EFFECTS OF DDT AND
OTHER INSECTICIDES
ON FISH AND WILDLIFE

SUMMARY OF INVESTIGATIONS DURING 1947

fMR3

WOODS HOLE,

CIRCULAR 15

UNITED STATES DEPARTMENT OF THE INTERIOR

FISH AND WILDLIFE SERVICE

EFFECTS OF DDT AND
OTHER INSECTICIDES
ON FISH AND WILDLIFE

SUMMARY OF INVESTIGATIONS DURING 1947

L

W00D:> hUU,

CIRCULAR 15

UNITED STATES DEPARTMENT OF THE INTERIOR

FISH AND WILDLIFE SERVICE

United States Department of the Interior, J. A. Krug, Secretary
Fish and Wildlife Service, Albert M. Day, Director

FOREWORD

During the war and postwar period many new poisons have been and
are being developed which, because of their effectiveness in the control
of insect, rodent, or plant pests, are likely to be distributed widely over
the lands and waters of the United States. DDT is the best known, but
several others are being introduced that have similar potentialities for
harm. The Fish and Wildlife Service is gravely concerned over the
eifects on beneficial fishes and wildlife of such widespread use of toxic
agents, and has conducted a variety of investigations during the past 3
years to measure the harmful effects and, when possible, to determine
procedures or levels of treatment that will reduce them. This circular
summarizes the important results to date and contains recommenda-
tions that will be of interest and value to individuals and agencies
concerned with control of insects and other pests by chemical means.

Albert M. Day, Director.

UNITED STATES GOVERNMENT PRINTING OFFICE: 1948

For sale by the Superintendent of Documents, U. S. Government Printing Office, Washington 25,

D. C. Price 10 cents each

Effects oF DDT and Other Insecticides

on Fish and Wildhfe
Summary of Investigations during 1947^

By JOSEPH P. LINDUSKA and EUGENE W. SURBER, B/o/og/s/s, Fish and Wildlife Service

CONTENTS

Page

Introduction 1

Forest insect control 3

Moscow, Idaho 3

Teton National Forest, Wyo 5

Black Hills National Forest, Wyo 7

Orchard insect control 8

Allegany County, Md 8

Albany, Ga 8

Tick control 10

Camp Bullis, Tex 10

Field tests 11

Agricultural Research Center, Beltsville, Md 11

Patuxent Research Refuge, Laurel, Md 12

Back Creek, W. Va 12

Laboratory tests 13

Toxicity to fishes of new insecticides 13

Effects of DDT on oysters 14

Chronic toxicity to quail of new insecticides 15

Summary 17

Recommendations for minimizing danger to wildlife 18

INTRODUCTION

Since 1945 the Fish and Wildhfe ligations have been summarized

Service, in cooperation with other periodicahy. This, the third ^ such

agencies, has been conducting in- summary report, presents the find-

vestigations to determine the ings of work done in 1947, when

effects of some of the new insecti- major attention again was given

cides on fishes and wildhfe. In to evaluations of DDT (dichloro-

order that control workers and diphenyltrichloroethane) .

others interested in this growing It has become increasingly ap-

problem may have current infor- parent from these studies that,

mation, the results of these inves- aside from the dosage of DDT ap-

' This circular presents the results of field work conducted during 1947 by Stanley P. Rhoades, of the
Forest Service, and Dr. Clarence H. Hoffman, of the Bureau of Entomology and Plant Quarantine,
United States Department of Agriculture ; and the following members and collaborators of the Fish
and Wildlife Service: Joseph P. Linduska, Eugene W. Suroer, David W. Johnston, Lowell Adams,
Mitchell G. Hanavan, Dr. N. W. Hosley, Johnson A. Neff, Robert E. Stewart, Dr. Eugene P. Odum,
Robert A. Norris. William Stickel, Lucille Stickel, John L. George, Chandler S. Robbins, E. Ediger,
Dr. V. L. Loosanoff, C. A. Nomejko, F. D. Tommers, and Allan J. Duvall.

^ The findings of the 1945 and the 1946 investigations on the effects of DDT on fishes and wildlife
were published in Fish and Wildlife Service Circular 11, DDT: Its effect on fish and wildlife, by Clarence
Cottam and Elmer Higgins, 1946 ; and Fish and Wildlife Service Special Scientific Report 41, DDT
investigations by the Fish and Wildlife Service in 1946, by Arnold L. Nelson and Eugene W. Surber,
May 1947 [processed].

CIRCULAR 15, FISH AND WILDLIFE SERVICE

plied, many factors are involved
in determining its ultimate effects
on fishes and wildlife.

The type of formulation, size of
the area, and the method, fre-
quency, and time (season) of ap-
plication are some of the highly
important variables. Many com-
binations of these are to be found
in the numerous methods of con-
trol, and for this reason it is diffi-
cult to make specific recommenda-
tions that will apply to the use of
DDT generally.

Because of the intricate rela-
tionships existing between many
forms of wildlife and their inver-
tebrate food species, there are defi-
nite limitations to what can be
accomplished in the laboratory by
way of evaluating effects of con-
trol agents on wildlife. The fact
that a product is of high toxicity
to vertebrates in the laboratory
may not in itself be a valid basis
for judging its full effects under
conditions of field use. The sum-
mary removal of a basic food sup-
ply by a control operation may
prove critical to fishes and wildlife
even though the direct kill by poi-
soning is nominal. Consequently,
in the continuing studies of eco-
nomic poisons and wildlife, em-
phasis is being placed on evalua-
tions under conditions of actual
use.

During 1947 studies were con-
ducted in several western forest
areas during which DDT in quan-
tities of 1 to 10 pounds to an acre
and the gamma isomer of benzene
hexachloride in quantities of 1
and 2 pounds to an acre were ap-
plied by airplane. The size of
treated areas varied from small
experimental plots of 25 acres to
one that included more than 400,-
000 acres. An experimental aerial
treatment of a forest area near
Beltsville, Md., was made, using a
dosage of 5 pounds of DDT to an
acre; and a 1-mile section of a
West Virginia bass stream was
treated experimentally with a
dosage of 1 pound of DDT to an
acre.

Other studies in 1947 included
follow-ups of the effect of apple-
orchard spraying in Maryland and
pecan-weevil control in Georgia.
Detailed studies were made of the
effects on wildlife of an experi-
mental attempt at tick control in
Texas. Laboratory tests also were
made at Leetown, W. Va., to de-
termine the acute toxic levels for
fishes of several new insecticides ;
and at the Patuxent Research Ref-
uge, Laurel, Md., the chronic poi-
soning effects of several new ma-
terials on quail were measured.
At Milford, Conn., DDT, as it is
used in certain insect-control prac-
tices, was evaluated for its possi-
ble effects on oyster management.

EFFECTS OF DDT AND OTHER INSECTICIDES

FOREST INSECT CONTROL

MOSCOW. IDAHO

In May and June 1947 about
400,000 acres of forest land near
Moscow in northern Idaho were
treated for control of the Douglas
fir tussock moth. DDT in oil, in a
dosage of 1 pound of the toxicant
to an acre, was applied by airplane.
Follow-up studies were made of
the eflTects on fishes, birds, and
mammals.

This project offered an unusual
opportunity for evaluating on a
large operational scale some of the
findings on relationships between
wildlife and insecticides that have
been obtained on much smaller
experimental plots. Unfortunate-
ly, however, the control phases of
the project were divorced from the
investigational work, so planned
studies could not be made. The
spraying schedule, for instance,
was highly flexible, and spray
dates for specific areas could not
be determined in advance. With-
out this information it was im-
possible to time "before" and
"after" studies to the best advan-
tage.

Mammals

An attempt was made through
live-trapping in two plots to deter-
mine the possible effects of the
spraying on small mammals. A
40-acre study unit area was locat-
ed near the center of a treated
area of 50 square miles. Live-
traps were placed grid fashion at
4-chain intervals. A second study
unit, 11/2 acres in size, was near

the edge of a large treated block.
Traps in this case were set at 2-
chain intervals. In both units 76
traps were operated for 428 trap-
nights, and 67 individual mam-
mals were taken a total of 147
times. The species taken by live-
trapping included the red-backed
mouse, white-footed mouse, jump-
ing mouse, and two species of
chipmunks. These limited sam-
ples of the population revealed no
marked effects of the spraying.
Aside from the mammals taken in
trapping, others were under ob-
servation. In all, 16 species or sub-
species were seen before, during,
and after the period of spraying.

Birds

Populations of birds were stud-
ied intensively on two 20-acre
plots, one located within a large
sprayed block and another in an
untreated check area. Censusing
of the plots began June 2 and was
continued until July 11. Spray
was applied to the study area on
June 21. Six censuses were taken
in the treated area before, and five
after, the treatment. The check
plot was censused five times be-
fore, and five times after, the
study area was sprayed.

The spraying had no apparent
effect on the populations of 44
species of birds in the area con-
cerned. Prior to spraying, the
treated area had a density of 435.5
pairs of birds per 100 acres. An
average of counts taken after
spraying showed a density of

CIRCULAR 15, FISH AND WILDLIFE SERVICE

394.0 pairs per 100 acres, a de-
cline of 9.5 percent. In the check
area, populations during- this same
interval declined 10.6 percent,
from 376.5 to 336.5 pairs per 100
acres. The slight drop in numbers
in both areas was believed due to
completion of nesting. Territorial
maps accounted for practically all
the original individuals through-
out the study, and numerous nests
and family groups appeared un-
affected.

A possible effect of the spray
on bird behavior was noted in
Townsend's warbler. This spe-
cies, normally a canopy feeder,
was commonly seen feeding at or
near the ground level after the
spray application. This unusual
habit was not noted prior to treat-
ment of the area. A careful check
of nests and young of the species
showed no measurable effect on
either the young or the adults.

Fishes

Of the more than 50 streams in
the treated area, 40 were known
to contain trout and 18 were listed
as fair to excellent fishing streams.
Rainbow, eastern brook, and cut-
throat trout were not affected by
the insecticide during the 5-week
period of observation. Large pop-
ulations of speckled dace and red-
sided bream were also unaffected
by the poison but cottoids, moun-
tain suckers, and black catfish
suffered heavy losses in rather
limited areas.

Seventy-two trout stomachs
were examined, of which 35 were
from trout taken from stream sec-

tions treated with DDT. Volu-
metric comparison indicated a 50-
percent reduction in available
food, largely in aerial insects and
riffle forms. Ants and worms
were important items of diet both
before and after treatment. Cray-
fish, paralyzed by DDT, com-
prised 99.2 percent of the contents
of the stomachs of 21 brook trout
taken in one treated locality,
whereas no crayfish were found
in stomachs of fish taken in un-
treated areas. All specimens were
caught by rod-and-line fishing, and
there was no evidence that the
vitality of the fish declined after
treatment.

The ecology of stream sections
that received a heavy deposit of
spray was considerably altered.
Annelids and molluscs were not
affected, but insect larvae and
nymphs were virtually eliminated
from the riffle fauna. Even in
fast-moving streams, lethal quan-
tities of DDT were not transmit-
ted far beyond the areas of direct
application. Such limits were
definitely less than 3 miles, prob-
ably not more than 1 mile, con-
sidering the possible drift of air-
borne spray.

Stream sections in which a se-
vere kill of invertebrate life had
occurred were soon marked by a
luxuriant growth of algae, which
completely blanketed many of the
riffles. The earliest replacement
of riffle organisms was a hatch of
mayflies noted 2 months after the
area had been treated.

Although there was no evidence
of immediate damage to game-fish

EFFECTS OF DDT AND OTHER INSECTICIDES

populations, the importance of the
wholesale decline of food organ-
isms could not be determined on
the basis of the single season of
study.

TETON NATIONAL FOREST. WYO.

During July and August 1947,
the Bureau of Entomology and
Plant Quarantine, in cooperation
with the Forest Service, both of
the United States Department of
Agriculture, made an experimen-
tal attempt to control the moun-
tain pine beetle in the Teton Na-
tional Forest, Wyo. Four plots,
totaling 480 acres, were treated.
On three of these (288 acres) , the
dosage applied was 5 pounds of
DDT to an acre, and on the fourth
(192 acres) the dosage was 7i4
pounds of DDT to an acre. In
each case two treatments, using
one-half the total quantity for
each, were made with an 8-day
interval between them. A care-
ful check of results showed that
control of this pine beetle was not
gained. The lack of success was
attributed chiefly to the inade-
quate deposit of DDT on the boles
of the trees by aerial application.

Studies of the effects on wild-
life of this control attempt were
made by members of the Fish and
Wildlife Service and of the Bu-
reau of Entomology and Plant
Quarantine.

Mammals

Plots for studying the effect on
small mammals were selected, one
in an area that received an appli-
cation of 5 pounds of DDT to an

acre, one in an area that received
an application of 7yo pounds to an
acre, and another in an untreated
check area. In all of these an
index to the population level was
obtained by live-trapping both be-
fore and after each of the two
applications. The methods and
intensity of the study were such
that only marked population
changes were likely to be noted.
From the trapping returns
there was no indication of a
marked effect on any of the fol-
lowing species : red-backed mouse
(Clethrionomys gapperi satura-
tus) , field mouse (Microtus lon-
gicaudus) , white-footed mouse
(Peromyscus maniculatiis artemi-
siae) , jumping mouse (Zapus
princeps princeps) , chipmunk
(Eutamias amoenus luteiven-
tris) , and pine squirrel (Tamia-
sciunis douglasii). There were
some indications from field obser-
vations, however, that the heavy
dosages may have caused abnor-
mal behavior and possible mor-
tality. On August 31, the day fol-
lowing the second application on
one of the areas treated with a
dosage of 5 pounds to an acre,
Stanley Rhoades, of the United
States Forest Service, reported an
unusual condition among trapped
chipmunks. Practically all ani-
mals handled at that time were
alternately sluggish and in a state
of muscular tremors. Similar
symptoms were noted in at least
one free chipmunk, which would
indicate that confinement was not
the cause of the atypical condition
noted among trapped individuals.

CIRCULAR 15, FISH AND WILDLIFE SERVICE

In another of the areas receiv-
ing a dosage of 5 pounds of DDT
to an acre, Dr. Clarence Hoffman,
of the Bureau of Entomology and
Plant Quarantine, noted a shrew
in a condition of extreme excita-
bility. It died a few minutes
after it was observed. Although
it was not definitely established
that the shrew died as a result of
DDT poisoning, the symptoms
were highly suggestive.

Birds

Observations were made on
birds from July 19 to August 4.
Since nesting by most species was
completed at that time, a census
could not be obtained. A record,
however, was kept of individuals
seen while the investigator was
traversing marked paths through
the study plots, and this modified
"strip-count" provided a rough
index to numbers and species in
the areas both before and after
spraying. There was consider-
able movement of birds in the
study areas. Each of the treated
blocks, however, was an isolated
unit, all of which was completely
treated, so that the birds in a
given unit were subjected to the
same conditions of spraying. In
all, 33 species were under obser-
vation.

In the area that received 714
pounds of DDT to an acre, the
average daily number of birds
seen prior to spraying was 69.
After the first application of
spray (S%, pounds to an acre)
the same working procedure re-
sulted in a count of 51 birds, a

decline of 26 percent. After the
second treatment the average
daily count dropped to 21 birds, a
decline from the prespray counts
of 69.5 percent.

In the area treated with 5
pounds of DDT to an acre a 42-
percent increase in counts of birds
occurred after the first applica-
tion, and after the second spray-
ing 22 percent more sight records
were recorded than in the period
before treatment. Counts taken
in a check area showed marked
increases during the same period.

As was to be expected, the
greatest numbers of dead and dy-
ing birds were found in the area
that received 71/2 pounds of DDT
to an acre. Of the five victims
found in this unit, three were
pink-sided j uncos. Five species
of woodpeckers were not observed
to be aff'ected by the heavy dosage,
and two families of grouse, one
with five young and the other with
three, survived the 5-pound treat-
ment.

Although the population studies
were inadequate to determine the
true effects, the complete absence
of some species following treat-
ment and the numbers of affected
individuals seen were indicative
of substantial kills in both the
area treated with the 5-pound
dosage and the one treated with
the 7l^-pound dosage.

Fishes

Three of the four plots selected
for treatment were so situated
that aquatic life was little af-
fected. The fourth plot was bor-

EFFECTS OF DDT AND OTHER INSECTICIDES

dered by a small creek, Rock
Creek, for a distance of % mile.
The creek, which had a flow of
only 0.7 cubic foot a second, con-
tained 34 beaver ponds in the sec-
tion studied and supported a large
population of cutthroat trout
(Salmo clarkii lewisi) . The area
was sprayed by airplane with
DDT in the proportion of 5 pounds
of the insecticide to an acre ap-
plied in two equal treatments.
The first spraying of 2.5 pounds
of DDT to an acre was done on
July 22, and a thorough coverage
of the stream resulted. The sec-
ond treatment was applied to the
area on July 30, at which time
almost none of the poison fell on
Rock Creek, except for a light
drift deposited on some parts of it.
After the first spraying only 11
dead fish were found. This kill
was much lighter than was ex-
pected considering the dosage,
and actually was not as great as
has occurred with DDT dosages
of less than half the quantity used
in this test. Certain conditions of
the stream may have greatly min-
imized the loss : a nearly continu-
ous chain of beaver dams slowed
the flow of water so that little
mixing of the spray with the
water of the creek occurred, and
most of the DDT remained sus-
pended at the surface; also, the
stream contained much organic
debris and was very muddy as a
result of activity by the beavers.
Studies have shown that the toxic
action of DDT may be reduced
under such conditions. Another
factor would involve the suscepti-

bility of the cutthroat trout to this
poison. Although toxic levels are
not known for this species, trout
in general have been found less
susceptible to DDT poisoning
than are a number of other fresh-
water species.

In conformity with the in-
creased feeding activities of fishes
observed after DDT has been ap-
plied to a stream, the average
stomach contents of 11 trout
taken at this time were four times
as great as those of 32 fish taken
before spraying. The riffle organ-
isms were greatly reduced in
numbers but were not entirely
wiped out, there being some sur-
vivors among all susceptible in-
sect larvae and nymphs.

BLACK HILLS NATIONAL FOREST.
WYO.

The Bureau of Entomology and
Plant Quarantine and the United
States Forest Service cooperated
in experimental attempts to con-
trol the Black Hills beetle in the
Black Hills National Forest, near
Sundance, Wyo. Each of five
plots varying in size from about
15 to 90 acres was sprayed aeri-
ally with one of the following
toxicants: 10 pounds of DDT to
an acre, 71/2 pounds of DDT to an
acre, 5 pounds of DDT to an acre,

1 pound of gamma isomer of ben-
zene hexachloride to an acre, and

2 pounds of gamma isomer of ben-
zene hexachloride to an acre. The
Fish and Wildlife Service investi-
gated the effects of these experi-
ments on wildlife.

An index to the small mammal

CIRCULAR 15. FISH AND WILDLIFE SERVICE

populations was obtained by live-
trapping both before and after
spraying, and an intensive search
was made for mortalities. No
evidence was found that any of
the five species of small mammals
taken by trapping was measur-
ably reduced by any of the spray
applications.

A systematic coverage of plots
also showed little effect on the
varied bird population. The small

size of the plots, however, several
of which were also long and nar-
row, and the fact that few indi-
viduals were restricted to terri-
tories by nesting activities, un-
doubtedly minimized the effects of
the treatment. Arctic three-toed
woodpeckers in a nest near the
center of the plot that received the
application of 71^ pounds of DDT
to an acre were unaffected by the
spraying and developed normally.

ORCHARD INSECT CONTROL

ALLEGANY COUNTY, MD.

A rather cursory survey of bird
populations in an orchard area in
Allegany County, Md., indicated
that DDT as used for codling
moth control may have pro-
nounced effects on the bird popu-
lations. Late in July, a bird cen-
sus was taken on a 22i/4-acre plot
in an orchard that had been
sprayed with DDT, and four
species were found present in the
ratio of 31 pairs to 100 acres. A
similar plot in a nearby orchard,
unsprayed because of early frost
damage, had a population of 89
pairs to 100 acres and represented
by nine species.

The spray schedule followed in
the treated orchard called for the
deposition of an equivalent of 15
to 22.5 pounds of DDT to an acre
for each application. At the time
of the study two applications had
been made ; hence 30 to 45 pounds
of DDT to an acre had been dis-
tributed on the area. Additional
cover sprays brought the total

quantity of DDT applied to the
orchard during the season to 60
to 70 pounds or more to an acre.

ALBANY, GA.

Between July 30 and August 28,
1947, Dr. Eugene P. Odum and
Robert A. Norris, collaborators of
the Fish and Wildlife Service,
conducted studies on the effect on
birds of DDT used in pecan weevil
control near Albany, Ga. Ten
pecan groves were under observa-
tion. Four of these received one
application of DDT, three re-
ceived two applications (about 2
weeks apart), and three un-
sprayed groves were used as check
areas.

The spray formulation was 6
pounds of 50-percent wettable
DDT powder (3 pounds of DDT)
to each 100 gallons of water. The
quantities of the mixture applied
by individual owners contained
DDT in amounts ranging from
0.18 to 0.43 pound to a tree or
from 2.0 to 6.5 pounds to an acre

EFFECTS OF DDT AND OTHER INSECTICIDES

(the average being 4.3 pounds to
an acre). The spray was con-
fined mostly to the trees and little
reached the ground level between
or under the trees.

By the time spraying was be-
gun most birds had completed
nesting. Nevertheless, without
considering juvenile and transient
birds, a reasonably stable popula-
tion was worked with, the birds
numbering 50 to 104 individuals
to 100 acres in different orchards.

Population counts indicated lit-
tle effect of the DDT spraying. A
decline in numbers of birds in
treated areas was noted, but this
was about comparable with the
decreases observed in check or-
chards. No dead birds or birds
showing symptoms of DDT poi-
soning were seen. Of four nests
under observation, both before
and after spraying, the birds in
three progressed normally but the
fourth nest was deserted after the
second spraying. The cause of
desertion could not be definitely
determined.

For a day or more after the
spraying operations numerous
dead and dying insects, represent-

ing many species, were conspicu-
ous on the sparsely covered
ground. With minor exceptions,
the birds were not attracted to
this ready source of food but con-
tinued to forage in their normal
niches.

The dosages of DDT used in
pecan weevil control are known to
be critical for birds when used
under other conditions. Factors
that might mitigate the effects on
birds in the type of operation con-
ducted at Albany, Ga., would
probably include : (1) the limited
size of the orchards, the birds not
being confined to the treated area,
and their summer feeding range
extending beyond the orchard
limits; (2) the period of spraying
was later than the peak nesting
period, and only a few late-nest-
ing individuals were concerned
with the nearly continual job of
food-gathering required of birds
with nestling young; and (3) ex-
cept for a few ground-feeding
species, the birds appeared not to
be attracted to the abundant
ground supply of fallen, contami-
nated insects.

10

CIRCULAR 15, FISH AND WILDLIFE SERVICE

TICK CONTROL

CAMP BULLIS. TEX.

During the summer of 1947, the
vahie of DDT dust for tick control
was investigated in a large-scale
field experiment by the United
States Army and the United
States Department of Agricul-
ture. The treated area was a
206-acre plot at Camp Bullis,
Tex., within the Leon Springs
Military Reservation, about 18
miles northwest of San Antonio.
A mixture of 10-percent DDT in
pyrophyllite was applied to the
ground and vegetation by means
of two dry-fog orchard dusters.
The rate of application was 43.56
pounds of the dust mixture, or
4.36 pounds of DDT, to an acre.
The effects of the experiment on
wildlife were studied by members
of the Fish and Wildlife Service.

Mammals

Small mammals were too few in
numbers to carry on intensive
population studies by live-trap-
ping methods. Other larger,
wider-ranging species, although
plentiful, were not limited by
normal range to the 206-acre
treated plot, and so were not well
suited for study subjects. Never-
theless, intensive studies prior to
and after treatment showed that
the following species apparently
were unaffected or only slightly
affected by the DDT operations:
white-tailed deer, raccoon, striped
skunk, armadillo, jack rabbit, and
cottontail rabbit.

Birds

An abundant bird population
was studied by comparing popula-
tion trends in a 40-acre study plot
in the treated area with those in a
check area of similar size. An
intensive search was made for
mortalities. In all, 86 pairs of
adult birds, representing 33 spe-
cies, were recorded on the study
area. A comparable predusting
population of 90 pairs was found
on the check area.

The first evidence of bird kill
was noted on the day after appli-
cation of the dust. From all indi-
cations deaths continued through
the fifth day. Fifteen dead birds
were found — 9 cardinals, 2
painted buntings, 2 lark spar-
rows, 1 yellow-breasted chat, and
1 white-eyed vireo. Because dense
ground cover in many places
made the recovery of poisoned
birds difficult, the true extent of
the kill is better indicated by the
decline in the census counts from
86 pairs before, to 39 pairs after,
dusting. The population in the
check plot dropped from 90 to 78
pairs during the same period.
The individuals found dead indi-
cated that the species primarily
affected were the ground and low-
strata feeders. Population rec-
ords for the 9 species of birds that
appeared to be most seriously af-
fected by application of DDT dust
are given in table 1.

EFFECTS OF DDT AND OTHER INSECTICIDES

Table 1. — Population records for 9 species of birds that appeared to he most
seriously affected by application of DDT dust

Species

Texas wren

Carolina wren

Kentuclty warbler

Yellow-breasted chat

Cardinal

Blue grosbeak

Painted bunting

Lark sparrow

Field sparrow

Total

Number of pairs
counted before

dusting

Number of pairs counted during the first 6
days after dusting

1st day 2d day 3d day 4th day 5th day 6th day

17

Other Species of Wildlife

Four insectivorous rough green
snakes (Opheodrys aestivus) and
one large spiny lizard (Sceloporus
olivaceous) were found dead in
the study area after the dusting

operations. It is believed that
mortality among these forms of
wildlife was heavy, although be-
cause of their secretive habits and
the heavy ground cover compara-
tively few victims were found.

FIELD TESTS

AGRICULTURAL RESEARCH

CENTER,

BELTSVILLE. MD.

At the Agricultural Research
Center, Beltsville, Md., a 90-acre
tract covered with a 5-year-old
growth of scrub and saplings was
sprayed experimentally with DDT
in the proportion of 5 pounds to
an acre, and a detailed study was
made of the effects on the bird
population.

Prior to spraying, repeated cen-
suses determined the nesting-bird
population on a 30-acre plot at the
center of the test area and also in
a comparable check plot situated
half a mile away. The area was
sprayed on the morning of July 3,
1947, and the effects on the birds
were noticeable within 24 hours.
Although the extremely dense

undergrowth impeded the search
for sick or dead birds, seven indi-
viduals with typical DDT symp-
toms were seen on the day after
the spray application. Census
counts revealed a rapid decline in
populations. The number of Mary-
land yellowthroats decreased 63
percent in the first 24 hours, and
the total decrease for the species
during the period of the study
was 79 percent. Prairie warblers
declined 64 percent in numbers
during the first day and at the end
of 48 hours they were down to 7
percent of their prespray popula-
tion. A slight increase in the
numbers of this species was noted
a week later, however, which may
have been due to movement of in-
dividuals into the plot from sur-
rounding areas. House wrens de-

12

CIRCULAR 15, FISH AND WILDLIFE SERVICE

creased 59 percent in numbers
during the first 24-hour period
and continued to decrease during
the six succeeding days. Red-
eyed towhees showed a drop of 35
percent in numbers, which may
have been a reflection of their
habit of feeding in duff and litter.
Of the five commonest species in
the area, three — the Maryland
yellowthroat, prairie warbler, and
house wren — were reduced 80
percent. The total decrease in
numbers of the five most abun-
dant species, which comprised 77
percent of the original popula-
tion, was 65 percent.

The populations of the small
mammals in the area were too low
for detailed studies of effects to be
made. One dead meadow vole
was found, however, and DDT
was recovered from the tissues.

PATUXENT RESEARCH REFUGE.
LAUREL, MD.

Late in May 1947 a 117-acre
tract of bottom-land woods on
the Patuxent Research Refuge,
Laurel, Md., was sprayed with
DDT by airplane for the third suc-
cessive year. For that applica-
tion the DDT was used at the rate
of 2 pounds to an acre. A casual
check of bird residents revealed
no effects on the group. No at-
tempt was made to get detailed
evaluations of the spraying, since
the primary objective of this par-
ticular investigation is to deter-
mine any cumulative effects from
repeated yearly treatments. Ex-
haustive studies of both the insect
and the vertebrate life will be

made after the fourth or fifth
annual treatment of the area, and
the findings compared with the
detailed information obtained
prior to the first spraying.

BACK CREEK. W. VA.

A one-mile section of Back
Creek, W. Va., was sprayed in
1946 with DDT in suspension at
the rate of 1 pound to an acre.
The results of this experimental
treatment were given in the sum-
mary of DDT investigations for
that year. During 1947, addition-
al studies of the bottom fauna were
made to determine the extent of
recovery. Although bottom or-
ganisms were reduced 70 percent
in numbers at some stations after
the spraying in 1946, investiga-
tions a year later showed that re-
covery was practically complete.

On July 23, 1947, a 1-mile sec-
tion of Back Creek was again
sprayed with DDT in the same
proportion as in 1946, but mixed
with oil instead of held in suspen-
sion. The average quantity of
DDT deposited at water level was
0.27 pound to an acre, whereas in
the tests the year before a some-
what greater quantity of 0.39
pound to an acre was deposited.
Some differences in effect were
noted between the two types of
formulations. The DDT in sus-
pension used in 1946 did not ma-
terially reduce the numbers of the
surface Coleoptera and Hemip-
tera. These same groups, how-
ever, were immediately and
markedly affected by the lasting

EFFECTS OF DDT AND OTHER INSECTICIDES

13

surface film of the DDT in oil used
in 1947. The reduction of bot-
tom fauna in 1947, as in 1946, was
very heavy and amounted to 90
percent at two of the lower sta-
tions. The bottom species affected
by the oil spray were about the

same as those hardest hit by the
suspension. The kill of fish, also,
was somewhat heavier with the
oil formulation, and in contrast to
the results with the DDT in sus-
pension, a number of adult fish
were among those killed.

LABORATORY TESTS

TOXICITY TO FISHES OF NEW
INSECTICIDES

Tests were made at the experi-
ment station of the Fish and Wild-
life Service at Leetown, W. Va.,
to determine the toxicity to fishes
of some of the new insecticides.
Although these studies have not
as yet been completed, pond and
aquarium tests have shown the
relative toxicities of several com-
pounds to be about as follows :

Chlorinated camphene is con-
siderably more toxic to fishes than
is DDT and is lethal to silverling
minnows, spotfin shiners, creek
chubs, fallfish, and black-nosed
dace in concentrations of less than
0.04 p. p. m. (parts per million).
In outdoor ponds an application of
0.125 pound to an acre (0.02
p. p. m.) killed all these species,
but goldfish survived.

Repeated tests on bluegill sun-
fish and young rainbow and brown
trout indicated that bluegills were
less sensitive than trout, which
were killed even at concentrations
of 0.005 p. p. m. (one part in 200,-

000,000) . The threshold limit for
bluegills was 0.01 p. p. m.

Benzene hexachloride is less
toxic to fishes than is DDT. Ap-
plication of 1 pound to an acre
(0.18 p. p. m.) in a field formula-
tion ^ on daphnia ponds did not kill
bluegill sunfish, goldfish, creek
chubs, black-nosed dace, common
shiners, fallfish, blunt-nosed min-
nows, sculpins, golden shiners,
and darters. In aquaria, inch-
long bluegills tolerated concentra-
tions of 0.45 p. p. m.

A comparison of the beta, delta,
and gamma isomers and their ef-
fects on rainbow and brown trout
at 0.05, 0.2, and 0.5 p. p. m. in ace-
tone solutions of the pure chemi-
cals showed a marked difference
in toxicity to the fish. Gamma
isomer killed all fish exposed at
these rates; beta isomer showed no
effect ; and delta at the two higher
levels produced symptoms of tox-
icity (pectoral fins forward, loco-
motion affected), but the fish re-
covered. Rainbow trout were
more susceptible to the gamma
isomer than were brown trout.

* Field formulation:

1 lb. tech. benzene hexachloride (12 per-
cent gamma isomer)
2,846 ml. aux. solvent (PD-544-B)
Fuel oil No. 2 to make 1 gallon.

14

CIRCULAR 15, FISH AND WILDLIFE SERVICE

Chlordan is less toxic to fishes
than is DDT but more toxic than
benzene hexachloride. Applica-
tions of 1 pound to an acre to out-
door ponds killed 87 percent of the
bluegill sunfish. With applica-
tions of 0.5 pound to an acre most
of the bluegills as well as other
species survived, and v^^ith those
of 0.25 pound to an acre practi-
cally all fishes survived. A 12-per-
cent chlordan solution (w^t/vol) in
fuel oil was used in all applications.

TEPP (Tetraethyl-pyrophos-
phate). Tests with TEPP indi-
cate its toxicity to fishes is com-
parable with that of DDT. Con-
centrations of 0.25 p. p. m. or more
were found to be lethal in aqua-
rium tests.

Parathion. In the purest form
available parathion did not kill
one-inch rainbow and brown trout
at 0.063, 0.189, and 0.378 p. p. m.
Experimental work on the effects
of this insecticide has not been
completed. The observation, how-
ever, that 0.2 p. p. m. is near the
threshold point for bluegills was
confirmed. Preliminary experi-
ments with 25-percent emulsi-
fiable parathion powder on blue-
gill sunfish showed scattered mor-
tality at 0.1 and 0.2 p. p. m., and
approximately 50 percent mortal-
ity at 0.3 p. p. m.

Bis (p-chlorophenoxy) methane
was tested only with bluegill sun-
fish approximately 1 inch long.
There was no mortality at 0.05
p. p. m., and very low mortality at
0.10 p. p. m. All fish treated died

when the concentration reached
0.2 p. p. m.

EFFECTS OF DDT ON OYSTERS

DDT is being widely used for
mosquito control in many salt-
water areas and for control of flies
in fish-packing areas. The spray-
ing of piles of oyster shells with
DDT to eliminate fly nuisance is a
rather common practice. As these
same shells may be used as cultch
for a new generation of oysters, it
is important to know whether
spraying them with DDT will in-
hibit their later use for collecting
young oysters.

To determine some of the rela-
tionships between insect control
through the use of DDT and oys-
ter management, a number of
studies were carried on at the Mil-
ford Biological Laboratory, Mil-
ford, Conn. The results of these
investigations have been reported
in a manuscript * prepared for
publication by V. L. Loosanoff,
C. A. Nomejko, and F. D. Tom-
mers, from which the following
summary is taken:

Neither DDT nor kerosene alone
substantially depressed the rate
of setting of oysters, but the com-
bined effects of DDT and kerosene
reduced the setting on shells
dipped for 30 seconds in a 5-per-
cent solution of DDT in kerosene.

The effect of the DDT solution
was not noticeably diminished
even when shells were dipped in
the solution several weeks before
planting them.

* Effects of DDT on oysters, by V. L. Loosanoff,
C. A. Nomejko, and F. D. Tommers. [Unpub-
lished.]

EFFECTS OF DDT AND OTHER INSECTICIDES

15

DDT in emulsion appeared to be
more toxic than in a solution of
the same concentration in kero-
sene.

The spraying- of oyster shells
with a 5-percent solution of DDT
in kerosene at the rate of 1 pound
to an acre did not interfere with
the setting of oysters. Spraying
the same solution at the rate of 3
or 5 pounds of DDT to an acre,
however, may somewhat affect
the intensity of setting, although
this was not clearly shown in the
experiments.

The spraying of oyster beds
with DDT solution or emulsion at
the rate of li/^ pounds of DDT to
an acre caused no unusual mor-
tality among adult or young oys-
ters. Beds sprayed with DDT
emulsion usually showed a lighter
set than did the untreated control
beds or beds sprayed with a 5-per-
cent DDT solution in kerosene.

DDT-painted vertical concrete
collectors had somewhat fewer
oysters than the kerosene-painted
collectors or those in the un-
treated control beds. Untreated
controls collected the largest num-
ber of spat.

No significant difference was
found in the average size of oys-
ters on the untreated and the
DDT-treated collectors.

The dipping of adult oysters in
a 5-percent solution of DDT and
kerosene resulted in the same rate
of mortality as that of oysters
dipped in kerosene without DDT.
It did not significantly affect their
rate of growth or increase in
weight.

The shell movement of oysters
kept in aquaria to which a 5-per-
cent solution of DDT was added
in quantities of approximately 5
pounds of DDT to an acre was not
different from that of control
oysters. No mortality was ob-
served during exposure ranging
from about 5 to 8 days and for 6
weeks after exposure.

Oysters kept in a concentration
of one or two parts of DDT in
emulsion per million parts of
water, although showing abnor-
mal shell movements, survived
periods of exposure ranging from
about 5 to 8^2 days. It is doubt-
ful^ therefore, that sufficient con-
centrations created under natural
conditions for comparatively short
periods would seriously affect
adult oysters.

The treatment of oyster shells
with a solution or emulsion of
DDT virtually prevented the set-
ting of barnacles.

CHRONIC TOXICITY TO QUAIL OF
NEW INSECTICIDES

Several new insecticides were
tested at the Patuxent Research
Refuge for their chronic effect on
quail. For these tests, four floor-
less brooder coops each having a
base area of 46.7 square feet were
used to confine groups of 20 quail
(10 males and 10 females). In the
first test, the effects of spraying the
habitat were studied. Wettable
mixtures of DDT, DDD (dichloro-
diphenyldichloroethane) , benzene
hexachloride, and chlorinated
camphene were applied to the veg-
etation in the pens, one mixture to

16

CIRCULAR 15, FISH AND WILDLIFE SERVICE

a pen, at the rate of 5 pounds of
the toxicant to an acre. Water
and a full diet of untreated food
were provided the birds. All veg-
etation in the pens was consumed
by the quail within two to three
days, and the birds showed no ill
effects or loss in weight when the
test terminated on the 10th day.

These quail were then placed on
a diet that included 0.025 percent
of the same toxicant previously
sprayed in their respective hold-
ing pens. The 0.025 percent rep-
resented the quantity of DDT in
the diet that had previously been
found lethal for 50 percent of
young quail over a period of 2
months. All the feed mixtures
were readily accepted.

The first signs of abnormal
behavior (extreme excitability)
among these quail were noted
among the DDT-fed birds on the
8th day. The first mortalities oc-
curred in the same group, when 3
individuals died on the 11th day.
On the 14th day a female on the
DDD diet was found dead, and a
second female from the same
group found moribund in the
morning of that day died during
the day without showing unusual
symptoms. No other mortalities
occurred among any of the test
groups until the 32d day, when a
female on the chlorinated cam-
phene diet died. This quail at the
beginning of the test period was
lighter in weight than the average
weight of the birds and may have

had more than an average suscep-
tibility to the poison. On the 34th
day a male on the benzene hexa-
chloride diet died. No other
losses were recorded up to the
44th day when tests were termi-
nated. The total losses attributed
to poisoning by the insecticides
were: DDT-fed birds, 3 deaths;
DDD-fed birds, 2 deaths; ben-
zene-hexachloride-fed birds, 1
death ; and chlorinated-camphene-
fed birds, 1 death (questionable).
Weight records for the quail in
these tests showed no marked dif-
ferences, although DDT-fed birds,
which suffered the highest mor-
tality, also showed the least gain
in weight.

Some of the toxicants used in
these tests may be stored in
body tissue, and so animals held
on a sublethal diet may accumu-
late considerable quantities of the
poison. Other studies have shown
that acute toxic symptoms may
appear when partial starvation
causes a utilization of fat reserves
and a release of the stored toxi-
cant. An attempt was made to
determine this point for the quail
given the diets just described. At
the conclusion of the feeding tests
all food was withheld for an in-
terval of two days. A quantity
of feed adequate for one day of
feeding was then provided each
group, and a second 2-day period
of starvation was imposed. This
treatment had no apparent effect
on any of the test groups.

EFFECTS OF DDT AND OTHER INSECTICIDES

SUMMARY

17

Investigations during 1947 of
insecticide-wildlife relationships
included field and laboratory tests,
and evaluations of actual opera-
tions.

In one area of more than 400,-
000 acres of forest land in Idaho,
DDT in oil was applied by airplane
at the rate of 1 pound to an acre
for control of the Douglas fir tus-
sock moth. Studies near the
center of a large, continuously
treated block indicated about the
same wildlife eff'ects as had pre-
viously been found in smaller
units. Birds and mammals were
unaffected. Fishes were affected
but slightly in the area as a whole,
but rather heavy losses of some
species were noted in limited re-
gions. Uneven spray distribution
or unintentional retreatment may
have been the cause for the heavy
fish kill in some parts of the area.

In two forest areas in Wyoming
aerial applications were made of
DDT in quantities of 5 to 10
pounds to an acre and of the
gamma isomer of benzene hexa-
chloride in quantities of 1 and 2
pounds to an acre. In the tests on
the Teton National Forest, treat-
ments of 5 and 7i^ pounds to an
acre caused heavy bird damage,
and there were indications that
mammals were also affected by the
heavier application. The destruc-
tion of fishes was not so heavy as
has been found elsewhere with
much lighter dosages. A continu-
ous chain of beaver dams, which
retarded the flow of the stream

and reduced the mixing of the
DDT-oil solution with the muddy,
debris-filled water, probably mini-
mized the effects of the spray.

None of the experimental appli-
cations of DDT and benzene hexa-
chloride in tests in the Black Hills
produced measurable effects on
birds or on five species of live-
trapped mammals. The small size
of the plots and the fact that the
birds were through nesting and so
not restricted to territories prob-
ably lessened the possibilities of
poisoning.

Evidence that the size of the
treated area and the time of spray-
ing with reference to seasonal bird
activity may strongly modify
spraying effects was also found in
studies made near Albany, Ga.,
where DDT at the rate of 2 to 6.5
pounds to an acre was applied to
an area in pecan weevil control
operations.

Indications of a heavy song-bird
mortality were found in prelimi-
nary studies in a Maryland apple-
orchard district where seasonal
totals of more than 50 pounds of
DDT to an acre had been used.

In an experimental progranl of
tick control in Texas in which
DDT dust in the quantity of 4.36
pounds to an acre was used, there
was a 50-percent reduction in the
bird population. Mammals were
slightly affected, if at all, and some
kill of amphibians and reptiles was
observed.

In a Maryland woodland the ex-
perimental aerial treatment of

18

CIRCULAR 15. FISH AND WILDLIFE SERVICE

scrub and sapling growth with 5
pounds of DDT to an acre caused a
heavy bird mortahty. Three of
the commonest species were re-
duced 80 percent in numbers, and
the total reduction for the 5 com-
monest species was 65 percent.

The aerial application of DDT
in oil at a rate of 1 pound to an
acre to a 1-mile section of Back
Creek, W. Va., caused a nominal
kill of fishes but a heavy kill of
bottom fauna. At the lower end
of the 1-mile section more than
90 percent of the aquatic organ-
isms were killed.

Laboratory tests of several new
insecticides showed that chlo-
rinated camphene was consider-
ably more toxic to fishes than was
DDT; TEPP (tetraethyl-pyro-
phosphate), parathion, and bis
(p-chlorophenoxy) methane were
about of the same toxicity as DDT;
and chlordan and benzene hexa-
chloride were slightly less toxic in

field formulations. In chronic tox-
icity tests with quail, DDT ap-
peared to be slightly more toxic
than were DDD, benzene hexa-
chloride, and chlorinated cam-
phene. The last named was ap-
parently the least toxic of the
group.

Detailed studies of the effects
of DDT on oysters indicated that
these shellfish are fairly resistant.
Spraying of oyster beds at the
rate of li^ pounds of DDT to an
acre, applied either as an emulsion
or in an oil solution, caused no
mortality among adults or young.
Application rates up to 5 pounds
to an acre showed no evidence
that spraying shell piles for fly
control appreciably reduced the
value of the shells for collecting
set. In fact, spraying the shells
with DDT appeared to have a posi-
tive value in that it prevented the
attachment of barnacles.

RECOMMENDATIONS FOR MINIMIZING
DANGER TO WILDLIFE

Additional investigations have
shown no cause for modifying ap-
preciably the recommendations
given first in Fish and Wildlife
Circular 11, DDT: Its Effect on
Fish and Wildlife, and restated in
the summary of the 1946 studies.
With minor revisions these are
given again herein :

Use DDT for the control of an
ineect pest only after weighing
the value of such control against
the harm that will be done to

beneficial forms of life. Wher-
ever more than a small area is in-
volved, consult county agricultural
agents. State or Federal ento-
mologists, wildlife and fishery bi-
ologists, and United States Public
Health Service officials.

Use DDT only where it is
needed, and in all cases use only
the minimum quantity necessary
for control. Wherever it is ap-
plied by airplane, provide careful
plane-to-ground control to insure

EFFECTS OF DDT AND OTHER INSECTICIDES

19

even coverage and to prevent local
overdosage.

Because of the sensitivity of
fishes and crabs to DDT, avoid, as
far as possible, direct applications
to streams, lakes, and coastal
bays.

In aerial applications over
aquatic areas, use one-fifth pound
or less of DDT to an acre in oil
solution to avoid damage to fishes,
crabs, or crayfishes. If treatment
is repeated several times in a sea-
son, use one-tenth pound to an
acre or less. As a greater per-
centage of the applied dosage is
deposited at the water surface by
most ground methods of applica-
tion, these dosages should be re-
duced by 50 percent when ground
spray equipment is used.

In forest areas use less than 2

pounds of DDT to an acre to avoid
damage to birds, amphibians, and
mammals. Because of its great
toxicity to many aquatic forms,
use smaller quantities of DDT in
emulsions.

Wherever DDT is used, make
careful before and after observa-
tions of mammals, birds, fishes,
and other wildlife.

In the control of early appear-
ing insect pests, apply DDT, if
possible, just before the emer-
gence of leaves and the main
spring migration of birds ; for late
appearing pests, delay applica-
tions, whenever practicable, past
the nesting period of birds. Ad-
just crop applications and mos-
quito-control applications so far
as possible to avoid the nesting
period.

U. S. GOVERNMENT PRINTING OFFICE 791813

MBL who: Library - Serials

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