LIBRARY 
 STATE M<WF7 BOARD E-726 
 
 United States Department of Agriculture 
 Agricultural Research Administration 
 Bureau of Entomology and Plant Quarantine 
 
 EXPERIMENTS WITH DDT FOR THE CONTROL OF THE GYPSY MOTH, 
 PARTICULARLY WITH AERIAL EQUIPMENT 
 
 By Philip B. Dowden l/ 
 Division of Forest Insect Investigations 
 
 During 19^5 a series of plots infested with the gypsy moth (Porthetria 
 dispar (L.)) vere 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-tall Moths Control applied the insecticides. Both these 
 Divisions and the States of New York and Pennsylvania checked on results. 
 
 AIRPLANE APPLICATION 
 
 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 k 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. 
 
 l/ 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. 
 
- 2 - 
 
 Eighteen of the plots were laid out in the Wendell, Mass., State 
 Forest. Each was 10 acres in area. They were too close together to he 
 entirely satisfactory. The first applications demonstrated that spray 
 intended for one plot might drift onto another and thus confound the re- 
 sults. Since this fact was recognized, however, it is believed that the 
 results for each plot can be clearly defined. 
 
 As a check on the effect of an oil spray containing no DDT, one plot 
 in the Wendell State Forest was treated with kerosene plus xylene mixed 
 as in the regular formula containing these oils. Cloth trays placed in 
 the plot to obtain an estimate of dead larvae falling to the ground in- 
 dicated that very little mortality took place during or subsequent to 
 the application. 
 
 Seasonal Infestation 
 
 The 19^5 season was very unusual. Unseasonably warm weather in March 
 and early in April caused one of the earliest general hatches on record. 
 This was followed by several weeks of cold, rainy weather, during which 
 the small larvae remained massed 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 Wendell, Saxtons River, and 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 untreated check plot increased fivefold. Spring con- 
 ditions were comparable 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 of 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 bursting, 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 ins tars, and 
 they gave excellent results. There was some survival, though, on four 
 plots not included in this study, which were treated after pupation had 
 begun. To be effective, therefore, sprays should be applied Just be- 
 fore or during the larval period. 
 
 Coverage 
 
 It is important to determine the optimum volume of spray to apply 
 per acre. The amount will vary with many different factors, including 
 species of insect to be controlled and density of stand. Of equal im- 
 portance is the evenness of spray distribution, which largely depends up- 
 on the distributing apparatus in use and the skill of the pilot. 
 
The pla^ies used In 19^5 flew at about 80 miles per hour 50 feet above the 
 treet«-ps, and in almost all the experimental work distributed l6 gallons 
 of spray per uinute. To check the spray coverage and evenness of dis- 
 tribution, glass plates were placed in all the plots and a visual esti- 
 mate was made of the amount of DDT deposited on them. The plates were 
 usually placed at the corners of the l/U-acre observation areas in a 
 fairly open space. 
 
 .;.e amount of insecticide 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 l/2 
 to 1 pound of DDT in 1 to 1 2/3 gallons of spray per acre. Since com- 
 plete control^/ 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 19^5 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 l/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 
 moth larvae. 
 
 Dosages 
 
 To establish the minimum dosage of DDT vhich will give complete con- 
 trol of the gypsy moth, it will, of course, be necessary to run several 
 series of tests in vhich dosage is the only variable. Although it was 
 impossible to run a complete series of this sort in 19^5, posthatch 
 
 2/ Complete control as used in this paper indicates that a thorough 
 scouting of the area showed no new egg clusters. 
 
- h - 
 
 treatments made on five plots offer a fair comparison. On each plot 1 
 gallon of spray was applied per acre, and in each case xylene was used as 
 an auxiliary solvent for DDT, with kerosene as a diluent. The results 
 are summarized in table 2. 
 
 Complete control of larvae was obtained at a dosage of 1 pound of DDT 
 per acre, nearly complete control at dosages of 1/2 and l/k pound, end in- 
 effective control at 1/8 pound per acre. With the l/8-pound dosage the 
 estimated number of egg clusters per acre vas reduced from 1,906 in the 
 spring to 309 in the fall. However, natural mortality in this area was 
 high, 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 exceptionally well sprayed, very little spray drifting out of the 
 plot. New egg clusters were well distributed over the entire plot in 
 the fall. 
 
 Among the 30 plots sprayed after the larvae had hatched, k were 
 treated with less than 1/2 pound of DDT per acre, and at least a few new 
 egg clusters were found on all of them. Of the 8 plots treated at the l/2- 
 pound dosage, complete control was effected on 5 plots and a single new 
 egg cluster was found on each of 2 plots. On 1 plot at Moosic egg clus- 
 ters were found in three widely separated areas, indicating incomplete 
 spray coverage on those areas. Eleven plots were treated with 1 pound of 
 DDT per acre, and new egg clusters were found on 3 of them. All 3 were 
 sprayed under adverse weather conditions . Six plots were sprayed with 
 more than 1 pound 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 1S&5, complete control of the gypsy moth 
 is almost always effected when DDT is applied at the rate of 1 pound in 
 one or more gallons of oil spray per acre after hatching has occurred; 
 also that complete control is frequently obtained at dosages as low as 
 l/2 pound per acre . 
 
 Formulations 
 
 The DDT formulations used in these tests were prepared as solutions 
 in kerosene or fuel oil, with and without an auxiliary solvent, as an 
 emulsion, and as a suspension. The two oil sprays used against the 
 gypsy moth during 19^5 appeared to be about equally effective. The emul- 
 sions and suspensions were somewhat less effective, but they were not 
 adequately tested. 
 
 Almost complete control of the gypsy moth was effected on plots 
 sprayed with 1 pound of DDT in 1 2/3 gallons of fuel oil or kerosene per 
 acre before hatching 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 somevhat 
 more DDT than kerosene and is a little cheaper. Both solutions have much 
 to commend them. The oils are easily procured and the price is reasona- 
 ble. The solutions are easily mixed and they make effective sprays. They 
 have some disadvantages. The oils dissolve comparatively little DDT and 
 
they do not hold the insecticide in solution veil at temperatures near 
 freezing. The highest concentration of DDT used in kerosene or fuel oil 
 was 1 pound of DDT in 1 2/3 gallons of oil, a 7.2-percent solution. The 
 solutions were mixed indoors and stored in a warm building when neces- 
 sary, and no difficulty was experienced from DDT 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), Solvesso-Xylol, 3/, j*/, an< ^ L ' two aromatic pe- 
 troleum fractions Velsicol AB-50 and PD 5k%-C. 5/ Excellent control was 
 obtained on all these plots except where the dosage of DDT was greatly 
 reduced or weather conditions were particularly unfavorable. The ex- 
 periments did not show that any one of the auxiliary solvents was su- 
 perior to the others. 
 
 An auxiliary solvent is necessary if it is desired to use higher 
 than 7 or 8 percent solutions of DDT in kerosene or fuel oil. This may 
 be an advantage 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 temperatures. The disadvantages of an auxiliary sol- 
 vent are the added cost of spray materials and difficulties encountered 
 in mixing. 
 
 Four plots were sprayed with DDT mixed as an emulsion. Complete con- 
 trol was effected on two of them, in which xylene was used as a solvent 
 and Igepal CA Extra (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 kj (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 sufficient 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 an accurate report on the experiments, trade names 
 are used in this paper. 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. 
 
 h_/ Product of the Colonial Beacon Oil Co. 
 
 5/ Product of the So cony -Vacuum Oil Co. 
 
 6/ Experimental products of the E. I. du Pont de Nemours and Co., Inc. 
 
- 6 - 
 
 unaffected by drift) caused 100 percent mortality of larvae held in labo- 
 ratory trays. 
 
 Weather Conditions 
 
 No particular study was made regarding the influence of climatic fac- 
 tors on the efficiency of the airplane sprays. Nevertheless, the experi- 
 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- 
 tioned: 
 
 (1) The prehatch spraying was completed at 8:30 a.m. on April 29. 
 At 11:U0 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 l6 a 66-acre plot at Moosic, Pa., was sprayed at the 
 rate of l/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 Eiver, Vt., was sprayed 
 at the rate of 1 pound of DDT in 1 l/2 gallons of spray per acre. PD 
 5^-C was used as an auxiliary solvent and kerosene as a diluent. Foliage 
 vas wet when sprayed, and a few hours after the spraying there was a 
 heavy downpour with 1 l/2 inches of rainfall. When the plot was surveyed 
 in the fall, only one new egg cluster was found. 
 
 Larval Mortality 
 
 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 days 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 may be summarized 
 as follows: 
 
 (1) Very little feeding was done by larvae affected by DDT. 
 
- I - 
 
 (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 l/4 a - 11 ^ l/ 2 pound 
 of DDT per acre caused complete mortality of larvae when the foliage was 
 collected before it was exposed to rainfall, hut 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. 
 
 (H) 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- 
 ment . 
 
 (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 
 treatment . 
 
 (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 Pain 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. 
 
 Power Sprayers 
 
 Four plots were treated on April 18 and 19. At that time many of the 
 larvae had hatched, but most of them were still on the egg clusters. The 
 four plots were sprayed with l/h to l/2 pound of DDT per 100 gallons of 
 tank mix at dosages of 1 l/2 to 3 pounds of DDT per acre. Complete con- 
 trol was effected on all plots, but undoubtedly they were all "over- 
 sprayed." 
 
 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 per 
 acre is apparently necessary to effect complete control, but a considera- 
 ble reduction in infestation was effected when only 2 ounces (0.125 lb.) 
 of DDT were applied per acre. 
 
- 8 - 
 
 Knapsack Fire Pumps 
 
 Two 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 ground. 
 Probably 95 percent of the egg clusters on these plots were below this 
 height. Hatching had commenced 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 gallons of spray, 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 number of egg clusters was 
 3,2?3 in the spring and 70 in the fall on the plot treated with the emul- 
 sion and 1,725 in the spring and 17 in the fall on the plot treated with 
 oil. 
 
 DISCUSSION 
 
 DDT and the development 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, the cost of the 
 spray materials per acre is about one-fifth that of the materials used in the 
 hitherto conventional method of treatment with power sprayers, which re- 
 quires 30 pounds of lead arsenate and 6 pints of fish oil per 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 burst; 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 tine 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 pupate before con- 
 suming a lethal dose of the insecticide. 
 
 The practicability of spraying DDT on tree trunks and undergrowth 
 with hand-operated pumps is also a distinct advantage over the 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 19^5, 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 lasting dam- 
 age, except possibly to fish and other aquatic life. 
 
 SUMMARY 
 
 During 19^5 a series of plots infested with the gypsy moth ( Porthetrla 
 dispar (L) ) were sprayed with DDT insecticides applied either from the air 
 
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 l/2 pound was distributed. A dosage of l/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 19^5, w& s 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 ±2 to 3 pounds of DDT per acre, but 
 undoubtedly the plots were "oversprayed." The other four were sprayed 
 with dosages of l/8, l/U, l/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 19^5. 
 
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 Table 2. --Effectiveness of airplane sprays containing different dosages of DDT 
 against the gypsy moth. 
 
 Plot location 
 
 Dosage of DDT 
 Der acre 
 
 Larval instar at time 
 of treatment 
 
 Results 
 
 Wendell, Mass, 
 
 Hope, N.Y. 
 
 Pounds 
 1/8 
 
 iA 
 
 1/2 
 
 1/2 
 
 1 
 
 3 and 4 
 2 and 3 
 
 2 and 3 
 2 and 3 
 
 Slight control 
 
 4 new egg clusters 
 found along roadside 
 border 
 
 Apparently complete 
 
 control on sprayed are 
 
 1 new egg cluster found 
 
 Complete control 
 
 Table 3. --Egg cluster counts on 1-acre plots treated with DDT applied from the ground 
 by a powt.r sprayer 
 
 DDT in 
 
 Composition of spray 
 quantities per acre 
 
 Estimated 
 clusters per acre 
 
 100 gallons 
 of tank mix 
 
 DDT 
 
 Yelsicol 
 AE-50 
 
 Igepal 
 CA Extra 
 
 Water 
 
 Before 
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 Gallons 
 
 Number 
 
 Number 
 
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 0.125 
 
 0.31 
 
 0.02 
 
 600 
 
 1063 
 
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 .22 
 
 .55 
 
 .03 
 
 525 
 
 1673 
 
 122 
 
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 17 
 
 2.72 
 
 1.02 
 
 2.55 
 
 .16 
 
 6oo 
 
 2579 
 
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 Checks (no 
 
 treatront) 
 
 -- 
 
 -- 
 
 -- 
 
 105 
 
 558 
 
 -- 
 
 -- 
 
 -- 
 
 -- 
 
 -- 
 
 1533 
 
 4234 
 
INIVERSITY OP FLORIDA 
 
 3 1262 09227 9974