes  in  dense  masses  as  on  the 
heads  of  poultry  and  the  ears  of  dogs  or  cats.  Bishopp  reports  it  as  frequently 
attacking  dogs,  cats,  rabbits,  ducks,  turkeys,  and  only  occasionally  man.  It  is 
not  known  to  parasitize  man  to  any  extent,  though  children  may  become  in- 
fested. 

THE  FAMILY  PULICIDAE 

HUMAN  FLEA:  Pulex  irritans  Linn.  (Figs.  221,222  c)  is  known  as  the 
human  flea.  It  occurs  in  practically  every  part  of  the  earth  frequented  by  man 
and  man  is  its  primary  host.  It  also  attacks  badgers,  skunks,  dogs,  squirrels,  and 


Fig.  221.  Pulex  irritans,  the  human  flea.  Left:  Male.  Right:  Female.  (After  Bishopp.) 

other  animals.  It  is  said  to  be  the  predominant  flea  on  the  Pacific  coast,  where 
it  is  very  annoying  to  man.  It  can  be  distinguished  from  the  other  common 
fleas  by  the  characters  given  in  the  keys.  This  flea  secretes  itself  in  the  cracks 
and  crevices  of  houses,  in  floors,  rugs,  and  bedding,  coming  out  at  night,  like 
the  bedbug,  to  attack  its  hosts.  It  breeds  freely  in  all  situations  occupied  by  man 
and  is  extremely  resistant  to  all  adverse  conditions.  This  flea  may  act  as  a  vector 
of  bubonic  plague  and  should  be  regarded  as  a  dangerous  pest  during  an  out- 
break of  the  disease. 

THE  DOG  AND  CAT  FLEAS:  The  dog  and  cat  fleas  (Ctenocephalides 
canis  Curtis  and  C.  jclis  Bouche)  are  practically  cosmopolitan  in  their  dis- 
tribution. The  cat  flea  (Fig.  222  a)  is  more  abundant  in  temperate  climates 
and  is  found  as  commonly  on  cats  as  dogs  throughout  the  United  States;  in 
fact,  it  is  the  dominant  flea  of  our  domestic  pets.  The  dog  flea  (Fig.  222  b)  is 
said  to  be  more  prevalent  in  warm  climates,  though  it  is  widely  distributed 


552  MEDICAL  ENTOMOLOGY 

in  temperate  climates.  The  cat  flea  appears  to  have  a  wider  range  of  hosts; 
however,  both  species  readily  bite  man  and  have  been  taken  from  rats,  skunks, 
and  other  mammals.  The  two  species  can  be  separated  with  difficulty,  and  the 
main  differentiating  character  is  the  shape  of  the  head—short  and  rounded 
in  cams,  long  and  pointed  in  felis.  Both  species  can  be  readily  separated  from 
any  other  of  our  common  fleas  with  similar  habits  by  the  two  conspicuous 
combs,  one  on  the  head  and  the  other  on  the  pronotum.  These  two  species  are 
usually  the  common  ones  found  in  our  houses  and  are  very  annoying  on  ac- 
count of  the  avidity  with  which  they  bite  many  people.  They  sometimes  occur 
in  houses  in  enormous  numbers,  especially  where  cats  and  dogs  are  kept  as 
pets  and  have  their  sleeping  quarters  in  the  rooms  or  cellar.  These  fleas  usually 
lay  their  eggs  on  their  hosts,  and  they  drop  off  in  showers  when  the  animal 
shakes  itself  or  they  fall  off  in  the  sleeping  quarters.  Such  enormous  numbers 
of  the  cat  flea  have  been  reported  as  present  in  vacant  houses  that  when  oc- 
cupied the  residents  could  not  remain.  The  writer  has  seen  lawns  in  Ithaca 
so  heavily  infested  with  the  cat  flea  that  the  inhabitants  could  scarcely  move 
about  without  collecting  large  numbers  of  them.  Here  the  fleas  probably  bred 
in  moist,  sandy  areas  occupied  as  sleeping  quarters  by  stray  dogs  and  cats  or 
the  domestic  pets  of  the  household. 

ORIENTAL  RAT  FLEA:  Xenopsylla  cheopis,  the  Oriental  rat  flea  (Fig. 
222  /),  is  probably  the  most  important  species  because  it  appears  to  be  the  prin- 
cipal vector  of  plague.  Originally  of  African  origin  (Nile  Valley),  it  has  spread 
with  its  host,  domestic  rats,  to  all  parts  of  the  world.  It  is  essentially  a  flea  of 
warm  climates  and  does  not  become  permanently  established  in  regions  with 
long,  freezing  winters.  In  the  United  States  it  is  present  on  the  east,  south,  and 
west  coasts,  being  the  dominant  flea  in  our  southern  ports.  It  is  readily  trans- 
ported from  port  to  port  by  ship  rats,  the  black,  roof,  and  Norwegian  rats.  In 
recent  years  this  flea  has  been  found  in  various  parts  of  the  interior  of  the 
country:  Indiana  (1925),  Iowa  (1934),  Minnesota  (1936),  Tennessee  (1940), 
and  other  states  as  Illinois,  Ohio,  New  York,  and  Kansas.  Though  primarily  a 
parasite  of  rats,  it  readily  attacks  man.  Its  relation  to  disease  is  discussed  later. 

Other  important  species  are  X.  astia  Roth.,  widely  prevalent  in  the  Orient 
and  particularly  in  India;  X.  brasiliense  Baker,  an  African  species  that  is  now 
widespread  in  southern  India,  Africa,  and  South  America.  These  three  species 
are  primarily  parasites  of  rats,  mostly  of  the  black  rat  (RattuS  rattus  and  its 
varieties)  and  the  brown  rat,  Rattus  norvegicus.  The  three  species  can  be  dis- 
tinguished most  easily  by  the  shape  of  the  spermatheca  (Fig.  223).  Another 
species,  X.  eridos,  is  prevalent  on  the  rodents  of  the  South  African  veldt  and  is 


THE  SIPHON  AFTER  A:  FLEAS 


553 


associated  with  endemic  plague  occurring  there.  Many  other  species  belonging 
to  this  genus  have  been  described. 

OTHER  RODENT  FLEAS 

Here  belongs  a  group  of  fleas  that  are  not  placed  in  the  Pulicidae  but  in 
other  families.  One  of  the  most  important  species  is  Nosopsyllus  fasciatus 
(Bosc.),  the  common  rat  flea  (Figs.  217,222  d),  which  is  widely  distributed 
in  all  temperate  climates.  Its  chief  hosts  are  rats  and  mice.  It  requires  a  rather 
cool  climate  for  its  best  development.  In  Ithaca,  New  York,  the  life  cycle  re- . 


Fig.  22 j  (left).  The  spermatheca  oiXcnopsylla  species,  (a)  X.  cheopis.  (/?)  X.  brasilcnse. 
(c)  X.  astia.  (Modified  from  Rothschild.) 

Fig.  224  (right).  Intestine  of  "blocked"  flea.  Note  the  distension  of  the  esophagus  with 
fresh  blood.  FB,  fresh  blood;  O,  esophagus;  P,  proventriculus;  PC,  culture  of  plague 
bacillus;  S,  stomach.  (Redrawn  from  Bacot  and  Martin,  Journal  of  Hygiene.) 

quires  about  37  days  (the  fleas  were  reared  in  a  warm  room  during  the  win- 
ter)— egg  stage,  6  days;  larva,  13  days;  pupal  period,  18  days.  The  larvae 
apparently  require  blood  for  their  development  and  it  is  obtained  from  the  fecal 
wastes  of  the  adult  fleas.  This  flea  readily  attacks  man,  is  one  of  the  important 
agents  in  maintaining  plague  among  rats  in  nature  and  aids  in  the  spread  of 
plague  among  humans.  Oropsylla  (Diamanits)  montana  (Baker)  (acutus 
Baker)  is  a  common  squirrel  flea  in  the  western  United  States  and  readily 
bites  man.  The  larvae  live  on  the  dried  pellets  evacuated  by  the  adults.  The 
flea  is  of  importance  as  it  maintains  plague  infection  among  squirrels  and  is  a 
potential  transmitting  agent  to  man.  Other  species  are  O.  silantiewi  Wagner 
of  Mongolian  marmots  and  C.  tesquomm  of  ground  squirrels  of  Asiatic  Rus- 
sia, both  species  being  vectors  of  bubonic  plague.  Leptopsylla  segnis  is  pri- 


554  MEDICAL  ENTOMOLOGY 

marily  a  parasite  of  mice  and  rats,  will  occasionally  attack  man,  and  acts  as  a 
vector  of  plague.  Hoplopsyllus  anomalus  Baker,  a  parasite  of  ground  squirrels 
(Citellus  spp.)  in  parts  of  California  and  Colorado,  is  known  to  be  a  vector  of 
plague  among  these  animals  and  it  occasionally  feeds  on  man.  A  number  of 
other  rodent  fleas  in  various  parts  of  the  world  are  known  to  be  of  some  im- 
portance in  distributing  plague  among  their  hosts. 

I 

FLEAS  IN  RELATION  TO  MAN 

Fleas  have  at  least  three  important  relations  to  man.  These  are: 

1.  The  annoyance  caused  by  their  bites  and  the  consequent  irritation,  es- 
pecially to  susceptible  persons,  and  as  direct  causative  agents  (Tttnga  pene- 
trans)  of  diseased  conditions. 

2.  As  intermediate  hosts  in  the  developmental  cycle  of  parasitic  helminths. 

3.  As  vectors  of  disease  among  animals  and  as  vectors  of  such  diseases  to  man. 

BITES 

(_  To  most  people  the  bites  of  fleas  are  extremely  annoying.JSome  people  seem 
to  be  immune,  at  least  they  claim  they  are  never  bitten,  while  others  appear 
to  be  particularly  susceptible  and  suffer  tortures  from  even  a  single  flea.]  When 
a  flea  bites  it  injects  a  certain  amount  of  salivary  secretion  into  the  wound, 
which  probably  produces  the  irritation  and  itching.  Ordinarily  the  irritation 
subsides  in  a  short  time,  though  in  some  cases  it  does  not.  The  application  of 
soothing  lotions  such  as  menthol  and  camphor,  carbolated  vaseline,  or  mild 
solutions  of  ammonia  in  water  will  often  reduce  the  irritation. 

INTERMEDIATE  HOSTS  OF  PARASITIC  HELMINTHS 

Fleas  serve  as  the  intermediate  hosts  of  certain  tapeworms,  some  of  which 
are  occasionally  parasitic  in  man.  Dipylidium  caninum,  a  common  tapeworm 
of  cats  and  dogs,  has  as  its  intermediate  hosts  the  dog  flea,  Ctenocephalides  cams, 
and  the  human  flea,  Pulex  irritans.  The  eggs  of  the  tapeworm  are  discharged 
by  its  host  and  are  eaten  by  the  larvae  of  the  fleas.  Within  the  larvae  the  eggs 
hatch  and  the  embryos  bore  through  the  intestinal  wall  and  remain  within  the 
body  cavity  without  much  change  till  after  pupation  and  emergence  of  the 
adult  fleas.  Within  the  adults  the  cysticercoid  stage  develops,  and  new  infec- 
tions arise  from  swallowing  infected  fleas.  Although  over  a  hundred  human  in- 
fections of  this  tapeworm,  mostly  in  children,  have  been  recorded,  it  is  not  re- 
garded as  a  serious  parasite  of  man.  Children  obtain  the  fleas  by  playing  with 
cats  and  dogs  or  drinking  milk  in  which  infected  fleas  have  fallen. 


THE  SIPHONAPTERA:  FLEAS  555 

(Nosopsyllus  jasciatus,  Xenopsylla  cheopis,  and  Pulex  irritans  (?)  have  been 
recorded  as  intermediate  hosts  o£  Hymenolepis  diminuta^JrLowwcr,  this  tape- 
worm has  numerous  other  insect  intermediate  hosts  of  much  greater  signifi- 
cance to  man. 

VECTORS  OF  DISEASE 

(^PLAGUE:  Fleas  became  of  the  greatest  importance  to  man  when  it  was 
finally  demonstrated  that  rat  fleas  were  the  transmitters  of  bubonic  plague, 
Bacillus  (Pasteur ella)  pestis,  by  the  British  Plague  Commission  in  India  in 
1906-1907.  Plague  ranks  as  one  of  the  scourges  of  the  human  race,  frequently 
occurring  in  epidemic  form  and  killing  large  numbers  of  the  population.  Its 
place  of  origin  does  not  seem  to  be  definitely  known,  though  Scott  (1939) 
traces  the  disease  to  at  least  300  B.C.  (then  a  fatal  disease  in  Libya,  Egypt,  and 
Syria)  and  probably  back  to  the  time  of  Homer  (1184  B.C.).  The  first  accurate 
account  of  a  great  epidemic  was  of  the  one  that  raged  throughout  Europe  dur- 
ing the  fourteenth  century,  killing  ofl  fully  one-fourth  of  the  entire  population. 
From  then  till  near  the  end  of  the  seventeenth  century  it  was  almost  constantly 
present  in  Europe.  In  1665  the  great  plague  of  London  took  place  and  nearly 
70,000  persons  perished  out  of  a  total  population  of  460,000.  Since  then  plague 
has  appeared  sporadically  in  parts  of  Europe,  but  it  is  said  to  have  practically 
disappeared  by  the  middle  of  the  nineteenth  century.  Toward  the  end  of  the 
nineteenth  century  sporadic  outbreaks  occurred  in  certain  European  seaports; 
in  1894  it  appeared  at  Hong  Kong,  one  of  the  great  shipping  ports  of  the  world, 
whence  it  spread  by  commerce  to  nearly  all  the  seaports  of  the  world.  In  1896 
plague  appeared  in  India  (Bombay),  in  1898  in  Egypt,  in  1899  at  Manila,  the 
same  year  at  Buenos  Aires  and  Rio  de  Janeiro,  in  1900  at  San  Francisco,  and 
in  1914  in  New  Orleans.  It  has  also  become  established  in  Mexico,  Australia, 
and  other  parts  of  the  world.  Since  plague  appeared  in  India  (1898),  Heiser 
states  that  over  10,000,000  people  have  died,  the  annual  death  rate  between  1898 
and  1918  being  500,000.  At  the  present  time  the  death  rate  is  probably  less  than 
50,000  (as  of  1935).  The  widespread  introduction  of  the  disease  took  place 
largely  before  our  present  knowledge  of  its  epidemiology  was  known.  How- 
ever, there  is  constant  danger  of  fresh  introductions,  and  once  the  disease  has 
become  established  in  the  rodent  population,  particularly  in  the  wild  rodent 
population,  it  is  a  strenuous  and  expensive  fight  to  eliminate  it.  Witness  the 
introduction  into  Java,  where  over  100,000  people  perished  in  a  few  years. 
As  a  result  of  the  widespread  distribution  of  the  disease  and  its  establishment 
in  native  rats  and  other  rodents,  great  endemic  centers  are  now  known  to 
exist.  The  principal  ones  are  in  Manchuria,  Mongolia,  Central  Asia,  southeast 


556  MEDICAL  ENTOMOLOGY 

Russia,  India,  parts  of  Central  and  South  Africa,  parts  of  South  America,  and, 
in  North  America,  a  large  area  of  the  western  United  States  extending  from 
the  Pacific  coast  east  to  the  Dakotas,  Kansas,  and  Oklahoma,  south  to  Arizona 
and  New  Mexico,  and  north  to  British  Columbia.  In  this  extensive  area  natu- 
rally infected  wild  rodents  occur,  though  human  cases  are  rare, 
if  Plague  or  black  death  is  an  acute,  specific,  febrile  disease  caused  by  Pasteu- 
rella  pestis;  it  usually  spreads  to  man  from  infected  rats  through  the  agency  of 
fleasjThe  mortality  both  in  man  and  rats  is  very  high.  It  was  not  till  1894  that 
Yersin  and  Kitasato  independently  isolated  the  causative  organism,  Pasteurella 
(Bacillus)  pestis,  and  the  former  established  that  the  plaguelikc  disease  in  rats 
was  identical  with  that  in  man.  Simmonds  in  1898  suggested  that  fleas  were  the 
transmitting  agents,  and  Liston  (1905)  demonstrated  the  development  of  the 
bacilli  in  the  gut  of  Xenopsylla  cheopis,  the  Oriental  rat  flea.  The  British  Plague 
Commission  in  India  fully  demonstrated  the  role  fleas  play  in  the  dissemina- 
tion of  the  disease  (1906-1907).  Finally,  in  1914,  Bacot  and  Martin  definitely 
established  the  mechanism  by  which  infected  fleas  transmit  the  disease  from 
rodent  to  rodent  and  to  man.  Their  observations  were  made  on  Xenopsylla 
cheopis  and  Nosopsyllus  fasciatus.\When  the  fleas  imbibed  blood  containing 
Pasteurella  pestis,  definite  brownish  specks  appeared  in  the  stomach  in  a  day 
or  two.  Later  these  increased  in  size  as  cultures  of  P.  pestis  and,  in  many  cases, 
grew  to  such  an  extent  as  to  occlude  the  stomach  at  its  entrance.  Further 
growth  blocks  the  proventriculus  (Fig.  224)  and  extends  into  the  lower  end 
of  the  esophagus  (blocked  fleas).  While  this  growth  is  continuing,  the  fleas 
take  blood,  which  furnishes  an  ideal  cultural  medium  for  the  bacillus.  Fleas 
when  "blocked"  and  unable  to  pass  fresh  blood  into  the  stomach  are,  never- 
theless, persistent  in  their  efforts  to  obtain  blood.  When  they  do  the  blood 
can  only  swell  the  esophagus,  and  on  the  cessation  of  the  act  of  pumping  (by 
the  pharynx),  some  of  the  blood  is  forced  back  into  the  wound.  Such  blood 
is  heavily  loaded  with  the  plague  bacilli.  Such  infected  (blocked)  fleas  live 
for  a  considerable  time,  persist  in  their  efforts  to  feed,  and  are  a  constant 
menace  to  those  on  whom  they  attempt  to  obtain  blood.  Frequently  the  blocked 
food  canal  clears  and  the  fleas  can  feed  normally^  Fortunately,  blocked  fleas 
are  unable  to  withstand  dry,  hot  weather  and  die  off  rapidly.  In  addition,  feces 
from  infected  fleas  are  usually  virulent,  and  human  infection  may  occur  from 
scarifying  the  skin  with  fecal  wastes. 

Plague  is  essentially  a  disease  among  rodents)  Rats  suffer  from  it,  epizootics 
occurring  among  them  frequently  wherever  plague  is  endemic  or  where  it  has 
recently  been  introduced.  Man  and  other  animals  become  infected  through 
the  agency  of  infected  fleas.  (Trie  spread  of  plague  represents  an  etiologtcal 


THE  SIPHONAPTERA:  FLEAS  557 

chain — the  parasite,  Pasteurella  pestis;  the  susceptible  hosts  or  reservoirs  of  the 
disease;  and  the  vectors  (fleas).  In  this  case  fleas  are  not  true  intermediate 
hosts  but  simply  act  as  culture  media  and  protective  carriers  of  the  bacillus^  An 
outbreak  of  plague  is  practically  always  heralded  by  an  epizootic  among  rats; 
then,  the  fleas  finding  their  normal  hosts  missing,  attack  man.  The  maintenance 
and  spread  of  plague  is  dependent  on  a  great  variety  of  rather  complicated 
circumstances,  which  it  does  not  seem  wise  to  enter  into  here.  The  main  points 
that  may  be  stressed  are  the  reservoirs  of  the  disease  (rodents)  and  the  carriers 
(fleas) .  The  principal  reservoirs  from  which  man  is  infected  are  rats — Rattus 
rattus,  the  black  rat,  and  Rattus  norvegicus,  the  brown  rat,  and  their  varietiesTj 
From  these  domestic  to  semidomestic  rats,  Pasteurella  pestis  may  be  carried 
to  a  great  variety  of  wild  rodents  and  thus  a  permanent  reservoir  becomes 
established.  When  this  happens  there  is  always  constant  danger  of  an  epizootic 
among  the  wild  rodents  that  may  spread  to  the  domestic  rats  and  thence  to 
man.  The  principal  wild  rodents  that  are  known  to  serve  as  dangerous  reser- 
voirs are  marmots  (Marmota  hobac]  in  Manchuria;  and,  in  the  United  States, 
ground  squirrels  (Citellus  spp.),  mantled  ground  squirrels  (Citdlus  spp.), 
marmots  (Marmota  spp.),  prairie  dogs  (Cynomys  spp.),  chipmunks  (Euta- 
mias  spp.),  wood  rats  (Neotoma  spp.),  native  mice  (Peromyscus  spp.),  and 
some  other  animals.  According  to  Eskey  (1940),  the  main  reservoirs  in  the 
United  States  arc  in  ground  squirrels,  wood  rats,  and  prairie  clogs.  In  Central 
Asia  and  Russia  ground  squirrels  (Citellus  spp.)  serve  as  reservoirs.  The  ger- 
biles,  karroo  rats,  and  the  multimammate  mouse  (Mastomys  sp.)  are  important 
in  South  Africa.  Many  other  species  have  been  reported  from  various  parts 
of  the  world. 

A  large  number  of  fleas  has  been  shown  experimentally  to  be  vectors  of 
plague.  The  following  list,  though  not  complete,  gives  the  principal  species 
and,  as  far  as  practicable,  the  principal  regions  where  they  are  important  vectors 
of  the  disease.  Certain  species,  moreover,  are  known  to  be  "good"  or  dan- 
gerous vectors  in  one  region  and  "poor"  vectors  in  others  for  reasons  not 
clearly  understood  though  generally  given  as  climatic  factors. 

PRINCIPAL  FLEA  VECTORS  OF  PLAGUE 

Xenopsylla  cheopis  Roth.  (Oriental  rat  flea.)  Throughout  the  world  wherever 
plague  is  present  and  this  flea  occurs  in  abundance;  mainly  tropical  and 
subtropical  countries. 

Xenopsylla  astia  Roth.  Not  regarded  as  a  "dangerous"  vector;  said  to  be  of 
importance  in  drier  parts  of  India. 

Xenopsylla  brasiliense  Baker.  Experimentally  it  can  carry  plague  but  very  little 


558  MEDICAL  ENTOMOLOGY 

is  known  about  its  importance;  reported  an  important  vector  in  Kenya. 
Xenopsylla  eridos  Roth.  Regarded  as  important  in  the  spread  of  rodent  plague 

on  the  veldt  of  South  Africa. 
Nosopsyllus  jasciatus  Bosc.  (Common  rat  flea.)  Mainly  important  in  temperate 

climates  where  it  serves  to  spread  plague  among  rodents  and  probably  to 

man. 
Oropsylla  (Diamanus)  montana  Baker.  (Squirrel  flea.)  Known  to  spread 

plague  among  ground  squirrels  and  rodents  in  the  western  United  States. 
Oropsylla  silantiewi  (Wagner).  Abundant  on  marmots  of  Mongolia  and 

probably  plays  a  role  in  the  spread  of  plague. 
Ceratophyllus  tesquorum  (Wagner).  Spreads  plague  among  ground  squirrels 

in  Asiatic  Russia. 

Pulex  irritans  Linn.  Considered  an  important  vector  of  plague  during  epi- 
demics. Cosmopolitan. 
Leptopsylla  segnis  Schon.  Probably  of  little  importance  though  it  can  spread 

plague  among  rats. 
Hoplopsyllus  anomalus  Baker.  Acts  as  vector  among  ground  squirrels  of  the 

western  United  States. 
Ctenocephalides  canis  Curtis.  (The  dog  flea.)  May  be  of  importance  during 

epidemics.  Cosmopolitan. 
Ctenocephalides  felts  Bouche.  (The  cat  flea.)  Plays  a  role  similar  to  that  of  the 

dog  flea.  Cosmopolitan. 

Ceratophyllus  anisus  Roth.  Plague  vector  in  the  East  Indies. 
Stevalius  ahalae  Roth.  Plague  vector  among  field  rats  in  Java. 

SYLVATIC  PLAGUE:  In  recent  years  plague  as  found  in  wild  rodents  has  been 
designated  as  "syl vatic  plague,"  and  the  plague  endemic  in  domestic  rodents 
as  "marine  plague."  Sylvatic  plague  may,  however,  be  transmitted  to  domestic 
rodents  and  thence  to  man  or  man  may  become  infected  from  wild  rodents  if 
bitten  by  infected  wild  rodents.  Unfortunately  a  great  variety  of  wild  rodents 
are  known  to  serve  as  reservoirs  of  the  plague  organism,  Pasteurella  pestis. 
Among  these  rodents  a  large  number  of  flea  species  has  been  proved  experi- 
mentally capable  of  transmitting  plague  from  animal  to  animal.  This  means 
that  a  constant  reservoir  of  plague  may  be  maintained  from  year  to  year  and 
gradually  spread  over  the  entire  country.  In  the  United  States  wild  rodents 
(ground  squirrels)  were  first  proved  naturally  infected  in  the  region  of  San 
Francisco  Bay  in  1908.  Since  then  infection  in  a  great  variety  of  native  rodents 
has  been  demonstrated  over  the  entire  region  west  of  the  Rocky  Mountains 
and  east  to  South  Dakota,  Kansas,  and  Oklahoma  and  south  to  Arizona  and 
New  Mexico.  The  infection  appears  to  be  gradually  spreading  eastward,  and 


THE  SIPHONAPTERA:  FLEAS  559 

the  invasion  of  the  great  river  valleys  of  the  central  states  may  prove  very 
serious. 

In  order  to  restrict  plague  among  wild  rodents,  it  is  necessary  either  to  con- 
trol such  rodents  or  accurately  to  determine  their  fleas  and  to  know  which  fleas 
are  the  important  vectojrs.  If  such  vectors  are  few  in  number,  it  might  be 
possible  gradually  to  eliminate  such  fleas.  Unfortunately  all  evidence  indicates 
that  a  large  number  of  flea  species  are  capable,  experimentally,  of  transmitting 
plague  among  their  hosts.  Eskey  and  Haass  (1940)  state  that  nearly  50  species 
of  fleas  have  been  taken  from  wild  rodents  in  the  United  States  alone.  Of  this 
number  they  list  14  species  capable  of  transmitting  plague  experimentally  and 
28  species  that  became  infected  when  fed  on  infected  guinea  pigs. 

Table  10.  The  important  species  of  fleas  incriminated  as  vectors  or  experimentally  in- 
fected among  native  wild  rodents  in  North  America. 


Species 

Principal  hosts 

Distribution 

xxHoplopsyllus  anomalus  Baker 

Ground  squirrels 
(Cite/  Ins  spp.) 

Western  United  States 

*Malareus  tclchinum  (Roth.) 

Deer  mice  and  other 
wild  mice 

Western  United  States 
British  Columbia 

*Monopsyllus  ciliatus  (Baker) 

Chipmunks 

Western  United  States 

*Monopsyllus  eumolpi  (Roth.) 

Chipmunks 

Western  United  States 

°Monopsyllus  wagneri  (Baker) 

Deer  mice 
(Perornyscus  spp.) 

Western  United  States 
(east  to  Iowa);  western 
Canada 

°NeopsyIlus  in  op  in  a  Roth. 

Ground  squirrels 
(Citcllus  spp.) 

Western  United  States, 
British  Columbia 

*xOpisoci'ostis  bruneri  (Baker) 

Ground  squirrels 

Great  Plains  west  to  Rocky 
Mountains,    north    to    great 
plains  of  Canada 

xOpisocrostis  hirsutus  (Baker) 

Prairie  dogs 

Throughout    the    range    of 
prairie  dogs. 

*Opisocrostis  lab'is  (J.  and  R.) 

Ground  squirrels 

Western  United  States 
and  western  Canada 

K0pisocrostis  tuberculatus  (Baker) 

Squirrels 

Western  United  States 

xxOrchopeas  sexdentatus  (Baker) 
and  varieties 

Wood  rats 

Western  United  States 
(western  Canada) 

**0ropsylla  (Diamanus)  montana 
Baker 

Ground  squirrels 
(Citellus  spp.) 

Western  United  States 

°0ropsylla  idahoensis  (Baker) 

Ground  squirrels 

Western  United  States 

*0ropsylla  rupestris  (Jordan) 

Ground  squirrels 

Western  United  States 

and  western  Canada 


560 


MEDICAL  ENTOMOLOGY 


**Thrassis  arizoncnsis  (Baker)  Ground  squirrels         Wptern  United  States 

(southern  part) 

*Thrassis  a.  acarnantis  (Roth.)         Marmots  Northwestern  United  States; 

Western  Canada 


*Thrassis  bacchi  (Roth.) 

*Thrassis  jrancisi  (Crox) 
*Thrassis  h.  howclli  (Jordan) 

*Thrassis  pandora  Jcllison 
°Thrassis  petiohtus  (Baker) 


Ground  squirrels 


Alberta    south    through    the 
Dakotas 

Ground  squirrels       '  Utah,  Nevada,  Idaho 

Woodchuck  California,   Oregon,   Nevada, 

1      Idaho 

Ground  squirrels  /        Northwestern    United   States 
(CiteUiis  spp.)    » 

Ground  squirrels         Northwestern   United  States; 
western  Canada 


xxlmportant  vectors.        ^Experimental  transmission.        Experimentally  infected. 

ENDEMIC  TYPHUS,  MUR1NE  TYPHUS  OR  FLEA  TYPHUS:  Dyer, 
Rumreich,  and  Badger  (1931)  demonstrated  that  fleas  could  transmit  a  mild 
typhuslike  disease  from  wild  rats  to  experimental  animals.  Since  then  this  dis- 
ease has  been  demonstrated  to  be  caused  by  RicJ^cttsia  mooscri;  the  reservoir, 
rats  and  mice.  Fleas  (Nosopsyllus  jusciatns,  Xenopsylla  chcopis,  and  others), 
the  rat  louse  (Polyplax  spinulosa),  and  the  tropical  rat  mite  (Liponyssus 
bacot'i)  maintain  the  reservoir  in.  the  wild  hosts.  Man  becomes  infected  from 
the  bites  of  infected  fleas  and  mites,  from  infected  flea  feces  rubbed  into 
wounds,  or  from  foods  contaminated  by  infected  rat  urine  (see  pp.  98,  207). 

CONTROL  OF  FLEAS 

The  problem  of  flea  control  involves  a  number  of  distinct  measures.  These 
may  be  roughly  classified  as  (i)  control  of  fleas  on  domestic  pets  and  in  the 
home;  (2)  control  of  fleas  on  poultry  and  domestic  animals  and  in  their  living 
quarters;  (3)  control  of  fleas  on  rats  and  other  wild  rodents  that  are  sources  of 
plague;  (4)  prevention  of  the  spread  of  plague  by  controlling  the  movement 
of  infected  rats  and  their  fleas. 

In  private  homes  and  public  buildings  the  most  essential  and  elementary 
principle  in  flea  control,  as  with  so  many  other  inject  pests,  is  strict  cleanliness. 
/Dirty  corners,  unclean  rugs  and  carpets,  dusty  cracks  and  crevices,  greasy 
kitchens,  uncared-for  and  unkempt  Bathrooms  and  toilets,  closets  used  as 
dumping  places  for  dirty  clothing,  cellars  littered  with  rubbish  and  filth,  and 
other  uncared-for  places  where  the  e^gs  of  fleas)  undisturbed,  may  hatch  and 
the  larvae  obtain  sufficient  food  and  moisture  serve  as  constant  sources  for 


THE  SIPHONAPTERA:  FLEAS  561 

flea  multiplicatioi^jCleanliness  is  the  only  remedy^for  such  situations.  Cats 
and  dogs  are  the  main  sources  for  fleas  in  the  home  and  public  buildings. 
The  destruction  of  stray  cats  and  dogs  and  the  maintenance  of  our  pets  in  a 
clean  conditionyWith  clean  living  quarters  will  practically  assure  the  house- 
hplder  freedom  from  fleas. 

(^In  cases  of  home  infestations  the  first  procedure  is  the  destruction  of  fleas  on 
the  dogs  and  cats  and  in  their  breeding  places.  If  the  house  is  infested,  a 
thorough  treatment  with  a  5  per  cent  DDT  in  oil  (either  in  xylene,  kerosene, 
or  preferably  anthracene)  should  be  given.  This  should  be  applied  to  all  in- 
fested rooms,  spraying  the  floors  and  about  two  feet  up  the  walls.  The  cellar 
should  be  cleaned  and  given  a  thorough  spraying;  if  there  is  no  cellar,  the 
ground  beneath  the  house  should  be  sprayed^The  fleas  on  the  dogs  and  cats 
may  be  eliminated  by  dusting  them  with  a  10  per  cent  DDT  powder,  placing 
the  powder  along  the  back  and  rubbing  it  into  the  hairs.  All  out-door  premises 
such  as  kennels,  storehouses,  sheds,  and  the  ground  about  them  or  where  dogs 
and  cats  sleep  should  be  sprayed.  In  all  probability  fleas  can  be  controlled  by 
simply  dusting  with  a  10  per  cent  DDT  powder.  However,  the  powder  is 
more  annoying  in  the  household  and  young  children  may  swallow  some  of  it. 
Its  residual  efTect  is  not  so  lasting  if  the  dust  is  swept  up  or  vacuum  cleaners 
are  used.  Effective  treatments  of  houses  can  also  be  done  by  "fogging"  by  ap- 
proved operators.  In  treating  cats  it  is  best  not  to  use  too  much  DDT  as  cats 
lick  it  and  it  may  cause  sickness. 

In  large  establishments  as  public  buildings,  warehouses,  and  similar  struc- 
tures and  in  rural  areas  spraying  or  dusting  with  DDT  should  prove  effective. 
This  is  much  safer  and  the  operation  probably  just  as  or  more  effective  than 
fumigation  with  hydrocyanic  acid  gas.  Furthermore  in  buildings  infested  with 
rats  the  spray  treatment  with  10  per  cent  DDT  will  usually  reduce  the  rat  flea 
population  to  a  minimum.  In  rural  areas  experiments  in  spraying  have  given 
good  results  when  the  10  per  cent  DDT  spray  was  applied  at  such  a  rate  as  to 
leave  200  mg.  per  square  foot.  The  residual  action  is  lasting,  usually  for  three 
or  four  months.  Recently  the  work  of  Nicholson  et  al.  (1948)  demonstrated  ef- 
fective control  of  fleas,  mosquitoes,  and  the  tropical  rat  mite,  Liponysstts  bacoti, 
by  using  a  water  emulsion  of  DDT.  The  spray  was  prepared  from  a  concen- 
trate of  35  per  cent  DDT  in  xylene,  and  Triton  X-I55,  diluted  i  part  in  6  parts 
water.  The  spray  was  applied  as  for  mosquito  control:  walls,  ceilings,  and 
about  two  feet  of  the  floor  next  the  walls  were  sprayed  so  as  to  leave  a  residue 
of  300  mg.  per  square  foot.  Rat  holes,  the  cellars,  and  the  ground  beneath  the 
buildings  were  also  sprayed,  using  more  material.  All  outbuildings,  storage 
houses,  and  similar  structures  were  also  treated,  care  being  taken  to  avoid  con- 


562  MEDICAL  ENTOMOLOGY 

tact  with  food.  Such  a  treatment  indicates  effective  control  of  both  mosquitoes 
and  fleas  for  several  months  and  should  be  very  effective  in  reducing  endemic 
typhus  and  malaria. 

V  Rats  are  being  effectively  controlled  by  the  ratproofing  of  building^  and  by 
the  use,  in  experienced  hands,  of  the  newer  poisons,  1080  and  antu.  It  is  in- 
teresting to  note  that  a  plague  epidemic  at  Tumbes,  Peru,  was  completely 
stopped  in  a  short  time  by  the  use  of  a  10  per  cent  DDT  powder  and  the  poison 
1080.  The  city  of  10,000  persons  was -without  a  central  water  supply  or  a 
sewage  system.  Most  of  the  houses  were  constructed  of  bamboo  or  wattle  with 
mud  floors/ Thorough  treatments  (2  treatments)  with  the  DDT  powder  al- 
most completely  eliminated  the  fleas,,  1080  reduced  the  rat  population,  and 
plague  was  eliminated  (Macchiavello,  1946). 

REFERENCES 

Alicata,  J.  E.  Experimental  transmission  of  endemic  typhus  fever  by  the  stick- 
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*Bacot,  A.  A  study  of  the  bionomics  of  the  common  rat  fleas  and  others  associated 
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(Plague  Suppl.  n):  447-654,  1914. 

Bacot,  A.  W.  The  fleas  found  on  rats  and  their  relation  to  plague".  Jl.  Roy.  Sanit. 
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,  and  Didgewood,  W.  G.  Observations  on  the  larvae  of  fleas.  Parasitology, 

7:  157-175,  1914- 

,  and  Martin,  C.  J.  Observations  on  the  mechanism  of  the  transmission  of 

plague  by  fleas.  Jl.  Hyg.,  13  (Plague  Suppl.,  in):  423-439,  1914. 

*Baker,  C.  F.  A  revision  of  American  Siphonaptera  or  fleas,  together  with  a  com- 
plete list  and  bibliography  of  the  group.  Proc.  U.S.  Nat.  Mus.,  27:  365-470,  1904. 

.    The  classification  of  the  American  Siphonaptera.    Ibid.,  29:  121-170,  1905. 

Bishopp,  F.  C.    Fleas  and  their  control.    U.S.  Dept.  Agr.,  Farmers'  Bull.  897, 

J931- 
Blanc,  G.,  and  Baltazard,  M.     Transmission  experimental  du  typhus  murin  par  la 

puce  de  1'homme  (Pulcx  irritans).    C.  R.  Soc.  Biol.,  127:  1058-1059,  1937. 
Brigham,  G.  D.    Susceptibility  of  animals  to  endemic  typhus  fever.    U.S.  Pub. 

Hlth.  Repts.,  52:  660-662,  1937. 
.    Two  strains  of  endemic  typhus  fever  virus  isolated  from  naturally  infected 

chicken  fleas  (Echidnophaga  gallinacea).    U.S.  Pub.  Filth.  Repts.,  56:   1803- 

1804,  1941. 
Ceder,  E.  T.,  Dyer,  R.  E.,  Rumreich,  A.,  and  Badger,  L.  F.    Typhus  fever;  typhus 

virus  in  feces  of  infected  fleas  (Xenopsylla  cheopis)  and  duration  of  infectivity 

of  fleas.    U.S.  Pub.  Hlth.  Repts.,  46:  3103-3106,  1931. 


THE  SIPHONAPTERA:  FLEAS  563 

**Costa  Lima,  A.  da,  and  Hathaway,  C.  R.    Pulgas.    Instit.  Oswaldo  Cruz, 

Monograph  4,  1946. 
Cumpston,  H.  H.  L.,  and  McCaullum,  F.    The  history  of  plague  in  Australia. 

Australia  Dept.  Hlth.  Serv.,  Pub.  32,  1927. 
Davis,  David  E.    The  control  of  rat  fleas  (Xenopsylla  chcopis}  by  DDT.    U.S.  Pub. 

Hlth.  Repts.,  60:  485-489,  1945. 
Dove,  W.  E.,  and  Shelmire,  B.    Some  observations  on  tropical  rat  mites  and 

endemic  typhus.    J.  Parasit.,  18:  159-168,  1932. 
Dunn,  L.  H.    Fleas  of  Panama,  their  hosts  and  their  importance.     Amer.  Jl.  Trop. 

Med.,  3:  335-344,  1923- 

-  ,  and  Parker,  R.  R.    Fleas  found  on  wild  animals  in  the  Bitter  Root  Valley, 
Mont.    U.S.  Pub.  Health  Repts.,  38:  2763-2775,  1923. 

Dyer,  R.  E.    Endemic  typhus  fever.  Susceptibility  of  woodchucks,  house  mice, 
meadow  mice,  and  white-footed  mice.    U.S.  Pub.  Hlth.  Repts.,  49:  723-724, 

*934- 

-  ,  Badger,  L.  F.,  Ceder,  E.  T.,  and  Workman,  W.  G.     Endemic  typhus  fever 
of  the  United  States:  history,  epidemiology  and  mode  of  transmission.    Jl.  Amer. 
Med.  Assoc.,  99:  795-801,  1932. 

,  Ceder,  E.  T.,  Rumreich,  A.,  and  Badger,  L.  F.     Experimental  transmission 


of  endemic  typhus  fever  of  the  United  States  by  the  rat  flea  (Xenopsylla  cheopis). 
U.S.  Pub.  Hlth.  Repts.,  46:  2415-2416,  1931. 

-  ,  Ceder,  E.  T.,  Workman,  W.  G.,  Rumreich,  A.,  and  Badger,  L.  F.    Typhus 
fever  —  transmission  of  endemic  typhus  by  rubbing  either  crushed  infected  fleas  or 
infected  flea  fcces  into  wounds.    Ibid.,  47:  131-133,  1932. 

-  ,  Rumreich,  A.,  and  Badger,  L.  F.    Typhus  fever.  A  virus  of  the  typhus  type 
derived  from  fleas  collected  from  wild  rats.    Ibid.,  46:  334-338,  1931;  47:  131- 
133,  1932. 

Eskey,  C.  R.    Murine  typhus  fever  control.     U.S.  Pub.  Hlth.  Repts.,  58:  631- 

638,  1943- 

-  .     Fleas  as  vectors  of  sylvatic  plague.     Amer.  Jl.  Pub.  Hlth.,  28:  1305-1310, 

i938. 

-  -  ,  and  Haas,  V.  H.    Plague  in  the  western  part  of  the  United  States.    U.S. 

Pub.  Hlth.  Repts.,  54:  1467-1481,  1939. 

Ewing,  H.  E.    Notes  on  the  taxonomy  and  natural  relationships  of  fleas,  with 
descriptions  of  four  new  species.    Parasitology,  16:  341-354,  1924. 

-  -  ,  and  Fox,  I.    The  fleas  of  North  America.    U.S.  Dept.  Agr.,  Misc.  Pub.  500, 

*943- 
Faust,  E.  C.,  and  Maxwell,  T.  A.  The  finding  of  the  larvae  of  the  chigo,  Tunga 

penetrans,  in  scrapings  from  human  skin.    Arch.  Dermat.  Syph.,  22:  94-97, 

1930. 
Fox,  C.,  and  Sullivan,  E.  C.  A  comparative  study  of  the  rat-flea  data  for  several 

seaports  of  the  United  States.    U.S.  Pub.  Health  Rept.,  40:  1909-1934,  1925. 


564  MEDICAL  ENTOMOLOGY 

*Fox,  Irving.    Fleas  of  the  eastern  United  States.    Ames,  Iowa,  1940. 

Goyle,  A.  N.     On  the  transmission  of  plague  by  Xenopsylla  astia  and  X.  cheopis. 

Preliminary  observations.     Ind.  Med.  Gaz.,  62:  317-318,  1927. 
Grubbs,  S.  B.,  and  Holsendorf,  B.  E.    The  ratproofing  of  vessels.     U.S.  Pub.  Hlth. 

Kept.,  40:  1507-1515,  1925. 
Gunther,  C.  E.  M.    The  probable  vector  of  endemic  typhus  in  New  Guinea.     Med. 

Jl.  Australia,  2:  202-204,  1938. 
Hampton,  B.  C.    Plague  infection  reported  in  the  United  States  during  1944  and 

summary  of  human  cases,  1900-1944.'   U.S.  Pub.  Hlth.  Repts.,  60:  1361-1365, 

1945. 
.    Plague  infection  reported  in  the  Territory  of  Hawaii  during  1944  and 

summary  of  human  cases,  1899-1944.     U.S.  Pub.  Hlth.  Repts.,  60:  1365-1368, 

1945. 
Hicks,  E.  P.    The  early  stages  of  the  jigger,  Tunga  pcnctrans,    Ann.  Trop.  Med. 

Parasit.,  24:  575-586,  1930. 
Hirst,  L.  F.    On  the  transmission  of  plague  by  fleas  of  the  genus  Xenopsylla. 

Ind.  Jl.  Med.  Res.,  10:  789-820,  1923. 

*Hubbard,  C.  A.    Fleas  of  western  North  America.    Ames,  Iowa,  1947. 
**Jellison,  W.  L.,  and  Good,  N.  E.    Index  to  the  literature  of  Siphonaptera  of 

North  America.    Nat.  Inst.  Hlth.,  Bull.  178,  1942. 
Kohls,  G.  M.    Siphonaptera.    A  study  of  the  species  infesting  wild  hares  and 

rabbits  of  North  America.    Ibid.,  175,  1940. 

Lantz,  D.  E.    How  to  destroy  rats.    U.S.  Dept.  Agr.,  Farmers'  Bull.  369,  1909. 
Listen,  W.  G.    Plague,  rats  and  fleas.    Jl.  Bombay  Nat.  Hist.  Soc.,  16:  253-274, 

1905. 
.    The  Milroy  lectures,  1924,  on  the  plague.    Brit.  Med.  JL,  i :  900-903,  950- 

954»  997-IOOI>  i924- 
Macchiavello,  A.    Plague  control  with  DDT  and  "1080."  Results  achieved  in  a 

plague  epidemic  at  Tumbes,  Peru,  1945.     Amer.  JL  Pub.  Hlth.,  36:  842-854, 

1946. 
Maxcy,  K.  F.    An  epidemiological  study  of  endemic  typhus  (Brill's  disease)  in 

the  south-eastern  United  States  with  special  reference  to  its  mode  of  transmis- 
sion.   U.S.  Pub.  Hlth.  Repts.,  41:  2967-2995,  1926. 
Meyer,  K.  F.    The  known  and  the  unknown  in  plague.    Amer.  Jl.  Trop.  Med., 

22:  9-36, 1942. 
Mitzmain,  M.  B.     Some  new  facts  on  the  bionomics  of  the  California  rodent  fleas. 

Ann.  Ent.  Soc.  Amer.,  3:  61-84,  I9I°- 
.    General  observations  on  the  bionomics  of  the  rodent  and  human  fleas.    U.S. 

Pub.  Hlth.  Serv.,  Bull.  38,  1910. 
Nicholson,  H.  P.,  Gaines,  T.  B.,  Me  Williams,  J.  G.,  and  Vetter,  M.  H.    Combined 

typhus-malaria  control   residual   spray   operations  with   five   per   cent  DDT 

emulsion.    U.S.  Pub.  Hlth.  Repts.,  63:  1005-1013,  1948. 


THE  SIPHONAPTERA:  FLEAS  565 

Parman,  D.  C.    A  brief  history  of  the  sticktight  flea  and  the  fowl  tick  in  the 

United  States.    Jl.  Econ.  Ent.,  19:  644-648,  1926. 
Prince,  F.  M.     Report  on  the  fleas  Opisocrostis  bruncrl  (Baker)  and  Thrassls 

bacchl  (Roth.)  as  vectors  of  plague.    U.S.  Pub.  Hlth.  Repts.,  58:  1013-1016, 

*943- 

.     Plague — the  survival  of  the  infection  in  fleas  or  hibernating  ground  squir- 
rels.   U.S.  Pub.  Hlth.  Repts.,  62:  463-467,  1947. 
Rothschild,  N.  C.     A  synopsis  of  the  fleas  found  on  Mus  norvegicus  (decumanus), 

Mus  rattus  (alexandrlnus)  and  Mus  musculus.     Bull.  Ent.  Res.,  i:  89-98,  1910. 
Strickland,  C.     The  biology  of  Ccratophyllus  jasciatus  Bosc.,  the  common  rat 

flea  of  Great  Britain.    Jl.  Hyg.,  14:  139-142,  1914. 
Sullivan,  K.  C.    The  use  of  calcium  cyanide  for  the  control  of  fleas  and  other 

insects.    Jl.  Econ.  Ent.,  17:  230-237,  1924. 
Trembley,  H.  L.,  and  Bishopp,  F.  C.   'Distribution  and  hosts  of  some  fleas  of 

economic  importance.    Ibid.,  33:  70 1-70 --5,  1940. 
Waterston,  J.     Fleas  as  a  menace  to  man  and  domestic  animals.     2nd  ed.     Brit. 

Mus.  Nat.  Hist.,  Econ.  Ser.  No.  3,  1920. 
Wayson,  N.  E.     A  disease  in  wild  rats  with  gross  pathology  resembling  plague. 

U.S.  Pub.  Filth.  Repts.,  40:  1975-1979,  1925. 
Wiley,  J.  S.     Recent  developments  in  m urine  typhus  fever  control.     Amer.  Jl. 

Pub.  Filth.,  36:  9/4-983,  1946. 
Wu,  Lien-Teh.     Practical  aspects  of  plague  in  wild  rodents.     Trans.  Cong.  Far 

East.  Assoc.  Trop.  Mcd.  (6th  Cong.,  Tokyo,  1925),  2:  815-836,  1926. 
,  Chun,  J.  W.  H.,  Pollitzcr,  R.,  and  Wu,  C.  Y.     Plague,  a  manual  for  medical 

and  public  health  workers.     Shanghai,  1934. 
Yersin,  A.     La  peste  buboniquc  a  Hongkong.     Ann.  Inst.  Pasteur,  8:  662-667, 

1894. 


CHAPTER  XIX 


Poisonous  and  Urticating 
Arthropods 


THE  ill  effects  of  the  bites  of  various  bloodsucking  arthropods  have  already 
been  indicated  in  the  preceding  pages.  The  irritation  and  the  serious 
conditions  not  infrequently  produced  by  such  bites  are  duj^^th 


of  the  secretions  of  the  salivary  glands  into  the  wounds.  It  has  been  shown  that 
the  secretions  of  the  salivary  glands  of  bloodsucking  arthropods  have  various 
functions,  such  as*  the  prevention  of  coagulation  of  the  blood  (possess  and- 
coagulins),  and  may  cause  hemolysis  (possess  hcmolysins)j  produce  paralysis 
(contain  neurotoxins),  or^ct  as  direct  irritants  causing  various  reactions  on 
the  part  of  their  hosts.  (For  accounts  of  such  reactions  see  the  discussions 
under  the  different  species.)  We  need  again  to  call  attention  to  one  important 
feature  which  is  not  stressed  under  each  group  of  bloodsucking  insects.  When 
a  bloodsucking  insect  bites  there  is  always  the  possibility  thatjJie^  proboscis 
may  be  contaminated  with  pathogenic  jorganisms.  If  such  organisms  become 
localized  near  the  point  of  puncture  or  gain  access  to  the  blood  stream,  the 
results  may  be  serious.  It  is  always  well  to  use  some  disinfectant  as  alcohol, 
tincture  of  iodine,  or  other  antiseptic,  and  to  press  out  blood,  if  possible,  from 
the  bites  made  by  the  insects.  Dr.  Walsh  (1924)  recommends  an  ointment  of 
dimol  well  rubbed  into  the  puncture  and  points  out  that  Lord  Carnarvon's  ill- 
ness and  subsequent  death  arose  from  an  insect's  bite  he  received  at  the  opening 
of  Tutankhamen's  tomb.  The  septic  invasion  took  place  at  the  point  of  punc- 
ture, spread  with  great  rapidity,  and  death  ensued  from  septic  pneumonia. 
When  going  into  any  place  where  bloodsucking  insects  are  abundant  it  is  al- 
ways well  to  be  provided  with  several  kinds  of  disinfectants  and  ointments. 
There  remain  to  be  briefly  described  the  effects  of  poisonous  arthropods,  those 
species  that  normally  do  not  act  as  bloodsucking  parasites  but  occasionally  bite 
or  sting  man  and  those  that  possess  substances  in  their  body  covering  of  spines, 
hairs,  etc.,  which,  coming  into  contact  with  man,  irritate  his  skin  and  often 
produce  systemic  and  nervous  disorders. 


POISONOUS  AND  URTICATING  ARTHROPODS  567 

POISONING  ARTHROPODS 

Poisoning  arthropods  normally  use  their  venom  to  kill  or  paralyze  their 
prey  or  as  weapons  of  defense.  Man  is  bitten  or  stung  when  he  accidentally 
or  purposely  intrudes  upon  them.  Here  may  be  included  those  arthropods 
that  possess  poison  glands  and  utilize  their  secretions  when  they  bite  or 
sting.  Such  are  the  poisoning  Arachnida,  centipedes,  millipedes,  and  certain 
stinging  insects  as  bees,  wasps,  and  stinging  ants. 

THE  CLASS  ARACHNIDA 

THE  ORDER  SCORPIONIDA:  Probably  the  most  famous  of  the  Arach- 
nida are  the  Scorpions  (Fig.  225).  Their  characteristic  form  with  their  long, 
segmented,  taillike  abdomen  ending  inj^bulbous  sac  and  sting  is  familiar  to 
everyone.  Another  feature  is  the  long,  somewhat  formidable-looking  pedipalpi 
that  terminate  in  chclatc  claws  si  mjlar_tp_those  of  the  lobster.  Scorpions  are 
found  principally  in  warm  countries,  and  certain  species  attain  considerable 
size  (up  to  eight  inches  in  length)  though  most  of  them  arc  small.  They  are 
nocturnal  animals  and  of  rapacious  habits,  feeding  on  spiders,  insects,  and  other 
small  animals.  They  seize  them  with  their  pedipalpi  and  sting  them  to~cTeath 
with  the  caudal  sting.  During  the  day  they  hide  away  under  stones,  wood, 
trash,  or  in  small  pits  which  they  dig  in  the  soil. 

The  poison  glands  of  scorpions  are  located  in  a  bulbojislike  .welling  in  i-fa 
last  abdominal  segment  that  terminates  in  a  strongly  curved,  chitinous  spine. 
The  openings  of  the  ducts  from  the  poison  glands  are  near  jjie  apex  of  the 
sting.  Scorpions  rarely  sting  man  and  then  only  under  provocation.  Though 
the  sting  is  very  painful,  the  poison  rarely  proves  fatal  to  adults.  The  stings 
of  the  large  tropical  species  often  produce  serious  wounds  and  may  cause  alarm- 
ing symptoms  even  in  adults.  In  children  under  five  years  of  age  the  stings  of 
the  larger  species  are  serious,  frequently  causing  convulsions,  vomiting,  and 
even  (fcath.  Wilson  (1004)  records  a  considerable  number  of  deaths  among 
children  each  year  at  Omdurman  (Sudan)  from  the  effects  of  scorpion  stings. 
Bacrg  (1929)  gives  an  extended  account  of  the  famous  scorpion,  the  "Du- 
rango"  scorpion  of  Mexico,  (Centruroides  suffusus  Pocock).  The  sting  of  this 
scorpion  is  fatal  to  many  children  (one  to  seven  years  of  age).  He  records  1608 
deaths  due  to  the  sting  of  this  scorpion  in  the  city  of  Durango  (population 
between  40,000  and  50,000)  from  1890  to  1926.  In  1927  forty  deaths  are  recorded 
and  seventeen  for  1928.  The  effects  of  the  poison  arc  very  rapid,  death  usually 
nprs;  ^  the  patient  lives  more  than  three  hours  re- 


covery is  practically  assured,  though  death  may  occur  six  to  eight  hours  after 


568  MEDICAL  ENTOMOLOGY 

the  sting.  The  stings  o£  the  scorpions  appear  to  be  more  fatal  during  the  hot 
season,  April  to  July.  The  effects  of  the  stinp-  are  very  marked  —  immediate 
drowsiness,  excessive  salivation,  tongue  slu^ffish.  distortion  and  severe  con- 
traction of  the  muscles  ^f  the  lower  jaw,  while  the  temperature  rises  rapidly 
to  104°  or  104.8°  F.:  there  is  scarcity  of  uripc  and  usually  a  pronounced  stra- 
bismus ;  there  may  be  hemorrhages  of  the  stomach,  lungs,  onr] 


convulsions  come  in  waves  and  increase  in  severity  for  about  one  and  oneJialf 
to  two  hours  or,  in  fatal  cases,  until  death. 


Fig.  225  (left).  A  scorpion. 

Fig.  226  (right).  Lactrodecttts  mactans.  Upper:  The  chelicerac  with  the  poison  glands 
in  place.  Lower:  A  claw  with  the  duct  from  the  poison  gland  passing  through  it.  (After 
Baerg,  Scientific  Monthly.) 


The  scorpion  occurs  in  various  parts  of  western  M^xim  and  the  southern 
part  of  Arizona  but  in  no  place  so  abundantly  as  in  the  city  of  PurangQ,  Few 
deaths  are  recorded  outside  the  city  of  Durango.  In  the  city  the  scorpion  fre- 
quents ruins,  and  Baerg  found  it  almost  exclusively  under  adobe  bricks.  .It  is 
also  a  common  inhabitant  of  the  houses  and  other  buildings  in  the  city. 

Comstock  (1048)  records  some  twenty  species  of  scorpions  from  the  United 
States.  The  stings  of  our  species  are  not  considered  serious  though  they  may 
cause  severe  pain  and  slight  systemic  disorders.  The  stings  may  be  treated  with 
weak  ammonia  and  this  usually  gives  prompt  relief.  Ammonia  may  also  be 
given  internally.  In  cases  of  severe  stings  by  the  larger  species  prompt  medical 
attention  should  be  obtained.  If  not  available  a  ligature  should  be  applied 
proximad  to  the  wound  ;  the  wound  should  be  freely  excised  so  as  to  cause  a 


POISONOUS  AND  URTICATING  ARTHROPODS  569 

free  flow  of  blood  and  washed  frequently  with  a  strong  solution  of  potassium 
permanganate. 

The  principal  species  of  scorpions  in  the  United  States  which  may  sting 
man  are  I  some  tr  us  maculatus  (occurs  in  southern  Florida  and  California; 
widespread  in  subtropical  and  tropical  countries;  adults  measure  from  two 
to  three  inches  in  length);  Centruroides  spp.  (seven  species  found  in  the 
southern  states  and  California) ;  Diplocentms  spp.  (two  species,  one  in  Florida 
and  the  other  in  Texas  and  California) ;  Vejovis  spp.  (some  seven  species  found 
in  the  Far  West  and  Southwest) ;  Had  runts  hirsutus  (a  very  large,  hairy  species 
which  occurs  in  the  Southwest) ;  and  a  few  others. 


Fig.  227.  Lactrodcctns  mdctans,  the  black  widow  spicier.  Left:  A 
ventral  view  of  female  to  show  the  hourglass  mark  on  the  ventral  sur- 
face of  the  abdomen.  Right:  Dorsal  view  of  male.  (After  Baerg,  Sci- 
entific Monthly.') 

THE  ORDER  ARANEIDA:  The  true  spiders  differ  from  all  other  arach- 
nids in  having  the  abdomen  unsegmented  and  attacher),  \Q  f 
by  a  short  pedicel  (Fig.  227).  The  four  pairs  of  ]cg,s  arr •  nt-tarhpfl  rn  r)-»f 
thorax.  The  mouth  parts  consist  of  a  pair  of  chelicerae  and  a  pair  of  leglike 
pcdipalpi  surrounding  t-he  mnnth  npnijno  Each  chelicera  (Fig.  226)  consists 
of  a  large  basal  segment  and  a  claw.  The  claw  is  harcl,  curved,  pointed,  and 
freely  movable  in  one  plane  only.  The  claw  is  traversed  by  the  duct  of  the^ 
poison  gland  (Fig.  226) .  Simple  cyesJ2  to  8)  are  usually  present,  though  some 
species  are  blind. 

Spiders  are  much  feared  by  the  average  person.  Such  fears  arc  usually  quite 
unwarranted  as  spiders  seldom  bite  man  and  then  only  under  provocation. 


570  MEDICAL  ENTOMOLOGY 

However,  spiders  possess  distinct  poison  glands,  which  open  by  means  of 
ducts  at  the  tips  of  the  claws  of  the  chelicerae  (Fig.  226) .  All  spiders  are  pre: 
daceous,  the  prey  being  seized  by  the  chelicerae  and  crushed,  and  the  injection 
of  the  poison  either  paralyzes  or  kills  the  victims. 

THE  POISON  OF  SPIDERS:  All  true  spiders  possess  poison  glands.  The  poison 
glands  are  two  in  number  and  are  located  in  the  anterior  portion  of  the 
cephalothorax  or  in  the  basal  segment  of  the  chelicerae  (tarantulas).  The 
glands  (Fig.  226)  arc  more  or  less  saclikc ' and  the  lumen  of  t|ie  sac  server  ps  .1 
reservoir  for  the  venom.  Each  gland  discharges  through  a  duct  that  opens  near 
the  tip  of  the  claw  of  the  chelicera  of  the  corresponding  side  of  the  body 
(Fig.  3).  The  secretion  of  the  glands  is  "an  oily,  translucent,  lemon-yellow- 
colored  liquid. with  an  acid  reaction  and  a  hot,  bitter  taste/'  Kobert  (1893) 
considers  that  there  are  two  poisons  present:  (i)  a  toxin  which  causes  local 
symptoms  and  is  secreted  by  the  glands;  (2)  a  toxalbumin  distributed  through- 
out the  body  (not  secreted  by  the  glands)  and  producing  general  symptoms. 
In  those  spiders  whose  bites  produce  systemic  disturbances  it  is  believed  that 
the  latter  poison  greatly  predominates. 

Though  the  bites  of  spiders  have  long  been  considered  dangerous,  there 
is  little  positive  evidence  to  support  the  view.  Comstock  (1948)  concludes  from 
long  experience  with  spiders  that  there  are  none  in  the  northern  half  of  the 
United  States  that  need  to  be  feared.  In  the  southern  half  the  bites  of  species 
of  Latrodcctus  are  to  be  feared  and  probably  those  of  certain  species  of  taran- 
tulas. In  the  North  tropical  tarantulas  are  frequently  brought  in  on  bunches 
of  bananas  but  they  rarely  can  be  induced  to  bite. 

LATRODECTUS  SPP.:  The  hourglass  spider  or  the  black  widow  (Latrodectns 
mactansFabr.)  (Fig.  227  $  ,  $  ),  is  widely  distributed  in  the  southern  half  of 
the  United  States.  It  is  a  coal-black  spider  marked  with  red  or  yHlnw  or  both 
Though  the  markings  vary  greatly,  the  most  constant  and  distinguishing  mark 
is  the  hourglass  one  on  the  ventral  n^pert-  nf  tj^  ahrV>meg  (Fig.  227).  The 
full-grown  female's  body  measures  about  %-inch  in  length  or  over  all  i% 
inches;  the  male  i%  inches  over  all.  People  generally  recognize  the  venomous 
nature  of  the  bite  of  this  spider.  Merriam  (1910)  records  the  Indians  of 
California  as  dreading  it  and  says,  "All  the  tribes  know  that  the  spider  is 
poisonous  and  some  of  them  make  use  of  the  poison"  (by  rubbing  the  points 
of  their  arrows  in  the  mashed  bodies  of  the  spiders).  Riley  and  Howard  (1889) 
describe  the  ill  effects  from  the  bite  and  report  a  fatal  case.  In  all  their  reports 
the  actual  biting  of  the  spider  was  not  observed  except  in  one  case  and  in  that 


POISONOUS  AND  URTICATING  ARTHROPODS  571 

case  the  specimen  was  lost.  Kellogg  (1915)  describes  an  actual  case.  The  spider 
(Lactrodectus  mactans,  female)  bit  the  glans  of  the  penis  while  the  man  was 
sitting  on  an  outdoor  closet.  Ten  minutes  later  the  patientsuffered  from^dizzi- 
ness,  weakness  in  the  legs,  and  abdominal  cramps.  He  walked  a  mile  to  jhe 
nearest  physician  and  arrived 


being  fully  three  indl^  i"  dinmpi^r  at-  \\\?  glans.  The  heartbeat  was  reduced  to 
^o  per  minute  and  the  respiration  was  labored.  Treatment  consisted  of  hypo- 
dermic injections  of  strychnine  1/40  follov^eiJ  in  t-pn  minutes,  with  nifrn- 
glycerine  i/ioo.  The  site  of  the  bite  was  treated 


The  heartbeat  went  as  low  as  27  per  minute  but  was  restored  to  45  after  re- 
peated injections  of  strychnine.  At  the  end  of  three  hours  the  strychnine  treat- 
ment was  stopped  and  10  min.  of  brandy  administered  hypodcrmically  every 
hour.  At  the  end  of  nearly  ten  hours  after  the  bite  the  heartbeat  had  risen  to 
55  per  minute,  and  then  a  small  dose  of  atropin  and  morphine  was  given  to 
relieve  the  pain.  The  patient  fell  asleep  and  awoke  next  morning  with  a  fine 
rash  all  over  the  body.  The  penis  had  returned  to  nearly  normal  size.  Com- 
plete recovery  took  place  in  about  four  days. 

Baerg  (1923)  describes  the  results  of  an  induced  bite  of  the  same  species  on 
the  inner  surface  of  the  basal  joint  of  the  third  finger.  Though  he  suffered 
considerable  pain,  was  compelled  to  spend  a  day  in  bed,  and  had  medical  at- 
tention, yet  the  effects  were  not  marked.  The  experimenter  records  that  fre- 
quent hot  baths  and  the  keeping  of  the  bitten  hand  in  hot  water  were  most 
efficacious  in  reducing  the  pain  and  restlessness. 

Bogen  (1926)  reviews  the  reported  cases  due  to  the  bites  of  this  spider.  He 
records  some  150  cases  from  the  United  States  and  Canada.  Fully  two-thirds 
of  them  are  from  California  and  most  of  the  victims  were  males  who  were 
bitten  on  the  penis  or  adjacent  parts  while  sitting  on  outdoor  privies.  He 
reports  12  deaths.  He  also  records  15  cases  at  the  Los  Angeles  General  Hospital. 
All  were  males  ranging  from  2  to  65  years  of  age.  Ten  were  bitten  on  the 
penis.  The  symptoms  were  acute  pain,  localized  and  general,  profuse  per- 
spiration, restlessness,  nausea,  vomiting,  labored  breathing,  and  constipation. 
Treatment  consisted  of  the  administration  of  sedatives  as  morphine  or  codeine, 
bromides,  etc.,  hot  applications,  such  stimulants  as  ammonia,  caffeine,  and 
strychnine,  and  the  use  of  purgatives  as  magnesium  citrate  or  sulphate.  Thorp 
and  Woodson  (1945)  summarize  the  cases  of  spider  bites  in  the  United  States, 
a  total  of  1291  cases  (1726-1943)  with  55  deaths. 

Other  species  of  Latrodectus  occur  in  various  parts  of  the  world,  especially 
in  the  tropics,  and  are  generally  regarded  as  dangerous.  All  of  them  are  black 


572  MEDICAL  ENTOMOLOGY 

or  of  a  dark  color  marked  with  white,  yellow,  or  red  spots.  L.  hasseltii  is 
widespread  in  the  Philippines,  New  Zealand,  and  Australia.  Its  bites  are  re- 
garded as  serious. 

TARANTULAS:  Tarantulas  are  very  large,  hairy  spiders  (Fig.  228)  belonging 
to  the  family  Aviculariidac  and  commonly  occur  in  the  subtropics  and  tropics. 
On  account  of  their  size  and  fierce-looking  appearance  they  are  regarded  by 
most  people  as  very  dangerous.  There  is  little  reason  for  this  fear  as  there  is 
no  evidence  that  their  bites  produce  any  serious  effects.  Baerg  (1923)  induced 


Fig.  228.  A  tarantula  (Avicuhiria  sp.) 

a  tarantula  (Eurypclma  steindachneri)  to  bite  him  on  the  finger  but  the  effects 
were  even  less  than  those  of  an  ordinary  bee  sting.  Scriocopclnni  com  munis 
Cambr.  is  a  common  and  much  feared  tarantula  in  Panama.  Haerg  (10.29) 
reports  this  species  capable  of  killing  guinea  pigs  by  its  bite;  on  man  its  bite 
produces  somewhat  disturbing  a  fleets. 

The  term  tarantula  was  first  applied  to  an  European  spider  (Lycosa  tarcn- 
tula)  which  does  not  belong  to  this  family.  Lycosa  tarentula  is  the  famous 
spider  whose  bite  was  supposed  to  be  the  cause  of  a  peculiar  disease  known 
as  tarantism  and  prevalent  in  southern  Europe  during  the  Middle  Ages. 
Warburton  (1909)  thus  describes  the  supposed  elite  is  ot  this  spider: 

The  bite  of  the  spider  was  supposed  to  induce  a  species  of  madness  which  found 
its  expression — and  its  cure — in  frantic  and  extravagant  contortions  of  the  body. 


POISONOUS  AND  URTICATING  ARTHROPODS  573 

If  the  dance  was  not  sufficiently  frenzied,  death  ensued.  In  the  case  of  survivors, 
the  symptoms  were  said  to  recur  on  the  anniversary  of  the  bite.  Particular  descrip- 
tions of  music  were  supposed  to  incite  the  patient  to  the  excessive  exertion  necessary 
for  his  relief;  hence  the  "Tarentella."  In  the  Middle  Ages  epidemics  of  "tarantism" 
were  of  frequent  occurrence,  and  spread  with  alarming  rapidity.  They  were  seizures 
of  an  hysterical  character,  analogous  to  the  ancient  Bacchic  dances,  and  quite  un- 
connected with  the  venom  of  the  spider  from  which  they  took  their  name.  The 
condition  of  exaltation  and  frenzy  was  contagious,  and  would  run  through  whole 
districts,  with  its  subsequent  relapse  to  a  state  of  utter  prostration  and  exhaustion. 
The  evil  reputation  of  the  tarantula  appears  to  have  exceedingly  little  basis  in 
fact. 

THE  CLASS  CHILOPODA-THE  CENTIPEDES 

The  centipedes  (Fig.  229)  are  wormlike  creatures  with  the  head  distinct  and 
a  pair  of  antennae  with  many  joints  (at  least  14) ;  the  body  consists  of  nu- 
merous fairly  similar  segments,  each  with  a  pair  of  legs.  They  are  tracheate 


Fig.  229.  Scolopendra  obscura.  (After  Koch,  Die  Myriapoda.) 

animals  and  are  mostly  terrestrial.  The  class  is  divided  into  a  number  of 
families  and  the  species  are  quite  common  and  abundant,  especially  in  warm 
countries.  They  are  all  predaceous  and  prey  upon  small  animals.  They  are 
active,  swift-moving  creatures  and  are  found  in  dark  places  as  under  stones, 
logs,  rubbish,  and  dried  leaves. 

Centipedes  are  regarded  as  very  dangerous  by  many  people.  They  possess 
a  pair  of  distinct  poison  glands  that  open  near  the  tips  of  the  fangs.  The  fangs 
are  the  modified  legs  of  the  first  body  segment  and  are  located  directly  behind 
the  mouth  parts.  Each  fang  is  a  curved,  horny  structure  (Fig.  230)  and  the 
duct  from  the  poison  glancl  opens  just  behind  the  tip.  Our  larger  species  be- 
long to  the  genera  Scolopendra,  Lithobius,  and  Geophilus.  Some  of  the  species 
attain  a  length  of  nearly  seven  inches.  Cornwall  (1916)  investigated  the  poison- 
ous properties  ol  three  Indian  species  (all  in  the  family  Scolopendridae)  and 
found  the  toxic  action  of  the  venom  relatively  low.  He  considers  the  main 


574  MEDICAL  ENTOMOLOGY 

function  of  the  poison  gland  to  be  the  secretion  of  digestive  ferments  rather 
than  to  furnish  a  lethal  agent.  Norman  (1896)  records  Scolopendra  morsitans, 
a  species  common  in  Texas,  as  capable  of  killing  mice  by  its  bite.  Baerg  (1924) 
made  definite  experiments  on  rats  and  himself  with  Lithobius  mordax  Koch, 
Theatops  spinicaudus  Wood,  Scolopendra  heros  Gir.,  and  Scolopendra  poly- 
morpha Wood.  These  species  are  more  or  less  common  in  the  southwestern 
United  States.  Herms  (1923)  records  S.  heros  as  common  in  southern  Cali- 
fornia and  much  feared  by  the  people.  Baerg's  experiments  consisted  in  having 
the  centipedes  bite  rats,  noting  the  effects,  and  then  inducing  them  to  bite  him 
on  the  inside  of  his  little  finger.  Lithobius  mordax  had  no  effect  on  rats  and 
was  unable  to  puncture  the  skin  of  Baerg's  finger;  Theatops  spinicaudus  pro- 
duced no  ill  effects  on  rats,  and  though  it  bit  his  finger  and  injected  poison, 
no  ill  effects  could  be  noted;  Scolopendra  heros  (a  specimen  over  5%  inches 


Fig.  230.  Fangs  of  centipedes  with  poison  glands  in  place.  Left:  Scolopendra  heros. 
Right:  S.  polymorpha.  (After  Baerg,  Scientific  Monthly.) 

in  length)  caused  some  pain  to  the  rat  by  its  bite  but  the  pain  apparently 
disappeared  in  a  few  hours;  on  himself  the  bite  produced  slight  pain  with  a 
little  swelling,  which  disappeared  in  the  course  of  a  few  hours;  Scolopendra 
polymorpha  (a  specimen  nearly  6  inches  in  length)  bit  the  rat  readily  but 
caused  little  discomfort;  on  himself  the  effects  were  even  less  than  those  of 
the  preceding  species. 

Judging  from  the  experiments  of  Cornwall  and  Baerg,  it  would  appear  that 
centipedes  are  practically  harmless.  However,  some  people  might  suffer 
severely  from  the  same  bites.  Though  centipedes  should  be  avoided,  there  is 
no  reason  to  fear  them  or  dread  their  bites.  When  bitten  by  them  the  ap- 
plication of  weak  ammonia  water  and  the  use  of  antiseptics  are  recom- 
mended. 

THE  CLASS  DIPLOPODA— THE  MILLIPEDES 

The  millipedes  or  "thousand  legs"  are  wormlike  creatures  (Fig.  231)  and 
are  all  air-breathing,  terrestrial  arthropods.  The  entire  body  is  more  or  less 
cylindrical.  The  head  is  distinct  and  the  following  four  segments  are  gen- 


POISONOUS  AND  URTICATING  ARTHROPODS  575 

erally  referred  to  as  the  "thorax."  The  remaining  segments  constitute  the 
abdomen  and  each  segment  usually  bears  two  pairs  of  legs.  The  mouth  parts 
are  such  that  they  do  not  possess  poison  glands  and  are  of  no  value  in  inflicting 
wounds.  However,  many  of  the  millipedes  possess  segmentally  arranged 
glands  that  secrete  a  liquid  that  is  an  irritant  to  the  skin.  The  liquid  from 
these  glands  can  be  squeezed  out  or,  in  some  cases,  squirted  with  considerable 
force  and  to  some  distance.  Loomis  (1936,  1941)  reports  large  millipedes 
(Rhinocricus  lethifer  and  R.  latespargor)  in  Haiti  as  squirting  their  fluids 


Fig.  2j/.  A  millipede,  Spirobolns  marginatus.  (After  Comstock.) 

several  inches,  at  least  24  to  36.  Similar  reports  come  from  New  Guinea  and 
Africa,  and  the  natives  of  many  tropical  countries  regard  these  animals  with 
fear.  The  fluid  secreted  is  a  strong  skin  irritant  and  if  injected  into  the  eyes 
may  cause  temporary  or  permanent  blindness.  Burtt  (1947)  gives  an  excellent 
summary  and  bibliography  of  injury  from  millipedes. 

URTICATING  INSECTS 

Urticating  insects  are  those  whose  body  hairs  (special  types)  when  falling 
on  or  rubbed  against  the  human  skin  cause  local  irritation,  inflammation,  or 
even  systemic  disturbances;  and  also  those  whose  body  fluids  when  placed 
on  the  skin  cause  blistering  (blister  beetles).  The  principal  urticating  insects 
are  found  among  the  caterpillars  of  the  Lepidoptera  (moths)  and  the  beetles 
(Meloidae,  or  blister  beetles). 

LEPIDOPTERA:  The  chief  urticating  caterpillars  belong  to  the  following 
families:  Megalopygidae,  Eucleidae,  Lymantriidae  (Liparidae),  Saturniidae, 
and  Thaumetopoeidae.  A  few  are  recorded  from  the  families  Arctiidae,  Noc- 
tuidae,  and  Nymphalidae  (butterflies). 

The  urticating  properties  of  these  caterpillars  are  due  to  the  possession  of 
special  hairs  or  spines  that  are  supplied  with  a  poison-gland  cell.  These  hairs 
are  hollow  and  filled  with  poison.  When  they  come  into  contact  with  the 
skin,  the  fine  barbed  hairs  penetrate  or,  if  coarse,  the  poisonous  substance 
spreads  over  the  skin  and  produces  the  rash.  According  to  Gilmer  (1925), 
there  are  two  distinct  types  of  poison-gland  hairs  or  setae.  These  he  classifies  as 


576 


MEDICAL  ENTOMOLOGY 


P- 


Fig.  232.  Various  types  of  hypodermal  glands  of  insects,  more  particularly  those  that 
are  protective.  (/)  Poison  seta  of  white-marked  tussock  moth  (Hemerocampa  Icuco- 
stigma).  (2)  Somewhat  diagrammatic  illustration  of  a  poison  spine  of  Parasa  hilarata 
(caterpillar),  (3)  Somewhat  diagrammatic  illustration  of  poisonous  spine  of  the  puss 
caterpillar  (Mcgalopyge  opercularis) .  (4)  Schematic  illustration  of  a  poison  gland  cell 
of  the  browntail  moth  (Euproctis  phaeorrhoca).  (5)  Molting  fluid  gland  from  the  cab- 
bage worm  caterpillar  (Pieris  rapac}.  A,  cup  of  gland;  C,  collar  of  shaft;  Cgl,  cup  of 
poison  gland;  Cu,  cuticula;  Cui,  new  cuticula  forming;  D,  diaphragm  at  base  of  spine; 
Ga,  molting  gland;  H,  hypodermis;  P,  plug  of  pigment  at  end  of  poison  spine;  PC,  pore 
canal  for  the  hypodermis;  Pel,  poison  duct;  Pg,  poison  gland  cell;  Ps,  poison  sac;  S,  spine; 
Sp,  spicule  hairs  that  are  easily  detached;  T,  tip  of  spine;  Tr,  trichogen  cell.  (/  and  4 
redrawn  from  Gilmer,  2  from  Mills,  3  from  Foot.) 

the  primitive  hair  type  (Fig.  232  /)  and  the  modified  hair  type  (Fig.  232  2). 
The  primitive  hair  type  consists  of  a  single  seta,  usually  smaller  and  stiiTer  than 
the  other  hocly  hairs  of  the.  caterpillar,  and  supplied  with  a  gland  cell  that 
opens  directly  through  a  pore  canal  into  the  hollow  o£  the  seta.  The  seta  con- 


POISONOUS  AND  URTICATING  ARTHROPODS  577 

tains  the  poisonous  secretion  or  venomous  cytoplasm  of  the  gland  cell. 
These  setae  retain  their  urticating  properties  long  after  they  are  shed  by  the 
caterpillar  and  their  efficacy  does  not  seem  to  be  impaired  by  drying. 

The  modified  hair  type  is  found  in  many  of  the  caterpillars  of  the  Lyman- 
triidae  and  some  Thaumetopoeidac.  The  most  striking  type  is  that  found  in 
the  caterpillars  of  the  brown-tail  moth  (Euproctis  phaeorrhoea).  On  the  sub- 
dorsal  tubercles  of  the  caterpillars  are  found  minute  papillae  or  cuplikc  struc- 
tures crowded  together.  In  these  cups  are  borne  three  to  a  dozen  short  spicule- 
like  hairs  of  peculiar  structure.  These  hairs  consist  of  telescoped  units,  the  fine 
point  of  one  is  inserted  in  the  broad  end  of  the  part  below  it  and  the  basal 
point  is  inserted  in  the  "cup"  of  the  gland  (Fig.  232).  These  cups  are  con- 
tinuous with  the  cuticle  and  each  cup  is  connected  with  a  large  poison-gland 
cell  located  in  the  hypodermis.  A  true  poison  is  secreted  and  passes  out  to  the 
tips  of  the  fine  barbed  hairs.  As  these  minute  hairs  are  shed  they  come  in 
contact  with  the  skin  and  penetrate  it,  causing  the  distinctive  ''brown-tail 
rash." 

Another  type  is  the  so-called  "spine  type"  (Fig.  232).  This  type  is  prevalent 
in  the  caterpillars  of  the  Megalopygidae,  Eucleidae,  Saturniidae  and  Nymphali- 
dae.  Here  the  spine  is  usually  quite  large,  the  hollow  interior  is  lined  with  a 
thin  hypodermis,  and  the  center  is  in  direct  communication  with  the  poison- 
gland  cell  (Fig.  232).  The  tip  of  the  spine  can  penetrate  the  skin,  breaks  off 
readily,  and  liberates  some  of  the  poisonous  secretion.  When  numerous  spines 
penetrate  the  skin  there  is  produced  a  serious  rash,  often  with  systemic  dis- 
turbances. 

The  nature  of  the  poison  found  in  these  urticating  hairs  has  not  been 
determined.  Foot  believed  it  to  be  a  true  venom  combined  with  protein 
vehicles.  Gilmer  does  not  think  it  a  true  protein  as  he  failed  to  obtain  any 
reaction  with  various  protein  reagents. 

The  general  effects  of  these  poison  hairs  vary  according  to  the  susceptibility 
of  the  individual.  On  some  people  the  effects  are  very  marked.  Foot  (1922) 
says,  "The  lesions  produced  by  the  sting  of  these  genera  [see  list]  vary  from 
simple  erythema,  with  burning  or  itching,  to  extensive  inflammation,  with  the 
production  of  papules,  vesicles,  or  bullae."  Bishopp  reports  that  Megalopyge 
opcrcularis  sometimes  occurs  in  such  abundance  as  to  cause  an  epidemic  of 
dermatitis.  At  times  the  schools  of  San  Antonio,  Texas,  have  had  to  be  closed 
because  of  the  abundance  of  this  caterpillar  about  the  school  grounds. 


578 


MEDICAL  ENTOMOLOGY 


Fig.  233.  Some  urticating  caterpillars.  (/)  Euproctis  phacorrhoca,  browntail  moth. 
(2)  Automeris  io,  lo  moth.  (3)  Sibine  stimulca,  saddle-back  moth.  (4)  Mcgalopyge 
opercularis,  puss  caterpillar.  (5)  Mcgalopyge  crispata.  (Photographs  by  Slingerland.) 

PRINCIPAL  URTICATING  CATERPILLARS 

Megalopygidae : 

Megalopyge  crispata.  Flannel  moths.  Northern  United  States. 
Megalopyge  opercularis.  Puss  caterpillars.  Southern  United  States. 
Megalopyge  pyxidijera.  Flannel  moth.  Southern  United  States. 


POISONOUS  AND  URTICATING  ARTHROPODS 


579 


Fig.  234.  Upper:  Adults  of  Mcgalopygc  crispata.  Male  and  female. 
Lower:  M.  opercularis. 

Norape  ovina  (Cerama  cretata).  United  States. 

As  far  as  known  all  caterpillars  of  this  family  possess  urticating  hairs  and 
the  species  are  numerous  in  South  America. 

Eucleidae  (Limacodidae) : 
Adoneta  spinuloides.  United  States. 


580  MEDICAL  ENTOMOLOGY 

Parasa  Moris.  United  States. 

Parasa  hilarata.  Sino-Japanese  area. 

Parasa  indetermina.  United  States. 

Parasa  latistriga.  South  Africa. 

Phobetron  pithicium.  United  States. 

Sibine  stimulea.  Saddleback  caterpillars.  United  States. 

Numerous  species  in  tropical  regions  of  both  hemispheres  possess  urticat- 

ing  properties  of  varying  intensities. 

Thaumetopoeidac  : 

Thaumetopoea  processionea.  Processionary  caterpillar.  Europe, 
Several  other  species  in  Europe  and  North  Africa. 

Lymantriidae  (Liparidae)  : 
Euproctis  chrysorrhoea.  Gold-tail  moth.  Europe. 
Euproctis  flava.  China. 

Euproctis  phaeorrhoea.  Brown-tail  moth.  Europe  and  United  States. 
Hemerocampa  leucostigma.  White-marked  tussock  moth.  North  America. 
Stilpnotia  salicis.  Satin  moth.  Europe  and  North  America. 
Probably  many  others  of  this  family. 

Arctiidac  : 

Euchaetias  egle.  United  States. 

Halysidota  caryae.  Hickory  tiger  moth.  North  America. 
Probably  a  few  others  affect  delicate  skins. 

Noctuidae: 

Apatela  populi  and  Apatcla  oblinita.  United  States. 
Catocala  sp.  United  States. 

Effects  from  the  larvae  probably  very  insignificant  except  on  the  most 

delicate  skins. 

Saturniidae: 

Automeris  io.  The  lo  moth.  United  States. 
Automeris  spp.  Probably  many  species  of  the  genus  possess  urticating  hairs 

or  spines. 

Coloradia  spp.  Probably  all  species. 
Hemileuca  lucina.  United  States. 
Hcmileuca  maia.  The  buck  moth.  United  States. 
Hemileuca  oliviae  and  Hemileuca  nevadensis.  Western  United  States. 
Hemileuca  spp.  Probably  all  species  of  the  genus  possess  urticating  hairs. 
Pseudohazis  eglanterina  and  Pseudohazis  hera.  Western  United  States. 


POISONOUS  AND  URTICATING  ARTHROPODS  581 

Undoubtedly  many  other  species  in  various  parts  of  the  world,  particularly 
in  tropical  countries. 

Nymphalidae : 

Euvanessa  antiopa.  The  mourning  cloak.  North  America  and  Europe. 
Vanessa  to.  Europe. 
Very  mild  urticating  properties,  even  to  the  most  susceptible. 

URTICATING  (Vesicating)  BEETLES:  The  principal  urticating  or 
vesicating  beetles  belong  to  the  family  Meloidae,  or  blister  beetles.  A  few 
species  are  known  from  the  Staphylinidae  that  possess  urticating  or  blistering 
properties.  In  the  Meloidae  the  urticating  or  blistering  substance  (cantharidin) 
is  contained  in  the  body  fluids.  Commer- 
cially it  is  extracted  from  the  dried  bodies 
of  various  species.  The  extract  is  used  in 
medicine  both  as  a  blistering  agent  and  in- 
ternally in  small  doses  as  a  diuretic  and  a 
stimulant  to  the  urinary  and  reproductive 
organs. 

Blister  beetles  frequently  occur  in  vast 
numbers  and  are  very  destructive  to  foli- 
age. When  such  beetles  (Fig.  235)  are 
handled,  crushed  against  the  skin,  or  in 
other  ways  come  in  contact  with  the  body, 
there  is  produced  a  distinct  dermatitis 
(vesicular).  Treatment  consists  of  prick- 
ing the  blisters  and  covering  with  anti-  . 

&        .  *  Fig,  235.  Blister  beetle   (Meloe  sp.) 

septic  dressings. 

In  the  Staphylinidae  (rove  beetles)  practically  only  one  genus,  Paederus, 
is  known  to  possess  vesicating  properties.  The  genus  contains  over  two  hun- 
dred species,  widely  distributed  throughout  the  world.  The  beetles  are  small, 
the  elytra  are  short;  they  have  the  habit  of  curling  up  the  abdomen  when  dis- 
turbed. When  handled  roughly  or  crushed  they  produce  typical  blisters  on  the 
hands  or  body.  Some  of  the  more  important  species  are  Paederus  jusdpes 
(Oriental  region) ;  P.  sabaeus  (tropical  and  South  Africa) ;  P.  cribripunctatus 
(East  Africa);  P.  peregrinus  (Java);  P.  amazonicus  (Brazil);  P.  columbinus 
(Brazil) ;  and  P.  irritans  (Ecuador) .  Gordon  states  that  the  blisters  do  not 
appear  until  a  day  or  two  after  contact.  The  blisters  are  somewhat  difficult  to 
heal.  Treatment  is  similar  to  that  recommended  for  blister  beetles.  In  all  cases, 
blister  beetles  and  rove  beetles  should  be  handled  with  care  or  avoided. 


582  MEDICAL  ENTOMOLOGY 

STINGING  INSECTS 

Stinging  insects  are  provided  with  a  sting,  a  modified  ovipositor,  which  is 
connected  with  special  poison  glands.  All  stinging  insects  belong  to  the  ordcn 
Hymcnoptera^  The  principal  families  that  contain  stinging  forms  are  the 
Apidae  (the  honeybee,  etc.);  the  Bombidae  (bumblebees);  the  Vespidae 
(wasps  and  hornets) ;  the  Sphecidae  (digger  wasps) ;  the  Mutillidae  (the  velvet 
ants) ;  the  Formicidae  (stinging  ants) ;  and  probably  a  few  others. 

The  worker  honeybee  possesses  a  very  effective  sting  and  an  adequate  supply 
of  poison  provided  by  two  types  of  poison  glands.  When  it  stings  the  entire 
sting,  the  tip  of  the  abdomen  and  poison  glands  are  left  attached  to  the  wound. 
The  muscles  continue  to  contract,  forcing  the  barbs  deeper  into  the  wound 
and  discharging  more  poison.  When  stung,  the  first  treatment  is  the  immediate 
removal  of  the  sting — not  by  seizing  it  and  pulling  it  out  (this  only  forces  in 
more  poison)  but  by  pressing  it  out  by  means  of  the  fingernail  or  a  knife 
blade.  Then  bathe  the  parts  with  weak  ammonia  and  treat  with  hot  com- 
presses. In  some  people,  especially  when  they  are  stung  over  the  eye,  on  the 
lips,  the  scrotum,  etc.,  the  effects  may  be  very  severe,  as  extensive  swelling  may 
develop,  accompanied  by  great  weakness,  labored  breathing,  etc.;  a  physician 
should  be  consulted  at  once. 

The  stings  of  wasps,  hornets,  and  bumblebees  produce  somewhat  similar 
effects,  and  the  treatment  is  the  same  as  for  the  stings  of  the  honeybee.  There 
are  many  species  of  stinging  ants,  some  of  which  possess  very  effective  stings. 
Bequaert  (1926)  calls  attention  to  the  severity  of  the  stings  of  a  ponerine  ant, 
Paraponera  davata  Fabr.  This  ant,  the  so-called  "tucandeira,"  occurs  over  an 
extensive  area  in  Central  and  South  America.  They  are  very  fierce  ants,  readily 
attacking  when  disturbed,  and  their  stings  are  very  severe. 

Within  the  past  few  years  attention  has  been  called  to  the  production  of 
coryza  and  asthma  by  the  hairs,  scales,  and  the  like,  given  off  by  various  insects. 
Parlato  (1929,  1930,  1932)  has  demonstrated  that  the  hairs  from  caddis  flies 
and  the  scales  from  moths  and  butterflies  may  be  the  cause  of  allergic  coryza 
and  asthma.  This  investigator  prepared  allergens  suitable  for  diagnostic  tests 
of  individuals  susceptible  to  such  agents.  Figley  (1929)  found  four  cases  in 
which  individuals  suffered  from  asthma  due  to  the  inhalation  of  minute 
particles  of  the  shed  skins  (windblown)  of  the  subimago  of  mayflies.  An 
extract  was  prepared  for  diagnosis  and  one  case  desensitized  by  the  injection 
of  allergen.  Benson  and  Semenov  (1930)  studied  bee  allergens,  not  only  the 
venom  and  the  adhering  pollen  but  also  an  intrinsic  bee  protein.  Ellis  and 


POISONOUS  AND  URTICATING  ARTHROPODS  583 

Ahrens  (1932)  have  found  cases  of  hypersensitiveness  due  to  air-borne  bee 
allergens. 

Many  persons  are  very  susceptible  to  insect  bites  and  stings.  Though  some 
work  has  been  done  in  attempts  to  immunize  sensitive  individuals,  the  results, 
so  far,  have  not  been  very  satisfactory.  McKinley  (1929)  briefly  summarizes 
the  results  of  previous  work.  He  has  also  attempted  to  immunize  sensitive  in- 
dividuals against  mosquito  bites.  Though  he  prepared  potent  extracts  of  the 
salivary  glands  (2000  glands  of  Aedes  uegypti),  he  failed  to  produce  any 
apparent  immunity  in  sensitive  individuals  or  even  localized  immunity  in 
small  skin  areas  by  repeated  injections  of  the  extract.  However,  he  observes 
that  some  results  indicate  that  individuals  after  prolonged  stay  in  association 
with  Aedes  aegypti  become  immune  to  its  bites.  The  problem  of  immunizing 
or  desensitizing  individuals  who  are  allergic  to  insect  bites,  stings,  or  cuticular 
products  is  one  of  considerable  importance,  and  we  may  expect  to  witness  in- 
creasing interest  and  progress  in  this  particular  line  of  work. 

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Hoffman,  C.  C.,  and  Vargas,  L.    Contribuciones  as  conocimiento  de  los  venenos 

de  los  alacranes  mexicanos.    Bol.  Inst.  Hig.  Mex.,  2  (4):  182-193,  1935. 
Illingworth,  J.  F.    Distressing  itch  from  a  moth,  Euproctis  flava  Bremer,  in  the 

Orient.    Proc.  Hawaiian  Ent.  Soc.,  6:  267-270,  1926. 
Ingram,  W.  W.,  and  Musgrave,  A.    Spider  bite  (arachnidism):  a  survey  of  its 

occurrence  in  Australia.    Med.  Jl.  Australia,  2:  10-15,  J933- 
Kellogg,  V.  L.    Spider  poisoning.    Jl.  Parasit.,  i:  107-112,  1915. 
Kephart,  C.  F.    The  poison  glands  of  the  larva  of  the  brown-tail  moth  (Euproctis 

chrysorrhoeaLmn).    Ibid.,  pp.  95-103,  1914. 


POISONOUS  AND  URTICATING  ARTHROPODS  585 

McKinley,  E.  B.    The  salivary  gland  poison  of  the  Aedes  aegypti.    Proc.  Soc. 

Exp.  Biol.  Med.,  26:  806-809,  1929. 
Mills,  R.  G.    Observations  on  a  series  of  cases  of  dermatitis  caused  by  a  liparid 

moth,  Euproctis  flava  Bremer.    China  Med.  Jl.  351-371,  1923. 
.    Some  observations  and  experiments  on  the  irritating  properties  of  the 

larvae  of  Parasa  hilarata  Staud.    Amer.  Jl.  Hyg.,  5:  342-363,  1925. 
Norman,  W.  W.    The  poison  of  centipedes,  Scolopcndra  morsltans.    Proc.  Texas 

Acad.  Sci.,  pp.  118-119,  1896. 
Parlato,  S.  J.    A  case  of  coryza  and  asthma  due  to  sand  flies   (caddis  flies). 

Jl.  Allergy,  i:  35-42,  1929. 
.    The  sand  fly  (caddis  fly)  as  an  exciting  cause  of  allergic  coryza  and  asthma. 

Ibid.,  pp.  307-312,  1930. 
.     Emanations  of  flies  as  exciting  causes  of  allergic  coryza  and  asthma.     Ibid., 

3:  125-138,  1932. 
Pavlovsky,  E.  N.    The  cutaneous  poison  of  the  beetle,  Paedcrus  juscipes.    Trans. 

Roy.  Soc.  Trop.  Med.  Hyg.,  20:  450-451,  1927. 

Phisalix,  Marie.     Animaux  venimeux  et  venims.     Paris,  1922.     2  vols. 
*Smithers,  R.  H.  N.     Contributions  to  our  knowledge  of  the  genus  Latrodectus 

in  South  Africa.     Ann.  S.  Afr.  Mus.,  36:  263-313,  1944. 
*Thorp,  R.  W.,  and  Woodson,  W.  D.     Black  widow,  America's  most  poisonous 

spider.     Chapel  Hill,  N.C.,  1945. 
Tonkes,  P.  R.     Recherchcs  sur  les  polis  urticants  des  chenilles.     Bull.  Biol.  France 

etBelg.,  67 144-99,  1933. 
Tyzzer,  E.  E.     The  pathology  of  the  brown-tail  dermatitis.     JL  Med.  Res.,  16: 

43-64,  1907. 

Walsh,  D.     Insect  bites  and  stings.    Jl.  Trop.  Med.  and  Hyg.,  27:  25-26,  1924. 
Wilson,  W.  H.     On  the  venom  of  scorpions.     Records  of  the  Egyptian  Government 

School  of  Medicine,  Cairo,  2:  7-44,  1904. 


CHAPTER  XX 


Collecting,  Preserving, 
and  Mounting  Insects 


TO  THE  average  worker  the  collection  and  preservation  of  insects  present 
many  difficulties.  The  identification  of  insects  can  be  undertaken  only 
by  specialists.  No  individual  can  hope  to  identify  all  the  groups,  not  even  those 
that  are  bloodsucking,  and  so  must  depend  on  the  generosity  of  co-operating 
specialists.  In  order  that  insects  can  be  identified  it  is  essential  that  they  be 
properly  collected,  prepared,  and  preserved. 

COLLECTION 

DIPTERA,  COLEOPTERA,  HEMIPTERA  AND  SIMILAR  INSECTS: 
For  these  insects  a  collecting  equipment  is  needed  and  should  be  of  the  simplest 
kind,  easily  handled  and  stored.  Elaborate  equipment  may  be  purchased  from 
dealers  in  natural  history  supplies,  but  this  is  not  necessary.  Of  course  the  kind, 
amount,  and  variety  of  equipment  will  depend  on  the  extent  of  the  work  the 
investigator  intends  to  undertake.  This  brief  outline  is  not  intended  for  the 
specialist  but  for  the  beginner,  the  medical  man,  the  public  health  worker,  or 
others  who  may  desire  to  carry  on  some  entomological  investigations.  A  col- 
lecting net  is  essential,  and  this  may  be  a  homemade  affair  or  purchased.  For 
most  of  our  insects  it  can  consist  of  a  piece  of  wire,  heavy  brass  or  ordinary 
galvanized  wire  of  sufficient  weight,  bent  into  a  circle,  some  TO  to  12  inches 
in  diameter,  the  ends  of  which  are  twisted  about  each  other  to  form  a  handle 
or  the  ends  may  be  carefully  twisted  about  a  small  cylinder  and  thus  form 
a  more  comfortable  handle.  Small  muslin  bags,  about  i  to  i %  feet  deep,  are 
prepared,  and  one  is  sewed  on  the  ring.  The  extra  bags  should  be  carried  as 
reserves.  For  collecting  aquatic  forms,  as  the  larvae  of  mosquitoes,  black  flies, 
and  the  like,  a  special,  rather  heavy  net  is  required.  In  order  to  combine  both 
the  air  net  and  water  net,  the  writer  uses  a  cane  especially  fitted  with  a  brass 
tip  (Fig.  236).  Into  the  brass  tip  is  inserted  a  stout  screw  which  can  be  easily 


COLLECTING,  PRESERVING,  MOUNTING  INSECTS  587 

removed.  When  it  has  been  removed,  nets  fitted  on  stout  brass  rings  of  various 
sizes  (5  to  6  inches  in  diameter  and  about  5  inches  deep  for  aquatic  collecting; 
10  to  12  inches  in  diameter  and  15  to  1 8  inches  deep  for  the  air  net)  can  be 
screwed  in  and  collections  made  when  desired.  The  air  net  is  so  made  that  it 
folds  together  when  removed  from  the  cane.  By  inserting  the  screw  an  ex- 
cellent cane  is  available.  Such  an  outfit  can  be  prepared  at  almost  any  garage 
where  mechanics  are  available.  On  a  long  collecting  trip  it  is  always  advisable 
to  have  several  collecting  bags  or  one  made  of  good  material  such  as  bolting 
silk.  Bolting  silk  (the  most  suitable  quality  is  No.  oo),  though  expensive, 
makes  the  equipment  quite  permanent.  Instead  of  using  an  aquatic  net,  col- 


Pig.  236.  Details  of  a  cane  collecting  outfit  used  by  the  author.  Left:  The  cane  fitted 
with  a  brass  cap;  the  end  screw  removed.  Center:  The  small  water  net  (about  5  inches 
deep  and  5  inches  in  diameter).  Right:  The  air  net  (about  16  inches  deep).  (After 
Matheson.) 

lections  can  be  made  by  using  the  common  strainers  (3  to  5  inches  in  diameter) . 
The  strainers  may  be  tied  to  a  rod  and  used  from  the  shore  or  they  may  be 
used  alone  while  wading.  With  the  strainer  a  white  enameled  cup  of  about 
the  same  diameter  as  the  strainer  should  always  be  at  hand.  After  dipping  or 
collecting,  the  strainer  is  placed  over  the  cup  nearly  full  of  water,  and  any 
aquatic  forms  may  easily  be  observed  and  collected. 

KILLING  BOTTLES  :  Collections  may  be  made  in  small  bottles  and  the  specimens 
killed  later  in  the  laboratory  or  kept  alive  for  future  experimental  work. 
Killing  bottles  can  be  made  from  heavy  glass  tubes  (Fig.  237)  or  wide-mouthed 
bottles  (Fig.  238).  The  chloroform  bottle  is  probably  the  simplest  type  as  it 
can  be  easily  prepared  and  renewed.  In  the  bottom  of  the  tube  or  bottle  place 
cut  rubber  bands  or  small  pieces  of  rubber  to  the  depth  of  an  inch.  Fill  the 
bottle  with  chloroform  to  the  top  of  the  rubber.  Place  over  this  a  small  wad  of 


588  MEDICAL  ENTOMOLOGY 

cotton.  On  top  of  the  cotton  place  several  layers  of  blotting  paper  cut  to  fit 
the  tube  closely.  The  rubber  will  absorb  the  chloroform,  and  it  is  given  up 
gradually  so  that  such  a  bottle  should  last  several  days.  Sodium  or  potassium 
cyanide  makes  effective  killing  bottles.  Select  a  large-mouthed  bottle  or  tube 
and  place  a  small  amount  of  sawdust  in  the  bottom  (about  one-half  inch). 
Over  this  place  finely  powdered  sodium  or  potassium  cyanide;  then  add  an- 
other half-inch  of  sawdust.  This  should  be  well  packed  down,  slightly  moist- 
ened (a  few  drops  of  water),  and  covered  with  at  least  two  layers  of  thick 


Fig.  237  (left).  A  simple  chloroform  bottle  for  collecting  mosquitoes.  (After  Mathe- 
son.) 

Fig.  238  (right}.  Collecting  apparatus,  (a),  (c),  and  (d)  Cyanide  types  of  bottles. 
(b)  Chloroform  or  ether  bottle  packed  at  base  with  cut  rubber  bands,  (e)  Aspirator  tube 
(glass  tubing  with  diameter  of  %-to-%  inch  bore;  place  a  piece  of  cheesecloth  over  end 
of  glass  tube  before  inserting  it  in  the  rubber  tubing;  this  can  be  made  any  desirable  size; 
very  effective  in  collecting  small  flies  such  as  mosquitoes.) 

blotting  paper  cut  to  fit  the  bottle  closely.  Though  the  sawdust  method  is 
simple,  most  persons  prefer  plaster  of  Paris.  Instead  of  the  sawdust  place  a 
layer,  about  one-half  inch,  of  dry  plaster  of  Paris  in  the  bottom  of  the  bottle; 
over  this  add  a  layer  of  powdered  (or  small  lumps  will  do)  sodium  or  potas- 
sium cyanide.  Pour  over  this  a  layer  of  plaster  of  Paris  and  water  of  the  con- 
sistency of  thick  cream.  Allow  to  set  and  when  dry  place  over  it  two  or  three 
layers  of  heavy  blotting  paper,  cut  to  fit  the  bottle.  All  killing  bottles  should 
be  tightly  corked.  In  order  to  prevent  insects  from  becoming  rubbed  in  the 
killing  bottles  it  is  always  well  to  have  small  strips  of  soft  paper  placed  in  the 
bottles  (Fig.  238). 


COLLECTING,  PRESERVING,  MOUNTING  INSECTS  589 

PRESERVATION  AND  MOUNTING 

Adult  insects  can  be  preserved  in  alcohol  (85  per  cent),  in  formaldehyde 
(4  to  6 per  cent),  or  in  other  preserving  fluids.  A  fluid  that  is  very  satisfactory  in 
preserving  them  in  a  soft  and  pliable  condition  is  Kryger's  solution.  It  is  pre- 
pared as  follows: 

Acetic  acid  (33%)   62.5  cc. 

Mercuric  chloride  solution  (i  to  1000) 62.5  cc. 

Glycerine   62.5  cc. 

Alcohol  (90  or  95%)  500.0 cc. 

Distilled  or  ordinary  water 3I2-5  cc- 

In  general,  insects  preserved  in  liquids  are  not  easily  identified  and,  in  many 
cases,  are  impossible  of  identification.  They  may  be  preserved  dry  and  care- 
fully packed  (not  too  many)  in  small  pillboxes  between  layers  of  smooth  sheets 
of  cotton.  By  this  method  large  numbers  may  be  stored  in  small  space.  At  any 
later  time  they  can  be  prepared  for  pinning.  It  is  always  essential  that  full 
data  on  when,  where,  and  how  collected  should  be  placed  in  the  pillboxes. 

The  most  satisfactory  method,  though  tedious  and  time-consuming,  is  to 
pin  material  as  soon  as  possible  (within  a  few  hours)  after  collecting.  The 
size  of  pins  to  be  used  will  vary  with  the  size  of  the  insects.  For  small  insects 
such  as  mosquitoes  and  black  flies,  numbers  oo,  o,  and  i  are  the  most  useful. 
The  more  minute  and  fragile  flies  should  be  pinned  on  minuten  Nadeln.  The 
various  methods  are  illustrated  in  Fig.  239,  with  mosquitoes  as  examples.  In 
pinning  insects  great  care  should  be  taken  not  to  injure  or  destroy  essential 
structures  (as  hairs,  spines,  scales,  etc.)  needed  for  identification.  Large  Diptera 
can  be  pinned  directly  through  the  thorax,  preferably  behind  the  transverse 
suture  (if  present);  small  Diptera  can  be  pinned  in  a  similar  manner  using 
very  fine  pins  (No.  oo),  or  they  can  be  pinned  through  the  side.  In  most  cases 
it  is  preferable  to  pin  first  on  minuten  Nadeln,  then  insert  the  minuten  Nadeln 
in  a  bit  of  pith,  cork,  or  balsa  wood;  a  stout  pin  is  then  driven  through  one  side 
of  the  pith,  and  the  specimen  is  ready  for  labeling  (Fig.  239  b).  Most  workers 
keep  a  series  of  cork  blocks  with  the  minuten  Nadeln  driven  through  them, 
ready  for  pinning  small  insects.  For  Hemiptera,  Hymenoptera,  and  some 
other  large  insects  the  pins  are  driven  directly  through  the  thorax.  Coleoptera 
(beetles)  should  be  pinned  through  the  right  elytra,  the  pin  driven  in  a  slanting 
fashion  so  that  it  emerges  in  the  middle  line  on  the  ventral  side.  In  pinning 
insects  it  is  always  a  good  practice  to  have  sheets  of  thin  cork  or  balsa  wood  at 
hand,  and  these  serve  as  backgrounds  on  which  to  pin.  In  handling  these  fine 


590 


MEDICAL  ENTOMOLOGY 


pins  good  forceps  should  be  available  and,  preferably,  a  suitable  pinning  for- 
ceps (Fig.  240) .  Exceptionally  fine  pinning  forceps  are  the  so-called  "Cresson" 
type  of  entomological  pliers  manufactured  by  the  Cleveland  Dental  Manu- 
facturing Company. 

After  the  insects  are  pinned  each  one  should  bear  a  label  stating  the  place 
and  time  of  collection,  the  collector's  name,  and  any  other  pertinent  data.  The 
pinned  material  should  be  stored  in  insect  cases,  of  which  a  great  variety  are  on 
the  market.  Old  cigar  boxes  lined  with  sheet  cork,  balsa  wood,  or  even  corru- 
gated paper  make  excellent,  temporary  storage  places.  In  the  tropics  and  damp 


Fig.  239  (left).  Various  methods  for  mounting  insects,  (a)  A  mosquito  pinned  on  a 
cardboard  point,  (b)  Pinned  on  a  minutcn  NadeL  (c)  Pinned  directly  through  the  thorax. 
(d)  Adhering  to  a  drop  of  shellac  on  the  side  of  the  pin.  (After  Matheson.) 

Fig.  240  (right) .  A  type  of  pinning  forceps  (not  the  "Cresson"  type) . 

climates  it  is  very  difficult  to  keep  pinned  insects  unless  they  are  stored  in  tight, 
dry  receptacles.  Christophers  recommends  pinning  small  insects  on  short,  fine 
pins  on  small  sheets  of  cork,  which  are  stored  in  vials,  corked,  and  sealed  with 
paraffin.  Large  insects  can  be  pinned  on  the  cork  of  the  bottle,  then  the  cork 
is  inserted  and  sealed. 

When  insects  have  been  allowed  to  dry  or  have  been  stored,  they  must  be 
relaxed  before  they  can  be  pinned.  The  simplest  type  of  relaxing  jar  is  a  large, 
deep  petri  dish.  Place  moistened  filter  or  blotting  paper  on  the  bottom  of  the 
dish;  over  this  add  some  soft  nonabsorbent  paper  and  then  add  the  insects 
to  be  relaxed.  Cover  and  allow  to  remain  until  the  insects  have  become  suf- 
ficiently soft  that  they  can  be  pinned  without  danger  of  breakage.  In  this  work 
avoid  too  much  moisture  and  too  many  insects;  be  careful  not  to  let  the  speci- 
mens remain  too  long  in  the  moist  chamber.  It  usually  requires  overnight  or, 


COLLECTING,  PRESERVING,  MOUNTING  INSECTS  591 

ill  the  case  of  large  insects,  a  day  or  two.  After  they  are  relaxed,  pin  in  the 
ordinary  fashion. 

Insect  cases  of  all  kinds,  even  the  best  manufactured,  soon  become  infested 
with  small  museum  pests  that  may  destroy  the  dried  bodies  of  the  insects  if 
care  is  not  exercised.  As  a  precaution  always  sprinkle  naphthalene  flakes  in  the 
bottoms  of  the  cases,  or  store  in  small  boxes  in  the  cases,  or  use  the  prepared 
cones.  "Globol,"  a  patented  product,  is  very  effective  and  usually  can  be  pur- 
chased from  dealers  in  natural  history  supplies.  When  a  collection  becomes 
infested,  fumigate  with  carbon  disulphide,  pouring  the  liquid  directly  in  the 
cases  or  on  cotton. 

TICKS:  Ticks  (Ixodidae)  may  be  collected  from  their  hosts  or  in  their  hosts' 
habitats  (the  Argasidae).  In  searching  an  animal  for  ticks,  exercise  great  care 
and  examine  all  parts,  particularly  around  and  in  the  ears,  back  of  and  under 
the  head,  over  the  root  of  the  tail,  and  inside  the  flanks.  For  most  argasid  ticks 
the  host's  habitat  should  be  searched,  examining  all  cracks  and  crevices,  cracks 
in  the  soil,  trash,  and  any  other  debris.  In  many  cases,  as  with  certain  Ornitho- 
doros  species  that  bury  themselves  in  the  soil,  collect  the  soil  and  sift  it  over 
white  paper  or  cloth.  This  method  is  also  effective  when  the  habitats  of  burrow- 
ing animals  are  searched.  Ticks  should  be  removed  from  their  hosts  with  care 
so  as  not  to  leave  the  capitulum  deeply  buried  in  the  skin.  Usually  the  applica- 
tion of  chloroform  or  vaseline  will  induce  the  tick  to  withdraw  its  capitulum. 
Ticks  should  be  preserved  in  alcohol  (85  per  cent)  in  small  vials  with  the  exact 
name  of  the  host  and  time  and  place  of  collection.  Never  mix  collections  from 
different  hosts. 

OTHER  MITES :  In  the  case  of  permanent  parasitic  mites  as  Sarcoptes  spp. 
and  Psoroptes  spp.,  the  skin  should  be  carefully  scraped  so  as  to  reach  the 
deeper  parts.  In  the  case  of  dead  animals,  parts  of  the  diseased  skin  should  be 
cut  out  and  preserved.  Always  be  sure  to  obtain  sufficient  material  and  preserve 
in  alcohol  (85  per  cent).  If  it  is  desired  to  fix  such  material  for  histological 
purposes,  place  in  the  desired  fixing  fluid  and  follow  the  technique  advised  for 
the  particular  fixative.  Patton  strongly  advises  Bles's  fluid  as  a  general  and 
effective  fixing  solution.  It  is  prepared  as  follows: 

70%  alcohol  90  parts 

Formalin  (40%  formaldehyde)   7  parts 

Glacial  acetic  acid 3  parts 

The  greatest  defect  of  this  simple  fluid  is  that  it  has  to  be  prepared  fresh  for  it 
rapidly  deteriorates.  Fix  in  it  for  24  hours;  decant  and  add  fresh  Bles's  fluid; 


592  MEDICAL  ENTOMOLOGY 

leave  for  24  hours;  decant  and  preserve  in  70  per  cent  alcohol,  which  should  be 

changed  to  85  per  cent  for  permanent  storage. 

LICE:  Sucking  lice  are  always  found  on  their  hosts.  The  simplest  method 
of  removal  is  by  means  of  a  fine-toothed  comb.  Some  infested  hair  should  be 
cut  off  and  preserved.  Always  cut  the  hair  close  to  the  skin  so  as  to  obtain  the 
eggs  (nits)  and  the  nymphal  stages.  As  lice  usually  remain  and  die  with  their 
host  they  can  be  collected  from  the  preserved  skins  or  carcasses.  Remove  them 
with  a  comb.  When  collecting  living  lice  always  keep  them  alive  till  they 
have  digested  their  blood  meal;  it  is  much  easier,  then,  to  prepare  th0$&  for 
study.  Always  preserve  in  alcohol  (85  per  cent). 

FLEAS:  Fleas  are  most  easily  obtained  directly  from  their  hosts.  The  col- 
lection of  therh  is,  at  times,  rather  difficult.  In  places  where  they  arc  abundant, 
as  frequently  in  rat-infested  buildings,  basements,  houses,  etc.,  they  can  be  col- 
lected in  numbers  by  walking  about  with  the  legs  wrapped  with  sticky  flypaper. 
The  fleas  will  be  caught  on  the  paper  and  can  be  removed  later.  For  the  chigoe, 
sand  flea,  or  jigger,  animals  such  as  small  pigs  can  be  used  as  traps.  The  pigs 
are  allowed  to  roam  over  the  infested  ground  or  they  are  held  on  their  backs. 
Castellani  and  Chalmers  state  that  the  fleas  readily  collect  on  them  and  can 
be  removed.  Fleas  normally  leave  their  hosts  at  the  time  of  the  latter's  death. 
When  shooting  birds,  squirrels,  small  rodents,  and  the  like  for  the  purpose 
of  collecting  fleas,  the  dead  animals  should  be  placed  promptly  in  tight  paper 
bags  and  the  bags  securely  tied.  The  fleas  can  be  collected  later.  We  have  found 
that  a  most  satisfactory  method  (devised  by  Dr.  Wilson)  for  the  collection 
of  both  biting  lice  and  fleas  is  the  prompt  wrapping  of  the  dead  animal  in  a 
layer  of  cheap  absorbent  cotton;  the  fleas  and  biting  lice  leave  the  body  of  the 
host  as  soon  as  it  is  cold  and  become  entangled  in  the  fine  cotton  fibers.  When 
the  cotton  is  removed,  the  fleas  and  lice  can  be  seen  as  small  black  spots  and  are 
easily  collected.  In  fact,  the  cotton  wrappings  can  be  removed  in  a  day  or  two, 
the  dead  animal  thrown  away,  and  the  cottons,  labeled  and  stored,  can  be 
searched  at  any  convenient  time.  The  fleas  and  lice  will  be  found  entangled 
in  the  cotton  fibers.  When  burrows  of  rodents,  birds'  nests,  etc.,  are  searched 
for  fleas,  the  simplest  method  is  to  collect  a  large  amount  of  the  earth  and 
debris  in  and  about  the  burrow  (take  the  entire  bird's  nest),  place  in  a  tight 
paper  or  closely  woven  cotton  sack,  and  examine  later. 

MOSQUITOES:  Mosquitoes  are  difficult  to  collect  in  an  ordinary  air  net 
because  they  become  so  rubbed  when  removing  them  tediously  by  hand.  Most 
workers  have  to  contend  with  the  collecting  of  adult  anophelines  from  build- 
ings, under  bridges  and  houses,  from  hollows  in  trees,  etc.  This  work  is  time- 


COLLECTING,  PRESERVING,  MOUNTING  INSECTS  593 

consuming,  especially  if  one  collects  with  the  ordinary  cyanide  bottle  or 
attempts  to  capture  the  mosquitoes  in  individual  bottles  in  order  to  obtain 
living  specimens.  Fig.  238  e  illustrates  what  has  been  called  an  "exhauster"  or 
aspirator,  which  is  easily  constructed  by  anyone.  With  such  an  apparatus  small 
insects  such  as  mosquitoes  can  be  readily  collected  and  then  blown  out  into 
cyanide  jars  or  other  containers  if  desired  alive.  Large  numbers  can  be  col- 
lected quickly  when  the  technique  is  mastered. 

,,XHE  PREPARATION  OF  SMALL  INSECTS  FOR  STUDY 

Most  of  the  smaller,  parasitic  arthropods,  as  mites,  lice,  fleas,  and  larvae  of 
all  kinds,  have  to  be  prepared  for  microscopical  examination.  If  detailed  his- 
tological  study  is  the  objective,  the  methods  of  killing,  fixing,  and  preserving 
the  specimens  in  suitable  media  can  be  found  in  any  of  the  numerous  standard 
texts  on  histological  technique.1  To  prepare  for  microscopic  mounts  the  fol- 
lowing method  is  probably  the  simplest  and  most  easily  carried  out:  If  the 
specimens  are  in  alcohol,  formaldehyde,  or  other  preservative,  soak  them  in 
water  for  some  time — a  few  hours  to  a  day.  Then  place  them  in  cold  potassium 
hydroxide  (10  per  cent  solution)  and  allow  to  remain  until  clear  (usually  a  few 
hours  to  a  day).  If  speed  is  essential,  bring  the  cold  potassium  hydroxide  slowly 
to  the  boiling  point  and  boil  only  long  enough  to  destroy  the  fleshy  parts  (this 
time  can  be  learned  only  from  experience,  usually  a  few  seconds  to  several 
minutes).  With  many  insects  as  lice,  fleas,  and  larvae,  it  is  essential,  in  order 
to  obtain  good  mounts,  that  the  insects  be  punctured  or  cut  with  fine  scissors 
or  scalpel.  The  worker  must  learn  his  procedure  from  experience.  (The  writer 
punctures  lice,  fleas,  and  other  insects  before  soaking  them  in  potassium 
hydroxide,  the  punctures  being  so  made  that  no  injury  is  done  to  essential 
structures.)  When  suitably  cleared,  remove  them  from  the  potassium  hydroxide 
and  bring  to  a  boil  in  a  large  amount  of  water.  (The  writer  usually  makes 
two  changes  of  water,  bringing  to  a  boil  each  time.)  The  water  removes  the 
caustic  potash  and  most  of  the  remaining  fleshy  parts.  If  the  insects  or  parts 
are  small,  transfer  directly  from  the  water  to  a  slide  and  begin  to  dehydrate 
by  starting  with  50  or  70  per  cent  alcohol.  Then  run  through  the  alcohols 
directly  on  the  slide,  allowing  a  few  minutes  (5  to  10)  for  each  grade.  Finally 
dehydrate  in  absolute  alcohol  2  and  mount  in  euparal.  The  writer  finds  cuparal 
the  best  and,  at  the  same  time,  the  most  permanent  mounting  media.  This 

1  Pattern  recommends  Bles's  fluid  as  the  best  all-round  fixing  fluid. 

2  Dehydration  can  be  done  directly  from  water  with  cellosolve — from  water  to  50  per 
cent  cellosolve  for  5  to  10  minutes,  then  in  pure  cellosolve  for  the  same  time.  Mount  with 
euparal. 


594  MEDICAL  ENTOMOLOGY 

media  clears  in  less  than  24  hours  and  hardens  in  about  the  same  time.  If  the 
specimens  are  thick  or  should  not  be  compressed,  the  writer,  instead  of  using 
the  expensive  hollow-ground  slides,  employs  small  pieces  of  crushed  glass  in 
the  mounting  media  or  narrow  strips  of  thin  or  thick  cardboard  or  microcells 
(the  microcells  are  of  glass  or  hard  rubber;  these  can  be  purchased  in  almost 
any  size  and  thickness) .  In  handling  small  insects  or  parts  of  insects  the  writer 
always  manipulates  the  parts,  as  legs  and  genitalia,  while  they  are  in  the  water 
on  the  slide.  This  is  done  under  the  binocular  microscope  and  it  is  easy  to 
spread  out  the  parts  while  they  are  soft.  Final  arrangement  (orientation  of 
the  specimens)  is  made  in  the  euparal  by  means  of  minute  needles  (ordinary 
sewing  needles,  inserted  in  small  wooden  handles;  the  points  being  carefully 
ground  on  fine  carborundum). 

For  larvae,  especially  mosquito  larvae  and  others  of  about  the  same  size, 
the  writer  finds  the  most  satisfactory  method  is  to  kill  in  hot  water  (at  about 
the  boiling  point),  run  through  the  alcohols  (beginning  with  30  per  cent), 
dehydrate  in  absolute  alcohol,  and  mount  direct  in  euparal.  The  mosquito 
larvae  are  cut  (either  in  the  absolute  alcohol  or  in  euparal  on  the  slide)  just  in 
front  of  the  eighth  segment.  By  this  means  a  lateral  view  of  the  siphon  and 
last  two  segments  is  obtainable.  The  entire  larvae  clear  and  make  permanent 
mounts  of  great  value  (I  have  them  in  perfect  condition  after  thirty  years). 
Furthermore,  in  the  euparal  the  finest  hairs  and  spines  stand  out  with  the 
greatest  clearness  (due  to  the  refractive  index  of  the  euparal). 

Other  methods  are  extensively  used.  Such  are  mounting  in  glycerine  and 
glycerine  jelly.  Prepare  material  as  outlined  above  but  instead  of  dehydrating 
in  the  alcohols  mount  direct  (from  the  water)  in  glycerine  and  seal  the  cover- 
slip  (various  sealing  media  are  on  the  market  but  the  writer  has  found  Bell's 
cement  to  answer  best  for  every  purpose) .  Mounting  can  also  be  done  directly 
from  water  to  glycerine  jelly,  though  it  is  preferable  to  place  the  material  first 
in  50  per  cent  glycerine  (water  and  glycerine  in  equal  parts).  The  glycerine 
jelly  is  placed  on  the  slide,  warmed  till  it  melts,  and  the  object  placed  in  it  and 
covered  with  a  cover  slip.  Such  mounts  must  be  sealed.  Unfortunately,  all 
glycerine  or  glycerine  jelly  mounts  dry  out  in  time  despite  the  most  careful 
sealing.  Canada  balsam  is  probably  the  most  extensively  employed  mounting 
medium,  but  the  writer  has  not  used  it  for  the  past  thirty  years,  preferring 
euparal  for  all  purposes,  even  for  the  finest  histological  preparations.  If  Canada 
balsam  is  desired,  prepare  as  outlined  for  euparal  but  before  mounting  (after 
treatment  with  absolute  alcohol)  3  clear  in  xylol,  clove  oil,  or  other  clearing 

3  If  absolute  alcohol  is  not  available  it  can  easily  be  prepared  from  commercial  95  per 
cent.  Dehydrate  copper  sulphate  crystals  by  dry  heat  till  they  become  a  fine  white  powder. 


COLLECTING,  PRESERVING,  MOUNTING  INSECTS  595 

media  and  then  mount  in  the  balsam.  Mounts  made  in  euparal  or  balsam, 
especially  if  the  parts  are  thick,  should  be  watched  as  they  dry,  and  small 
drops  of  the  mounting  media  added  at  the  side  of  the  cover  slip  to  avoid  the 
development  of  extensive  bubbles. 

For  the  larger  larvae  as  those  of  the  Muscidae  it  is  better  to  preserve  in  alcohol 
(85  per  cent)  or  Kryger's  solution.  For  examination  of  the  chitinous  parts 
the  entire  larvae  or  parts  of  them  can  be  boiled  in  caustic  potash  and  then 
prepared  and  mounted  in  the  usual  manner. 

DISSECTIONS  OF  INSECTS 

The  dissections  of  insects  involve  technique  and  skill.  Carefull  attention  to 
details  and  the  utilization  of  practically  fresh  or  recently  killed  material  are 
required.  With  the  larger  forms  it  is  possible  to  make  fair  dissections  with 
fixed  material,  but  this  is  rarely  advisable.  As  far  as  the  average  worker  (ex- 
clusive of  the  laboratory  worker,  investigator,  and  teacher  for  whom  this  out- 
line is  not  intended)  is  concerned,  the  most  important  technical  problem  is  the 
dissection  of  mosquitoes  for  the  examination  of  the  salivary  glands  or  stomach 
for  infection  with  the  malaria  parasites.  This  dissection  is  comparatively  easy 
and  can  be  done  by  the  average  beginner  with  considerable  assurance  of  suc- 
cess. Equipment  need  be  only  some  small,  sharp  dissecting  needles  (ordinary 
sewing  needles  inserted  in  small  wooden  handles  serve  excellently;  the  larger 
needles  can  be  made  into  microscopic  scalpels  by  carefully  grinding  them  on  a 
fine  stone  under  a  hand  lens  or  a  binocular  microscope) ;  a  few  miscroscopic 
slides,  pipettes,  cover  slips,  saline  solution  (0.9  per  cent),  a  dissecting  micro- 
scope (not  essential),  and  a  compound  microscope.  If  a  binocular  microscope 
(magnifications  24*  to  72x)  is  available,  the  worker  is  relieved  of  many  trials. 

Kill  the  mosquito  with  chloroform  (do  not  wet  the  mosquito)  or,  as  the 
writer  does,  stupefy  it  with  tobacco  smoke  in  a  small  vial.  Place  the  mosquito 
on  a  slide  and  cut  off  the  wings  and  legs.  Remove  the  scales  and  hairs  with  a 
small  brush.  With  the  mosquito  on  its  side  cut  across  the  base  of  the  thorax 
(Fig.  242)  so  that  the  abdomen  is  set  free.  Now  transfer  the  abdomen  to  a 
clean  slide  in  a  drop  of  saline  solution.  With  fine  needles  gradually  cut  the 
abdominal  wall  around  the  base  of  the  seventh  segment  (Fig.  241),  being  care- 
ful not  to  penetrate  too  deeply  into  the  body  cavity  and  cut  the  alimentary 
canal.  With  this  operation  completed  the  alimentary  canal  can  be  removed  by 
traction.  Insert  a  needle  in  the  dorsal  part  of  the  thorax  and  place  another  in 

Place  a  varying  amount  in  95  per  cent  alcohol  (depending  on  the  quantity  of  absolute 
alcohol  desired)  and  allow  the  copper  sulphate  to  settle.  In  a  few  hours  decant  off  the 
alcohol  and  it  will  be  nearly  100  per  cent  pure. 


596  MEDICAL  ENTOMOLOGY 

the  separated  tip  of  the  abdomen  (Fig.  241).  By  gently  pulling  and  relaxing," 
you  can  remove  the  alimentary  canal  with  its  attached  organs.  It  can  then  be 
examined  in  saline  solution  under  a  cover  slip  or  prepared  in  any  way  desired. 
To  dissect  out  the  salivary  glands,  prepare  the  mosquito  as  directed  above. 
Then  make  two  clean  cuts  across  the  thorax  as  indicated  in  Fig.  242.  The  sali- 
vary glands  are  minute  glands  lying  in  the  thorax  just  above  and  slightly  in 
front  of  the  first  pair  of  legs  (Fig.  242  S.).  Place  the  cut-ofT  anterior  portion 
in  a  drop  of  saline  solution.  Insert  a  needle  in  the  head  and  one  in  the  thorax 
above  the  second  pair  of  legs.  Then  by  gently  drawing  the  two  needles  apart 
the  neck  membrane  should  rupture  and  the  glands  and  other  tissues  be  drawn 


Fig.  241  (/<?//).  The  dorsum  of  the  abdomen  of  a  mosquito  with  needles  in  position  for 
cutting  around  the  tip  of  the  seventh  abdominal  segment.  (2)  Needles  in  position  gradu- 
ally to  withdraw  the  intestinal  tract. 

Fig.  242  (right).  The  upper  figure  shows  the  two  cuts  across  the  thorax  of  a  mosquito 
preparatory  to  the  removal  of  the  salivary  glands.  The  lower  figure  shows  the  needles  in 
position  ready  to  pull  out  the  glands.  S,  position  of  glands. 

out.  The  salivary  glands  may  be  recognized  by  their  glistening  appearance  and 
their  structure.  Patton  recommends,  after  removing  the  wings  and  legs,  placing 
the  entire  mosquito  in  some  saline  solution;  then  insert  a  needle  in  the  head 
and  another  in  the  thorax;  make  a  number  of  gentle  pulls  with  more  or  less 
side  to  side  movement;  at  the  same  time  exert  pressure  on  the  thorax  to  force 
the  blood  into  the  head.  This  will  cause  the  neck  to  bulge;  if  these  movements 
are  gently  continued,  the  membrane  will  break  and  the  glands  may  be  drawn 
out  and  examined  as  already  indicated. 

To  determine  the  presence  of  the  malaria  sporozoites  or  oocysts  it  is  not 
necessary  to  fix  and  stain  the  salivary  glands  or  the  stomach.  Simply  mount 
in  saline  solution  and  examine  with  the  high  powers  of  the  compound  micro- 
scope. The  characteristic  sporozoites  can  be  seen  in  the  glands  or  in  the  sur- 
rounding fluid;  the  oocysts  can  be  recognized  in  the  walls  of  the  stomach.  If 


COLLECTING,  PRESERVING,  MOUNTING  INSECTS  597 

a  staining  is  desired,  tease  out  the  glands  or  stomach  so  that  they  adhere 
firmly  to  the  slide  but  do  not  allow  them  to  become  dry.  Fix  and  stain  with 
one  of  the  Romanowsky's  stains.  (Wright's  modification  is  an  excellent  routine 
stain;  it  can  be  purchased  of  any  reputable  house  dealing  in  chemical  reagents.) 
For  the  dissection  of  other  insects,  fresh  material,  patience,  and  skill  will 
reward  the  worker  with  beautiful  results.  A  little  ingenuity  and  not  too  much 
equipment  is  usually  the  sine  qua  non  of  good  work. 

THE  REARING  OF  INSECTS 

The  methods  of  rearing  and  handling  insects  under  experimental  conditions 
have  been  developed  to  a  high  state  of  perfection  in  certain  groups.  It  would 
take  us  too  far  afield  and  occupy  too  much  space  to  outline  these  methods  here. 
Instead  it  is  proposed  to  call  the  attention  of  the  beginner  as  well  as  the  ad- 
vanced student  to  specific  articles  or  books  that  outline  in  some  detail  the 
methods  employed  by  specialists.  In  most  cases  the  simplest  and  least  com- 
plicated procedure  will  give  not  only  the  desired  but  oftentimes  the  best  results. 
Extensive  accounts  of  rearing  technique  will  be  found  in  the  various  references 
given  under  the  different  chapters  of  this  book.  These  should  be  consulted. 
Only  a  few  will  be  listed  in  the  references  to  be  given  at  the  end  of  this  chapter. 

Here  again  the  most  pressing  problem  to  the  average  worker  is  the  rearing 
of  mosquitoes.  In  practically  all  genera,  except  the  genus  Anopheles,  it  is 
possible  to  determine  the  different  species  from  the  examination  of  the  larvae 
(fourth  stage).  With  Anopheles  it  is  always  desirable  to  breed  out  the  adults. 
This  can  be  done  with  the  simplest  of  equipment.  Ordinary  finger  bowls  make 
excellent  rearing  dishes  (practically  any  kind  of  dishes  will  serve).  When 
making  larval  collections  for  the  purpose  of  rearing,  care  should  be  exercised 
to  secure  larvae  from  definite  water  area  types.  Each  collection  should  be  kept 
separate  and  a  supply  of  the  various  types  of  water  brought  in  for  the  rearing 
work  (ordinary  tap  water  is  usually  not  very  suitable) .  Always  place  the  larvae 
at  first  in  a  large  dish  with  plenty  of  water.  When  the  larvae  appear  in  the 
fourth  stage,  separate  them  into  individual  rearing  dishes,  a  single  larva  to 
a  dish.  The  simplest  individual  rearing  dish  is  a  6-  to  8-drachm  vial.  These  vials 
can  be  placed  in  a  large  board  in  which  holes  have  been  bored  partially 
through  the  wood.  Cotton  plugs  or  cheesecloth  will  serve  to  close  the  vials. 
In  this  way  large  numbers  of  larvae  can  be  isolated  without  too  much  labor. 
If  the  larvae  are  young  when  placed  in  the  vials,  it  is  desirable  to  change  the 
water  every  second  day.  The  writer  has  found  the  best  and  most  easily  obtain- 
able food  is  yeast  (Fleischmann's  yeast  cakes) — a  small  particle  to  each  vial. 
Be  careful  not  to  add  too  much. 


598  MEDICAL  ENTOMOLOGY 

When  each  larva  pupates,  the  larval  skin  should  be  removed,  carefully  ex- 
panded in  water  on  a  slide,  then  dehydrated  (the  writer  starts  with  70  per  cent 
alcohol 4),  and  mounted  in  euparal.  Treat  the  pupal  skin  similarly  and  mount 
on  the  same  slide  with  the  larval  skin.  (The  writer  uses  5-mm.  cover  slips  so 
that  it  is  easy  to  mount  larval  skin,  pupal  skin,  and,  if  a  male,  the  genitalia  on 
the  same  slide.)  The  adult  should  be  pinned  and  some  system  should  be  de- 
vised so  that  slide  material  can  be  connected  with  the  pinned  specimens.  If 
mounting  of  the  skins  is  not  feasible,  preserve  them  in  small  vials.  Always 
be  careful  to  label  all  material.  If  this  simple  procedure  is  followed,  extensive 
biological  data  can  be  secured  with  a  minimum  of  labor  and  equipment. 

MYIASIS-PRODUCING  FLIES:  When  maggots  are  removed  from 
wounds,  cavities,  and  the  like,  or  are  passed  in  the  feces  and  urine  or  vomited, 
it  is  highly  desirable  to  rear  the  adults.  It  is  almost  impossible  to  make  specific 
identifications  of  fly  larvae.  If  the  worker  has  the  time  and  facilities  he  can 
usually  determine  the  family  to  which  a  larva  belongs  by  an  examination  of 
the  posterior  spiracles  and  by  using  the  key  given  on  page  531.  In  the  case  of 
specific  myiasis-producing  flies  the  writer  has  found  (following  the  method 
devised  by  Walker)  the  simplest  procedure  is  to  place  the  maggot  on  a  piece 
of  fresh  beef  on  about  two  inches  of  moist  sand  in  a  large  glass  tube.  Plug 
tightly  with  cotton  or  cover  with  several  layers  of  cheesecloth  held  in  place 
by  a  rubber  band.  Examine  each  day  and  replace  the  meat  when  it  begins  to 
decay.  When  the  maggot  enters  the  soil  remove  the  meat  and  await  the 
emergence  of  the  fly.  Always  search  for  the  empty  puparium  and  preserve  it. 
In  the  case  of  semispecific  myiasis-producing  flies  this  method  may  serve 
equally  well  but  it  is  preferable  to  use  decaying  vegetable  matter  for  the  mag- 
gots of  most  of  the  Muscidae. 

Medical  men  should  always  make  records  of  cases  of  myiasis  and,  if  the  mag- 
gots cannot  be  reared,  preserve  them  and  send  to  specialists.  The  author  is 
always  glad  to  receive  material  and  will  identify  or  obtain  identification  by 
specialists  (in  groups  with  which  he  is  not  familiar). 

A  NEW  MOUNTING  MEDIUM:  Recently  there  has  been  introduced  a 
new  medium  for  the  mounting  of  small  insects.  It  is  especially  valuable  for  the 
permanent  mounting  of  mites,  lice,  fleas,  mosquito  larvae,  mosquito  genitalia, 
and  dissected  material.  The  writer  has  found  the  following  formula  most  use- 
ful (Downes,  Science,  95:633,  1942). 


4  Cellosolve  is  an  excellent  dehydrating  medium.  Start  with  a  50  per  cent  mixture  of 
cellosolve  and  water;  then  go  directly  to  pure  cellosolve.  Mount  in  euparal  without  further 
clearing. 


COLLECTING,  PRESERVING,  MOUNTING  INSECTS  599 

Dissolve  polyvinal  alcohol  (of  medium  vicosity)  in  hot  water  till  it  makes 
a  thick  syrup.  This  is  the  stock  solution.  Make  up  the  medium  as  follows: 

Stock  solution 56% 

Lactic  acid 22% 

Phenol  (C.P.)    22% 

The  percentages  are  all  by  volume.  Mix  the  lactic  acid  and  phenol  in  a  warm 
solution  (stock)  until  it  clears.  If  bubbles  form",  heat  the  mixture  and  allow  it 
to  stand  until  it  is  clear.  Store  in  bottles  and  use  as  a  mounting  medium. 
Mounting  can  be  done  directly  from  water,  with  living  or  dead  material.  Cover 
with  the  usual  cover  slips;  drying  and  hardening  are  rapid.  For  rapid  clearing 
the  slides  may  be  warmed.  Such  mounts  appear  to  be  permanent. 

REFERENCES 

Banks,  N.    Directions  for  collecting  and  preserving  insects.    U.S.  Nat.  Mus., 

Washington,  D.C.,  Bull.  67,  1909.  (Excellent  account  with  many  illustrations.) 
Blacklock,  B.  Notes  on  an  apparatus  for  the  individual  breeding  of  mosquitoes. 

Ann.  Trop.  Med.  Parasit.,  15:  473-477,  1921. 
Boycl,  M.  F.,  et  al.    The  inscctary  rearing  of  Anopheles  quadrimaculatus.     Amer. 

Jl.  Trop.  Mcd.,  15:  385-402,  1935. 
MacGregor,  M.  E.     Mosquito  surveys.     London,   1927.     (Extended  account  of 

mosquito  technique.) 
Needham,  J.  G.,  et  al.    Culture  methods  for  invertebrate  animals.    Ithaca,  N.Y., 

I937- 
Sellards,  A.  W.    Technical  precautions  employed  in  maintaining  the  virus  of 

yellow  fever  in  monkeys  and  mosquitoes.     Amer.  Jl.  Trop.  Med.,  12:  79-92, 

1932.  (Splendid  account  for  those  who  plan  to  work  with  insect-borne  diseases.) 
Trembley,  H.  L.  Mosquito  culture  technique.  Mosq.  News.,  Dec.  1944,  pp. 

103-119. 

Consult  the  references  under  each  of  the  groups. treated  in  this  book.  Practically 
every  worker  gives  a  brief  or  extended  account  of  his  rearing  and  experimental 
technique. 


Index 


Abdomen,  22,  149 
Acalyptcratae,  227 

nigripfs,  281 
nubilns,  355 

418 

punctocostalis,  -354 

Acampis  woodi,  113 

punctor,  281,  290 

Acarina,  24 

scapularis,  355 

key  to  suborders  and  super- 

sen  tell  arts,  289,  362 

families,  25 

scrratus,  355 

Acrostichals,  224 

simpsoni,  289,  354 

Adenitis,  362 

sollidtans,    265,    281,    290, 

Adoneta  spinuloides,  579 

3ii 

Acdacgus,  159 

spencer  it,  281,  311 

Aedes,  281,  282-291,  316,  317 

squamiger,  290,  311 

Aedes  aconitus,  362 

sticticus,  281 

aegypti,  5,  6,  284-288,  310, 

stimulans,  260,  267,  281,  290 

358,  362,  365,  583 

j/o^/,  354 

var.  queen  standicus,  354 

taeniorhynchus,    281,    290, 

africanus,  290,  354 

3H,  356,  362,  365 

albopictus,  6,  288-289,  354, 

/ay/or/,  354 

358 

ten-ens,  355 

alternant,  3  1  1 

thibaulti,  362 

argenteus,  see  aegypti 

/o^o/,  362 

calopus,  see  aegypti 

trie  hunts,  282 

campestris,  281 

triseriatus,  355 

canadensis,  282,  365 

vexans,  252,  281,  290,  311, 

cinercus,  264 

312,  365 

communis,  281,  290 

vigilax,  311 

dorsalis,  281,  290,  360 

vittattts,  354 

excrucians,  281,  282,  290 

Aedimorphus,  283 

fitchii,  282,  291 

Aedomyia,  316,  318 

fluviatilis,  355 

African  eye  worm,  3 

julvithorax,  355 

Aleppo  boil,  244 

geniculatus,  356 

Allergens,  582 

intrudens,  282 

Allodermanyssus      sanguineus, 

irritant,  354 

96 

later  alts,  281,  311 

Alonatta  senicidus,  357 

leucocelaenus,  355 

Amblyomma,  46,  63 

lutfocephalus,  354 

Amblyomma  americanum,  49, 

mctallicus,  354 

63,74,78 

nearticus,  281 

cajennense,  49,  64,  68,  74, 

nigriccphalus,  354 

356,5i8 

hebractim,  49,  65,  79,  82 

maculattim,  49,  64 

rotundatttm,  48 

variegatum,  82 
American  roach,  166 
Amphipncustic,  157 
Anal  veins,  147 
Analgcsidac,  99 

Anaplasma  marginale,  66,  80 
Anaplasmosis,  80 
Anemia  of  horses,  446 
Anopheles,  292-307 

dispersion   and   flight,   307- 
310 

keys  to  genera  and  species, 

3M-323 
Anopheles  aconitus,  310,  345 

ait^cni,  297 

albimanns,    297,    303,    304, 
309,  318,  342,  363 

albitarsns,  303,  342,  363 

algcriensis,  363 

anrictus,  363 

annandalei,  297 

annitlaris,  297,  345 

annulipes,  347 

aquasalis,  303,  304,  342,  363 

argyritarsis,  297 

atropos,  303,  319 

bailey i,  297 

bancrojti,  347,  363 

barberi,  303,  319 

barbirostris,  346,  363 

bariancnsis,  297 

bcllator,  305,  342 

bifurcatus ,  343 

boliviensis,  297 

bradleyi,  302,  319 

claviger,  343 

constant,  363 

crucians,  302,  308,  319,  363 


602 

Anopheles  (continued) 
cult  a  fades,  297,  310,  345 
darlingi,    303,     304,    343» 

363 

carlci,  296,  301,  319 
eiseni,  297 

jarauti,  297,  347*  3^3 
fluviatilis,    297,    310,    345, 

355 

jranciscanus,  302,  320 
jreeborni,  296,  299-301,  308, 

319,  342,  366 
juliginosttSf  363 
junestui,  307,  310,  344,  363 
gamlnae,  297,  305,  309,  344, 

363 

garhami,  297 
georgianus,  302,  319 
£W  297 
hancocki,  344 
hargreavesi,  307,  344     • 
hyrcamts,  297 

var.  sinensis,  345,  363 
implextis,  297 
jeyporensis,  297,  345,  363 
#»#/,  297 
^0<r/;/,  346 
labranchiae,  306,  343 

atroparvtis,  306 
Icucosphyms,  345 
lungae,  347 

mactilatus,  297,  345,  362 
maculipalpis,  363 
maculipennis,      306,      309, 

343 

mangy  anus,  346 
melanoon,  306 

subalpinus,  306 
messae,  306,  343 
minimus,  297,  346,  363 

flavirostris,  346 
mogttlensis,  297 
moucheti,  307,  344 
multicolor,  310,  343 
neomaculipalpus,  297 

»'///  307.  344 
occidentalis,  301,  319 
ostvaldoi,  297 
pallid  us,  363 
parapunctipcnnis ,  297 
pessoai,  343 

pharoensis,  3 07,. 3 43,  344 
philippensis,  346,  363 
pretoriensis ,  307 
pscudopunctipennis,  297, 
301,310,320,342,343 


INDEX 

punctipennis,  264,  268,  294, 
320,  323 

piinctulatus ,  347,  363 

quadrimaculatus,  261,   297- 
299,  319,  323,  342 

ram  say i,  363 

rhodesicnsis,  363 

sacharovi,    306,    309,    310, 
343 

scrgenti,  310,  344 

splendidns,  363 

sqttamosHS,  363 

step  hen  si,  310,  346,  363 

strodei,  297 

subpictus,  346,  363 

sundaiciis,  310,  346,  363 

superpictus,  310,  344 

ttit'khudi,  297 

umbrosus,  346 

varuna,  364 

waller i,  250,  272,  294,  303, 

319 
Anophclinc  larvae,  264 

key  to  species,  321 
Anopheline    mosquitoes,    292- 
310 

key  to  adults,  318 
Anoplura,  162 

characteristics,   194 

suborders,  194 
Antennae,  141 
Antcpygidial  bristles,  559 
Anthocoridac,  170,  188 
Ant/wconts  insuliostts,  188 

^/»^/,  1 88 

sylvcstrts,  188 
Anthomyiidae,  230 
Anthrax,  434,  474 
Anthropophilic,  280 
Antricola,   45 
Apatela  oblinita,  580 

/w/w//,  431 
Apatolestcs,  431 
Apidae,  582 
Apiochaeta,  527 
Arachnicla,  18 

characters,  22 

mouth  parts,  23 

synopsis,  24 
Araneida,  24 
Arctiidae,   580 
^rgw  brumpti,  43,  50,  51,  68 

mianensis,  68 

persicus,  37,  39,  41,  43,  48, 
50,  81 

reftexus,  43,  50,  51 


vespertilionis,   43,   51 
Argasiclac,  characters,  42 

external   anatomy,  36-37 

internal  anatomy,  37-41 

key  to  genera,  43 

key  to  species,  43 
Arilus  cr is  tat  us,  187 
Arista,  232 

Armigeres,  315,  316,  318 
Armigeres  ob turbans,  358 
Armillifer  armiUatus,  117 

monilijormis,  119 
Arthropoda,   i,   18 
Aschiza,  227 
Assassin  bugs,  181 
Astacus  japonic  us,  22 

similis,  22 
Asthma,  582 
Astigmata,  26 
At cl cits  atcr,  357 
Alt  a  gen  us  pi  ecus,  529 
Atylotus,  431 
Auchcromyia  lutcola,  509 
Aural  inyiasis,  ttr  Myiasis 
Australian  roach,   166 
Austrosimuliuni,   409 
Autotncris  io,  580 
Auxiliary  vein,  147 
Aviculariidae,  572 
A/olla,  393 

Eabeiia  bot'is,  63,  70,  80 

rrf/W//',  80 

a/«/V,  66 

re////,  80 

motasi,  80 

or/y,  sec  motusi 
Bacillus  anthracis,  470 

ro//,  470 

cuniailidda,  470 

dyscntcriac,  470 

cntcritidis,  470 

paratyphostts,  470 

pcstis,   470 

tuberculosis,  470,  477 

typhosus,  470 
Backswimmers,   189 
Bacterium  tnlarense,  8,  75,  17] 

433,  470 
Bandicoots,  76 
Bartonella  bacilli jormis,  241 
Basis  capituli,  30 
Bdcllolarynx,  440 
Bedbugs,  172-180 

bites,  177 

control,  179 


dispersal,  175 

and  disease,  177-178 
Beetles,  vesicating,  581 
Belostomidae,  171,  189 
Benzyl  benzoate,  112 
Biliary  fever,  80 
Bird  malaria,  368 
Bironella,  292,  314 
Black  death,  see  Plague 
Black  flies,  401 

biology,  405-409 

bites,  410 

classification,  409 

control,  414 

personal  protection,  413 
Black  widow  spider,  570 
Black  water  fever,  350 
Blatella  germanica,  166 
Blatta  orientals,  166,  168 
Blister  beetles,  581 
Blood,  157 
Blood  gills,  156 
Blowflies,  498 
Bluebottle  flics,  498 
Body  louse,  see  Pediculus  hu- 

manus 

Bombidae,  582 
Boophilus,  35,  46 
Boophilits  annulatus,  4,  49,  57- 
58,  67,  80 

ans trait's,  58,  80 

decoloratus,  59,  80,  81 

dugesii,  49 

microplus,  59,  80 
Borax,  481 
Borrelia,  71 
Botflies,  523 

Boutonneusc  fever,  78-79 
Brachyccra,  227 
Breakbone  fever,  sec  Dengue 
Brill's  disease,  207 
Broad  tapeworm,  20-21 
Brown-banded  roach,  166 
Browntail  moth,  578 
Brucella  abortus,  470 
Buffalo  gnats,  401 
Bugs,  bites  of,  188-189 
Builis  fever,  78 

Caccobius  mutans,  529 
Calcipala,  409,  412 
Calliphora,  477,  487 
Calliphora  erythrocephala,  138, 
504 

livid  a,  498,  504 

vicina,  498,  504 


INDEX 

vmdescens,  488,  504 

vomitoria,  488,  504 
Calliphoridae,  231,  498 
Callithrix  albicollis,  357 

pcnicilata,  587 
Callitroga,  487 

Callitroga  americana,  498-502, 
532 

macellaria,  502,  532 
Calypteratae,  228 
Camcrstome,  30 
Canestrinidae,  99 
Canthariasis,  529 
Cantharidin,  581 
Capitulum,  30 
Carccag  of  sheep,  80 
Carrion's  disease,  6,  241 
Cat  flea,  550 
Cattle  dips,  82 
Cebus  flat'us,  357 

macrocephala,  357 

variegatus,  357 

verstttttf,  357 

Cediopsylla  simplex,  546,  551 
Centipedes,  573 
Centrwoides  suffusus,  567 
Cephalobacnida,  118 
Ccphalopharyngcal      structure, 

461,  463,  504 
Ccratophyllus  anisus,  558 

galltnae,  544,  547 

tes quorum,  553,  558 
Ceratopogonidae,  229,  401,  414 
Ccrcoccbus  torqitatus,  357 
Cercopithccns  nicitans,  357 

tantalus,  357 
Chactotaxy,  flies,  222-226 

mosquitoes,  256 
Chagas'  disease,  184-187 

reservoirs,  186-187 

vectors,   185-186 
Chagasia,  292 
Chaoborinac,  250,  251 
Chaoborus  punctipennis,  251 
Chara,  393 
Cheese  skipper,  528 
Chelicerac,  23 
Cheliceral  sheaths,  32 
Chicken  mite,  95 
Chiggers,  106,  108 
Chilomastix  mesnili,  471 
Chilopoda,  19,  573 
Chironomidae,  229 
Chloropidae,  231,  483-486 
Choantacnia  infundibulum, 
471 


603 

Cholera,  474 
Chorioptcs,  100 
Chorioptes  bovis,  106 

cqui,  1 06 
Chrysomya,  487 
Chrysomya  albiceps,  504 

bezziana,  503 

chloropyga,  504 

marginalis,  504 

rufi jades,  504 
Chrysops,  424,  428,  431 
Chrysops  celcr,  428 

ditnidiata,  3,  433 

discalis,  8,  76,  429,  433 

ft  avid  us,  424 

silacea,  433 

unit'ittatus,  425 
Citnex  hcmipterus,  176,  356 

lectularius,  172-176,  356 

pilosellus,  178 

pipistrelli,  178 
Cimexopsis  nyctalis,  178 
Cimicidae,  171,  172 
Claspers,  262 
Claspcttcs,  262 
Claws,  144 
Cnemidocoptcs,   i  oo 
Cnemidocoptcs  galltnae,    106 

mutans,  106 
Cnephia,  409 

Cncphia  pccuartim,  405,  408 
Cochliomyia,  sec  Chrysomya 
Cockroaches,  165-169 

key  to  species,  165 
Col  copter  a,  163 
Collecting  insects,  586-593 
Colorado  tick  fever,  78 
Congo  floor  maggot,  509 
Conjunctivitis,  475 
Contarninativc,  1 1 
Copra  itch,  see  Dermatitis 
Cordylobia  anthropophagi , 

508 

Coreidae,  170,  171 
Coryza,  582 
Costa,  147 

Cottontail  rabbits,  75 
Coxa,  144 

Coxiella  burneti,  76,  77 
Coxites,  262 
Crab  louse,  203 
Crithidia,  9 
Cross-veins,  148 
Croton  bug,  166 
Crustacea,  19 

and  human  disease,  20 


604 

Ctenidium,  539 
Ctenocephalides  cams,  356, 

538,  543.  546,  550, 

554.  558 

jells,  546,  550,  558 
Ctenophthalmus  pseudargyrtes, 

547 

Cubitus,  147 
Culex,  275 
Culex  annulirostris,  362 

apicalis,  310 

erraticus,  362 

jatigans,  3,  280,  310,  354, 
358,  362,  365 

j use  anus,  362 

habilitator,  362 

pallidothorax,  362 

pipiens,   95,    261,    275-280, 
310,  362,  365 

pipiens  pollens,  281,  362 

quinqtiefasciatus,  sec  jatigans 

restuans,  310,  365 

salinarius,  310,  362,  365 

sinensis,  362 

tarsalis,  280,  362,  366 

thalassius,  354 

tritaeniorhynchus,  281,  362 

vishnui,  362 
Culicidae,  230,  250-323 

biology,  274 

chaetotaxy,  256 

classification,  312 

genitalia,  260 

mouth  parts,  254 
Culicine      mosquitoes,      275- 

292 

flight,  310-311 
Culicoidcs,  414,  415,  417 
Culicoides  austcni,  418 

canithorax,  416 

cockjcrelli,  416 

diabolicus,  416 

dovei,  416-417 

furens,  416,  418 

grahami,  418 

gtittipennis,  416 

tneleus,  416 

obsoletus,  416 
Culiseta,  315,  317 
Culiseta  inornata,  366 
Cutaneous  myiasis,  jrc  Myiasis 
Cuterebra,  533 
Cuterebra  buccata,  522 
Cuterebridae,  516,  517 
Cylops,  20,  21,  22 
Cyclops  bicuspidatus,  22 


INDEX 

coronatus,  22 

strenuus,  22 
Cyclorrhapha,  226 
Cynomyopsis,  532 
Cytoleichidae,  100 

Dasypus  novemcinctus,  186 
Davainea  cesticillus,  471 

tctragona,  471 
DDT,  169,  179 

control  of  black  flics,  414 

control  of  dogflies,  446 

control  of  fleas,  561 

control  of  flies,  480 

control  of  Glossina  flies,  456 

control  of  punkies,  418 

control  of  sand  flies,  246 

control  of  ticks,  86 

and  delousing,  212-213 
DDT,  as  an  aerosol,  390 

solvents  of,  389 
Deer  flics,  423 
Deer  fly  fever,  8,  433 
Definitive  host,  n 
Definitive  host  reservoir,  u 
Deinocerites,  315 
Delhi  boil,  244 
Delousing,  211 
Demodex  bovis,  116 

cants,  116 

cati,  116 

equi,  116 

jolUculoritm,  116 
Dcmodicidae,  116 
Demodicoidea,  25,  94,  115 
Dengue,  6,  357-359 

reservoirs,  358 

vectors,  359 
Dental  scleritc,  461 
Depluming  mite,  106 
Dermaccntor,  46 

key  to  species,  47 
Dermacentor  albipictus,  47,  48, 
62,  67,  81 

andersoni,  7,  28,  31,  33,  47, 
49,  59-61,  69,  74,  78, 
81 

marginatus,  76 

nut f alii t  78 

occidentals ,  47,  49,  74,  76, 
81 

pammapertus,  47,  61 

reticulatus,  49,  80 

variabilis,  34,  59,  69,  74 
Dermacentroxenus  rickettsi,  7, 
73 


Dermal  leishmaniasis,  244 
Dermanyssidae,  94 
Dermanyssus  gallinae,   8,   81, 

95-96 

sanguineus,  96 
Dermatitis,  114-115 
Dcrmatobia,  368,  532 
Dertnatobta  hominis,  517-521 
Dermestidae,  529 
Desmodus  rotundus  murinus, 

435 

Deutovum,  109 
Diachlorus  jerrugatus,  432 
Diaptomus  graciliodes,  22 

gracilis,  22 

orogoncnsis,  22 

vulgaris,  22 
Digestive  tract,  housefly,  153 

mosquito,  151 
Dimethyl  phthalate,  112 
Diphyllobothrium    laturn,    20- 

22 

Diplocentms  spp.,  569 
Diplopoda,  19,  574 
Diptera,  162,  218-235 

chaetotaxy,  222-226 

characteristics,  218 

classification,  226-233 

habits,  218 

key  to  families,  adults,  228 
larvae,  231 

and  disease  relations,  219 
Dipylidium  caninum,  210,  471, 

554 
Dirofilaria  immitis,   115,  364- 

365 

Discal  scleritc,  136,  139 
Discal  scutcllars,  224 
Dissection  of  insects,  595 
Dog  flea,  550 

Dogfly,  see  Stotnoxys  calcitrant 
Dolichopsyllidae,  546 
Dormitator  latijrons,  392 
Dorsocentrals,  224 
Dracunculus  medinensis,  3,  20, 

22 

Drosophilidae,  231 
Duck  disease,  413 
Durango  scorpion,  567 
Dysentery,  amoebic,  473 

bacillary,  473 

East  coast  fever,  81 
Eberthella  typhosa,  471 
Echidnophaga  gallinacea,  207, 
546,  549 


Echinophtheriidae,  195 
Elephantiasis,  361 
Empodium,  145 
Encephalitides,  359 
Enccphalomyelitis,  365-368 
Endamoeba  colt,  168,  471 

histolytica,  168,  471 

nana,  471 
Endemic  typhus,  207 

and  fleas,  560 
Entomostraca,  19 
Epimeron,  142 
Epipharynx,  130 
Episternum,  142 
Eretmapoditcs,  316,  318 
Erctmapodites  chrysogaster, 

291,  354 

Eristalis,  see  Tubifera 
Erthrocebus  patas,  357 
Esox  lucius,  22 
Espundia,  245 
Euchaetias  egle,  580 
Eucleidae,  575 

Eucorethra  underwoodi,  251 
Eupodoidea,  26 
Euproctis  chrysorrhoea,   580 

flat>at  580 

phaeorrhoea,  580 
Euratyrus  cuspid  at  us,  183 
Eurypclma  steindachneri,  572 
Eusimulium  damnosum,  8,  411 
Eutrombicula  aljreddugesii, 
107-110 

batatas,  108-110 

masoni,  108 
Euvancssa  antiopa,  581 
Eyed  and  eyeless  tampans,  51 

Facial  bristles,  223 
Fannia,  486 

Fannia  canicularis,   477,   511, 
533 

sealant,  477,  5M>  533 
Femur,  36,  144 
Ficalbia,  316 

Filaria  sanguinis  hominis,  2 
Filariasis,  2,  359-365,  418,  432 
Finlaya,  283 
Flannel  moth,  578 
Flea     typhus,     see     Endemic 

typhus 
Fleas,  538-561 

bites,  554 

blocked,  556 

hosts  of  helminths,  554 

longevity,  544 


INDEX 

control  of,  560-562 

and  disease,  555-560 
Flics,  carriers  of  bacteria,  470 

carriers  of  helminths,  471 

carriers  of  Protozoa,  471 

see  also  Diptera 
Fly  traps,  468,  482 
Formicidae,  582 
Fowl  pox,  368 
Framboesia,  2,  475 
Frontal  bristles,  223 
Fronto-orbital  bristles,  223 
Fumigation,    hydrocyanic   gas, 
1 80 

sulphur,  179 

zyklon  discoids,  180 

Gambian    fever,    sec   Sleeping 

sickness 
Gambusia  affinis,  392 

holbrooly,  392 
Gamctocytes,  337 
Gasterophilidae,  231,  523 
Gasterophilus  haemorrhoidalis, 
524.  S32 

intestinalis,  524,  532 

n  as  alts,  524,  532 
Gastric  myiasis,  see  Myiasis 
Genal  comb,  546 
Gene's  organ,  32,  42 
Gcnitalia,  149,  260 
German  roach,  166 
Giardia  intestinalis,  168,  471 
Gigantodax,  409 
Glossina,  440,  486 

flics,  447-455 
Glossina  brevi palpi s,  455 

jttsca,  454 

morsitans,  4,  448,  450,  454, 
455 

pallidipes,  454,  455 

palpalis,  448,  450,  455 

swynncrtoni,  448 

tachinoides,  454,  455 
Glyciphagus  domesticus,  115 

pmnorum,  115 
Gocldia,  356 
Gonglyonema  orientale,  169 

pulchrum,  169 
Goniops,  431 
Goniops  chrysocoma,  430 
Grabcr's  organ,  430 
Grain  itch,  see  Dermatitis 
Grain  itch  mite,  114 
Grasshopper,  structure  of,  125- 
'33 


605 

Green-headed  flies,  423 
Grocers'  itch,  see  Dermatitis 
Groin  louse,  203 
Guinea  worm,  20 

Habronetna  megastoma,  471 
njicrostotna,  441,  471 
tnuscae,  471 
Hadrurus  hirstttus,  569 
Hacmagogus,  291,  315 
Hacmagogtif  capricornii,   292, 

355 

equinus,  355 

janthinomys,  292 

spegazzinii  jalco,  292,  355 

splendcns,  355 
Haemaphysalis,  45,  66 
Haemaphysalis  bispinosa,  66 

condnna,  79 

htmicrosa,  66,  7 6 

japonica,  79 

Icachi,  49,  66,  79 

leporis-paliistris,  34,  49,  76, 

78 

pttnttata,  49 
Haematobia,  440 
Hacmatobia  irritans,  447 
Hacmatobosca,  440 
Haematomyza  elephantis,   195 
Haematomyzidac,  195 
Hacmatopinidac,  195 
Haematopota,  423,  431 
Hacmodipsus  vcntricosus,  210 
Hactnoprotcus  columbiac,  228 
Hair  follicle  mites,  115 
Hairs,  stinging,  575 
Ilaller's  organ,  36 
Ha  here,  144 
Halysidota  curyae,  580 
Harvest  mites,  see  Jiggers 
Haustellum,  135 
Head  louse,  see  Pcdicnlus 
Hectopsyllidac,  545,  547 
Hcleidae,  229,  401,  414 
Hellebore,  481 
Hematosiphon,  172 
Hemato siphon  inodora,  179 
He m  eroca m pa  lettcostig m a, 

580 

Hemichlora,  486 
Hemilcttca  lucitia,  580 

tnaia,  580 

nevadensis,  580 

oliviae,  580 
Hemipneustic,  156 
Hcmiptera,  162,  165,  170 


6o6 

Hemoglobinuria,  80 
Henrietta  illucens,  528 
Herpetomonas,  9 
Hetcroptera,  163,  170 

key  to  families,  171 
Heterostigma,  26 
Hexapoda,  19,  125 

abdomen,  149 

antennae,  140 

appendages  of  abdomen,  149 
of  head,   128 
of  thorax,  144 

blood,  157 

body  wall,  126 

classification,  162 
key  to  orders,  162 

digestive  system,  150 

external  anatomy,  125-150 

internal  anatomy,  150-159 

legs,  144 

mouth  parts,  128-139 

muscular  system,  157 

reproductive  system,  158 

respiratory  system,  155 

salivary  glands,  152 

thorax,  140 

wings,  145 
Hippelates,  475 

and  disease,  484,  485 
Hippelates  palllpes,  485 

pusio,  483,  484 
Hippoboscidae,  229 
Hodgesia,  315 
Holoconops,  414 
Holopneustic,  156 
Homolomyia,  486 
Hoplopsyllus    anomalus,    546, 

55i»  558,  559 
Hornets,  582 
Hornflies,  447 
Horseflies,  423-435 

breeding  places,  428 

classification,  430 

control,  435 

habits,  424 

larvae,  428 

mouth  parts,  425-427,  428 

and  disease,  432-435 
Hour-glass  spider,  571 
Houseflies,  common  about 

homes,  486-488 
Housefly,  459-483 

breeding  places,  464 

control,  478-483 

description,  459 

feeding  habits,  466 


INDEX 

flight,  467 

food,  466 

hibernation,  463 

longevity,  468 

mouth  parts,  134-139,  461 

and  disease,  469-477 
Human  flea,  550 
Humeral  bristles,  224 
Hyalomma,  46 
Hyalomma  aegyptium,  48,  49 

lusitanicum ,  81 
Hytnenolopis  carioca,  441 

nana,  471 

Hymenoptera,  162,  582 
Hypoderma,  531 
Hypoderma  bovis,  522,  533 

lineatum,  522,  533 
Hypodermatidac,     516,     522, 

533 

Hypodcrmodes,  486 
Hypopharynx,  129 
Hypopletiral  row,  224 
Hypostomal  sclerite,  462 
Hypostome,  23,  30 
Hystrichopsyllidae,  546 

Immunity  to  bedbug  bites,  177 

to  black  fly  bites,  411 

to  flea  bites,  554 

to  mosquito  bites,  334 
Infantile    paralysis,   see   Polio- 
myelitis 
Ingcstive,  n 
Inoculative,  1 1 
Insecticides,  see  insecticides  by 

name 

Insects,  collecting,  preserving, 
and  mounting,  586-598 

see  also  Hexapoda 
Instar,  161 

Interbifid  grooves,  137 
Intermediate  host,  n 
Intestinal  myiasis,  see  Myiasis 
Intra-alars,  224 
Ischnopsyllidae,  546 
Isle  of  Wight  disease,  113 
Isodon  torosus,  76 
Isometrus  maculatus,  569 
Itch,  see  Dermatitis 
Ixodes,  45,  62 
Ixodes  calif ornicus ,  63 

canisuga,  50 

coofai,  63 

hexagonus,  50 

holocyclus,  63,  70,  76 

pacificus,  63,  68 


persulcatus,  79 

pilosus,  63,  70 

ricinus,  35,  50,  68,  70,  80 
Ixodidae,  42,  45 

keys  to  genera,  45-46 
Ixodiphagus  caucnrtei,  86 
Ixodoidea,  26-29 

Jail  fever,  205 
Janthinosoma  lutzii,  518 
Japanese  encephalitis,  8,  367 
Japanese   river   fever,  7,   no, 

112 

Jiggers,  107,  547 
Journals,  list  of,  14-15 

Kala  azar,  6,  243 
Kedani  fever,  7,  110 
Kenya  tick  typhus,  79 
Kertcszia,  305 

Keys,  classes  of  Arthropoda,  18 
families,  Anoplura,  195 
Diptera,  228 
Hcteroptera,  171 
Ixodoidea,  42 
Pcntastomida,  117 
Sarcoptoidca,   99 
Siphonaptera,  545 
Genera,  Anophilini,  314 
Argasidae,  43 
Ceratopogonidae,  415 
Common      muscid      flies, 

486 

Culicini,  316 
Ixodidae,  45 
Sarcoptidae,  i  oo 
Simuliidae,  409 
Orders,  Acarina,  25 
Arachnids,  24 
Hexapoda,  162 
Species, 

Anopheles,  311 
Argas,  43 
Cockroaches,  166 
Common  muscid  flics,  488 
Dermacentor,  44 
Ornithodoros,  44 
Larvae  of  Diptcra,  231 
of  myiasis-producing  flies, 
531 

Labella,  136 
Labium,  129 
Labrum,  128 
Labrum-epipharynx,  130 
Lagothrix  lagotricha,  357 


Lasiohelea,  414,  417 

Lygaeidae,  171,  189 

Lateral  facial  bristles,  223 

Lymantriidae,  580 

Latrine  fly,  514 

Lymphangitis,  362 

Latrodccttis  hasselti,  572 

Lynchia  maura,  228 

mactans,  570-571 

Leeutvenhoefya      australiensis, 

Macacus  cynomologus,  357 

112 

juscatus,  358 

Lcishmania,  6,  9 

innus,  357 

Leishmania  braziliensis,  239 

nemestrinus,  357 

donovani,  178,  243,  245 

philippincnsis,  358 

infanttim,  243 

rhesus,  5,  352,  357 

tropica,  178,  239,  244,  245 

sinicus,  357 

Leishmaniasis,    244-246 

Macrogametc,  337 

Lemna,  393 

Macrogametocyte,  337 

Lcontoccbus  Ursulas,  357 

Malacostraca,  19 

Lepidoptera,   162,  575 

Malaria,  4 

Leprosy,  476 

carriers,  340-341 

Leptidae,  436 

distribution,  339,  340 

Lcptocitnex  boucti,  178 

duration  of  infection,  348 

Leptoconops,  414,  417 

etiology,  334-338 

Lcptoconops  torrcns,  416 

natural    infection    in    mos- 

Leptomonus, 9 

quitoes,  341 

Lcptopsylla   scgnis,   547,    551, 

sources  of  infection,  340 

553.  558 

vectors,  summary,  342-347 

Lcptospira  ictero  h  ae  tnor- 

control  of,  349-350 

raghiae,  351 

Malignant  pustule,  474 

ictcr  aides,  5,  351 

Mallophaga,  162 

intcrrogans,  351 

Malpighian  tubules,  155 

J^ptus  irritant,  107 

Mandibles,  128 

Lethocents  amcncanus,   \  89 

Mandibuiar  sclerite,  461 

Leucocytozoon  anatis,  413 

Mange,  106 

Lice  and  disease,  205-209 

Matisonclla  ozzurdi,  418 

Litnatus,  356 

Mansonia,  316 

Liinnophora,  518 

Mansonia  africanus,  355,  364 

Linguatida  rhinaria,  118 

albicostii,  355 

scrrata,  118 

annul  at  a,  364 

Linguatulidae,  118 

anntdipcs,  364 

Liparidae,  580 

chrysonotum,  356 

Liponyssus,  94 

fasciolata,  356 

Liponysstis  bacotl,  97,  98 

indian  us,  364 

bursa,  97 

justamansonia,  356,  364 

sylviarum,  97 

perturbans,  366 

Listrophoridac,  99 

pseudotitillanSf  364 

Lithobius  mordax,  574 

titillans,  356 

Loa  loa,  3,  157 

Marginal  scutellars,  224    • 

biology  of,  432-433 

Maxilla,  128 

and  disease,  433 

Mayflies,  582 

Ijota  mactdosa,  22 

Megahpyge  crispata,  578 

Lucilia,  487,  532 

opercularjs,  578 

Lucilia  caesar,  507 

pyxidifera,  578 

cuprina,  507 

Megalopygidae,  575 

illustris,  488,  507 

Megarhinini,  314 

pallescens,  507 

Megaselia  scalaris,  527 

sericata,  488,  507 

Melania  libertina,  22 

Lung  fluke,  21 

Melanolestcs  abdominalis,  188 

Lycosa  tarentula,  572 

picipes,  187 

INDEX  607 

Meloiclac,  581 
Melophagus  ovinus,  228 
Menopon  pallid um,  96 
Mcron,  144 
Mcrozoitcs,  337 
Mesonotum,  143 
Mcsopleural  row,  224 
Mesoplcural  suture,  223 
Mesosomc,  262 
Mesostigmata,  26 
Metamorphosis,   159 
Mctanotum,  143 
Metapneustic,  157 
Micro  filaria  dittrna,  3,  4^3 
Microgamete,  337 
Microgamctocyte,  337 
Micro/ us  tnontcbclli,  110 
Millipedes,  574 
Mites,  control  of,  112 
Mochlonyx  clnctipcs,  251 
Mo n  Hi  form  is   m  o  nil  if  or  m  is, 

169 
Monkeys  and  dengue,  358 

and  yellow  fever,  357 
Morellia,  486 
Mossman  fever,   118 
Mosquito  control,  376-399 
aerosols,  390 
airplanes,  388 
DDT  for  adults,  391 
DDT  for  larvae,  389 
drainage,  379 
filling,  381 
gratling,  381 

on  impounded  waters,  383 
natural  enemies,  392 
oils  and  oiling,  384 
organization,   598 
other  methods,  393 
paris  green,  387 
personal  protection,  395 
poisons,  387 
pyrethrum,  385 
repellents,  396 
screening,  395 
special  problems,  396 
streams  and  ponds,  381 
Mosquitoes,  250-323 
biology,  274-312 
characteristics,  250,  254 
classification,  311-323 
dispersion,  307 
flight  range,  308-312 
structure,  254-271 
Mosquitoes,  and  bird  malaria, 
368 


6o8 

Mosquitoes   (continued) 
and  black  water  fever,  350 
and  dengue,  357-359 

vectors  of,  358 
and  encephalitides,  365-368 

vectors  of,  366 
and  filariasis,  359-364 
vectors  of,  362-364 
and  fowl  pox,  368 
and    human    malaria,    334- 

349 

vectors  of,  342-347 
and  myiasis,  368 
and  tularemia,  76 
Moth  flies,  234 
Mouth  parts  (adults),  bedbug, 

130 

black  fly,  403 
culicoides,  416      V 
flea,  540 
grasshopper,  128 
housefly,  134 
human  louse,  197 
phlebotomus,  236 
stable  fly,  441 

Mouth    parts    (larvae),    mos- 
quito, 264 
muscid  fly,  461 
tabanus,  428 
Murine   typhus,   see  Endemic 

typhus 
Musca,  486 
Musca    domestica,    509,    518 

(see  also  Housefly) 
nebula,  477 
sorbens,  477 
vicina,  477 
Muscidae,  230,  532 
Muscina  assimilis,  488 
pascuorum,  488 
stabulans,    477,    488,    510, 

532 

Mutillidae,  582 
Myiasis,  368,  492-528 

aural,  492 

cutaneous,    492,    496,    498, 

524 

gastric,  492,  510,  514,  527 
intestinal,  492,510,511,  514, 

525.  528 

nasal,  492,  503,  526 
ocular,  492,  496,  503,  516, 

527 

rhinal,  492,  503,  529 
urinary,  510,  515,  527 
vaginal,  410,  503,  515,  526 


INDEX 

Myiasis-producing  flies,  529 

larvae  of,  531 

lists  of,  530 
Myiopsila,  487 
Myodaria,  227 
Myodopsylla  insignis,  551 
Myzomyia,  307,  314 

Nabidae,   171,  188 
Nagana,  4,  445 
Nairobi  sheep  disease,  82 
NBIN  formula,  103-104 
Nemathelminthes,  8 
Nemocera,  227 
Nine-mile  fever,  76-78 
Noctuidae,  580 
Norape  ot'ina,  579 
Norwegian  itch,  100 
Nosopsyllus  fasciatus,  207,  542, 
544>  547,  55i,  556>  558 
Notoedres,  100 
Notonectidae,  171,  189 
Notopleural  suture,   223 
Notopleurals,  224 
Notum,   141 
Nycteribiidae,  228 
Nymphalidac,   581 
Nysorrhynchus,  303,  314,  318 

Ocellar  bristles,  223 
Ochlerotatus,  282-283 
Oeciacus,  172 
Oeciacus  himdinis,  178 

vicar  MS,  178 
Oestridae,  230,  515 
Oestrus  ovis,  516,  533 
Onchocerca  caecutiens,  8,  412 

gutterosa,  413 

volvulus,  8,  411 
Onchocerciasis,  411-413 
Onthophagus  bifasciatus,  529 

uni fasciatus,  529 
Oocyst,  337 
Ookinete,  337 
Ootheca,  166 
Ophthalmia,  475 
Oral  disc,  134,  136 
Oriental  sore,  6,  244 
Ornithodoros,  43 

key  to  species,  43-45 
Ornithodoros  braziliensis,   44, 
45,  68 

coriaccus,  44,  55 

delanoei,  56 

erraticus,  56,  72 

joleyi,  44,  56 


gurneyi,  68 

hermsi,  38,  44,  50,  52,  72 

kfUyi,  56 

lahorcnsis,  44,  56,  68 

marocanus,  56 

migonei,  see  rudis 

moubata,  7,  29,  36,  44,  50, 

51-52,  68,  72,  356 
nereensis,  72 
nicollei,  44,  66,  74 
normandi,  56 
papillipes,  see  tholozani 
parkeri,  38,  45,  54,  72,  74 
rostraius,  44,  56,  68,  356 
rudis,  44,  55,  68,  356 
savignyi,  44,  48,  50,  52,  72 
talaje,  38,  44,  54,  72 
tholozani,  44,  56,  72 
turicata,  38,  45,  50,  53,  68, 
71,  72 

Oropsylla  montana,  547,  551, 

553>558 
silantiewi,  558 

Oroya  fever,  241-242 

Orthopodomyia,  316,  318 

Orthoptera,  162,  163,  165 

Orthorrhapha,  226 

Oscinidae,  483 

Otobius,  43 

Otobius  lagophilus,  45 

megnini,  45,  49,  56-57,  77 

Otocentor,  46 

Owlet  midges,  234 

Oxyuris  vermicularis,  471 

Pacderus  amazonictis,  581 

columbinus,  581 

cribripunctatus ,  581 

juscipes,  581 

irritans,  581 

peregrin  us,  581 

sabaeus,  581 
Palpi,  30 

Pangonia,  424,  430 
Pangoniinae,  430 
Punstrongylus  geniculatus,  183 

megistus,  175,  182 
Pappataci  fever,  6,  236,  240-, 

241 
Paragonimus  westermani,   21- 

22 

Paraponera  clavata,  582 
Paraproct,  261 
Parasa  c Moris,  580 
Paras  a  spp.,  580 
Parasimulium,  409 


Parasitoidea,  26,  94,  98 
Paratriatoma  hirsuta,  183 
Pasteurella  (Bacillus]  pestis,  6, 
178 

tularensis,  75,  433 
Patatta  mite,  108 
Pecten,  267,  268 
Pedicininae,  195 
Pediculidae,  195 
Pediculinae,  195 
Pediculoides  ventricosus,  114 
Pediculus  humanus  var.  capitis, 
196 

bionomics,  201 

feeding  habits,  199 

life  cycle,  199 

mouth  parts,  197 

and  disease,  205 
Pediculus  humanus  var.  cor- 
poris,  see  Pediculus  hu- 
manus var.  capitis 
Pedipalpi,  23 
Pedipalpida,  24 
Pedisulcus,  409,  412 
Pentastomida,  116 
Perca  flavescens,  22 
Periplaneta  americana,  166 

australasiae ,  166 
Peripneustic,  156 
Phallosome,  262 
Pharyngeal  pump,  130,  132 
Pharyngeal  sclerite,  462 
Phlebotominae,  229,  232,  235- 

240 
Phlebotomus,  235-240 

flies  and  disease,  240-246 
Phlebotomus  argentipes,   238, 
241,  244 

arthuri,  245 

chinensif,  244 

diabolicus,  238 

fischeri,  245 

intermedius,  238,  244,  245 

longipalpus,  244 

macedonicum,  245 

major,  244 

migonei,  245 

noguchii,  239 

papatasii,  6,  236,  245 

perniciosus,  244 

peruensis,  239 

pessoai,  245 

sergenti,  238,  244 
mongolensis,  244 

verrucarum,    6,    234,    239, 
242 


INDEX 

609 

whitmani,  245 

Pseud  otrachcae,  136 

Phobetron  pithicium,  580 

Pseudotyphus,  118 

Phoridae,  230 

Psorophora,  316,  317 

Phormia,  487 

Psorophora  cingulata,  356 

Phormia  regina,  508,  532 

confinnis,  364 

Phthirus  pubis,  203-204,  210 

ferox,  356 

Phyllotria,  393 

lutzii,  518 

Phytomonas,  9 

Psoroptes,  100,  104 

Pier  is  brassicae,  529 

Psoroptes  communis,  105 

Pink  eye,  484 

var.  bovis,  105 

Pi  op  Ma  casei,  528 

var.  cuniculi,  105 

Piophilidae,  231 

var.  equi,  105 

Piratinae,  181 

var.  of  if,  105 

Piroplasma  bigemina,  4,  70 

Psychoda  albipennis,  527 

Piroplasmosis,  80 

Psychodidae,  229,  234 

Pit  he  da  monacha,  357 

Psychodinae,  235 

Plague,  i,  6,  476,  555-560 

Ptinus  tectus,  529 

sylvatic,  558 

Pulex  irritans,  542,  543,  546, 

vectors,  557-558 

550,  554,  558 

Plasmodium   falciparum,   334, 

Pulicidae,  546,  550 

335,  338 

Pulvillus,  36,  144 

malar  iae,  334,  338 

Punkies,  228 

ov  ale,  334 

Pupa,  1  60 

vivax,  335-338 

Puparium,  226 

Pleurites,  142 

Pupipara,  228 

Pleuron,  141 

Pyrcllia,  488 

Poison  glands,  567,  570 

Pyrochorridae,  171,   188 

Poisoning  arthropods,  567 

Poliomyelitis,  8,  445,  476 

"Q"  fever,  76-78 

Pollenia  rudis,  477,  487,  498, 

cattle  infection,  77 

509 

distribution,  77 

Polyplax  spinulosa,  207 

tick  vectors,  77 

Poroccphaliasis,  119 

Porocephalus  clavatus,  1  1  9 

Rabbit  louse,  210 

crotali,  119 

Rabbit  tick,  66 

stibulijer,  117 

Radius,  147 

Post-alars,  224 

Rasahus,  187 

Post-humerals,  224 

Rasahus  biguttatus,  187 

Postnotum,  143 

thoracicus,  187 

Potamon  dehaani,  22 

Rats,  and  endemic  typhus,  207, 

obtusipcs,  22 

560 

Prcscutellar  row,  224 

and  plague,  556 

Prestomal  teeth,  139 

Rattus  norvegicus,  552,  557 

Presuturals,  224 

rattus,  552,  557 

Propncustic,  157 

Rearing  insects,  596 

Prosimulium,  409 

Red-water  fever,  80 

Prosimulium  magnum,  408 

Reduction  of  land  values,  368 

Prostigmata,  26 

Rcduviidae,  171 

Protocalliphora,  487 

key  to  subfamilies,  181 

Protocallip  hora  aviutn,  509 

Rcduvius  personatus,  187 

hirudo,  509 

Reighardiidae,  118 

Protophormia,  487 

Relapsing    fever,    louse-borne, 

Pseudocebus  azarae,  357 

209 

Pseudohazis  eglanterina,  580 

tick  -borne,  71-72 

hera,  580 

Reproductive  system,  40,  158 

Pseudoscorpionida,  24 

Respiratory  system,  155 

6io 

Rhagionidae,  230,  423 
Rhinal  myiasis,  see  Myiasis 
Rhinocricus  late  spar gor,  575 

let  hifer,  575 

Rhinoestrus  purpureus,  517 
Rhipicentor,  46 
Rhipiccphalus,  46,  65 
Rhipicephalus    appendicnlattis, 
49,  66,  81 

bursa,  66,  80,  81 

capensis,  66 

evertsi,  48,  49,  66,  80 

sanguincus,  34,  49,  74,  78, 
81 

sinms,  49,   66,  70,  81 
Rhodesian    sleeping    sickness, 

454 

Rhodnius  prolixus,   183,    187 
Rhyphus  jcnestralis,  '528 
Ricfoftsia  a/^ari,  97,  98 

bumeti,  76 

conori,  78 

tnooseri  (typhi),  207 

orientalis,  113 

prowazekj,   206 

quintan  a,  8,  208 

ricl^ettsi  conori,  79 

/H//WI,  79 
Rickettsial  pox,  96 
Rocky  Mountain  spotted  fever, 

7.  73-74 

Rodent  fleas,  553 

Rodents  and  plague,  556-560 

Rostrum,  134 

Russian    spring-summer   ence- 
phalitis, 79 

Sabethini,  313 

Sabcthoides,  356 

Saddle-back  caterpillars,  580 

Saimiri  scireus,  357 

St.  Louis  encephalitis,  8,  80,  95 

Salivary  glands,  40,  152-153 

in  Aedes  aegypti,  155,  583 

agglutinins  in,   154 

in  Anopheles  spp.,  154 

anticoagulin,  154 

functions,   116 

in  Musca  cra&irostris ,  154 

of  ticks,  40 

Salivary  pump,  130,  153,  426 
Salmonella  paratyphi,  471 

schottmtilleri,  471 
Sand  flies,  234 

control,  240 
Sarcophaga,  531 


INDEX 

Sarcophaga  fuscicauda,  498 

haemorrhoidalis,  497 

sarracentae,  498 
Sarcophagidae,  231,  495,  531 
Sarcoptes,    100 
Sar copies  bo  vis,  104 

cant's,  104 

equi,  104 

avis,  104 

scabiei,  101-103 

stu's,  104 

Sarcoptic  itch,  lop 
Sarcoptidae,   100 

key  to  genera,  100 
Sarcoptoidea,  26,  94,  98 

key  to  families,  99 
Saturniidae,  575 
Scabies,   100 
Scaly  leg,  106 
Schizont,  335 
Schizophora,  227 
Schongastia  blestowel,  113 
Sclerite,    141 
Scoleciasis,  528 
Scolopendra  heros,  573 

morsitans,  574 

obscura,  573 

polymorphc,  574 
Scorpionida,  24 
Scorpions,  567-569 
Screening,  479 
Screwworrn  fly,  498-502 
Scutellum,  143 

Secondary  screwworm  fly,  502 
Scpsidac,  231 

Scriocopelma  commttnis,  572 
Sheep  botfly,  516 
Shigella  dysenteriae,  473 

paradysenteriae,  473 
Si  bine  stimulea,  580 
Silvius,  430-431 
Simuliidae,  229,  401-414 

biology,  405 

key  to  genera,  409 

mouth  parts,  403 

relation  to  disease,  409-413 
Simulium,  409 
Simulium  ad  cm,  408 

arcticum,  402 

argyreatum,  408 

atratum,  408 

aureum,  407 

avidum,  413 

bracteatum,  405,  407 

cdllidum,  408,  413 

columbaschcnsis,  408 


damnosum,  408,  411 

equinum,  408 

crythroccphalum ,  407 

griseicolc,  408 

latipes,  408 

metallicum,  408,  413 

mexicanum,  408 

mooseri,  413 

naevi,  408 

nigroparvum,  413 

ochraceum,  408,  413 

ornatum,  408,  413 

pictipes,  406,  413 

venustum,  405,  407,  413 

virgatum,  408 

v ittat urn,  407 

willmani,  408 
Siphonaptera,  538-561 

bionomics,  542-543 

breeding  places,  543-544 

classification,  545-547 

external  anatomy,   538-542 

habits,  544-545 

longevity,  544*545 

mouth  parts,  540-541 

vectors  of  disease,  554-559 

control,  560-561 
Siphunculata,   194    (see  under 
Anoplura) 

key  to  families,  4495 
Siphunculina     funicola,     483, 

485 

Sleeping  sickness,  distribution, 
452 

Garnbian,  450 

Rhodesian,  451 

vectors,  452,  454,  455 
Smallpox,  476 
Smear  62,  505 
Snipe  flics,  423,  436-437 
Solpugida,  24 
South  African  tick-bite  fever, 

79 

Spaniopsis,  436 
Spermathcca,   158,  553 
Sphecidae,  582 
Spiders,  bites  of,  570-574 

poisons  of,  570 
Spines,  stinging,  576-577 
Spinose  ear  tick,  56 
Spiracles,  39,  155 
Spirillum  cholera,  470,  474 
Spirochaeta  duttoni,  7,  71,  7* 

gallinarum,  51,  8 1 

hcrmsi,  72 

hispanicum,  72 


marchouxi,  7  (sec  also  gal- 
linarutn) 

obermeieri,  71 

parpen,  72 

recurrentis,  71,  209 

turicata,  72 

venezuelensis,  72 
Spirochaetosis,    see    Relapsing 

fever 

Sporogony,  337 
Sporozoites,  337,  338 
Stable   fly,   see   Stomoxys  cal- 

ci  trans 

Stadium,  161 
Staphlinidae,  581 
Staphlococcus,  470 
Stegomyia,  283-284 
Stenotabanus,  431 
Sternopleural  suture,  224 
Sternopleurals,  224 
Sternapleuron,  143 
Sternum,  141 
Stcvalius  ahalae,  558 
Sticktight  flea,  549 
Stigmata,  35 
Stilpnotia  salicis,  580 
Stinging  insects,  582 
Stizostcdion  citnadense,  22 

griscum,  22 

vitreum,  23. 
Stomoxyidinac,  440 
Stomoxys,  486 
Stomoxys  calcitrant,  356,  435, 

44»»  477 

distribution,  441 

habits,  444 

life  cycle,  443 

mouth  parts,  441 

control,  446 

and  disease,  445 
Stomoxys  nigra,  435 
Stonemyia,  431 
Streblidae,  229 
Stygeromyia,  440 
Subcosta,  147 
Sublateral  row,  225 
Summer  diarrhea  and  flics,  473 
Supella  supellectilium,  166 
Supra-alar  row,  226 
Surra,  and  horse  flies,  435 

and  stable  flies,  445 
Suture,  141 
Sylvatic  plague,  558 

flea  vectors  in  North  Amer- 
ica, 559-560 
Sylviligus  floridanus,  75 


INDEX 

Symphoromyia  atripcst  437 

hirta,  437 

kjncaidi,  437 

pachycerus,  437 
Synthesiomyia,  486 
Syrphidae,  230,  524 

and  rnyiasis,  526 

Tabanidae,  230 

biology,  427-430 

habits,  424-425 

key  to  common  genera,  430- 
43i 

mouth  parts,  425-427 

relation  to  disease,   432-435 
Tabaninae,  430 
Tabanus,  428,  431 
T  ah  anus  atratus,  423 

itnportunus,  435 

lineola,  424 

ncmorcdis,  435 

phacnops,  427 

punctifer,  428 

rein  ward tii,  429 

septentrionahs,  429 

.f trial us,  434 

Tables,  Crustacea  and  human 
parasites,  22 

factors  in  disease   transmis- 
sion, 10 

flea      vectors      of      syl  vatic 
plague,  559-560 

life  cycles  of  fleas,  543 

tick  bites  and  their  effects, 
68 

tick-borne     diseases,     sum- 
mary, 83-85 

tick  relapsing  fever,  72 

triatomc  bugs  and   Chagas' 
disease,   185-186 

vectors  of  malaria,  342-347 

yellow    fever    vectors,    354- 

356 

Tachinidae,  230 
Taenia  marginata,  471 

sen  at  a,  471 

soli  urn,  471 
Tarantella,  573 
Tarantism,  572 
Tarantula,  572 
Tarsonema  ftoricolus,  116 
Tarsonemoidea,  26,  94,  113 
Tarsus,  36,  144 
Tenehrio  molitor,  529 
Tenebrionidac,  529  * 

Tcnent  hairs,  145 


611 

Tergum,  141 
Texas  fever,  80 
Thautnetopoea      processionea, 

580 

Thaumetopoeidac,  575 
Thcatops  spinicaudus,  574 
Theileria  parva,  81 
Three-day  fever,  236,  240 
Tibia,  36,  144 
Tick  bites,  67-68 
Tick -borne  diseases,  summary, 

83-85 

Tick  control,  82-87 
Tick  paralysis,  68-70 
Tick  typhus,  78 
Ticks,  28-93 

biology,  47-66 

classification,  42-46 

distribution,  29 

egg  laying,  50 

external  anatomy,  30-37 

food,  29 

hosts,  29 

life  cycles,  49 

many-host,  48-49 

one-host,  48-49 

reproduction,  48 

starvation,  50 

three-host,  48-49 

two-host,  48-49 

types  of  development,  49 

and  disease,  67-82 
Tongue  worms,  116 
Trachea,  structure  of,  156 
Trachoma,  sec    Conjunctivitis 
Transmission,  n 
Transovarial  transmission,  74 

of  Piroplustna  bigemina,  58, 
80 

of  Rickcttsia  burneti,  77 

of  Rict(fttsia  ricf(ettsi,  74 

of  Spirochaeta  spp.,  71-72 

of  tick-borne  encephalitis,  79 
Transverse  suture,  223 
Trench  fever,  8,  208 
Trcponcma,  2' 
Trcponema  pertenue,  2,  475 
Triatoma,  181 
Triatoma  dim'vdiata,  183 

gerstaccferi,  184 

lectularius  occulta,  184 

Ion  goes,  184 

raegista,   5    (see   also   Pan- 
strongylus  megistus) 

protracta,  184 
woodi,  184 


612 


INDEX 


Triatoma  (continued} 
rubrofasciata,  182 
sanguisuga,  182,  184 

Triatomes  in  relation  to  dis- 
ease, summary,  184- 
186 

Triatominae,  181 

Trichinella,  2 

Trichodectcs  cams,  210 

Trichoprosopon,  356 

Trichuris  trichiura,  471 

Trochanter,  144 

Trombiculu    a^atnushi,    no- 

m»  113 

autumnalis,  no 

dclitnsis,  in,  113 

fletcheri,  112,  .113 

hirsti,  112 

walchi,  112,  113 

wichmanni,  112,  113 
Trombiculid    mites    and    dis- 
ease, 112-113 
Trombiculinae,  106 
Trombidiidae,  106 

key  to  subfamilies,  106 
Trombidoidea,  26,  94,  106 
Trophozoite,  335 
Tropical  ulcer,  475 
Trypanosoma,  451 
Trypanosoma  anamense,  435 

brucei,  4,  445,  454,  455 

cazalboui,  446 

cruzi,  5,  184,  451 

dimorphon,  446 

equiperdum,  435,  451 

evansi,  435,  445,  451 

gambiense,  5,  446,  450,  454 
development  of,  454 
distribution,  452 

hippicum,  435 

melophagium,  228 

rhodesiense,  445,  450,  451, 

454 

soudanense,  435 

ugandense,  452 

Trypanosomiasis,  4,  435,  445 
Tsetse  flies,  5,  447 

biology,  449 

distribution,  447 


and  disease,  450-455 

Vertical  bristles,  223 

control,  455 

Vesicating  beetles,  581 

Tsutsugamushi  disease,  7,  no, 

Vespidae,  582 

112 

Vibrio  comma,  470,  474 

Tuberculosis,  476 

Vomit  drop,  140 

Tubifera,  533 

Tubifera  arbustorum,  527 

Warble  flies,  522 

dimidiatus,  527 

Wasps,  582 

tenax,  525 

digger,  582 

Tucandeira,  582 

Water  moccasin,  120 

Tularemia,  8,  75-76 

White-marked   tussock   moth, 

distribution,  75 

580 

natural  vectors,  76 

Wohlfahrtia,  531 

Tunga  penetrans,  546-548 

Wohljahrtia  magnified,  497 

Turkey  disease,  413 

meigenii,  497 

Typhoid  fever,  471-472 

opaca,  497 

carriers,  472 

vigil,  495-497 

and  flies,  472 

Wollfia,  393 

Typhus,  endemic,  207,  560 

Wuchcreria  bancrojti,  157,  359 

and  mites,  98 

development  in  mosquito, 

and  fleas,  560 

359-36i 

epidemic,  8,  205-206 

microfilariae  of,  360 

Tyroglyphoidea,  26,  94,  115 

mosquito  hosts,  list,  362- 

Tyroglyphus,   and   dermatitis, 

364 

115 

malayi,  364 

and  intestinal,  urinary,  and 

Wyeomyia,  356 

bladder  infection,  115 

Tyroglyphus  longior,  115 
var.  castdlani,  115 

Xenopsylla,  546 
Xcnopsylla  astia,  552,  557 

siro,  115 

hrasilienst.  «;t2.  f;^? 

Uranotacnia,  315 
Urinary   myiasis,   see   Myiasis 
Urticating  arthropods,  566 
Urticating  caterpillars,  578 
Utricularia  spp.,  393 

Vaginal  myiasis,  see  Myiasis 

Vampire  bat,  435 

Vanessa  io,  581 

Vanillism,  115 

Veins,  147 

Velvet  ants,  582 

Venation,  Comstock-Needham 

terminology,  147-149 
terminology    of    dipterists, 

147 

Verruga   peruana,   see   Oroya 
fever 


cheopis,  207,  543,  544,  546, 

55i,  552,  556,  557 
cridos,  552,  558 

Yaws,  475 

Yellow  fever,   5,  351-357 
and  bedbugs,  356 
and  monkeys,  357 
and  mosquitoes,  summary, 

354-356 
spread  of,  357 

Yellow    fever    mosquito,    see 
Aedes  acgypti 

Zeugnomyia,  315,  318 
Zoophilic,  280 
Zygote,  337 
Zyklon  discoids,  180