!TATE PLA'I-f BOARD
March 1946 a-84
United States Department of Agriculture
Agricultural Research Administration
Bureau of Entomology and Plant Quarantine
SSUMWARY OF 1945 DDT INVESTIGATIONS FOR CONTROL OF FOREST INSECTS
WITH SPECIAL REFERENCE TO AERIAL APPLICATION
By F. C. Craighead and R. C. Brown
Division of Forest Insect Investigations
The promising results in the control of forest insects with DDT
in the preliminary work of 194 encouraged planning tests on a much
larger scale for the 1945 season, primarily aerial applications. The
high toxicity of DDT and the consequent effectiveness of low dosages,
its ease of formulation in sprays, and the long residual effect give
a combination of factors especially favorable to aerial application.
Thus, for the first time, there is promise of developing practical
and economical methods for the control of widespread infestations of
certain forest insects, such as defoliators. Coincident with these
developments, the extensive outbreak of the spruce budworm in Canada
and the threat of its spread into our Northeastern States provided
the stimulus for obtaining additional funds to study this problem in
the United States. Results of the season's work are here briefly
brought together for the purpose of analyzing the over-all picture.
Many workers are mentioned who will later present detailed reports
on special phases of the problem.
The program, which involved a number of cooperators in the
United States and Canada, had the following objectives:
1. The determination of the most effective spray formulas for
aerial application of DDT and the minimum dosages necessary for the
control of the spruce budworm, the gypsy moth, and other forest
2. The development of better equipment for airplanes for dis-
tributing sprays over the forest and the working out of operational
3. The determination of the biological effect of DDT on bene-
ficial insects and wildlife in the forest.
General Plan of Experiments and Cooperation
The experimental work was conducted in cooperation with several
other organizations. Without their whole-hearted active cooperation
it would have been impossible to carry out more than a fraction of
the program. The greater part of the work centered around the spruce
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budwom., because of the -'"n.io.is threat to the timber in the North-
eastern State-3, and around the mo: oth control program.
The spr :::e bu vvorm work wva tied in closely with that of the
Canadian Division of 2ntomolo: i, Forest Insect Investigations.
Through J. J. de Gryse, in chi-"e, the cooperation extended to the
Department of L--dz ;d- Forests of the Provinrs of Ontario cv'
uebec, In Ontario the spray applications v.-re handled by L. 1.
Johnston, chief of the Division of Research, and in Quebec by L.
Daviault, chief of the Bureau of Entomology. In the Northeastern
St -.tes, '. .:. Foss, superintendent of Forest Pest Control, .ewi York
State Conservation Department; H. L. Bailey, director of the Verc.ont
Division of Plant Pest Control; J. C. Conkdin, of the University of
New Hampshire; and R. E. RendaLL and H. B. Peirson, of the Maine For-
est Service, actively cooperated in spruce budworm surveys and
All experimental work with the gypsy moth was conducted cooper-
atively with the Division of Gypsy and Brown-Tail Moths Control of
this Bureau. Several State organizations participated in the experi-
mental spray applications, including the Pennsylvania Department of
Agriculture, Bureau of Plant Industry, through T. L. Guyton; New York
State Conservation Department, through W. M. Foss; and the Connecti-
cut Agricultural Experiment Station, through R. B. Friend.
The development of spraying equipment for planes was handled
through the Division of Agricultural Engineering of the Bureau of
Plant Industry, Soils, and Agricultural Engineering, D. A. Isler
having immediate responsibility for this activity.
During the war the United States Coast Guard developed the -;se
of the helicopter in sea rescue work and at the same time, in cooper-
ation with the manufacturers, began adaptations for its postwar use.
A cooperative arrangement was set up between the Bureau of Medicine
of the Navy, the Coast Guard, and the Bureau of Entomology and Plant
Quarantine to test the helicopter for distributing insecticidal
sprays. The experimental work was conducted in Connecticut, New Yolk
and New Jersey. Orchards, truck crc-, fore-ts, and uosquito-in-
fested swamps were sprayed. Lt. (>.. j. S. Yuill, of the Bureau of
Medicine of the Navy, represei.,te' that Qr ,J'ticr in the project
and D. E. Parker represented this Bur'-.a-. The Coast Guard .:si;:.-ed
Ensign David Gershowitz as pilot -ad Hoy ,iagner as mechanic.
Studies of the broader biological effects of DDT on the pnneral
insect population of the forest were conducted in this Bureau by the
Division of Forest Insect Investigations in cooperation with the
Division of Insect Identification. The responsibility for determin-
ilg the effect of DDT on other wildlife was assumed by the Fish and
Wildlife Service, United States Department of the Interior, most of
the studies coming under the immediate jurisdiction of A. L. Nelson,
assistant chief of the Division of Wildlife, and E. W. Surber, of the
Division of Fishery Biology. R. J. Womelsdorf, representing the
Pennsylvania State Board of Fish Commissioners, gave much assistance
in the treatment of trout streams. J. L. Corliss, of the Division of
Gypsy and Brown-Tail Moths Control, assisted greatly in this study.
Types of Aircraft
Several types of planes and apparatus were used in these experi-
mental aerial applications of DDT.
A Navy N-3-N trainer fitted with a 50-gallon spray tank and a
pumpwhich fed the spray liquid into a hollow tube fitted with noz-
zles and supported under the lower wing.,was used for many of the
applications. This distributing apparatus, constructed by D. A.
Isler, was a slight modification of earlier equipment designed by
this Bureau. It proved to be a very simple and satisfactory device.
A White Standard plane fitted with the so-called spinner-disk
device, developed for applying heavy, concentrated suspensions, was
used successfully in much of the gypsy moth work.
An Interstate-Cadet plane owned by a commercial company was used
in tests against the pine tip moth and the spruce budworm in Colorado
and Nebraska. A 2-inch pipe leading from the supply tank in the
plane opened into a venturi under one wing.
Four CANSO amphibian planes, each fitted with two spray booms,
were used by the Royal Canadian Air Force in spruce budworm spraying
for the Province of Ontario near Lake Nipigon. A Waco plane on
floats and equipped with a spinner disk was used for the spruce bud-
worm work at Kabonga, Quebec, which was conducted cooperatively by
the Dominion Government and the Province of Quebec.
Two Waco land planes fitted with spinner brushes were used by a
private company in the hemlock looper work in Oregon.
The Coast Guard helicopter (Army YR-4) was equipped with a
spraying device consisting of a pump, a tank, and a nozzle bar. It
put out a very fine mist, with droplets averaging under 100 microns
in diameter. The helicopter was capable of flying very close to the
tree tops, and the downward rotor blast carried the finp particles
thoroughly through the foliage. Excellent control was obtained of
practically all the insects which are susceptible to DDT. .'ore
,- iformj distribution of spray droplets and better control of the size
'e droplets can be obtained with the helicopter than when the
: ,- is subjected to the influence of the slipstream of faster air-
,rii The small type used in these experiments has definite limi-
--is as to pay load, capacity, and range of operation. Much more
wk is needed with helicopters, particularly the larger types now
The matter of distributing equipment and the type of plane most
suitable and economical for treatment of large forest areas needs
extensive investigation. Will large land planes, capable of carrying
2 or 3 tons and operating 100 miles or more from a central base, be
more economical than small planes that are based locally thus ne-
cessitating the trucking of gas, oil, and insecticidal materials to
the different points of operation? Such problems seem to be more the
problems of engineers than of biologists and probably can best be
answered by the industry.
Aerial Application of DDT
Toward the end of the 1944 season it became evident that a con-
siderable portion of the DDT solution released from airplanes was not
rpachin the forest canopy. During 1945 some effort was made to de-
ter.iine the amount of DDT that was deposited in the forest. In some
instances only one-tenth to one-half of the insecticide was found to
be deposited on the experimental plots. Under ideal conditions, such
as often existed for an hour or so in the early morning, and with the
plane flying close to the tree tops, larger amounts were recovered.
Meteorological factors are of predominant importance. Under forest
conditions it is hazardous to fly below 50 feet, and some pilots show
a terLdency to ke.,p up around 100 to 200 feet with smaller planes and
even higher with larger types. The deposition of these sprays under
favorable meteorological conditions seems to be governed largely by
the droplet size. The size of the droplets varies from less than 50
to about 500 microns, depending on the character of the solution and
the speed of the plane. It appears that a large portion of the drop-
lets less than 50 microns in diameter, when released at 50 or more
feet above the tree tops, tend to drift about in the air and never
reach the foliage. They may eventually evaporate, leaving crystals
that fall ineffectively through the foliage. Pilots, in applying oil
spray, have reported that they frequently fly through an oil mist
sometimes 1/2 mile or more from the point of release.
This loss of material has resulted in a tremendous variation in
the control of the same insect, at different times and with the same
dosa-e. Sometimes good kill was obtained with 1/4 pound or less of
DDT per acre. On other flights even 1 to 2 pounds per acre gave poor
control. The loss of this material in terms of increased cost is
not too important, but if no loss occurred the same plane load could
cover two to five times the area. Again, under favorable atmospheric
conditions all the material may be deposited and cause unnecessary
mortality to useful insects and wildlife. Studies of the effect of
DDT on aquatic life have indicated some danger witt a dosage of 1
pound per acre. On occasions, with heavier dosages at least, the
spray has drifted considerable distances from the treated area and
killed numerous fish in ponds. Consequently the objective should be
to use no more DDT than the lowest effective dosage.
Efforts to analyze and correct this condition were prosecuted
throughout the season. R. H. Nagel and S. F. Potts, of the Division
of Forest Insect Investigations, Donald Whittam, of the Division of
Gypsy and Brown-Tail Moths Control, as well as D. A. Isler, of the
Bureau of Plant Industry, Soils, and Agricultural Engineering, gave
considerable attention to this problem the latter part of the season,
in tests at Beltsville, Maryland. R. H. Carter, of the Division of
Insecticide Investigations, and R. F. Anderson, of the Division of
Forest Insect Investigations, aided in the development of a method
in which dyes were used for estimating DDT recovery. Kenneth Stewart
and Kenneth Graham, entomologists in the Canadian Division of Ento-
mology, aided throughout these studies. The United States Weather
Bureau gave considerable assistance through R. N. Culnan and others,
who set up a weather station on the Beltsville airfield.
It was found that the use of more viscid and heavier liquids
tended to form larger droplets than did alterations in outlets and
nozzles used in these tests. The pattern of the DDT deposit across
the swath showed a high peak, often 50 to 80 feet wide and much
above the desired dosage, immediately under the plane, with a rapid
falling off for 100 to 200 feet on either side. Much valuable in-
formation on the dissemination and distribution.of DDT sprays was
Formulations and Dosages
Several formulations containing DDT, including oil solutions,
emulsions, and suspensions, were tested. These preparations were
made up with several solvents and carriers that left either a crys-
talline deposit of DDT or a deposit of a tacky or oily nature.
Several emulsifiers were also tested. Most of the applications were
of 10- to 12-percent solutions, at the rate of 1 pound of DDT per
acre, with some as low as 1/8 pound per acre. The volume of spray
per acre was also important and ranged from 1/2 to 5 gallons; about
1 gallon appeared ample for most conditions. This work was largely
in the hands of R. H. Nagel, P. B. Dowden, and R. A. St. George, of
the' Division of Forest Insect Investigations, in close cooperation
with R. C. Roark, H. L. Haller, D. F. Starr, and R. H. Carter, of
the Division of Insecticide Investigations.
In general all these formulas and dosages were so effective
that no ccuclusions could be reached as to their relative value.
Lore concentrated solutions (25 to 40 percent) and less gallonage
per acre need further study.
Oil solutions are easy to make but more objectionable to handle
than emulsions and suspensions. The last two present less of a
transportation problem for use in out-of-the-way places. Long re-
sidual effect was obtained with both emulsions and solutions. The
suspensions were not sufficiently tested in this respect, but
appeared to lose their toxicity more quickly. Differences in tox-
icity appeared to depend much more on the dosage of DDT than on the
formi-lation. Tacky or smeary films killed more quickly than crystal-
As the work progressed it became more and more evident that for
many insects dosages well under 1 pound per acre are entirely effect-
ive provided they are efficiently applied. Loss of material, as
discussed elsewhere, proved to be the most serious problem in regu-
latin the dosage. For the present it is recommended that for large
areas, especially where fish streams are involved, dosages be kept
at around 1/2 pound per acre and should not exceed 1 pound. Advice
from experienced entomologists and biologists should be sought be-
fore large areas are treated.
The Control of Injurious Insects
Spruce budworm (Archips fumiferana Clem.). Because of the
widespread outbreak of the spruce budworm in Canada and of no known
activity of this insect in timberlands of the Northeastern States,
the treatments for this species v;ere planned for Ontario and Quebec.
This program was primarily a cooperative one. Late in the winter of
1944-5 representatives of this Bureau, the Dominion Division of Ento-
mology, and the Departments of Lands and Forests of Ontario and Que-
bec held several meetings to make plans for accomplishing as much as
possible through combined effort. This Bureau, with a year's experi-
ence in the aerial application of DDT, assumed considerable responsi-
bility for the technical features of this project.
Three cperaticns were planned. The first was carried out early
in the season on a series of small plots in Algonquin National Park,
Ontario, to determine the minimum dosage that could be used later in
the season. The second operation was begun 2 to 3 weeks later on a
series of 25- and 50-acre plots, totaling about 2,000 acres, in the
Kabonga section of Quebec, in cooperation with the Dominion Division
of Entomology and the Quebec Department of Lands and Forests. The
Bureau of Entomology of that Province provided the plane, materials,
living quarters for the men, and much of the assistance in this
operation. The Canadian International Paper Company also gave some
assistance. The third operation was on a much larger area (about
100 square miles) in the vicinity of Lake Nipigon, Ontario, which
was treated by the Royal Canadian Air Force for the Ontario Depart-
ment of Lands and Forests.
All three operations were greatly disrupted by the peculiar
season. Insect activity started nearly a month earlier than normal
owing to an unusually warm spring, but was followed by a cold period
of several weeks which retarded insect development. A late frost,
which killed balsam bads, made it very difficult to appraise the
results of the treatment. The Kabonga plots were most productive of
results; they indicated that the spruce budworm could ba controlled
with dosages of 1/2 to, 5 pounds of DDT per acre in several different
formulas and gallonages. The difficulty in controlling the appli-
cation of spray appeared to be the biggest factor influencing the
results of these treatments.
The Nipigon area was treated at the rate of a little less than
1 pound per acre. The final results are not yet at hand, but the
operational report indicated that the spray was very finely atom-
ized and drifted considerably so that much of it may have been lost.
Much valuable information was obtained, however, on operational
problems of so large an undertaking.
Later in the season spruce budworm infestations were discovered
in the Adirondack area of New York, and immediately steps were taken
to conduct spraying experiments in cooperation with the New York
State Conservation Department. W. G. Howard and W. M. Foss, of that
Department, gave considerable assistance in this work. Three 40-
acre plots were treated with 1/4, 1/2, and 1 pound of DDT per acre
in 1 gallon of xylene and kerosene about 1 week before pupation of
the budworms. All dosages gave good results. A few weeks later,
just as the moths were appearing, a 200-acre tract was sprayed at
the rate of 1 pound per acre in an effort to destroy the moths and
prevent oviposition. The results of this treatment will not be
available until next year.
On the Roosevelt National Forest in Colorado 120 acres of Doug-
las fir were sprayed at the rate of 1 pound of DDT in 1 gallon per
acre and 30 acres at the rate of 2 pounds of DDT in 2 gallons per
acre. Esso Heavy Aromatic Solvent, Velsicol AR-60, and xylene were
used as solvents, and fuel oil No. 1 as a carrier. The spraying was
done on May 17 about the time the young larvae moved from their
hibernation quarters into the needles. This work was under the
technical direction of N. D. Wygant, of this Division. A subsequent
cold period greatly curtailed the activity of the larvae and killed
many of the Douglas fir buds. From 60 to 80 percent control was
obtained. Incidentally, plots in this vicinity that were sprayed
with ground sprayers in May and June 1944 showed very good control
in 1945. Thus, one treatment may give control of two generations,
the larvae present at the time of spraying and the adult moths that
come to oviposit several weeks later.
Present indications are that aerial applications of DDT as low
as 1/4 pound per acre will effectively control the spruce budworm.
Whether treatment of rather large blocks would prevent mortality
of trees in treated stands is difficult to say, but it is believed
that such a treatment properly timed would at least delay tree mor-
tality for several years during which time the more valuable timber
might be salvaged.
Gypsy moth (Porthetria dispar (L.)). Several large tracts of
woodland infested with the gypsy moth were treated with DDT to de-
termine effective dosages and formulas and to study operational
problems. Thirty-four plots, covering more than 1100 acres, were
treated. Sixteen 10-acre plots were located at Wendell, Mass., one
50-acre plot at Athol, Mass., two 25-acre plots at Saxtons River,
Vt., eight 35- to 65-acre plots near Hope, N. Y., five 35- to 95-
acre plots at Moosic, Pa., and two plots, one of 97 acres and the
other of 193,at Spring Brook, Pa. P. B. Dowden represented this
Division in conducting this work.
It was planned to begin treating the gypsy moth areas a month
or so ahead of foliage appearance or egg hatch, relying on the
residual effect of DDT to kill the newly hatched larvae, and then
to follow with applications immediately after hatching, in mid-
development of larvae, and in the later instars. An unusually early
spring andcdlays in obtaining aerial equipment made it impossible to
begin operations on schedule. Work was initiated on April 29 and
continued until larvae were full-grown. The range in dosages was
1/8 to 3 pounds of DDT in 1/2 to 3 gallons of liquid per acre.
Several formulas were used, including solutions, suspensions, and
emulsions. Practically all treatments were effective except the
1/8-pound dosage. Further work is needed with early applications
of the lower dosages and to make accurate comparisons with differ-
ent formulas of solutions, emulsions, and suspensions.
Pine tip moths (Rhyacionia frustrana bushnelli Busck and R.
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neomexicana(Dyar). Late in April 637 acres of ponderosa pine plant-
ation on the Nebraska National Forest were sprayed for the control
of tip moths. This work was supervised by N. D. 'Iygant. The Forest
Service supplied the materials and hired the plane, Velsicol AR-50,
xylene, and Esso Heavy Aro;aatic Solvent were used as solvents and
No. 1 and No. 2 fuel oils as carriers. One plot was treated with an
emulsion containing Triton X-100 (an aralkyl polyether alcohol) as
the emulsifier. The applications ranged from approximately 1/2 to
3 1/2 pounds of DDT per acre and the reduction in infestation ranged
from approximately 50 to 95 percent with the heavier dosages. Here
again unseasonable weather played a large part in reducing the
effectiveness of the sprays because of the long interval of retarded
insect development. In general, the results were very favorable,
and more extensive treatments are planned for the coming year. No
satisfactory or economical method for the control of this insect had
been found previously.
Hemlock looper (Ellopia fiscellaria (Guen.)). A total of 2200
acres were treated with DDT for the control of the hemlock looper
in Clatsop County, Oreg., under the direction of R. L. Furniss.
The private owners of the timberlands and the State Forestry Depart-
ment paid for material and application. The applications were made
between June 5 and July 15, beginning with the first hatching of the
looper eggs. Six formulas were used in dosages from 1/5 to 1 pound
of DDT per acre, including a proprietary emulsion. The total cost
of these applications was about $2.30 per acre. During the same
period 9300 acres were treated with a lead arsenate concentrate at
the rate of 10 to 15 pounds per acre, at a cost of approximately
$3.50 per acre.
Very cool and wet weather continued throughout the month of
June, retarding development and hampering operations. These condi-
tions undoubtedly tremendously affected the results, but, although
control varied considerably, the over-all result appeared to be
Saratoga spittle bug (Aphrophora saratogensis (Fitch)). On
July 13 and 14 several plots, totaling 478 acres, of pine plantations
in Wisconsin were treated for the control of the Saratoga spittle bug
under the direction of H. C. Secrest, of this Division. The sprays
were applied just before the adults appeared. Kerosene and fuel oil
solutions were used with Velsicol AR-50 as a solvent and applied at
rates from 1/4 to 5 pounds of DDT per acre. Some control was ob-
tained with 1/2 and 1 pound, at 2 pounds 50 to 80 percent of the
adult spittle bugs were killed, and 5 pounds in 3 gallons of liquid
gave 100 percent control. Further work should be done to determine
whether effective control can be obtained with smaller dosages. It
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is possible that the reduction in flagging,which will not be fully
apparent until the spring of 1946, may indicate that the 1-pound
dosage will give practical control.
Red-headed pine sawfly (Neodiprion lecontei (Fitch)). A total
of 252 acres of red pine plantations in Oneida Co., N. Y., were
treated on July 4 and 5 for the control of the red-headed pine saw-
fly, under the direction of J. V. Schaffner, Jr.,of this Division.
Of this total, 146 acres were treated at the rate of 1/2 pound of
DDT in 1 gallon of liquid per acre, kerosene being the solvent, and
106 acres were treated with 1 pound of DDT in 1 gallon of a xylena-
kerosene mixture per acre. About 40 percent of the sawfly eggs had
hatched at the time of treat-.nent. Practically complete control was
obtained with the 1-pound dosage, and only a few larvae survived the
1/2-pound treatment. It is possible that the eggs from which these
survivors came did not hatch until after the residual effect of the
lower DDT dosage had worn off. This illustrates the importance of
synchronizing DDT application with insect development. Further ex-
periments in aerial spraying for the control of sawflles should be
White pine weevil (Pissodes strobi (Peck)). Plans were made to
spray white pine plantations in Hew York for the control of white
pine weevil adults early last spring before eggs were deposited.
The abnormally early spring and lack of aerial equipment frustrated
these plans, and it was possible to treat only a few small plots
with hand sprayers. The small-scale tests indicated that dosages as
low as 1/2 pound of DDT per acre would kill adult weevils. Mr.
Schaffner also directed this work.
The weevils feed on the bark of pine twigs for a few weeks in
the fall before going into hibernation. Consequently three plots,
totaling 220 acres, in Jefferson County, N. Y., were sprayed from
an airplane on September 13 for the control of the freshly emerged
adult weevils. Dosages of 1/2 and 1 pound of DDT in 1 gallon of
solution per acre were applied. Results of treatment cannot be
measured until 1946. A more thorough study of the possibilities of
combating this important pest of white pine by aerial application of
DDT is planned for next season.
Sprays were applied with a helicopter on small plots (5 to 20
acres) for the control of cankerworms, the gypsy moth, a sawfly
(Diprion frutetorum (L.)) on red pine, the orange-striped oak worm
(Anisota senatoria (A. & S.)), the European pine shoot moth (,_ya-
cionia buoliana (Schiff.)), the elm bark beetles (Scolytus spp.),
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the periodical cicada ('iancicada septendecim (L.)), andr^he pine
bark aphid (Pineus strobi (Htg.)). Dosages ranged from as low as
1/8 pound of DDT per acre on one of the sawfly plots to as high as 8
pounds per acre in an elm bark beetle plot. The main objective of
the work was to study the adaptability of the helicopter for treat-
ment of various types of areas under different conditions. Allob-
servers were favorably impressed with the operation of this type of
aircraft for treatment of plantations and small wooded areas. One
distinct advantage, in comparison with a fixed-wing plane, was the
ability of the helicopter to operate from almost any small open
space near the area to be treated. A disadvantage was the small pay
load of spray which could be carried. Twenty-five gallons of spray
was the maximum load that could be carried with safety by the
machine used in these tests.
In general, good control of the defoliators was obtained. The
treatment was ineffective against the periodical cicada and the
European pine shoot moth at the strengths applied. Further study is
needed before any report can be made on results of treatment for
control of the elm bark beetles and the pine bark aphid.
Effect of DDT Sprays on the General Insect Population
Many insects are not injurious. In fact, relatively few species
are serious pests. The importance of insects in furnishing the
principal food supply for many mammals, birds, fishes, frogs, and
other animals is not generally appreciated. Likewise, the effect in-
sects have on each other, particularly the beneficial effects of pre-
dacious and parasitic insects in holding in check their destructive
hosts, cannot be ignored. When applied over large areas DDT h?.s been
found greatly to reduce the insect fauna for various lengths of time.
Considerable effort was expended during the past season in measuring
these effects and in determining whether sufficient control of ob-
noxious species can be obtained without too much interference with
the beneficial and desirable insect species.
Three large areas, of approximately 100, 300, and 1,200 acres,
near Scranton, Pa., were sprayed with 2, 1, and 1 to 5 pounds of DDT
per acre, respectively. C. H. Hoffmann and H. H. Swift, of this
Division, and H. K. Townes and R. I. Sailer, of the Division of
Insect Identification, conducted these studies. The areas were
studied intensively just before treatment and, except for the 30'-
acre area, for a long period afterwards. Sampling methods were de-
veloped, and a thorough and comprehensive knowledge of the insect
fauna of treated areas and check areas before and after treatment
was obtained. Much valuable ecological information was obtained
aside from the main objectives. All treatments produced immediate
and pronounced effects on the insect population. Tremendous nLumbers
of insects were killed, and the insect fauna was greatly reduced for
a time. Flies, caterpillars, parasites of caterpillars, and leaf-
ho-pers were most severely affected. '"any of the moths, aphids,
scale insects, syrphid larvae, and coccinellid larvae were either
less affected or not harmed. Leaf-feeding and leaf-resting species
were severely affected, whereas forms inhabiting soil and leaf
litter apparently suffered very little. The rate of reestablishment
of the insect population was in proportion to the degree of treat-
ment. On the areas treated with the 2-pound and 5-pound dosages
effects lasted about 2 weeks and 2 months, respectively, with grad-
ual reestablishment of a population similar to that found in the
Aquatic life was, in general, much more seriously affected than
arboreal or terrestrial forms. One-half pound of DDT per acre can
destroy tremendous numbers of aquatic insects, crustaceans, and
other forms. This depletion of food for fish might have some effect
on the stocking of the streams. One area, through which a stream
flowed, was treated at the rate of 1 pound per acre, but actually
only about 1/4 of a pound per acre was deposited in the water. The
stream was practically depleted of insect life, but relatively little
direct harm was done to trout. The fish population was determined
by E. W. Surber, and further study in the spring of 1946 should show
whether or not starvation resulted from the reduction of food supply.
Much more research iork is necessary, but present information indi-
cates that as little as 1/4 pound of DDT per acre actually going in-
to the streams should be avoided if possible.
Effect of DDT Spray on Fish and Wildlife
The Bureau of Entomology and Plant Quarantine, realizing the
possible danger that DDT applications over extensive forested areas
might have on fish and wildlife, requested the assistance and coop-
eration of specialists in this field to aid in obtaining facts. In
the spring of 1944 a cooperative agreement was entered into with the
Illinois Natural History Surveys and late that fall their report in-
dicated high toxicity of DDT to fish when applied at rates of 1
pound or more per acre.
In the spring of 1945 a cooperative agreement was made with the
Fish and Wildlife Service, after which a program of work was arranged
for that season by A. L. Nelson, E. W. Surber, and C. H. Hoffmann.
Three large areas, many ponds, and three streams were treated during
the summer. The principal facts obtained from this study were
briefly stated in a press release of the Fish and Wildlife Service
dated August 22, 1945, and will be fully reported in a forthcoming
publication of the Department of the Interior. In general, fish in
ponds and streams can be se'.-A ected at rates of 1/4 to 1
pound of DDT per acre. However, th:oe amounts on certain occasions
produced little effect on fish Life. Much more information is
Birds and mammals are affected less than fish, at least directly,
by applications of DDT sufficient for the control of forest i,,3ects.
In the 1200-acre study -A4a in Fur-nsylvwLria several d.:-, and .i a
birds were found and there was a significant reduction in the number
of insectivorous birds left on the sprayed area 3 d;!rs after the
application. It was several weeks before it was repopulated. This
reduction was due in part to the Jeath of the birds, but the exact
proportion attributable to this tae was not deter.-dried. Some of
the reduction was due to birds' leaing the area beca-use of lack of
food. Parts of this area appeared to receive much more than 5 pounds
of DDT per acre because of the drift of the insecticide. There was
a heavy population of cankerworiTs and leaf rollers on oak, and num-
erous caterpillars on other trees at the time of spraying, and in-
sectivorous birds were freely feeding on them. No effects on birds
were reported in the 100- and 3CO0-acre areas in Pennsylvania. It
is reasonable to conclude, therefore, that dosages which are quite
satisfactory for the control of forest insect pests--i.e., 1/4 to 1
pound per acre-will not disturb the bird or mammal populations to
any appreciable extent. However, it is not yet fully understood how
these birds were affected, and until more is learned about the use of
DDT, caution is necessary in applying it on large acreaqes,
As indicated throughout this report, practically every .- ase of
the work touched upon is still in a preliminary stage of development.
In the light of the past season's results it appears that the most
important angles for further irjvaestigation in the ie ate fture
are as follows:
(1) It is essential to obtain a more uniform cove. je and less
loss in the spray materials liberated from airplanes in jrder to
economize on materials and to avoid injury to wildlife. The relation
between the viscosity and density of the spray fluids, particle size,
pattern of dispersal, height of flying, and the amount. of 10T de-
posited on the foliage should be determined.
(2) More work is needed on the toxic effects of 'D;T7 to fish and
other wildlife. More must be knrw,. about the action of this poison
on aquatic sad terrestrial forms-iLn particular, hcv it kills. For
example, are fish and birds affected through eating insects coated
with DDT? If so, proper timing of spray applications could be of
much importance in avoiding injury.
UNIVERSITY OF FLORIDA
3 1262 09238 7470
(3) Further work is needed on the toxicity to insects of vari-
ous DDT formulations, particularly a comparison of oil solutions,
emulsions, and suspensions, and on the possibility of applying them
in greater concentrations and less gallonage than the 10- to 12-
percent solution in 1 gallon per acre used in most of the applica-
tions of last year.
(4) There are many operational problems in the use of planes
for applying insecticides over forested areas. The size of the
plane in relation to economic distances of operation from the base,
height of flying to give the greatest safety within limits of ob-
taining effective control of the insects treated, and marking of
areas to aid pilots in securing satisfactory coverage are all im-
portant to the practical control of forest insects by this means.
An extensive series of cooperative tests in aerial application
of DDT for the control of forest insects such as the spruce budworm,
gypsy moth, hemlock looper, pine tip moths, spittle bugs, pine saw-
flies, and white pine weevil were conducted in 1945. These experi-
ments were designed to give information on minimum dosages needed
for effective control, to compare various DDT formulations, to im-
prove equipment used in releasing sprays from aircraft, and to study
the effects of DDT on other forms of animal life in treated areas.
It has been determined that DDT in low dosages is a very
effective insecticide for the control of many forest insects-
probably 1/8 to 1/4 pound being sufficient for satisfactory control
of many forms when the material is effectively applied. Much more
work is needed with emulsions and suspensions in order to study
their effectiveness as compared with that of oil solutions. The
emulsions and suspensions have certain advantages, the principal
one being the use of water as a diluent. Suspensions are apparently
less injurious to aquatic life. They form larger droplets, and less
material is lost in application. Spray applicators for airplanes
and operational problems need much more study. Much better control
of the material distributed from planes is necessary before we.can
take full advantage of the low dosage requirements and residual
effect of DDT and at the same time avoid danger to fish and wildlife.
Good progress was made in determining the degree of danger of
DDT to animal life inhabiting streams and forests and the broader
effects of DDT on the beneficial insect population in these environ-
ments. In general, the control of many forest insects with DDT
seems assured with dosages of sufficiently low volume to cause no
serious permanent injury to beneficial insects and other animal life.
The interested and wholehearted cooperation of the numerous
individuals concerned representing Federal and State agencies, pri-
vate owners, and commercial companies was in the final analysis the
chief factor in the success of the season's work.