STATE j64N BOARD E-726
United States Department of Agriculture
ricultural Research Administration
.ureau of Entomology and Plant Quarantine
EXPERIMENTS WITH DDT FOR THE CONTRMuL r Gh~ GYPSY MOTH,
PARTICULARLY WITH AER4l l EQUTLME-N'
By Philip B. Dowden i/
Division of Forest Insect Investigations
During 1945 a series of plots infested with the gypsy moth (Porthetria
dispar (L.)) were sprayed with insecticides containing technical DDT ap-
plied either from the air or from the ground. The work was carried out as
a cooperative project. The Division of Forest Insect Investigations was
responsible for the general plan of experimentation. The Division of Gyp-
sy and Brown-tail Moths Control applied the insecticides. Both these
Divisions and the States of New York and Pennsylvania checked on results.
Two single-motor biplanes were used in the airplane experiments.
Twenty-six plots were treated from a White Standard equipped with a 100-
gallon supply tank and a spinner-disk distributing device, and eight plots
with an N-3-N (Navy Trainer) equipped with a 60-gallon tank and a nozzle-
type distributor. Each plane released about 16 gallons of liquid per
minute distributed as a fine mist.. Since the results with both planes
were very similar, the effectiveness of the treatments is discussed under
the various objectives for which the experiments were designed, regardless
of the plane used. Very little foliage injury was observed which was
attributable to spray deposits. A complete list of treatments, together
with the egg-cluster counts in the spring before treatment and in the
fall after treatment, is given in table 1.
Description of Plots
Plots for airplane spraying were laid out near Wendell and Athol,
Mass., Saxtons River, Vt., Hope, N. Y., and Moosic and Spring Brook, Pa.
They ranged in size from 10 to 173 acres, and presented a wide variety
of flying conditions. Within each plot from 4 to 12 quarter acre areas
were delineated in which the numbers of gypsy moth egg clusters were
estimated before treatment and again in the fall after egg deposition
was completed. The fall estimates were augmented by a survey conducted
throughout the entire plot.
I/ Many workers participated in these experiments. Donald Whittam
and Raymond Dion acted as pilots in the aerial work. Ralph Holbrook and
David Crosby laid out plots, took egg-cluster counts, and took part in
other phases of the work at Wendell and Athol, Mass., and Saxtons
River, Vt. A. J. Pruett, R. L. Hardy, Roy Herbert, and John Regan did
the plot work and rearing of larvae at Moosic and Spring Brook, Pa.
Robert Sweet and others carried out the field work at Hope, N. Y.
Eighteen th' i -'te "wie- laid out in the Wend&. UL, Mass., State
Forest, -'.. -ae ' .u.' in area. The., were too close together to be
entirely sat '-.factory. Thq first .ppl.icatiora demounaitrated. that spray
intendea for one plot :i.t dr'.J,: onto another and thus confound the re-
sults. Since this fact was recotriized, however, it is believed that the
results for each plot can be clearly defined.
As a check -on the effect of an oil spray z -,ta'n-. no DDT, one plot
in the Wendell S1tate For'-t was treated with kerosene plues xylene mixed
as in the regular foi'.Lla containing these oils. Cloth trays placed in
the plot to obtain an estimate of dead larvae falll'rm-- to the grou.nd in-
dicated that very little ortality took place d.-i' o- or subsequent to
The 1-5 Pei'.Forl'l wvas very unusual. Unseasonably warm weather in March
and early in April caused one of the earliest general hatches on record.
This was follow' by several weaks of cold, rainy weather, during which
the small larvae remained rcL d at or near the egg clusters for days at
a time. On May 11 there was a snowfall of several inches, and many of
the small caterpillars died. Later in the season "wilt" disease was
prevalent at W6edell, Saxtons River, -nd Athol. Estimates of the egg
clusters present on untreated check plots in the fall showed that the
number had dropped to about one-third of those present in the spring.
However, at Pittston, Pa., near Moosic and Spring Brook, the number of
egg clusters on an untr'eaited check plot increased fivefold. Spring con-
ditions were comi.-arable to those at Wendell, but little or no wilt was
observed later in the season. There were no check plots under observation
at Hope, N. Y., but the infestation was generally light.
Time cf Application
The first four treatments in table I were applied on April 29. At
that time about 75 percent of the egg clusters had hatched, the buds of
oak were just b1urstirg, and the leaves of gray birch and poplar were
small. Hatching continued during most of May. The almost complete con-
trol effected with the 1- and 3-pound dosages of DDT indicates that these
sprays are toxic to young gypsy moth larvae for a long time and that
early spraying is a practical method of treatment. The remaining treat-
ments were applied when larvae were in the first to fifth inetars, and
they gave excellent results. There was some survival, though, on four
plots not included in this study, which were treated iftor pupation had
begun. To be effective, therefore, sprays should be ,''cpiled Just be-
fore or during the larval period.
It is important to determine the optimum volule of spray to apply
per acre. The amount will vary with many different factors, including
species of insect to be control-,ed and density of Bt!V.-l. Of equal im-
portance is the evenrneias of spray distribution, which '-.rigely depends up-
on the distribute v,-; apparatus in use and the skill of the pilot.
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The pl a 1 ,I15 flew at about 80 miles per hour 50 feet above the
treetops, -A im almost all the experimental work distributed 16 gallons
of Qir-y per i .nute. To check the spray coverage and evenness of dis-
tribution, glass plates were placed in all the plots and a visual esti-
at .s made of the auiAA.r.t of DT deposited on them. The plates were
*18-" .! placed at the corners of the 1/4-acre observation areas in a
.'Fr.. oCp r space.
"it, oA 1 biclde released over a plot often differed con-
siderably from the amount actually deposited within the plot. Evapora-
tion, wind drift, and many other factors may have reduced the amount of
spray. Furthermore, there may have been a wide variation in the even-
ness of distribution. It is therefore incorrect to state that a plot
was treated with an exact amount of DDT per acre in an exact amount of
spray, or to infer that a certain dosage was evenly distributed over an
entire plot. Actually the correct figures are unknown. Nevertheless,
a measure is necessary for comparative purposes, and the most convenient
one to use is the amount of spray released.
On the 2 plots at Wendell treated with 1 pound of DDT in 1 2/3 gal-
lons of spray per acre on April 29, before foliage was fully developed,
a few gypsy moth larvae survived. Since the glass plates were almost
completely covered with a light film of oil, the survival of a few larvae
can hardly be attributed to a deficiency in the volume of spray applied.
Twenty plots were sprayed, after foliage was fully developed, with 1/2
to 1 pound of DDT in 1 to 1 2/3 gallons of spray per acre. Since com-
plete control2_/ was effected on 12 of them, there seems to be no doubt
that sufficient spray was used to give adequate coverage. Therefore, the
optimum volume of spray, for the 1945 distributing apparatus at least,
was probably between 1 and 1 2/3 gallons per acre. Only 1 plot was
treated with less than 1 gallon of spray per acre. This plot of 10 acres
at Wendell was treated with 1/2 pound of DDT per acre, applied in 2
quarts of spray, the rate of discharge being cut to 8 gallons of spray
per minute. As a result a considerably finer spray was released. The
spray drifted more than usual, and at least a trace of spray deposit
was recovered over about 25 acres. Effective control was confined to
about 10 acres in the central portion of the area, and where only a trace
of insecticide was deposited there was considerable survival of gypsy
To establish the minimum dosage of DDT which will give complete con-
trol of the gypsy moth, it will, of course, be necessary to run several
series of tests in which dosage is the only variable. Although it was
impossible to run a complete series of this sort in 1945, posthatch
2/ Complete control as used in this paper indicates that a thorough
scouting of the area showed no new egg clusters.
treatmerts made on five plots offer a fair .'o:m.arison, On each lc.t 1
gallon of ir,i' was appl'ed .er acre, and in each case xylene was used as
an auxiliary solvent for LJT, with kerospene as a diluent. The results
are sumv.rized in table 2.
Complete control of larvae was obtained at a dosewe of 1 pound of LD'
per acre, ne rly complete control 't dosages of 1/2 and 1/4 pound, end In-
effective control at 1/8 pound per acre. With t'.e 1/8-pound dosaf'e the
estimated number of .. clusters per acre was reduced fror. 1,906 in the
spring to 309 in the fall. However, natural mortality in this area was
hi2.;, and probably if the plot had not been treated there would not
have been more than 600 new egg clusters per acre in the fall. The plot
was excepti--.. .I ell sp .iyed, very little spray driftir-g out of the
plot. New clusters were well distri-uted over the entire plot in
;_.. the 3D plots sprayed after the larvae had hatched, 4 were
treated with less than 1/2 poun.d of DDT per acre, and at least a few new
e,:; clusters were found on all of them. Of the 8 plots treated at the 1/2-
pound dosage, complete control was effect-5d on 5 pe,1 and a sirl-l new
egg cluster was f:;,..id on each of 2 plots. On 1 plot at Moosic egg clus-
ters were fojnid in three widely separated areas, indicati.%- in.oplete
spray coverage on those arese. Eleven plots were treated with 1 pound of
DDT per acre, and new -g6 clusters were found on 3 :" them. All 3 were
sprayed under idverse weather conditions. Six plots were sprayed with
more than 1 ..-ind of DDT per acre, and complete control was effected on
all of them.
Considering all these facts, the results indicate that, with the
distributing apparatus used in 1945, complete control of the gypsy moth
is almost always effected when DDT is applied at the rate of 1 pound in
one or more .znllons of oil spr-': per acre after hatching has occurred;
also that complete control is frequently obtained at doses as low as
1/2 pound per acre.
The DDT formulations used in these tests were prepared as solutions
in kerosene or fuel oil, with and without an auxiliary solvent, as an
emunlsion, and as a suspension. The two oil sprays used .tgalr.st the
gypsy moth during 1945 appeared to be about eqlly effective. The emul-
sions and suspensions were somewhat less effective, but they were not
Almost complete control of the gypsy moth was effected on :lots
sprayed with 1 pound of DDT in 1 2/3 gallons of fuel o1i or kerosene yer
acre before hat-1hlrV was completed, and complete control was effected on
plots sprayed with the same solutions after the larvae had hatched. Re-
sults with the two oils were very similar. Fuel oil dissolves somewhat
more DDT than kerosene and is a little cheaper. Both solutions have much
to commend hth.-. The oils are easily procured and the -rice is reasona-
ble. The solutions are e..sily mixed and they make effective opr.ys. They
have one disadvans'_-'m.e Tl,- oils dissolve compF:ratively little DDT .-ni
they do not hold the insecticide in solution well at temperatures near
freez'.'. Th^ Li..':-t concentration of Ti7 used in kerosene or fuel oil
i.,.- 1 pound of DT in 1 2/3 gallons of oil, a 7.2-percent solution. The
solutions were iaxed indoors and stored in a warm building when neces-
sary, and no difficulty was experienced from D'iT crystallizing out.
Sprays made up by dissolving DDT in a solvent and adding kerosene
as a diluent were used on 13 plots. The following solvents were used:
Xylene (technical grade), Solveseo-Xylol, 3/, 4/, and two aromatic pe-
troleum fractions Velsicol AB-50 and PD 547-C. 5/ Excellent control was
obtained on all the.s-. plots except where the dczLa^.e of DDT was -rejtly
reduced or weather cc..irtions were particularly unfavorable. The ex-
periments did not show that i.-ay one of the auxiliary solvents was su-
perior to the others,
Au .axiliary solvent is necessary if it is desired to use higher
than 7 or 2 percent solutions of DDT in kerosene or fuel oil. This may
be an advaiint-q in that it permits the application of a given amount of
the insecticide in a smaller volume of spray, and the DDT can be held in
solution at lower term.eratures. The disadvantages of an auxiliary sol-
vent are the added cost of spr-y. materials and difficulties encountered
Four plots were sprayed with DDT mixed as an emulsion. Complete con-
trol was effect-d on two of them, in which xylene was used as a solvent
and >-epal CA I rci (an alkyl aryl polyglycol ether) as an emulsifier, but
only part of the larvae that were fed the sprayed foliage in laboratory
trays were killed. One plot was sprayed with an emulsion using Mentor
25 V (a heavy aromatic petroleum fraction) as a solvent with Igepal CA
Extra as an emulsifier. Only partial control was effected, probably be-
cause the leaves were wet when the spray was applied. The fourth plot
was sprayed with a 25-percent emulsifiable DDT concentrate 6/. Unfor-
tunately there was ? efficient drift of spray material from a nearby plot
sprayed with an oil solution of DDT to confound the results.
Only one plot was sprayed with a suspension of DDT. This was a 50-
percent DDT water-dispersible powder. 6/ This plot was also affected by
drift from a nearby plot sprayed with oil. Sprayed foliage (probably
3/ In order to give n accurate report on the experiments, trade names
are used in this paeqr. Their use does not imply endorsement, guarantee,
or warranty of the materials so mentioned, or that other similar, untested
products may not be used in the same manner with equal results.
4_/ Product of the Colon 'n eracon Oil Co.
5/ Product o-- the Socony-Va-u-.m Oil Co.
6/ Experimental products s of the E. I. du Pont de Ne-.ours and Co., Inc.
unaffected by drift) caused 100 percent mortality of larvae held in labo-
No particular study was made regarding the influence of climatic fac-
tors on the efflcienr.. of the airplane sprays. Nevertheless, the exper'-
ments showed that oil sprays containing DDT could be satisfactorily sprayed
on wet foliage, and that, even when heavy rains occurred soon after the
sprays were applied, sufficient residues remained to effect complete or
nearly complete control of the gypsy moth. Three examples may be men-
(1) The preha-tch -pr\ying was completed at 8:30 a.m. on April 29.
At 11:40 there was a light shower and it was followed by another late in
the afternoon. From May 1 through May 19 there were nine rainy days with
a total precipitation of 6.9 inches. Throughout this period gypsy moth
egg clusters were hatching.
(2) On June 16 a 66-acre plot at Moosic, Pa., was sprayed at the
rate of 1/2 pound of DDT in 1 2/3 gallons of fuel oil per acre. Foliage
was so wet at the time of application that as the plane was flown over
the plot the down-draft from the propeller caused a heavy fall of water
from the leaves. A few seconds later the fine mist spray of insecticide
could be seen drifting down. In the fall only one new egg cluster was
found within the plot.
(3) On June 19 a 25-acre plot at Saxtons River, Vt., was sprayed
at the rate of 1 pound of DDT in 1 1/2 gallons of spray per acre. PD
544-C was used as an auxiliary solvent and kerosene as a diluent. Foliage
was wet when sprayed, and a few hours after the spraying there was a
heavy downpour with 1 1/2 inches of rainfall. When the plot was surveyed
in the fall, only one new egg cluster was found.
On all plots sprayed with DDT after hatching was completed the lar-
vae were killed more quickly than where lead arsenate is used. Eight
cloth-covered trays, 3 feet square, were put out in each plot to obtain
some idea of the number of dead larvae falling to the ground. Results
on one of the plots in the Wendell State Forest are considered typical.
A total of 835 dead larvae were recovered; 72 percent of these were re-
covered the first day, 87 percent the first 3 days, ,99 percent the
first 8 days, and none 12 deys after treatment. Most of the larvae re-
covered several days after the treatment had been dead for some time but
had lodged in the foliage.
Foliage from each of the treated plots was collected and placed in
trays with healthy larvae, usually 50. The results aey be summarized
(1) Very little feeding was done by larvae affected by DDT.
(2) Foliage from almost all plots treated with oil sprays at 1 pound
of DDT per acre caused complete mortality of larvae even after long peri-
ods of weathering and heavy rainfall.
(3) Foliage from plots treated with oil sprays at 1/4 and 1/2 pound
of DDT per acre caused complete mortality of larvae when the foliage was
collected before it was exposed to rainfall, but mortality was incomplete
after the foliage had been exposed to weathering, and the percentage of
mortality decreased as the length of the weathering period increased.
(4) Foliage from plots sprayed with DDT emulsions at the rate of
1 pound per acre caused rather low mortality 9 and 20 days after treat-
(5) Foliage from a plot sprayed with DDT in suspension at the rate
of 1 pound per acre caused complete mortality of larvae 18 days after
(6) Foliage from a plot treated with xylene plus kerosene but no
DDT caused no mortality.
(7) In check trays of larvae fed untreated foliage the mortality
was very low.
APPLICATIONS FROM THE GROUND
All experimental work in the application of DDT against the gypsy
moth, using ground equipment, was carried out in the Green Run area of
Spring Brook Township, Pa. Eight 1-acre plots were sprayed with a power
sprayer and two with knapsack fire pumps. The objective was to de-
termine the minimum dosage of DDT that would give satisfactory control
when applied as an emulsion with a power sprayer, both before and after
hatch, and whether satisfactory control could be obtained by treating the
forest floor and tree trunks up to a height of 5 or 6 feet.
Four plots were treated on April 18 and 19. At that time nmin, of the
larvae had hatched, but most of them were still on the egg clusters. The
four plots were sprayed with 1/4 to 1/2 pound of DDT per 100 gallons of
tank mix at dosages of 1 1/2 to 3 pounds of DDT per acre. Complete con-
trol was effected on all plots, but undoubtedly they were all "over-
Three plots were treated on June 7 and a fourth on June 13, when
larvae were in the fourth and fifth instars. These tests are summarized
in table 3.
A striking correlation exists between the reduction in numbers of
egg clusters and the increase in dosage of DDT. A dosage of 1 pound pr'
acre is apparently necessary to effect complete control, but a conaidev.-
ble reduction in infestation was effected when only 2 ounces (0.125 lb.)
of DDT were applied per acre.
Knapeack Fire Pumps
hw.-. 1-acre plots were treated on April 19 with hand-operated fire
pumps that produced a fine-mist spray up to about 6 feet above the -romund.
Probably 95 percent of the e'S, clusters on these plots were belcw this
height. Hatching had cc.r.ybjced at the time, and a few larvae were ob-
served on the foliage. One plot was treated with 2.3 pounds of DDT mixed
as an emulsion in 23 *1 :l-:is of prey, and the other with 5 pounds of DDT
in 10 gallons of light oil. Very striking, although incomplete, control
was effected on both plots. The estimated nm.ber of egg clusters was
3,223 In th3 spring 1r 7. in the fall on the plot treated with the emul-
sion and 1,,',^' in the -"- and 17 in the fall on the plot treated wIth
DDT and the develop ,3-t of airplane applications of insecticides pro-
vide new and powerful tools for use against the gypsy moth. One important
advantage in using DDT is the low cost of the material. Since 1 pound of
DDT will give effective control on an acre of woodland, t]e cost of the
spray materials per acre is about one-fifth that of the materials used inthe
hitherto conventional method of treatment with power sprayers, which re-
quires 30 po,.nd. of lead arsenate and 6 pints of fish oil -er acre.
The use of DDT also doubles the length of the period during which
spraying can be done effectively. Prehatch sprays are practical and af-
ford an opportunity for excellent coverage before the buds j urst; wet
foliage does not interfere seriously with the residual toxicity of the
insecticide; and, since DDT is a contact insecticide, applications can
be made up to the time of pupation. Lead arsenate, on the other hand,
cannot be satisfactorily applied until the leaves are well developed;
wet foliage delays applications considerably; and sprays applied late in
the season are relatively ineffective because larvae pu;ate before con-
suming a lethal dose of the insecticide.
The practicability of spraying DDT on tree trunks and uin.rgrowth
with hand-operated pumps is also a distinct advantage over t-he use of pow-
er sprayers in small, isolated, or special infestations. The advantages
of airplane applications over spraying with a power sprayer are obvious.
At best a ground crew can spray only about 200 acres of woodland a sea-
son. A pilot, operating one of the planes in use during 1945, can proba-
bly treat about 10,000 acres a season.
DDT can be harmful to fish, wildlife, and beneficial insects when
used indiscriminately. It should be applied over extensive forest areas
only under competent supervision. On the basis of present information a
dosage of 1 pound or less per acre will not cause serious or lastivT dam-
age, except possibly to fish and other aquatic life.
Durlri-, 1945 a series of plots infested with the gypsy moth (Porthjtria
dispar (L)) wore spray.- with DITL insecticides sppliedi either from the air
- .7 -
or from the ground. Twenty-six plots were treated with a White Standard
biplane equipped with a spinner-disk distributing device and eight plots
with an N-3-N biplane equipped with a nozzle-type distributing device.
Results were similar with both planes.
Early sprays applied before gypsy moth hatching was completed ef-
fected almost perfect control when 1 pound of DDT was distributed in
1 2/3 gallons of kerosene or fuel oil per acre. Oil sprays applied after
hatching was completed almost always effected perfect control when 1
pound of DDT was distributed in 1 to 1 2/3 gallons of spray per acre, and
frequently when 1/2 pound was distributed. A dosage of 1/8 pound per
acre effected only partial control. The two oil sprays appeared to be
about equally effective, and there seemed to be no difference in results
when any one of several auxiliary solvents was combined with kerosene.
The oil sprays were effective when sprayed on wet foliage or when heavy
rains occurred soon after application. On most plots a high proportion
of the larvae that died succumbed within a few days after the spray was
applied. Foliage from all plots treated with DDT-oil sprays caused heavy
mortality of healthy caged larvae even after long periods of weathering.
Oil sprays containing no DDT caused practically no larval mortality. The
cost of spray materials, when 1 pound of DDT was distributed per acre, for
the mixtures used experimentally in 1945, was about one-fifth that of
the conventional treatment with lead arsenate and fish oil.
Eight 1-acre plots were sprayed from the ground with a power
sprayer. On four of them, sprayed just as larvae were hatching, complete
control was effected with dosages of 11 to 3 pounds of DDT per acre, but
undoubtedly the plots were "oversprayed." The other four were sprayed
with dosages of 1/8, 1/4, 1/2, and 1 pound of DDT per acre when larvae
were in the fourth and fifth instars. Mortality was complete with the
1-pound dosage. Survival on the other plots was closely correlated with
dosage, and there was a considerable reduction in infestation when only
2 ounces of DDT were applied as an emulsion in 525 to 600 gallons of
water per acre.
Two 1-acre plots were sprayed with hand pumps which produced a fine-
mist spray up to about 6 feet above the ground. The spray was applied
just as egg clusters were hatching. One plot was sprayed with an emul-
sion and the other with an oil spray. The gypsy moth population was
greatly reduced on both plots, but control was incomplete.
DDT and the development of airplane application provide new and
powerful means of combating the gypsy moth. DDT is a more efficient and
a cheaper spray than lead arsenate. Only about 200 acres of woodland
can be treated during a season with a power sprayer, whereas about 10,000
acres can be treated with a small plane similar to those used in 1945.
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- 13 -
Table 2.--Effectiveness of airplane sprays containing different dosages of DDT
against the gypsy moth.
Dosage of DDT
Plot location per acre
Larval instar at time
3 and 4
2 and 3
2 and 3
2 and 3
4 new egg clusters
found along roadcide
control on sprayed are
1 new egg cluster found
Table 3.--Egg cluster counts on 1-acre plots treated with DDT applied from the ground
by a powbr sprayer
Composition of spray Estimated
DDT in quantities per acre clusters per acre
100 gallons Velsicol Igepal Before After
of tank mix DDT AR-50 CA Extra Water treatment treatment
Ounces Pounds Pints Pints Gallons Number Number
0.33 0.125 0.31 0.02 600 1063 436
.68 .22 .55 .03 525 1673 122
1.36 .46 1.15 .07 550 1446 17
2.72 1.02 2.55 .16 600 2579 Nor.e
Checks (no treatir.nt) -- -- 105 558
UNIVERSITY OF FLORIDA
3 1262 09227 9974 I
3 1262 09227 9974