Field studies on the effect of DDT on aquatic insects


Material Information

Field studies on the effect of DDT on aquatic insects
Physical Description:
20, 6 p. : ill. ; 27 cm.
Hoffmann, C. H
United States -- Bureau of Entomology and Plant Quarantine
United States Department of Agriculture, Agricultural Research Administration, Bureau of Entomology and Plant Quarantine
Place of Publication:
Washington, D.C
Publication Date:


Subjects / Keywords:
DDT (Insecticide) -- Field experiments   ( lcsh )
Aquatic insects -- Control   ( lcsh )
federal government publication   ( marcgt )
non-fiction   ( marcgt )


Additional Physical Form:
Also available in electronic format.
Statement of Responsibility:
by C.H. Hoffmann ... et al..
General Note:
Caption title.
General Note:
General Note:
"August 1946."

Record Information

Source Institution:
University of Florida
Rights Management:
All applicable rights reserved by the source institution and holding location.
Resource Identifier:
aleph - 030292386
oclc - 780065593
System ID:

Full Text
E-702 August 1946

United States Department of Agriculture
Agricultural Research Administration
Bureau of Entomology and Plant Quarantine

By C. H. Hoffmann, Division of Forest Insect Investigations,
H. K. Townes and R. I. Sailer, Division of Insect Identification,
and H. H. Swift, Division of Forest Insect Investigations

During 1945 a number of streams and ponds were given experi-
mental treatments with DDT to obtain data on its effect on their
macroscopic invertebrate faunas. In studying a given body of
water, the procedure was to obtain pretreatment information on the
species present and the population density of each. The treatment
was applied shortly after this estimate was completed. The
species present and the population density of each were checked
after treatment by the same methods, and the differences, when not
paralleled in similar untreated habitats, construed to be due to
DDT. The occurrence of dead or dying specimens after the treat-
ment was considered evidence that DDT was responsible for deple-
tion or elimination of a species. Population surveys at intervals
after the treatment gave information on how long DDT was present
in lethal amounts, the rate of repopulation, and additional data
on the species eliminated oi, reduced.

Studies on Aquatic Invertebrates in Streams

Parts of three trout streams near Scranton, Pa., and a sec-
tion of the Patuxent River near Bowie, Md., were treated by air-
plane with an oil solution of DDT. The dosage ranged from 1 to
5 pounds of DDT per acre, but the amount actually deposited on
the water surface was estimated to be one-fifth to one-third of
that applied. Each of these treatments is discussed as a separ-
ate experiment.

2/Acknowledgment is made to the Division of Gypsy and Brown-
tail Moths Control, especially to J. M. Corliss, for supervising
the spraying of the streams; to the Division of Insecticide In-
vestigations for the DDT analyses; to the Fish and Wildlife Ser-
vice of the U. S. Department of the Interior, for data on the rate
of flow of Ash Creek and on the amount of DDT deposited on the
Patuxent River; and particularly to the following specialists for
assistance with the determination of specimens: Jay Traver,
Massachusetts State College (Ephemerida); J. P. E. Morrison,
Smithsonian Institution (Mollusca).

SEP 1 94


Collection methods.--Quantitative data on the bottom faunas
were secured with a stream square-foot sampler designed by A. D.
Hess.- This sampler consists of a cylinder 2 feet high, open at
the ends, of a diameter (13.6 inches)to cover 1 square foot of
stream bottom. The side of the cylinder placed upstream is covered
with 16-mesh screening, allowing the current easy access. The
downstream side is covered with heavy canvas, which directs the
current into a long conical bag of scrim netting sewed to an open-
ing in the canvas. Stones and vegetation in the enclosed square
foot.are washed by hand as clean as possible of organisms, and the
remaining gravel is stirred vigorously with a stick. Once de-
tached, the organisms are washed into the bag by the current, and
at the completion of the collection the bag is emptied into white
enameled pans and the catch separated from the debris with pi-
pettes and forceps. Figure 1 shows the apparatus in use.

To obtain accurate results the sampler should be used by a
person knowing the habits and distribution of the organisms being
sampled, and the work must be done under favorable conditions. It
is important to have the lower edge of the sampler fit the stream
bottom tightly. Large stones frequently prevent this and make
accurate sampling impossible, as many of the organisms are washed
through the cracks around them. Under good conditions probably
about 80 percent of the larger specimens present are collected.
In the present study collections were made only in riffles.
Slower stretches contain fewer specimens and are more difficult to

A valuable supplement to the square-foot sampler is a screen
collector. This consists of a piece of 16-mesh wire screening
about 3 feet wide and 2 feet high, the ends of which are tacked
to wooden stakes that project upwards as handles. In use, the
screen is placed across the current and held in place by means of
the wooden handles. With one foot or a stick the operator can
then stir the bottom stones and gravel upstream. The current
washes the dislodged organisms against the screen, which when
lifted from the water brings them with it. This is a very simple
and effective device, but it is not practical for obtaining quan-
titative data because the size of the area collected is difficult
to control.

/Hess, A. D. New limnological sampling equipment. Lim-
nological Soc. Amer. Spec. Pub. 6: 2-3, illus. 1941.


The ravine brook.--The stream referred to here as the ravine
brook is located in Spring Brook township, near Scranton, Pa.,
about 4 miles southeast of the town of Moosic. It empties into
Spring Brook a few hundred feet below the mouth of Green Run. It
is about 0.4 mile long, arises in and flows through a broad ravine
on the side of a small mountain, and consists of alternating drops,
pools, and short riffles. In the drier part of the summer all but
its lower few hundred feet dries to an under--round trickle. At
other times it is about 2 feet wide and 2 to 4 inches deep. In
1945, a wet summer, it was about this size all summer except for
a few days late in July when most of the stream went dry. Because
of the temporary nature of the stream, its fauna is rather scanty,
consisting of species able to survive during dry periods in iso-
lated pools or in the dampness or percolating water of leaf drifts
and gravel.

From May 21 to June 1 all but the lower 800 feet of the
stream and its watershed was sj-rayed by airplane at the rate of
4 to 5 pounds of DDT per acre. The area was covered in sections
as weather permitted airplane operation. The formula, per gallon
of spray, was 1 pound of DDT, 1 quart of xyleue, and 2.Fe2 quarts
of horticultural r -r.. oil. The course of this str-l.m va -. through
moderately thick forest the foliage of which caught much of the
spray, so that the DDT reaching the surface of the ?treir: averaged
probably less than a pound per acr-eS, with local variations. The
actual deposit was not mr-eas',red. An unknown "- ,t., of 0.:-
drifted onto the lower 800 feet of the stT Er which,. -i int....
to be untreated.

Within an hour after the o!jr y was applied, nymphs lar-av&e
of Ameletus, Leuctra, Dploer, Pcnosyche, and others could
be seen swimming and crawling in the sane erratic and a: vrdly
ineffective manner that characterizes terrestrial insects affected
by DDT. Collections in the stream 10 da;-- later showed decaying
remains of large numbers of various aquatic inc-:-ts n- of cray-
fish in the stream bottom, most of them in the bottf.I!:, of the
small pools to which the., had3 been carried by the iirre -t.

Pretreatment quantitative collections of t.he bottom fauna
were taken with the stream souare-foot sarcler on hay 5 and 17.
The samples were taken at two stations near the lv.r edpe of the
area to be strayed with DDT and at one station 750 feet below it.
Ordinarily two square-foot samples v.ere taken at each station on
each date. On June 6 and 29, 5 and 28 days after treatment, the
collection stations were visited again and square-foot samilles
taken, two at each station on June 6 and three at each station on
June 29. On June 29 and August 27 the screen collector was used
five times at each station in an effort to collect scarce species

missed in the square-foot samples.

The forms taken in each square-foot sample are listed for
each station in table 1.

The table shows that at two stations in the sprayed section
of the stream all invertebrates except worms and some of the more
resistant insect species were apparently exterminated. i-ost of
the insect survivors iere those protected in leaf drifts. The
reduction in the number of invertebrates present at the upper
station was 92 percent and at the middle station 87 percent. At
the third, or lower, station, about 750 feet below the sprayed
area, the fauna was subjected to spray drift and to DDT carried
down by the stream. Between the sprayed area and this station,
however, there is considerable seepage through leaf drifts and
gravel, which probably removed much of the DDT. A few of the
more susceptible species seem to have been exterminated here, but
most were r::.,ce' only moderately or not at all. Because these
fev, susceptible species made up a large portion of the pretreat-
ment population, their elimination resulted in an over-all re-
duction of FO percent.

The table includes an estimate as to whether a gIven species
was exterminated, reduced, or not affected by the DDT treatment.
This estimate takes into account the figures in the table and in
addition the information from the screen collections '-n-i whatever
other 'c-ivled-'e was available about the habits of the -- LL-1
their susceptibility to DDT. In the case of irany species too few
sfecinmens were found to warrant a conclusion.

Ash Creek.--Ash Creek is a clean, cold stream located in
Clifton township, Pa. It empties into the LehiIh River near the
town of Clifton. Ash Creek arises in a dense rhododedron sv.anp
and flows through an open marshy area immediately above the sec-
tion treated. T:-,e upper r.iie of the treated section of the
stream averages about 10 feet wide snd 10 inches decr, with a can-
opy mostly of large overhanging trees. The 12..: 2 i..iles is in-
creasingly more open, exceIt for occasicral areas overgrown by
alder, with alternatirn7 riffles and pools. T:, the mouth there
are deep slow stretches v.'here he stream is 12 to 18 feet wide.
At one collection station the rate of flow ..,.- about 4,300 .allons
per minute. There is an abundance of aquatic vegetation, with
Fontinalis on rrany of the stones and in a heavy growth of
Ranunculus trichophyllus Choix and many patches of Callitriche
heterorh;ylla IPursh. The clean water, abundance of aquatic vege-
tation, and swampy origin iiake Ash Creek very rich in insect life.

On August 9 the lower 3 miles of Ash Creek was sprayed with

DDT by d .e at the rate of 1 pound in a gallon of solution per
acre. T!, formula per gallon of spray was 1 pound of DDT to 1
quart of xylc ia and 3 quarts of kerosene. The method of spraying
was to fly a single swath the length of the stream and then to
cover with a second swath the bends of the stream which could not
be cover.w ,jth the first.

To estimate the actual amount of DDT deposited on the stream,
27 filter-pjaper disks 13 inches in diameter were laid out on sup-
ports in the center of the stream, along the banks, and as far as
100 feet from the stream center. The deposits on these disks were
analyzed for DDT and found to range from 0.009 to 1.40, and aver-
age 0.23 poiunds per acre. The data obtained were inconclusive,
but indicate that only a fraction of the DDT released, possibly
a fourth, actually reached the stream.

Pretreatment collections of the bottom fauna were taken with
the stream square-foot sampler on July 14 and 30 and on August
8 (1 day before treatment). The collections were made at stations
200 feet, 1 mile, and 1.5 miles above the mouth of the stream.
Ordinarily, two square-foot samples of the bottom fauna were taken
at each station on each date.

On August 23 (14 days after treatment) the same three statics
were visited again and two square-foot collections made at each.
The collecting screen was used four times at each station to de-
termine the presence or absence of species too scarce to be col-
lected with the square-foot sampler. To find out whether or not
the relative scarcity of certain species after the spraying could
be explained as a result of their normal life cycles, a square-
foot collection was made in Silver Creek, a smaller stream about
half a mile away having a fauna and ecology similar to those of
Ash Creek.

Table 2 gives the contents of the square-foot samples in Ash
Creek on July 14 (before treatment) and on Auust 23 (after treat-
nent) and of the check sample taken in Silver Creek on August 23.
The pretreatment collections of July 30 and August 8 are not
listed in the table. They were made under the difficult conditias
of very high water and are therefore scantier than those of July
14. Hov.ever, a study of their contents indicates that there was
no material change in the abundance of the various insect species
between July 14 and August 8, 1 day before the treatment.

According to table 2 there was a 48-percent reduction of the
invertebrates at the upper station, a 90-percent reduction at the
middle station, and a 78-percent reduction at the lower station.
The last figure is somewhat misleading because much of the



survival is represented by a single species, Ephemerella rotunda
M4org. The individuals of this species taken after the spraying
were all very small, and it is probable that many of them did not
hatch until after the spray was applied. If this species is elim-
inated from consideration, the reduction at the lower station was
90 percent. The relatively small reduction at the upper station
is probably due to the fact that the stream section above it is
largely covered by a forest canopy, and much of the DDT that did
reach its surface was probably lost in the swamps, trash, vegeta-
tion, seepage areas, and short underground stretches that charac-
terize this section of the stream. Below the upper station the
stream is relatively uninterrupted. Moreover, the organisms at
the lower stations were subjected to more run-off of treated water
from upstream.

Data presented in table 2, supplemented by data from the
square-foot collections of July 30 and August 8 and the screen
collections of August. 23, show rather conclusively the degree to
which the commoner species survived the spray. An estimate of the
survival of most species is given in the table.

Bowback Creek.--Bowback Creek is in Spring Brook township,
near Scranton, Pa. It enters Rattlesnake Creek about 2 miles above
Nesbitt Reservoir. It bears no name on the maps known to us. We
have accepted the name used by a local farmer. It rises in and
flows for about half a mile through upland swampy areas. The sec-
tion studied is below this, where the stream flows through a nar-
row valley. Here it is about 6 feet wide and 6 inches deep. Its
bottom is of slab rubble underlain by gravel, and it drops steeply
over frequent or almost continuous riffles. Part of it is open
to the sun and part covered by trees and bushes. Its fauna of
aquatic insects is abundant and varied.

On June 9 a 350-acre tract including about 60 percent of the
watershed of Bowback Creek was sprayed by airplane with DDT at the
rate of 1 pound per acre. The formula per gallon of spray was 1
pound of DDT to 1 quart of xylene and 2.82 quarts of horticultural
spray oil. No measurement of the actual deposit was taken.
Through a misunderstanding the pilot tried to avoid spraying the
stream. Nevertheless, the lower 1,000 feet (more or less) in the
treated area was covered by the spray.

Pretreatment collections were made with the square-foot
stream sampler at three stations in the area to be treated--about
100 feet, 350 feet, and 800 feet above the lower boundary. To see
whether DDT would be carried down by the stream in a quantity suf-
ficient to kill aquatic insects, pretreatment collections were
made on the stream about a quarter mile below the sprayed area


(just above its mouth) and in Rattlesnake Creek about 800 feet be-
low the entry of Dowback Creek. Two square-foot samples of the
bottom fauna were taken at each of these five stations on ?!,ay 3-4
and on June.6-7. Posttreatment collections were made on June 28-
29, on July 25-26, and on August 28. The June and July collec-
tions were made with the square-foot sampler, two samples at each
station, supplemented by screen collections at each of the three
stations within the sprayed area. The August collecting was done
with the screen collector only.

Since the station in Bowback a quarter mile below the treated
area and that in Rattlesnake Creek below the mouth of Povwback both
showed no change in fauna attributable to DDT, they made satis-
factory check stations. Table 3 gives the contents of each of the
square-foot samples. Material from the screen collections is not
included. Information on 27 forms on which the results seemed
significant are given, though 127 forms were studied.

Collection data for June 28 indicate reductions of 71, 87,
and 63 percent from the June 7 population counts at the upper,
middle, and lower stations in the sprayed area. At the urper and
lower stati-n i C 1 n4
.lower stati., C op-.tLs larvae made up a larp'e portion
posttreatment population. Since these larvae were probably from
eggs hatching after the spraying, the species may with some jus-
tice beeliminated from the data as not a true s-r'.- '.: i-, '7vinM
a reduction of 76, 89, and 85 percent at the resi- 've tions
Collection data for July 25 indicate reductions nd '"
percent from the numbers at the three stations eii J'- 7, ..-o
topus not being present on July 25.

Table 3 shows that at the Bowback Creek and -.ttle eek
check stations there were natural reductions exci.i -topus
of 30 and 32 percent between June 7 and June 28 and a :. tion of
89 and 44 percent between June 7 and July 25. T-, : r:ainly
to the emergence of adults from maturing nymphs . larvs. Even
susceptible Ephemerida were present in numbers at th9. two check
stations after treatment, an indication that little, if any, of
the reduction was due to DDT carried down from thl treated section
of Bowback Creek. Tater in the Bowiback check sta'-ion was Vr. low
on July 25, which is the probable reason for the small number of
specimens collected then. Thus, the July 25 data fromr the Eow-
back check station were not used in computing the reduction due to

To take into account natural seasonal reduction as indicated
by the check stations, one uses the formula (X-Y)lOO/X = the
percent reduction due to DDT alone, where X is the percent sur-
vival at the check stations and Y is the percent survival at the


treated stations. Using this formula one arrives at a June 28 re-
duction due to DDT of 65 percent at the upper station, 84 percent
at the middle station, and 78 percent at the lower station. On
July 25 the reductions at the three stations were 13, 84,and 77
percent. These percentages are probably nearer to the true effect
of the treatment.

In table 3 an estimate is 7iven of the effect of DDT on each
species at the middle and lower stations in the sprayed area.
This estimate takes into consideration the screen collections as
well as the square-foot collections, also what information we have
about the biologies of the various species. "When only a few speci-
mens of a species were taken, several species were grouped, as
"Other Ephenerida."

Patuxent River.--The Patuxent River flows through the Patux-
ent Research Refuge, near Bowie, Lid. Here the river is flat and
slow-flowing, about 60 feet wide, and with an average depth of
about 20 inches. It carries a heavy load of silt and some sewage
pollution. Riffles are rare, and aquatic vegetation is scanty.
These unfavciT'or e factors result in a poor fauna of aquatic in-
sects. iclu ale rather abundant.

A 117-acre tract on the Patuxent Research R.fu-e, with a
0.9-mile stretch of the Patuxent River flowing through it, was
sprayed with 5DT by airplane at the rate of 2 pounds per acre on
June 5. The foirjul6 per gallon was 1 pound of DDT, 1 quart of
xylene, and 2.65 quarts of fuel oil No. 2. Eighteen petri plates
4 inches in diafi.:'ter were exposed to the syray deposit alo'v the
river bank. These plates received an average of 0.6 Fco-d of DDT
per acre (range 0.004 to 1.44 lb.). Since some of them were under
overhanging foliage, the average deposit on the river was probably
a little higher.

On June 1 pretreatment quantitative collections of the bottom
fauna were made with the square-foot sampler and with the screen
collector at three likely points on the river. The only collect-
ing station that yielded enough aquatic insects to warrant further
study was at a i iffle at the lower end of the area to be sprayed.
Three squ-re-foot samples and a number of screen :-ollections were
taken here. On June 20, 15 days after the spray, this station was
visited again and a like number of square-foot saml:les and screen
collections were made.

These collections showed no reduction in the fauna which could
be attributed to DDT. Aquatic snails (Hlelisoma ancers (Menke),
Goniobasis virginica (Gmel.), Clappia virginica (T.k.), Physella
heterostropha (Say), and Fossaria humilis (Say)) and three other


less common species and a small clam (Sphaerium) were as abundant
as before. Among the aquatic insects, nymphs of Perlesta placida
(Hag.) were much less numerous than before the spray, but the re-
duction seemed to be due to the emergence of adults, as on June 1
most of the nymphs were mature. Larvae of Dineutes and Hydro-
baeninae (Tendipedidae) and nymphs of Macromia were about as
common after the spraying as before. Too few of other forms were
taken to warrant drawing conclusions about them.

Studies on Aquatic Invertebrates in Ponds

Description of ponds.--In late March and early April of 1945
seven small ponds on the Patuxent Research Refuge near Bowie, Md.,
and two larger ponds near Beltsville, Wd., were studied to ascer-
tain the effects of DDT on the kinds of macroscopic invertebrates
inhabiting them. The size and depth of each pond and the rate and
kind of spray treatment are summarized in table 4. Ponds 1 to 7,
on the Refuge, are part of a series of rectangular artificial ex-
perimental ponds with practically vertical sides, dug during 1937
and 1938 in clayey terrace land. The deeper ones have emergent
grasses, sedges, Juncus, and other plants around their margins,
and the shallower ones also have emergent vegetation in the cen-
tral part, with a resulting mat of decaying vegetable debris over
the bottom. Ponds 4 and 5 are relatively barren of vegetation.
When rains are insufficient, these ponds are filled with water
piped in. Each one has an overflow drain. Ponds 8 and 9 are on
the lands of the Agricultural Research Center at Beltsville, Md.
SThey are in abandoned mine pits, have steep sides (with a few
shallow coves), and a marginal fringe of Sphagnum, emergent vege-
tation, and Nuphar. Their bottoms are of fine soft muck overlain
with dead leaves and the decaying remains of aquatic plants. Pond
8 is more open to the sun than pond 9 and has more aquatic vege-
tation and a more abundant fauna. It has an outlet, a small slow
streamlet; pond 9 has no outlet.

Treatments.--Ponds 3 to 8 were treated with a DDT-oil solu-
tion (DDT 1 lb., xylene 1 qt., and fuel oil No. 2 to make a gallon)
at the rates of 1, 3, and 5 pounds of DDT per acre of water sur-
face (table 4). To differentiate between the effects of DDT and
of its solvent, ponds 1 and 2 were treated with the solvent used
for the DDT (xylene 1 qt. and fuel oil No.2 3 qt.) at the rate
that would be used to apply 5 pounds of DDT per acre. Pond 9 was
treated with DDT in an emulsion (DDT 1 lb., xylene 1 qt., Igepal
alkyll aryl polyglycol ether) 20 ml., and water to make 1 gallon)
at the rate of 5 pounds of DDT per acre. Ponds 1 to 7 were
sprayed on April IU, pond 8 on April 2, and pond 9 on March 28.

Sprays for ponds 1 to 7 were dispensed from a small hand

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atomizer, which gave a continuous fine spray. Air currents were
taken into consideration during the applications, and the operator
frequently moved from one side of a pond to another, depending
upon the direction of the wind, in order to deposit a maximum
quantity of the spray uniformly over the water surface. A small
amount of the spray, however, was lost as a result of drift. The
oil droplets reaching the water coalesced quickly and formed a
continuous film over each pond. A compressed-air sprayer equipped
with a nozzle adjusted to give a coarse spray was used on ponds 8
and 9, which also became covered with a continuous oil film. On
pond 8 rain fell during and after the application, which may have
helped mix the spray with the water.

Five-gallon subsurface water samples t aken 8 days after
treatment in pond 5 showed a presence of 0.017 p.p.m. of DDT, or
0.076 pound of DDT per acre, and similar samples taken from pond
9 after 9 days showed 0.021 p.p.m. of DDT, or 0.29 pound per acre.
Two other samples from the same ponds, taken to include 12 square
feet of undisturbed surface film with each sample, gave DDT analy-
ses about 40 percent higher than the subsurface samples, indicat-
ing a concentration at the surface film. All DDT analyses were
made by a colorimetric method.

Collection methods.--Efforts were made to get a reasonably
accurate idea of the species present in each pond and their
abundance before and at intervals after the treatments, and to
make observations and counts on dead and dying insects after the
treatments. Population surveys were made by several methods.
The surface insects, such as gerrids and gyrinids, were counted
or their numbers estimated, and the free-living and bottom forms
were collected by dip nets. The dip nets were used in a random
way for general reconnaissance and with a certain number of
sweeps of a certain length for quantitative data. The observa-
tions on ponds 1 to 7 were made on April 10, 11, 16, 19 and June
19, on ponds 8 and 9 on April 2, 3, 6, 16 and June 21, and on
pond 8 also on March 29.

An Ekman dredge was used to obtain data on the small forms
of the bottom. This type of dredge takes up the bottom mud and
debris of an area 6 inches square to a depth of about 2 inches.
Each haul is washed in a close-meshed bag to rid it of mud and
the residue washed into white-bottomed pans, where the organisms
can be picked out with forceps or pipette. If the work is done
carefully, the resulting sample is an accurate measure of the
fauna of one-fourth square foot of the bottom. Tediousness of
handling the material limits the number of samples that may be
taken with an Ekman dredge. Two dredge samples from ponds 1 to
7 were taken on April 10 to 19, and one from each on June 19.

- 11 -

Results.-- In ponds 1 and 2, which were treated only with the
solvent used for the DDT in other experiments, all surface and sur-
face-breathing insects were dead within a day. They did not die so
quickly as in the DDT-treated ponds, but the extermination was com-
plete. Repopulation was under way 5 days after treatment, sooner
than in the ponds treated with DDT. Subsurface and bottom forms
showed no harmful effects from the spray.

In ponds 3 to 7, which were treated with DDT at 1 to 5 pounds
per acre, most of the surface and surface-breathing insects were
dead in a few hours and all within a day, with the exception of Belo-
stomatidae. There had been a moderately heavy population, including
Dineutes, Gyrinus, hydrophilids, Gerris, Hydrometra, Mesovelia, Noto-
necta, and corixids. Repopulation by migrants was searched for 5
to 8 days after treatment. Except for a few belostomatids, which
appeared to be survivors, three specimens of Gerris marginatus Say
on pond 4, 8 days after the application, is all that was found.
Eight days after the application dip-net collections of the subsur-
face insects in pond 4 showed a reduction of the Enallagma nymphs
and an apparent extermination of Callibaetis; in pond 7 an apparent
extermination of the formerly abundant EnallaMa nymphs; and in ponds
4, 5, and 7 no reduction in the population of Libellula lydia Drury,
a resistant species. No survivors were found in ponds 3 or 6, but
their pretreatment faunas were relatively scanty. The bottom organ-
isms collected by the Ekman dredge showed some (perhaps not signifi-
cant) reduction of certain species of tendipedid larvae in pond 3,
possibly some reduction in ponds 4 and 5, and apparently no reduc-
tion in ponds 6 or 7. There was apparently no reduction of larvae
of other Tendipedidae, Heleidae, Empididae, Chrysops or of small
annelid worms (Naididae and Tubificidae).

On June 9, 59 days after treatment, all these ponds had an ap-
parently normal fauna, showing no obvious effects of a DDT treatment.
The species and age groups present were largely different from those
found in April. Adults of aquatic Hemiptera and large nymphs of
dragonflies which were characteristic of the April faunas had been
largely replaced by young nymphs. Small bottom-living species were
scarce in all ponds, including those treated with the solvents alone.

Pond 8, which was treated with DDT at 1 pound per acre, con-
tained large numbers of many species of aquatic insects. Most of
the surface and surface-breathing species were dead within a day
after the treatment. Of the subsurface forms, Odonata nymphs,
Callibaetis, and Chaoborus were reduced but still alive in num-
bers a day later. Four days after treatment Callibaetis and
Chaoborus had been exterminated and Odonata nymphs were still
further reduced. Fourteen days afterwards the reduction had
reached its probable maximum, when all but the resistant species

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cf Odonata were at less than 1 percent of their former abundance.
Another common subsurface species, Pelocoris femorata, was not
affected by the treatment. The first evidence of repopulation
was also found 14 days after treatment, when adults of Gerris
and Dineutes and freshly hatched nymphs of Aotonecta were present
in small numbers. By June 21, '0 days after treatment, the pond
population appeared to have regained its normal variety and

On pond 9, which was treated with a DDT emulsion at the rate
of 5 pounds of DDT per acre, no pretreatment studies were made,
but collections of dead specimens 1 and 6 days afterwards showed
that its population of aquatic insects had been abundant and rel-
atively varied. At the latter time the only live surface or sur-
face-breathing insects were three adults of Gerris marqinatus.
Subsurface insects were represented by little more than Odonata
nymphs. These declined in numbers until 19 days after treatment,
vhen only Chrysops larvae and two species of Odonata nymphs could
be found, and these in small numbers. Repopulation was slow.
tUntil 19 days after treatment the only surface insects seen \-ere
two or three adults of Gerris marginatus at a time, one of which,
9 days after treatment, was apparently affected by DDT. Adults of
Pineutes and Gerris were present 48 days after spraying. Eighty-
four days after treatment various surface and surface-breathing
insects were present in small numbers. An untreated pond nearby
then contained the same species in very large numbers. At this
time subsurface insects had increased only a little above their
low point of 19 days after the application.

Annotated List of the Pond Species Observed

The following list indicates the species on which observa-
tions were made and our opinion on the effect of the DDT appli-
cations on particular species. Only those recorded as common or
abundant afforded enough data for drawing definite conclusions,
but the others are included. After each species are the ponds,
listed by number, from which it was recorded and a symbol for its
abundance in each. The symbols used for abundance are a, abundant;
c, common; f, frequent; and r, rare. These refer to abundance as
obtained by the methods employed, and for some species may have
little relation to. the actual abundance. It should be kept in
mind that ponds 1 and 2 were sprayed with the solvent alone, not
with DDT.



Tubifex?. 2(c). Not affected.

Limnodrilus. l(a), 2(f), 3(a), 4(c), 5(r), 9(c). Not affected.

Placobdella parasitica (Say). 8(f), 9(r). Not affected.


Daphnia. 8(c). Not affected. Increased after treatment.

Cyclops. 8(c), 9(c). Not affected. Appeared to increase after
the treatments.

Asellus sp. 3(r). Not collected after the treatment.

Cambarus sp. A few dead specimens found in the Patuxent ponds
after treatment.


Podura aqugatica L. l(c), 2(a),3(c), 4(c), 5(c), 6(a), 7(f),
8(a), 9(c). Specimens on the surface of the ponds were ex-
terminated within a day, but on ponds 1 to 6 the species was
back in numbers 5 days after treatment. Pond 7 had Podura on
its surface again 8 days after treatment. This species was on
pond 8, 1 day after treatment and on pond 9, 6 days after.
The species apparently can repopulate a pond surface from its
margins as soon as the oil film has left.

Callibaetis. 4(c), 8(c). Exterminated in both ponds. In pond
8 many specimens were alive the day after treatment, but none
were alive 5 days after.

Caenis. l(c). Not collected after treatment.


Lestes. 8(a), 9(a&. Almost exterminated in both ponds. In
pond 8, this species was abundant 1 day after treatment but
less than 20 percent were alive 4 days later, and only about
1 percent 14 daya afterwards. In pond 9 they were found alive
in small numbers until 19 days after treatment, but the pre-
treatment abundance is unknown.

Argia sp. 8(f). Five specimens were taken 14 days after treat-
ment, none earlier. Presumably the species had until then
been hibernating in the mud.

PsT LP40


Nehallenia. 1 (r), 8 (r). Hot affected in pond 1. One specimen
taken in pond 8, 14 days after treatment.

Chromarion sp. 9 (r). One specimen taken 8 days after treatment.

EnallaMna sp. A. 1 (r), 2 (r), 4 (c), 7 (a), 8 (a). Probably not
affected in ponds 1 or 2, though not collected in pond 1
after treatment. In pond 4 reduced to perhaps 30 percent 8
days after treatment. In pond 7 apparently exterminated. In
pond 8 about 20 percent vere alive 1 day after treatment, 5
percent 4 days after, and less than 1 percent 14 days after

Enallagma sp. B. 4 (r), 7 (r). In pond 4 one specimen collected
8 days after treatment. In pond 7 one collected before and
none after treatment.

Ischnura verticalis (Say). Not found in the ponds before treat-
ment, but on June 19 it was abundant and a dominant form in
ponds 1 to 7.

Anax junius (D .) 8 (c). Present in numbers until at least 14
days after treatment.

Aeshna. 8 (c), 9 (c). Apparently not affected in pond 8. In
pond 9 one live nyrmph taken 6 days after treatment, two dead
nymphs taken 9 days after treatment, and none later.

Celithemis. 1 (r), 3 (r), 8 (r). One nymph each takern in ponds
1 and 3, 8 days after treatment, and one in pond 8, 4 days

Libellula lydia Dru. 3 (r), 4 (f), 5 (c), 7 (f), 9 (r). Appar-
ently not affected in any of the ponds except possibly in
pond 9. Here one nymph was collected 6 days after treatment,
none later.

Libjllula pulchella Dru. 8 (r), 9 (r). One taken in pond 8, 14
days after treatment and one in pond 9, 6 days after.

Libellula spp. 4 (r), 6 (f), 8 (c), 9 (c). Not reduced in any
of the ponds.

Pachydiplax longipennis (Burm.). 9 (r). One dead nymph collected
14 days after treatment.

Iiesothemis simplicicollis (Say). 8 (c), 9 (f). Not reduced in
either of the ponds.

- 15 -


Mesovelia mulsanti bisignata Uhl. 2 (c), 7 (c). Exterminated on
both ponds.

Hydrometra martini Kirk. 2 (r), 3 (r), 4 (f), 6 (a), 8 (a). Ex-
terminated on all ponds.
Gerris marginatus Say. 2 (c), 3 (f), 4 (r), 6 (f), 8 (c), 9 (c).
Exterminated on all ponds.
Gerris remigis Say. 4 (r). Not found after treatment.

Microvelia hinei Drake. 3 (f), 4 (f), 7 (r), 8 (r). Exterminated
on ponds 3, 4, and 7. One specimen taken on pond 8 the day
after treatment.
Notonecta undulata Say. 2 (c), 4 (c), 5 (a), 6 (c), 7 (a), 8 (c),
9 (c). Exterminated in all ponds. Recently hatched nymphs
were present in pond 8, 14 days after treatment.

Buenoa. 2 (r). Not found after treatment.

Pelocoris femoratus (P.deB.) 6 (r), 8 (c). In pond 6 one dead
specimen found 8 days after treatment; in pond 8 not reduced
at all.

Ranatra fusca P.deB. 7 (r). Not found after treatment.

Lethocerus americanus (Leidy). 5 (r), 6 (f). In pond 5 one live
specimen taken 5 days after treatment. In pond 6 two dying
specimens 5 days after treatment and one dead specimen 8
days after.
Belostoma flumineum Say. 3 (r), 8 (r). One live specimen in pond
3, 8 days after treatment and one in pond 8, 1 day after.
Arctocorixa interrupt (Say). 4 (c), 5 (f), 7 (r), 8 (c).
Probably exterminated in all ponds.
Sigara spp. 4 (c), 5 (r). Probably exterminated in both ponds.

Megamelus davisi V. D. 2 (a), 8 (a). Exterminated on both ponds.
A few specimens were back on pond 2, 8 days after treatment.

GCauliodes. 8 (r). One specimen found dead the day after treat-

- 16 -

ment. In a preliminary experiment a shallow swampy area near
Bowie, Md., was sprayed early in Karch. Within an hour large
numbers of this forai were cominig out of the mud and dying.

Sialis. 1 (r). Pot collected after the treatment.


Haliplus sp. 8 (r). One specimen taken the day after treatment.

Hydrocanthus sp. 8 (r). Adults probably exterminated.

Hydroporus sp. 6 (r). Adults probably exterminated.

Ilybius. 8 (c) Adults probably exterminated.

atu_ s sp. 8 (r). Adults probaLly exterminated.

Acilius fraternus (Harr.). 9 (c). Adults exterminated.

Grarhcdorps liberi (Sy). 4 (r), 8 (c). Adults exterminated.

Dineutes. 2 (a), 4 (a), 5 (a), 6 (f), 8 (c), 9 (c). Adults ex-
terminated on all Ijnds.

Gyrinus. 2 (c), 4 (f), 6 (f), 7 (c), 8 (r). Adults exterminated
on all ponds.

Berosus. 1 (r), 3 (r). Adults probably exterminated.

Hydrous triangularis (Say). 3 (r), 6 (f), 7 (r). Adults prob-
ably exterminated.

Tropisternus spp. 4 (f), 5 (f), 6 (f), 7 (r), 8 (c), 9 (c).
Adults probably exterminated.

Enochrus. 8 (f). Adults probably exterminated.

Helodidae (larvae). 6 (r), 7 (r), 8 (f). One dead at the edge
of pond 6 a few hours after treatment, one 3ead at pond 7,
8 days after, several dead at pond 8 the day after treatment,
and one alive at the same pond 4 days after treatment.

Donacia (larvae). 2 (r), 3 (f). Not affected in either pond.

Polycentropus. 3 (r). Not collected after treatment.


Ptilostomis. 1 (r), 6 (r). Not collected after the treatment.


Dasyhelea. 1 (r). Not collected after the treatment.

Sphaeromias? sp. 1 (a), 2 (c), 3 (a), 4 (r), 5 (c), 6 (f), 7 (f).
Not affected by the treatments in any of the ponds.

Bezzia? sp. 1 (f), 2 (f), 3 (f), 6 (f). Numbers not reduced in
any of the ponds.

Chaoborus. 5 (r), 7 (r), 8 (a), 9 (a). In pond 5 one dead speci-
men taken 8 days after treatment, in pond 7 one before and
none after treatment. In pond 8, the day after treatment,
thousands of half-grown larvae were dead and dying. Full-
grown larvae and the one pupa seen were still unaffected.
Five days after treatment all found were dead except for a
few dying. In pond 9 thousands of dead larvae were found
5 days after treatment, none alive.

Pentaneura. 1 (a), 2 (c), 3 (c), 4 (r), 5 (f), 7 (f), 8 (r).
There seemed to be no change in numbers in ponds 1, 2, and 5.
The species was not found again in pond 4 after treatment,
and in pond 7 the only specimens collected were five dead
ones 5 days after treatment. The only collection in pond 8
was one live specimen the day after treatment.

Procladius culiciformis (L.)? 1 (a), 2 (c), 3 (a), 4 (a), 5 (r),
6 (f). The numbers of this species remained approximately

Olinotanypus caliginosus (Joh.)? 1 (f), 3 (c), 4 (r), 5 (r). No
reduction in numbers in any of the ponds.

Polypedilum sp. 1 (a), 2 (f), 3 (a), 4 (c), 5 (a), 6 (c), 7 (c).
There seemed to be no reduction in any of the ponds.

Glyptotendipes paripes (Edw.). 2 (c), 4 (r), 5 (r), 7 (r).
Specimens were found in ponds 2 and 4, 8 days after treat-
ment, but not in ponds 5 or 7.

Glyptotendipes lobiferus (Say). 1 (r), 7 (c). Not collected in
pond 1 after treatment. In pond 7 the number was apparently

Tendipes (Limnochironomus) sp. 9 (r). One collected 5 days
after treatment, none later.

- 18 -

Tendipes decorus (Joh.)? 9 (r). One collected 5 days after
treatment, none later.

Tendipes tentans (F.)? 2 (r), 3 (r), 7 (f). Collected after
treatment only in pond 2.

Cryptochironomus. 4 (r). One collected 8 days after treatment.

Harnischia. 2 (r), 4 (c), 5 (c). Apparently not reduced in any
of the ponds.

rVicropsectra? 1 (r), 2 (r), 3 (r). Collected after treatment
only in pond 2.

Chrysops. 1 (c), 2 (f), 3 (c), 5 (r), 6 (c), 7 (c), 9 (r). Not
collected in pond 5 after the treatment. Collections in the
other ponds show no reduction in numbers.

Empididae (larva). 1 (r), 3 (c), 6 (r), 7 (r). The single speci-
men collected 8 days after treatment in pond 7 was a dead
one. Otherwise there was no evidence of adverse effects of


? Oribatella aquatica Bks. 1 (a), 2 (a). All dead the day after

Hydrachna sp. 6 (r). One collected 8 days after treatment.

Diplodontus despiciens (Lull.). 3 (f), 6 (f), 8 (a). I:ot
affected. There was an increase after treatment.
Arrhenurus. 8 (a). Not affected. There was an increase after

Dolomedes sexpunctatus Hz. 1 (f), 3 (r), 8 (c). No careful
observations were made, but this species seemed to be
greatly reduced.

- 19 -


Various aquatic species show great differences in suscepti-
bility to DDT. The Planaria, Oligochaeta, Entomostraca, Hydra-
carina, and Mollusca that we encountered seemed totally immune to
the dosages used. Most Ephemerida, smaller Plecoptera, adults of
Elmidae, most Trichoptera, Simuliidae, and many Tendipedidae
(= Chironomidae) were very susceptible. Nymphs of larger dragon-
flies, Pteronarcys (Plecoptera), Nigronia (Megaloptera), some
Heleidae (Diptera), and GChrysops seemed little if at all affected.
For some groups variation in susceptibility is explainable by
differences in opportunity to contact the poison. Insects living
on the surface of the water or coming to the surface to breathe
were extremely susceptible to an oil solution of DDT, and those
living in the bottoms of ponds and streams relatively immune. In
swift streams are many species securing all or much of their food
by straining it from the water. This habit probably accounts for
the susceptibility of Isonychia (Ephemerida), many Trichoptera,
Simuliidae, and some Tendipedidae.

On ponds a 12-percent solution of DDT in oil at the rate of
1 gallon per acre (1 lb. of DDT), or of five times that amount of
the solvent and carrier alone, exterminated practically all the
surface insects and those breathing at the surface. Casual ob-
servations suggest that these forms are similarly affected on
streams sprayed with DDT. Most free-swimming or crawling insects
in ponds were severely reduced in numbers by the lowest dosage
and some were exterminated. Insects in the bottoms of ponds were
relatively safe at the dosages used.

A deposit of a DDT-oil solution on Ash Creek at the rate of
about 0.25 pound per acre killed about 90 percent of the total in-
sect population and apparently exterminated about one-third of the
species studied. In the ravine brook an estimated deposit of 0.8
pound of DDT per acre killed about 85 percent of the insect popu-
lation, leaving only the resistant species and a few scattered
survivors of those moderately resistant. Much of the survival in
the ravine brook was of species protected in leaf drifts. In
Bowback Creek a deposit of perhaps 0.25 pound per acre on a 0.2-
mile stretch had no observable effect at 0.25 mile below. Results
in the ravine brook also indicate that streams carry lethal amourts
of DDT for only a short distance. Our experiments lead us to be-
lieve that, when a stream and its watershed are sprayed by air-
plane, most if not practically all damage to the stream's fauna
is by DDT deposited on its surface, not by DDT washed or leached
into the stream.

- 20 -

The rate of repopulation of a pond or stream depends upon
how soon the DDT disappears from the water and the length of life
cycle, number of survivors, and possibilities for migration of the
species involved. In a pond the DDT may remain in lethal amounts
for days or weeks, depending on dosage, drainage, and other fac-
tors. In a stream most of it is probably carried off in a day.
Many pond species have several generatiorsa season, and it is be-
lieved that as a group they have a greater tendency to migrate
than do stream species. Hence a small pond should, and according
to our observations does, regain most of its fauna a few weeks
after the DDT is no longer effective. Most stream species take a
year for a generation, and many of the larger predators several
years, with the result that repopulation is slow. The ravine
brook treated in late May showed no repopulation by late August.
Bowback Creek, with a short part of its course treated in early
June, seemed to show a little recovery in late August.

The present studies show the approximate effect of DDT on
aquatic invertebrates in certain kinds of ponds and streams.
There is a great need, however, for more exact information derived
from studies on different formulations and dosages used on aquatic
habitats. A cardinal need for further experimental work is better
control of the airplane application and more knowledge of the dis-
tribution of DDT in the habitat.

Fig. 1-The stream square-foot sampler in use. The scrim
collecting bag trails downstream from the sampler.

4 44 a 00 00 4 4M0M00mM mom a o

01 0%

m01 C4 ow w


Cm 01

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14*- Ue" PI O


Table 2.--Number of invertebrates pr square foot in Ash Creek and Silver Creek bottom samples.

Stenonema Ithaoa (C.&L.)
Stenonema pudloum (Hag.)
lieptagenia aphrodite MoD.
Heptagenia julia Tray?
Iron vitreus (Wlk,)
Isonychia thalia Trayv.
guttata MoD.
Paraleptophlebia mollie Eat.
Habrophlebia vl brans Ndm.?
iphemeralla oornutella MOeD.
Lphemerella defiolena Morg.
Ephemerella rotunda Morg.
Ephemerella invaria (Wlk.)
Baetie app.
Pseudooloeon dubium (Walsh)
punotiventri (MoD.)
Other Ephemerida
Other Odonata
Pteronaroys biloba Newm.
Peltoperla arouata Ndm.
Isoperla holochlora (Klap.)
Ne ophaaganophora
oapltata (Plot.)
Other Plecoptera
Nigronia earrioornis (Say)
Stenelmis orenata (Say)
Heterlimnius tardellus
(Fall) (adult)
lieterlinnius tardellus
(Fall) (larva)
Hoeterliamius ovalle (Leo.)?
Other Coleoptera
Rhyacophila fusoula (Wlk.)
Rhyaoophlla ep. B
Trentonius diatlnotus (WIlk.)
Hydropsyohe simulans Rosa
Hydropsyohe ap. A
Other Triohoptera
Hexatoma spinosa (O.S.)
Heleidae op. A
Iydrobaeninae ap. F
Hydrobaeninae app.
Other Diptera
Other hydraoarina


Percent reduction,
Inol. E. rotunda

Percent reduction,
exol. E. rotunda

Upper station Middle station Lower station Silvr Crek
Pretreatment Posttreatment Pretreatment Posttreatment Pretreatment Posttreatment Efft of
July 14 Aug. 23 July ll 23 July Aug. 23 Aug. 23 Itreatint/
(1)1/'(2) (I) (2) (1) (2) (1) (2) (1) (2) (1) (2) (1)

1 2


5 1


6 19


7 1
24 16

3 1


13 6
2 1

1 3

10 12
9 9

1 1

1 1

49 34

5 2



1 3
6 3
11 5
11 5
J. 5
6 7
5 6
1 3

34 1

1 1


3 12

3 2


3 37
1 2

196 159 72 114



2 1

2 2


7 5

16 21

2 2

64 148

7 9
1 33

5 6

l 3
262 112
45 117
17 14


2 2
1 1

36 8

12 7


1 2
6 19

l 6



6 28
1 1 2
1 1 5 2

2 1 1 2
4 23 1 4
8 38
S 58
2 1
12 44 1
10 12 1
38 178 1
9 24

2 1

3 2
1 1 2

698 903 69 86




5 l

1 3

23 50



4* 5

1O 1 1

1 1

7 4 1 3

10 2


2 2



1 5


418 183 49 81























numbers in parentheses refer to different square-foot samples taken on the tame date.
EA not affected; B, reduced; C, exterminated; D, nearly exterminated; L, exterminated except at upper station.

Table 3.--Number of invertebrates per square foot in Bowback Creek and Rattlesnake Creek bottom samples.

-rtr Upper station _____ddle station
Forms Pretreatment Posttreatment Pretreatment Posttreatment
May 4 June 7 June 28 July 25 Lay 3 June 7 June 28 July 25
~~~_____~~__ _____(1)-2) (1) (2) (1) (2) (1) (2) (1) (2) (1) (2) (1) (2) (1) (2)


Tubific idae
Cambarus b. bartonil (F.)
Stenonem nr. pulchellum (Walsh)
Baetis flavistriga McD.
Baetis epp.
Pseudocloeon carolina Bke.
Other Ephemerlda
Pteronarcys biloba Newmn.
Acroneuria carolinensia (Bks.)
Other Plecoptera
Nigronia aerricornis (Say)
Trentonius distinctus (Wlk.)
Diplectrona modesta Bks.
Hydropsyche sp. A
Other Trichoptera
Hexatoma spinosa (O.S.)
SirnuL iidae
Heleidae ap. A
Other Tendlpedidae
Other Diptera

Totals (excluding Cricotopus)

Percent reduction from June 7

Percent reduction due to DDT

1 /

Numbers in parentheses refer
2, not affected; B, reduced;

8 48 2

2 11

2 1
2 1
2 2

5 1 1 13 1 5 2 4

6 4
2 1

7 1

1 4
6 1
2 1
5 1 9
4 11 20
19 6
59 2 1
70 28 35
6 1 3
3 4

281 229 131 128


1 2 2

5 1

1 2


2 1


1 12 1

47 15 100 26

1 1 1

3 12
6 3

2 3
4 4


1 4 1

11 12

2 39


3 1
2 4 4

1 3

.1 8
.6 22
2 1

85 89

2 1
9 2


1 1 1

1 3 1 1

11 2


76 111

9 12 11 6

to different square-foot samples taken on the same date.
C, exterminated.

3 4

Pretreatment Posttreatment Pretreatment losttreatment Pretreatment Posttreatnent
,-ay 3 June 7 June 28 July 25 1ay 4 June 6 June28 July 25 L-Ay 4 June 7 June 2E July 25

(1) (2) (1) (2) (1) (2) (1) (2)

1 2

10 4
3 4 5 16
2 1 3
9 6 1 1

1 1
2 2 7 9
8 8 3

2 2 1

3 2
5 1 5 2
4 1
1 3 3

1 1




1 1


2 1

23 8

1 5 3

2 2

3 1 2

53 110 27 6
10 6 7 2 45 43
17 7 3 2 2 2
61 46 22 39 24 8

7 3



5 2 2
1 1


2 2

5 1
9 3

11 4
103 63
2 2

1 1

11 16

5 6

13 5

1 1
4 3

5 11

trea -

. I I- 4

1 2

1 8
1 7
48 199

3 5

5 9

1 1 1 2
5 4
35 20 14 24

8 3 6 2

4. 4

1 1 1 10 1

1 8

4 24 21 10
13 4 1 5

7 4

2 2


2 4
1 3
4 12
8 3



1 5
4 2
4 8

1 2

2 9


1 1

1 19

3 1

_____ ___ L 164 57 28__
97 5V 53 78 10 9 7 10 1237 140 107 180 123 77 19 13 100 297 93 58 38 64 57 28

85 7 30 89 32 74

78 77


J? Y

2 1 4
2 1
.7 6 15
1 1
1 1

Lower station

Bowback Creek check

Rattlesnake Creek check

(1) (2) (1) (2) (1) (2) (1) (2)

(1) (2) (1) (2) j (1) (2) (1) (2)


Table 4.--Description and treatment of 'the ponds used for DDT studies

Inches Pounds per acre

1 20 x 50 fte



3 Abundant









Xylene 1 qt. v
fuel oil 3 qt.


DDT 1 lb. *
xylene 1 qt.
fuel oil
2.65 qt.






DDT 1 lb.
xylene 1 qt. *
Igepal 20 ml.
water 2.64 qt.



3 1262 09238 7553