Historic, archived document

Do not assume content reflects current
scientific knowledge, policies, or practices.

| Washington, D. C. | April, 1926

_ THE CATTLE GRUBS OR OX WARBLES, THEIR BIOLOGIES
AND SUGGESTIONS FOR CONTROL

———n

By

_ F.C. BISHOPP, Entomologist, E. W. LAAKE, Associate Entomologist, and H. M. BRUNDRETT
Assistant Entomologist, and R. W. WELLS, Entomologist, Investigations of Insects
Affecting the Health of Animals, Bureau of Entomology

eucrek st
rrr tg te a ip Sl he a

CONTENTS
History . A
Life History in Brief “
Distribution . :
Economic Importance .
Injury to Man A ;
Common Names and Podalat Ideas “ Pa eh ences
Hosts . ji (,
Actions of Cattle When ‘Attacked by Adult Hytodetan
Description of Stages . °
How the Larvz of Hypoderma Hiniestiien Gain Faas ie the Host
Development and Habits UL ReaD cihudoray Nari elrc 6
- Seasonal History .
Natural Control .
Artificial Control. %
Possibilities of Eradication By Systematic Domus of Grubs
_ Legislation on Grub Control Sih ele felts
Summary abies

Literature Cited — -

=

sepa as sw a Soe

ss

4
ee |
5
ie
i
Hat

WASHINGTON
GOVERNMENT PRINTING OFFICE
1926

gt tte te
eet te ete
N45

Washington, D. C.

THE CATTLE GRUBS OR OX WARBLES, THEIR BIOLOGIES
AND SUGGESTIONS FOR CONTROL

By F. C. BisHopp, Entomologist, E. W. LAAKE, Associate Entomologist, and 4

H. M. BRUNDRETT, Assistant Entomologist, and R. W. WELLS, Entomologist,
Investigations of Insects Affecting the Health of Animals, Bureau of Ento-
mology

CONTENTS
Page Page
ETERS Tih Tey zea aE as Ee 2 | Development and habits___________ 41
Life history in brief______________ 6 | Seasonal history -~-22 === 74
Distribution= 2 ee ee ahs 6 | Natural control ________ Sree a sae vs)
Economic importance______________ 11 | Artificial control _______ os 85
TSO 508 0 ae 0S ee ce 17 | Possibilities of eradication | by sys-
Common names and popular ideas__ 19 tematic destruction of grubs_____ 108
PET OS ibs tins set Ne Se 20 | Legislation on grub control________ 110
Actions of cattle when attacked by SU Tn AUT See Sec Se ee ee 110
adult Hypoderma_______________ Zee awitorature -Citeds: 425 are es ee 114
Description of stages_______--____ 26
How the larve of Hypoderma line-
atum gain entrance to the host___ 33

The cattle grubs (Hypoderma lineatum De Villers and H. bovis Coe A

De Geer *) are among the most widespread and injurious insects with
which our livestock are beset. Nearly every owner of cattle is
familiar with these larve, which are found under the skin on the
backs of cattle in the early spring. Few, however, connect them
with the adult insects which are known as heel flies or warble flies.
Still fewer people have ever seen a heel fly, and many stockmen say,
“‘T have heard all of my life of the heel fly and have seen the cattle
run from it but I have never seen one.” This has led many to regard
the fly with something akin to superstition or to consider ts exist-
ence a myth.

Among scientific workers there is also a very meager iihcheiedee
of the true life history or importance of these insects. Although a
considerable number of veterinarians, zoologists, and entomologists
have made observations and published articles, much of this work
has been of a fragmentary character and most of the important bio-
logical facts have been established during the last decade. It is the
writers’ desire to set forth briefly the knowledge gleaned to date, and
especially to present facts yet unpublished regarding the life his-

1Resigned July 24, 1928. 2Order Diptera, family Oestridae.
58252 °—26——_1

2 BULIETIN 1369, U. 8S. DEPARFMENT OF AGRICULTURE

tories, habits, injuriousness, and means of repression of cae two
species, as obtained during this investigation.*

HISTORY

The heel flies or warble flies, or at least the effects of their fiacle.
have been known to man from time immemorial. The writings of
Virgil and Shakespeare contain statements which undoubtedly ‘refer
to these pests. Their peculiar and injurious habits have attracted
the attention of many naturalists, zoologists, and veterinarians, and
the results of the observations and deductions beginning with the
articles on this subject published in 1710 and 1718 by the Italian
naturalist Vallisnieri (102, 103)* make very interesting reading.
Linné (67), in 1739, published information on the related reindeer
bot (Oedemagena tarandi L.) and expressed his opinion that the
eggs were attached to the skin or hairs and were not pushed through
the skin 2s was believed by all previous writers, and as some so
sequent writers have believed.

In 1797 Clark (20) published a notable account for that day of
the Oestride, including observations on the habits of the cattle
grubs. This modified and amplified views were published in 1827
(27) and 1848 (22).

In 1863 the Austrian entomologist emer (S) published his
monograph of the Oestride, which added much to the knowledge
of the species. He describes the last two stages of the larve, and

in a subsequent article (9) he indicates a simple method of dif-

ferentiating the last larval stages of H. lineatum and ZH. bovis.

Most writers up to the time of Clark’s observations, and in fact
many subsequent writers, were of the opinion that the flies place
their eggs under the skin of the host. This idea probably originated
from the fact that the cattle are driven to a frenzy by the oviposit-
ing flies, the conclusion being that the flies must stine when lay-
ing the evos—this, despite Linnaeus’s statement in 1739 regarding
the placement of the reindeer bot eggs on the hairs.

Up to the publication in 1888 by Hinrichsen (4/) on the find-
ing of Hypoderma larve in the spinal canal, only the subdermal
or last larval stages were known. Hinrichsen reported the com-
mon occurrence of these (now known to be third-stage) larve in
the spinal canal of cattle in December, January, March, May, and
June. He also concluded, apparently without having seen the ege
or the fly ovipositing, that the hosts take up the eggs with grass
and that the young larve reach the spinal cavity from the diges-

3The present studies have been carried on incidental to other projects for a number of
years and during the last seven years have received major consideration. During the
prosecutien of the work the writers have been materially assisted by many individuais
and organizations, to whom thanks are extended. The Bureau of Animal Industry,
through its various agents, has aided by sending immature stages. Dairymen, especially
in the vicinity of Dallas, Tex., and Herkimer and Middletown, N. Y., have assisted
materially by permitting the use of their cattle in the writers’ experiments. Many
specimens and much information have been obtained from correspondents, including
dairymen, cattle raisers, hide dealers, butchers, packers, and others interested in the
problem. The management of the leading pane plants in Dallas and Fort Worth,
Tex., have been especially courteous in furnishing material for examination and in per-
mitting examination of cattle during slaughter. Of necessity, a number of entomologists
have been more or Jess associated with the writers in the carrying out of the observa-
tions and experiments. Whe following men have contributed materially to the results
as herein given: D. C. Parman, O. G. Babcock, Oscar Pool, E. E. Wehr, H. P. Wood,
and W. E. Dove.

4 Numbers in italies refer to ‘‘ Literature cited,” p. 114.

pak e

ae Dy

THE CA. CATTLE GRUFR Ox WARBLES | 2

tive tract, thence migrating up to the subcutaneous tissues of the

back. In 1889 one of these early-stage larvee found in the brain of °

a horse by Poulson was described by Boas (5) as a first-stage Hy-
pederma larva. From this time on the veterinarians, especially
of Denmark and Germany, made important contributions regard-
ing the voung stages within the bodies of cattle.

During the decade beginning in 1884, the English entomologist
Ormerod made a number of contributions to the literature of this

subject culminating in reports published in 1894 (77) and.1900 (72).

In these articles much valuable information is presented, especially
as regards losses. This writer entertained the old idea that the
larvee penetrate through the skin of the backs of the cattle.

In America, interest in this pest began to be evident during the
eighties; and articles were contributed by Riley (52, 53) in 1889.
In 1890 Cooper Curtice published a note (24) reporting the finding
of larvee 10 to 15 millimeters long in the walls of the esophagus, in
the pleura near the eleventh rib, in the subcutaneous tissues of the
back, and in subcutaneous tumors which opened through the external
skin. He states that the finding of larvee in the early stages in these
situations suggests that-—

It is possible that the eggs or young larve are licked by the cattle from the
back; that the larve made their way into the esophageal walls and from
thence, during the proper season, through the back in the neighborhood of the
eleventh rib, to the skin.

Curtice gives in 1891 (25) a full account of his work along this
line. This hypothesis was based upon the finding of these immature

stages in the submucous membranes of the gullet and in other tissues

of the body, often months before the larve appeared on the back and
eut holes through the skin. He also observed that the larve and
inflammation disappeared from the gullet by the end of January or
early in February. Apparently no observations were made on the
actual habit of oviposition of the flies. In 1892 Riley (84) published
a very good résumé of the knowledge of the life history and habits
of H. lineatum up to that date. He concluded from an examination
of material from various sources that H. lineatwm was the predomi-
nant if not the only species found in the United States. In this
article he also incorporated an account, based on observations of
G. Schaupp and others, regarding the actual method of oviposition
of this species, and the true first stage was described for the first
time. e accepts Curtice’s theory of the entrance via the mouth,
and eoncludes that an additional link in the chain of circumstantial
evidence pointing toward this method of ingress is supplied by the

_ fact that the eggs are laid largely on the legs and that the cattle lick

themselves in that region. In 1897 Marlatt (64) presented a concise
summary of the information available at that time.

Horne, working largely on the immature stages within the bodies
of cattle, published in Norway in 1894 (45) observations showing
that the larve are truly migratory. He observed them in various
situations, including the spinal column from one end to the other,
sometimes under the pleura, in the abdominal cavity, and on the
surface of the kidney. The following year the veterinarian Ruser
(86) published his observations on the occurrence of the larve in
the spinal canal and reported that he had found traces of larval
tracks in the muscles of the back. In 1898 Koorevaar (54), working

4 BULLETIN 1369, U. 8. DEPASPARTFMENS) aGRICULTURE

in Holland, gave definite proof that the small larve found in the
spinal column of cattle were really Hypoderma. Some of these were
introduced under the skin of a goat, and 12 days afterwards swellings
appeared, from which later 1. bovis was reared. In the same article
he also described experiments in which 26 larve from the spinal
canal of cattle were introduced under the skin of a dog. When the
animal was examined two weeks later some of the larve were found
in various parts of the animal, including the gullet and spinal canal.
Similar larve fed to dogs and introduced into the gullet of a rabbit
through a tube were not recovered. From these tests Koorevaar
concludes that in bovines the larvee reach the gullet or spinal canal
after extensive wanderings from the place where they bored through
the skin, and that they do not reach the gullet by way of the mouth.
Further studies on the migration and seasonal occurrence of the larve
within the host were published the same year by Koorevaar (55).

Following the publication by Curtice and the subsequent one by
Riley, practically all scientists accepted Curtice’s theory. In 1903
Koch (53) published a very valuable contribution as the result of
several years’ study of the larve of Hypoderma within the bodies
of cattle. He shows that the young larve are widely distributed
within the body cavity and in the intermuscular tissues of the back,
and that larvee as small as 2.2 millimeters in length may be found
in the submucous tissues of -the gullet. He concludes from the
data presented that—

It will presumably be apparent that the entrance of Hypoderma larv# to
the bodies of the cattle takes place through the alimentary system and not
through the skin, and further that the larve migrate through the cesophagus
and vertebral canal to the skin.

In 1907 Jost (52) reviewed the life history of HY. bovis. He con-
cluded that the eggs hatch in the gullet and that the larve bore
through the mucous lining of it. He also makes the erroneous
statement that the life cycle requires about nine months. Sdérensen
(93) in 1908 discussed the literature and concluded that the larvee
enter by mouth.

During the period 1908 to 1922, Carpenter and his associates in
Ireland published a series of papers (/2 to 19) dealing especially
with experiments with the muzzling of calves in an effort to prevent
their infestation. The earlier results were conflicting and the
authors changed their viewpoint from year to year. In 1914, how-
ever, Carpenter, Hewitt, and Reddin (77) published the results of
their observations on the penetration through the skin of larve of
both H. lineatum and H. bovis. They first noticed soreness and
scabs in the regions near where eggs of Hypoderma were attached.
Beneath these they found holes indicating penetration and from
one of these was squeezed, along with serum, a first-stage larva of
H. lineatum which had evidently penetrated through the skin at
the spot. They followed this with tests of newly hatched larve of
H. bovis placed on clipped hair on a calf and found that they quick-
ly passed down the hair and began to burrow into the skin immedi- -
ately. They conclude: 3 |

We believe therefore that no further doubt is possible as to the entrance of
young Hypoderma larve into its host through the skin close to wherever the
eggs may have been laid, and the results of the muzzling experiments show
that entrance by the mouth is unlikely.

aries saa
3 ete Saal
er eee T Pe Ty

THE CATTLE GRUBS OR OX WARBLES 5

They have also expressed the opinion that it is not improbable

that the larve may go from the legs to the gullet and thus to the

back. Hadwen, working in British Columbia, has also made some
valuable contributions to our knowledge of Hypoderma. In a paper
published in 1912 (32), he presents data on the injuriousness of the
cattle grubs in Canada and adds some valuable information on the
method of egg laying of ZH. bovis.

The seriousness of injury by cattle grubs in Germany led to the
appointment of a commission to study all phases of this subject.
Several years were spent in this investigational work and the results
were published in. parts in the years 1912 to 1919 (67). A large
amount of information was obtained on the losses due to the pests,
relative numbers of the two species, life histories and habits, and
control work.

C. Stub (95-99) carried on observations on cattle grubs in Den-

_ mark and published his records in 1912, 1913, 1915, and 1919. He

added to the information on the life history and habits of the
insect and reported that, in collaboration with Prof. Phil Boas, he
found beneath a number of eggs a burrow through the skin which
they interpreted as the entrance hole of a newly hatched larva.
Stub also found larve from 2 to 7 millimeters long in the subdermal
connective tissue of calves. In early records, he concluded that the
larvee burrow directly through the skin, but was under the erroneous
impression that the eggs are laid on the back. In 1919 (99) he
definitely traced the course of young larvee from the inside of the

~right tibia to the esophagus.

Hadwen published further observations on the life history and
seasonal development of both species in 1915 (33). In this paper he.
showed that larve removed from the gullet and placed under the
skin on the leg of calves would work upward rapidly through the
connective tissues and ultimately reach the back. In 1916, Hadwen
and Bruce (38) attempted to trace the larve as they left the gullet
and suggested that they pass up the crura of the diaphragm or along
the posterior borders of the ribs to the neural canal and out through
the posterior foramen to the subcutaneous tissues of the back. In
another paper (34), in 1916, Hadwen added further data on the
seasonal development of the larve and demonstrated the ability of
the newly hatched larve to penetrate bovine skin. He also described
lesions on cattle chargeable to the penetration of Hypoderma larve.
Later a concise account of the cattle grub problem was issued by
Hadwen (36).

In 1920 Carpenter and Hewitt (78) described in detail a successful
experiment with warble eradication on Clare Island, Ireland; and in
1922 in the sixth report (79) on the problem, Carpenter, Phibbs, and
Slattery presented further information on the life and seasonal his-
tory of both species of Hypoderma and further experimental evi-
dence that larve enter the host through the skin only and not by
way of the mouth. This report also summarizes tests with various
dressings applied to the backs of cattle to kill the grubs, especially
tobacco-powder wash. The biologies of Hypoderma and _ other
aspects of the grub problem were summarized by Seymour-Jones
(91) and Warburton (770) in 1922.

6 BULLEBTIN 1369, U. 8. DEPARTMENT OF AGRICULTURE
LIFE HISTORY IN BRIEF

There are two distinct species of cattle grubs and these of course
present differences in appearance and habits in each of their stages.
In a general way, however, the life histories of the two are similar,
and the following summary of that of Hypoderma lineatum will
serve as an illustration. Beginning with the large grubs which are
well known to practically everyone who handles livestock, the life
may be traced as follows: |

As the grubs reach maturity in the subdermal tissues of the back
during the late fall, winter, spring, or early summer, the holes
through the skin gradually become larger and finally the grubs
crawl out and drop to the ground. They seek protection under any
loose material at hand and the outside skin shrinks, becoming hard,
and within this the flies develop, emerging from 30 to 60 days later.
These flies mate soon after emerging and without partaking of food
begin to deposit eggs on cattle. The eggs are laid for the most part
on the legs, probably the majority of them being below the knee or
hock joint. The eggs hatch in from 214 to 6 days, depending upon
the temperature. The young larve crawl down the hair to the skin
and immediately begin burrowing into it. At the point of entrance
serum usually exudes and rather characteristic scabby and tender
areas remain for a few days. After penetration little is known of
the minute larves from the time they pass through the skin until
they appear in the body eavity, especially in the submucous layers
of the gullet of the host, having increased considerably in size and
become more opaque, and evidently having passed through a molt.
They spend several months in the host, mainly in the tissues between

the mucous membranes and the muscular walls of the gullet, and ~

evidently, as shown by one of the writers (Laake, 57, 58), pass
through a molt in that situation or en route to the back. Growth
continues during the summer months, and in the fall or winter the
grubs have attained a length of from 15 to 17 millimeters and are
ready to start on their migration to the back. Here again the exact
route followed is not absolutely known; but these larve, which are
of sufficient size to be found easily, have been met with in various
places in the chest and abdomen and on the diaphragm. Not infre-
quently they are observed in the spinal canal and a little later are to
be found in the connective tissues beneath the skin along the back.
A hole is cut through the skin almost immediately after the larva

reaches that situation and within 2 to 6 days the larva again molts”

and a wall of tissue begins to form around it in the form of an
encystment sac. The next molt takes place about 24 days later, and
the insect is now in its final larval stage. The duration of this stage
averages about 30 days. It is thus seen that the development requires
approximately a year’s time, there being one generation during the

year. The major part of this time, from 9 to 11 months, is spent —

within the body of the host.
DISTRIBUTION
The distribution of the two species of Hypoderma affecting cattle

has received comparatively little attention, certainly not as much
as the subject deserves. It appears that the grubs reach their maxi-

¥ WS

THE CATTLE GRUBS OR OX WARBLES Fh

mum development in numbers in parts of Germany. They are
known to be abundant in Switzerland, Denmark, Holland, and the
British Isles, and probably occur throughout Europe. They are
abundant throughout the greater part of the United States and
southern Canada.

It is very doubful if either species of Hypoderma will ever become
an established pest in the Tropics or subtropics. Both have been
repeatedly introduced there with cattle, but there are no records of
subsequent breeding. It is true, however, that positive information
is very meager as to the presence of Hypoderma in parts of the
world other than those in which it is a pest. A. H. Ritchie informs
the writers that in the West Indies he has never seen the warble
except in four animals imported from the United States.

No records are known to the writers of the occurrence of Hypo-
derma in South America. The genus is replaced in tropical America
by Dermatobia, and its similar injury to hides leads some to think
‘Hypoderma is present there.

Hypoderma is not indigenous to South Africa and apparently has
never become established through introductions. Lounsbury (62)
and Hutcheon (47) state that they have no knowledge of the occur-
rence of either species of Hypoderma in native cattle in the Union
of South Africa. Lounsbury says in a letter: “Now and then
warbles are found under the skin of animals imported within a
matter of months, but I have never heard of any being found in
_ animals bred in the country or here for a number of years.”

Howard (46) reports the finding of larve of H. lineatum in
Mozambique, East Africa, but does not say if from native or im-
ported cattle.

James Bequaert has informed the writers that in his extensive work
in Belgian Congo he has never seen or heard of an authentic case
of the occurrence of either species of Hypoderma in that country.
He also directs attention to the statement of Roubaud (85), who has
‘paid special attention to dipterous parasites of mammals in Belgian
Congo and French West Africa, that he has never seen Hypoderma
on cattle in that region. In northern Africa, Hypoderma evidently
occurs. KE. E. Austen writes that the British Museum contains a
male of 7. bovis from Algeria near Béne, collected May 5, 1896, by
A. E. Eaton. Vaney (704) in 1911, states that H. bovis occurs in
Algeria. Willcocks (1/2), in 1918, says that H. bovis occurs in
_ Egypt, but whether or not it is a common pest 1s not known.

In Australia, likewise, neither species seems to have gained a foot-
hold. Tryon, in 1906 (700), and again in 1912 (101) reported the
apparent stamping out of a local introduction in the Richmond
| district. Pound (79) describes the appearance of warbles in im-
| ported stock and adds, “It is difficult to assign any definite reason
_ why the cattle grub fly has not become established in Queensland.
_ Evidently the conditions of environment are unfavorable.” Smit
| (92) states that H. bovis imported into the Dutch East Indies from
_ Holland apparently failed to establish itself, as no records in native
_ cattle have been made.

__ Regarding the nonoccurrence of Hypoderma in Hawaii, Van
Dine and Norgaard (108) write: “One and possibily both of the
bot flies attacking cattle have been brought to Hawai with 1m-

8S BULLETIN 1369, U. S. DEPARTMENT OF AGRICULTURE

ported cattle. So far neither of them seem to have become estab-
lished here.” i |

Hypoderma bovis is essentially a northern form. This point has
been brought out by a number of writers. Glaser (29) found that
in Germany bovis predominated over the northern part of the em-
pire while /éneatum was more in evidence in the southern part. It
is also worthy of note that Hypoderma larve are much more abund- :
ant in northern than in southern Germany (56). A writer (/) in :
Germany has pointed out that, with the interruption of the control
work in that country due to the war, the insect had spread to pre- 4
viously uninfested areas. In Denmark, although /éneatum is present,
bovis is far more prevalent. Bequaert (in litt.) says:

In Belgium and France H. bovis is by far the most common species, and in
some regions quite abundant. I do not know of any record of AH. lineatum. in
Belgium. In France that species is very rare and of recent introduction; it
was not known there at the time Joly (51) wrote his monograph, 1846.

TET tek Grail oe

In fact H. lineatum was not recorded from France until 1894 4
(SO). Brauer (8, 9) states that H. bovis is distributed from Scan- Fe
dinavia to the southern part of Europe and over Asia, Africa, and
North America. He writes that this is the only species found in
upper and lower Austria, Styria, and Hungary. He records the
distribution of H. lineatum as South Russia, Norway, the Balkans,
the Caucasus, and England. Vaney (/04) reports H. bovis to be :
common in the Lyonnaise region in France. He and his associates |
(59, 60, 105, 107) observed the number of grubby hides to range
during the height of the season from about 12 to 21 per cent in
different years. Vaney reports the occurrence of H. bovis only in
the Lyonnaise region. Third-stage specimens, however, which he
sent the writers from the gullets of cattle of that region, prove
to be H. lineatum. In England and Ireland both species are com-
mon but sufficient data are not at hand to show their relative num-
bers. Hadwen (36) states that in Canada the two species have
equal distribution, but that their distribution in the northern part
of the country has not been determined. He makes no definite state- 2
ment, however, regarding the relative abundance of the two. =

A. Gansser, chairman of the Warble Fly Commission of Basel, =
Switzerland, states in correspondence that both H. lineatum and
H. bovis are present in that country. H. bovis apparently con-
stitutes about 60 per cent of the total number. The insects appear
to be very abundant in certain sections of that country. Gansser
states that they are generally distributed in the Alps and Jura
Mountains up to 6,000 feet. He mentions heavy injury in the can-
tons of Valais, Vaud, and Grisons. Bornand (7) also comments on
the abundance of H. bovis in cattle of the Jura and the Alps.

Until recently practically nothing definite has been known of the
occurrence of Hypoderma in India. Maxwell-Lefroy and Howlett
(66) write:

It seems probable that Hypoderma, the common European genus, is confined
to western India from the Punjab southward probably as far as Gugerat.
O’Quinlan (superintendent, C. V. D., Bengal) informs us that he has rarely or
never seen warbles in Bengal cattle, and this agrees with our experience.

Patton (75) secured a specimen of H. lineatum from Doctor An-
nandale from India in 1922 and later others were sent him by Capt.
H. E. Cross, who at the same time sent to the writers specimens of

——_—_—__________nhneEEEE ae
ws
hes

THE CATTLE GRUBS OR OX WARBLES : 9

several larval stages of H. lineatwm from the Punjab. He also fur-
nished data showing an infestation of shghtly over 35 per cent of
some 41,000 head of cattle which he examined in different parts of
the Punjab. C. W. Howard has written that he has never seen
Hypoderma larve in southern China, except in cattle that were be-
ing imported. C. P. Clausen made some inquiry regarding the oc-
currence of Hypoderma in Manchuria in 1923. He informed the
writers that although cattle in that Province were not infested, those
from Mongolia were heavily infested. Clausen’s informant stated
that although many infested cattle were brought into Manchuria
from Mongolia, they became free from grubs in one year. Clausen
also learned from Dr. H. Okamoto that near Sapporo, Japan, there
is a small locality in which this pest has become established, prob-
ably through introductions of cattle from America. Doctor Mat-

¢
é
6

‘

4
fe
H
i

sa
Sires es Oa

\
4 os.

o
®,
EG:

Fie. 1.—Distribution of Hypoderma lineatum in the United States. Hach dot repre-
sents a locality where this species has been collected during this investigation

sumura also informed Clausen that 7. bovis occurs on cattle in the
vicinity of Akita.

Through correspondence and by personal examinations by agents
of the bureau, the distribution of the cattle grubs in the United
States and their relative abundance have been determined with fair
accuracy. A summary of the information on this subject was pub-
lished by one of the writers in 1915 (4), and Mote (69) has made a
valuable contribution regarding the distribution of Hypoderma in
Ohio. A study of the accompanying maps (figs. 1 and 2) will best
illustrate the distribution of the two species of Hypoderma in the
United States. It is apparent that H. lzneatwm is much more widely
and generally distributed in this country than is 77. bovis, in fact, the
entire area wheze 7. bovis occurs is also infested with H. lineatum.
The former species had never been recorded in the United States up
to 1910 (0). Riley (84), basing his information on a number of
collections mainly from the Central and Southern States, concluded
that probably H. bovis did not occur in this country. Hadwen (32)

10 BULLETIN 1369, U. §. DEPARTMENT OF AGRICULTURE

in 1912 showed that H. bovis occurred in abundance in southern
British Columbia, and further evidence of the distribution is given
by Hewitt (42) in 1914. Hence it is problematical as to just when
that species was introduced, if in fact it is not anative. Records indi-
cate, however, that it has been introduced rather recently. HZ. linea-
tum, on the other hand, has been known in this country for many
years and has been bred from the native bison, suggesting the possi-
bility that that form may be in reality an American species and not
introduced from Europe. As indicated by the map, H. bovis is now
generally distributed in the Northern States from [linois to Maine
and occurs in more or less isolated areas throughout the Northern
States to the Pacific.

As stated by one of the writers (4) in regard to H. bovis, this
species “must have some well-marked climatic barriers which have

PNG

mceyenn

Fic. 2.—Distribution of Hypoderma bovis in the United States. Each dot repre-
sents a locality where this species has been collected during this investigation.
Hee points shown in the Southern States are collections of larvae shipped in in
cattle

prevented its general dissemination through the country.” As also
pointed out in the publication referred to, there are certain areas in
the United States which are almost, if not entirely, free from grubs.
The most notable example of this is in the valley of the Red River
of the North. In the southern two-thirds of Florida grubs are ap-
parently not to be found except in imported animals. This condi-
tion may be due to some combination of naturalkcontrol factors, as
humidity, salt spray, and drainage. In eastern Massachusetts, the
coastal area of New Hampshire, and parts of southwestern Illinois,
grubs are relatively scarce. Similar areas of scarcity have been
noted by Hadwen in Canada, and he has also observed that the
warbles are more abundant in the western Provinces than in the
eastern. The writers’ observations and reports from stockmen in-
dicate that there is a marked variation in the abundance of grubs in
different localities even when not distinctly separated. Sufficient
data are not at hand for drawing final conclusions in regard to the

eee, ae

THE CATTLE GRUBS OR OX WARBLES 11

areas of unusual abundance or scarcity; but it is believed that the

effect of drainage, soil conditions, and the presence of certain types
of vegetation are factors. In general, the lhghter soils and good
drainage, especially in the areas of heavy rainfall, appear to be
favorable to the development of grubs. The presence of timber or
moderately heavy vegetation also seems to favor them. There ap-
pears also to be an inhibiting influence existent along the coast,
especially on the Atlantic.

It has not been possible to determine any special correlation be-
tween altitude and the abundance of grubs. It has been noted, how-
ever, that they seem to thrive admirably in fairly high altitudes.
This is especially true with H. léneatum, which is known to be
abundant at elevations above 7,000 feet. Some reports received

- from hide dealers indicate that they think grubs relatively fewer in

numbers in the mountain ranges, but the writers’ observations do
not bear this out.

The evidence seems clear that in general where caitle are kept
on the range, especially during the spring months, the grubs are
more abundant. This condition is associated with the care the
cattle receive, the absence of protection from the flies by barns and
sheds, and the lack of cultivation of large areas. It is also probable
that the poor and weak condition of stock on the range during early
spring gives the flies a better opportunity of successfully depositing
their eggs on them. Cultivation is apparently destructive to many
of the larve, although the reduction in the number of grubs may
be brought about by the combination of conditions which usually ac-

company intensive cultivation of large areas.

There is considerable variation in abundance of grubs from year
to year in any given region, but in general this variation does not
prevail throughout the entire country. Statistics on the percentage
of grubby hides during the years 1921 to 1923, inclusive, furnished
by some of the leading meat packers as recorded at their principal
plants, show a distinct increase (average of 10 per cent) in grubbi-
ness during this 4-year period. At first thought this might be at-
tributed to seasonal conditions; but the fact that this increase was
greatest and most consistent in the North, where H. bovis is known
to be gaining a foothold, indicates that it may really be due in part
at least to the spread of that species. If this is true, a very con-
siderable further increase in percentage of grubby hides and degree
of infestation may be expected.

ECONOMIC IMPORTANCE

That grubs are highly injurious to cattle is generally conceded.
Opinions vary greatly, however, as to the exact extent of the in-
jury, and it is a difficult matter to determine with any degree of
accuracy the ill effects caused through the activity of the various
stages of these insects. Injury is produced in a number of different
ways. These may be classed in two general groups—(1) annoyance

~ caused by the flies during the deposition of eggs, and, (2) irritation

produced by the larve within the bodfes of the hosts. The first
group, of course, varies with the abundance of the insects and also.
with the species present. Hypoderma Yovis causes thé most excite-
ment to stock and hence, where it occurs, produces the greatest dati

(A SEE ES a EES a ae SS
(RA a a rer or hae Foe a ee = t= Ss += z : =

es ee ee
i i

—

se RN OR I ES

= —

=

net Aen s:
. Mh Ss ea ok:

vee FA tabs a be SS

—

Sigg eS ee eee ee

De ee

12 BULLETIN 1369, U. S. DEPARTMENT OF AGRICULTURE

age in this respect. Losses caused by this annoyance include marked
reduction in milk flow, failure to put on flesh normally, mechanical
injury due to the wild efforts of the animals to escape attacks, and
not infrequently loss from the miring down of cattle when they
rush into ponds or mud holes, or their injury or destruction when
running over embankments or cliffs. These attacks usually occur
at a time when the stock are in a weakened condition in early spring,
hence the danger of miring and abortion is increased. The exas-
peration and often death loss resulting from stampedes caused by heel
flies is well known to stockmen. ‘The second group may be divided
into four sections: (1) The soreness and pain produced by the pene-
tration of the young larve through the skin; (2) the irritation pro-
duced in the gullet and in other internal organs due to the migrating
larve; (3) inflammation produced along the spinal cord and on the
main branches of the nervous system by the burrowing of the larve
along the spinal canal and the ingress and egress of that canal;
and (4) the irritation produced by the later larval stages in the
subdermal tissues of the back, with accompanying pus formation.

The exact extent of loss produced by these various stages and
activities of the insect can not be determined, but it may be well to
point out some facts along this line. Considering the loss produced
by the flies at the time they are depositing eggs, many dairymen
affirm that they know immediately by reduced production of milk
when the heel flies become active. Of course the amount of loss at
this time depends to a large extent upon the number of flies, the
quantity of feed supplied the cattle, and the protection afforded
them during the day. In regions where the grubs are abundant some
dairymen estimate the milk loss at from 10 to 25 per cent during
the period of fly activity. The season when the adult flies are active
varies, lasting from one to four months. It can be well understood
how this marked reduction in milk flow is brought about when the
frantic efforts of the cattle to escape attack are observed. They are
frequently seen standing closely bunched in the shade or in the
middle of a pond or stream during the major part of the day when
they should be grazing. :

The annoyance produced by the penetration of the young larvee
through the skin is by no means small, although the period when it
occurs is comparatively short. This irritation is indicated by the
violent licking of the heels and other parts where the penetration
is taking place, accompanied by intermittent kicking and stamping
of the feet. There are also extensive external lesions, their loca-
tion indicated by hair matted and rough from the exuding serum
and sometimes by rather extensive areas denuded of hair or even by
sloughed areas. This injury is more severe in the case of H. lineatum
than -with H. bowis, owing to the fact that with the former many
larvee penetrate the skin at nearly the same spot, the eggs from
which they emerged having been laid together, whereas the eggs
of the latter are placed singly. | |

Little is known as to the annoyance produced by the migration
of the first-stage larve aftér* they have passed through the skin.
It is: possible, however, that this is of minor importance. As the
larvte increase in size, and especially when they are numerous, there _
is-Ho doubt that-their migration through the body influences the

ie ~ “ Ror

THE CATTLE GRUBS OR OX WARBLES rah 3

productivity and health of the host. When the larve reach the
esophagus 1n numbers, however, marked irritation is often in evi-
dence. The submucous tissues are edematous, usually yellowish, and
sometimes bloody in the region of the larve. Cases are on record |
in which heavy infestations of the esophagus produced edematose
conditions with large swellings. Instances are also recorded in
which the larve burrowing along the spinal canal have caused
paralysis of the posterior parts, although this seems to be unusual,
considering the large number of cases in which infestation of the
canal occurs.
Abundant testimony is at hand as to the injurious effect-of the
last-stage larvee under the skin in the backs of cattle. Many stock-
men believe, and their opinion in most cases seems well founded,
that heavy infestations of the grubs in the backs of calves are a
prime factor in causing their death. It has been observed repeatedly
that where these larve are removed, the calves begin to “ pick up”
promptly. ‘The effect of heavy infestations in the backs of dairy
cattle is also responsible for decreased milk flow. Danish literature
contains a reference to a case observed by Boas (6), in which a
cow producing daily from 30 to 32 pounds of milk increased the
yield to 40 pounds a few days after 80 larve had been extracted
from the back. Feeders frequently comment on the difficulty of
fattening animals in which a considerable number of grubs are
present. Those who feed steers on an extensive scale during the
winter have informed the writers that in most cases when an animal

-is not making proper gains, it will be found upon examination to

have a heavy infestation of grubs in the back. When these are ex-
tracted the animals usually respond well to the feed. Exact in-
formation on this subject is meager. Schottler and Glaser (88)
have reported upon an experiment which they performed in Ger-
many on the effect of grubs on the fattening of cattle. The grubs
were extracted from one-half of the herd and the other half kept
as a check. The portion from which the grubs were removed showed
a gain in weight of 5.16 per cent over the infested portion of the herd.

Aside from the damage produced by the holes cut in the skin,
there is other injury produced to the host itself by the grubs while
located in the subdermal tissues of the back. When the young larve
first reach the subcutaneous tissues along the back, marked swellings
are often produced. These are evidently painful, as indicated by
the action of the host when they are touched. Just how much irri-
tation is produced after this is problematical. Undoubtedly the
spiny armature of the fourth and fifth stages causes considerable
irritation, but it is supposed that the encystment sac surrounding the
larger larve is practically free from nerves, and for this reason
the host probably does not experience any considerable amount of
pain or annoyance. Not infrequently, however, pus organisms gain
entrance to the openings, and often large abscesses are formed under
the skin. These are associated usually with the death of the larva,
either by crushing or by its imprisonment and suffocation from the
firm plugging up or scabbing over of the hole in the skin. In a
number of instances abscesses have been observed which were half
as large as the crown of a man’s hat and very sore. If these are
well opened and drained they soon heal, but where they are not

14 BULLETIN 1369, U. 8. DEPARTMENT OF AGRICULTURE

properly drained they may discharge for considerable periods, and
sometimes large encystments occur which may form a permanent
blemish on the animal.

Another injury of distinct type, but directly connected with the
infestation with grubs, has been discussed by Hadwen and Bruce
(39). They have shown that the injection of the juice of a few
grubs into a bovine may cause death by anaphylactic shock in a
few minutes, and that the crushing of a number of grubs in the back
of an animal may cause marked anaphylactic symptoms. Their ex-
planation of this is that when an animal has. been infested with
larve of Hypoderma it becomes sensitized, and if the contents of
erubs are introduced either by absorption through natural crushing
of the larve in the back or by injection into the animal, anaphylactic
symptoms are produced. In nature cases of anaphylactic shocks
are probably rather rare, though they might follow the crushing of
a considerable number of larve in the back of an animal, as some-
times happens.

In addition to the direct effect of the larve on the host itself,
there is also an influence on the value of the meat as human food.
The presence of the larve in the connective tissues of the back pro-
duces a very repulsive if not actually injurious condition in that
portion of the carcass.* This necessitates the trimming off of the
affected parts, frequently resulting in the loss of 2 pounds of meat
and at best leaving the carcass unattractive and hence less salable.
This infiltrated edematous tissue is yellowish and more or less
bloody, and appears watery or jelly-hke. It is seldom that more
than the connective tissue and fat immediately under the skin are
affected.

The loss in the value of hides due to the holes cut by the larve
is one which can be more nearly figured in dollars and cents than any
other. Furthermore, this loss is constantly brought to the attention
of hide dealers. Some very interesting information has been gleaned
from the replies of about 100 packers, butchers, hide dealers, and
tanners in all parts of the country through a questionnaire sent out
in 1920. It has been computed from these replies that 19 per cent of
all hides handled are classed as “ grubby ” and over 50 per cent of
the hides taken off in grub season are so classed. The method of
classing grubby hides varies considerably in different sections of
the country. Most packer hides are sold on a grub-selection basis.
The percentage of grubby hides is determined by the individual
inspection of a sample of each lot of hides. Any grub injury which
will permit of a skewer being pushed through is considered a grub
hole. Country hides are usually sold “flat for grubs;” that is, the
percentage of grubby hides is not determined by inspection, but the
price is reduced during the grub season sufficiently to cover the low-
ered value of the hides. )

On the Chicago market it is the custom of the trade to inspect, for —
grubs, branded cow hides and Texas steer hides from November 1 to
June 1, Colorado steer hides from December 1 to June 1, and all
other classes except bull hides from January 1 to June 1. It is ob-
vious that these periods do not fully cover the seasons of grub dam-
age; for instance, in the Northern States where H. bovis occurs,
some grubs are present throughout the summer. Bull hides and calf-

|

THE CATTLE GRUBS OR OX WARBLES 15

skins are seldom classified as regards grubs. On this market it is
customary to place all packer hides with five or more grub holes in
grade No. 2 and discount them 1 cent per pound. With a country

APRN ERS

Fie. 3.—‘‘ Grubby ” hide after being tanned, practically ruined by holes made by
cattle grubs in most valuable part

hide, one grub hole makes a No. 2. Some recognize a No. 3 grade,
placing in it all hides with more than 10 grub holes. Extremely
grubby hides are frequently called “ pepper boxes” (fig. 3) and are
sold as glue stock at one-half price. The discount for grub holes in

SSS a ea RE I I RE TT
SSeS. “web 9 Swen ec eee TERT Ty en

owed — + 1 am erence

ee — ,; ~
paecnigreanns enn ea eet ee ee

0s

eS a eS SS
wee

16 BULLETIN 1369, U. S. DEPARTMENT OF AGRICULTURE

leather varies considerably, but usually ranges between 3 and 10
cents per pound, according to the number of grub holes in the side.

Practically all those concerned in the hide and leather business
agree that the scars resulting from grub attack are not desirable in
leather, but the opinion as to the percentage of injury produced dif-
fers considerably. Some say that even when completely healed -
grubby hides are undesirable in their business, on account of ap-
pearance, weaker fiber, etc.

It is generally agreed that the nominal discount of 1 cent per
pound applied to grubby hides (grade No. 2) by trade custom is far
too low. Many tanners state that they would gladly pay double the
1 cent per pound additional charged for hides of No. 1 grade if they
could obtain grub-free hides. In fact, tanners of hides for certain
purposes make every effort to avoid the grub season in purchasing
their stocks; and this practice, in addition to tying up considerable
capital for several months, introduces another indirect loss. Under
present methods of storing green salt hides there develops in them,
when held for several months, a condition known as “salt stain ”
which materially damages them. This loss is in a large measure
chargeable to the warble. There are also a number of tanners who
are purchasing Argentine and other foreign hides primarily to avoid
grub damage. Grub holes are especially to be avoided when the
leather is to be used for certain purposes; for instance, in upholstery
leather even one or two holes coming in the center, as they usually
do, would cause the entire hide to be discarded for that purpose.

Estimates of the actual monetary loss in hides and leather in
the United States due to the grubs run from $5,000,000 to $10,000,000
annually. Although the percentage of infested hides varies some-

-what from year to year and the number of cattle slaughtered also

varies, it is thought that the figures for the winter of 1921-22 are
about normal. In the period from November 1 to June 1 of these
years, 4,448,793 cattle were slaughtered under the inspection of the
Bureau of Animal Industry. It is estimated that about 40 per cent
of the cattle killed. in the United States that year were under in-
spection. Thus, the total number of cattle slaughtered in the United
States during the period mentioned would be 11,121,980. Accepting
the estimate that 50 per cent of these hides are infested with at least
5 grubs each and hence are placed in grade No. 2, we would have
5,560,990 of this grade. At an average of 40 pounds each and apply-
ing the nominal 1 cent per pound discount the loss would amount to
$2.224,396. During the same period the number of calves slaughtered
under inspection was 2,277,165. By the same method of figuring as
for cattle, but considering only 30 per cent of the skins infested
and the average weight at 20 pounds, there would be experienced a
loss of $341,575, or a total annual loss among cattle hides and calf
skins of $2,565,971.

Taking into consideration the number of hides which are damaged
but not taken off during the season of grub classification, the num-
ber which are perforated by less than five grubs, the number which
are placed in grade No. 2 or thrown into glue stock at one-half
price owing to extreme infestation, the loss through salt stains in
storage, and the increased cost of handling in making grub selections
of the hides, side leather, and cut leather, and accepting the state-

=

ee er rr

2 =.

THE CATTLE GRUBS OR OX WARBLES 1b

erent of hide dealers and tanners that the discount of 1 cent per

pound is really too small, we may reasonably place the total loss
to the hide, tanning, and leather industries of the United States at
$5,000,000 each year. Coppens (23), in connection with a discussion
of losses produced by this insect in Europe, states that the War
Ministry at Brussels found that the wearing properties of grubby
hides as leather is only 30 per cent of that of sound hides. Mason

(65) also touches on the importance of grubs to the tanning in-

dustry. De Vries (27) and Ostertag (74) also discuss losses in
Europe due to these insects.

After a careful consideration of the various losses brought about
by the cattle grubs the writers have concluded that they are con-
servative in placing the annual loss in the United States chargeable
to them at $50,000,000.

INJURY TO MAN

Many cases are on record in which larve of Hypoderma have

| been extracted from man. They are found usually in the subdermal

tissues, where they produce what is often called “creeping myiasis.”
There seems to be a tendency for the larve to work upward and
most of them are finally extracted from the head, face, or upper ex-
tremeties. These migrations are often extensive and rather rapid,
accompanied by considerable pain. In some cases the larve appear

under the mucous membranes of the mouth.

The source of these infestations in man is not known, but most of
them have been in children and usually the affected individuals have
been more or less associated with the cattle. It is probable that
the flies occasionally oviposit on the hair of the heads or legs of
children or on their clothing and the larve penetrate the skin
upon hatching. In the experience of Glaser (29, No. 5, p. 35) while
experimenting with the grub, there is an example of the deposition

| of an ege on woolen clothing. In this case the resulting larva

hatched and penetrated the skin of the leg. Some time later its

| presence in the gastric and esophageal regions was detected by an
| uncomfortable feeling. The larva apparently passed up the esopha-
| gus and was later extricated at the base of one of the lower molar

teeth.
Hamilton *® records a case of a boy who was suffering for some

months from swollen glands on the neck, accompanied by a fetid

ulceration around the back teeth on the lower jaw. After three

| months of unsuccessful treatment a well developed tawny warble

larva was discovered in the ulcer at the root of the tongue. The
case resulted fatally.

The writers have obtained through W. A. Riley, of the Uni-
versity of Minnesota, the clinical history, as prepared by O. A.
Kimble, of a case of dermal myiasis. As this case is typical, and
as opportunity has been afforded of examining the larva, a résumé
of the case is given. A child 6 years old, living on a farm, was
brought to Doctor Kimble’s office during the first week in Novem-
ber, 1920. She complained of a swelling of the left forearm with

5 Hamilton, John. Medico-entomology. In Ent, News, vol. 4, pp. 217-219, 1893,

98252 °—-26—_-2

18 BULLETIN 1369, U. S. DEPARTMENT OF AGRICULTURE

some stiffness and pain in the wrist. The pulse and temperature —
and general physical condition were normal. Three weeks later the
child exhibited a swelling of a similar nature in the lumbar regton
on the left side. This lasted only a few days. During the first
week in December the child was again brought in with a slightly
edematous area, about the size of the palm of the hand, on the
left side in the midaxillary region. Two or three days later this
area showed two small perforations of the skin about an inch
apart. A similar area next occurred on the lower border of the
right scapula. Pain was felt in the area and a few hours later
two punctures appeared. A few days later the child’s father
saw a larva moving in a hole which appeared on the upper angle
of the left scapula following a similar clinical experience. Two
days later a larva was pressed from a puncture which appeared at
the base of the mastoid process of the left temporal bone. This larva
was found by the writers to be H. dineatum in the third stage.
Another interesting case has been brought to the writers’ at-
tention by R. A. Cooley. Dr. O. E. Patterson, who attended this
case, and the mother of the infested child have kindly furnished a
very complete history of the case. This infestation occurred in a
child of 5 years who lived on a stock farm near Moiese, Mont. From
late November, 1921, to March 1, 1923, 14 larvee were removed from
the patient. Seven of these appeared on the head and face, one each
from the neck, arm, shoulder, and chest, and one each from the
thigh and from the calf of the leg. The symptoms accompanying
the appearance of each larva were very similar but most acute
with those on the face. Several hours (sometimes 24) preceding
the appearance of each larva there was malaise and pain in the
stomach, accompanied later with marked fever. These symptoms
then gave way to retarded heart action, cold limbs, and drowsiness.
When these symptoms had practically disappeared a local pain
and swelling occurred in the region where the larva came to the
surface. The duration of each attack ranged from one and one-
half to four days. After several larve had been expelled symptoms
of neuritis began to manifest themselves in stiffness of the legs,
weakness of the leg muscles, and finally almost complete paralysis
of the lower extremities, which lasted several weeks, only subsiding
after practicaly all larve had come to the subdermal region. A
year later this paralytic condition had not completely disappeared.
These symptoms suggest that some of the larve may have entered
the spinal canal and produced lesions there. |
The writers have examined two of the specimens from this case _
and found them to be third-stage larve of H. lineatum.
Riley (84) has given a rather complete account of the infestation —
of a child in Pennsylvania. A physician was called to attend this —
child, which was supposed to be suffering from erysipelas. The —
child, a boy of 3 or 4 years, was suffering sufficient pain from some- —
thing working under the skin to prevent his sleeping at night. This _

larva had been noticed five months before under the skin near the 24
sternal end of the right clavicle, and during the intervening time ~
it had traveled up and down the chest, in front down one arm to —

the elbow, and over one side to the back. Prior to the calling of the ©
physician no serious annoyance had been experienced. This larva —

THE CATTLE GRUBS OR OX WARBLES 19

after removal was positively identified by Riley as H. lineatwm in
the next to the last stage. ~ :

Schoyen (S89) has presented a résumé of a large number of cases
which have been encountered in Norway and elsewhere. He states
that he has examined many of these grubs and that they are without
doubt H. bovis. He further says:

As a rule they have accomplished long ramblings under the skin, always
in an upward direction previous to their appearance through an open tumor
oh the upper part of the body, head, neck, shoulders, ete. All of them have
lived in this manner for months and came out in the course of the winter
months, but were always Still too young to go through their transformation.
It is especially with persons who look after or take care of cattle in the
summer months that such grubs are to be found during the winter.

It is of course conceivable that these larve in their migrations may
cause some rather serious symptoms, which in many cases may not
be attributed to the larve at all.

COMMON NAMES AND POPULAR IDEAS

It is not surprising, considering the wide distribution and common

occurrence of Hypoderma on cattle, that the insects should have
come to the attention of nearly all of the cattle raisers of the country.
As with most other insect pests, various colloquial names have been
appled to them. In the Southern States the larve are commonly
spoken of as “wolves” and sometimes as “grubs.” In the North
and West the term “warbles” is commonly used for the larvee
although they are frequently spoken of as “grubs.” By butchers,
hide dealers, and tanners throughout the country, the name “ grub”
is applied very generally to the larve of both species and the infested
hides are spoken of as “grubby.” Certain individuals sometimes
also speak of the larve as. “worms” and others call them “ cattle
bots” or simply “bots.” The term “heel fly ” is commonly apphed
to the adult insect throughout the United States, but in most cases
the stockmen do not connect the heel fly with the grub in the backs
of the cattle. The term “heel fly ” is very appropriate, especially for
Hypoderma lineatum, as it fittingly describes the habit of the fly in
attacking the lower extremities, particularly the heels, during ovi-
position. “ Warble fly.” is applied to the adult insect by some stock-
men, especially those from England, and “gad fly” is used for it
in some localities. The use of the last name is not desirable, as it
is more frequently applied to the horse flies (Tabanidae).
- In Great Britain the term “ox warble” is used for both species.
In Germany the words “ Dasselfliege” and ‘“ Dasselbeule” are
applied specifically to the fly and the larvae in the back of the host,
while “ Dasselplage” refers to infestations. In France the word
“varron ”’ is used.

There is need for common names to designate the two species.
The propriety of adopting the name “ox warble” for the two forms
might be open to question, on the ground that the use of the word

|. “ox” as applied to cattle is almost obsolete in this country and

that the word “warble” is more aptly applied to the swelling pro-
duced by the larva in stu and is essentially an English term.

Owing to the aptness and general use of the term “cattle grub,”
the adoption of this name for the larval stages of the two species 1s |
advised. Since H. bovis is not to be found in the South but thrives

20 BULLETIN 1369, U. S. DEPARTMENT OF AGRICULTURE
in the North, the term “northern cattle grub” is suggested for this
species; and since //. /ineatum is abundant and widely distributed —
throughout the country it may be termed the “ common cattle grub.” —
When referring to the adult the word “fly ” could be added after
either of the names and thus the habits of the larve would be sug-
gested; but the well-established term “ heel fly,” with the modifying
words “northern” or “common” preceding it when it is desired to |
refer definitely to one species, is preferable. |
The most prevalent idea as to the cause of the grubs in the backs
of cattle is that the animals are stung by the large black horse fly |
(Tabanus atratus Fab.) (fig.
4). This idea originates |
from the observation that
these flies attack the cattle |
primarily along the back
where the grubs occur and
that they annoy the stock
considerably. A good many
stockmen are of the opinion |
that the running of cattle in |
the spring is caused by the
pain produced by the grubs
in the back, especially at
the time they are dropping |
out. This erroneous suppo- |
sition is, of course, corre- |
lated with the fact that the
heel flies are seldom seen in |
action, owing to the rapidity |
with which the cattle leave |
a spot when the heel fly |
appears. There are many |
different notions held by |
IG. 4.—The black horse-fly (Vabanus atratus), stock raisers as to how grubs |
ontte arabs. Mach elarged -<-pet inte the backs solve ae
and what causesthem. These |
are often colored by the theories propounded by naturalists as |
reviewed in the preceding historical sketch. |

HOSTS

The normal host of Hypoderma bovis and H. lineatum is cattle, §
Bos taurus. The American bison, Bos bison, is known to be infested |
at times with 77. lineatum, but bison do not appear to be so heavily —
infested as are cattle raised under similar conditions in the same |
regions. The migration and development in bison appear to be |
practically the same as in cattle.

A number of reports are at hand of the occurrence of H. lineatum @
larvee in the subdermal tissues of the backs of horses. A few speci- |
mens of larvee from this host have been examined by the writers and |
found to be H. lineatum. Most of those seen were in the fifth stage. §
Stockmen have informed the writers that oceasionally one of their }
cow ponies becomes infested with as many as 10 or 15 grubs. These §
sometimes produce abscesses, probably due to the crushing of the }

'

THE CATTLE GRUBS CR OX WARBLES Gig veal

Jarvee by the saddle. The writers have no authentic records of the
complete development of larve within a horse, but this probably
occurs occasionally.
Brauer (8) has described a Hypoderma iarva from the horse and
was uncertain of its identity. Ormerod (7/) gives considerable in-
formation on the occurrence of Hypoderma larve in horses in Eng-
land, but none were positively identified. It is very probable that
H. bovis or H. lineatum was concerned in these cases.
The writers have made but a single test of the development of
Hypoderma larve in a horse. On March 15, 1922, and the following
day two flies (/7. lineatum) caught in nature were permitted to
oviposit on the hairs, on the feet, and at the base of the tail of a
horse. Five days later most of the eggs had hatched and the larvee
had penetrated the skin as indicated by a copious exudation of
serum, some of which was slightly tinged with blood. There was
also some swelling in the region where the larve penetrated at the

base of the tail. However, the animal did not show any indication
_of irritation at the time the penetration took place. In about a
_week the heavy scab formed by the dry serum loosened. Frequent —
examination of the host during the next year failed to reveal the
_ presence of a single larva.

Since it appears that Hypoderma larve may occasionally develop

in the goat (Capra sp.), several tests were made of this possibility
with Angora goats. In 1921, 25 eggs were placed by a fly upon a
_goat’s heels. Three days later some of these were observed to be
hatched and the larve penetrating, but the animal showed no special
‘uneasiness. During the following spring about 86 eggs of H.
lineatum were. placed on the legs of another goat. Some of these
_were ready to hatch when the hairs bearing them were cemented
on the animal. Other eggs of this lot were shown to be viable
_ by incubator tests, but no lesions could be found on the host. Unfor-
| tunately one of these.goats was lost the following summer, but the
other failed to develop any larve. On April 10, 1923, a fly was
| induced to deposit 61 eggs on the legs of a kid. Although the eggs
| trom this fly were fertile, the host showed no uneasiness and exhibited
‘no lesions of penetration. Apparently the eggs were lost before
hatching. No special difficulty was experienced in getting the flies
to lay eggs on this host. |
| On December 22, 1920, 30 larvee, 10 to 15 millimeters in length,
| taken from the gullets of cattle, were inserted under the skin between
the knee and the hip of an Angora goat. A few days later a careful
examination of the skin showed the presence of small objects a few
inches from the point of insertion, which were thought to be some
| of the larve. On January 17, 1921, two of the larve reached the
| back in the lumbar region and perforated the skin. These soon
| scabbed over, however, and on March 4 the lumps were considerably
reduced in size, and the larve were found to be dead.
Two Angora goats were infested on November 29, 1922, by means
| of an incision on the lower part of the thigh. One of these received
) 18 and the other 20 larvee of H. Lineatum, averaging 13.2 millimeters
im length, from the gullets of cattle. On the former of these two
} goats 3 larve appeared under the skin of the back in the lumbar
| region, 2 on December 12, and 1 on December 19; and on the latter

Dey BULLETIN 1869, U. S. DEPARTMENT OF AGRICULTURE

2 larvee appeared on the back December 12, also in the lumbar
region. Each larva had cut a hole through the skin, and from these
holes there was an extensive discharge of serum which hardened,
matting the hair over the grub, thus indicating a marked reaction
on the part of the host against the larve. All evidence of the
presence of the larvee disappeared in a few days.

During 1922 H. E. Cross forwarded a series of Hypoderma larvee
from goats on the Punjab, India. Most of these proved to be ZH.
crossi Patton, but there were two larve of H. lineatum, one in the
fourth and one in the fifth stage.

Peter (76) placed 45 larvee, removed from the spinal canals of cat-
tle, under the skin of two goats; a single larva finally completed its
development.

Koorevaar (54) showed that it is possible for larve of H. bovis
to complete development in a goat after their removal from the
spinal canal of cattle and introduction under the skin of the goat.

Brauer (8) records sheep (Ovis aries) as a host for Hypoderma
larvee, stating that Winnertz had seen a number of flies following a
flock and that Schwabs asserted that grubs occur under the skin of
shorn sheep. These he pronounced to be 7. bovis. It is noteworthy
that Brauer placed a question after Ovis aries as a host. The writers
have never observed a larva of Hypoderma on a sheep in nature, nor
have they seen any indication of the attack of sheep by heel flies.

The writers have carried out a few experiments to illustrate how
larvee will develop in sheep. The flies seem averse to laying eggs on
the wool, but oviposit readily on the hairs of the legs. Forty eggs
attached by a fly above the hoof of a sheep apparently did not hatch,
or-at least no lesions indicating penetration were observed. These
eggs were known to be viable. During the spring of 1922 about 75
eggs were deposited on the legs of a sheep; subsequent examinations
failed to indicate that hatching or penetration had taken place.
Some of the eggs of this lot were known to be fertile. During the
spring of 1923 at least a few eggs of a number deposited on the leg
of a sheep hatched and the larve penetrated, as indicated by the
presence of lesions.

Two grade Shropshire sheep were infested November 29, 1922, |
by inserting under the skin a few inches above the right hock 20 | |
H. lineatum larve averaging 13.2 millimeters in length, taken from
cattle gullets. These were probably all second-stage larvee when in-
troduced. On December 7 one larva appeared on the back of one —

of the sheep, and on December 9 one came up on the other host. e |

Larvee continued to reach the subdermal tissues of the backs of both |
sheep at intervals of a few days until January 3, 1923, when a total _
of 11 had reached the back of each animal. They were rather gen- |
erally distributed over the backs, but more numerous in the lumbar ~
region. There was more or less exudate from the grub holes, and in ~
no case did the larve remain longer than about 10 days before suc- —
cumbing. Several dead larve, all in the fourth stage, were found at —
different times in the wool. :

Many people are of the opinion that Hypoderma larve are to be ~

found in small domestic and wild mammals. There are no published |

records of such. occurrence in nature, and the examination of many
small mammals in the course of the work leads ig the belief that —

= ie

oe
_ ie

THE CATTLE GRUBS OR OX WARBLES 23

Hypoderma seldom, if ever, develops in them. Cats are not infre-
quently infested with oestrid larvee, but so far as known these all
belong to another genus, Cuterebra.

Many dogs kept under conditions which would favor an infesta-
tion by Hypoderma larve have been examined with negative results.
In one instance three adults of H. lineatwm were permitted to ovi-
posit upon the legs of a dog. About 50 eggs were placed in this

way; although the eggs were viable, no penetration appeared to take ~

place. Unfortunately, the dog was lost before an opportunity was
had for the larve to reach the back.

Koorevaar (54) found that larvee from the spinal canal of a calf,
introduced under the skin of a dog, had migrated extensively when
the animal was dissected two weeks later. Some were found in the
gullet and some in the spinal canal.

Four tests of the possibility of the development of 7. lineatum
in rabbits were made by allowing the flies to oviposit upon the hairs
of different parts of the rabbit. Three of these 4 hosts developed
lumps on the body within 45 to 100 days after being infested. Some
of these had openings through the skin, but the presence of the
larvee in them was not definitely determined, and none persisted for
more than a week or two. In one instance several newly hatched
larvee of H. lineatum were introduced into the eye of a rabbit. They
were watched for over an hour, but none burrowed into the tissues.

Two experiments were made with the introduction of larve of
H. lineatum from the gullets of cattle into rabbits. On December
22, 1920, 15 larvee measuring from 11 to 15 millimeters in length
were introduced into an incision near the left hip joint of a Belgian
hare. The rabbit died from infection two days later. Upon dis-
section four dead larvee were found, but none of these were far from

_ the point of introduction.

On November 15, 1922, 10 larvee of H. lineatwm from the gullets
of cattle were introduced under the skin of a rabbit on the left side
of the back in the lumbar region. The average length of these was
14 millimeters. The following morning the rabbit was ill, and had

| considerable swelling below the point of incision. The infiltrated
| area extended down the side and under the belly where there was a

considerable accumulation of serous material, which was drained.

On the second morning the animal was worse, with fever, labored

breathing, stiff hind quarters, and an accumulation of puslike ma-
terial in the eyes. In the afternoon the animal, which was very

low, was chloroformed and dissected. Four living and one dead
| larva were recovered. ‘Two of these were in the connective tissue
| from 114 to 2 inches from the point of introduction. One was on
| the surface of the large intestine about opposite the kidney, and the
| fourth was rather deeply imbedded in the connective tissue on the
| inside of the left leg at the knee joint. It was possible to trace this
| larva with considerable certainty by an infiltrated path down the
| side to the median line of the belly, thence backward between the legs
| and upward to the pin bone, and thence to the inside of the leg, the
| point at which it was feund. Thus this specimen had traveled 6 or
| ( inches in the subdermal tissue. 7

In an experiment carried out by Peter (76), several larve were

| placed under the skin of two rabbits. In one of these four living

24 BULLETIN 1369, U. S. DEPARTMENT OF AGRICULTURE

We ella

larvee were found four months later, but they were not seen subse-
quently.

A few tests have been made to determine if /. lineatum larve will
develop in guinea pigs. Flies were induced to deposit nearly 100
eggs on 2 guinea pigs on April 10 and 11, 1923. Eggs from these
females were shown to be fertile by tests in an incubator, but both
guinea pigs apparently lost all the eggs before hatching began.

Several larve of . lineatum from cattle gullets were introduced
through an incision of the skin on the backs of two guinea pigs.
Both animals were somewhat stiff and inactive the following day
and the female soon became very sick. An edematous swelling
developed on the belly. This finally broke and the animal slowly
recovered, but there was no evidence of the presence of the larve..
The male guinea pig recovered rapidly and a few weeks later
developed a small lump with a hole through the skin over it, just
behind the shoulders. This was a typical grub lesion, but the larve
could not be seen. This disappeared in a few days and no further
evidence of the infestation was seen.

As is shown in the discussion of “ injury to man,” infestations of
humans, especially children, by Hypoderma are not uncommon,
although it appears that man is not a favorable host.

ACTIONS OF CATTLE WHEN ATTACKED BY ADULT HYPODERMA

The reactions of cattle to the attack of these insects is so remark-
able and so much discussed that a brief statement on this subject
seems warranted.

As with the reactions of a host to various other stimuli, we find
a marked variation in the effect of Hypoderma attack on different
individuals. This is, however, mainly a matter of degree of violence
of reaction rather than of kind. As has been mentioned, the fright
produced by “4. Govis is much more pronounced than that produced
by H. lineatum, but the latter often causes a wild stampede.

In the case of both of these species the female has a very flexible
telescopic ovipositor, in no way fitted for pricking the skin. In fact
it can scarcely be felt on one’ s hand when it is extended by the fly.
Convincing evidence of this is also afforded in the fact that flies
have frequently been seen to approach an animal unnoticed and
deposit many eggs without any annoyance whatever.

Careful observations among cattle during heel-fly activity will
soon convince anyone that it is the attack of the fly which produces
the fright. The writers agree with Hadwen (36) that this fear is
produced mainly by the persistent attack of the fly. This is par-
ticularly true in the case of H. bovis. When the fly first attacks
cattle at the beginning of the season the reaction against it is usually
not very violent. The animal kicks or shakes the foot, but the’ |
immediate return of the enemy alarms the cow and she starts walk
ing away; being pursued, the fright becomes more pronounced and
she may run a ~ short distance and begin walking again. The fly
immediately resumes its attack and then the animal dashes away
in terror (fig. 5 5, 6), with the insect often at its heels, in the fashion
of a dog. There is reason to believe that the fear of this insect
is to some extent instinctive; also that, as the areas of attack become

2 | a

THE CATTLE GRUBS OR OX WARBLES 25

sore and tender from the penetration of the larve, the animals are
more easily aroused and terrorized.

After a herd has been attacked for a few days in spring, it is only
necessary to have a single fly begin to oviposit on an animal in order
to start the whole herd from pasture to some protected place. When
water is at hand it furnishes the preferred and most effective pro-

ild dash for pro-

king w
d, calves crowding into shade to escape heel-

is ma

°
?

lm to escape heel-fly attack

‘
c

attacked by adult Hypoderma: a, Cow showing attitude assumed when heel

©
«

eatum) first attacks; 6, heifer attacked by Hypoderma bov

stre

in

ing

and

€
re

of eattle when

Actions
c, cows st

(Hypoderma lin
9

5.
tection
fly attack

fly

lia.

‘tection. Animals have been observed to remain standing in the
water practically all day when adults of H. lineatum were numerous,
and apparently without ever being molested by flies (fig. 5, c), even
though the water was not more than a few inches deep. Shade offers
‘considerable protection and is usually sought in the absence of water.
(Fig. d,d.) H. bovis is less easily repelled either by water or shade

26 BULLETIN 1369, U. S. DEPARTMENT OF AGRICULTURE

than is H. lineatum. Frequently cattle will run for a knoll if shade
is not at hand, and when the breeze is strong the grouping of the
stock on high ground seems to give some: immunity from attack.
When these natural protections are not accessible the flies, especially
H. bovis, will keep up their attack intermittently, causing the cattle
to run from one part of the pasture to another, in small pastures
causing them to run round and round until they froth at the mouth,
breathe heavily, and even drop from exhaustion. Under range eon-
ditions the stock usually have better opportunity of escaping, but the ©
tendency to a general stampede is increased, especially if cattle are
being worked in large herds.

When grazing, cattle usually detect the presence of a fly very
quickly, largely by sight and ‘hearing, but also by touch. Cattle
readily differentiate between the presence of a heel fly and other i in-
sects. The listening attitude assumed when a fly is in the vicinity is
characteristic, as 1s “also the action of shaking the foot (fig. 5, @) to
dislodge a fly, the rolling action of the tail, “and the look of fright
when a fly attacks in earnest.

~%
FT

DESCRIPTION OF STAGES
THE EGG

The egg of Hypoderma lineatum (fig. 6, a: fig. 7) is dull yellowish white
and the surface is smooth and shining. It is narrowly ovoid, slightly larger
at the base than at the tip, and its greatest diameter is at the middle. The
average length of the egg proper is 0.76 millimeter and the average diameter at
its greatest thickness is 0.21 millimeter. The unattached end of the egg hasa
slight ridge across it from side to side along which the egg splits when hatching
takes place. (Fig. 6, 0.) This ridge crosses the end slightly on the side toward
the hair and the micropyle is located centrally at the apex. The clasp with
which the egg is attached to the hair is oval in outline. The average length of
the base attached to the hair is 0.381 millimeter. The petiole averages 0.1
millimeter in length. It is flat and curved and very narrow when viewed from
the side. The position of the eggs when attached in a row is at an angle of
about 45° to the axis of the hair, except the last one toward the tip of the
hair, which is usually more nearly parallel with it. :

The eggs of H. bovis are sim:-lar to those of H. lineatum except in size, meas-
uring 0.81 millimeter in length and 0.29 millimeter in width. The clasping
base is slightly more truncate at the end toward the tip of the hair and the
petiole arises from the clasp more nearly at its middle than in H. lineatum.
The most striking difference between the eggs of these two species is the attach-
ment of the petiole to the base of the egg. With H. lineatum the attachment is —
on the side of the base of the egg away from the hair whereas with H. bovis the
attachment is more nearly in the middle of the base and the petiole is more —
elbowed. (Fig. 8.) Furthermore, the eggs of H. lineatum are normally at-
tached to the hair in rows, whereas with H. bovis the eggs are always laid
singly. 3

ay THE LARVA

FIRST STAGE

The larva of Hypoderma lineatum when hatched from the egg measures
from 0.55 to 0.65 millimeter in length and from 0.15 to 0.18 millimeter in width ~
at its greatest diameter. The width is greatest at the posterior end and the ©
larva tapers to the head. It is creamy or dull white in color, and densely
covered with spines on all segments, the anterior borders bearing the
heaviest spines in transverse rows, followed usually by six rows of spines, —
more or less regularly placed, and slightly decreasing in size toward the pos-—
terior border of the segment. The anal segment differs from all those pre-
ceding in that it bears spines of three distinct types. The posterior spiracles, —
which are represented by two dark circular spots, are protected by two or ~
three rather large, triangular spines located near their borders. The cephalo-

THE CATTLE GRUBS OR OX WARBLES | BE

Fic. 6—Hypoderma lineatum: a, Unhatched eggs attached to hair; b, hatched
eges on hair; c, third-stage larva, side view; d, fourth-stage larva, side view;
e, fourth-stage larva, ventral view; f, posterior end of third-stage larva; g, pos-
terior end of fourth-stage larva, just before molting (note fourth-stage spiracles
in center with fifth-stage spiracles showing beneath) ; fh, posterior spiracles of
fifth-stage larva. All much enlarged

wt is
5 feo

798 BULLETIN 1369, U. S. DEPARTMENT OF AGRICULTURE

pharyngeal skeleton is composed of two long and nearly parallel rods slightly
curved outward at the tip on which two crescent-shaped mouth hooks articulate.
The hooks are pointed at each end, especially the forward one, which termi-
nates in a sharp point. A prominent inward-curving tooth is located about
one-third the length of the entire hook from the anterior tip (figs. 9 and 10).
A stout, sharp spine directed forward projects slightly between the mouth
hooks. The anterior spiracles appear as two minute circular |
elevations above the mouth parts and at the tip of the head.
The armature and spiracles of the first-stage larva of
H. bovis do not differ materially from those of H. lineatum, but
the larve are slightly larger. The outstanding difference is_
that the mouth hooks of H. bovis are well forked at the anterior
end and more truncate at the posterior end. The articulation |
of the mouth hooks is on a small knob extending laterally nearly
at right angles to the axis of the pharyngeal skeleton, which is
not curved at the anterior tip like that of H. lineatum.

SECOND STAGE

The second or next known larval stage of H. lineatum
found in the esophagus of cattle (fig. 11) varies in length from
less than 3 millimeters up to 13 millimeters or sometimes even
longer. It is cylindrical in form and tapers slightly at both.
extremities. The spinous armature is present on all segments. |
On the body segments the spines are- arranged in transverse |
rows beginning with the heaviest spines along the anterior |
border and extending well back toward the posterior border.
The spines are more numerous per row, thinner, and longer
than those of the corresponding segments of the first stage.

The posterior half of the anal segment is covered with stout,
sharp-pointed, curved ‘spines; unlike the spines in this group on -

H first-stage larve these are provided with a heavily chitinized,
PIG. i tigen, large, circular, elevated base. |
tum: Row The second-stage larva of H. bovis, which was first described by
of eggs at- Phibbs (78), is remarkably similar to that of H. lineatum in the |
ee same stage excepting the cephalopharyngeal skeleton and mouth |
ly enlarged hooks, which exhibit the same differences as in the first stage.

THIRD STAGE

The third-stage larva of H. lineatum (fig. 6, c), sometimes found in the;
gullet just before migration to the back, and later immediately after punc-
turing the skin of the host, is from 12 to 16 millimeters long and from 2.5
to 3.5 millimeters wide. It is cylindrical, with the ends tapering and ;
often with the anal end slightly curved toward the dorsal side. With few
exceptions segments 2 to 10 inclusive are free from spines, and at the anterior
end only the group of spines below the mouth parts is present.
The posterior half of the anal segment is thickly dotted with
spines having heavy circular bases greater in diameter than the
length of the spine and nearly three times as great as that of the
second stage (fig. 6, f). The posterior spiracles measure 14
microns in diameter, and the triangular spines on the border of
the spiracles are greatly reduced in size. The form of the
mouth hooks, although heavier than in the preceding stages,
remains the same.

The third-stage larva of H. bovis is slightly larger than that of [',S--Hune

H. lineatum, but the spinous armature shows no material differ- Egg attached

ences. The cephalopharyngeal skeleton and mouth hooks show to hae
the same specific characteristics as in the earlier stages (figs. ae ah ene
12 and 18).

FOURTH STAGE

The fourth-stage larva of Hypoderma lineatum (fig. 6, d, e, g) is from 13 to |
18 millimeters long and from 3.5 to 6 millimeters wide. It tapers consider-—
ably from the fourth, fifth, or sixth segments to the posterior extremity. The
spinous armature varies greatly with different specimens.

Bei RE Ain inte

<2 2
MESS

Po a. -,
PY ts Da be ho
eee wy

.
s.0:° were
’ s 2S %e

> we

terior spiracles (Carpenter and Hewitt)

4

Ventrally segments 2 to 9 are provided fairly con-
‘stantly with a heavy band of spines along the posterior
‘border, but it is not uncommon to find specimens in which
‘segment 10 is also armed and others with segment 9
naked. The spines on the anterior borders of the seg-
‘ments, ventrally, vary even more, and usually end on
‘the eighth or ninth segment. Laterally the armature is
‘very irregular and rarely extends behind the sixth seg-
‘ment on the ventrolateral or the fourth segment on the
‘mediolateral and dorsolateral areas. Dorsally the arma-
‘ture is almost entirely wanting. The greater part of the
/ anal segment posteriorly is thickly covered with small
‘spines surrounding the posterior spiracles, but the tri-
‘angular spines are no longer present. The two posterior
)Spiracles may be round or very irregular in outline.
‘They consist of a group of circular rings or disks. The
‘color of the stigmal plate is orange or yellowish brown,
‘and the disks are separate or loosely connected in groups
‘but always very distinct in individual outline. The num-
‘ber of disks varies from 12 to over 30, but usually with
Specimens collected in Texas it is from about 18 to 25
(fig. 14).
|. The fourth-stage larva of H. bovis is similar to that of
| H. lineatum, but when grown it is slightly larger. The only
‘Specific distinguishing characters that can be relied upon
‘are the posterior stigmal plates. In AH. bovis the stigmal
)plates are composed of disks or rings that are dark brown
or black in color, and usually the whole group is closely
fused together. The number of disks in H. bovis is
‘usually considerably higher than in H. lineatwm, running
from 29 to above 40, with the normal number about 32
to 37 (fig. 15).
v3

THE CATTLE GRUBS OR OX WARBLES

29

Fic. 9.—Hypoderma bovis: First-stage larva. I, Lateral view; II, ventral view;
’ III, cephalopharyngeal skeleton with spine and mouth hooks; IV, caudal segment.
Ph, Skeleton of pharynx; H, mouth hooks; M, spine; 77, air tubes; P. sp., pos-

Fic. 10.—Hypoderma

lineatum: Ventral
view of first-stage
larva. A, Mouth
hooks; B, anterior
spiracles ; C, cepha-
lopharyngeal skele-
ton; Fs, flattened
spines on border of
posterior spiracles ;

sp., posterior
spiracles. > <eaPal
(Laake)

30 BULLETIN 1369, U. 8. DEPARTMENT OF AGRICULTURE

FIFTH STAGE

The fifth or last larval stage of H. lineatun (fig. 16, a—c) tapers considerably
toward the anterior extremity from about the eighth segment. The size of the
larva varies from about 16 to 26 millimeters in length and from 7 to 11 milli-
meters in width. The surface is more rugged than in the preceding stages,
especially on the sides. The spinous armature is heavy; and, although varying
greatly with different specimens on the dorsal and lateral sides, it is constant

Fic. 11.—Second-stage larva of Hypoderma lineatum in submucous tissues of gullet.
Enlarged
ventrally on the posterior borders of segments 2 to 10, inclusive, and presents
an excellent distinguishing characteristic for this species. The posterior stig-
mal plates are somewhat kidney shaped, flat, or slightly excavated toward the
pseudostigmatie orifice, and have radiating furrows which are very distinct in
the younger specimens (figs. 16, d; 17).

THE OATTLE GRUBS OR OX WARBLES 31

The fifth-stage larva of H. bovis is slightly larger, but otherwise very similar
in shape to that of H. lineatum. The armature arrangement is similar to that
of H. lineatum, except ventrally, where only segments 2 to 9, inclusive, are
armed; very rarely a specimen is found with armature on the tenth segment
and with a single-or a few spines on the. anterior
border only. In H. lineatum there is always a
fairly broad band of spines on the posterior
border. The posterior
stigmal plates of dH.
bovis are deeply exca-
vated or funnel shaped
toward the pseudostig-
mal orifice. This ehar-
acter is very reliable
for distinguishing the
species in this stage
(fig. 18).

THE PUPARIUM

The puparium retains
all the larval charac-
ters, except that it as-
sumes a different shape
and darkens in color
to almost black. Its
dorsal side is nearly
straight and flat, with
the anterior end plain-
ly showing the opercu-
lum (fig. 16, d-f). The
flat stigmal plates of
H. lineatum and the wg, 13.—Hypoderma bovis:

- funnel-shaped plates Cephalopharyngeal skele-
Fie. 12.—Hypoderma lineatum-: : . ton and mouth hooks of
Cephalopharyngeal _ skeleton of H. bovis remain the Raiedestaee ipcual A,

and mouth hooks of third-
stage larva. A, spine; B, an-
terior end, and D, posterior
end of mouth hooks; C, tooth.
Greatly enlarged (Laake)

same as in the ma-
ture larva and serve
to distinguish the two
species.

spine; 8B, anterior end,
and OC, posterior end, of
mouth hooks. Se as
(Laake)

THE ADULT

The adult of H. lineatum (fig. 19) measures from 12 to 13 millimeters in
length and has a wing expanse of from 23 to 25 millimeters. The female
with ovipositor fully extended measures 17 millimeters in length. The gen-
eral color of the adult is black, banded with yellowish and orange hair. The
shade of the colors *varies somewhat with different specimens and also
changes according to the position and light in which the insect is viewed.
The front, sides, and back of the head are covered with yellowish-white hairs.

The thorax is vee
clothed with
yellowish hairs
except dorsal-
ly, where the
posterior part
of the protho-
Tax, ane the
mesothorax are
he reer ee, more ein y
Biniee of ene age covered with
arva. Greatly en- black and some
larged (Laake) yellow hairs.
On this area
there are four distinct longitudinal lines which are nearly naked and shining.
The basal segments of the abdomen are covered with grayish-yellow hairs, the
middle segments are brownish black, and the terminal segments are clothed in
orange-yellow hairs. The femora are black and the tibiz and tarsi brown. The
entire legs are well covered with black and orange-colored hairs. The wings
are Slightly fuscous and the veins are dark brown to black.

: Posterior
stigmal plates of fourth-stage larva.
Greatly enlarged (Laake)

Fie. 15.—Hypoderma bovis:

ic. 16.—Hypoderma linedtum: a, Fifth-stage larve, newly molted to mature
(ventral view, except mature larva, which is dorsal); 0, fifth-stage larva,
dorsal view; ec, section of ventral side of mature larva; d, puparium after
emergence of fly, dorsal view; e, ventral view of pupa; /f, puparium,
side view

8
ee
a

THE CATTLE GRUBS OR OX WARBLES 33

The fly of H. bovis (fig. 20) is considerably larger and much stouter than that
of H. lineatum. This is especially true of the thorax, which is much broader.
The color is similar to that of H. lineatum, but the band of yellowish hairs
across the prothorax dorsally is markedly wider and the shade slightly deeper
than in H. lineatum. The shiny longitudinal lines of the thorax are obscured
anteriorly by the hair. The color of the abdominal vestiture is similar to that

of H. lineatum except on the terminal segments, which have a wider and more

and yellow hairs, and the tarsi are brown

sharply defined band of lemon yellow, distinctly paler than in H. lineatum.
The wing veins of H. bovis are of a reddish-brown color. The femora and the
tibize are black and well covered with black

and much less hairy than in H. lineatum.
HOW THE LARV# OF HYPODERMA

LINEATUM GAIN ENTRANCE TO
THE HOST

The method of ingress of various se
animal parasites is often a point of wee |
considerable economic importance. Fic. 17—Hypoderma lineatum: Pos-
As has been indicated in the historical oe ue eel Laue

sketch, the opinions held by various

investigators in regard to the way in which Hypoderma larvee enter

the host have been at wide variance; and even up to the present time
there are but few who feel certain of the method of ingress of these
parasites.

During 1916 plans were laid at the Dallas laboratory to carrry out
a series of tests to determine accurately the way in which the larvee
enter the host. These tests have been continued along similar
lines up to date. Since a full knowledge of the habits of oviposition
of adult H. lineatum has been gained, it is evident that there are
really only two ways in which the larve might get into the host, one
of these being by direct penetration through the skin and the other
by being taken in by mouth in the egg or young larval stage.

The following plan, with slight modification, was carried out in
all of the tests: Certain animals were placed in fly-proof cages and
thus protected from all possibility
of attack by heel flies during the
season of fly activity. To these
animals were administered by
mouth the eggs of newly hatched
larve. Most of these were ap-
plied to the tongue or inside of
the lips of the host, but some were
placed in capsules and the host
made to swallow them. Certain
Fic, 18—Hypoderma bovis: Posterior of these animals were dissected

Gereatly ehinreed (Gasket a time when the Jarves should

be present in the gullets or other
portions of the carcass commonly infested, to ascertain if possible
whether any of them escaped from the digestive tract. Others
were kept and watched the following fall, winter, and early spring
for the appearance of larve in the subdermal tissues of the back.
At the time that these animals were being fed with the larve and
eggs, others were infested on the legs or elsewhere by allowing
flies captured in nature or reared in cages to deposit eggs upon

58252 °—26——_3

34 BULLETIN 1369, U. S. DEPARTMENT OF AGRICULTURE

them. These hosts were kept securely muzzled throughout the
season when flies were likely to be about, except for the time that
they were being fed,
when they were placed in
specially constructed
stanchions which wouid
not allow them to lick
any part of themselves.
Thé muzzles used were
made of heavy wire, ex-
tending well up the nose
and covered with closely
woven ducking, except
for two small holes above
the nostrils.

As will be seen by ref-
erence to Table I, dur-
ing 1917 three animals
(Nos. 164, 169, and 176)
were infested by alliow-
ing flies to oviposit on
them. One of these re-
ceived the eggs on the
Bic: 19. Dacia ew of call pate (oF atatme helen le ee

on the legs, shoulder, and
neck, and the third on the back. In each of these a considerable num-
ber (45, 27, and 10, respectively) of grubs came to the subdermal
tissue and cut holes
through the skin of the
back the following fall
and winter. Another
animal (No. 174) was
given, by way of the
mouth, 386 newly
hatched larve and 82
eggs which were about
ready to hatch. Nine
of these larvee were ad-
ministered down the
throat in a capsule.
No grubs appeared on
the back of this animal!
during the fall and
winter, although it
was shown that it was
a favorable host by the
fact that it had a good
infestation during the
previous year. eves

In 1918 three ani- F!%: a Sig aerate Mach sheet of Hypoderma
mals were used, two of
these (Nos. 212 and 217) receiving infestations on the heels and one
(No. 214) by way of the mouth, Both of those having eggs de-

THE CATTLE GRUBS OR OX WARBLES 35

posited on the heels developed grubs in the back.. One had 45, with

‘a about an equal number on each side of the backbone, and the other

had 2 when the animal was disposed of on December 23. Pessibly
other grubs would have come up later. The animals to which the
young larvee were fed was observed throughout the fall and winter
and no larvee whatever came to the back.

In 1919 11 animals were used in the tests. Four of these (Nos.
411, 412, 418, and 415) received eges on the heels and front feet,
one near the hips (No. 419), and three on the heels and elsewhere
(Nos. 409, 410, and 414). Three (Nos. 416, 417, and 418) were
fed eggs and newly hatched larve. One of those receiving eggs
on the heels and elsewhere (No. 410) was killed shortly after the
egos began to hatch in an effort to determine the presence of larvx
in or under the skin. No larve were found but some small holes
were clearly visible in the skin beneath one group of the eggs, and
the connective tissue under the eggs was yellowish and edematous,
just as it appears when the larve are present. On July 9, one
of those animals which received eggs on the heels, front feet, hock,
and side of abdomen (No. 409) was killed and examined; 76 larvee
were found along the gullet. One of the animals which received
egos on the heels and front feet (No. 411) was killed October 7
and no larve were found owing, it is believed, to the fact that
the eggs were infertile. In the case of this animal no irritation
or lesions indicating penetration were observed, after what should
have been a normal period of incubation. All of the 112 eggs de-
posited on this animal were laid by one fly and some of the eggs
clipped from the host and placed in an incubator failed to develop
Jarve. Of the other three receiving eggs on the heels and front
feet, all showed moderate infestations of grubs (average of 14.3)
in the back the following fall and winter. The animal receiving
the eges on the hips only (No. 419) developed a total of 13 grubs
the following winter, and the one having the eggs placed on the
hock, front feet, and udder (No. 414) developed a total of 20. On
the other hand, two of the animals (Nos. 417 and 418) which re-
ceived fertile and well-incubated eggs, as well as healthy larve,
by way of the mouth, failed to develop a single grub during the
subsequent fall and winter. The third (No. 416) was killed July
9, and a careful dissection failed to reveal the presence of a single
larva in the gullet or elsewhere.

In the tests begun in the spring of 1920 10 experimental animals
were employed. Three of these (Nos. 167, 159, and 417) were in-
fested on the legs, mostly on the hind ones from the hock down; one
received eggs only on the top of the shoulders; two (Nos. 158 and 22)
had the eggs placed on the front and rear legs and on the belly
near the flank; and two (Nos. 160 and 414) received larve and eggs
by way of the mouth. Two other animals (Nos. 92 and K23) were
used to test the migratory tendencies of the second-stage larvee, which
were removed from the gullets of slaughtered cattle. These were
inserted in pockets cut under the skin near the hock.

,» U. S. DEPARTMENT OF AGRICULTURE

BULLETIN 1369

36

‘OL ‘uel 0} ST AON yoeq Uo UTS pozes0j.10d JT
*[ ‘00q yoVvq UO UIYS poeyesojsod T
"6 (00
09 ‘esojeq JO ‘TZ “AON yYovq uo urys poyesojiod ¢
“yoeq UO poyelojiod VBAIv, ON

‘%Z uel 019 ‘09d Youd uo ulys poyesojs0d TT
“EC “90M

04 ‘o10Joq 10 ‘T ‘00q yowq UO UIYS poyesojs0d OT
'¢ ‘UCL

04 ‘e10joq IO ‘6, “AON yoeq Uo UIYS peyesojiod ET
‘py 00d

04 ‘etojoq JO ‘JT “AON Youqd WO UIYS poxesojszod ZZ
“6% “99,

0} ‘a10Joq 10 ‘JT “AON Youd WO ULYS peyesoj1ed OZ

“Od

“yoeq WO UIYS poyeslojiod VAIv] ON
“punoj BAB] ou ‘poqoossip “6 Aine
*punoy BAI] OU ‘poqoossip ‘7 400
‘4o][NB Ul BAIL] 9) ‘posoqysneys “6 A[nE
“yyeomeq
HONBINPUL PUB UIYS Ul SOFOHY “FZ “AVIA, Pojoossiqy

‘yoeqg UO UIYS poyerojiod BAIv] ON
“4SO] SBM

4soy uoy ms ‘ez “00 HIV WO UIYS poyesojiod pey Z
i “g uee

04 ‘a1ojoq 10 ‘ZZ “AON YoVqg UO ULYS poyesoj1od oF

0% ‘00 YoRd UO UNIS pozvaojiod pey OT
‘yorq UO ULYS poyetojsod AIL, ON

‘9% “AON OBG WO UIYS poxesojiod pey 21z
Te 00d 040Z “AON Yovqg UO ULTS poyVsojsod BAIL] OF

synsoy

9€T

aa
891

98T

-mInN

SH EL NTN 6s ngs UR Pe Va en s[99H

Soh eee aarp 400} 4uo1y ‘Too

secenna--- diy 1¢0u opis youy

Br Ma Jeppn pue ‘ssey “400.7

sdij puv on3u07} Uo ‘YNOUI UT
“Sdif optsur

pue ‘ensu0}) Uo ‘YI Nou UT

huENL bees ensuo} UO ‘YyNoUuL UT

SS Ti a EI ee 400} JUOIj ‘Joo,

“"---==TeulopqeB ‘sseT ‘sfeo eT
‘snue Aq

pue ‘yuey ‘uouopade ‘sjooy{

~; peyxeuU ‘onsm07 UO YANOUL UT

-------~------------- yovg ua
“soynsdvo

Ul puve ; poyvu ‘YINOUL UT

|--"“Jopynoys pure ‘yoou ‘ssery]

Ri Aa MT ne Yay} pur sjoo}{

\

poyjour pue oor] Gg

TAONTEES FTE el VOTE ag $33]

ptr ees alist rare va Puta id S33

Ves, ree ear ~BAIV] PUB SBSH

~=-------- s33e pure BAI]

op---"-
a gga eine Fe pn. a koe IRS S33

03819

BAIL] 93V48-JSIy puvsssq | Gg adv 09 Ez “ARIA
“7-""" =" 9584S ISI ‘BAIT |--G ad y 03 ZZ “IVIL

~----- Bl OVO eTNie Sin ie sae sae SIBOm Co leneesOD> aa) Gem
waeens SL OL ORSINI Wie 0S OD ay ae OD" 7) 607
so -e—S eee ZL IVIL + caer Jeb aan ERO K-T ~~“ JOJO | LOT
en Lo te 0161 “LB TAL Bea eee an 14213 Fae CP ee ONG) O9T
0261
------------ Op TTT" Sy90M g [7-7 - "Op" - "| STF
oh ks 1% 04 LI ‘sey, |-7--"--------syoows g |-----op---] zip
----------- VCAPIGIN) Gn Bemis het TLC OAGT: ~~“ JOJIOFL | 61P
wean a ne --- ZOD ei asl) pea es CSABOL.L FOU la sas Ops =| CLP
meee eee eK QT “IVIN Pie rea reet at SAO AER er err) VIP
teeta Ee qeak [ |--~JoyeFI | STP
oe Re aa a Sivek Z |-"7-"Op" | LIF
sae e Ze 01 0Z “IVI GPE pee No SCONCE 2 PAOD) 91h
Sere soos Nac Ue Niele oe eee = OSU UOUL Ge ema nO Dama Titi?
see OT 074 OL “IVIL ee ene SUL LOULLEG, perme LLL 607
------ 0Z 09 OT “IBIN eee SU LOLLIRG ~~ ~~ 19945 OL?
6161
iA 6% 07 ST “ABIL [7777777777 SIBOA F I-----MOD | FIZ
ie ig gL aey, [77-7777 saead %4T |----s009g | 21z
--=-——— al 03 ¢ IVT Taree tae ce STB OARS enum AA OG) GIG
ST6I
----------- LI ‘IRIN Siabies Sie oa Scams TO Ae TT OO aH (ope ]k
== se Ig 09 LT “TBTAL Te ee cap SOC OACC ae a0) Osa PLT
Se SCT 04 GL “IVA heen ae Ne sivek Oils ar MOO 691
--=----- PI 07 LZ “dey, | 7 sagmoul Y |-- ~~ 19099 | FOT
LI61
ee |
os [eulay “ON

poyseyuy

qsoy o7ut WnjnDaUr) DULapOdh Fy fo ssashur fo poyjawm fo worourmiajag — | AIA I,

od

WN
=
4
rai)
fq
<
=
*
oe)
ra
co
M
fea)
©)
fom
oD
eq
4
al
H
es
.@)
a
q
H

"S837 ¢

CG UBL
01 8 ‘Uer YOVq puv ‘yURp ‘Sal UO ULYS poyesojsed FT

“ST “Uef 0}
‘g10jaq 10 ‘J “UBL YOVG PUB PIS UO UTYS po}viojiod g
‘ZS “UCL 04 2Z “AON Youd UO UTYS poywlojsod CZ
“patdAOdel GT ‘6L “AON poqoossiq

‘gue

0} ‘alojoq 10 ‘CZ “AON yoeq UO UTYS popVAojiod g
“GT UBL

0} ‘alojoq JO ‘Gi “AON yowq uo Uys peyelojiod CT

‘od

“yoeq WO ULYS peIe1ojiod VUON
- “PL 99d

yovq UO UIYS poyvsoysod [ {WorNIOsS siiJep ur poddiq
‘p 00d

yovq UO VIYS peyesoyied [ ‘dip o4o0soel0 ur peddiq
‘% uve

0} ‘9TOJoq IO ‘TZ “AON YIeVq WO UTYS poyeioji0d 6
"2 09

04 ‘o10Joqy JO ‘fT “AON yowq Uo UrTyAS poyesOJIed 9z

‘ZS 00d 02 0F “AON Woe UO ULyS poyesojsod 6
“poIeAO0del VAIL] OT ‘peyoosstp ‘27 “390
*€ 09 0} ZI “190 Yovq Wo ULYS poyesojsod F
‘ZL AON 038 “AON Youd WO ULyS poreroj.iod Z
“TL 00d 0} ZT “400 Youd WoO ULYS poyviojied vt

LE PO
04 ‘e10joq IO ‘OZ “4990 YoVeq Uo uryS poyesojsod ¢
“yoeq UO UIYS pozeioj.ied sUON
‘PUL 01 1Z YOO YOVA WO Uys poyeso0ji0d Fg
*peyozey ouou Ajjusiedd y

i

‘$Z (99d 03 6 ‘AON YoVq UO ULYS poyerojI0d g
"8G AON
04 ‘eroyeq JO ‘0zZ “400 YoRq Uo urys pares0jsod eT

-puer

04 “e10joq IO ‘[Z “AON yoeVq WO UTySs poyesojied ze

“puno}y BVAIV[ OF ‘poqoossip ‘e Arne

“IVOI OF [IV “LT-fPl “od Yovq uo Uys poyerojsod 6
‘Od

‘pourmexe jou ‘ures, Aq pol[Ly ‘GZ “990

*PHNOJ BAIV] OU PUB PoyDaSSIP 9z “AON

~— AOFTO HT

---9SlOFL
=== p7=-

“~~ JOJO

~~ - JOH

BAIVT; *SULIOAOD J9y}O IO B[NSdvd B JO OSN JNOYJIM SUOMI ,,POYN,, 1
““S9, PUIY IYSM ULyS Jopug |--~~7--- qoypns WO BACT RICE Gere acne sey pouer \--sqqaou OL ‘sivok F
; ve61
[.c SOPPULU US LULLIS OVW Ol sore amGam mae aan ODate at Ciee apes nas AORN G fla = Gy Se rae sivak we
~-"sse] puly 40d Uys Jopuy, {7777777 Joys Wooly BAIVYT |8Z°00q PUBFIT AON [7-7-7777 777 Syoom ¢
Saar ere Sse] PUI ‘UIYS JopuQ, |~~ 777777 ATUL YOM, [7777 PL AON [7777777777 QUO T
G61
|
Fe et OER es a Sjooy wot yo |7 97777 saay 7777777 -- op =" --|--“sqquour 7 ‘sivod ¢
z *sjeoy PUY “sido
‘rey pus Uys UO pooR[g | puw BAIR, 9984S-ISIR [7-77-7777 OCS ICN a Ressaces tas SHIM Z
“TIBI JO aseVq
PUL Sool) 4WOIT! PUe eos Issacs 3 ae oe Sao hi a5 OL DUC Get ICINT sewn soe a SIvdk ZI
"7>>>>>"-—-9nsuo1 UO pedBi[d |~~ 7-777 BAIV[ 08B4S-ISIT | 7 7 CVA ONL (NE OkBNE boas soe ee sivok F
ncaa ok ee ea ODae eg |2 5 ae ae aoe ees OD = aaa nea O10) Qe dUINT |eecrn eee SU QUOUUI: ey
Ba ae vues ae Sjeoy PUTA [7777777777777 77777 Op 7-71 - > OT pues g “rey, | ~ >>> 7 sqguoul ¢
Se ON ee duini pue Hoe |-~ 7-7-7775 7777 Op t1-- > g pues 2 “rey, |7 ~~ > 7-7 sqgmou OT
Rea see Sd0[ PUIG WO SOOM fossa foo 2 carey 1777-3 sre0k €
Gc6L
bat aaiy ote, SES aE ARTS ES OD Rae alae ee eee Rae gO Doe taal ats estar Olen AOINT ac cieme aaa ae ee OT LO ULL ST
Bela aS ont Sina Tee Cm ODS eae ga ceca ee SO Dre aal roe eon 2 Ge IO Di meee SU VUO MING
Relea rae Sol DULY ULYS ISPU A Ss cans eae eee es COD sacral) aes cos a ODt |) aS }UOUL.G“sIBekg
FELT Se pn FOCELUOMUIYS IS PU) |i yen en ae LOD pnemalenae: come = pm ODier sss ancy cagSUQUOUL Oe
“ULyS Jopun 1v9 JUSSI pulyog |--77 77 TT OD Se 5G SC etn eae OC SVE | aoa SUIUOW GZ
er airinen aaah ULYS JopUn Soy PUIFA |~ ~~ 77> ~~ Jo] [NB Wol Barer |--~---- 7-7 g ABP [777777 saeok 44g
~">> ~~ 400} pury oy ‘ULYS UD | 7 7-777 BAIV] O8VIS-JSILY | 7777 GZS AGING - feet ee DR ee Pe mes
=) 00S" FU0I} PUG SOU OL i er ee a ODe ea Cul | Si neem aes 9I aay ------------ sy}UOUL $
sey capers ae JOOP DUC SVOUSI ON aie aac = oe wees an are SO5 (er nena me a ie GT\T
“JO0J JUOLJ FYB UTYS
UQ ‘Sspoy Joy pue JYOSIY | BAIC[esv4s-isig puBss3sy |---- 7 Qi. OF Gi GIA s| ese) ener ~"qqyuow T
Rea TRS, 39 pay ‘ULys Jopug |~~~~~---geT[Ns Wod eatery |-~~---7--->--g ABYT |-- >>> > syyQuoU gg
Ié6L
“MOISIOUL Aq Uys Jopun ‘Yoox, | - 77> ~~ qoy[NS Wo BAe] |-7-77 QROUN kn ten annme SqJUOUL 17
Saree oe Afjoqd pue JOOP, |7 7777777777 seu |7 77 8G 09. 2S “AVI. | ~ — SOU 9
MoIs~oul Aq ULys Jopun qsIy, |~~~~~~ ~~ qoT[Ns UIOI BAIwT |-~-> 7 PeeROGY G Waliaioe wc in © oe q}UOU T
Sein a is car Oa (OOULPWE MOO scsi eet eae OD ae alba oe (HEROES Bade NE Wenge area pa sivak §
“Jeppn ivsu puv ‘Ajjoq ‘sjooHy | 77 Seistape mens es CTO OE QmUGTA teem a seen ase Sq}UOU Z
1 peYeU ‘onsuUo} -
UO pUue sdij opisul ‘yynour Uy '~~~~--7-7 BWAIV[ 93BIS-JSIT YY ~~ 777 BOW BAT aie one etna sieod 6

38 BULLETIN 1369, U. S. DEPARTMENT OF AGRICULTURE

Of the three animals receiving the eggs on the legs, one (No. 417)
was accidentally killed by a train during the late summer and no
examination could be made. In November, larve first appeared
under the skin on the backs of the other two cows (Nos. 167 and 159),
and during the fall and winter one of them had 8 larve to reach
the back, while the other had 17. With the animal infested on the
shoulders (No. 163), a single larva appeared on the back during the
following winter; but it had been observed that many of the eggs
on this animal were infertile and had failed to hatch. One of the
two animals with infestations on the legs and belly (No. 158) was also
killed by a train and not examined, but the other (No. 22) was
slaughtered and carefully dissected on July 3. <A total of 40 second-
stage larvae were found on the viscera and along the gullet. One
of the two hosts infested by way of the mouth (No. 414) was dis-
sected on November 26 and no larvee were found in the gullet or
elsewhere. The other animal (No. 160) was observed carefully and
repeatedly during the fall and winter and not a single larva came to
the back. The two animals (Nos. K23 and 92) receiving the second-
stage larvee through incisions cut near the hock showed 9 and 32
larvee, respectively. ‘These appeared along the backs during the fall
and winter.

During the spring of 1921 two heifers were infested by flies which
deposited eggs on their hind legs. One of these (No. K23) received
about 110 eggs on the feet, but apparently none of the 45 eggs
hatched which were deposited on this animal on March 3. The first
larva came to the back on October 27, and a total of 64 larve ap-
peared during the winter. The other heifer (No. 22D) received
far more eggs on the legs but developed only 8 larve on the back,
the first appearing November 9.

During the season seven bovine hosts were infested by placing,
in pockets cut under the skin, larve of H. lineatwm removed from
gullets of slaughtered animals. ‘Two of the hosts (Nos. 92 and. 160)
were infested May 8 with larve (4.5 to 5.5 millimeters in length)
inserted above the hock. Each developed an infestation in its back
in the fall. The first larva reached the back October 20 or shortly
before. Four cattle were infested with 26 gullet larve per animal
on August 26; two received them in the right hind leg, one behind
the ear, and one in the back about 8 inches behind the shoulder and
3 inches from the spinose processes; this was in order to compare
the dates of appearance of larve on the back and the number suc-
cessfully reaching that region.

One of the two hosts infested on the leg (No. 159) had larvae
present on the back on October 17, and at that time the other animal
(No. 167-1) was killed and dissected. On a post-mortem examina-
tion 10 larvee were recovered, 3 in the subdermal connective tissue
of the back (but no holes had been cut through the hide), 1 under
the spleen on the paunch, 1 on the paunch near the esophagus,
3 in the mesentery of the colon, and 2 in the submucous tissue of the
cullet. One of the latter was near the paunch end of the gullet and
measured 13.7 millimeters in length; the other was in the middle
of the gullet and measured 11.6 millimeters. Both were headed
toward the paunch.

| THE CATTLE GRUBS OR OX WARBLES gf: 39

In the case of the cow infested at the base of the ear (No. 25-D)
the first larva reached the back October 17, and a total of 15 came
to that region; with the cow infested on the back (No. 167) only
two appeared (November 8 to 12). On November 16 a bull calf was
infested in the hind leg by inserting in the skin 14 larve taken from
the gullet of a slaughtered animal. These larve measured 11 to
15 millimeters in length and the first appeared on the back November
30. Nine of the 14 succeeded in coming to the back for normal
development.

In the calf (No. 24-D) five first-stage larvee were applied for a
study of penetration. Although some of these were observed to
penetrate the skin, none reached the back.

During 1922 seven cattle were used in the tests. One of these
(No. 92) was protected from flies, but fed 89 newly hatched larve
by placing them on the tongue and in the lips. In this animal not
a single larva reached the back the following fall and winter. Of
the other six hosts, five were infested on the heels and legs and
muzzled to prevent ingress of newly hatched larve through the
mouth. In all of these animals larve reached the back, the number
per host varying from 1 to 26, despite the fact that two of the ani-
mals had the legs immersed in insecticides every day. The other
animal (No. K-23), which received eggs on the back, developed
nine larve in that region. The date of first appearance of larve
in the subdermal tissue was not influenced materially by the date
of infestation or by the point of ingress into the animal.

On November 14, 1923, 20 larve taken from the gullets of slaugh-
tered cattle were placed beneath the skin by incision, on each of two
calves (Nos. 92-1 and 25D-1). The point of introduction was
about 6 inches above the hock joint on the outside of the right hind
leg. The larve averaged slightly over 12 millimeters in length.
On November 19 the older calf (No. 92-1) (1 month old) was dis-
sected and 15 larvee were recovered. Most of these were ranging
upward in the connective tissue under the skin where there was
marked infiltration, and one had passed between muscles on the rear
of the thigh and was apparently following a large nerve, being only
3 inches from the spinal canal. In the other calf (No. 25D-1) 6
larve had reached the back and had perforated the skin, 4 on the
right and 2 on the left side. On December 28 another lot of 16
larvee from gullets were put under the skin of this calf on the left
hind leg just above the hock. These were from 12 to 16 millimeters
in length. Immediately preceding January 8. 12 grubs had reached
the back and had punctured the skin. These were about equally
distributed on each side of the spine; 7 others reached the back by
January 22, making a total of 25. On December 28, 29 larvee from
12 to 16 millimeters in length were introduced in an incision through
the skin on the right hind lee of a cow, just above the hock. On
January 7, or shortly before, the first larva appeared behind the
right hip, and 7 others cut holes through the skin during the period
up to January 18. One of these was only 7 inches above the point
of introduction and the last one was on the left side just in front
et oe hip, a distance of about 33 inches from the point of intro-

uction,

40 BULLETIN 1369, U. S. DEPARTMENT OF AGRICULTURE

On January 4, 1924, 21 larve from 11 to 16 millimeters in length,
from gullets, were introduced subcutaneously above the hock of
another cow. On January 8 one larva cut through the skin 51,
inches above the incision. On the following day 5 others punctured
the skin, one of these being 30 inches above the point of introduc-
tion. The following day 3 others appeared, 1 of these being near
the spinal column on the right side about 7 inches behind the shoul-
der, a distance of 40 inches in a line from the incision. A total of
14 grubs perforated the skin, all being on the right side.

It appears from these tests that when larve which are ready

to leave the gullet are introduced subcutaneously they may not
travel far from the point of introduction before puncturing the
skin, and that they appear to pass upward under the subdermal con-

nective tissue without penetrating deeply into the tissues as oc- |

curs when young larve from the gullet are introduced.

To recapitulate, in the tests carried out at the Dallas laboratory,
28 animals were infested by allowing flies to oviposit on the legs
and bodies and were prevented from reaching any part of their
bodies with tongue or mouth. Of these 28 animals, 2 were acci-
dentally killed and not examined. In one of those slaughtered
for dissection no larve were found, but in this case no hatched
eggs were observed on the animal and other evidence indicated
that none of the eggs placed upon it were viable. One of the other
animals was killed immediately after the eggs hatched and, al-
though no larvee were found, there were strong indications of the
penetration of larve through the skin. Two of the other animals
killed showed an abundance of grubs along the gullet and on the
viscera. Twenty of these animals were kept for observation during
the fall and winter, and in every one of them grubs came to the |
back during the normal grub season. In all of the 11 cattle which
were infested by introducing larve from the gullets of slaughtered
cattle under the skin on the legs, behind the ear, and on the back,
larve appeared under the skin at the usual time during the fol-
lowing fall and winter. Larve were also recovered in 2 animals
which were dissected after larve had been introduced under the
skin in this way. On the other hand, among the 8 animals to
which larve and eggs were given by mouth, neither of the 2 which
were carefully dissected showed the presence of larve, and in
not a single instance among the 6 cattle held for observation did
a grub appear along the back. 7

In 1922 Carpenter, Phibbs, and Slattery (/9) report similar
results in experiments carried out in Ireland. No grubs were
recovered in calves to which numerous larve were fed but heavy
infestations developed in carefully muzzled calves exposed to the
oviposition of flies.

The fact that the larve penetrate through the skin is established
by the following evidence: x ae

1—The eggs are usually laid on the hairs comparatively close
to the skin, which would favor penetration. They are firmly at-
tached and the eggshells, after the larve have escaped, remain at-
tached to the hair.

2—The eggs are not fitted with an operculum as in the case
of the horse bots, the ends merely splitting as the larve emerge.

_ larvee from the inside of the right

Ps

THE CATTLE GRUBS OR OX WARBLES Al

3—It is not necessary to apply friction to the eggs to cause
them to hatch, as the larvee have been observed in many instances
by the writers and others to crawl from the shells when their

‘development was completed, provided the proper temperature was

maintained. ;
4.—Much skin irritation in areas where eggs have been attached
to the hairs is in evidence about four days after the eggs have

been deposited. It has been observed repeatedly that violent stamp-

ing, kicking, and licking of the affected parts by the host occur
soon after the hatching of the eggs begins, and a few days later
soreness and the formation of scabs due to the exudation and
hardening of serum are apparent. When these scabs are removed,
a cluster of hatched eggs is usually
found attached to the hair in their
midst, | (His. 21: ) |
5.—The actual penetration of a
number of larvee soon after hatch-
ing has been observed by the
writers and their associates. This
process will be described later.
6.—Stub (95) has been able to
trace the route pursued by young

tibia over the shoulder and around
the muscles of the neck to the
connective tissue of the esoph-
aAgUS.

Taking the evidence set forth cs eae
herein and considering the obser- Fic. 21.—Scab removed from a_lesion

$ 5 g on a cow, caused by penetration of
vations of other investigators newly-hatched larvee HOF Hypoderma
whose work entirely corroborates lineatum.. Note the thfee hatched eggs

: on the hair
it, there seems now to be no doubt :

that the normal method of ingress for the larve of both H. lineatum
and H. bovis is directly through the skin at the point where the eggs
are attached, and proves that there is comparatively little likelihood
of infestation occurring by means of larvee taken in by the mouth.
It is desirable to stress at this point the demonstration given, by the
slaughtering of some of the animals as above outlined, that the larve

_ entering cattle through the skin on the lower legs may be found in
_ the gullet in considerable numbers during the succeeding months.

This proves the fallacy of the suggestion frequently made by investi-
gators that those larvee which are found in the gullet were probably
taken in by the mouth and that they may perish and never reach the
back. It should be noted that the writers have shown herein that
larvee of H. lineatum removed in the second instar from the gullets
of cattle and introduced under the skin of uninfested bovines will not
only appear under the skin on the backs of the new hosts in the
proper season, but may and probably usually do pass again into the
body cavity and even return to the gullet before going to the back.

DEVELOPMENT AND HABITS
NUMBER OF EGGS ON HAIR

The eggs of 1. lineatwm are usually laid in a series of from 5 to 12
and occasionally as many as 20 may be attached to a single hair. The

42 BULLETIN 1369, U. 8. DEPARTMENT OF AGRICULTURE

number depends to some extent upon whether the fly is disturbed
during the process of oviposition and also upon the length of the —
hair. In the case of H. bovis the eggs are always deposited singly
on the hair.

DISTRIBUTION OF EGGS ON HOST

fH. lineatum shows a marked tendency to oviposit on the heels of
cattle which are standing, the favorite place apparently being the
short hair overhanging the rear of the hoof and between the hoof
line and the dewclaws. Many eggs, however, are deposited higher
on the legs in the region of the hocks and a few above the hock line.
Some eggs are also deposited on the belly, flanks, and forelegs, and
occasionally on the sides, shoulders, and neck. In practically all of
the writers’ observations of depositions on cattle which are not lying
down, it seems evident that many of the eggs deposited elsewhere |
than on the heels are laid after the fly has been disturbed by the ©
actions of the host. Many eggs are also deposited along the es- —
cutcheon, on the outside of the thighs, on the tail, and on the base of
the udder, and some along the side and on the forelegs in the region
of the elbow joint. Infestations in these regions are especially com-
mon among quiet stock, oviposition taking place while they are
lying down. In one instance over 200 fresh eggs were found attached
to the hair on an area not over 2 inches square just behind the upper
end of the scapula. The writers’ observations on flies in nature and
upon those placed on hosts in captivity indicate that they prefer the
short, comparatively coarse hairs to the long, dense, silky ones.

H. bovis also prefers the heel or lower leg for a place of attach-
ment for its eggs, but since this species frightens the animals much
more, and since the flies continue to follow the cattle, depositing eggs
while pursuing the rapidly running animals, a much larger per-
centage of eggs is deposited higher on the legs, especially in the
region of the thighs and on the rump. Although a considerable
number of eggs are laid on other parts of the body, especially along
the sides, they tend to be concentrated on the hind quarters.

METHOD OF ATTACHMENT OF EGGS

As has been indicated under its description, the egg is provided

with a definite attachment area or clamp. In addition to the place-

ment of the clamp around the hair, each egg appears to be provided
with a cement which when dry firmly glues it to the hair. Eggs
have been observed to remain attached on the host for several weeks,
sometimes the distal end gradually breaking away so as to leave
only a portion of the shell. As shedding of the winter coat usually
takes place about the time the eggs are deposited, many of them
are shed off and perish before they have had an opportunity to
hatch.

The eggs are nearly always attached very close to the skin, and
this renders them inconspicuous, as they are usually covered by the
overhanging hair. This is particularly true of H. bovis.

INCUBATION

The incubation period of H. lineatum, as observed in many lots
of eggs kept under varying conditions, was found to range from

THE CATTLE GRUBS OR OX WARBLES A3

64 hours to 10 days. It is evident that the period of incubation is
markedly affected by temperature. With eggs deposited on a host
this would vary according to their proximity to the skin and the
insulation from air temperatures by the hair. With normally placed
egos the basal ones on the hair are usually very close to the skin,
but in the case of eggs deposited on fairly long hair the distal ones
may be half an inch away from the skin.

Table 2 sets forth a number of observations on the period of
incubation of eggs of H. lineatum. Many of the records are only
approximate, the time of hatching having been determined largely
by the irritation of the host produced by penetration of the larve.
It will be observed that in one instance irritation was evident approx1-
mately 284 days from the time the eggs were deposited on the legs
of a calf. This incubation period was almost exactly the same as
that observed on a portion of the same batch of eggs placed in an
incubator at approximately 98° F. The writers’ observations indi-
cate that the usual incubation period on the host is from 3 to 6
days, probably most of the eggs hatching toward the end of the
third day and early in the fourth.

]

TABLE 2.—Incubation. of eggs of Hypoderma lineatum in situ and in incubator
at Dallas, Tex.

NGAGE r Air temperature
neu- iia
Deposited pe Place and method Date of hatching bation Alder
1917 1917 DOYS NS TRE OH, OE.
Mar. 7, 4.30 p. m___| 100 | Calf’sleg_.______.____- UN Meer ree lel ieee Si ie 4— | 84 30 65. 6
Mar. 8, 4.30p.m___| 20 |----- GOES Sah as wee es me Ses Os ee en 3— | 84 30 63. 4
Nici Arabs 6 we a 175 | Incubator Mar. 15-18_| Mar. 17 to 18___________- 3+ | 87 85 86
Migros ce ae ets te NO) Leases (6 \o) Ss ah tages De ales ee te dA LS a A es RN a 2+ | 87 85 86
1918 1918
Vie G2 eee a Oe (3 Koei ean Mar. 18, a. m. to p. m__- 2+ | 97 96 96. 5
Mar. 26, p. m.?_.__- 20. /b2- 2 COs eee ee Mian. 295 a.m) 2225-2 2 8 - 234-++ | 99 97 98
1919 1919
AAU rat Q)gs ala rae aa Gon Caliicilepet sees ANA Ga ee BGS see anaes a es ee 6=— | 77.5.) 37.5 | 60:5
Mar. 10, 5 p. m____- 175 | Calf’s belly______-___-- Ea Nee Cae SR aR er oe eli | aie) It COE
Mla )2 0 oe Se _.| 40] Vest pocket and in- | Mar. 22 to 24____________ 10+ | 81 Sie feb ABV? 11
cubator.
Mian W4eaiei eye 40g E32 GOA Rs oy SEG INT aT DD NR an 8+ | 81 40.5 63.8
Mar. 16, p. m______- 60 | Cow’slegs and body__| Mar. 201_______________- 4— | 79 40.51 61
Mar. 19, 5 p. m__--- 100 | Incubator____-__-.___- Mar. 22, 2.30 p. m., to] 3to4 | 90 90 90
: Mar. 23, 11 a. m.
1D YO) 5 eee ean 25° | Calf’s belly 2.22. === 2: INVA Lee pe) ns aie SS ae ed 3 81 40.5} 63.2
OM eee tenes Stale Galt cee pe per. eee Mita 22) pss eee 3— | 81 40.5 | 63.2
Mar. 20, 1 p. m____- 3 oe ealf and in incu- | Mar. 24________________- 4— | 90 90 90
ator.
Ware 2teileaatm2.42| 2310! Inculbators---. 2.20.4 .- Mar. 23,7 p.m. to Mar. | 2-3-+ | 90 90 90
24, a. m.
Mars27, 2:30 pim~=.! , 260.|i_._- (GLO Mar. 30, 6 p. m. to 10 3+ | 90 90 90
p. m.
Mar. 27, p. m______ 77 | Cow’s body2_-.---_ 2 Wake yes Bile oy anise e Ge ce 4— | 93 35.5 | 60.3
IDOE eee nea ae TN ORM Glee OS ea Mare oie lisseetrn se hers oe se 4— |} 93 3040 60. 3
1920 1920
Mar. 6, 4p. m______ 80 | Calf’s heel and belly__| Mar. 9, 5 p. m.1________- 3— | 55 20.5 | 38
1D oe wee: ee See 200 | Calf at hoek___________ Miar9;,p smd 2 3— | 55 20.5 | 38
Mar. 10, 5 p. m_____ 52 | Calf’s shoulder_______- Mer. i 2 m.,! one-half | 434— | 76 36 61. 1
atched.
IME Y RSE Tih esac eee 200 | Calf’s heels___________- Meare Ges ed aie: 4— | 76 36 61
Mar. 18,5 p. m_____ 100 | Calf’s shoulder_______-_ IMMUNE OPA tested tne e Moan See 334— | 81.5 | 42 63. 4
Mar. 99. 5 psc 2 _ PI5O WE Calies me ay thas. Mar: 2Gte Renee 9s 4— | 80 | 46 61.7
War: 28, 5p.m._.__- 95 | Calf’s legs and belly___| Mar. 31, 6.30 p. m., to | 3-3.5 | 90 40 63. 7
Apr. 1, 3.15 a. m.

1 Hatching determined by the kicking and rubbing of host, some checked by actual examination.
4 Collected from animals infested under natural conditions. Exact, time of deposition unknown.

AA BULLETIN 1369, U. S. DEPARTMENT OF AGRICULTURE

TABLE 2.—IJncubation of eggs of Hypoderma lineatum in situ and in incubator
at Dallas, Tex— Continued

Nein | Air temperature _

her Inecu-
Deposited of Place and method Date of hatching bation =
: period |Mavxi-| Mini-}-.
eggs . Soe Se Mean
Joo ps Se es RS aE ee eee ee
1921 i 1921 Days 90" | Pee OF
Marat5, 11-30'asan=3|5) 704) aie bator 225s a Mar. 18,9 a.mtop.m__ 3— | 98 98 98
0. sae eee 155°] -Cansieet ==. War18, Oa. mS 3— | 87 63.5 |- 74.6
Mar. 16, 5 p. m_-__- AOA Calf’sleg. wees 74 War: 10, sara aés - s2eeees - 24— | 87 68.5 | 74.5
1D 16o-Incoabapors-= =~ ae Mar. 19,9a.m.to12m_| 234— | 98 98
1922 1922 |
Mars 155415 ppm. =|— 154 Incubator = Vin 185 bo. pe al == = 3— | 30 90 90
Mar. 16, 2.30 to 2.45 re (ees dO neass yFea sera Mar. 19, 10 a. m. to 4.40 3 Se $0 30
p. m. p. m. |
er 20, 12.50 to 85 | Cow’s heels: 2. = 2 Mar. 24, 10.30 a. m______ | ~4— 1 84 | 36 | 648
1.10 p. m. E :
D0 Se SE (4:\ Incubator--2- === Mar. 22, a.m. tc p. m____| 3 | 90 =| 90 20
Mar. 15, 3.13 to 3.15 Soule. oe OSes ES Mar. 18, 11 a. m. to 1 3— | $0 g0 | 90
De 1: p. m. a
Mar 285 3:1570'3230 |e t72e doe =< tite asa Mar. 31, 8a. m. (before) | 214) 90 | 90 |° 90
p. m. | | f0-8.15 aie
| |

1 Hatching de‘ermined by the kicking and rubbing of host, some checked by actual examination.

Glaser (29), without making it clear whether he is dealing with
EH. bovis or H. lineatum, states that he has observed the incubation
period of eggs clipped from the host to be 12 days. He also says
that on living animals development is completed in less than 3 full
days. Hadwen (36), basing his statements on observations in
Canada, states that the eggs when removed from the host hatch
in about 7 days, the shortest period being from 4 to 5 days, but
apparently he made no observations on the incubation of eggs on
the host. ? 7

The writers have made few exact observations on the incubation
period of H. bovis. At Middletown, N. Y., 2 out of a lot of 6
eggs deposited on a calf June 8 at 5.30 p. m. had hatched on June
11 at 12.15 p. m., a period of approximately 3 days. These were
left on the host. In one instance in which eggs were sent by mail
from a northern State to the Dallas laboratory and placed in an
incubator they hatched in less than 7 days after collection. Car-

penter (77) observed eggs attached to a host to be hatched in ~

slightly less than 4 days.

The writers, in their work with reared flies, have obtained a
considerable number of eggs from females which were not as-
sociated with males, and in none of the cases was there any hatch-
ing, indicating that parthenogenesis does not occur in this species.
The percentage of viable eggs deposited by fertilized females
seems to vary considerably. Im some instances a hatch of almost
100 per cent has been observed, whereas in other cases the examina-
tion of a series of eggs showed a hatch of less than 50 :per cent.
It seems certain that the percentage of the hatch is higher when
the eggs are deposited and allowed to remain on a host than when
they are removed and placed in an incubator, although in a few in-
stances a hatch of above 90 per cent was obtained among eggs
kept in an incubator.

In general it appears that the eggs attached lowest on a hair
hatch slightly earlier than those toward the distal end. When this

=
“y

THE CATTLE GRUBS OR OX WARBLES Ad5

occurs it is probably due to the fact that the lower eggs, being
closer to the skin, are kept at a slightly higher temperature.

Several hours before hatching, the segmentation and rows of
spines are distinctly discernible through the shell. The larva be-
comes active shortly before hatching and can be observed through
the eggshell pressmg the mouth parts forward against the end of
the egg. Finally the suture across the end of the egg is ruptured
and the larva crawls out rather rapidly.

LARVAL ACTION AFTER HATCHING

The larva of H. lineatum after hatching usually crawls directly
down the hair which bears the egg and after feeling about with the
mouth parts begins to burrow directly into the skin at the base of
the hair. The body is usually more or less extended along the hair,
and during the initial efforts there is considerable twisting, expan-
sion, and contraction. After the first few segments have been
worked into the skin the larva becomes more quiet. The burrow-
ing is slow but usually rather steady in case of vigorous specimens.
Progress is retarded as the middle body segments reach the surface
of the skin, and usually it is slightly accelerated when the larva
has become almost completely imbedded. The time occupied for
a larva to disappear after it has begun burrowing has been ob-
served to be about one and one-half hours and sometimes consider-
ably longer. | 3

In nature it appears that several larvee frequently enter the host
through the same hole, and this no doubt greatly facilitates the pene-
tration after the first larva has gained entrance,

Considerable difficulty was experienced in watching the penetra-
tion of the larve into the skin, mainly owing to the difficulty of
holding a host quiet for considerable periods of time but also to the
fact that the larve, on account of their small size and delicate struc-
ture, are very easily lost sight of. Most of the writers’ observations
on penetration were made with freshly hatched larve taken from an
incubator. Even with the most careful handling there was a high
mortality, apparently much greater than when the eggs are attached
to the host in the natural way. It was observed repeatedly that
larvee removed from an incubator and placed on hair would wander
about for a time before attempting to burrow and in so doing it
seemed that they became more sensitive to drying, probably through
the rubbing off of the gelatinous material with which their bodies
are covered when they first emerge from the egg. Many larve put
on hosts in this manner began burrowing, but perished during the
process. In making observations a calf was usually placed on a
table and firmly held or even strapped down so that the actions of
the larve could be followed under hand lenses or binoculars. Where
the hair had been clipped closely, early tests with the penetration
of larve through the skin were unsuccessful, and all subsequent
| observations on penetration were made on hair one-fourth inch long
| orlonger. In order to reduce the chances of escape without detection,
| it was the usual practice to clip closely or shave a narrow area around
a tuft of hair and to place the larve upon this tuft.

Several attempts were made to observe the penetration of larvee
on the hands or arms of man. Usually the larve were watched

46 BULLETIN 1369, U. S. DEPARTMENT OF AGRICULTURE

for periods of from 10 to 30 minutes, but they were not allowed
to remain indefinitely. Aithough some of the larve made slight
attempts to penetrate into hair follicles, in no case did they
succeed in making much progress. In one instance a number of
larvee were placed on the conjunctiva of the eye of a rabbit. Thev
moved about actively for some time and could be seen for an hour
or more in the conjunctival region, but apparently they made no
von to penetrate, and produced only a very slight irritation to
the eye.

The writers have made no observations on the penetration of larve
of 17. bovis, but have frequently observed the lesions produced by the
burrowing of this species. |

In 1914 (77) Carpenter, Hewitt, and Reddin recorded observations
on the penetration of H/. lineatwm through the skin of cattle at
points where eggs were attached. In addition to finding lesions at
those points they succeeded in squeezing from the penetration holes
along with serum a newly hatched maggot of this species. In the
same publication the authors record observations on the penetration
of first-stage larve of H. bovis, stating that it required about six
hours for them to get into the skin. Prior to this Glaser (29) had
failed in attempts to get the young larve to penetrate through the
shaven skin, but in one case previously mentioned the larve pene-
trated through the skin on his own leg. The time occupied from the
detection of the presence of the larva until it had disappeared was
one and three-fourths hours.

In 1916 (53) Hadwen published a number of observations on the
action of larve, both on living hosts and on pieces of skin freshly
cut from cattle. He failed to observe the penetration of larve on
living animals, but in a number of tests on hide removed from a
bovine he observed larvee to burrow partially, and in a few cases
completely out of sight.

LESIONS PRODUCED BY THE PENETRATION OF FIRST-STAGE LARVZ

The presence of exudate and pimples on cattle immediately under
the eggs of Hypoderma from which the larve had emerged was
first recorded by Carpenter, Hewitt, and Reddin in 1914 (17).
Hadwen (33) has rather fully described the skin lesions of the
two species of Hypoderma. He proposes the name “ hypodermal
rash” for the condition resulting from larval penetration.

When the newly hatched larvee have burrowed into the skin and
when their posterior segments are about flush with the skin sur-
face there begins to appear a watery secretion, presumably blood
serum. After the larva disappears this exudate increases in quan-
tity and several hours later small pimples form which in some
instances, at least, have been found to contain pus. In the case
of H. lineatum where a number of larve often penetrate near one
another, the inflammation and exudate become more marked and
often the hair is matted, making a scab. . With lZineatum this irrita-
tion is often very marked, the entire area near where the penetra-
tion occurs becomes swollen, and in certain instances where a large
number of larve have penetrated the heels of a calf the hind leg
from the hock down has been observed to be swollen. These swol-
Jen areas are more apparent when large numbers of eggs are de-

THE CATTLE GRUBS OR OX WARBLES 47

posited along the back of the thighs, on the escutcheon (fig. 22),
or on the base of the udder. A number of instances have been
observed where the soreness and swelling extended down the rear
quarters to the udder and the tenderness made milking difficult.

Beneath the skin these swellings are similar in appearance to
the “ licked-beef ” condition ordinarily found along the back when
the last-stage larve reach that region. The connective tissue around
the point of penetration is edematous, tinged with yellow, and some-
times slightly bloody.

The scabs become dry within a few days and can be removed.
Usually a small quantity of hair comes off with them and a num-
ber of pits are left in the skin indicating the points where the
larve have penetrated. If the scabs are not removed artifically
they disappear in the course of a week or two. Animals slaughtered
during the period of larval penetration have the hides more or less
damaged at points where
the larvee penetrate, and
slight infiltrated areas are
visible on the carcass.

As has been stated by
other writers, these lesions
may serve as portals
through which disease or-
ganisms, such as anthrax
or tuberculosis, may enter.

The actions of the ani-
mals at the time the larvee
penetrate have been men-
tioned in a general way.
The first inclination of an
animal, after penetration
on the heel begins, is to
shake the foot... This is ['# L : 2)
usually followed by licking Fic. 22.—Iesions on escutcheon of cow, caused by
(fig. 23), which is often ee ee of newly-hatched larve of Hypoderma
very vigorous and _ pro-
longed, and animals have been observed to continue it for two
minutes without stopping. When the individuals are not allowed to
lick the heels they usually twist, squirm, kick, and stamp, thus
showing marked pain or irritation.

OCCURRENCE IN THE GULLET AND BODY CAVITY

On account of the minute size and translucent appearance, it is not
surprising that various investigators have been unable to observe
the course followed by the first-stage larve after penetration of the
skin. Stub (95), working in Copenhagen, has given us the only
definite record. In a post-mortem he observed an infiltrated area
im the superficial connective tissue on the inside of the right tibia,
and succeeded in following the track over the shoulder, around the
muscles of the neck to the tissue on the esophagus, where it enters
the thoracic cavity. Here he found a number of larve in close
proximity and measuring 1 to 2 millimeters in length. Hadwen (40)

AS BULLETIN 1369, U. S. DEPARTMENT OF AGRICULTURE

has observed the tracks of the larve up the tendons to the knees or,
hocks in the elbow and patellar regions and in some cases farther
up the legs; no larve, however, were recovered in these regions.
For many years it has been known that larvee of the genus Hypo-
derma are found in considerable numbers in the connective tissue
between the mucous lining and the muscular coat of the gullets of
cattle. Since one of the writers (57) has found a method of deter-
mining accurately the species of the larve in any stage of their
development, numerous collections of specimens have been examined
from the gullets of cattle in regions where H. bovis occurs plenti-
fully, and only one specimen of ‘that species has been found. These
observations involved the examination of 1,140 larve removed from
the gullets of 563 cattle, and during every ‘month of the year when
they were found to be present in that part of the host. It is safe
to conclude from these observations that the larvee of this species
do not have the habit of going to the gullet and spending some time

Fic. 23.—Cow licking hee! where larve of Hypoderma lineatum are penetrating

there as occurs with H. lineatum.- The single larva of H. bovis
found in a gullet was taken at Chester, N. Y., on December 19, 1922.
It was 10 millimeters long and was found lying loose on the tissue
at about one-fourth the length of the gullet from the pharynx.

Since it appears that 7. bovis does not frequent the gullet it may
be taken for granted that all, or practically all, of the published
statements of the occurrence of Hypoderma in the gullet appertain
to H. lineatum, and the following discussion relates to that species
only:

The principal data appertaining to the occurrence of the larve
in the gullets are given in Tables 3 and 4. It will be observed that
there is a gradual increase in the average size of the larve from
their first appearance to their migration from the gullet. The range
in sizes is observed by the writers to be from 1.5 to 16.9 millimeters.
Among the larve found in the gullet only a small percentage. are
in the third stage, the others being in the second. Hadwen (40)
reports finding in the submucosa of the gullet of a heifer a larva
at least 2 millimeters long which he donedered in the first stage.

‘THE CATTLE GRUBS OR OX WARBLES 49

TABLE 3.—Number, size, and direction of travel of larve of Hypoderma lineatum
in each of 10 divisions of gullets of cattle examined during each month at
Dallas, Tex. :

E: 2 |e
im
a ed Bd Sena wage
= rs mB | o by Bs + [) S 2 3 3
Sei isr len] ASS ets) ge aud Sale ge Dahle
Se ley denies Clete op) NVA WIE eS qialS
Number of larve headed toward pharynx and
paunch in each of 10 divisions of the gullet
from pharynx to paunch:
First— ;
Tver yaar eee ares ae SESS ON ee AUP SAT OS Ore oe Biles Ae Ole Os ei47
Beater Late tena a eens race ae aint Ne a oh Oy) BH Ne oe a 4 6} 16 Ae Al Te Ola oo
Second—
TPN OYS EN 0G Be ee eR SONS 7 es ean es Oe Gia Oleic Sie 16 18) il TOR Ol O67,
PEt asrn Les oe echo eae Ty es PAL = pe (0) BY os NSF ols) Tl eG lean lil Ole Oi
Third—
TE Ea ear ay Tae ea ene ge Coe 2 elle Ol a) SH ar Non ABs Ol Ose 7A
BOUT Claes ee toes ta lee ye iy Ee OZ OD IS) ele IA Gh 2s Ole 97
Fourth—
| Dlakear Wp obee aie e BY Sepia Aeon See ey ea Dear Ole Oe Wil sOle 228 el 4 22h Ole id
TBteyW tail ays teee tyes aaa ty ame Sn anol se ae Oo lees teen: Al 22) S02 el6leu 4) 22092
Fifth—
TRY ove Wey yeh comes tiene se RCI POSS Oo eee ee Oe 2 2 20 52529) 30 a a2 sO a0) 130
Rane hiss cee aR Ooh aan eee Ol Chee OF 7-5 Sis 2oles Boie. LO mieo aS la tO tee
Sixth—
TENS chyi0b.4a 8 Sees Ree ras Sire Sete eae Ole Si Sie eesle sols > BOlac AN NO e220 OO 15
TEPzU BD OG) Bes ape ae ae CoS ae Dak cee Dae eae eS alG lai Ale 20 aGla. WieO le 142
Seventh—
Hbv airy al ee es ed ROS epee nk Ta UE A ON Ne 24) ADI 39l2 222d Oh ah
eV Cites Sater Eas a as Se aS ae le Pie On ORD) 4 AAG BA NO Qh ol aeemas Lod
Highth—
TPIS WEN ma bees prolate rey acne aH ee a ME ar AAG helene Clem ool) OUlee 2 sero) me 22 ie net Ol te 200
AYU TG hs spe ee ee SON ei sole soll 291 50) tl P24 eee O | 206
Ninth—
TEA DEW Enna gb Cee TNC eT ee ety Soars aie ea Sie Sie LO 4 26) Ol Ate ll WOR elie Ole. 202
JERD GANG) Oss ces oem hrs ee ieee a Pee ey re UES ele 82 Obie so2| a 2Ole sali ole 1Olee 220
Tenth—
ig oiraya xe te a epee SE Qe 2 Olen Dl e020) AS a4 9} 18 38] O| 154
TEU BG TG EEG) ee Recent ieee: came ie Oh oeAlis weiss OA ier Bye lbs aKGye Sl Oe ake ah
Total number of larve headed to-
ward—
PIN a Ty fees oe eS ec ee 10} 50) 40} 18) 179) 367) 295! 152) 183) 14] 0/1, 308
IPA Chess tire ere a 8} 59} 28) 23) 144) 329] 337) 126) 175) 33) 1/1, 263
Grand totale cess cee are 18] 109) 68] 41] 323} 696) 632) 278) 358) 47) 12,571
Length of larvee (millimeters) :
Thaby 90) DN Onligeee ene pao 2 Spam nea Eye ceapae ace 2. 6] 1.5) 3.4) (@) | 3.6) 3.8] 6.0) 6.0} 8.0} 9.6)12. 0)_____
NW Reepexeb TNT an eS a a fe or ie ac 4,9} 6.9} 5.2)____] 12.4) 14.0} 15. 5) 15. 9/16. 9/15. 8/12. O}_____
PAVELA CCN p BR See iy SNS ads ek \3. 98] 3.7) 4.4)____| 6.7] 7.4] 10.3] 11. 9/12. 9/13. 4/12. O)_____
Number of gullets examined__________________- 38} 119] 21) 8 380) 60} 29) 22) 46) 182) 146) 697
Average number of larve per gullet ___________ 0. 55|0. 92 3. 24 5. a 7711. fue ee 64|7. 78)0. 26)0. 01) 3. €9
|

1 Larves not measured.

By reference to Table 3 it will be seen that throughout the season
the majority of the larve occurred in the paunch half (last five
divisions) of the gullet, the percentage of the total number in this
half being 67.87. It was hoped that some indication of the place
of entrance into and exit from the gullet might be given by a study
of the postion and direction of travel of the larve during different
seasons but one can draw no definite conclusions from an analysis
of the figures. During the first five months the number of larve
heading toward the pharynx was greater than the number head-
ing toward the paunch. This, together with the fact that 76 per
cent of the larve present during the first 5 months of infestation
were in the lower half of the gullet clearly indicates that the larve
do not enter the gullet at the pharynx end. The evidence, however,

98252 °—26—_4.

50 BULLETIN 1369, U. S. DEPARTMENT OF AGRICULTURE

is not clear that the larve enter or leave the gullet tissue at the
paunch end. It is possible that some of them reach the connective
tissue by penetrating the muscle along the sides of the gullet. The
writers’ observations indicate that there is considerable variation
in the size of the larvee at the time they reach the gullet, and that
the larvee continue to reach the gullet over a much longer period
than is covered by the entrance of the larve into the host.

TABLE 4.—Number, size, and direction of travel of larve of Hypoderma lineatum
in each of 10 divisions of gullets of cattle examined during each month in
New York State.

[| 5 |e | |
co) o| 8 >
2(#/8/]elelel| 41. | |
y = Ss =
ae gle/B/e8/8/2/81/8|2 |e lElzi2
= :
Sls|<|a/o|z2}als/ale aisle
= OS | se | | Ss | | |
Number of larve headed toward pharynx | |
and paunch in each of 10 divisions of |
the gullet from pharynx to paunch: Es
First pharynx _____- EES aR as FLAS tee Ol Ole 61 Ole 2 0) 2| li @- of OF 13
IESE ANTIOCH = Sec ep oe eer eee | O} Ol. > ab 0) a Ot eee se
Second -phtary Bit = ea ee 0} Ole 5) oto 0 3} 1 3} ~ GO| 0: 16
Second: paunch=++ 2522S ee ee 0} 0] 5} O TE OlseSh eseok 2 1S co OP 11
PRHIEGEpNAL ya Vee ee eee ee ee qo. 0} 68 1 6) Of 62 3 0} Of =O) 15
Thirdspausch S- 12 es. SS ee eS of. o} 4 1 3} Oo oY Of 6 ho CoO C8
‘Rourth pharynxe > 26 ea === 0s 0 2). - 3) <2) 0) 22) A) 2 Al SaaS cee ee
Heurth pancho. ese ee 0} 0) 4 ot a0} 22) 5) = 6 Oana 6
Hut hepharynxse se ao eS Ole OF SS ae eel ae 2| 1} Oo} OF 33
Pith pauneh. =. ee SE Pe S20). S/S 6) na 14 aes 5 Oo} 0} OF 35
Gix (huplaryaix 22 es ae ee OS Sal Ole -4lS 7) a6 71 2 OF OG} 40
Sixth paguch 2o 25 325 55 Ss Oj. -0| 11] 3] 25] of 4} 7 8| 3 a OF 60
Seventh pharynx. ____..-_____-_.-___-_- } Oo oF 8 14) is} of 21 12} 9 | of OF 65
Seventh paunch_.......___.-_..______ |} of of 8 6 29] -0| <3| 4b Si at ee ad
Pishth. pharyns oh: Ore eee 0} 0} = 16) 41 -- 19-0) 2) 7) = 5) = Se 78
Highth-panuchS = == se o|- oO} 11) 10 -37/- O}- 1) 9| G6 2 Oo - O 7%
Ninth pharynx: - ==) =. 222-2 == O|- 1} 15] 141 221 of Oo] co) 14) 4 0) 0 87
INimth pannchs=" 232 se ee Q} 2] ‘17] ~=8} 481 «O}) 1} 15] «1h = 2} -- oF Oo 104
Tenth pharynx: = 620 eo. ee ee O| 2] 14t 7-23] 0}. - 0} 19] 1-0 OF 7
Montavpaunch <0 = ono 2 Ge ee Soke Oo} 1) 141 5 46]-.0; -1| 25 9} 4 0} 0; Jo2
Total number of larve headed toward— hese | | aaaeS
Phar ynks 2028s Ss se ee i 0} 4} 70; 61; 133] 0} 13] 91) 55] 13; Oj} @| 440
Paonehe 22:8: 0s: eS oe Se eS _| O| 8] 84) 42) 203]. 0) 17; 71) 55; 11) 0} 0} 486
Deebiint ee o}- oO -7 1] OF 1; 3} 2} 8 3 25
Grand: totals 23s Ne | O} 7|-161| 104; 336] 1) 23) 164; 118} 27; 0} 0} 951
Length of larve (millimeters): | | es |
ininGine = te a Se a eS | 3.5] 3.01 3.0) 4.0! 5.0: 7.3] 6.5! 8.7) 10. 0)-22-2 Bs
I Miccbna paige ee es ies Se) a ee ae | 4.0} 6.0} 7.3) 8.0] 5.011. 1/14. 7] 14.9) 15.6)--__|-__ Pes
PAC VET AT Or shat pment age ee ee (3. 82.4: 62-5. 52; .6. 08} 5. 5\8. 69/9. 97/12. 13)13. 65)____|____ eee
Number of gullets examined________________ | 15) 61) 68} 28) 25] 15) 2i| 27| 72; &8| 5) 15} 440
Average number of larve per gullet___-____-_ : 0} : we eos 71,13. 44) . 67 1. 516. 07; 1.64; .31) 0 oF 16
| |

Table 4 presents some of the data obtained during the examina-
tion of gullets in several localities in New York. Most of them
were taken from cattle kept in the vicinity of Ithaca, Chester,
Albany, and Buifalo. The combining of the records obtained in
several different localities makes the figures more irregular than
those obtained at Dallas. The figures show that about 77 per cent
of the larva: were found in the posterior half of the gullet. It will
be noted that there is considerable irregularity in the average
number of larve per gullet, there being a marked decline in the
number in November and December, where it seems almost cer-
tain from analogy that the maximum should have occurred. The
low average in these two months can be explained by the fact that
the gullets were taken from a very few lots and were probably
from a very small number of herds of cattle. It is well known
that the extent of infestation varies in different herds.

THE CATTLE GRUBS OR OX WARBLES 51

The occurrence of larve, varying considerably in size, on the
surface of various abdominal organs has been noted by a number
of investigators. For instance, Koch (53) records having found
larvee on the pleural side of the gullet as well as under the mucous
coats; on the surface of the spleen; some on the paunch and one
between the muscular and mucous layers of it; a few among the
intestines; and some in the connective tissue of the thoracic cavity
just below the vertebral column. Horne (45) has on several oc-
casions observed several larve in the connective tissue around the
kidneys, and Hadwen and Fulton (40) have observed several
larvee on the pericardium. Berg (3) has found larve in the con-
nective tissue between the small loin muscles and the muscle of
the hip, and Koch (43) has observed a single larva in the inter-
muscular tissue of the back. Many writers have recorded the
finding of larvee, sometimes in considerable numbers, in the spinal
column throughout the greater portion of its length and also pass-
ing through the posterior foramina. Hadwen and Bruce (38)
state that larve observed by them in the spinal canal were found
in the areolar tissue which surrounds the dura mater. Their
presence was accompanied by evidences of green pigmentation and
gelatinous infiltration at different points along the cord. .

In the writers’ own work they have encountered larve in nearly
all of the locations where they have been reported by others. - It is

Pharynx
End

Fic. 24.—Hypoderma lineatum: Diagram showing position, direction of travel, and
length of larve in millimeters in gullet of calf (No. 22)

not at all uncommon for the larve to be present just under the
pleura along the esophagus. The larvee found in that region were
practically of the same size as those in the submucous connective
tissue of the gullet. Wide distribution of the larvee within the ab-
dominal cavity has been noted in the case of the experimental ani-
mals infested at one definite period, indicating that there is a general
scattering of the larve of the same age. On account of the interest-
ing distribution of the larve observed in experimental calf No. 22
the location of the larvee will be briefly summarized. This animal
had about 300 eggs deposited upon it by flies on March 22 and 28.
Most of these were laid in the region of the dewclaws on the hind
legs. On July 3 the animal was killed and carefully dissected. In
the connective tissue beneath the mucous lining of the gullet 17
larvee were found. One of these was crushed and its position not
noted. The position of these larvee in the gullet and direction they
were headed are shown in Figure 24. Their size ranged from 3.6
to 6 millimeters in length, the average being 5.3 millimeters. On
the paunch 12 larve were found. Six of these were almost immedi-
ately under the spleen, but none were attached to that organ when it
was peeled off. The other six were scattered over the rumen at
widely varying distances from the gullet entrance. These ranged in
size from 5.8 to 8 millimeters, with an average of 6.8 millimeters.
Some of these had the anterior end pointing toward the gullet en-
trance, others were pointing directly away from it, and others were

52 BULLETIN 1369, U. S. DEPARTMENT OF AGRICULTURE 4

pointing in various directions. Some of those closest to the gullet

entrance were headed toward it. A number were along the line ;
of attachment of the first and second stomachs. On the surface 9
of the second stomach a single larva, 7 millimeters long, was found. 9

On the surface of the colon, about 15 inches from the anus, one larva,
7 millimeters long, was taken headed forward. Seven larve were
taken in various places in the mesentery of the small intestines. Six
of these were 7 millimeters and the other 6.8 millimeters long. One

larva, 6.1 millimeters long, was found on the surface of the sixth ©

rib, just under the pleura, about half way between the sternum and
the vertebra. This larva was headed ventrally and was rather

slender. One larva, 6 millimeters long, was found free on the basal —
portion of the twelfth rib after the muscular tissue had been stripped |

off. A careful examination of the other internal organs, diaphragm,
muscular tissues of the back, and muscles of the legs was made with-
out finding any indication of the presence of larve.

It is noteworthy that the larve in the gullet averaged smaller |
than those in the paunch or elsewhere in the abdomen. This of itself |

might suggest that the older larve were passing backward from the
gullet to the paunch or elsewhere. When consideration is given to

the fact that larve much larger than these are found in considerable ©

PhAarynx
End

Fig. 25.—Hypoderma lineatum: Diagram showing position and direction of travel
of larve in gullet of calf (No. 409) : A, pleural side; B, mucous side

numbers in the gullet during the latter part of summer and through-
out the fall, however, the drawing of such a conclusion is hardly
justified. 2

Another experimental calf (No. 409, fig. 25) which was infested
with about 268 eggs on the abdomen and hind legs on March 10
and 16 was slaughtered on July 9. A cursory examination of the
viscera, walls of the diaphragm, chest, and abdominal cavities failed
to reveal any larve. On the gullet, however, in the submucous
tissue 60 larve were found and on the muscle side of the gullet 16
larvee were taken in the stroma beneath the pleura. These larvee
ranged in length from 5 to 5.6 millimeters, but only a few were
carefully measured. The length of those on the pleural side of the
eullet was practically the same as those on the mucous side. Of those
in the submucous tissue 17 were pointing toward the stomach, 40
toward the pharynx, and 2 were not noted. On the pleural side 9
were pointed toward the stomach and 7 toward the pharynx. The
diagram (fig. 25) shows the distribution and the direction of point-
ing .of these larve.

The exact course followed by the larve in passing from the body
cavities to the back has not been determined with accuracy, though
the presence of larve followed by greenish and gelatinous streaks
indicates the lines of migration and the probable routes. The find-

|

THE CATTLE GRUBS OR OX WARBLES Do

ing of larve along the ribs, on the diaphragm, and in the neural
_ canal indicates that they pass from the gullet across the diaphragm

.| to the ventral ends of the ribs and thence follow the connective

}/| tissue beneath the pleura up to the back. Some probably work their
| way between the muscles and pass directly up the diaphragm from
the gullet to the back. A number of these no doubt gain entrance to
the neural canal, later pass out through the posterior foramen, and
_ then go up to the connective tissue beneath the skin along the back.

| Both of these routes are probably followed in migrating from the
)/ gullet to the back.

_ The writers’ observations indicate that the migration from the
_ gullet to the back is rather rapid. The first larvee begin to appear
_ in the subdermal tissues of the back very soon after the maximum
_ size has been reached in the gullet. As soon as the number of larve
|) are observed to decrease in the gullet they are observed to appear
on the back, with practically no increased growth.
| Unfortunately it has not been possible carefully to dissect ani-
mals infested only with H. bovis so as to determine just where the
| larvee occur from the time they enter the host until they appear
on the back. In New York, where both species are present, the new=
ral canals of 140 slaughtered animals were examined and all the
larve found were H. bovis. Thirty specimens were located, with
-a maximum of four in one canal. Larvee were found in this situa-
‘tion during the months of October to March inclusive. The size
ranged from 6.5 to 14 millimeters, the larger ones being found later
in the season.

At Dallas, Tex., Cabere HT. lineatum only occurs, about 75 beeves
were examined rather carefully as they were dressed. Only one
_ Hypoderma larva was found in the neural canal, a third-stage speci-
men located in the central portion of the second lumbar vertebra
and measuring 14 millimeters in length.

This observation indicates that the larve of H. bovis enter the
neural canals of cattle more frequently than do those of @. lineatum.
It seems unlikely, also, that all larve found in this situation are
en route directly to the back, as the larve found during October
were only from 6.5 to 9 millimeters long, and never have such small
larvee been encountered in the subdermal tissues of the back. Fur-
thermore, the larve did not begin to appear under the skin of the
backs of cattle in that locality for over three months after these
larvee were taken in the neural canals.

PREPARATION FOR THE EGRESS OF FULLY DEVELOPED LARVA

The appearance of third-stage larvee under the skin on the back
is frequently accompanied by considerable local inflammation, in-
dicated by edema of the connective tissue and sometimes marked
swellings and soreness.

Certain cattle are more prone to such manifestations and show
swellings as large as 10 inches in diameter around each larva as
it comes to the subcutaneous tissue of the back. From one to three
days after the appearance of one of these swellings a minute hole
is cut by the larva near the center, after which the swelling soon
subsides. Although no conclusive evidence is at hand, the writers
are of the opinion that the holes are cut through the skin almost

.

54 BULLETIN 1369, U. S. DEPARTMENT OF AGRICULTURE

immediately after the larve reach it, and never more than three
days later. Usually the first indication of a break in the skin is
in the nature of a minute, irregular hole which is usually accom--
panied by sight bleeding. Within a day or two after the first break
is made the edges of the hole become more smooth and round. In
several instances the writers have observed a circular plug of skin
about 2 millimeters in diameter and bearing hair, seated in a freshly
cut hole. In two cases these plugs were still attached at one side as
though the cutting process was not complete.

The only evidence to indicate which end of the larva does the
cutting is that in every case where larve have been extracted the
posterior end is always outward. This has been found even before
the cutting of the hole was completed. It is conceivable that the
larve may do the major part of the cutting with the mouth parts
and then turn around and complete the enlarging of the hole with
the posterior end. When these early stages are removed by pres-
sure they appear to be in a position perpendicular to the skin rather
than lying horizontally under it as is the normal position in sub-
sequent stages.

DEVELOPMENT OF THIRD-STAGE LARVZ

The first molt under the skin, from the third to the fourth stage,
takes place soon after the hole is completed. The determina-
tion of this period with exactness is very difficult, but the records
of the writers show that the molt in H.-lineatum may take place in
about 24 hours after the hole is completed, or the stage may last
from 6 to 8 days. The average period, based on 17 records made
at Dallas, Tex., with considerable exactness, is 4.5 days, and the ©
average period based on 13 records made in New York is 4.26 ©
days. The period from the cutting of the hole in the skin to the
molt in H. bovis, as observed in New York, ranged from 1 to 6
days with an average of 3.35 days.

For several hours prior to the molt the spiracles of the fourth
stage can be seen beneath the skin of the larve. The exuvia are
very delicate, but seem to be shed almost in their entirety at one
time. The break in the larval skin is very irregular. The posterior
ends of the tracheal tube where they join the spiracles are rather
highly chitinized and they are shed along with the skin. _

The writers’ observations show that not infrequently the third-
stage larva may move to a new location under the skin, usually
within a few inches of the first, and cut a second hole or even a
third hole before it molts.

ENCYSTMENT AND DEVELOPMENT OF FOURTH-STAGE LARVZ

It appears that about simultaneously with the molt to the fourth
stage the tissues of the host change their form of resistance from
an active leucocytosis to a segregation of the insects by the forma-
tion of encystment sacs (fig. 26). With the development of these
pouches the general inflammation of the connective tissue subsides.
The skin of the third stage remains in the sac, which is formed
very rapidly, and gradually the walls of the sac become thicker as
the growth of the larva continues. During this and all subse-
quent stages the larva remains with its posterior spiracles toward

THE CATTLE GRUBS OR OX WARBLES | 55

the hole in the skin, usually keeping them just a short distance be-
low the surface. During the course of development of the fourth
stage the hole may be completely closed by scabs, but an effort
is always made to keep it open. ‘This frequently results in the
formation of what the writers have called “a perforated plug.”
This apparently consists of secretions which harden within the hole,
becoming somewhat free from its edges, and the larva maintains a
minute hole through the center of the mass.

During the development of the fourth stage the body is nearly
horizontal, the dorsal side outward, and the posterior end bent
upward so that the spiracles are close to the aperture in the skin.

The duration of the fourth stage of H. lineatum at Dallas, Tex.,
has been observed in one instance to be from 5 to slightly more than
13 days, and in another from 10 to 13 days. It is thought, how-
ever, that the minimum periods mentioned are possibly erroneous,
owing to the chance of failure to record the molt to the fourth
stage with accuracy, and that 15 days is nearer a true minimum for
this stage. The maximum period recorded in one instance was be-
tween 44 and 53 days. The average duration of this stage based
upon 21 individuals as recorded at Dallas was 24.5 days. The
duration of this stage in the backs of cattle in New York is prac-
tically the same as in Texas. Some of the records for this stage are
given in Table 7.

In H. bovis the length of the fourth stage was observed with
fair accuracy in 18 specimens in New York. The minimum period
among these was 21+ days, the maximum period 35 to 88 days,
and the average 27.1 days (see Table 5).

TABLE 5.—Duration of fourth stage of Hypoderma bovis in New York

Tonalit Larvee molted to Larve molted to Duration of
Caan, fourth stage fifth stage fourth stage
1921 1921
Days

Leia ahaa Ysy pee gOS cot a ee I ea ee ee ee May 10 (before) ______- JUIN Q eles a See 22+
TD XO) is Sep a SR Oa a AGN gel (0 Ogee Sa a eae aa AP OUONES 7c Se 28+
EU) Cp eS ms one avn cr aNR ae EE Wa 50) ge AIR ea JUNC OMe we esc. 30+
TD Yo) ee Satna ee OL bial Eels orate She pen ee May 15 (before) _._____|_____ GOMES eed 25+

BUD) (Peace settee Det TL Rk Se Belay Lzdge stele Seas We ay ea Omer eee owe 23
MD) Oras pes Se ae ae ES ANS ESE May 19 (before) _______|____- COTE ek, 21+
BI) Re ieee Oe ee ea Tene ate MGT May 24 (before) ______- Afb aVe\ Types eae Gee 24--
DD) OR Be eh aaa Nats OU eee AE alte 2 May 25 (before) ______- UDO LS excess 24+
IS) Cee eu pee om ena sErGsc 22 ae Oa = Saya June 20 shel 26+

EID) (0 ae ata ce th al ae I ike a BV E29 ee aloe Mises MUM Dee eee 29
UD 0) Aa eM Nee OR a Neco ta Pc June 2 (before) _______- JUDIE OD yh teen ere east 23--
[DY teeta 8 eo A ol rar ce PE 2 Wa ls ARI ak pn PS OR ORS ak ne UU iy SNA eee ae 31+
1 Yop ks lp Min a ae pata ne tebe a abe Seema June 6 (before) ______..- delay TU aos ee 35+

1922 1922

VET ale to wien eo et ce SN cA Telit Oe ak May 8 to9_______- 35 to 38

ID) ORAL ak HE ERAN TN a eae kaa! Ve ING Oe te HO) Ge MMLERY 1 HO Sees S 26 to 28

LD (opie Ges oes ar OE a 2 ee Rr rs De ADE. 15 COM 222s e== 22s) IME US OR oS 28 to 31

5 YY NT ge aa EC es ea Apr lO o20 ee May 14t015_____-_ 24 to 26

VO 0 Sa eeeenee ts sees eae re aerate yeaa pa pe aaa ISS Ob Fy PPA HO) PH a oe yee May 20 to 24_-___-_ 26 to 32

The molting of the fourth instar is apparently preceded by a
short period of comparative inactivity. The fifth-stage spiracles
appear as pale yellow objects deep beneath the integument two or
three days before the molt takes place. As the time for molting
approaches the spiracles become more distinct in outline and just

56 BULLETIN 1869, U. 8. DEPARTMENT OF AGRICULTURE

prior to the molt their details of structure are well defined beneath
the skin of the fourth stage (fig. 6, 7). As in the preceding molt,
the rupture in the integument seems to be irregular and does not

Fig, 26.—Under side of hide just removed, showing cysts, some of which are cut open
to expose cattle grubs

always occur in the same place. The exuvium remains in the cysts
and can often be removed by continued pressure after the fifth-stage

grub has been forced out.

57

THE CATTLE GRUBS OR OX WARBLES

DURATION AND DEVELOPMENT OF THE FIFTH STAGE

Immediately after molting, the larve are more or less translucent
and the integument comparatively tender. The spiracles at first ap-
pear more or less iridescent and are yellowish with a slight orange
tinge. Growth in this stage is rapid. The integument becomes
heavier and tougher and the spiracles darker. This darkening
begins on the rims and gradually the entire spiracles become dark
brown to almost black. Along with the darkening of the spiracles —
and the rapid growth of the larve, there is a general darkening of
the entire integument. Just prior to emergence from the host the
grub becomes shorter and broader. Along with this change comes
the darkening of the integument to a deep brown or black.

The duration of the fifth stage is extremely variable. At Dallas,
Tex., the minimum length of ‘this stage in /7. lineatum has been
observed to be between’ 18 and 21 days. More than 100 larve were
‘observed. In another instance there was a period of from 19 to 21
days, but it appears that very few complete this stage in less than 23
days. The average, based on 71 records made at Dallas, Tex., was
30.3 days. Some of these records are given in Table 7.

The length of the fifth stage was recorded in six larve of Z.
lineatum at Herkimer, N. Y. The maximum was 47 days, the
minimum 29 days, and the average 38.5 days. In 1922 in Orange
County, N.Y, the length of the instar was determined in 19 larve.
The een was 39, “the minimum 16, and the average 29.5 days.

The duration of the fifth stage of Z/. Bovis was determined i in the
case of 58 larve at Herkimer, N. Y., in 1921, and in the case of 19
larvee at Middletown, N. Y., in 1922. The maximum, minimum, and
average in the former were 62, 96, and 39.6 days, and in the latter 45,
35, and 40.1 days. Some of these records are presented in Table 6.

TABLE 6.—Duration of fifth stage of Hypoderma bovis in New York

| |
Mature |Dura- os

| ae larve -| tion Larve molted to | Mature larve em- ye

Locality to fifth emerged | of Locality fifth stage be- erged from host of fifth

stage from fifth tween dates between dates erga

host stage s
1921 1921 1922 1922

Days Days
Herkimer____| May 13 | June 27 45 || Middletown |. Apr. 1 and 3_____- May 11 and 13____| 38 to 42
AD QE May 18 | June 2% Boule G5 fies ee Apr. 10 and 13____| May 20 and 24____|37 to 44
5 B Yo eS ariel (ates do____| June 18 Sileylseneere do______| Apr.19and 20____-_ June 1 and 3_____- 42 to 45
1 DO pate IAS Ue aie) Gk 0 ees ea fs (0) ee do______| Apr. 24and 22____| June 3 and 5______ 42 to 45
Dos fe o____| June 14 PAGy =| hes eee do______| Apr. 22 and 24____| May3land June3_| 37 to 42
BD Oe eee feo do____| June 28 AQ We See dO sees doses es (22 June and: 35.252 38 to 42
WMoesa 2 May 21] July 4 BAe See doses Apr. 25 and 26____| June 7 and9______ 42to 45
Doses: May 25 | June 20 PA Sed es 2 GOs Apr. 26 and 27____| June 5and 7-__-_-_-- 39 to 42
Does fu: May 27] July 4 Bye) Alte COE 5 a Oe June 7 and 9_____- 41 to 44
DOs May 31! July 7 Ore Se Gone 2s Apr. Dp andioe ec ke! dG see 40 to 44
DOs os = June 2| July 14 MD | aoe AOA S| eo ee ees Ne KOO RU ae el 40 to 44
Dor June 4/1] July 16 42} 25 don sos | Apr. 2 and 28____| June3 and 5______ 36 to 39
Doses June 6] Aug. 7 G2 eee (al chested as tate BG [ocala eal clears GORE Ss a ee: 36 to 39
Dols. June July 17 easy | oem OO. 2e= Apr. 29 and May 1_| June 5 and 7_____- 35 to 39
Doz essz June 10| July 20 40 ||_____ 022225. May Pandi2-22 2 June 7 and 9_____- 36 to 39
DOs = = |25, dona. July: 125 Za Ne ee do____--| May 4and 5_____- June 12 and 14____|38to41
iDgees June 27| Aug. 4 Sot ses does x4 May 5 and 6______ June 14 and 16____|39 to 42
IDO eet June 29} Aug. 9 Alesis cae do____..| May 12 and 13____| June 19 and 21_~___| 37 to 40

It is in chs fifth or last larval stage that stockmen usually observe
the presence of the grubs, as the sizes of the lumps increase with the
growth of the larvee. The sizes of the openings: through the skin

58 BULLETIN 1369, U. S. DEPARTMENT OF AGRICULTURE

vary considerably, but they are usually much larger after the molt
to the fifth stage, and measure from 3 to 4.5 millimeters in diameter
(fig. 27). It is seldom that any scabbing or other obstruction is
found in the aperture over a fifth-stage larva. There is usually to

Fic. 27.—Close view of portion of cow’s back infested with cattle grubs.. Hair is
clipped from around holes

be seen a rim of exudate, part of which is considered to be excrement,
around the outside edge of each hole.

The position of the larva is similar to that in the fourth stage.
The posterior end of the segments is bent slightly so as to bring the

THE CATTLE GRUBS OR OX WARBLES 59

spiracle to the hole and almost perpendicular to it. Thus the hole
in the skin is always near the posterior end of the larva, which may
have the anterior portion in any direction. The majority of the
cysts have the aperture near the upper side.

TOTAL DEVELOPMENTAL PERIOD IN THE BACKS OF CATTLE

As with other stages of Hypoderma, there is a variation in the
total period required for the development of the larve from the time
the holes are cut through until the larval growth is completed. The
determination of this period with accuracy is of much importance
in control and especially in eradication work, since the interval
between treatments
should be governed
by such data.

In a large num-
ber of cattle of sev-
eral breeds warbles
of both species were
followed through
their entire develop-
ment in the subder-
mal tissue. Owing
to the high mor-
tality among the
larve, especially
when examined re-
peatedly to deter-
mine molts,_ etc.,
only a comparative-
ly few records of
complete develop-
ment were obtained
among the hundreds
of warbles observed.

In order that the
duration of the lar-
val stages might be

determined various
individual cattle Fie. 28.—Headlight outfit used He examining cattle grubs
in cysts

were observed from |
the time warbles began to appear until all grubs had made a normal
egress. These observations were made as frequently as time would
permit, usually once each day. Through practice the touch was
developed to a high degree and one could readily detect the first
indication of a foreign object under the skin or a minute amount of
exudate from a puncture of the skin.

In making the examinations a headlight was developed which
proved of great value (fig. 28). It consisted of a shortened flash
light attached to a head band, and served by two dry cells carried
on a belt. The focus was adjusted to permit the observer to use a
hand lens.

With the younger stages of the larve in particular it was found
necessary to apply pressure around them to force them toward the

60 BULLETIN 1369, U. $§. DEPARTMENT OF AGRICULTURE

surface, where they could be seen distinctly. Not only the time of
molting was observed in this way but the changes in color of the

last stage could be observed and the approach of complete develop- —

ment noted and emergence watched for.

In order to eliminate any possible adverse effect on the develop- —

ment of the larve by these repeated observations, the appearance im

>

the subdermal tissues of several hundred third-stage larve was deter-

mined by the method indicated, following which they were not dis-
turbed except to make occasional notes on their presence until about
the date of emergence from the host. The average time for the
development in the case of those larve examined for molts, ete.,
was practically the same, however, as in the case of those which
were not disturbed.

As a method of checking up on the observations on the various
larvee it was found best to make a rough diagram of the backs of the
hosts, indicating the position of each larva and assigning it a num-
ber. In order to facilitate the location of each larva the position
on the animal’s back was indicated by clipping the hair. In the
early observations the hair was clipped close to the skin immediately
over the warble hole. Later, as it was thought that the development
might be interfered with by exposure, clips were made in the hair
of the host just above or below the position of the warble.

The minimum period of development of larve of H. lineatum in
the backs of cattle at Dallas, Tex., based on about 200 records, was
between 35 and 47 days. Another period noted was 38 to 40 days,

4

and still another 39 to 46 days. In several other cases the period ©

ranged between 39 and 50 days. The maximum period was between
78 and 89 days. The average total developmental period, based on
104 warbles examined at frequent intervals, was 56.3 days. A few
representative records of the development in the backs of cattle are
given in Table 7.

The average period of development of 222 other larve of HZ.
lineatum in which the date of appearance under the hide and the
date of emergence from the host were determined without disturb-
ing the larve by making observations on molts was 57.74 days.

At Uvalde, Tex., D. C. Parman recorded the duration of the
larval period in the backs of cattle for larve of H. lineatum. The
minimum period noted was 43 to 45 days, the maximum 54 days,
and the average 49.4 days.

Six accurate records of the period of development of H. bovis
in the backs of cows were made in New York. The maximum was
77 days, the minimum 65 days, and the average 72.8 days.

Apparently the duration of development in the backs of cattle
is not influenced by individual, breed, or age of the host. The
writers’ records indicate that the development may be slightly
‘shorter at Uvalde, Tex.. than at Dallas, and that the time spent in
the subdermal tissues of cattle averages slightly longer in the case
of larve coming up to the backs in the early part of the season.
For example, the average period of those which appeared in the
subdermal tissue in October and early November was about 58

days, whereas in those which appeared during the latter part of —

December and in January it was about 51 days.

61

“s0581S [BAIB]

ee JO U01VINP OY} WO SP10D0I 94BINIOV YOR 09 OTQISSOdUII SVM 41 SB ‘e3deYS YOR UL SACP JO UOTJIPpe WOIJ.40U pue ysOY 944 UI0IJ BUIddOIp Jo 0jep 07 porvodde eLAIvy] ojyep WOIs poINSL A z
- “SpOl1od OT qISsOd jsasUO] PUB 4Se410YS SOpNyUT Sesvys JO UOYeING {
fe
< CO OBL Ss hs CHGS re Se ee POPU 2A Ct ree tees he eas GG OUT | pa ee 7G PUB OG UBL | QiOT Sige a ieee Wie ee QDS C6 SWE EES oS G UBL PUB TE “90
= 99101 OS re eeiOG ONE. | Senses Sones 8Z PUB OS “APH | 26 0496 | ONCE GCae Iereret reeony Gua OG AUG flees G3 OF. OUI eS ea ee ee GG;PUC OG OOGE | ass obi s ee e 9G PUL FZ ‘90T
Bi 7 ONE eI OIG ee SS ee thd SN GONE I Sire eat oe Salle percent Gk bee EL, 96 PUB CZ “99d | eee oe ee (Q10j90)-O1 (00Gi || fasts ee $f Pus ZI “90d
ca €9017h | v€99GC |e GON PUB RG “UPL | GZ 01 OT | POM ENED 7% — g uUBr puB TE ood | SLOAN Gea eae. aa Gav ea eae OG290. GE ek ears GT pus ZT ‘090d
ie) OS ON Ne SOM NG || PSs SG DEC PG aUGIP ela hT O1CT Fir aie peor en cee e ae aeome 96 PUB FZ V9 | He SOM GNS WaNGR aces ipa a5 (@10J9Q) OT OOG. |Sey= i aa ies ee eens od
4909 8G | 5566/03 CS | 9 5 te eT PUBL GOW 155 80.09 8G 55 92 OF Ge papa een sie ee g pue g -Uef | POV: |For aes aa C-DUC Tie09 Gia G7 es ee Oi IT PUB 6 “99
Bs Oi OMAR eee = IS OG en SES Seta ge VG PUB OS UBL | (CON GAS ee CONGR PEr seers os 96 PUB BT “99M | OSORIO asteess ae Ieee wee OP Sareea ee ii eR Ree goa 0d
LS O09 ese | ie VG. O8 Oa eaten see IT pUey Gon | 2602 0€ | po OF OF 9G? Raa ae ee GL PUB BZ UBL) ROLY || SR ae ee (O10J9C) Gl 00Gh |. ima ce eee oe pas = od
NM 690409 | 989} 8¢ | € “Go pues ge “UBL | 6% 0106 | 660406 | CCT PUB GES OPM | Craps eee (CHD CLD ORKGE Be Ra 2 Geek se 6 PuB g “00d
jaa) PSEOT CG Syst oe (Ges Ae es a ere GG WE esl ELS: OMG Gar EE th te enlistees ee Bani eo SG (eens smi" NaN nS Vi RL eapiaty See wi a es Go ae ep te RE od
=) CORON: Lees eee OU OG eran waa ae 86 PUB PS “UCL | GOST | ESE ONG Se Se DEE AGG | OU 6 ORK El ne ON OE OR RTE yn Se BE OO Gre | SaBa Ne eae ge 8 pus g “90d
fae 0903 79. |) 789196 |= 8 'Ceu pues ec UeL | (8609.96 | 91 OF FI G. UME DUC TER OOGL ln glen is br lis oe Gee ke (OIOFOS) WAT OO Cie |e eg es her ss ea G 09d
és) Lv OF: Oirmes|ee 166 ON SCelite Wie wild 0. as OG Ue ameOI CATT | tenes CP Ol shies | See Gere ae 6 PUBSS “99M | POA Gees eeiy Sere capes (OlOTOG) S000 |> > ier oa ear uee Shel oe od
SFO AO GSS lee ces OH OG ieee ee eens 8G PUB PS “UBL | ZZ O16T | LONG ss ASE OES ois 9G DUB FG O89 | GOA NVAICSS ta tee Geek degen aks 029.0 GI Ss eis se Sars “Ren cae g pue p “9090
oa GHOU OY Se Ge Ol CG oe Tee ode VG PUB OS “UBL | ES 07 BT | Cle OW Os seb eaeee ss 9G PUB EG 99d | ORO9 Raleaearege ioe (Q10}0C) (ST OOGl -|iseane ten tae se ¢ pue ¢ “00d
om QQFO9! Sieg SCE OF BCP eth pe oak 86 PUB FG “UBS | FEO ES | GUAR ceges BP ee ee WE ONKOL. We GOV RU Bee tae & (CHOLGKO Cte INGE Shee Se BRT Pp pus € “90d
Re EON AO Oct | ae ees ON 89 Cre re ty en nee ae Jey ONDE GE ES AS ONG en bs ee Pag Doe ae oe 8 puB Eg “UBS | OT Sr ea en ae (CHOC TS ONG E Gee SB oe oS ¢g puss 909d
» CORON Teer salen = FEL ARY Mts so bach © eee OL GHOUCYE Me Masi cir ec | bie aie ne rUeaiar lllG Bc koran: Seeien Mentem Daren qe iugeoy POU ee ee (@10]90)) Ors 00 CIis\ =o ase tence ae ee § pues 09d
O PS 04 67 ees OV LGel Sai ane teen VGRUR OG AUCs Ses 86:04 0 Gr epee etry | ere etn rae 6) LOLA Gs OX G Leal ese es coy ah dil ectaen wiih Sibley a8 (OOOO) 2G, OCG |i oat Coen ee eee 6 PUB T “99
ey OOF 6 Gece | Se LC ONG Eas as SIPEG Le eS ORT ee ena area seen ie ofS mera GD MEIC T00 GIsl ie eae Chal ene aes ote (010j8q) TT “O8Cl | ose aay 86 PUB 0S “AON
ical BoROT ) Poet Wee OL LGN ner sees ons yao ODT wer GEO 7 Bl ie eee Rea oom Lae cI OUD WEST 09 Gta Aaa erick Oe br kpc ey Sate NT eae be ll 0 eg oe ieee ga od
a8 SSO |S S O16 C0) knee ars TL DUC Uelas Se IOGOlMG per eeeersoasn isl Save actif) Fe) O04 2/1 | REY Cel a Saas aera | oe Cae oe te eee Gar, eer ce ene 96 puv 6f “AON
eH OCR e | Ehe ama thes OGRA 2 Sas ete oe ore ge Peewee ate isl a Uneaten Alea Re GR ey ears COO Gir pregame oe Sees atin a eee, yee eB het Cael erm ene ear aaa gee 61 AON
ROO Sx | Cee CeO Goel agers pais ee SC DUC TCRUGIy er Vy OF SSy ia ea eae Se te 9G DUC PG sOO Chat pais We Ape ak Mar gel ot aeREN | ORAS Dy Onl Cog age, Mie amit ime 61 PUB ZT °AON
GRIO1S Ze | BIG ECT GC at Gee aan ate TG PEGG WEI OS OF yee were 28 Sap Se Se COPD UE! Gas 00 Cag nist oeae SEA ea A pu etn ies CHO COD OEIG ES teee t= Ae § “AON pue LZ “JO
shod LG & 0261 shog sing 02-6161 shod 03-6161 02-6 {61
z soy jo 93R4S 1 SesdR4s 1 osB41S 1 osBIS
youd Ul yy. soyep u0aM40q qyAnoj pue loumaatey | soyep U90M4Oq O8eysS parry} seyep WeeM4oq 9394S soqyep
posed jo 4sOy Wd] poss Uy paryy jo jo UII Of pogjour eAsey jo YANO] 07 poj[OUT BAIT usaMjoq polvodde waseyT
1230.L uoneing mo1neindg§ uoTyVInGg uoryVind

. “Hay, ‘soyyoq ‘az7709 fo syapg ut wniwauy DUusapodhpT fo yuaumdojaiag—'), ATAV],

62 BULLETIN 1368, U. S. DEPARTMENT OF AGRICULTURE
THE METHOD OF EGRESS OF GRUBS FROM BACKS OF CATTLE

When the fifth-stage larve complete their growth they become
more active and the posterior segments are extended and forced
into the openings through the skin and then quickly withdrawn.
With this action the sides of the holes are cleaned of the rim of
exudate and more or less covered with the pus forced up by the
_larve. When the actual process of emergence begins the posterior
segments are forced into the aperture and the larve slowly work -
their way out by expansion and contraction of the body rings. —
The actual process of emergence of the grubs takes from one to

HIOWR: OF EIIERGENWCE OF LARLAE FRO/T HOST

tS SS LS Ee)
FE. GF GIO JOM PISEAEVAEL ESB FF LES FOO

SS SS Se Se
La
FE
FE |
44
FZ

NU/IIBER OF LARVAE
ONAAHISTISSNHUITENRRGS

Fic. 29.—Diagram showing hours when larve of Hypoderma lineatum emerge from
the host for pupation

three minutes, but the preparatory activities may be begun several
hours before the grubs make a serious attempt to escape.

TIME OF EMERGING FROM HOST

With H. lineatum fairly accurate observations have been made
on the time of day when 181 warbles emerged from the host, and
less accurate observations on 211 others. Glaser (29) pointed out
that he observed in Germany a large percentage of warbles dropped
in the early morning hours, the percentage being from 49.4 to 68.2
between the hours of 5 and 7 a. m. The writers’ observations do
not agree closely with his in this respect, for, as is shown on the
accompanying diagram (fig. 29), the largest number dropped in
the middle of the forenoon from 8 to 10 a. m., and the emergence

er
ngs
» ‘

THK CATTLE GRUBS OR OX WARBLES 63

was greatly reduced in the middle of the day, increasing again in
the middle of the afternoon.

The number of larve recorded as dropping in the earlier morn-
ing hours is undoubtedly too small, as fewer examinations were
made between 8 and 9 a. m. than in later periods, and a much
smaller number still between 7 and 8 a. m. It is believed, how-
ever, that by adding all of those which may have dropped between
7 and 9 a. m. the total would not nearly equal the number which
dropped between 9 and 10 a. m. Of the 269 larvee the hour of
emergence of which was noted with considerable accuracy, 140, or
52 per cent, left the host between 8 a. m. and noon, and 129, or 48
per cent, between nocn and 6 p.m. There is undoubtedly a greater
disparity than these percentages indicate, as the number of hours
in the forenoon period was smaller than the number in the after-
noon. Also, as stated above, some warbles that dropped in the
early morning hours were not recorded.

The percentage of grubs dropping in the night was compara-
tively small. Considering the entire 392 larve upon which
the writers have records, only 88, or 22.4 per cent, dropped out
during the 12 hours from 6 p. m. to 7 a.m. Asa matter of fact,
this percentage is too high, as in it are included larve which on
several occasions were found to have dropped from animals when
they were first examined in the morning; sometimes this examina-
tion being made as late as 8 or 9 o’clock.

From their observations and the study of the data accumulated
the writers are led to believe that the activity of the host has
much to do with the dropping of the larve. Feeding of the
animals usually took place between 8 and 9 a. m. and up to about
that time the animals were comparatively quiet, usually lying
down. In the noon period following the morning feeding they
again became quiet and lay down much of the time, until 4 or
5 p. m., when feeding again took place. Just how activity of the
host should influence the dropping of the larve it is not easy
to see. Possibly the muscular movements stimulate them. There
is a possibility also that the warming up of the back of the
animals by the sun following the cool night may tend to stimulate
dropping. In the instances cited by Glaser it appears that feeding
took place very early in the morning and hence his observations
may tend to substantiate this hypothesis.

DISTRIBUTION OF THE LARVA ON THE BACKS OF CATTLE

As is well known, the larve occur in the greatest numbers along
each side of the spinous processes from the shoulder to the hip bones.
In diagraming the backs of hundreds of cattle the writers have
observed that this distribution is very irregular, sometimes several
larve being in one group and the rest of the back comparatively |
free, while in other cases they are widely scattered over the entire
area. It seems certain, however, that this is simply a matter of
chance. In summarizing their figures on the distribution of the
larvee the writers find that about 50 per cent of them occur in the
region of the dorsal vertebre and the other 50 per cent in the
lumbar region. As a rule they are more concentrated in the area
over the last three ribs. Although it is not unusual to find grubs on

64 BULLETIN 1369, U. §. DEPARTMENT OF AGRICULTURE

the shoulders, that is, above the scapulas or behind the hip bones,
the percentage occurring in these regions is comparatively small,
the writers figures indicating slightly less than 1 per cent for the
latter. Occasionally grubs are met with on the tail 3 or 4 inches
below its base, and also on the neck some inches in front of the
shoulders. One instance of the occurrence of a grub below the
point of the pin bone has been observed by the writers. Laterally
most of the grubs are confined to a strip about 1 foot on each side
of the backbone in grown animals, but it is not especially unusual
to find them on the ribs half way Gown the side of the animal. The
‘midline of the back is comparatively free (fig. 30).

The writers’ experiments show that there is no relation between
the distribution of the eggs on the host and that of the late stages

Fic. 30.—Cow with back infested with cattle grubs. Hair is clipped from around
holes

of the larve resulting therefrom. As the larve are known to
migrate freely all through the host, such a relationship would not
be expected. :

PUPATION AND DURATION OF THE PUPAL STAGE OF HYPODERMA LINEATUM

When the larve have freed themselves from the hole in the skin
in the back of the host they begin contracting and expanding and
soon roll off on the ground... For the collection of larve as they
emerged from the hosts, burlap bands were placed around the bodies
of cattle, as shown in Figure 31. They are not very active.and their
progress in crawling is very slow. There is a tendency for the larve
to crawl under any loose objects which may be at hand and which
would offer some protection; but ordinarily they do not go more
than a short distance from the place where they drop, and their

THE CATTLE GRUBS OR OX WARBLES 65

tendency to dig into the ground is not very marked. Not infre-
quently specimens will bury themselves in loose débris, such as straw
and broken leaves, but they do not burrow into compact soil or sand
to any extent. The larve show marked negative heliotropism, and
one was observed to crawl more than 10 feet, seeking shade in which
to pupate. Usually within a few hours they become quiet and within
1 to 12 days the integument hardens and. changes its shape into the
typical puparium form. The average prepupal period recorded in
the case of 238 larvee of H. lineatum was 3.4 days. Representative
records are presented in Table 8. The prepupal stage observed
among 7 specimens, kept in a screened insectary in Middletown,
N. Y., in 1922, ranged from 1 to 4 days. This period may vary
several days in the case of larve leaving the host the same day, but
the total time required for their transformation to adult is not in-
creased to that extent.

It is evident that where the larve drop normally the prepupal
period is markedly influenced by temperatures.

The pupal period at Dallas, Tex., ranged from 16 to 75 days, the
average being 38.2 days, as recorded for 196 specimens. Representa-
tive data are given in Table 8.

TaBLE 8.—Duration of prepupal and pupal stages of Hypoderma lineatum at
Dallas, Tex.

Larvs emerged F Temperature
from host : Pupated Flies emerged Period| dropping to adult
Pree from
onal Pupal| drop-
- q Ba oa NG Sasa period ping Aver-
Num- er 0 0 P age
Date nen Date ber Date bet of fe- adult | Max-| Min. daily
males mean
1916 1916 Days 1916 Days | Days | °F. | °F. | °F

Hepety—- 225 2 1 | Feb. 21 1 344| Mar. 21 |______- 1| +2 33 | 91.5 | 23.7 | 58. 26

Feb. 18___--- eae dose 1 3 Mar. 20 | Cea Rea ee 28 31 | 91.5 | 23.7 | 57.71

Feb. 21__--__ 1 | Feb. 22 1 34| Mar. 21 Dah ees eah ae Et +28 29 | 91.5 | 23.7 | 58.94

Que 1 | Feb. 23 1 2eel ear 22) gasses 28 30 | 97.9 | 23.7 | 59. 68

HED. 22-2228 3 | Feb. 24 3 262 do=s= 1 27 29 | 97.9 | 23.7 | 59.80

Wian4 2225. 1| Mar. 6 1 23) doses Le ee a eee 16 18 | 97.9 | 28.0 | 64. 65

Mar. 62-22. 1| Mar. 7 1 de Mar 28) |e one = 1 21. 22 | 97.9 | 34.0 | 64.32

RPAT Sf 288 1| Mar. 8 1 [es dos s=2 Pye we de 20 21 | 97.9 | 34.0 | 63.77
1917 1917 1917

Loi Bia eases 1| Feb. 3 1 3 | Mar. 13 Tela Sa 38 41 | 93.0] 9.5] 50.92

Hebetga2 2 2} Feb. 17 2 4 Mar. 20 1 1 31 35 | 93.0 | 25.0 | 56. 22

Mar. 10--___- 1 | Mar. 11 1 1 | Mar. 31 AE ess Sa 20 21 | 87.5 | 32.0 | 63.31
1918 1918 1918

anev20s_ 22 2} Jan. 25 2 5 | Mar. 11 2) eae 45 50 | 97.5 | 33.5 | 49.46

Vaneol. =. 2| Feb. 6 2 6 Mar. 13 1 1 35 41 | 97.5 | 12.5 | 53.86
1920 1920 1920

LE es ae 1| Jan. 8 1 2 | Mar. 18 nD fee aca oe 70 72 | 81.0] 19.0 | 48. 67

Lavy (ees Seas 1| Jan. 18 1 Lee Ole beeen 1 60 71 | 81.0] 19.0 | 48. 83

(20 0 eee 1} Jan. 16 1 7 Mars 2o0| ees 1 69 76 | 81.0! 19.0} 51.31

HebG2=.5 2 1] Feb. 9 1 Bie 2nd Opp Ae eos QE) 45 48 | 81.0 | 19.0 | 52.46

Keb: 18-2. .-.- 1 | Feb. 20 1 A WIM IBS Barf Meee 1 36 38 | 81.0 | 19.0 | 54.08

HeD2ose 1| Mar. 1 1 > | Wee. 74) | oe ee 1 24 31 | 81.0 | 19.0 | 52.61
1921 1921 1921

Liab eee 1} Jan. 15 1 4 | Mar. 1 | See a 45 49 | 83.0 | 26.0 | 52.03

(ee 1} Jan. 17 1 6 Ware Sian 1 45 51 | 83.0 | 26.0 | 52. 44

clits 28 Ft 38 1} Jan. 29 1 1 Mar. 12 Pp [tees = 42 43 | 83.0 | 27.0 | 54.91

Hep 5 eo be 2] Feb. 7 2 2 | Mar. 15 1 1 36 38 | 83.0 | 28.0 | 56.89

HehyG20 ook. 1] Feb. 8 1 2Py pe doza = 1 | (ate ee 35 37 | 83.0 | 28.0 | 56. 94

es ae 1] Feb. 10 1 Aire doses 1 I (pee re 33 37 | 83.0 | 28.0 | 56. 94

Mebnigo2.2 22 2| Feb. 14 2 1 Mar. 16 1 1 30 31 | 83.0 | 28.0 | 58.90

58252 °—26——_5

66 BULLETIN 1369, U. S. DEPARTMENT OF AGRICULTURE

Only four adults of H. lineatum were bred out in Middletown,
N. Y. Among these the pupal period ranged from 26 to 41 days, and
the period from date of leaving the host to emergence of the adult
ranged from 27 to 42 days. At Dallas, Tex., this period of trans-
formation ranged between 18 and 77 days, with an average of 41.7
days in the case of 221 specimens kept out of doors.

The average period of transformation was slightly shorter in males
than in females, being 42 days in the former and 44.4 in the latter, as
computed on 92 males and 80 females.

Hadwen (33) has presented records of the duration of the pupal
stage of 7. lineatum of from 13 to 19 days when the specimens
were kept in an incubator at 32° C., and Glaser (30) records a pupal
period in Germany for this species of 23 to 38 days. Carpenter
(72, 17) states that
he has observed the
pupal _period to be
about 7 to 8 weeks in
Ireland.

PREPUPAL AND PUPAL
STAGES OF HYPO-
DERMA BOVIS

Mature larve of
1. bovis show about
the same degree of
activity after emer-
gence from the host
as those of H. line-
atum, but they seem
to have a stronger
tendency to burrow
Fic, 31.—Heifer with bagging around body for urpose of puta tie so a

| eee cattle grubs as they emerge for: Host larvee of this Species

also show a great de-

sire to escape from direct sunlight, and one was observed to crawl

12 feet to a deep shadow, where ‘it pupated. If placed on loose soil,

most of them will bury themselves in a short time. Some burrow
down about an inch, but most of them go just below the surface. -

When the weather is warm the prepupal period is very short.- At
Dallas records were kept on several larvee which emerged normally
from cattle. All of these pupated, and 4 produced adults. The
prepupal period of these larvee was in every case somewhat less than
a day, and the pupal period of the 4 which emerged was from 14
to 15 days, making a total period from emergence from the host to
the appearance of the adult insects of from 15 to 16 days. Among
24 larve extracted from cattle at Dallas, Tex., and kept for rearing,
14, or 58.3 per cent, pupated and only 1 (4.2 per cent) produced
an adult. In the case of this specimen the prepupal period was
slightly more than a day, and the pupal period 14 days, a total
transformation period of 15 days. The writers succeeded in breed-
ing out 4 adults from 8 mature larve extracted from cattle at
Herkimer, N. Y. (Table 9). The prepupal period among these was
10 hours to 1 day, and the pupal period from 15 to 24 ‘days. The
total developmental period from extraction of the larvee to the

67

THE CATTLE GRUBS OR OX WARBLES

emergence of the adults was 16 to 25 days. All of these records were
_made in midsummer, and the specimens reared in New York were
kept in a building in which the temperature was warmer than out-
doors, hence the periods shown are probably shorter than would
| occur normally.

TABLE 9.—Duration of prepupal and pupal stages of Hyupoderma bovis

Adults emerged Temperature
: during period from
Date Duras Dura-|Per!04| dropping to adult
dropped yah how cian com
< or ex- ate (0) 3 rop-

Locality tracted | pupated | pre- Nua Num re al| Pine ree
from pupal} Date of |offe-| stage to } age
host stage minlesimales adult | Max.) Min. daily

mean
1918 1918 Days 1918 Days-| Days \ °F. | OF. | OF.
Dallas, Tex__...--- May 15 | May 16 IL JM bene B20) eee 5 if 14 15 | 98.4 | 54.0 | 78. 28
1D 0.3 SS ea May 24 | May 25 1| June 8 1 1 14 15 | 96.0 | 63.1 | 81. 62
DOs esse ee May 27 | May 28 Tt diwnoyey 119) 1 15 16 | 97.0 | 65.0 | 81.37
4 1921 1921 1921
Herkimer, N. Y_-_-| June 24] June 24 aA! Apoubig. uly coe if Gp AL sc Le el teaee ee he eet oa
De. ees July 14] July 15 il 4) dhbdbiee BO) gos 1 15 1 Ghee oe ees eae
IDOLS. Sees July 17]| July 17 TG AU ee nb) ees 1 TUE Ou eee eee ees SA
IDS aS ee Aug. 3/| Aug. 4 1 | Aug. 28 a al Ppa 24 PA ya | See rea Senet
1922 1922 1922
| Middletown, N. Y_} Apr. 20| Apr. 27 7 | June 4 | Pages 38 45 | 85.0 | 28.0 | 58.6
IDOS SS Bes Sales GS PAL ses 55e Geie=donse 1 1 38 44 | 85.0 | 28.0 | 59.1
ID) Obs Sess 3s oa PAV a2 ed Oe Arey |e Cl Ose 1 1 38 42 | 85.0 | 32.0 | 60.0
DD) OMe Se te Auprs 26) 22-002 52 eed oree. 1 3 38 39 | 85.0 | 32.0 | 60.9
DOM eee ke Apr. 28| May 1 Saeed omens 2 1 34 37 | 85.0 | 33.0 | 61.4
IDS ees = OO Me 2k aes Se ikedoe Hillmen 34 37 | 85.0 | 33.0 | 61.4
IDO) 5 eee ee Atpr 429) 22=d0n 224 Dred @ ses s8 1 3 34 36 | 85.0 | 33.0 | 61.9
1D YG) 5 ae ea re Pek Ose Ow eee 2 | June 5 il 2 35 37 | 85.0 | 33.0 | 62.1
1D) Oe ee Apr. 30 |_--do____-| 11%] June 4 1 1 3344 35 | 85.0 | 33.0 | 62.1
]DY0)-es = See eg May 4] May 8 4 | June 6 11s ie ee 29 33 | 85.0 | 40.0 | 62.8
ID) SS eee SECON ee PaCS ea 4 | June 7 Gules ee 30 34 ; 85.0 | 40.0 | 63.2
TD gee 4k gi ae Bacon! SB BG lout Oe Bo (oyuRnane 4 | June 8 1 2 31 35 | 89.0 | 40.9 | 63.6
IDXO)s 5 eis ee May 8| May 9 14%) June 7 Hei int ess 28% 30 | 85.0 | 40.0 | 63.8
LD) Qe et 2aCOs 232) IMleiy a0) Deere: 19 nouns 2 30 32 | 91.0 | 40.0 | 64.6
DOR ae May 12) May 13 1 | June 8 Oi eee oe 26 27 | 89.0 | 40.0 | 64.5
DO ess eS ed Ose ae i O(0 (oye iL June 9 3 4 27 28 | 91.0 | 40.0 | 64.9
1D) OSE ESTE OK ayattae FNS (0 Ko) eee 1 | June 10 1 1 28 29 | 92.0 | 40.0 | 65.3
ID Yaya) eae ah May 14 | May 15 14%) June 9 3 1 241% 26 | 91.0 | 41.0 | 65.0
1D) OR Sh > PedOse ee med Ose 14%) June 10 1 i see i 2514 27 | 92.0 | 41.0 | 65.5
IDOE Se seer ee SeGOus =a dom see 1144) June 11 |_____- 1 26% 28 | 92.0 | 41.0 | 65.8
ID) Qe May 17 | May 19 1Y4)__-do___- ifs | Utena 234% 25 | 92.0 | 41.0 | 66.5
ID oy nee elem Se dOea (2 aedoLene 14%| June 12 |_____- 1 24% 26 | 92.0 | 41.0 | 66.8
IDO) aaa May 20 | May 21 1 | June 11 dial ean 21 22 | 92.0 | 41.0 | 67.8
1DY0)s Saree eG Ova een | ean Omens dihare) WA eee 1 22 23 | 92.0 | 41.0 | 68.2
ID Oa ae May 25 | May 26 1 | June 16 Pe See a 21 22 | 92.0 | 41.0 | 68.3
WORE Ee oye tl May 27 | May 29 2 | June 19 | IH (eke 21 23 | 92.0 | 41.0 | 68.1

1 Half days are given to approximate more closely the time required for transformation.

At Middletown, N. Y., during 1922, a large number of adults were
reared from larve which emerged normally from the backs of cat-

tle. These pup were kept in a screened, roofed insectary out of
doors. The prepupal period ranged from about 10 hours to 7

days, with an average of 1.7 days; the pupal period, from 21 to
38 days with an average of 29.4 days. The time from leaving the
host to emergence of adults varied from 22 to 45, with an average
based on 167 records of 31.34 days. The longest period (Table 9) oc-
curred in the spring. As some larve left hosts in 1922 about April 1,
it is probable that some periods longer than the maximum shown
might have occurred among the larve dropped earlier in the spring.
_ In Canada, Hadwen (34) observed a period of 30 to 40 days to
intervene from the emergence of the larve to the appearance of

68 BULLETIN 1369, U. S. DEPARTMENT OF AGRICULTURE

the adult, the average for several being 34.7 days, and Glaser
(29) records this period as being 37 to 56 days in Germany. Under
just what conditions these pupe were kept is not known, but pre- |
sumably they were out of doors. Vaney (106) in Lyons, France, |
has observed that the period of transformation requires from 3 —
to 4 weeks. In the vicinity of Paris, France, Lucet (62) records ©
an average pupal period of 32.9 days, the range being from 29 to
40 days. In Ireland, Carpenter, Phibbs, and Slattery (29) record |
a pupal period of 32 to 46 days. Stub (97), working in Copenhagen,
found the pupal period to be from 40 to 53 days. — |

MORTALITY IN THE PREPUPAL AND PUPAL STAGES

Among larve which drop normally a considerable percentage fail —
to produce flies, even under what might be thought to be optimum —
conditions. The percentage of the larve which pupate is rather |
high. Among 559 larve of 4. lineatum which were noted at Dallas,
Tex., 514, or 92 per cent, formed pupe and 337, or 65.6 per cent, |
of the pupae emerged as adults, or 60.8 per cent of the total num- |
ber. Both species of Hypoderma are very dependent upon proper
conditions for completion of their development. Larvee removed from
the backs of cattle before they are ready to emerge are subject to
a high percentage of mortality. It is conceivable that by forcing
them through the holes in the hide they may be injured, but the
writers’ experience indicates that immaturity and not injury is the
cause of death. Among 325 well-developed larve of H. lineatum
extracted by hand and kept under optimum conditions for pupation |
and adult emergence, only 113, or 34.8 per cent, pupated, and out |
of this number 26, or 23 per cent, produced adults. This was 8 per |
cent of the total number of the larvee extracted and observed. All |
of these larve had practically attained their full growth. |

Among 221 larve of H. bovis which emerged normally from hosts |
and were kept in a screened insectary in Middletown, N. Y., 186,
or 84 per cent, produced adults. - |

Excessive moisture produces a high mortality among pupe. This |
point will be discussed under natural control.

EMERGENCE OF ADULT FROM PUPARIUM

In the case of both H. lineatum and H. bovis the flies appear |
mature within the puparia several hours before they emerge. The
majority of the adults reared by the writers have been found to ©
escape from the puparia during the early morning hours. 4

The cap of the puparium is first forced open by the head of the ©
fly, and in some cases it is broken off completely. The fly then
crawls out, and this process takes less than half a minute. Within |
a few minutes after the fly escapes it usually walks away from the —
puparium and begins to unfold its wings. Usually this process re- |
quires about five mintues. The ptilinum is completely retracted and |
the wings straightened to normal position in about 15 minutes after ©
emergence. The abdomen is conspicuously distended, showing —
that the insect is provided with an ample supply of food from
the larval stage. An occasional droplet of excrement is voided
during the drying process, Immediately after the wings are dried

|

a THE CATTLE GRUBS OR OX WARBLES 69

|

the abdomen is extended and retracted and the insect makes clumsy
attempts at flight. Within half an hour after emergence it is able
to sustain itself on wing, though rather clumsily.

The adults evince a very strong positive heliotropism. In cap-
tivity their main energies are devoted toward escaping. Very
_ few flies have been recovered in nature unless in the act of attack-
ing cattle, and just what place they choose for resting is not known.
Apparently, however, they remain on the ground or on grass and
‘shrubbery close to the ground.

PROPORTION OF SEXES

| The sexes were noted in the case of 284 reared adults of 7.
lineatum. Of these, 147, or 51.8 per cent, were males. The males
usually emerge from the puparia slightly before the females, al-
though this is not uniformly the case. Among 172 adults of ZH.
bovis which were reared and the sex noted, 81, or 47.1 per cent,

were males.
FOOD OF THE ADULT

Mention has been made of the supply of food carried over to
the adult stage from the larve. This appears to be sufficient to
meet the needs of the adult insect throughout its hfe. The writers
have repeatedly attempted to feed reared adults in captivity on
fruit, sirup, and water, but have never observed any indication that
they would partake of such substances. The mouthparts are de-
generate and probably not capable of functioning in feeding.

MATING

Many reared flies of /7. lineatum have been kept in various types
of breeding cages, usually supplied with sticks or branches of green
trees, and in the much greater number of these cases mating was
not observed to take place. Although a number of these reared
females were induced to oviposit, in most instances the eggs were
infertile. In four cases mating was closely observed. The act
usually took place immediately after the males and females were
placed in the same small cage. In each instance the male seized the
female as soon as they met, but in one case the male went through
some preliminary courting actions. He crawled over the female’s
back and head, then worked rearward on the back of the female and
mating began. The details of mating appear to be about the same
as with many other Diptera. The duration of the act ranges from
one to three minutes. In two instances mating was repeated a second
time immedistely after the first. In two of the four instances of mat-
ing observed in /Z. lineatum. both the male and female were 1 day
or more old. In the other instance, however, which occurred at
10.45 a. m., the male had emerged shortly prior to 9. a. m. of the
same day, and the female was observed to crawl from the puparium
at 10 a. m.; thus mating took place when the female had been out
only 45 minutes. It is interesting to note in this connection that
this female upon being placed on a calf 20 minutes after mating
deposited a considerable number of fertile eggs. :

HT, bovis evidently mates much more freely in captivity than
Hl, lineatum. The act has been observed in many instances to take

70 BULLETIN 1369, U. S. DEPARTMENT OF AGRICULTURE

place among reared specimens. Among a large number of adults |
of H. bovis which emerged early in the morning and were kept in —
lantern globes, many pairs were observed in copula about 10 a. m..
as the temperature rose. The duration of the act ranged from two

to two and one-half minutes.

OVIPOSITION

Reference has been made already to an instance of a fly begin- |
ning oviposition within about an hour of the time she emerged.
The writers’ observations in the field indicate that if favorable
weather conditions prevail oviposition usually begins on the same
day the adults emerge. It —
also appears that with flies —
in the field and with those
captured and placed on ex- |
perimental animals the ma-
jority of the eggs deposited |
by an individual are laid
during a single day. In|
several instances flies de- —
posited a large number of
eges during one day and a_
moderate number during —
the second day, but in no
case have specimens ovi-—
posited during three suc-_
cessive days. |

As has been pointed out
by Hadwen and other au-
thors, the methods of ovi-
position are very different —
in H. lineatum and A.
bovis. The former attacks
more stealthily than the
latter, and several eggs are
usually placed on a single —
Fic. 32.—Heel fly (Hypoderma lineatum) oviposit- hair, while with Z. bovis |

ne ane Wag he as Roe “the eggs are laid singly. —

This difference in the action”
of the flies during their oviposition is intimately associated with the
fright produced among cattle, as will be discussed later.

In the field when cattle come in the vicinity of a resting female
of H. lineatum the insect is observed to approach them on the wing
usually alighting on the ground close to an animal and frequently
approaching the hind legs of the host by a series of short flights
which resemble jumps. She sometimes lights directly on the heel,”
usually below the dewclaws, and immediately begins to extend the
ovipositor, g rasping the hair and cementing on her eggs (fig. 32)._
In other instances if the animal is not moving she may come close
to the heel of the host, turn around, and back up to the rear of —
the hoof with the ovipositor extended. In this way the short hairs —
between the hoofs are reached and the eggs are placed in position

THE CATTLE GRUBS OR OX WARBLES 71

while the fly remains on the ground. When the animal moves, the
fly usually follows, flying behind close to the ground, and when the
opportunity offers she may ahght on the host, commonly on the
hind legs below the hock. Under such conditions the animal is '
usually aware of the presence of the fly and often kicks at it, fre-
quently knocking it to the ground, in which case it usually arises
promptly and starts again after the host. With animals disturbed °
in this way the fly is more lkely to attack higher on the lees and
not infrequently on the sides, especially in the region of the flank
or on the forelegs or shoulders. |

In many instances the writers have observed females of ZZ. Tene
twm to oviposit on cattle while they were lying down. When not
disturbed the fly usually deposits a series of eggs, possibly 50 to
60, in rapid succession and then rests for a minute or two. Some-
times she moves slightly to a new position and then repeats the
operation.

Flies of H. lineatum captured by means of a net. while attacking
cattle in nature are readily induced to oviposit on experimental
animals kept under control; in fact, this was the method followed
in obtaining eggs with which to infest experimental animals and
for other purposes. After the flies were captured they were usually
placed in small tubes or jars and brought immediately to the
laboratory and placed upon experimental hosts. To accomplish this
the female was usually placed in a glass vial with the open end
placed against the host. Usually as soon as the fly comes in. con-
tact with the hair of the animal she begins extending the ovipositor
and starts laying eggs. After she has once begun itis often unneces-
sary to keep the restraining vial over her.

HZ. bovis attacks the animals viciously, usually approaching them
about the height of the hock, and very seldom lights on the ground.
On account of its more ‘persistent and ferocious attack the animals
are put to flight with the first period of oviposition. The fly strikes
the animal a number of times in rapid succession, cementing an
egg on, a hair in nearly every instance. After a number of these
strikes at the animal the fly may leave for a few minutes and then
return. and repeat the process as persistently as before. Frequently
when the host is active the fly may follow it around a small pas-.
ture, attacking repeatedly when it catches up to the fleeing animal.

Great difficulty was experienced in getting females of /7. bovis
to deposit. eggs after they had been captured. Hawden’s reports
indicate that he had no difficulty in getting females caught while
Ovipositing in nature to deposit under an insect. net. held to a bovine
or when released near a tethered animal. In Illinois and New
York, however, a number of flies captured in the field by the writers
and applied 1 in various ways to hosts under control gave very dis:
couraging results. Only a few ego's were secured and these for the
most part were dropped free in the hair.

During the summer of 1922 a large number of flies ae both sexes
of H. bovis were reared at Middletown, N. Y., and many attempts
were made to secure eges from them. Although they mated freely,
as has been stated, they ‘persistently refused to oviposit. Some were
kept in glass containers held against a calf; others were placed in
small screen cages attached to the host; and still others were liberated

;

ie BULLETIN 1369, U. S. DEPARTMENT OF AGRICULTURE =|

in cages containing calves. But in no case were any eggs deposited —
normally,

On account of the fact that H. lineatum deposits its eggs in series
on the same hair, the rate of egg laying is somewhat faster than with
H. bovis. In some instances the eggs of H. lineatum have been
seen to be deposited at the rate of nearly 2 per second, and 30 or 40
may be deposited in a minute.

NUMBER OF EGGS DEPOSITED

The number of eggs deposited, especially by H. bovis, is very
difficult to determine. The maximum number observed by the writ- —
ers for H. lineatum was 446. These were deposited by a female
taken in the act of ovipositing on a cow in a pasture, and hence this
fly may have laid many eggs before capture. Glaser (29) has ob-
served a female H. lineatum to deposit 538 eggs, and estimates the ©
total number deposited by this female as 550. In many instances ©
from 200 to 300 eggs have been obtained from a female caught in
the field in the act of oviposition. Females dissected after they
have become too weak to deposit) more eggs usually have a good
number of ova left in the abdomen, although many of these appear
to be only partially developed.

CONDITIONS UNDER WHICH OVIPOSITION TAKES PLACE

Both species of Hypoderma are stimulated to oviposition by
bright sunlight and usually egg laying takes place largely in the
sunshine. Both species have been observed, however, to deposit
eggs in the shade, and occasionally when the sun was fairly well
covered with clouds, especially if there were occasional bursts of
sunshine. Oviposition rarely takes place when the sky is heavily
clouded, and dense shade such as under large sheds appears to be
shunned by the females of both species. Females of both JZ.
bovis and H. lineatum have been observed to be active on days
when the temperatures were comparatively low, provided the sun
was shining brightly. No doubt in their protected places close
to the ground reflected heat and sunshine stimulate them to activity
when the general temperatures are very low. In one instance ovi-
position of H. lineatum was observed when the temperature was be-
tween 40 and 45° F. The minimum temperature at 7 o’clock that
morning was 20.5° F. and the maximum for the day 46° F. at 3 p. m.
It is difficult to say just what is the optimum temperature, as large
numbers of flies have been observed ovipositing under a wide range
of temperature conditions. Females of this species oviposit freely —
when the temperatures range between 55 and 85° F. provided the
sun is shining.

Apparently the range of temperature in which females of 4.
bovis will oviposit 1s narrower than in ZH. lineatum, although, in
localities where both species occur, females of H. bovis usually expe-
rience higher temperature, since they emerge later in the season.

High winds and even fresh breezes tend to check egg laying of
both species. Occasionally, however, the flies will oviposit on windy —
days when the cattle are standing in the sunshine in protected places.

——

THE CATTLE GRUBS OR OX WARBLES 73
LONGEVITY OF ADULTS

Owing to the fact that the adults of Hypoderma are very rest-
less when in captivity and since there seems to be no means of
keeping records of specimens in nature, the writers’ observations
on the length of life of the adults may give erroneous ideas. The
longevity of reared adults of H. lineatwm is shown in Table 10. It
ranged from 1 to 25 days and averaged somewhat longer for males
than for females. The markedly greater longevity observed among
about 50 adults reared in the laboratory during the spring of 1924
than had been noted previously indicates clearly the probability
that certain individuals which emerge prior to periods of uniformly
cool weather may live for a considerable time. The specimens re-
ferred to were hastened in their emergence by being kept in a
warmed room. After emergence the adults were transferred to
lantern-globe cages and kept in an unheated room. The tempera-
tures given in Table 10 for these records for 1924 were those re-
corded in a standard weather shelter out of doors, and hence un-
doubtedly show a much greater range of temperature than was
actually experienced. There is no question but that in nature the
flies would seek the sunshine and warmer places which would stimu-
late activity, and thus we should not expect to find such long periods
of existence as those referred to above. The writers’ observations
in the field also bear out this assumption. It seems certain that
when the weather is warm and the adults are active their lives are
uniformly very short.

TABLE 10.—Adult longevity of Hypoderma lineatum at Dallas, Tex.

Num- Temperature
um
Date her ber 1 a ae
adults of of Record of death ait Remarks
emerged Petes tes Bey Min. | Max.| AVe!-
males : age
1915 1915 Days C10 | ae OT
FADES V2i fe To | GA prelOw armas 620 ec ue 7 | 48.0 | 83.5 | 67.6 | In cage 1 foot by 1 foot
by 1 foot, with leaves.
ATS 19) oe Apic2e:sp Ms 2 a2a2 2 ee 3 | 54.0 | 82.0 | 69.0 In small cage, with
leaves.
1916 1916 ,
Mar. 20 1 3 | Mar. 21,2 9; Mar. 22,1 9; 1to 31! 61.5 | 97.9 | 80.2 | In cagel foot by 1 foot
Mar. 23,1 o. by 1 foot in sun.
Mar. 22 10 10 | Mar. 23,1 9; Mar. 24,167, 1to 7 | 38.0.| 88.0 | 61.7 | In small and. large
2 9; Mar. 25, 307, 59; cages and on cow.
Mar. 27, 29,1 o&; Mar
28, 26°; Mar. 29, 3c".
Mar. 27 2 2 pee ee: 2; Mar. 29,27, lto 2] 39.5 | 88.0 | 66.3 Do.
1918 1918 ;
Feb. 25 D4il pty Feb. 27,1; Feb. 28,1c_-| 2to 3 | 38.0 | 97.5 | 66.2 | In laboratory.
Feb. 26 1 5 Fe ae 1 o',3 9; Mar.1, 2to 3 | 38.0 | 87.0 | 58.2 Do.
Hebi27) | 222.8 Tf lah Ue ts Ue gs 2 eA ei a 2 | 38.5 | 87.0 | 56.2 Do.
Mar. 11 3 1 | Mar. 14, 2 o', 1 9; Mar. 3to 8 | 33.7 | 90.0 | 60.9 |; In 1-inch tubes (@ de-
19,16. posited).
Mar. 13 2 1 | Mar.15,1 9; Mar.19,2c¢'_| 2to 6 33.7] 90.0 | 56.5 | In 1l-inch tubes with
leaves.
1921 1921
Mar. 7 8 1 | Mar.14,2¢; Mar.15,4 4, 7to 9 | 36.0 | 87.0 | 63.4 | In lantern globes with
19; Mar. 16,2¢. leaves.

Mar. 8 8 1 | Mar.12,1 9; Mar.13,10; 4to 9 | 36.0 | 87.0 | 64.0
_ Mar. 15, 16°; Mar. 16,
4 9; Mar. 17,2.
Mar. 12 10 8 | Mar. 13,1 o&; Mar.15,1 @; 1to 8} 51.0 | 87.0 | 71.7 | In cage 1 foot by 1 foot
peat Bo 7 o',8 9; Mar. by 1 foot, with leaves.
, °

74

BULLETIN 1369, U. S. DEPARTMENT OF AGRICULTURE

TABLE 10.—Adult longevity of Hypoderma lineatum at Dallas, Tex.—Continued

di Temperature
Num
; . Date aa ber Tone
adults oF of Record of death ; Remarks
emerged |_ Of fe- BEVIUYs : Aver-
emlergec | males eae Min. | Max.|“ah6
1921 Days CT DE NAY TEN SG
Mar. 13 1 2 See 16,1 & i es Mar. 17, 3to 4 | 52.0 | 87.0] 71.1 iH lantern globes, with
iL eaves.
Mar. 14 6 3 Mar. 16,1 2; Mar.17,2 ¢, 2to “5 | 52.0 | 87.0 | 74.5 Do.
1 @; Mar. 18, 357, 1 Q; :
Mar. TOE TeeHe Be
Mar. 15 9 2 | Mar.17,1 6; Mar. 21,5 &, 2to 7 | 43.0 | 87.0 | 72.1 | In lantern globes, with
2 2; Mar. 22,3 ¢. 5 leaves. Copulated.
1924 1924
Feb. 7 Dalene se Feb. 13,1 6; Mar.3,1 o_--| 6 to 25 | 26.5 | 82.5 | 51.25 | In lantern globes in
cool room. Outdoor
temperatures are
given.
Feb. 9 Ag bee ae Feb. 27,1; Mar. i 1 &-__| 18 to 21 | 26.5 | 82.5 | 50593 Do.
Feb. 14 3 1 | Feb 27, 1 9; Mar. 4,2; | 13 to 23 | 26.5.| 82.5 | 52.55 Do.
Mar. 8, 1 oe :
Feb. 16 2 1 | Mar. 5,1; Mar. 8,1 9; ; 18to 23 | 25.0 | 77.5 | 51.10 Do.
Mar.10,1 9.
Feb. 18 5 5 | Feb. 27,2 6°; Mar.1,3 9; | 9to17 | 26.5 | 77.5 | 50.37 Do.
Mar. 3,1 o; Mar.4,1 9;
Ae 5,16; Mar. 6,1 6,
IpOE
Feb. 25 5 Mar. 6,1 &; Mar. 7,16 10 to 21 | 25.0 | 77.5 | 49.41 Do.
; 29; Wiar’i0, Omar
ile 3 ne

The longevity of H. bovis apparently does not differ much from
that of H. lineatum. Specimens reared at Dallas, Tex., lived from
2 to 4 days in cages. In Middletown, N. Y., a number of adults
were kept in cages in the shade and ‘supplied with green leaves.
These lived from 4 to 10 days with an average of 6 days. Speci-
mens of both species captured in nature live in confinement only 1
or 2 days.

SEASONAL. HISTORY

There are some distinct differences in the seasonal development of
H. bovis and H. lineatum. These must be considered in control
undertakings and they will be pointed out under the several topics
following. Both species are essentially single brooded.

SEASON OF ADULT ACTIVITY

Adults of H. lineatum appear under usual conditions during the
first warm days of spring. The actual date necessarily varies with
latitude and altitude as well as with local climatic conditions. It
appears that in the southern range of H. dineatum the period during
which adults of that species are active is longer than in any other
portion of the country. Not infrequently in southwestern Texas
adults begin to emerge in December and continue to appear during

warm periods throughout the winter. In this section the maximum
abundance of adults apparently occurs about the middle of Febru-
ary. Observations made by D. C. Parman at Uvalde, Tex., indicate
that during some years, at least, adults may continue to appear until
about April 1, thus extending the period of adult activity over about
four months. At Dallas, Tex., the adults rarely, if ever, emerge be-

THE CATTLE GRUBS OR OX WARBLES FEN

fore February 1 or after April 15. The maximum abundance usually
occurs between February 20 and March 15. Im the plateau region
of southwestern Texas in certain instances larve have been found to
mature early enough in the fall to permit of the issuance of a con-
siderable number of heel flies in the fall. It has not been possible
to determine if this really takes place, but the finding of a young
larva in the gullet of a cow on January 4 is fairly conclusive proof
that some eggs are deposited in October or November. It is certain
that some heel flies emerge and attack cattle during December, and
heel-fly activity has been observed on numerous occasions in Jan-
uary. The season of adult activity in New Mexico, Arizona, and
California appears to be about the same as observed at Dallas.
Throughout the central belt of States—that is, between the latitudes
385 and 45° N.—the period of activity 1s approximately between
March 15 and May 1, and in the northern tier of States between
April 1 and June 30. ‘These dates are only approximate, and vary
much during different years, as well as with altitude and local
conditions.

In New York adults of H. lineatum may begin oviposition as early
as the middle of April, are most abundant during the first three
weeks of May, and cease activity about the end of June. In the
territory where //. bovis occurs it 1s difficult to determine the date of
cessation of activity of the adults of H/. lineatum, since their seasons
of activity overlap.

In New York considerable numbers of adults of 7. bovis begin to
oyiposit during the first week in June and apparently some emerge
during the latter part of May. The flies are very annoying to cattle
during June and the first half of July, are less so during the re-
mainder of July and the first half of August, and during the re-
mainder of August and up to the middle of September only strag-
glers are abroad. Since normal larvee have been found in the backs
of cattle in New York after September 1, some fly activity is possible
throughout that month. No flies have been seen, however, nor have
the effects of their attack been noted, after September 14.

Hadwen (36) states that at Agassiz, British Columbia, adults of
H. bovis appear in the early part of June and continue up to the be-
ginning of August, and that adults of H. lineatwm were out from
April 15 to April 24. Carpenter (79) records the emergence of
adults of H. bowis in June and July, and deposition of eggs of ZH.
lineatum on May 8 and June 16, at Athenry, Ireland.

The season of oviposition of both species is about coincident with
that of adult emergence.

SEASONAL DEVELOPMENT OF LARVZE

Rather abundant data regarding the seasonal occurrence of larve
of 7. lineatwm in the gullets and viscera of cattle are presented on
page 47 and Tables 3 and 4. In general, approximately two and one-
half months elapse between the deposition of eggs and the earliest
appearance of larve in the gullets.

In the vicinity of Dallas, Tex., the larve first appear in the sub-
mucosa of the gullets of cattle at about the end of March and con-
tinue to enter that organ until the maximum is reached during Sep-

76 BULLETIN 1369, U. S. DEPARTMENT OF AGRICULTURE |

tember. There is then a gradual reduction in numbers until about
January 1, when all have migrated from the gullet.

In southwestern Texas the larvee begin to reach the gullets dis-
tinctly earlier than at Dallas, thus closely conforming with the
earlier appearance of adults in that region. ‘The earliest larva ob-
served by the writers to appear in a gullet was a single specimen 4.2
millimeters in length taken from an animal slaughtered in a Fort
Worth, Tex., packing house on January 4, 1924. This specimen evi-
dently developed from eggs deposited the previous fall. |

At Herkimer, N. Y., larvee began to appear in the gullet about the

middle of July and the last larve left that organ about April 1. |

Thus it is certain that the larve are to be found in the gullets for
about nine months. |

The seasonal prevalence of larvee in the subcutaneous tissues of
the backs of cattle is closely correlated with the time when the larva

reach the maximum size attained by them in the gullet, and to some

extent with the period of adult activity. Knowledge of this subject
is of vital importance in connection with any control procedure, yet
the information published is meager in the extreme.

The earliest appearances in the United States of larve of Z.
lineatum in the backs of cattle occur in the plateau region of
western Texas. On August 10, 1919, at Roosevelt, Tex., O. G.
Babcock observed grubs in considerable numbers in the backs of
cattle. A few collected on August 12 showed some to be in the
early fifth stage. Thus they must have appeared on the backs
about July 15. In 1923 fifth-stage larvee were found by Mr. Babcock
at Sonora, Tex., on August 22. These must have reached the backs
of the cattle about July 30. At Uvalde, Tex., records made by
D. C. Parman during several years show that the first appearance of
larvee in the backs of cattle is later than it is in the plateau region
to the north. The earliest appearance noted at Uvalde was on
August 12, 1918. The larvee in this case evidently had been present
about 10 days.

Mr. Parman’s records at Uvalde indicate that larve usually
begin to appear under the skin about the middle of September.
Some years, however, they may appear as late as October 9, as
was observed in 1920. During that season the maximum number
present was noted on January 15. 3 3 }

At Dallas, Tex., fairly accurate records of the earliest appearance
of larve in the subdermal tissue have been made in 10 different
years, during the period from 1907 to 1922. These dates have
been rather uniform, ranging from about October 10 in 1914 and
1918 to October 30 in 1916. The year 1923 was an exception, as
in that year the larvee appeared about September 8.

At Herkimer, N. Y., the date of appearance of larve of H.
lineatum in the subdermal tissue of the backs of cattle was found
in 1920 to be about March 1, and in 1922 about February 6. At
Middletown, N. Y., in 1920 larvee of H. lineatum came to the backs
about February 12, and in 1923 about February 1. At Watertown,
N. Y., in 1920 the date of earliest appearance was about March 3.

In Kane County, IL, C. C. Compton found a single small larva in ©

one of 200 cattle examined on February 7, 1924, thus showing the
earliest appearance to be soon after February 1. Subsequent col-
lections made by Mr. Compton indicate that this date is sub-

THE CATTLE GRUBS OR OX WARBLES Ar

stantially correct for that section in 1924. W. H. Brittain has
sent the writers specimens collected by W. E. Whitehead at in-
tervals during the spring of 1924 from cattle at Truro, Nova Scotia.
In an examination of a large number of cattle by Doctor Whitehead
on March 24 only 3 grubs were found. The largest one had been
in the back about 10 days. Records sent the writers by C. J. Drake
on collections of larve made by E. W. Dunnam and others at
Ames, lowa, indicate that larve of H. lineatum first reached the
backs in 1923 about January 8, and in 1924 about January 20.
Hundreds of collections have been made by the writers and by
correspondents throughout the country, and with these records as
a basis the dates of appearance of the earliest larvee of H. lineatum
have been estimated and the accompanying map (fig. 33) constructed.
Unfortunately, as the number of accurate records of the time of
first appearance is small, many discrepancies will be found, but it

Fic. 33.—Hypoderma lineatum: Date zones of first appearance of grubs in backs of
cattle, in the United States

is hoped that the data available will serve a useful purpose in
control undertakings and also stimulate others to add to these much
needed records.

The date when the first larvee become mature and leave the host
is an important one from an economic point of view. This date is
necessarily closely correlated with the date when the first grubs of
the season reach the back. It seems extremely rare for these earliest
grubs to complete their development in the minimum time, hence
the first emergence of larve from the cattle should be expected to
take place about 45 days after the grubs first reach the back. At
Dallas the earliest larvee become mature and begin leaving the host
between December 1 and 15 during average years. The follow-
ing are the approximate dates when mature larve began emerging
from cattle at Middletown, N. Y.: In 1920, March 26; in 1922,
March 16; and in 1923, March 19.

ib
ie

78 BULLETIN 1369, U. 8. DEPARTMENT OF AGRICULTURE

The time of maximum abundance of larve in the backs of cattle ©
varies considerably in different herds and during different years. At —
Dallas, Tex., this maximum usually occurs, on the average, about
January 10, and at Uvalde, Tex., about December 15.

The date when the last grub leaves the cattle varies considerably
in different herds, as well as in different localities and during a
series of years. This point is of little economic importance for ZH.
lineatum in those States where H. bovis also occurs, for the latter
always persists in the hosts later in the season, and the two species
must be dealt with asa unit. At Dallas, Tex., the date when cattle
become free from grubs in their backs has been determined during
several years. In 1915 this date was March 20; in 1916, April 12;
in 1917, March 18; in 1919, March 15; in 1921, March 20; and in
1922, March 16. At Uvalde, Tex., Mr. Parman has observed the
cattle to become free of grubs between January 20 and April 12. It
is interesting to note that Mr. Babcock found two specimens of
HT. lineatum in the back of a cow at San Angelo, Tex., on March 20,
1924. These larvee would not have been mature in less than 15 days.
Since the grubs of this generation began to appear in the backs of
cattle in that region about August 2, there is a remarkable and very
unusual period of infestation of the backs of cattle of about eight
months. Thus it appears that there is a wider variation from year
to year in this respect in southwestern Texas than occurs elsewhere.
A very general idea of the time when all larve of H. lineatum
have emerged from the cattle may be gained from the following
dates: March 1, southern Arizona and southern California; March
15, Alabama, Georgia, North Carolina, Oklahoma, and southern New
Mexico; April 15, Maryland, Missouri, and Nevada; May 1, Penn-
sylvania, Indiana, Colorado, Idaho, and Washington; June 1, North
Dakota and Michigan; June 15, New York and Montana. Observa-
tions made by W. E. Dove in 1924 indicate that all larve of Z.
lineatum would have left the cattle in the vicinity of Aberdeen,
S. Dak., about May 5, and at Minot and Dickinson, N. Dak., and at
Moorhead, Minn., about May 10. The season, however, was more
advanced that spring than usual. On May 1, 1924, all grubs were
found to have emerged from cattle at Sioux Falls, S. Dak.

In general the duration of the infestation of the backs of cattle
in H. bovis is longer than in H. lineatum. This is brought about
through the longer developmental period of the larve in this situa-
tion and the wider spread of time between the date the first larvae of
fT. bovis reach the back and the date the last ones appear there.
The writers’ records indicate that the earliest larve of H. bovis reach
the subcutaneous tissues from one to two weeks after those of Z.
lineatum. On the other hand, the larve of H. lineatum arrive in
that portion of the host in much larger numbers proportionately
during the first month or six weeks following their first appearance.

The writers have checked closely the earliest appearance of larvee
of H. bovis in the subdermal tissues, as well as the time of dropping
of the last grubs in herds of cattle in New York during three seasons.
The earhest appearance of H. bovis was February 2 in 1923 in
Orange County, N. Y. In 1920 they appeared about February 26,
and in 1922 about February 22. At Herkimer they first reached the
subdermal tissues about March 8 in 1920, April 15 in 1921, and

THE CATTLE GRUBS OR OX WARBLES 79

February 20 in 1923. The last date on which a third-stage larva
was observed to reach the region of the back was June 6, 1922, at
Middletown, N. Y. The record of earliest dropping of a mature
erub of this species at Middletown was April 11, in 1923. Emer-
gence from the host probably begins rather later than this on the
average. In New York the maximum number of grubs of this species
in hosts occurs about May 1. :

Judging by collections and observations made in other States
the seasonal occurrence of H. bovis tallies rather closely with that
noted in New York. One record of earlier appearance has been
made in western Pennsylvania, where in 1916 the grubs reached
the back about January 25. That year grubs seemed to have been
exceptionally early, especially in the Northeastern States. The dates
of earliest appearance in the backs of cattle as calculated from ob-
servations and collections in some of the infested territory are as
follows: Maine, February 15; New Hampshire, February 8; Ver-
mont, February 20; New Jersey, February 10; Ohio, February 8;
Indiana, February 3; Illinois, February 5; Michigan, February 25;
Wisconsin, March 2; Iowa, February 15; Wyoniing, February 15;
Washington, February 8. These dates are presented to give a
- general idea of the time of earhest appearance of larvee of H/. bovis
in the subdermal tissues. It is recognized that they are not based
on continuous accurate observations and that they will vary in
different parts of a State and during different seasons.

The date when all the grubs leave the host has been found to
vary widely and in general to be much later than has been sup-
posed. In New York in both Orange and Herkimer Counties most
of the grubs are out of the backs of cattle by August 1, but
healthy specimens have been taken as late as September 2 in 1922
at Middletown and August 30 during the same year at Herkimer.
Collections of H. bovis made by W. E. Dove at Aberdeen, S. Dak., on
April 21, 1924, indicate that the cattle would be free from grubs in
that locality about May 15. |

It is worthy of note that the development of grubs in cattle in-
fested in the North and shipped into the South agrees closely with
that which occurs in the native habitat of the species. For instance,
infested cattle shipped to Miami, Fla., from Syracuse, N. Y., during
the winter showed a good infestation of well matured grubs on
May 25. Larve of H. bovis in cows shipped from Michigan to
Dallas, Tex., continued to develop and emerge normally up to June
3, when the last one dropped. |

In Ireland, Carpenter, Phibbs, and Slattery (19) record the
presence of larvee of H: ineatum in the backs of cattle on March
29, and a few larve of H. bovis were still present on June 10.
Lehmann (49) and Vaney (105) found the highest percentage of
grubby hides to occur in July in the Lyonnaise region of France.

NATURAL CONTROL

The combined action of all agencies of natural control has a
marked effect on the abundance of both species of Hypoderma.
This is true even in areas where the pest is at its worst.

SO BULLETIN 1369, U. S. DEPARTMENT OF AGRICULTURE
DESTRUCTION BY BIRDS AND MAMMALS

Birds undoubtedly destroy many larve as they drop to the ground
after emerging from the backs of cattle. The pupz also are subject
to attack, since they often remain exposed on the surface of the
soil or only slightly covered. Several instances were observed
in New York in which robins (Planesticus migratorius) devoured
larvee of H. bovis with avidity. In one case a larva under observa-
tion as it burrowed into the soil was seen by a robin sitting on a
fence. The robin flew down, picked up the larva, and escaped with
it before the bird could be frightened away. ‘This larva was almost
covered by the soil as it burrowed in. Species of the larger ground
birds undoubtedly destroy many larve. Henry Polson of Mountain-
view, Wyo., makes the following statement: “ Sometimes magpies
pick holes in the backs of the cattle, trying to get the grubs out,
causing sores.” In rather extensive observations made by one of
the writers in areas where magpies (Pica pica hudsonia) abound,
this action has not been seen, hence it is thought to be rare.

Many larve which emerge from cattle in the barnyards where
poultry range are destroyed by fowls. Chickens have been observed
to devour greedily considerable numbers of mature larve when fed
to them.

It is probable that small rodents destroy. many larve and pupe.
Stegmann (94) states that the pupe on the ground are destroyed

by moles.
INSECT ENEMIES

No predacious insects have been observed to attack the larve or
pups of Hypoderma in the United States, and it is thought that
they are not an important factor in control.

No parasites have been found in nature, but very few pupe have
been recovered after exposure in fields. The writers have reared a
considerable number of specimens of Vasonia brevicornis Ashm. from
pup kept in screen cages in an outdoor insectary, in more or less
close association with parasitized pupe of muscoid flies.

A, Gansser, of the Warble Committee of Switzerland, states in a
letter that he thinks that a hymenopterous parasite which has not
been determined is an important factor in control in that region.

FUNGOUS GROWTHS

The writers have observed the growth of molds on and in the
puparia of Hypoderma, and there is some reason to believe that the
insects may be attacked in some cases. Lucet (63) expresses the
opinion that in France certian fungi destroy the pupe.

EFFECT OF SUBMERGENCE ON LARVZ AND PUPZ

In 1921 a considerable number of extracted larve of H. lineatum
were submerged in water for periods ranging from 3 to 23 hours.
These periods apparently had very little effect on the larve; at least
the percentage found dead at the end of three days was not greater
than in the untreated groups. During 1922 five mature larve were
submerged from 114 to 19 hours. The larva submerged the shortest
period produced an adult in normal time, but the four submerged

Press ys
~<
owes sis

THE CATTLE GRUBS OR OX WARBLES S81

614 to 19 hours failed to transform. In 1924 six larvee which had
emerged normally from a host were submerged in lots of two for
94, 30, and 40 hours. Adults emerged from all of these in normal
time. Two pup were also submerged for 30 hours and both trans-
formed to adults.

Six mature larve of H. bovis were submerged in water for periods
ranging from 49 to 122 hours. All except one, which was submerged
for 121 hours, produced adults in about the normal length of time.

From these tests it is clear that these stages are not easily drowned,
and this might enable them to survive carriage for considerable
distances by flood waters.

CLIMATIC CHECKS

Climatic conditions undoubtedly have a marked effect on the ©
distribution and abundance of Hypoderma. The relationship be-
tween climate and the distribution of the two species of Hypoderma
has been discussed in a general way under the heading “Distribution.”

One of the writers (4) has made the statement that he believes
that climatic barriers have prevented the general dissemination of
H. bovis throughout the United States. He says,

One explanation of this possible barrier will be found in the fact that H.
bovis is generally later in emerging from the backs of cattle than H. lineatum.
The grubs emerging from the backs of cattle shipped to the Southern States
would, on account of their later emergence, encounter excessively hot weather,
and this may account in part at least for the failure of the species to es-
tablish itself in the warmer portions of the country.

No facts appear to have come to light since the publication of the
foregoing statement which would tend to disprove this conclusion.
H. tineatum establishes itself in new sections with less difficulty, and
uninfested areas are less general with this species. It must be recog-
nized, however, that meteorological conditions are potent factors in
limiting its abundance as a parasite of cattle.

Climatic conditions appear to have very little direct effect upon
the development of the grubs within the host. Climatic influences
are therefore restricted to the portion of the year when the insects
are separated from their hosts; that is, while they are in the pupal
and adult stages. 3

Among the several meteorological factors which affect Hypo-
derma, rainfall and humidity during the pupal and adult stages are
probably the most important. It has been found that where the soil
beneath pupze is kept very moist the mortality is extremely high.
Under such conditions some of the insects appear to die before
development has proceeded very far, and others transform to adults
but are unable to escape from the puparia. This appears to be due
to the large size of the abdomens, which are not reduced sufficiently
through evaporation to allow them to be withdrawn from the pu-
paria. Ileavy rains coming at the time the adults emerge may de-
stroy many of them, and continuous rainy or even very cloudy
weather after the emergence of the adults will prohibit oviposition.
Since the longevity of the flies is limited, adverse weather conditions
of comparatively short duration will prevent individuals from ovi-
positing. Owing to the fact that large numbers of flies usually

58252 °—26—_6

82 BULLETIN 1369, U. S. DEPARTMENT OF AGRICULTURE

emerge at approximately the same time, regardless of the time the
pupe may have been formed, rainy weather immediately after
emergence of one of these large groups of flies may affect materially
the infestation of the following year.

Clouds have been mentioned as being a factor in repressing ovipo-
sition. Their influence is felt only by the adult insect, as cloudy
weather in the absence of unusual precipitation does not seem to
affect the development of the pups, except possibly to prolong
slightly the pupal stage. i

Winds apparently have a double influence: In the first place
they cause a more rapid drying of the surface soil, which would
benefit the pupz; and secondly they have an adverse effect upon
oviposition, since the flies, especially those of H. lineatum, will not
oviposit freely in a strong wind. ‘This influence is less potent than

the others, however, since it is not so generally operative. Cattle §

congregated in places protected from the wind are frequently at-
tacked by heel flies.

Temperature conditions probably rank next to precipitation in
their effect on these species. Periods of unusually warm weather
in the winter or early spring often tend to cause the emergence of
flies which are destroyed by succeeding days of cold or rainy weather.

As is generally known, warm bright days are most favorable for
the activity of H. lineatum. It is probable, however, that during
periods of high temperature, that 1s, when the daily maxima run
above 95° F., the total number of eggs laid by a fly is reduced.
When such higher temperatures are reached, oviposition occurs
mostly before the hottest part of the day. The destructive effect of
the direct rays of the sun on both H. lineatum and H. bovis is appar-
ent when caged flies are placed in the sun during moderately warm
weather. They become very active and fly most of the time, soon
weakening and falling to the bottom of the cage where they die,
sometimes very suddenly.

Oviposition of “7. lineatum takes place at surprisingly low tem-
peratures if the sun in shining. Often adults are active during the
day when the minimum temperature in the morning ranges between
19 and 22° F. Flies have been observed to oviposit when the tem-
perature was as low as 45° F., the maximum temperature for the
day being 46° F. There seems to be no doubt that heat is an im-
portant factor in restricting the southern spread of ZH. bovis.

Mature larve and pupe can withstand rather low temperatures.
The pups appear to be more resistant to cold than the larvae. A
considerable number of observations have been made by the writers
on the effect of cold on these stages of H/. lineatum at Dallas, Tex.,
but the minimum fatal temperature has not been determined with

accuracy. In 1918, when a minimum temperature of 3.5° F. was -_

reached, the larval and pupal transformations of a number of speci-
mens was under observation. Considerable protection was aftorded
these and a good percentage of adults emerged. Among a number of
larvee and pup exposed to 9.5° F. an adult emergence of 54.5 per
cent was secured. In other series of specimens which experienced
minimum temperatures of about 19° FE. approximately 68 per cent
produced adults. This is not much below the percentage of emer-
gence under outdoor conditions where the temperatures do not drop

THE CATTLE GRUBS OR OX WARBLES 83

_ below freezing. A mature larva of H. lineatwm placed in a freezing
room for 24 hours at a temperature of about 7° IF. failed to pupate,
whereas a fresh pupa exposed in the same way produced a normal
adult. Nine mature larve of H. bovis subjected for from 24 to
26 hours to temperatures in a freezing room of 7 to 9° F. failed
to pupate. Five larvee of this species placed in the room at 25
| to 29° F. for 26 hours gave an adult emergence of 80 per cent, and
five larve kept at from 32 to 33° IF. for 14 days pupated promptly
upon removal and 60 per cent emerged.

SOIL CONDITIONS AND DRAINAGE

Naturally soil character and drainage are linked with rainfall
in their relationship to Hypoderma. The writers’ observations in-
_ dicate that porous, well-drained soils are more favorable for Hy-

‘poderma than heavy, flat-lying lands.

In the valley of the Red River of the North, where Hypoderma
seldom occurs, there is probably a soil condition which prevents
fully developed larvee from producing adults. It is known that
animals infested with Hypoderma have been shipped into that sec-
tion, but the pest has never become well established.

HOST RESISTANCE AND OTHER CONTROL FACTORS

The great disparity in the number of grubs found in different
cattle in the same herd is well known. The writers’ investigations
indicate that this difference in degree of infestation is brought
about by a combination of several causes. Probably the main rea-
son why one animal will show a heavy infestation of grubs while
another will be free from grubs or comparatively so, is that there was
a marked difference in the number of eggs which were attached to
them. The reason why one animal may receive a much larger
number of eggs than another, however, is not altogether apparent.
Certainly the element of chance enters here strongly. The indi-
vidual idiosyncracies of the animals are also factors. Some ani-
mals seem more able to detect the presence of flies than others and
secure protection from them.

A large series of observations made on individual animals year
after year shows that the extent of infestation may vary greatly.
The writers have found, however, that certain animals are uni-
formly resistant to the grubs from the time the eggs hatch to the
time the larvee complete their development or die within the host.
This individual resistance is probably due in a large measure, as
pointed out by Hadwen (35, 40), to eosinophilia. That there is
a very definite reaction against the larve is apparent when they
penetrate the skin of such resistant hosts. The exudate at the point
of entrance is usually more profuse than ordinarily, and the infil-
tration of the connective tissue beneath is pronounced. Apparently
this strong reaction against the invading parasite is present
throughout its course in the body of the animal. It is after the
larvee have reached the subcutaneous tissues of the back, however,
that the destruction of the larve is most apparent. The reaction
against the larve appears to differ considerably in different hosts.
In some, large swellings occur; in others, the reaction seems to be

84 BULLETIN 1369, U. 8. DEPARTMENT OF AGRICULTURE _ '

more localized. In the latter case there is a tendency for the skin
to close the grub opening and cut off its air supply. In certain ©
animals there is also a strong tendency to form pus in and about ©
the cyst, and in such cases the grubs usually die. The writers’ obser-
vations show that the mortality in the subcutaneous tissues of the
back is very high. Their figures indicate that 60.5 per cent of those
which have cut holes through the skin die before reaching maturity.
Of this percentage approximately 16 per cent succumb in the third .
stage, 46 per cent in the fourth stage, and 38 per cent in the fifth
stage. It appears also that occasionally third-stage larve which
reach the subdermal tissues die before they succeed in cutting
through the skin.

There is a marked difference in the degree of infestation of
animals of different ages. Young stock, notably animals from 1 to
3 years old, almost always show a higher percentage of infestation
than mature animals. There is also some reason to believe that as
cattle become very old the degree of infestation is again increased.
Seymour-Jones (97) advances the theory that in young stock the
tenderness of the muscle (panniculus carnosus) immediately under
the skin enables the grubs to penetrate them, whereas in older cattle
they do not all get through. |

Hadwen (35, 40) is of the opinion that the difference in de-
gree of infestation between young and matured animals may be
explained by a gradual development of immunity following the
repeated attacks of parasites. He believes that a first invasion of
parasites in an unresisting host stimulates the production of both
antisubstances and eosinophiles to neutralize their cast-off products,
and in addition to this, that there must be a third substance which is
antagonistic to the parasites themselves; he believes that this sub-
stance is secreted by the eosinophiles, and that it paralyzes or kills
the parasites which are surrounded by the eosinophiles in the tissues.

The writers believe that the difference in the number of grubs
found in young and old cattle may be explained in part by this _
reaction, but that other factors enter into the question. In general,
young animals are more exposed to the attack of the flies, both be-
cause they are not housed so long in the spring and because they are
seldom placed in barns during the time when the flies are oviposit-
ing. It is also true that the young stock are frequently not as well
fed as the older animals. The statement is made frequently by
dairymen and stockmen that poor animals are more heavily im-
fested than fat ones. The writers have observed many instances in
which very fat animals were fairly well infested with grubs, but
their observations indicate that the poor cattle are usually more
heavily infested. It appears logical to believe that well fed, healthy
animals have more natural resistance to grubs than those in poor
flesh and with lower vitality. It is also certain that cattle in an
extremely impoverished condition will fall more ready prey to
the flies at the time of oviposition. It seems evident, however, that
the presence of a large number of grubs, especially in cattle not re-
ceiving an optimum amount of feed, will reduce flesh condition.

No marked difference in susceptibility seems to exist in different
breeds. When water or shade is readily available it serves as a
means of partially protecting from infestation the stock which have

a)

THE CATTLE GRUBS OR OX WARBLES 85

access to it. Large numbers of grubs and pupz are destroyed by
the walking of the catile, especially in pastures where the animals
are concentrated.

ARTIFICIAL CONTROL

In considering control or eradication it should be borne in mind

] that the flies do not feed, nor have any habits been noted which

could be utilized in accomplishing their destruction. The flies
also do not seem to be sensitive to the presence of foreign materials
on the host, and therefore are not easily repelled. The egg stage
is comparatively short, hence any treatment directed against it must
be applied frequently. During the greater part of the year the
larve are protected within the body of the host; that is, from the
time of penetration immediately after the hatching of the eggs

| to the appearance of the third-stage grubs in the subdermal tissues

of the back. There is, however, a rather definite period, usually
not exceeding four months, during the fall, winter, and spring,
varying according to latitude, during which the grubs are localized
in the backs of the cattle where they may be reached through the
apertures in the skin. The fact that both species are practically

f incapable of developing in hosts other than cattle is also a point
|, of distinct advantage in any control procedure attempted.

POSSIBILITIES OF CHECKING THE SPREAD OF HYPODERMA

No effort has been made in this country to check the spread of

|. either species of Hypoderma. In fact H. lineatum appears to have

long since established itself in all parts of the United States where it
is capable of existing. HH. bovis, on the other hand, is much more re-
stricted in distribution and it appears that it is capable of becoming
much more widely disseminated in this country.

It is probable that H. bovis, which at this time occurs west of the
Mississippi River only in scattered localities in the Northern States,
may cover that region solidly and extend its range well south along
the mountain ranges. Hewitt (42, 43, and 44) and others have
stated that Hypoderma appears to be increasing in abundance in
Manitoba. ‘The importance of /7. bovis as a cattle pest is sufficient
to warrant serious consideration of ways and means of checking its
spread in this country. It may not be advisable to take legal steps
to meet the situation, but certainly stock raisers should recognize the
danger of bringing cattle infested with H. bovis into regions where
that pest does not exist, and take due precautions to destroy all grubs
which reach the subcutaneous tissues of the backs during the spring
and summer following the arrival of the cattle. Certain uninfested
foreign countries have enacted legislation designed to prevent the, es-
tablishment of Hypoderma. Australia (2), for instance, has a law
prohibiting the introduction of cattle from the United States, the
British Isles, and other infested countries except during the period
from December 1 to May 31. Present knowledge of the seasonal
history of Hypoderma shows clearly that such a restriction would
not give a complete protection against the introduction of the pests.
It would appear, however, that some system by which the animals
could be kept under surveillance and all grubs destroyed during
the period of one full year after importation would be effective.

= peers a.

Dene cere iat ce ey

<
Be ee re

86 BULLETIN 1369, U. S. DEPARTMENT OF AGRICULTURE

EFFECT OF BURIAL ON LARVZ AND PUPZ

It is difficult to say just what degree of control is effected through
plowing. From reports on the abundance of grubs in cattle in the §
Central States in the eighties as compared with the number of grubs
in the same regions now, it apears that there has been a decrease in
abundance. Many think that the restriction of pastures to compara-
tively small areas and more general and intensive cultivation are
largely responsible for this. It is reasonable to suppose that plowing
fields where larvee and pup occur would destroy many of them.
Several mature larve and freshly formed pupe of H. lineatum
were buried in sand and black clay soil, at depths of from 2% to 4
inches. In most instances the larve worked their way to the surface
in a short time and pupated on top of the soil. In the black clay the
flies emerged in about the normal time and pushed out of the soil

even when the pupe were buried to a depth of 4 inches. In the fine ©

sand, however, the flies were found to have emerged and worked up-
ward about half an inch from the puparia, where they died and were
found later with a comparatively hard cell of sand formed around ~
them.

Many larve in pastures undoubtedly become covered with manure
as are those that drop in barns and are shoveled out with the dung.
To test the effect of burial under such conditions four mature larvee
were placed on a board and a large fresh cow dropping was laid on
them. None of them moved from where they were placed. Three
of them died without pupating and the other died as a half-developed
fly. This preliminary test probably indicates that burial in fresh
cow manure is very destructive and that many larve are destroyed
in this way, since often a large percentage of the grubs leave the
hosts in the barns.

Some larve of H. bovis buried from 1 to 6 inches in both clay and
sand came to the surface, while others pupated near where they were
buried. Some flies emerged from pupe buried to a depth of 6 inches,
but apparently the burial below 3 inches was detrimental, especially
if the soil was very moist.

PROTECTION OF CATTLE BY HOUSING AND NATURAL BARRIERS

There are abundant examples of the great reduction of infestations
effected by housing the herd during the periods of fly activity. Some
dairymen leave their barns open or provide sheds which the cattle
can enter when attacked by the flies. The flies, however, have con-
siderable opportunity to deposit eggs on the cattle before they can
get into the buildings. Such an arrangement has the advantage of
allowing the cattle to excape from continued annoyance and fright,
which is inevitable when no protection is afforded. Since the flies
will oviposit in the broken shade supphed by trees, the presence of
woods in a pasture will not greatly reduce infestation, but is bene-
ficial in that the worry to the catttle is lessened. Streams afford
effective protection against H. lineatum, but less against H. bovis.
The excitement, however, is greatly relieved and milk flow main-_
tained when cattle have access to streams or ponds. There is danger
of some injury to cattle, however, from standing in mud and water
for long periods when weather is favorable for continued fly activity.

THE CATTLE GRUBS OR OX WARBLES 87

The construction of sheds is advisable where they will perform

the double service of protecting the stock against heel flies and from
adverse climatic conditions.

REPELLENTS AGAINST HEEL FLIES

For many years various ill-smelling applications have been used

_ with the view of protecting cattle from the attack of heel or warble
fiies. Prior to the last few years, during which our knowledge of
_ the life history of these pests has clearly showed that the eggs are
_not deposited on the backs of the cattle, it was the custom to use
\ yarious repellent smears and washes upon the backs of cattle. As
it is now known that the eggs are deposited largely on the legs and
_ lower portions of the body, the futility of this practice is at once
_ evident. Inquiry into the results of the application of fly sprays
_ has led the writers to conclude that the claims that they are efficient
_ against grubs are unfounded.

The fact that the adults of Hypoderma do not partake of food

would suggest that their reaction toward attractant and repellent
. chemicals or other substances would be less than in those species
» which have the senses developed to aid them in finding food or breed-
'ing places. The writers’ experiments and observations along this
' line seem to bear out this conclusion. It appears probable that the
| application on the animals of materials which tend to cover the hair
or mat it together may affect oviposition more than those materials

possessing various odors supposed to be repellent. The experiments

/ in this field, however, have not been sufficiently extensive to enable
| final conclusions to be drawn.

During 1919 a dairy herd of 61 animals was used in tests of the

_ application of repellents and solvent solutions, as follows: 2 per cent
- compound solution of cresol, 10 per cent solution of acetic acid, un-

diluted fuel oil (petroleum), and a mixture of 1 gallon of fish oil

_ with 1 pint of commercial pine tar. These materials were applied

to the legs of cattle, some with a spray pump and others with a
brush. The applications were made at about 4-day intervals during
the period when heel flies were active. While the treatments were

| being administered heel-fly eggs were found on several of the treated

animals. Some were even present on the legs of those treated with
petroleum, and on those treated with a mixture of fish oil and pine
tar.

Observations made incidentally in the experiments discussed under
“ Destruction of eggs or larvee by the use of wading vats” indicate
that the application of 2 per cent coal-tar creosote dips at 4-day in-
tervals has no marked effect in repelling flies. The same is true of
wading-vat experiments with arsenical solutions.

On a number of occasions where cattle waded and got their feet
and legs well covered with mud the flies were found to deposit their
eggs Ireely on the legs above it. The application of gummy mate-
vials to the entire animal has not been tried, but this would hardly
seem feasible from a practical viewpoint.

DESTRUCTION OF EGGS OR LARV BY THE USE OF WADING VATS

The fact that a considerable percentage of the eggs of Hypoderma
are laid on the lower legs at once suggests the possibility of destroy-

|

88 BULLETIN 1369, U. S. DEPARTMENT OF AGRICULTURE =|

ing the eggs or young larve as they hatch, by applying insecticides
to those portions. One of the most convenient and effective methods
of accomplishing this is through the utilization of shallow vats.
In 1918 experiments were begun to determine the effect on the
infestation of dairy cattle of the use of standard arsenical solution.
One-half of the cows in a dairy herd was allowed to pass through ~
a wading vat containing the solution about 1 foot deep, at invervals
of four days. The other half of the herd was not treated, being
kept as a check. In the first year’s test 16 cows were treated and
the following season these were found to be infested to almost iden-
tically the same degree as the 16 cows which were not treated. In
1919 the same herd was utilized in a test under similar conditions,
a standard sodium arsenite solution containing about 19 per cent
arsenic trioxide being used in the vat. The following season the
dipped cows had an average infestation of 7.18 grubs per animal
and the untreated cows showed an average of 5.65 grubs per animal.
During the spring of 1920 the same herd was again utilized in the
same way, except that 18 cows were treated. For charging the
vat in this experiment a commercial arsenical dip was used which
in concentrated form was said to contain about 9 per cent of cresol
salts. In the first two treatments the strength of the solution was
about 0.19 per cent arsenious oxide. Subsequently this was raised
to approximately 0.22 per cent. The following spring the treated
cattle showed an average infestation of 2.5 grubs per head and
the untreated ones an average infestation of 3.33 grubs each. During
the spring of 1919 another dairy herd was utilized. Thirteen cows
representative of the herd in age and breeding were passed through
a wading vat at 4-day intervals and 14 cows were utilized as a
control. In this case the vat was charged with a commercial coal-
tar creosote dip diluted to about 2 per cent. The following season
a careful check of the grubs in the treated cattle showed an average
of 6.58 per animal, and the untreated animals showed an average
of 3.84 grubs each. The following year a similar test was carried
out at the same dairy. A count of the grubs present in the treated
and untreated groups made on December 30 showed an average of
6 per animal in the case of the former group and 8.14 in the latter.
In a subsequent examination made on February 7, the treated animals
showed an average infestation of 2.75 grubs each and the untreated
animals an average of 2.67 each.

It is possible that better protection would be afforded should the
dipping be done every day. It would not be feasible, however, to
dip so frequently with the strengths of solutions used and endeavor
to cover a greater portion of the legs by having the solution deeper
in the vats. In the experiments mentioned, the walking of the cows
through the vats, which were 10 feet long at the bottom and 18 feet
long at the top, brought the material into contact with the legs con-
siderably higher up than the actual depth of the dip (1 foot). In
fact it was found that the udders and bellies of the cattle were fairly
well drenched, especially on the cows that were inclined to hurry
through the vat.

Imes and Schneider (48) have published results of tests with the
application of used automobile cylinder oil, sodium silicate, and coal-
tar creosote dip by spraying and wading the cattle through vats

THE CATTLE GRUBS OR OX WARBLES 89

similar to those used in the experiments described above. They con-
cluded that the treatments had a very material effect on the infesta-
tion the following season. Since only 10 animals were used in the
| test the great variation in the degree of infestation may readily be
due to causes other than the effect of the treatments. Subsequent ex-
periments conducted by the Bureau of Animal Industry, however,
are said to show that a satisfactory degree of control may be brought
about in range cattle through the use of wading vats (68).

Studies of the distribution of the eggs of both species of Hypo-
derma made by the writers show that a large percentage of the eggs
are deposited elsewhere than on the legs. This is particularly true
with H. bovis, which deposits many eggs above the hock joint. It is
also the case with the deposition of eggs on dairy or quiet farm cattle
by H. lineatum. As has been pointed out in preceding pages, the
flies often approach such cattle while lying down and deposit large
numbers of eggs on the escutcheon, tail, and elsewhere, all of which
would be unaffected by dips apphed in wading vats.

LABORATORY TESTS OF DIPS ON EGGS OF HYPODERMA LINEATUM

Several authors have suggested the use of sprays or washes con-
taining materials designed to dissolve the attachment of eggs of cer-
tain species of Oestridae. Acetic acid is one of those which has been
advocated for this purpose. ‘Tests were conducted during 1919 in
which eggs of H. lineatwm were submerged in a 10 per cent solution
of acetic acid for periods varying from 3 minutes to 5 days. Follow-
ing this treatment the eggs were allowed to dry for periods ranging
from 30 minutes to 13 days, and then the firmness of attachment of
the eggs to the hairs was tested by scraping and pulling them with
a dissecting needle or forceps. In every instance the eggs were found
to be firmly attached. In most cases the eggshells would tear in two
without their attachment to the hair being disturbed.

Hairs bearing eggs of H. lineatwm were also submerged for a few
seconds. in 2 per cent coal-tar creosote dips and kept in incubators to
determine if the eggs would be destroyed. In one of these tests 29
eggs were submerged three times for an instant in 2 per cent creosote
dip at 3 p. m. and then placed in an incubator at 90° F. The fol-
lowing morning one larva had hatched and was very active. During
the day a total of 21 larve hatched from these eggs and were appar-
ently normal. Twenty eggs from the same lot mentioned above were
given three dippings as in the previous lot and on the following
morning they were again dipped in 2 per cent creosote dip and
returned to the incubator. These did not begin hatching until the
afternoon of March 25, a full day later than those in the previous
lot which were submerged but once. Sixteen or seventeen larva,
however, hatched from the 20 eggs and all were apparently normal.
Another series of 26 eggs which were about one-half through their
normal period of incubation were dipped in a 2 per cent solution of
a coal-tar creosote dip and placed in an incubator. From these, 19,
or 73.08 per cent, of the eggs hatched normally. In still another test
34 eggs were dipped in 2 per cent creosote dip before they were due
to hatch. An hour later 10 larve had hatched and were active. No
other larve emerged, thus making a hatch of 29.4 per cent, whereas
in a check lot the hatch was 31.3 per cent.

nd caoaeer bate deieabaein aa amet eee pe TEESE TED EP re ~

A NE a ee ae

90 BULLETIN 1369, U. S. DEPARTMENT OF AGRICULTURE

In 1923 two series of tests were made. In the first of these 192
eggs deposited April 10 on cow hair were divided into four lots,
each of which was kept in an incubator at about 90° F. The check
lot contained 99 eggs. ‘These began hatching on April 13, and
45 per cent of them hatched. The other three lots were submerged
for one minute after they had been incubated for 1 hour, 25 hours, |
and 49 hours, respectively. The respective percentages of larve |
which hatched in these three lots were 42, 45, and 57.5. All of
these lots began hatching on the same date as the check.

The second series contained 74 eggs deposited on April 11, 1928;
18 of these were submerged for three minutes in a 2 per cent solution
of a coal-tar creosote dip on April 18. These began hatching in |
the incubator on April 14, and 44 per cent of the larve emerged.
The other eggs were kept in an incubator except for the time re-
quired to submerge them for one minute in crank-case oil, drained |
from an automobile. Of the 22 eggs dipped immediately after ovi- —
position none hatched, of the 23 eggs dipped 24 hours after being
laid 26 per cent hatched, and of the 11 submerged 65 hours after
oviposition none hatched.

ATTACK DIRECTED AGAINST HYPODERMA LARVZ IN THE BACKS OF CATTLE

A number of facts point to the practicability of combating this
pest by destroying the larval stages while in the subcutaneous tis-
sues of the back. Control by this procedure is favored (1) by the
fact that the species confine their attack almost entirely to cattle,
(2) by the fact that there is a rather definite and somewhat re-—
stricted seasonal occurrence of the larvee in that situation, (3) by
the presence of an aperture through the hide immediately over the |
grub during its entire existence in the subdermal tissue, and (4) —
by the fact that the larve are limited in their distribution to the |
back of the host between the withers and tail. In order to proceed
intelligently against the species in this situation it is necessary to
have very definite information regarding its seasonal occurrence in
the subdermal tissues in each section where control work is under-
taken, as also a knowledge of the developmental period in the sub-
cutaneous tissues, particularly as to the minimum time required.

The possibilities of attacking the species in this situation appear to
have been recognized in a general way many years ago. Work along
this line. however, has been of a very superficial and sporadic na-
ture, with the exception, perhaps, of that carried on in certain dis-
tricts in Denmark (6), Holland, and Germany (67 and 77.)

EFFECT OF MATERIALS ON LARVA REMOVED FROM HOSTS

In order to determine the toxicity of various insecticides and
other materials to the larvee of Hypoderma, a series of tests was
carried out in which larve in different stages of development were
removed from the backs of cattle and submerged in these materials.
This method of testing the insecticidal value of various chemicals
is open to objection, owing to the fact that the conditions are ab-
normal. Another objection to the use of larvee extracted from hosts
is that practically none of them will produce adults even though

THE CATTLE GRUBS OR OX WARBLES 91

kept under the most favorable conditions, hence there is difficulty
in determining the percentage of mortality chargeable directly to
the treatment. The tests made show clearly, however, that Hypo-
derma larvee, especially in the later stages of their development,
are very resistant to contact insecticides. In these tests some 25
or 30 different materials were used. Those were selected which
would seem to be adapted to use in the destruction of grubs in the
eysts in the backs of the hosts. The period of submergence in most
cases was about two minutes.

Mention will be made of only a few of the results obtained, since
it appears impractical to determine by this method the efficiency
of the various materials when applied to the warbles in the cysts.
In these experiments it appeared that the saponified coal-tar creo-
sote products gave the highest percentage of mortality within the
first 24 hours. Tincture of iodine U. S. P. also gave a high per-
centage of kill soon after treatment. Certain other materials such
as iodoform with neutral carriers and 5 per cent solutions of silver
nitrate destroyed a high percentage of the grubs but the action was
siower. To illustrate the resistance of the larve to the action of
certain insecticides it might be mentioned that submergence for
two minutes in such materials as crude petroleum and spirits of tur-
pentine killed a comparatively small number.

APPLICATION OF MATERIALS TO GRUBS IN THE BACKS OF CATTLE

Many years ago the application of various smears to the backs of
cattle was advocated by many, including such authorities as Ormerod
(77) in England. The object in view, however, was not the destruc-
tion of the larve in the subcutaneous tissues but the prevention of
infestation. In connection with their work the present writers have
learned of the use by farmers and dairymen of the injection of such
substances as kerosene oil and turpentine into the cysts for the pur-
pose of destroying the grubs. Some men have practiced this method
for years and are well pleased with the results. In Germany the
warble commission (67) advocated the application of birch tar oil to
the grubs individually in the backs of cattle. In Ireland and Eng-
land, as a result of experiments carried out by Carpenter (78), the
application of a tobacco decoction in the form of a wash has been
advocated. Réne (87) advises, among other methods of control, the
injection of 1 cc. of tincture of iodine into the warble.

Attempts to employ gas against the grubs in the backs of cattle
have been reported on by Greve (37) and Duncan, Hewitt, and Jar-
dine (28). ‘The results were not encouraging.

In their own work, experiments along these lines have been carried
out by the writers on a rather extensive scale since 1918. Most of
these tests have been conducted in a way which made it possible to
secure accurate records on the percentage of grubs destroyed by the
various treatments. In this work various dairy herds were utilized
in the vicinity of Dallas and other points in Texas, in Peoria, Ill., and
in Orange and Herkimer Counties, N. Y.

Three different classes of materials were employed—powders, oint-
ments, and liquids. The powders were usually applied directly into
the grub holes by means of a shaker can. The ointments were in

92 BULLETIN 1369, U. 8S. DEPARTMENT OF AGRICULTURE

most cases applied with the fingers, care being taken to press some
of the material into the apertures in the skin (fig. 34). The liquids
were applied with hypodermic syringes, a blunt needle being used
and care being taken not to injure the grub; with oil cans (fig. 35) ;
with eye droppers; or in the form of a general wash thoroughly ap-
plied to the backs of the cattle with a stiff brush. In preliminary
tests with all of the materials the cattle were numbered and a dia-
gram made of the distribution of the grubs on the back, each grub
being numbered and the stage of development determined before
the application was made. In some instances the hair was clipped
from around the openings in the hide; but the results in each case
were checked afterwards by the treatment of other infestations in

Fig. 34.—Applying ointment to grubs in back of heifer

which the hair was left undisturbed immediately around the holes
and the position of the grubs marked by clipping the hair below each
of them. In injecting the materials into the cysts an effort was made
to fill the cavity around the erub with the liquid. The average
quantity used was something less than 1 cubic centimeter per grub.
In order to determine the results of the treatment in the early experi-
ment, each grub was carefully examined from four to six days after
the treatment was made. Then the larvee were extracted and notes
made on their condition and the condition of the lesions produced by
them. Following the preliminary tests, large numbers of grubs were
treated without determining the stage they were in or otherwise in-
terfering with them before the application. The percentage of mor-
tality in some cases was determined merely by continued observation

" THE CATTLE GRUBS OR OX WARBLES 93

of the larve zn situ. In such cases the observations were continued |
for several weeks to determine the effect on the host of the destruction
of the grubs by this method. In order to make accurate observa-
tions on the killing power of the various materials used, most of
these were administered after the major part of the grubs had
reached the fifth or last stage. In most cases a sufficient number of
erubs were in the younger stages so that the effect of the various
materials upon them could be determined. The tests indicated that,

although the younger stages may be more susceptible to the action

Fic. 35.—Injecting Hypoderma cysts with chemicals by means of an oil can

of the insecticides, in those stages they are probably more protected
against the materials, since the apertures in the skin are usually
much smaller.

Most of the tests in which the results were carefully checked are
given in Tables 11 and 12. It will be observed from a study of the
results that a number of the materials will produce a mortality above
80 per cent. The writers are of the opinion that materials which
will not accomplish the destruction of at least 80 per cent of the grubs
present should not be considered as practicable. On the other hand,
some of these materials which gave a very high percentage of de-
struction are not adapted to use in general practice on account of the
cost.

94

BULLETIN 1369, U. S. DEPARTMENT OF AGRICULTURE

TABLE 11.—Treatment of H eee hmeosuin in the backs. of cattle, Dallas,

=i
2121 Num- | Num: | Num-
3| S| y ber of | ber of - =
2) 2 tee pikstherabe peed ets
ow oiled not |doubt-| Stubs age
EIS killed | ful | 20R° |kille
Material and strength How applied S| & | —
S| —
ss 5 Stage | Stage | Stage | Stage dead
| 2 an
5 | E | l at | alive
zi 5 13/41 5 3 4/5|3/4/5|
fers va Satie al geal feel (| fas)
Argyrol, 10 per cent solution __-_-.--| Dropper, in hole -____- 2) 6] 0} 0} 6.0) O| 00 0 0! 0} | 0.100. 00
Breulce solution, 0.182 per cent | Syringe, in hole---____- I “| 0} 0} 3] O} O} 28) oO} ce 0} 05 9.68
As203.
Arsenical solution, 0.222 per cent |_____ dO:22— 2 eee 14) 28! 0} oO! -7| 0} 0} 3] Oj O6l Oo ° 2: 70. 00
ASs203. |
DG eee, ei ees Wash on back________- 2| 61] 0} 1] 0 ols1| 29! ol ol | 0] 0] | 1.65
ADD) es ee Sa ek es ee Wash, 2 applications, |14/100) 2) 10) 11) 0/21) 56) 0} 0| 0} 0} 0} 0} 23.00
b : 2 days apart. |
Arsenical solution, 0.237 per cent | Wash on back____-____ 7| 39} 0} 0} 1) 0} 0} 36} O} 0} O} O! O} 2] 2.70
As203. |
Benzol290iper cent == =--_ 3 Injected with oil can __| 8/115) 0} 11) 88) 0} 1; 5) 0} 0 0:0 010, 94. 29
Benzol, 100 per Celt a eee ee 03263 ee 56 240) 0 31/189) 0} 0} 8) 0 0} 3} O} O} 9} 96.49
Borax, saturated solution__________- Tate withisyeee- 2 13) 72) 0} 0} 3} 0} 6} 20) 0,18 16) 0} O} 9} 10. 34
Boracic acid, saturated solution ____|____.do________________- 2} 63} 0} 0} 3) 0/10) 23} 1) 9] 9) O} O| 8} 8.33
Carbolated petrolatum, 1/4 per cent_ Pea into holes_____ 5] 62).1 0 4) 1/31) 25) 0} 0) 0} 0} 0} O} 8.06
Carbon tetrachloride Siete eee Injected with oil can __|71/375) 0} 31/298) 0} 0} 8} 1) 0.10) 0} 2:25] 97. 63
Chiorotonntr Ce Re = eae See Injected with syringe__| 6} 24 0 0! 16 0| 0: .0} 0} O' 8} O; OF 0/100. 00
Gone aie bse saturated solution _|____- Ge nee Te es 10} 59| 1} 1] 31| 0; 0! 1) 0| 520) 01 O| O} 97.06
Caen acid, crude, 1 part; paraffin| Injected with oil can__j}11} 65} 0}; 5) 20} 0} 2; 26, 0) 0 0 9 0}12) 47.17
oil, 10 parts. :
Creosote oil (wood) _______----__._- [ess does Soa 77! 0} 4} 25] 0! 0: 28! 0] 0 O| O; 0/20) 50.88
Cresol compound, U. S. P. ce wee dose ae ra 52) 0] 0} 19] 0} 0} 7 0} 719) 0; O} 0} 73.08
water, 10 parts. : |
Cresol compound, U. 8. P., 1 part; |____- COLE) a 7/122, 0} 2) 16; 0} 3, 65) 0} 0, 0} O 0/36) 20.93
water, 5 parts. |
A ae compound, 1 part, water, | Injected with syringe__/45 136, v 12} 91} O} 1) 15 0} 2) 3 ° 0} 9) 84.48
parts. ; |
1) OS ee | ed eee ener Injected with oil can__| 8) 19] 0| 0) 12} 0| 0 7 0| 0 0 O O} O 63.16
WD Obs - ee es ee ee Injected with syringe__|15) 79) 0) 4) 54! 0} 0) 7| 0) 5 9) 0; O| 0} 89.23
A cresol Compound, 1 part: water, | Injected with oil can__|17|185] 1| 19|108| 0 0 S| 0| 0.0 y 0/24! 79. 50
part
CEESO8 dip (coal-tar), 1.66 per cent | Wash on back_________ 18/115} 19 178 | 0] 0| O| 128 | 10.34
solution. : |
Crees one dip (coal-tar), 8 per cent | Injected withsyringe__} 6} 46) 0 5) 27 a 0} 2) 0} 210 y 0} 0} 94.12
solution.
Cresol ointment, full strength ______ Pressed into holes_____ 12} 90} 0| 2] 51] 0} 0; 7 O} 1/29) Oj O} O 88.33
Derris extract (proprietary), 1 part; | Injected with oil can__/15) 97) 0) 14] 81; 0) 0} 0} 0} O 0; 0; O} 2)100.00
water, 10 parts, plus 4 ounces Soap
os gallon. | :
erris extract (proprietary), 2 per | Wash on back_________ 18/108) 0; 6] 7] 0} 3} 80} 0; 0} 1} O} O}11) 13.54
cent in water, plus 4 ounces soap |
per gallon. :
Derrisipowder,dry==—— Dusted into hole______ 22/133) 0} 7/110} 0) 0} 6 0| 2 1) O} O} 7} 95.12
Derris powder, 1 part; paraffin oil, jected with oil can __ i 24! 0} +5} 19; 0} Q} O ° 0, 0} 0} 0} 0/100. 00
5 parts.
Derris powder, 1 part; petrolatum, | Pressed into hole______ 76|234| 1220 15 0} 0 0} 0} O} 8) 97.77
2 parts. | |
Derris powder, 1 part; petrolatum, |____- GO s0 2h: BP eee a 82) 0 3 76, 0 0 1) 0} O 0} Oj O 2) 98.75
5 parts. |
Derris powder, 1 part; petrolatum, |____- GO Beggars 33/123] 5} 41) 66} 0} 0} 3} 0} 0; 1] 0} O 4 97.39
10 parts. | | |
Derris powder, 1 part; petrolatum, |____- GOs et et ee 15] $2) 2 43 40} 0) 0 3 0} 0} 2) 0} 0 | 96. 59
15 parts. |
Derris powder, 1 part; petrolatum, |___-- GOES. Soren Re 3} 82) a 2 25! 0} 0} 0} 0} O} 0} 0} 0} 0/100. 00
20 parts.
Derris powder, 8 ounces;soap, 4 | Wash on back, 2 appli- | 4 11} 0} 0} 7} 0| 0} 0} 0} Oj O} O} OF 4/100. 00
ounces; water, 1 gallon. cations. | } |
DOS. 2 St ote tig er eee eek Wash on back, 1 appli- |1 gli09 ie 134 | 0} 0} 0} 110 | 65.66
cation.
Derris powder, 12 ounces;soap, 4 | Wash on back, 2 appli- | 3 21! 0! 1) 19} 0} 0} 0} 0 0} 0 al 0} 1,100. 00
ounces; water, 1 gallon. cations. | Saat }
WO!. 2228 Se ee Wash on back, 1 appli- 2 ae 1| 51,137) 0} 0} 2/ 0} 0} 0} 0} 0; O} 98.95
cation. | |
Derris powder, 16 ounces; soap, |_---- CO ae ee 5.503} 1495 17 | 0 0} 0} 0} O 1) 98. 61
4 ounces; water, 1 gallon. Bre | |
OMe) 2 eee ee eee Wash on back, 2appli- 5) 92 189 0} 0} =O} 0} O} OF
cations; first appli-
cation, 4 ounces of |

derris.

1Includes all stages. Mostly fifth-stage lary, but allstages not determined.

He THE CATTLE GRUBS OR OX WARBLES 95

2

| Taste 11.—Treatment of Hypoderma lineatum im the backs of cattle, Dallas,
| Tex., 1918—1924—Continued

o| oC
SS asi Num- | Num-
8 5 ber of bene ber of er of| Per-
5/8 { grubs | 2U SUS | scrubs | cent-
2| 21 killed | ,BOt, |doubt-) “cone | age
B| killed | ful killed
Material and strength How applied S| & based
|e on
S S Stage | Stage | Stage | Stage | dead
oO; o
Rot os and
E 5 alive
lz |8| 4) 5 (8/4) 513) 4)5)3) 415
Derris powder, 12 ounces; water, | Washon back, lappli-|11} 78) 147 131 0} 0} O| 0} O} O} 60. 26
1 gallon. cation.
BeASOLITMO%: staat WE pe Se Iniected with syringe_! 9} 34! 0} 10) 14} 0} 0} 1} 0} 1) 8} O} O} 0; 96.00
TD Op cians Wel Se a ee ee cia Injected with oil can __|19] 91) 0} 6} 34) 0} 2} 17} 0} 0} 6] OF 0/26) 67. 80
mellebores drys 22 2: 2h ee Dusted into hole_____- 1{ 20} 0] 3] 8] O} 1} 4] 0; 1) 3} O} O} O} 68.75
Iodine, tincture, U.S. P., 25 per | Injected with syringe-| 1] 12} 0} 0} 5} 0} 0} 7| 0} 0} 0} O} O} O} 41.66
cent.
Iodine, tincture, U. S. P., 100 per |____- GO BE ee Be 68/437! 0} 0/204) 0) 0)111) 0/27/95) 0} 0} 0} 64. 76
cent.
Iodoform, 1 part; petrolatum, 10 | Pressed into hole_-____- 57|255| 0} 12/197} 0] 0} 12} 0} 0} 2) 0 be 94. 57
parts. :
Jodoform, 1 part; petrolatum, |____- CO Ko} sige Seapine ane ates eal 88/480} 1410 137 QO} 0} 1) 132 | 91.72
5 parts. ey a
1) REE ees 2 eee OEE ed See Se Rubbed on bumps_-_-_-|12} 21) 112 16 0} 0} Oo} 13 66. 66
| Jodoform, 1 part; petrolatum, | Pressed into holes-____- 10] 67] O| 1] 42) O] O| Oj} 0} 0} O} Of 0/24)100. CO
3 parts.
Jodoform, 1 part; petrolatum, |____-_ COE ae ee 41/223) 1] 8/179] 0} 3} 16} 0} 1) 4] 0} 0/11) 90.82
| 1 part.
' Kerosene emulsion, 22.2 per cent oil_| Wash on back, 2 appli- |13) 41] 0) 2| 8) 0} 1} 30} 0| 0} 0} 0} 0} 0} 24.39
cations.
- Kerosene, 25 per cent; lard, 75 per | Pressed into holes____- 9} 60} 0} 1) 11) O} 0} 17) O} 0/31} O| 0} O, 41.38
cent.
EOOSGITG Bee oie Ue) eee ee eek Injected with oil can__|10} 67} 6] 0} 32) 0} 1} 14} 0! O! 3} 0 017). 68.09
Lime-sulfur solution, 1.92 per cent | Wash on back, 2appli- |22|147/ 144 1100 12 0| O| 1) 30. 56
active ingredients. cations 24 hours
apart.
Lubricating-oil emulsion __-_______. Oilcan, l application __| 6} 59} 1} 5] 6 | 0/17] 27] 0) 0) 1) 0} 0} 2) 21.48
Nicotine sulfate, 0.08 per cent; | Washon back, 2appli- |28} 73] 0| 0} 14} 0] 1) 29] 0| 0) Ol 0} 0/29) 31.82
soap, 2 ounces per gallon. cations 36 hours |
apart.
Nicotine sulfate, 0.1 per cent; soap, | Wash on back 2 appli- |14| 52] 0] 0} 5) 0} 1] 28] 0} 0} 0} 0} 0/18) 14. 71
2 ounces per gallon. cations 48 hours
apart.
pecotine sulfate, 0.4 per cent nico- imaecied withsyringe__| 2) 10) 0} 3] 1] 0} 0} 4] 0} 0} 0} 0} 0} 2| 50.00
ine. .
Nicotine dust, 2 per cent __________- Dusted into hole_____- 27| 77| O| 0} 74| 0} O} 0} 0} O| O} O| O} 3/100. 00
Nicotine, free, 0.2 per cent__________- Injected with syringe, |14| 88] 0} 7] 15} 1/11] 42} 0} 0} 2} 0} 0/10) 28.95
te 1 application.
Nicotine, free, 0.52 per cent__.______|____- doses evens 18/164) 0) 17} 63] 0/23] 42) 0) 0; 1) 0) 0/18) 55. 17
Nicotine, free, 0.52 per cent; soap_--_|____- Goze Eis es ae 14}100] 0} 17} 54] O} 1} 12) 0} O} 1} O} 0/15) 84. 52
Nitrobenzene_-____- ye U i On ee he Injected with syringe_..|20} 68} 0] 16] 34] 0] 1) 7} 0) 0} 1] 0} 0} 9} 86. 21
No chemical used - -___._..--___-._- Stiff brush, hardrub___} 2} 10] 0} 0} 1] 0} G| 6] O} O} O} O} O} 3) 14. 29
Beibaeiit) Olle oe 0) 25 Se Fee ee Injected with Syringe_|18} 88} 0; 0} 55} 0} 0} 33} 0} 0} 0} 0} 0} 0} 62.50
meorolenm (fuel): oil 22-2) et do wes bela sie to 8} 30) 0} 0] 5} 0} OF 9} Of 1/15) O| O| O} 35.71
Pine-tar oil, crude, 34 per cent | Injected with oil can, |13/163] 3/125} 18) 0) 7| 6] 0} 2| O} 0} 0} 2| 91.82
phenol. 1 application.
mrine-tar oil, refined’. © __ 21.2.2. -2_|_2_-- GOs sR Ey seer 20/162] 0} 34] 55) 0) 0} 42] 0] 0} O} 0} 0/31) 67.94
TOG RRS GS ae ad eg Rubbed on bumps_-__-_| 6} 35} 0} 0} 13} 0} 0} 8] 0} 0/14] 0) 0] 0} 61.90
Pine-tar oil, commercial, 2 parts; | Dropped in holes______ 3] 14] 0} 2) 6 0} O} 6} 6} O} Oj O} O} OF 57. 14
furiural, 1 part; 90 per cent
benzol, 1 part.
Pine tar, 1 part; paraffin oil, 1 part___| Injected with syringe__| 4| 14] 0} 2] 6] 0| 0| 0} oj 1! 5] 0} 0] 0 100.00
Potassium permanganate, 25 per |_____ Gosesse ee Pees 4| 4) 0} O}| 4) 0} 0} O} O} O} O} O} 0; 0,100.06
cent ofasaturated solution.
Potassium permanganate, 50 per }__..2 Go tL hea ite sl 1} 6] Of 0} 5] 0} Of 1] 0} Of O} O| O| O| 83.33
cent ofasaturated solution.
Potassium permanganate, satur- |____- O22 ESS Sore. 24/146] 0; 5/101! 0} 0| 34! 0} 0} 6} O} O} O} 75. 71
- ated solution. 24g
-Pyrethrum flowers, 2 pounds; grain | Injected with oil can___|21| 75] 1) 30] 12|-0} 4| 24) 0] 0} 1/ 0| O| 3) 60.56
alcohol, 96 per cent, 1 gallon.?
Pyrethrum flowers, Ze DOuUNnds a|=aees (6 oer A se 2} 19] 0] 14) 5] 0] 0} 0} Oj O} O} O| 0} 0100.00
alcohol (denatured, formula 5),
1 gallon.2
Pyrethrum flowers, 2 pounds; | Wash on back_________ 21/111} 0} 11] 41} 0} 1) 39] 0} 0} 4) 0} 0/15) 56. 52
alcohol (grain, denatured, for-
mula 5), 1 gallon.? 2
Pyrethrum flowers, 2 pounds; | Injected with oil can___|11/126| 1) 74} 49] 0] 0] 1] 0] 0} 1) O} 0} 0} 99.20
benzol (90 per cent), 1 gallon.? |

1 Includes allstages. Mostly fifth-stage larve, but all stages not determined.
? Open pyrethrum flowers, Macerated for 24 hours and strained.

06 BULLETIN 1369, U. S. DEPARTMENT OF AGRICULTURE

TABLE 11.—Treatment of Hypoderma lineatum in the backs of cattle, Dallas, 4
Tex., 1918-1924—Continued ;

oh =) | |
}| 2 Num- | Num-
a| 3 wee ber of | ber of Nom Pas
2) | Der or | grubs | grubs | 2&8! ©
ee grubs not |doubt- grubs conte
Material and strength How applied Sis based
role on
alle Stage | Stage | Stage | Stage | dead
o|o
2/8 and
5 g alive
2|2|3| 4|5|9/4)9|s/4]/a]4/s
Pyrethrum flowers, 2 pounds; | Injected with oil can__|24/107| 8] 63) 35] 0] 0] | 0) G| 9} O! O} 1/100. 00
carbon tetrachloride, 1 gallon.? |
Pyrethrum flowers, 2 pounds; |____- O32 eee 20/173) 6/110) 47} 0) 2) 8] O| 0} 0} O} O} O} 94.22
kerosene, 1 gallon.? | ;
Pyrethrum-kerosene extract,?emul- | Wash on back, 1 appli- /12} 91) 0} 6} 9] 0! 9/ 58! 0} 0} O| 0} O| 9] 18.29
sified with soap and water, 0.44 cation. |
pound per gallon of emulsion con-
taining 0.22 per cent oil.
Pyrethrum powder (open flowers), | Pressed into holes_--_-- 22/100} 0} 8) 76} 0} 0} 0} O} O} 1} O} 0)15)100. 00
1 part; petrolatum, 2 parts.
Pyrethrum powder (open flowers), | Wash on back, 1 appli- | 8} 87] 0} 2) 9! 0} 2) 57] O} O| O} O| O}17) 15.71
1 pound; soap, 4 ounces; water, 1 cation.
gallon. x
Pyrethrum powder (open flowers)__| Dusted into holes_-_-_-_- 1] 22); 0} 2) 2) O| 1] 7} O} 3] 7 O} O} O} 33.33
Silver nitrate, 5 per cent____________ Injected with syringe__| 4] 30] 0} 0} 15] 0} 0} 0} 0} 0/15] 0} 0} 0/100. 00
Silver nitrate, saturated solution___|_____ GOS eae 1] 20} 0} 0} 20! 0} oO} 0} O} O} O} O} O} 0/100. 00
Silvol; Omer Cent == ie seee ee see | ae Goes 2 ae eee 2} 13] 0} 0} 12) O! O} 1) O} O} O} O} O} O} 92.31
Soap, 4 ounces; water, 1 gallon_____ Wiashion backe === 1} 21] 0 0 0} 0,19; 0} 0} 0} O' O} O} 3} 00.00
Sodium chloride, saturated solution_|_____ (6 Ua pet oes SO Gere 3} 21] 0] 0; 3) 0} 0} 18) 0} O} O} O} O} O| 14.29
Sodium/ehloride; dry ee Dusted into holes____- 16) 91} 0} O} 14! 0} 2} 45] 0} 0/30) 0} 0; O} 22.95
Sodium fluoride, 75 per cent, satu- | Injected with syringe__| 6] 22] 0} 1) 9] 6! Oo} 6] O} 3] 3] O| O} O} 62.50
rated solution. ; |
Sodium fluoride, dry___-__________- Dusted into holes____- 1} 3] 0] O} O} O} 1} 1} Oj O} 1} O} O} O} 00.00
Sodium hypochlorite, 1 ounce; | Injected with oil can__| 6} 46) 1) 1] 8} 1! 2| 33] 0! O} O| O} O} O} 21.74
water, 16 ounces. |
Sulfur, 1 part; petrolatum, 2 parts___| Pressed into holes__-__- 15} 45] 1) 16; 8] 0.10} 10} 0} 0} 0} O} 0} 0} 55.55
sOpateo dust, fine, 1.08 per cent | Dusted into holes_-___- 36/146) 0 RS 0} 1) 18} O} O} 0} O} 0/19} 85. 04
nicotine.
Tobacco dust, i part; petrolatum, | Pressed into holes___-_- 28/231) 0} 60,147; 0)14| 4} 0} 0} 0} 0} 0} 6; 92.00
2 parts; 0.33 per cent nicotine. | |
Tobacco-dust infusion No. 1 3_____- Injected with oil can__|12) 97] 0} 22) 15 olig 29) 0} O} 1; 0} O11) 43. 53
Tobacco-dust infusion No. 23_____- Wash, 2 applications | 4) 27) 117 19 0} 0} 0} O} O} 1] 65.38
on successive days.
Tobacco-dust infusion No. 3 3______|____- C0 (0 eee Se 5] 87| O| 9; 57] O; 4! 16] O} 9} O} O} O} 1) 76. 74
Tobacco-dust infusion No. 43______ Wash, 1 application___| 5] 77| 0| 4] 27] 010} 33] 0} 0} 0} Q} 0} 3} 41.89
Tobacco-dust infusion No. 5,3 0.22 | Wash, 4 applications; |39/360| 0/128/103) 032] 69| 0] 4) 6) 0} 0/18] 69.58
per cent nicotine. 2 on successive days;
2 weeks apart. |
Tobacco-dust infusion No. 6,3 0.22 | Wash, 2applications 2 |39,275] 0} 90) 56) 0/16] 77! 0] 8] 5) 0} 0/23) 61.09
per cent nicotine. weeks apart. |
Tobacco-dust infusion No. 7,3 0.22 | Wash, 5applications 1 |44 336] 0/134/115) 0.13] 44) 6! 4) 3| 0} 0!23) 81.37
to 0.32 per cent nicotine. week apart. |
Tobacco-dust infusion No. 8,3 0.52 | Wash, 1 application___|18/101) 0| 6} 34) 0) 8} 40) 0; 0} 0} 0} 0/18) 45. 45
per cent nicotine.
Tobacco-dust infusion No. 9,3 0.51 | Wash, 3-applications, 1,/21) 95} 0) 5} 53) 0} 2} 8) 0} 0} 0} 0} 0/27} 85. 29
to 0.54 per cent nicotine. then 2 one week later.
Turpentine spirits, undiluted______| Injected withsyringe__| 7} 78] 0] 0} 60) 0} 0} 4 0} 0/14) 0} 0} 0} 93.75
IE) 8 ears Se ee I eee Injected with oil can__/50,213) 0} 2) 80) 0| 2) 54! 0} 1) 2) 0} 0/72) 59. 42
ae (phenol, boracic acid, | Injected with syringe__| 3} 14] 0} 0} 9) 0) 0} 0} O} 0} 5} 0} 0} 0/100. 00
um).
{

3 These tobacco infusions, Nos. 1 to 9, were made with ingredients in the following proportions: No. 1,
4 pounds of tobacco dust, sufficient water to make 1 gallon; No. 2, 1 pound of English tobacco dust, 4 ounces ~
of stone lime, sufficient water to make 1 pint; No. 3, for first application, 1 pound of tobacco dust, 1 ounce
of lime, sufficient water to make 1 gallon; for second application, three-fourths pound of tobacco dust, 1
ounce of lime, sufficient water to make 1 gallon; Nos. 4, 5, 6, and 7, 4 pounds of tobacco dust, 1 pound of
lime, sufficient water to make 1 gallon; Nos. 8 and 9, 8 pounds of tobacco dust, 4 pounds of lime, sufficient
water to make 1 gallon.

THE CATTLE GRUBS OR OX WARBLES

97

TABLE 12.—Treatment of Hypoderma lineatum and H. bovis in the backs of
cattle, Orange County, N. Y., 1922

ES)
3 | 3 | Num Ne Nam Num-| 3
S| 8 | ber of | Per Of] ber of | pe of | Se
Bele grubs | grubs 12
= |.6 | tubs) “not |doubt- grubs! og
be eg se PRe9) kale |: tar 22° | Sc
Chemicals used How applied | § Es x Ads Species
— =] od
- = Stage | Stage | Stage | Stage a3
2\a seb it Bg
A 5 3 5| 3} 4] 5, 3) 4/5 a
= Co)
5 |Z 3/4] 5 4 £
Derris, 1 part; petrolatum, | Rubbed in, 1 4| 64) 164 | O| 0} O| 0; O| 0 O} 0) 0100.00) Hypoderma
10 parts. application. bovis and H.
lineatum.
Derris, 1 pound; soap, 4 | Washonback,| 9] 91) 163 12] 17 | OQ} 0} O| 75.00 Do.
ounces; water, 1 gallon. E applica-
ion. ;
Derris, 1 ounce; water, 300 |____- GO ee oo 2| 43] 0} GO} 0} 0} 0/43] 0} 0} O} 0; 0} O| 00.00) H. bovis.
ounces; soap, 514 ounces. |
Derris extract, 1 part; wa- |___-- do__-_----_| 6] 23] 0} O| 2) 0} 0/17) 0} OF OC} 14 | 10.53 Do.
ter, 100 parts; soap, 1 |
art. ; | i
Bedotorn, 1 part; petrola- | Rubbed in, 1 | 19) 206) 163 | 142 | 000 11 | 79.51) H. bovis and
tum, 5 parts application H. lineatum:.
Nicotine (free), 0.1 per | Washon back, 6} 100) 114 169 192 115 | 16.87) H. bovis.
cent solution. lapplication.
Tobacco dust, dry___-----_- Rubbed in, 1 4| 67) 13 160 1] 13 4.76 Do.
application.
Tobacco infusion: Tobacco | Wash on back, 3] 115} 119 156 1921 119 | 25.33 Do.
dust, 4 pounds; lime, 1 2 applica- | |
pound; water, 1 gallon. tions e hours | |
apart.
‘ Sodium hypochlorite, 2 |____- dot sas == 1} 5/0 4 2| 0 a 3] 0; 0; 0} 0; 0) 0} 40. 00 Do.
ounces; water, 16 ounces. | | | | | |

1 Includes all stages. Mostly fifth-stage larve, but all stages not determined.

Several different methods were considered of computing the per-
centage of the grubs destroyed by the various materials, but it was
finally decided to make this computation on the basis of the number
of grubs found alive or dead at the time of examination.
considerable advantage to those materials which had low killing
power, as in many cases the mature larve which were uninjured
Furthermore,
in the case of those substances which were very toxic, especially the
ointments, many of those grubs recorded as gone were no doubt

would leave the host before the results were checked.

killed or were so weakened as never to produce adults.

This gives

Those

recorded as doubtful were, for the most part, larvee which were ex-

tracted four or five days after treatment.

In the case of some of

the substances it was found difficult to determine for certain in
every case whether the grubs were dead or alive when observations
upon them were made so soon after treatment.
days proved to be the most satisfactory interval between treatment
and determination of result.

In general it may be stated that in the case of those materials
which gave a very high percentage of mortality relatively few grubs
were gone at the time of examination.
be noted as exceptions to this, as they were found to facilitate the
emergence of the grubs from the skin even though the grubs were

dead.

From six to eight

Some of the ointments may

Attention is especially directed to the results secured by the use of
the following materials: Benzol and carbon tetrachloride when in-

58252°—26——7

|

98 BULLETIN 1369, U. S. DEPARTMENT OF “AGRICULTURE

jected into the cysts; derris used in dry form, as an ointment wit |
petrolatum, or in suspension in water when injected into the cysts,
or applied as a wash (///); iodoform and petrolatum, also pyre-
thrum and petrolatum, when appled as an ointment; and very fine
tobacco dust and nicotine dust used in powder form.

The results of the writers’ work seem to indicate rather cleatia
that the percentage of mortality is not so high in the case of H. bovis
as with 7. lineatum.

The treatment of cattle in practice requires the application of a
method which will be as effective as possible under adverse con-
ditions. When treatments are given by the livestock owners them-
selves, washes applied to the entire back of the animal are probably
the most dependable, in that the inexperienced operator is more
likely to treat all of the grubs than if the latter have to be found
individually. On the other hand, there may be some objection to
the use of washes on the entire back of the animal under certain
adverse weather conditions. An objection to the use of the syringe
is that the instrument is an item of expense and may be broken even
if carefully handled. This tends to commend the oil can if the
grubs are to be injected individually. In the writers’ experience
they have found that an oil can with a comparatively slender curved
point is the most convenient to use. If the aperture in the spout
is not too large the spout can be utilized to advantage in finding the
grub hole. One advantage in the use of an ointment such as iodo-
form-petrolatum is that the operator can easily recognize which
grubs have been treated. The use of powders is favored by those
who do not wish to wet the animals during the winter, but some
objection might be had to them on account of the possibility of the
dust getting into the buckets duri ing milking. With certain washes,
however, the dust is left in the hair after the animal has dried. A
careful application of dust to the backs of cattle is almost as certain
to reach all grubs as the use of a wash.

Tobacco infusion has been advocated for the destruction of grubs
in the backs of cattle by Carpenter, Phibbs, and Slattery (19).
Although results of the writers’ preliminary tests with similar infu-
sions were not satisfactory, they continued their experiments after
receiving Carpenter's favorable reports. In his early publications
he gave no idea of the strength of the decoctions he used, and it ap-
pears that he must have employed infusions with a higher percentage
of nicotine than the writers were able to obtain from American to-
bacco dusts by using his formula. When, however, tobacco dust
from the same source as that employed by Carpenter (see Table 11,
tobacco infusion No. 2) was used, the mortality obtained (65.38 per
cent) was not nearly so high as reported by Carpenter. With most
of American tobacco dusts, which run from 1 to 1144 per cent nico-
tine, great difficulty was found in obtaining an infusion containing
0.5 per cent of nicotine. In order to get such a percentage the
amount of tobacco dust advised in Carpenter’s formula was doubled,
being 8 pounds of tobacco dust, 4 pounds of stone lime, and 1 gal-
lon of water. In preparing this the lime was first slaked in “the
water, and then the tobacco dust was stirred in and allowed to stand
about 24 hours. The mass was then placed in a sack and pressure

THE CATTLE GRUBS OR OX WARBLES Q9

applied at times with two boards hinged at one end. From 1 gallon
of water usually not more than 3 pints of infusion was obtained.
' Serious objections to the use of this decoction are the labor involved
in preparing it and the great variability in the strength of the infu-
_ sion obtained. These objections would cause the investigator or
_ stockman to turn to the standardized solutions of free nicotine or
\ nicotine sulfate, but the results obtained with these substances when
-used at strengths which would not endanger the host were unsatis-
| factory. Nicotine sulfate at a strength of 0.4 per cent when injected
into the cysts of the grubs gave a mortality of only 50 per cent, and
| free nicotine at a strength of 0.52 per cent with soap added resulted
in a mortality of 84 per cent. These strengths are greater than
would be advisable for use as general washes on the backs of cattle.
_ The toxicity, to larvee in different stages, of materials applied to
| the backs of cattle is a point of importance. It is necessary, of
course, to kill a high percentage of all stages of larve present at the
| time of treatment, but for several reasons it is desirable that treat- |
» ment be made with a view of destroying the grubs while small. To |
_ gain some information on this question a study of the percentage of
_ mortality among the different stages was made. For comparison
the percentages of mortality among the grubs in the fourth and fifth
« stages treated with fairly effective larvicides were compared. The
‘materials used were grouped according to method of treatment.
_ These groups and the mortality of the larve in each were as follows:
| Cysts injected with syringe or oil can, fourth stage 91.01 per cent, |
fifth stage 81.21 per cent; ointments applied to the opening in the |
|
|

skin, fourth stage 84.34 per cent, fifth stage 93.32 per cent; dusts |
apphed to the openings in the skin, fourth stage 83.33 per cent, fifth

stage 88.05 per cent; washes applied to backs of cattle, fourth stage
90.29 per cent, fifth stage 68.77 per cent. These figures should not be |
taken to indicate the relative merits of the different methods of |
treatment. They are of value, however, because they clearly show I
that the ointments and powders are relatively more effective
against the larvee of the fifth stage than against those of the fourth,
_ probably owing to the larger apertures in the skin, which permit the
materials more readily to gain access to the larve; but, on the other
hand, that the percentage of mortality is higher in larve of the
fourth stage than in those of the fifth when the insecticides are in-
jected into the cysts or applied as washes to the backs of the cattle.
It appears that the younger stages are somewhat more easily killed
than the fifth-stage larvee when they are actually brought into con-
tact with the insecticide. Exact observations on the mortality among
third-stage larve have not been made in a sufficient number of
specimens to form a reliable basis for conclusions, but for the pur-
pose of comparing the relative susceptibility of the three stages to
various treatments, it may be said that the mortality runs about 92
_per cent in the third stage, 89 per cent in the fourth stage, and 83
per cent in the fifth stage.

EXTRACTION OF GRUBS BY HAND

It is the common belief that the cattle grubs must be fairly well
matured before they can be successfully removed by hand. The
expression is often heard, “the grubs are not yet. ripe.”

100 BULLETIN 1369, U. S. DEPARTMENT OF AGRICULTURE

In the writers’ experience they have found that grubs may be ex- |

tracted at any time during the course of their development in the
backs of the cattle. They have found that, by removing the small
scabs which usually develop around the apertures cut by the young
or third-stage larvee, they can be pressed out with great ease. There
seems to be a period in the fourth stage during which extraction is
more difficult. By using care, however, practically every grub can
be removed by hand. (Fig. 36.)

lig. 36.—Extracting Hypoderma larva from cow by pressing down around cyst
opening

There is a very marked difference in the ease with which grubs
may be etxracted from the backs of cattle of different breeds. In
the case of the island breeds the skin appears more flexible and
elastic, and extraction 1s comparatively easy. Very often with the
Holstein-Friesian and certain beef breeds it is almost impossible to
squeeze the grubs out by hand. The condition of fiesh of the host
also has a considerable effect on the ease of extraction. Very poor
or extremely fat cattle are more difficult to treat than those in fair
condition.

The method of procedure in extracting grubs may be modified to
suit the individual and also the character of the skin of the host
under treatment. Inexperienced people often find extraction ex-
tremely difficult; but those who have considerable experience are able
to remove the grubs with comparative ease, and they seldom break

é
i |

THE CATTLE GRUBS OR OX WARBLES 101

the cyst and allow the larva to escape. Certain writers have advo-
cated the application of salt water or soapy water to the backs of
cattle before extraction is begun. It is probable in the case of cattle
with elastic skins that a weak saline solution applied to the backs
some time before extraction is undertaken will aid the work. In
the present writers’ experience, however, washes have not been
found materially to facilitate extraction. (See further discussion
under “ Cost of treatment or extraction of grubs,” p. 106.)

MECHANICAL EXTRACTION OF GRUBS

One often hears of the old-fashioned method of placing the mouth
of a heated bottle over the aperture of the grub.. Some larve may
be extracted by this method, but it is extremely slow. It suggests,
however, the possibility of utilizing suction and pressure in extrac-
tion work. For several years the writers have given considerable
attention to the question of developing an implement for remov-
ing the grubs from the backs of cattle by suction. One of the prin-
cipal Geultias encountered is in obtaining an airtight cup to fit
over the warble and to generate, without unduly complicated and
expensive apparatus, a sufficient vacuum to suck the grubs out of
the cysts. Brodersen (//), a veterinarian in Denmark, has devised
and patented a small suction pump operated by hand which he con-
siders a success for the removal of grubs. The principle employed
is a combination of pressure and suction. The end of the pump
barre] is fitted with a rubber cup which is applied to the back of
the animal over the grub hole. This is pressed down, against the
animal while the plunger is being pulled out, thus creating a par-
tial vacuum. Doctor Brodersen has very kindly furnished the writ-
ers with one of these instruments, but in their experiments it has
not worked well, especially on animals with inelastic skins. In cer-
tain instances, even though tremendous pressure was applied and
the plunger raised a great. many times, the grubs could not be pulled
out of their cysts. Before receiving Brodersen’s extractor, the
writers had developed a similar instrument made from an old au-
tomobile-tire pump (fig. 37). This, probably owing to a larger
barrel capacity, gave even better results than the imported extractor.
There is certainly some advantage in using’ an instrument. of this
kind if it can be developed to a point where a large percentage of
the grubs can be removed without consuming too much time. It
would be less trying on the fingers than hand extraction and the
operator would not have the disagreeable experience, which often
comes from squeezing the grubs out by hand, of having pus, or the
contents of the grub, squirted into the face. Furthermore, it is
probable that the chance of breaking the cysts or bruising the tis-
sues would be less than might result from hand extraction, espe-
cially by an inexperienced operator.

The use of forceps to assist in the extraction of larve naturally
comes to mind. The writers have investigated the possibility of
using various types of forceps in this work. One of the principal
difficulties is in obtaining a pair of forceps with sufficiently fine
points to enter the small holes in the hide and at the same time
with enough strength to extract the larve and not get out of order.
One of the most successfui forms of forceps tried is the alligator-jaw

102 BULLETIN 1369, U. S. DEPARTMENT OF AGRICULTURE

type (fig. 38). These permit one to place the tips well into the hole —
and then to open them and secure a firm hold on the grub. Another ©
type which has been found very successful is a simple forceps with —
stout shanks and provided at the tip with minute mouse-teeth.
These, however, often puncture the grub, which might be considered —
objectionable by some.

The enlargement of the grub holes in the hide by cutting, is a
method suggested by some, especially by veterinarians. It has been |
found that in most cases this practice causes the host too much dis-
comfort. There is also the possibility of cutting through the cyst,
if the incision is made too deeply, and thus allowing some of the
foreign matter to enter the tissues of the host. -

Certain stockmen have for years practiced the plan of puncturing
the grub before attempting to extract it. This led the writers to

Fic. 37.—Removing Hypoderma larve from back of cow by means of suction pump of
the Brodersen type

make a series of tests of this method. One of the procedures followed
was to press firmly around the grub, thus bringing it up to the
aperture in the skin, and then to clip the posterior end with a pair
of fine-pointed scissors. A small amount of pressure applied to the
cyst will expel the contents of the larva, after which the skin of the
erub may be easily extracted by pressure. or better, with a pair of
forceps. In certain instances grubs punctured in the way described
were left in the host. In a short time it was found that the skins of
most of these grubs had protruded some distance from the holes in
the skin, thus enabling one to remove them easily with the fingers.

EFFECT ON HOST OF DESTRUCTION AND EXTRACTION OF GRUBS

Despite the very general practice of extracting grubs by hand
which has been employed for many years, not until recently have

| been observed. The principal danger
_ seems to lie in the improper applica-
tion of pressure around the grub,

a THE CATTLE GRUBS OR OX WARBLES 103

any definite ill effects been attributed to this method. Brodersen

(20), working in Denmark, reports his observations upon a semiacute

malady which he terms “ Rosenfeber.” He records several cases in
_ which he has seen the sick cows very soon after the grubs had been
squeezed out. The description he gives of the sickness indicates
| clearly that it is of an anaphylactic nature similar to that described
| by Hadwen and Bruce (38), Jensen (49), and Van Es and Schalk

(709) in cases where they injected the juice of larve into animals

| sensitized by natural infestations. Brodersen’s cases were acute but
| not serious. Apparently the general depression, rapid pulse, and
| puslike secretion from the mucous membranes completely subsided

within a few hours. In the cases cited it appears that the grubs

| were squeezed out by men hired for the purpose and apparently the
| work was done in a very crude way. The experience, however,
| directs attention to the danger of handling cattle roughly during the
_ extraction process and further emphasizes the need of a proper under-

standing of the best method of remov-
ing the grubs. It should be noted
also that in cases in the writer’s ex-
perience in which the grubs have been
removed from large numbers of cattle,
some of them very heavily infested,
no instance in which any ull effects
whatsoever were noticeable has- ever

which causes the cyst to break and the
erub, after being crushed, to be forced
back into the connective tissue.

To lessen the danger of anaphylac-
tic shock to cattle following hand ex-
traction of grubs, Hadwen (37) has

advised that the back of the animal Fic. 38.—Alligator forceps, a type
well adapted for use in extracting

| be washed off with cold water. In grubs from the backs of cattle

very valuable animals and show herds,

it is suggested that the warble cysts be washed out with a hypodermic
syringe or oil can, using a normal saline solution or a 2 per cent
carbolic wash.

Aside from the anaphylactic reaction mentioned above it is claimed
by some that there is occasional formation of pus abscesses in the
subcutaneous tissue following extraction. The writers’ observa-
tions indicate, however, that with even moderate care in hand ex-
traction the chance of pus formation in the backs of stock is less-
ened rather than increased by removing the grubs. Great numbers
of cases have been encountered in which cows had developed large
abscesses without having been treated for grubs, usually because
of the closing of the orifice of the grub cyst before the grub reaches
maturity. In most cases this results in the death of the insect.
Such abscesses are always greatly relieved by discharging them as
soon as they are observed. 7
_ Realizing the fact that the leaving of foreign bodies in a host
is not good surgical practice, the writers were at first rather skep-
tical about the advisability of destroying the grubs in the backs

104 BULLETIN 1369, U. S. DEPARTMENT OF AGRICULTURE

of cattle by the application of insecticides. The difficulty of re- §
moving the grubs from certain breeds, however, led them to give ©
very serious consideration to this method of treatment. As a re-—
sult of rather extended experiments and practical demonstrations
of this method, it became evident that no ill effects were visible ©
in the host. It is true that certain materials may be used in the
destruction of the grubs which are detrimental to the host, as, for —
instance, copper sulfate. In the writers’ tests this material gave —
decidedly bad local effects. Abscesses were developed in a con- |
siderable percentage of the cysts treated. On the other hand, with
many of the most effective larvicides tried, pus formation in the ©
cysts was checked and the size of the lump caused by the grub was
rapidly reduced.

With some treatments, notably those with carbon tetrachloride,
and with derris in various forms, the exit holes of the grubs were
observed to close rather rapidly and there was little tendency for
the host to expel the insect. In most instances the grubs were found
to disintegrate rather rapidly under such conditions, especially if —

they were not in the late stages of development. At times some of
the grubs, especially in the late fifth stage, were found to rise in

the aperture in the skin and the posterior segments to harden, thus
retarding the closing of the hole in the skin. |

When the grubs are not further developed than the early part of |
the fifth stage, they are promptly absorbed after being killed by
substances apphed to the back of the host. After the skin and
spines have become thoroughly chitinized their elimination by the
host is more difficult. Some collapse and work out or are licked
out of the skin. Most of them are reduced in bulk by absorption —
and the skin heals up smoothly over them. A considerable per-
centage of these mature grubs may remain in the skin for several
months. This shows the advisability of applying treatments while
the grubs are young; furthermore, at this time the holes in the
hides are much smaller and heal up more quickly.

When ointments such as iodoform, derris, or pyrethrum and
petrolatum are used, the writers have found that a considerable
percentage of the grubs are expelled from the cysts after their —
death. Some of them are found completely emerged from the skin ~

of the host two days after treatment and they continue to be thrown
off for about two weeks. Some project slightly from the skin and —

may remain so for weeks if not mechanically removed. The per- |

centage of grubs which are expelled after treatment varies widely,

apparently differing with the character of the skin of the host. |
In order to determine the effect on the host and the rapidity —

of healing of the grub holes, some special observations were made —

on herds (1) where grubs left the hosts normally, (2) where the
larve were punctured and pulled out, (3) where they were ex-
tracted by hand, and (4) where various materials were applied
to the backs of the cattle. The rapidity of healing of the grub
holes was found to vary much in different animals, both when the
grubs emerged normally and when they were extracted or destroyed —
in situ. It was found that the time required for healing of holes
where the grubs emerged normally ranged from about 13 to 76 —
days. The scars from the skin injury often persist for several
months. The presence of foreign material in the form of a plug in

THE CATTLE GRUBS OR OX WARBLES 105

the grub aperture often retards healing. This may contain the
_ exuvie of the larve, but usually it seems to be composed of dried
excretions from the cyst. As the opening heals about this tough
material there often remains a pit containing a minute hole which
can be located with a pointed instrument.

Observations have been carried on to determine the rapidity of
healing of grub holes in the skin when the grubs are killed by the
application of insecticides or are extracted by hand. It has been
observed that where grubs are squeezed out, or even drop normally,
the old cyst and other material left within it require several weeks
for absorption. Grubs were extracted on one side of the backs of
cattle and on the corresponding side they were killed with insecti-
cides. - Two weeks later these animals were slaughtered and ex-
amined. The condition of the connective tissue around the grub
cysts was practically identical on both sides. When the skin was
removed no discolored or infiltrated tissue was left on the carcass,
but the former position of the grubs could be located on the under
side of the hide. The holes in the hide had healed to about the same
degree with the exception of a few cases in which portions of the
bodies of the dead larve were in the grub openings, thus preventing
the closing of the apertures.

In several herds in which insecticides were administered to the
backs of the cattle, a number of subsequent examinations were made
to determine the general condition of the infested areas and the
rapidity with which the skin healed. In most of these herds the
erubs were not treated until many of them were nearly mature.
Seventy-seven days following the treatment it was found that be-
tween 42 and 62 per cent of the grub holes had healed, and the fact
that the animals had been infested with larve could not then be
determined by touch. One hundred and twelve days following
treatment 75 per cent of the grub holes were completely healed and
smooth. At this time only 2 per cent remained open and in no case
was more than a very slight quantity of pus present. In one herd
treated with benzol it was found that the healing was less ad-
vanced at the end of 77 days. Only 30 per cent of the grub holes
were healed and smooth, and 48 per cent of the holes were still open.
The presence of the grubs was apparent in 25 per cent of the cysts.
In all cases, however, the warbles were distinctly reduced in size.

Since in certain animals extraction is greatly facilitated by
puncturing the grubs and squeezing out their contents before re-
moving the grub skin, the writers have treated over 200 head in this
way. Inno instance did the condition of the lesions and the rapidity

of the healing of the holes in the skin show any difference from —

those in cases in which the grubs were extracted by squeezing. In
a number of cattle the grubs were punctured and left in the cyst
after the body contents had been pressed out. No ill effects were
observed, but healing of some of the holes in the skin was retarded,
owing to the hardening in them of the skins of the grubs. One ani-
mal treated in this way had 60 well-developed grubs in its back.
Six days after the puncturing, about 10 of the grubs were project-
ing from the skin. These were shrunken and hardened, and seven
of these were pulled out. There was no more pus in any of the
cysts than would occur with living larve. ‘Twelve days later six

0

4
ET ES NEES NS SEES -

ee

106 BULLETIN 1369, U. S. DEPARTMENT OF AGRICULTURE

projecting grubs were pulled out; the cysts under these were small |

and the animal had improved noticeably in condition of flesh. At —
this time more than one-half of the holes were healed. When the
grubs are punctured before they are extracted the cattle are wor-
ried much less than when extraction by the usual method is prac-
ticed. Schottler (S7) states that in Germany a crochet needle has
been used for puncturing and extracting grubs, but that this method
had been found to be undesirable because the juice from the grubs
may cause nettle fever.

COST OF TREATMENT OR EXTRACTION OF GRUBS

To gain information on the expense of treating cattle for grubs,
records were kept on the time required in applying the different
treatments, the quantity of the material used, and its cost.

It was found that for cattle of the island breeds hand extraction
was the most economical. The time consumed in extraction varied
considerably with the breed and with the local conditions under
which the work was done, as well as with the experience of the
operator. The rate of extraction per hour ranged from 388 grubs
in Holsteins to 191 in a dairy herd of mixed breeds. It appears
that with the average herd of Jerseys or mixed breeds, not Holsteins.
the grubs can be extracted caretully and thoroughly at the rate of
about 125 per hour. Naturally the degree of infestation affects the
rate, as in very light infestations much time is occupied in going
from one animal to another and in very heavy infestations more
care is necessary to avoid missing some grubs.

In tests in which the backs of the cattle were thoroughly moistened
with soap solution the average number of larve extracted per hour
was 119, and where normal salt solution was applied prior to
the extraction the grubs were removed at the rate of 100 per hour.
These tests therefore seem to indicate that the wetting of the backs
of the cattle in the case of island or mixed breeds, not Holsteins,
tends to retard the rate of extraction.

In tests of the method of extracting the grubs after puncturing
them and expelling the contents, the average number of grubs re-
moved per hour was slightly over 88. This work was done without
special forceps, which if used would have hastened the work. AI-
though this rate of extraction is considerably slower than that of
the hand extraction in Jersey or mixed herds it is decidedly more
rapid than hand extraction in Holsteins.

The rate of treatment when injecting the cysts with a hypodermic

syringe ran about 170 grubs per hour. The time consumed in in- —

jecting the material by means of an oil can varied considerably,
ranging from 74 to 240 grubs per hour. The very slow record
mentioned was probably due to the fact that a large number of
the grubs had dropped, and it was necessary to examine each cyst
to determine if the larva was still present. Under good conditions
in a dairy it is thought that by the oil-can injection method 225
grubs per hour might be readily treated.

The application of such general treatments as dusts and washes
is considerably more rapid than the individual treatment of grubs.
The thoroughness with which either of these methods must be car-
ried out, however, causes more time to be consumed in the treat-

THE CATTLE GRUBS OR OX WARBLES 107

ment than would be supposed. On an average it required an hour
to treat about 98 grubs by, the apphcation of oitments, such as
iodoform-petrolatum to cysts in the backs of cattle. Undoubtedly
this work could be done much more rapidly in herds showing a
fairly heavy infestation.

The cost of materials and equipment should be considered, espe-
cially if large herds are to be treated. The fact that no instru-
ments or materials are needed for the ordinary hand extraction
commends that method. With the use of omtments, powders, and
washes practically no equipment is required. The cost of forceps
or scissors for the puncturing and pulling method of extraction is
not great, but this method requires rather more care and a higher
degree of training for the work than is necessary for using’ the
oil-ean injection method or for applying washes and powders.

The cost of the chemicals used varies considerably with the ma-
terial, and there is also considerable difference between the whole-
sale and retail prices of each. Iodoform-petrolatum ointment costs
about 814, cents per ounce at the usual wholesale price. The retail
price is about 15 cents per ounce. An ounce will treat between
125 and 200 grubs, thus making the retail cost of the ointment about
12 cents per 100 grubs. Pyrethrum ointment is much cheaper,
as it costs about 5 cents per 100 grubs. The only objection to this
ointment is that the pyrethrum powder must be fresh to be potent.

With such materials as carbon tetrachloride and benzol, it was
found that a pound of either would treat about 500 warbles. Since
these materials are comparatively inexpensive the cost is extremely
low.

As yet derris is not available on the open market in this country,
but it is probable that it will retail at approximately $1 per pound.
Tobacco dusts of all grades are very much cheaper, but they do
not appear to be equally effective in any strength, and furthermore
their strength as well as mechanical make-up varies considerably.
It is probable that if further tests prove that very fine tobacco dust
with a fairly high percentage of nicotine is as effective as the writers’
preliminary experiments indicate, this material may be standard-
ized for this purpose.

CONTROL THROUGH INDIVIDUAL EFFORT

The results of control measures applied by an individual cattle
owner when he is more or less closely surrounded by livestock are
likely to be disappointing. Three tests have been made by the writers
in which the grubs have been destroyed rather systematically for
periods of from two to four years. It is true that all grubs were not
destroyed each year, but the work was probably done as thoroughly
as it would have been if left to the cattle owners. The pastures where
the treated cattle ranged were in close proximity to others in which
untreated stock were kept. In none of these tests was a striking
reduction observed in the number of grubs during the year following.

The most thorough work along this line was done on the dairy
and breeding farm of J. T. Orr, near Dallas, Tex. From 45 to 100
head of cattle were carried on this place. During the grub season
of 1920-21 the cattle were examined and grubs destroyed only once,
on January 29. The average number of grubs per head then was

|
|

108 BULLETIN 1369, U. 8. DEPARTMENT OF AGRICULTURE
5.138. In 1921-22 the cattle were all examined and grubs extracted i
on December 16 and January 17, the average per head being 3.55. _
In 1922-23 the grubs were all extracted on November 28, Decem-
ber 28, January 29, and March 21, the average per head for the year
being 11.30. During 1923-24 the cattle were gone over four times
and an average for the year of 7.5 grubs per animal was found.
During the last three seasons the work was done very thoroughly,
yet it appears that enough flies entered the pasture from adjoining
farms to keep up the infestation. It is thought that this is a rather
peculiar case, however, on account of certain local conditions.
Duncan, Hewitt, and Jardine (28) have reported a similar ex-
perience on a farm in Ireland. The average number of grubs was
materially lowered after the first year’s destruction, but for several
succeeding years it remained rather constant, though relatively low.
‘The writers have observed a number of instances, however, where
well-isolated dairymen and breeders have largely, if not completely,
eradicated the pest from their herds by systematic destruction of
the grubs.
In attempting to control the insect on the individual farm it is im-—
portant to destroy the grubs in the young stock, and also to kill those =
larvee which reach the backs rather late in the season. =

AE ji

iri

=
.

\

, Wi

wae

ood

POSSIBILITIES OF ERADICATION BY SYSTEMATIC DESTRUCTION
‘OF GRUBS

uG

—

»

For many years the possibilities of completely eliminating this
destructive pest from given areas have been presented. In 1896
Osborn (73), after discussing methods of destroying the grubs, says:

While it is certain that this insect could be practically exterminated in the
United States in a single year, we realize fully the great difficulty in getting
every person owning cattle to know or appreciate the need of using the neces-
sary means... We can not close this sketch of remedies without present-
ing a plan which, though it may be styled fanciful or ideal, must if carried out
result in the extermination of the pest and the saving, we believe, of not less
and probably more than $50,000,000 per year to the farmers of the United
States.

He then briefly outlines his plan of having all cattle examined
and the grubs extracted or destroyed by chemical treatment. Other
authors have presented somewhat similar suggestions, but until re-
cently it would appear that the knowledge of the seasonal history
of the two species of grubs in this country has been too meager to
make possible the formulation of very definite plans. From studies
which have been made in various parts of the world on this problem
it appears certain that eradication from considerable areas, if not
from entire countries, can be accomplished and that such effort would
be very remunerative to the dairy and livestock industries. In con-
sidering the possibilities for eradication the following facts should
be borne in mind:

1. Both species of Hypoderma confine their attack almost ex-
clusively to domestic cattle. It is probable, however, that in vicini-
ties where bison range these grubs might readily be carried over in
numbers in such herds. Horses and goats are the only other hosts
which would have to be considered at all, and the writers’ observa-
tions clearly indicate that they would not play a part in perpetuating
this species if all grubs were destroyed in bovines.

THE CATTLE GRUBS OR OX,WARBLES 7 109

2. Every individual of both species of Hypoderma is present in
the subcutaneous tissues of the backs of the cattle for a period in
excess of 35 days, and while in this situation it 1s constantly amen-
able to treatments applied to the backs of the cattle or to extraction.

3. The larve are present in the subcutaneous tissues of the back
during a fairly well-defined and comparatively limited period of the

ear.

The difficulty of carrying out systematic extraction or the apph-
eation of ointments or washes under range conditions is at once
apparent. In the farming and dairying sections, however, where
the cattle are fairly gentle, systematic treatment would be fully
warranted even under present conditions.

No definite experiments have been possible to show the distance
‘the flies may travel, but circumstantial evidence indicates that they
do not go far from the place where they hatch out, and this lends
further encouragement to the efforts toward control. The writers’
experience with the systematic destruction of grubs among animals
on a single farm surrounded by infested cattle clearly indicates the
futility of the individual attempting to secure a high degree of con-
trol, to say nothing of eradication. Cooperative community action
is therefore clearly called for. Such an undertaking in Denmark is
reported by Boas (5). On a farm in the center of an area where
systematic grub extraction was carried out by a dairy association,
the following numbers of grubs were found present and destroyed
on seven succeeding years, beginning in 1889: 832, 215, 65, 229, 64,
0, 0. Complete eradication was not accomplished toward the edges
of the areas covered by this effort, but the grubs were greatly
reduced in numbers.

The stock raiser who has comparatively few grubs in his cattle
has not been given sufficient consideration in connection with the
sale of his cattle or hides, owing to the fact that it is the custom of
the hide buyers of a section known to be infested-by grubs to make
a horizontal discount for grubbiness without determining the degree
of infestation of the hides and even without the knowledge of the
producer. With the inauguration of systematic control work there
seems to be little doubt that hide buyers would pay a premium for
hides from areas practicing control work, and also that butchers
would slightly favor cattle from those areas.

In the initial undertaking of systematic control or eradication
work it would seem desirable that the plan be attempted on a con-
siderable area. Such a plan has been under consideration by the
writers for several years, although funds have not been forthcoming
to put it into effect (70). The writers believe that a large amount
of educational werk must be done in advance of any actual control
work, and in this connection all organizations of business men and
farmers should be thoroughly in sympathy with the undertaking.
In an initial attempt it is thought best to have all of the work of
destroying the grubs carried out by men specially trained in the pro-
cedure, and not to depend upon the volunteer efforts of the stock
owners. It is probable that such an undertaking would have to be
carried on during about three years, as inevitably a few grubs would
escape destruction even in the most carefully executed plan. It ap-

| =
a;

110 BULLETIN 1369, U. S. DEPARTMENT OF AGRICULTURE

pears that the mortality of grubs under natural conditions is high,
and there is the possibility that with only an occasional grub ma-
turing the male and female flies would fail to emerge at ‘the same
time and mating would not be possible. In carrying out such a
plan it is imperative that an exact knowledge of the seasonal devel-
opment of the grubs be obtained in advance, so that the date for be-
beginning the work will be known with a fair degree of accuracy.
Where both species of Hypoderma occur at least four treatments
will be required. The first should be completed some days before
the time of maturity of the earliest larve. All cattle exposed to fly
attack should be carefully examined. In the greater part of the
United States calves under-6 months old would not be found in-
fested, but under certain conditions animals as young as 5 months
of age may be infested.

The experiment carried out by Carpenter and his associates (/8)
on Clare Island, County Mayo, Ireland, amply demonstrates the
possibility of complete eradication of grubs, provided all cattle are —
systematically treated.

The fact that a few cases of temporary sickness have resulted in
cattle from careless hand extraction should not be allowed in any
way to interfere with the work of destroying grubs in the backs of
cattle. These cases are comparatively rare and the good accom-
plished by grub destruction far outweighs any loss which might be
sustained.

LEGISLATION GN GRUB CONTRGL

A very active interest is being shown in various parts of the world
in the matter of grub control. Great Britain has for many years
given attention to this problem, but her efforts took on more sys-
tematic form recently when the English Ministry of Agriculture in
collaboration with the Scottish Board and the Department of Agri-
culture for Ireland formed a commission of experts to devise meth-
ods of control or eradication of the pest. It seems that there is a
very strong sentiment in Great Britain in favor of the passage of
laws to bring about the systematic destruction of the grubs. In
Switzerland and France similar commissions have been organized
recently; Germany (67) has had its commission functioning for
several years; and in Denmark (26) a law was passed in 1923 by
Parliament, looking toward the destruction of all grubs in cattle
during the years 1923 and 1924 with a view to complete eradication
throughout ‘the nation.

This action by the legislative authorities of Denmark, it should be
remembered, followed years of individual or community effort
against the pest.

It is doubtful if any legislation on the part of our own country 1s
advisable at present. After there have been large-scale demonstra-

- tions of what may be accomplished in the direction of grub eradi-
cation through well-organized cooperative work, however, appro-
priate legislative enactments will no doubt be called for.

SUMMARY

Cattle grubs of the genus Hypoderma are abundant throughout
the oreater part of the “United States and southern Canada, and in

RIA WF catia"

;

Germany, Switzerland, Denmark, Holland, and the British Isles,

THE CATTLE GRUBS OR OX WARBLES 111

and probably occur throughout the remainder of Europe. They
have been reported also from North Africa, western India, Mongolia,
and parts of Japan. Of the two species, 47. bovis De Geer is essen-
tially a northern form as shown by its distribution, both in the
- United States and in Europe. In the United States 17. lineatum is
much more widely distributed than //. bovis, has been known for
many more years, and has been bred from the native bison; possibly,
_ therefore, it may be an American species, although now occurring in
_ other parts of the world. ZH. bovis, on the other hand, appears to
_ have been introduced into the United States from Kurope rather re-
cently.

Injury to cattle by these insects comes from (1) the annoyance
caused by the flies during egg deposition and (2) the irritation pro-
_ duced by the larve within the bodies of the hosts. The yearly loss
to the hide, tanning, and leather industries of the United States

caused by these grubs is estimated at $5,000,000 and the yearly losses
/ to the people of the United States at $50,000,000.

Cattle are the normal hosts for both 1. bovis and H. lineatum.
The American bison is also a host of H. lineatum. Although horses
_are attacked, in nature very few larve ever reach maturity in them.
( Goats may occasionally serve as hosts but in experiments with them,
as also with sheep, dogs, rabbits, and guinea pigs, no larve were
‘successfully reared. Several cases are known of the infestation of
'man by these parasites.

In several series of experiments with cattle controlled by muzzles
and cages it was determined that the larve upon hatching from the
eggs penetrate through the skin at the points where the eggs are
laid and do not enter the host by the mouth, either in the egg or
larval stage.

_ It was found that the place where the eggs are laid on the host

_ has no apparent effect either on the place where the larve reach the
subdermal tissues or on the time of their appearance. Larve enter-

ing the skin of an animal on the legs may go to the submucous layers

of the gullet, as may also larve removed from the gullets and intro-
duced by incision under the skin on the leg of a bovine.

H. lineatum prefers the heels as points for the attachment of its
eggs, but eggs may be found on many other parts of the host. /H.

bovis oviposits on the legs, but more eggs are laid on the thighs and
about the rumps of the cattle than with HZ. lineatum.
_ #. lineatum attaches its eggs in rows on the hairs; H. bovis de-
posits its eggs singly.
_ The usual incubation period for HZ. lineatum is from 3 to 6 days;
for H. bovis, about 3 days.
___ After penetrating the skin the larve apparently work upward in
_ the connective tissue and begin to appear in the chest and abdominal
_ cavity about two months after penetration. Although many larve
_ enter the connective tissue of the gullet it appears that many may
_never enter that organ. This is particularly true of H. bovis, as
_ only one larva of this species was found among 1,140 specimens re-
moved from 563 gullets in regions where this species abounds. Of
3,022 larve removed from 1,137 gullets, the majority were in the
second stage, only a few being in the third.

112 BULLETIN 1369, U. 5S, DEPARTMENT OF AGRICULTURE

The distance from the gullet and viscera to the subcutaneous tis- _
sues of the back is apparently traversed very rapidly by the larve. —
Soon after the larve reach the back they cut a hole through the
skin. The duration of the third stage of H. lineatum after the
skin of the back is punctured averaged 4.5 days at Dallas, Tex., and
4.26 days in New York; in H. bovis it averaged 3.35 days in New
York. The average duration of the fourth stage of H. lineatum was
24.5 days and of H. bovis, 27.1 days. The development of the fifth
stage of H. lineatum required an average of 30.3 days in Dallas, Tex.,
and that of H. bovis about 40 days in New York.

The total developmental period in the backs of cattle has been
determined with fair accuracy in many individuals at points in
Texas and New York. The three shortest developmental periods
recorded at Dallas, Tex., were between 35 and 47, between 38 and 40,
and between 39 and 46 days, respectively. The average at Dallas,
Tex., was 56.3 days in one series and 57.7 days in another, whereas at
Uvalde, Tex., it was 49.4 days. The developmental period of H. bovis
in the backs of cattle in New York was 77 days (maximum), 65 days
(minimum), and 72.8 days (average).

Mature larvee may emerge from the host at any time of day or
night, but the largest number as recorded by the writers emerged
during the middle of the forenoon. The time from emergence from —
the host to appearance of the flies of H. lineatum at Dallas, Tex.,
ranged from 18 to 77 days, with an average of 41.7 days. Inthe case
of H. bovis at Middletown, N. Y., this period ranged from 22 to 45
days, with an average of 31.34 days. ;

Mating of the adults of H. lineatum takes place very soon after
emergence, and oviposition may begin a few minutes after copulation.
There are some distinct differences in the habits of oviposition of
H. lineatum and H. bovis. Among other things the flies of the latter
species are more persistent in their attack on the cattle and induce
greater fear in them. H. lineatum may ovipost at a temperature as
low as between 40 and 45° F., but oviposits freely between 55 and
Sore ie

The adults of H. lineatwm lived in captivity from 1 to 25 days.
The average life of the adults of this species is about 5 or 6 days
and H. bovis has a similarly brief life span.

The seasonal history of H. lineatum varies widely according to
latitude and other conditions. In southwestern Texas the flies may
appear and lay eggs in the fall or early winter so that the whole life
cycle may be correspondingly earler than elsewhere in the country.
As the higher latitudes and altitudes are approached the various |
stages in the life history are later. In the northern edge of the
United States the adults do not begin to emerge until about April 1.
The seasonal development of the larvee is closely correlated with that
of oviposition; for instance, in southwestern Texas the earliest grubs
may reach the backs of the cattle in July, at Dallas, Tex., in Sep-
tember or October, at Ames, Iowa, during January, and at Herkimer,
N. Y.,in February. The earliest appearance of the larve of H. bovis
in the backs of cattle is somewhat later than that of H. lineatwm.
The dates in different regions when the earliest larvee become mature
and leave the host, and the dates when the last larva has reached the |
back, are matters of much importance in connection with control |

ae THE CATTLE GRUBS OR OX WARBLES 113

and have been determined and mapped with a fair degree of accu-
yacy in several parts of the country. In general the duration of
snfestation of the backs of cattle with ZZ. bovis is longer than with
H. lineatum, owing to the longer developmental period required by
H. bovis.

Temperature, humidity, cloudiness, and drainage are important
factors in natural control. Host resistance as acquired by age
is also an important factor in holding down the abundance. of
Hypoderma. No important insect enemies or diseases affecting
Hypoderma have been found.

The most effective time for the practice of control procedure 1s
during the period of development of the larve in the subcutaneous
tissues of the back. Destruction of the larve may be accomplished
by hand extraction with or without the aid of forceps. In the case
of certain breeds of cattle extraction of the grubs is very difficult.

Tests of the application of washes, powders, and ointments to the
backs of the cattle and also the injection of substances into the cysts
containing the larve show that each of these methods of treatment
is effective if certain materials are used. Among the most effective
should be mentioned: Derris used as a wash, as an ointment, or as
a powder; iodoform used as an ointment; pyrethrum applied as an
ointment; benzol and carbon tetrachloride injected into the grub
eysts; fine tobacco applied in powder form and nicotine dust applied
dry.

No adverse effects on the host have been observed in this country
from the destruction of the grubs in the backs of cattle with suitable

insecticides.

The cost of extraction or treatment depends on the skill of the
operator but in all cases it is small compared with the benefits
derived.

Experiments with the application to the feet and legs of cattle of
certain insecticides and repellents by means of wading vats show
that with the materials used control was not brought about, and indi-
cate that attack directed against the eggs or young larve in this way
will not be successful. |
Results of individual effort against cattle grubs is likely to be dis-
appointing, especially if the work is not thoroughly done and if
untreated cattle are in close proximity to the treated herd.
Systematic treatment of all infested cattle in a neighborhood either
by extraction or by the use of insecticides appears to be a practical
method of control or eradication. Although these methods are best
adapted to dairy or farm conditions it is probable that they may be
modified so as to be applied successfully to range cattle.

In order successfully to combat the insects by destroying the
larvee in backs of cattle it is necessary to treat all infested cattle at
intervals of not to exceed 35 days. The first treatment must be given
before the earliest larve have matured and left the host. In most
parts of the United States it is necessary to treat the animals four
times during a season to reach all of the larve. The time of begin-
ning the treatments in different parts of the country is indicated in
the discussion of seasonal history.

58252 °—26——_8

—

a RR EAN SI NETO
a mae ley a

EEE
ee

ae a

LITERATURE CITED

(1) ANONYMOUS.
1919. Die Dasselplage (Hypoderma bovis). Jn Ztschr. Angew. Ent..
Bd. 6, pp. 176-180.
(2) AUSTRALIA, COMMONWEALTH of.
1923. Quarantine Proclamation No. 108. Jn Commonwealth of Australia
Gazette, No. 21, March 22, p. 398, Melbourne.
(3) Bere, J.
1895. Lidt om vandrende Bremselarver hos Kyzeget. Jn Maanedsskr.
Dyrleger, 7. Bind, pp. 129-135.
(4) BisHopp, F. C.
1915. The distribution and abundance of the ox warbles, Eada?
lineata and H. bovis in the United States. Jn Ann. Ent. Soe.
Amer., vol. 8, pp. 359-364, illus.
(5) Boas, J. E. V.
1889. Bemerkninger til ovenstaaende Iagttagelse. Jn Tidsskr. Veteri-
nerer, 19. Bind, pp. 76—S3, illus.

(6)
1906. Om Oksebremsen og Midlerne til dens Udryddelse. Udgivet af
Landbrugsministeriet. 14 pp., illus. Copenhagen.
(7) Bornanp, M.
1920. L’hypoderme du boeuf et ses conséquences au point de vue écono-
mique. Jn Bul. Soc. Vaud. Sci. Nat., vol. 53, Procés-Verbaux,
pp. 55-58.
(8) Braver, F.
1863. Monographie der Aang Se. Heriisedcelen von der K. K. Zool.
Bot. Gesell. Wein. vi+292 pp., illus.
(9)

1890. Ueber die Feststellung des Wohnthieres der Hypoderma lineata
Villers durch Dr. Adam Handlirsch und andere Untersuchungen
und Beobachtungen an Oestriden. Jn Verhandl. K. K. Zool.
Bot. Gesell. Wien, Bd. 40, pp. 509-515, illus.

(10) BroprerseEn, L.

1919. Om Rosenfeber hos Kveg. Jn Maanedsskr. Dyrleger, 31. Bind,
pp. 321-3238.

(11)
1922. Om Oksebremsens Bekzempelse. Jn Maanedsskr. Dyrleger, 34.
Bind, pp. 305-310, illus.
(12) CARPENTER, G. H., and J. W. STEEN.
1908. The warble fly. Experiments on cattle as to its treatment and life
history. Jn Jour. Dept. Agr. Tech. Instr. Ireland, vol. 8, pp.
227-246, illus.

(13 , and W. F. PRENDERGAST.
1909. The warble flies. Further experiments as to life-history and
treatment. Jn Jour. Dept. Agr. Tech. Instr. Ireland, vol. 9,
pp. 465-476, illus.
(14 , and T. H. Corson.
1910. The warble flies. Third report on experiments as to life-history
and treatment. Jn Jour. Dept. Agr. Tech. Instr. Ireland, vol.
10, pp. 642-650, illus.
(15)
1910. Notes on the Oestridae. Jn Extrait du 1°” Congrés International
d’Entomologie, pp. 289-294, illus.
(16) , and’). Rew rer.

1914. Some new observations on the life-history of warble-flies. The
entrance of the maggot into the host’ t's ee In Irish Nat., vol.
23, pp. 214-221.
CER , and T. K. Reppin.
1914. The warble flies. Fourth report on experiments and observations
as to life-history and treatment. Jn Jour. Dept. Agr. Tech.
Instr. Ireland, vol. 15, pp. 105-182, illus.

114

ae

(18
(19)

(20)
(21)

(22)

(23)

(24)

» (25)

(26)

(27)

(28)

(29)

(30)
(31)

(32)
(33)
(34)

(35)

(36)

THE CATTLE GRUBS OR OX WARBLES 115

, and J. O. HEWITT.

1920. The warble fiies. Fifth report on experiments and observations
as to life-history and treatment. Jn Jour. Dept. Agr. Tech.
Instr. Ireland, vol. 20, pp. 452-459, illus.

, G. PuHipss, and T. SLATTERY.

1922. The warble flies. Sixth report on experiments and observations

as to life-history and treatment. Jn Jour. Dept. Agr. Tech.
Instr. Ireland, vol. 22, pp. 14-25.

CLARK, B.

1797. Observations on the genus Oestrus. Jn Trans. Linn. Soc. London,

vol. 3, pp. 289-3829, illus.

1827. Of the insect called Oistros by the ancients . . . In Trans.
Linn. Soc. London, vol. 15, pp. 402-411.

1843. An appendix or supplement to a treatise on the Oestri and Cute-
rebrae of various animals. Jn Trans. Linn. Soc. London, vol. 19,
pp. 81-94.

CopPrENsS, A.

1913. L’affection hypodermique du boeuf.—Le varon. Jn Ann. Méd. Vét.
ann. 62, pp. 309-328, 384-888.

CURTICE, COOPER.

1890. The larvae of Hypoderma bovis, De Geer. In U. S. Dept. Agr.,
Div. Ent., Insect Life, vol. 2, pp. 207-208.

1891. The ox warble of the United States. Jn Jour. Compar. Med. and
Vet. Arch., vol. 12, pp. 265--274, illus.

DENMARK, KINGDOM of.

1923. Om Foranstaltninger til Udryddelse of Oksebremsenlarven. J7
Lovtidenden, No. 65, pp. 351-352, Copenhagen. (Not seen.)

DE VRIES, H. J.

1910. Ein Beitrag zur Illustration des durch die Dasselfliege verursach-
ten Schadens, und die Bekimpfung derselben beim Rindvieh.
In Inaug.-Diss. Univ. Bern, 63 pp., illus.

Duncan, J. L., T. R. HEwitTt, and D. S. JARDINE.

1914. The destruction of warble maggots. Jn Jour. Dept. Agr. Tech.
Instr. Ireland, yol. 15, pp. 119-182, illus.

GLASER, H.

1912-13. Uber Dasselfliegen. In Mitteilungen des Ausschusses zur
. Bekiimpfung der Dasselplage, No. 2, pp. 1-16, illus; No. 3, pp.
29-37, illus.; No. 4, pp. 1-26; No. 5, pp. 1-89, iilus. Berlin.

1914. Le varon. Jn Ann. Méd. Vét., ann. 63, pp. 358-364.

GREVE, C.

1922. Zur Bekimpfung der Dasselplage mit giftigen Gasen. In Deut.
Tierarztl. Wechnschr., Jahrg. 30, pp. 689-640.

Hapwen, S.

1912. Warble flies. The economic aspect and a contribution on the
biology. Canada Dept. Agr., Health of Animals Branch, Bul. 16,
20 pp., illus.

1915. Warble flies. A further contribution on the biology of Hypoderma
lineatum and Hypoderma bovis.. Jn Parasitology, vol. 7, pp.
331-338, illus.

1916. A further contribution on the biology of Hypoderma lineatum.
Canada Dept. Agr., Health of Animals Branch, Sci. ser. Bul.
21, 10 pp., illus.

1918. Natural occurrence of oesinophilias. in Jour. Parasitology,
vol. 4, pp. 185-137.

1919. Warble flies. Hypoderma lineatum, Villers and Hypoderma bovis,
De Geer. Canada Dept. Agr., Health of Animals Branch, Sci.
ser. Bul. 27, 24 pp., illus .

eo

SS SEE — eee

ee

NE Se

116

(37)
(38)
(39)

(40)
(41)
(42)
(43)
(44)

(45)

(46)

(47)
(48)

(49)
(50)

(51)

(52)

(53)

BULLETIN 13869, U. S. DEPARTMENT OF AGRICULTURE

1922. Effects following improper methods of extracting Hypoderma
larvae from the backs of cattle. Jn Jour. Amer. Vet. Med.
Assoc., vol. 60, n. s. vol. 13, pp. 724-728.

, and EK. A. BRUCE.

1916. Observations on the migration of warble larvae through the tis-

sues. Canada Dept. Agr., Health of Animals Branch, Sci. ser.
Bul. 22, 14 pp., illus. ;

1917. Anaphylaxis in cattle and sheep produced by the larvae of Hypo-
derma bovis, H. lineatum and Oestrus ovis. In Jour. Amer. Vet.
Med. Assoc., vol. 51, n. s. vol. 4, pp. 16-4, illus.

, and J. S. FuLron.

1924. On the migration of Hypoderma lineatum from the skin to the

gullet. In Parasitology, vol. 16, pp. 98-106, illus.

HINRICHSEN.

1888. Ueber einen neuen Parasiten im Riickenmarkskanal des Rindes.

In Arch. Wiss. u. Prakt. Thierheilk., Bd. 14, pp. 219-223.

Hewitt, C. G.

1914. The occurrence of the warble fly Hypoderma bovis De Geer in

Canada. In Canad. Ent., vol. 46, pp. 1-2.

1917. Report of the Dominion Entomologist for the year ending March 31,
1917. Canad. Dept. Agr., 24 pp. Ottawa.

1920. Report of the Dominion Entomologist and Consulting Zoologist for
the two years 1917 and 1918. Canad. Dept. Agr., 23 pp., illus.

Horne, H.

1894. Bremserlarver i rygmarkskanalen og kj6det hos oxen. In Norsk
Veteriner-Tidsskr. [Kristiania], VII. Bind, pp. 33-40. (Not
seen. )

Howarp, C. W.

1912. Insects directly or indirectly injurious to man and animals in Mo-
zambique, East Africa. Jn Bul. Ent. Research, vol. 3, pp. 211-218.

Hutcheon, D.

1914. Bots or “ paapjes.” Jn Agr. Jour. Union 8. Afr., vol. 8, pp. 194-200.

ImMEs, M., and F. L. SCHNEIDER.

1921. Experimental treatment of cattle to prevent ox warble infestation.
In Jour. Amer. Vet. Med. Assoc., vol. 59, n. s. vol. 12, pp. 722-727.

JENSEN, C. O.

1919. Bemerkninger om Hypodermalaryernes Forhold til Rosenfeber.
In Maanedsskr. Dyrieger, 31. Bind, pp. 324-326.

JOHNSON, C. W.

1910. Some additions to the dipteran fauna of New England. Jn Psyche,
vol. 17, pp. 228-235.

JOLY, M.-N.

1846. Recherches zoologiques, anatomiques, physiologiques et médicales
sur les Oestrides en général, et particuliérement sur les oestres
qui attaquent homme. le cheval, le boeuf et le mouton. Jn Ann.
Sci. Phys. Nat. d’Agr. d’Ind. [Lyon], tome 9, pp. 157-805, illus.

JOST. dH.

1907. Beitrige zur Kenntnis des Entwicklungsganges der Larve von
Hypoderma bovis De Geer. Jn Ztschr. Wiss. Zool., Bd. 86, pp.
644-715. :

KOCH, “2:

1903. Om Oksebremsen Hypoderma bovis. Specielt Larvens Udvikling
og Vandring i Kvegets Legeme. Jn Maanedsskr. Dyrleger, 15.
Bind, pp. 129-159.

KOooREVAAR, P.

1898. De larvetoestand van Hypoderma bovis. Jn Tijdschr. Nederland.
Dierk. Ver., (2) deel 5, pp. 29-84. Translated in Ann. and Mag.
Nat. Hist., (7) vol. 4, pp. 69-73, 1899.

1898. Hypoderma bovis und ihre jiingsten Larven. In Centbl. Bakt.
[etce.], Abt. 1, Bd. 23, p. 888-892. :

(59)

(58) |

=

THE CATTLE GRUBS OR OX WARBLES LT 7

KRAUSE, R.

1912. Dasselschiiden und Abdasselung. Jn Mitteilungen des Ausschusses
zur Bekiimpfung der Dasselplage, No. 1, pp. 1-28. Berlin.

LAAKE, EK. W.

1921. Distinguishing characters of the larval stages of the ox-warbles
Hypoderma bovis and Hypoderma lineatum, with description of
a new larval stage. In U. S. Dept. Agr., Jour. Agr. Research,
vol. 21, pp. 4389-457, illus.

1924. Further observations on the molts of the ox bots Hypoderma bovis
De Geer and H. lineatum Villers. Jn U. S. Dept. Agr., Jour.
Agr. Research, vol. 28, pp. 271-274.

LEHMANN, N., and C. VANEY.

1911. Pourcentages et qualités des peaux attaquées par les larves de
Y Hypoderma du boeuf dans la région lyonnaise. Jn Compt.
Rend. Acad. Sci. [Paris], tome 152, pp. 1343-1345.

1911. Relations entre les conditions climatériques et la fréquence des
larves de lHypoderme du boeuf. Jn Compt. Rend. Acad. Sci.
[Paris], tome 152, pp. 1508-1510.

LINNE, K. von.

1739. Om Renarnas broemskulor i Lapland. (Oestrus.) In K. Svenska
Vetensk. Akad. Handl., vol. 1, pp. 119-130.

LounssBury, C. P.

1914. Warble flies. A danger with imported cattle. Jn Agr. Jour.
Union §S. Afr., vol. 8. pp. 61-64, illus.

LuceET, A.

1914. Recherches sur l’évolution de |}Hypoderma bovis De Geer et les
moyens de le détruire. Jn Compt. Rend. Acad. Sci. [Paris],
tome 158, pp. 812-814, 968-970.

MARLATT, C. L.

1897. The ox warble. U. S. Dept. Agr. Div. Ent. Cir., 2d ser., 25,
10 pp., illus.

Mason, F. A.

1921. Biology and its relationship to the leather industry. Jn Leather
Trades’ Yearbook, 18th ed., pp. 98-108, illus.

MAxWELL-LEFRoyY, H. M., and F. M. How.Lertt.

1909. Indian insect life. A manual of the insects of the plains (Tropi-
cal India). xii+786 pp. Calcutta, 1909.

Mitteilungen des Aussechusses zur Bekimpfung der Dasselplage. 1912—
1919. 7 reports. Berlin. (See references 29, 76, 87, and 88.)

MoHtLer, J. R.

1922. Report of the Chief of the Bureau of Animal Industry, U. S.
Dept. Agr., 62 pp. Washington.

MotTE, D. C. :

1917. Observations on the distribution of warble flies in Ohio. In
Ohio Jour. Sci., vol. 17, pp. 169-176, illus.

O’KANE, W. C.

1922. One year of the Crop Protection Institute. Jn Jour. Econ. Ent.,
vol. 15, pp. 209-213.

ORMEROD, E. A.

1894. Observations on warble fly or ox bot fly, Hypoderma bovis, De
Geer. 62 pp., illus. London.

1900. Flies injurious to stock, being life-histories and means of pre-
vention of a few kinds commonly injurious, with special ob-

Servations on ox warble or bot fly. pp. viii-+80, illus. London.

Osporn, H.

1896. Insects affecting domestic animals.... U. S. Dept. Agr., Div.
Ent., n. s. Bul. 5, 302 pp., illus.

OSTERTAG, R.

1906. Die Dasselfliegenplage und ihre Bekimpfung durch ein Gesetz.
In Ztsehr. Fleisch u. Milechhyg., Jahrg. 16, pp. 407-413.

PaTTon, W. S.

1924. Note on the occurrence of Hypoderma lineatum Villers in the
Punjab. Jn Indian Jour. Med. Research, vol. 11, pp. 961-962.

118

(76)

(91)

(92)

BULLETIN 1369, U. S. DEPARTMENT OF AGRICULTURE

PETER, B.
1912. Versuche mit Hypodermenlarven. Jn Mitteilungen Ausschusses
zur Bekimpfung der Dasselplage, No. 38. 18 pp., illus. Berlin.

1923. Gegenwirtiger Stand in der Bekimpfung der Dasselplage. In
Berlin. Tierértzl. Wehnschr., Jahrg. 39, pp. 207-210.

PHIBBS, G.

1922. The larval mouth-hooks of Hypoderma. Jn Irish Nat., vol. 31,
pp. 25-30, illus.

PounpD, C. J.

1915. Report of the Government bacteriologist. Jn Dept. Agr. Stock
Queensland Ann. Rpt. (1914-15), pp. 62-68.

RAILLIET, A.

1894. Recherches sur lorigine des larves doestridés de l’estomac du
chien. Jn Compt. Rend. Soc. Biol. [Paris], (sér. 10, tome 1).
tome 46, pp. 541-543.

RENE, C.

1917. Les larves d’oestres chez les animaux. Jn Progrés Agricole
[Amiens], 31° ann., pp. 410-411. (Not seen.)

Rimy.1C. Vv.

1889. The bot-fly of the ox, or ox warble. Jn U. S. Dept. Agr., Div. Ent.,
Insect Life, vol. 2, pp. 156-159, illus. =a

1889. The ox warble (Hypoderma bovis De Geer). Jn Insect Life, vol.-2,
pp. 172-177, illus.

1892. The ox bot in the United States. Habits and natural history of
Hypoderma lineata. Jn U. S. Dept. Agr., Div. Ent., Insect Life,
vol. 4, pp. 302-3817, illus.

ROUBAUD, E.

1914. Etudes sur la faune parasitaire de l'Afrique Occidentaie Fran-
caise. Fase. 1. Les producteurs de myiases et agents similaires
chez lhomme et les animaux. 251 pp., illus. Paris.

RUSER, WILHELM.

1895. Ueber das Vorkommen von Oestruslarven im Riickenmarkskanal
des Rindes. Jn Ztschr. Fleisch u. Milchhyg., Jahrg. 5, pp. 127-129.

SCHOTTLER, Doctor.

1912. Uber Abdasseln. Jn Mitteilungen des Ausschusses zur Bekam-
pfung der Dasselplage, No. 3, pp. 19-28. Berlin.

and H. GLASER.

1914. Der Abdasslversuch. Jn Mitteilungen des Ausschusses zur Be-
kimpfung der Dasselplage, No. 6, pp. 1-381. Berlin.

ScHOYEN, W. M.

1886. Om Forekomsten af Dipterlarver under Huden hos Mennesker.
In Ent. Tidskr., arg. 7, pp. 171-187, illus.

Sry MOUR-JONES, A.

1921. Warble flies and their maggots in cattle. Jn Leather Trades’ Year
Book, 13th ed., pp. 169-188, illus. London.

1922. The warble fly problem. Jn Jour. Amer. Leather Chem. Assoce.,
vol. 17, pp. 15-26.

SMre oH Se

1922. Parasitologische Studien in Nederlaéndisch-Indien. 11. Gastrophil-
uslarven in Nederlindisch-Indien. Jn Deut. Tierarztl. Wchnschr.,
Jahrg. 30, pp. 546-547.

SORENSEN, W. . 7

1908. Hvorledes lever Larven af Hypoderma bovis De Geer? In Ent 7:
Tidskr., Arg. 29, pp. 65-116, illus.

STEGMANN, P.

1920. Die Bekiimpfung der Dasselfiiege. 28 pp. Berlin.

StTus, C.

1912. Bidrag til Oksebremsens Biologi. Jn Maanedsskr. Dyrleger, 24.
Bind., pp. 409-410.

' 119

ie. THE CATTLE GRUBS OR OX WARBLES

O96 °
: 1913. Udklekning af Oksebremser. Oksebremsens Ophold og Auglegning
paa den levende’ Okse. Hypoderma-Larvers Forekomst hos
Kalve. Hypoderma lineatum’s. Forekomst in Danmark. I[n .-
Maanedsskr. Dyrleger, 25. Bind, pp. 336-340, illus.

(97 |
1913. Bidrag til Oksebremsens Biologi. Jn Maanedsskr. Dyrleger, 25.
Bind, pp. 482-487, illus.
(98
1915. Bidrag til Oksebremsens Biologi. Jn Nordisk Garvertidende, 58.
Bind, No. 21, p. 28. (Not seen.)
(99)

1919. Hypodermalarvers Indtrengen gennem Oksens Hud. Jn Maa-
lhe nedsskr. Dyrleger, 31. Bind, pp. 230-231.
~ (100) Tryon, H.
| 1906. Report of the Entomologist and Vegetable Pathologist. Jn Dept.
) Agr. Stock Queensland Ann. Rpt. (1905-1906), pp. 64-73.

101)
( 1912. Report of the Entomologist and Vegetable Pathologist. In Dept.
Agr. Stock Queensland Ann, Rpt. (1911-12), pp. 94-104.
| (102) VALLISNIERI, A.
Ke 4 1710. Considerazioni ed esperienze intorno alla generazione de vermi
| ordinarj del corpo umano. 160 pp., illus. Padova.
|= (103)
1713. Esperienze ed osservazioni intorno all’origine, sviluppi e cos-
tumi di varj insetti. 232 pp., illus. Padova.
| (104) VaANgEy, C.
1911. Le développement de Vhypoderme du boeuf. In Assoc. Fran-
caise pour le Destruction du Varron [Bul.] No. 1, pp. 24-388,
illus. Paris.
) «105) —
1911. Recherches sur la developpement de l’hypoderme du boeuf (Hy-
poderma bovis de Geer). Jn Compt. Rend. Acad. Sci. [Paris],
| tome 152, pp. 283-286.
_ (106) 5
| 1920. Conference sur le varron. In Extrait Bul. Assoc. Francaise
| Destruction du Varron. Juin. (Not seen.)
(107) , and G. TAINTURIER.
1911. Dégénérescence de quelques formes larvaires de l’hypoderme du

boeuf (Hypoderma bovis de Geer). Jn Compt. Rend. Acad.
Sci. [Paris], tome 152, pp. 1192-1194.

(108) Van Dine, D. L., and V. A. NorGaarp.
1908. Abstract of preliminary report on insects affecting live stock in
Hawaii. In Rept. 5th Ann. Meeting Hawaiian Livestock

Breeders’ Assoe., pp. 19-70.
4109) Van Hs, L., and A. F. ScHatx.
1917. Notes on parasitic anaphylaxis and allergy. N. Dak. Agr. Exp. i
Sta. Bul. 125, pp. 149-193, illus. i
(110) Warsurton, C.
1922. The warble flies of cattle, Hypoderma bovis and H. lineatum.
In Parasitology, vol. 14, pp. 322-341, illus. h
{111) Wetts, R. W., F. C. BisHopr, and BE. W. LAAKE. i
|
|
|

1922. Derris as a promising insecticide. Jn Jour. Eeon. Ent., vol. 15,
pp. 90-95.
{112) Witxcocks, F. C. |
1918. Notes on some insects found in Egypt of medical and veteri-
nary interest. Jn Bul. Soc. Ent. d’Egypte, ann. 10, pp. 79-90.

ORGANIZATION OF THE
UNITED STATES DEPARTMENT OF AGRICULTURE

March 23, 1926

NECreliary 07 AQMiCUitte = = eee W. M. JARDINE.
Assistant: Secretary > _Wwiiass eee R. W. DUNLAP.
Director of. Sctenvfic Work eS ——————__—_——

Director of Regulatory Work == 32. WALTER G. CAMPBELL.

Director of Extension Work 322-2 C. W. WARBURTON.
DUEClIOT-Of ANTOTMOAlMOn= = =— a ee NELSON ANTRIM CRAWFORD.
Director of Personnel and Business Ad-

BRUUUS UP OUIO Nt ST eee W. W. STOCKBERGER.
ORG OT, 2.2 vies na SW a a es Be eee R. W. WILLIAMS.
Weather Burequs 80s 1) a ver aaa CHARLES F. Marvin, Chief.
Bureau of Agricuitural Economics______~__. THOMAS P. Cooper, Chief.
Bureau of Animal Industry________=-_-__ JOHN R. Mouter, Chief.
Bureau of Plant Industry______ ee WILLIAM A] TAVEORS Cie
ores! Services = = teak. Het ee eae ee W. B. GREELEY, Chief.
Bureau of. Chemstry2 2 2" 2 > NRT ES C. A. BRowNE, Chief.
PRUTCOU OP <NOUS a eee 2 ea, ro awaetes See Ae . MILTON WHITNEY, Chief.
Buea Of FE ntomology= 262 ee eee ee L. O. Howarp, Chief.
Bureau of Biological Survey__________-____ E. W. NELSON, Chief.
PUL eO Of SEUNG OGUS === = as ee ee THOMAS H. MAcDOoNALD, Chief.
Bureau of Home Economics___-__--_ -___~ LOUISE STANLEY, Chief.
UTC Of DOUYING 22 oF Soe he ergs C. W. Larson, Chief.
Fixed Nitrogen Research Laboratory______ F. G. Corrrety, Director.
Office of Experiment Stations____________- EK. W. ALLEN, Chief.
Office of Cooperative Extension Work_____- C. B. Smiru, Chief.
PER EU) Pe i ey Ma a i as ee Ag CLARIBEL R. BARNETT, Librarian. )
Hederal Hor tieniural Boards ks Mass C. L. Mariatr, Chairman.
Insecticide and Fungicide Board_________~ J. K. Haywoop, Chairman.
Packers and Stockyards Administration__. JOHN T. CAINE, in Charge.
Grain Futures Administration____________ J. W. T. DUveEL, in Charge.

This bulletin is a contribution from

Ur Cual Of LNLOMOLOO YU. = == =e a L. O. Howard, Chief.
120

ADDITIONAL COPIES
OF 1HIS PUBLICATION MAY BE PROCURED FROM
THE SUPERINTENDENT OF DOCUMENTS
GOVERNMENT PRINTING OFFICE
WASHINGTON, D. C.
AT
25 CENTS PER COPY

V

ta a na ei eb ae sin Ieghnn

lg == ARR Se ea

en ae