STATE PLANT BOARD March 19^5 E "^ 2 United States Department of Agriculture Agricultural Research Administration Bureau of Entomology and Plant Quarantine A SUMMARY OF THE RESULTS OF THE WORK WITH DDT CONDUCTED BY THE DIVISION 05* TRUCK CROP AND GARDEN INSECT INVESTIGATIONS DURING THE SEASON OF 19Mt- Compiled by W. H. White, Division Leader Preliminary results on the vork conducted in 19^3 by "the Division of Truck Crop « nfl Garden Insect Investigations on DDT as an insectioide vere reported in the February 19*t4 issue of the Journal of Economic Entomology. Experiments vere continued during the season of 19^. They consisted of laboratory and small field-plot experiments, and in a fev instances of large field-plot experiments, against several common species of insects which attack vegetables, tobacco, and sugar beets. With a few exceptions the DDT vas used in dust mixtures containing pyrophyllite, and the final product vas prepared from a 10 percent DDT-pyrophyllite mixture vhioh vas supplied upon order by Geigy Co., Inc., l/ in compliance vith provisions promulgated by the War Production Board on supplies of DDT for experimen- tal purposes. This statement has been prepared from reports received from the various field laboratories of the Division, and is issued for the infor- mation and guidance of others interested in experimental vork vith DDT as a crop insectioide. Cabbage Caterpillars The vork on cabbage caterpillars vas conducted in field plots in southern California, at Charleston, S. C, and at Baton Rouge, La., against tlipennl s and the cabbage vebvorm ( Hellula undalis (F.)) . Several species of Agrotinae and Heliothls armigera (Hbn. ) vere also present. In the Charleston area the DDT appeared to be more toxic to the cabbage looper than to either the imported cabbage vorm or the larva of the diamondback moth and also more toxic than either rotenone or pyrethrum to the cabbage looper. Th<» results of this series of experiments seem to varrant the tentative con- clusion that heavy infestations of these three species of caterpillars may be controlled effectively by a 1 percent DDT-pyrophyllite dust applied at 10-day intervals, the first application being made as soon as feeding in- Jury is apparent. This conclusion is drawn vithout consideration or regard far the residue factor. In one experiment consisting of plots of cabbage, collards, and broccoli, a 1 percent dust mixture applied at 10-day inter- vals from the time the first true leaves appeared on the plants effectively controlled the cabbage looper, Imported cabbage worm, and several species of Agrotinae. The 1 percent DDT dust mixtures were not effective against the cabbage webworm, but vhen the strength vas increased to 2.5 percent adequate protection was obtained. 17 The Geigy Co. designated this material as "Neocid 15." - 2 - Tomato Fruitworm Comparative tests with DDT dust mixtures, calcium arsenate, and cryolite vere made in southern California against the tomato fruitworm ( Hellothls armigara (Bbn.)). The results of these tests, "based upon the relative number of damaged tomatoes at harvesttime, shoved that a 10 percent DDT dust mixture gave 92 percent control, a 5 percent DDT mixture 77 percent, and a 2.5 percent DUO? mixture 81 percent. By comparison an undiluted calcium arsenate gave 8l percent control, and a 70 percent cryolite mixture 2/ 60 percent control. In this experiment three appli- cations of dust vere made at intervals of 2 weeks, at an average rate of 30 pounds per acre-application. In another heavily Infested experimental field the following results vere ohtalned; 10, 5> and 2.5 percent DDT dust mixtures gave 97 percent, 8^ percent, and 79 percent control, respec- tively, whereas the undiluted calcium arsenate gave 65 percent and. the 70 percent cryolite 53 percent control. At Norfolk, Ya., a 5 percent DDT dust mixture was as effective against this insect on Fcrdhook lima beans as undiluted cryolite (90 percent). Flea Beetles on Potatoes Experiments comparing cryolite, calcium arsenate, and DDT dust mix- tures against the tuber flea "beetle ( Epltrlx tuber is Gentn.) and the western potato flea beetle (E. subcrlnlta (Lec.)) vere conducted In the Yakima Valley, Wash. In these experiments the tuber flea beetle, formerly designated as the western furm of E. cucumeris (Harr.), was the predom- inant species. The main objective of flea beetle control in this area is to protect the potato tuber from larval or grub damage; therefore, the results of the experiments are measured In terms of injury to the potato* tubers. Four applications of a 10 percent DDT dust applied at the rate of approximately 17 pounds compared with a 70 percent cryolite dust mix- ture applied at the approximate rate of 10 pounds per acre-application yielded the following results: DDT plots k2 percent damaged tubers, cryolite plots 5k percent damaged tubers. While the number of damaged tubers from the DDT plots vas about a third less than from the cryolite plots, the total yield of marketable potatoes was about the same for both treatments. Mexican Bean Beetle Studies during 19^3 shoved that DDT applied as a dust or as a spray suspension had little toxic effect on the Mexican bean beetle (Epilaehna varlvestls Male.). The experiments of 191+4 have given similar results. In field experiments conducted in North Carolina, the control from a 10 percent DDT dust, applied with hand dusters in two of the experiments and with a power duster In another, ranged from kl to 1*9 percent; a dust con- taining 0.5 percent of rotenone gave from 96 to 100 percent control. In field experiments at Columbus, Ohio, spray suspensions containing as high as 100 pounds of the 10 percent DDT dust per 100 gallons of water did not control the Mexican bean beetle. 2/ In this paper references to percentages of cryolite indicate the percentage of sodium f luoaluminate . - 3 - Plant Bugs on Beets Grown for Seed In the Phoenix, Ariz., area a ^.5 percent DDT dust vas compared vith a dust mixture consisting of pyrophyllite containing 0.2 percent of pyrethrlAS to which equal parts of sulfur had "been added. These dust mix- tures vere tested against three species of Lygus hugs vhlch Infest sugar beet seed stocks at the same time. The species Involved vere Lygus ohllneatus (Say), L. hesperus Knight, and L. ell bus Y en D. In small exper- imental plots the applications of the dust mixtures vere made at the rate of 50 pounds per acre. Two appli cations vere made of the pyre thrum dust mixture, one on May 11 and the other on May 19; and one application of the DDT mixture vas made on May 11. The results of the applications vere recorded on June 1. The DDT dust gave 77 percent control and the pyre thrum dust 67 percent. Germination tests of seed produced on the experimental plots shoved 65 percent of viable seed from, the undusted plots, 69 percent from the pyre thrum plots, and 91 percent from the DDT plots. At Albuquerque, N. Max., 7 acres of a 20-acre field of sugar beets vhlch had passed the blossoming stage vere dusted on June 5 with a 5 percent DDT mixture at the rate of kO pounds per acre. The application vas made vlth a traction duster. On June 6 and 16 the remaining 13 acres of the field vere dusted vlth the pyre thrum dust mixture as described above at the rate of 30 pounds per acre-application. Examination of the fields on June 27 shoved a reduction in Lygus bugs of 95 percent in the area treated vlth DDT and of 60 percent In the area treated vlth the pyrethrum mixture. The percentage of viable seed vas 78 from the DDT- treated area and 71 from the pyre thrum- treated area. In another field test at Safford, Ariz., 5 acres of a to-acre field of sugar beets vere dusted vlth a 5 percent DDT mixture and 5 acres vlth a 2 percent DDT mixture, the application being by airplane at the rate of 50 pounds per acre. On June 15, 7 days after the applications, an examination of the treated and untreated acreage shoved a 99 percent reduction of Lygus bug populations in the 5 acres receiving the 5 percent DDT dust and 75 percent in the acreage receiving the 2 percent DDT dust. Germination tests shoved a viability of 66 percent in the seed taken from the acreage treated vlth the 5 percent DDT and of 76 percent in the seed from the acreage treated vlth the 2 percent DDT mixture. At Phoenix, Ariz., on May 31, an 80-acre field of garden beans in- fested vith Lygus bugs and the Say Btinkbug ( Chlorochroa sayl Stal) vas treated vith 5 and 2 percent DDT dust mixtures! On June 3 the control of Lygus vas recorded as 100 percent in both plots; the numbers of these species taken by 50 sweeps of an Insect net in a comparable undusted plot increased from 83 on May 31 to 307 on June 3. Reduction of the Say stink- bug on June 3 vas 92 percent for the 5 percent dust and 79 percent for the 2 percent dust. The percentage of viable seed produced vas 92 in the 5 peroent DDT plot and 88 In the 2 percent DDT plot. The undusted plot yielded 73 percent of viable seed. Potato Leafhopper * Experiments conducted in southern Wisconsin showed that a 2.5 per- oent DDT dust mixture reduced infestations of the potato leafhopper -4 - ( Bmpoaaca fapae (Harr.)) on potatoes and beans 78 to 99 peroent. These figures vera obtained from counts of leafhopper nymphs 1 to 3 veeks after application. The DDT dust mixture gave a greater reduction in leafhopper populations than did a dust mixture containing 1 percent of dinitro-o- cyclohexylphenol and 50 percent of sulfur. In similar experiments in the Colunbus, Ohio, area DDT sprays and DDT-sulfur dusts gave hatter results than did the dlnitro mixture or a pyr e thrum- sulfur mixture containing 0.025 percent of pyrethrlns and 50 percent of sulfur. The PUT sprays contained up to 0.08 percent of DDT in a kerosene emulsion, and the dust mixtures consisted of 1.4 percent of DDT, 50 percent of sulfur, and the remainder pyrophylllte. Pea Weevil In laboratory experiments at Moscow, Idaho, in 19*3 relatively low mortalities of the pea weevil ( Bruchus plsorum (L.)) were obtained with a 10 percent DDT dust when the weevils were transferred from treated cage a to clean cages 5 minutes after treatment. Later tests showed that the mortality could be increased by retaining the Insects in the treated oages for a longer time. In 1944 rield experiments were conducted on plots 24 feet wide and located end to end around the edges of large fields of peas grown for seed. In 21 replicates a 5 peroent DPT dust reduced the adult pea weevil Infestation 99 peroent In 2 days, whereas a 0.75 peroent rotenone dust reduced the infestation 98 percent in a like period. In these tests the insectloides were applied with a power duster at the rate of 30 pounds of the DDT dust mixture and 20 pounds of the rotenone dust mixture per acre. In 7 replicates 2.0 percent of the dried peas in the DDT plots were weevlly as compared with 2.7 peroent in plots where rotenone dust was used. Pepper Weevil In a field experiment conducted at San Clemente, Calif., against the pepper weevil ( Anthonomus eugenll Cano) on bell peppers, DDT dusts at strengths of 10, 5, and 2.5 percent yielded higher mortalities than did a 70 percent cryolite mixture. The mixtures were applied with rotary hand dusters at 7 -day Intervals, at the rate of 15 to 25 pounds per acre depending upon the size of the plants. In another experiment In which the 10- and 5-percent strengths of DDT were applied at 14-day intervals, the kill of weevils was greater than where the cryolite mixture was applied at 7-day Intervals. Cabbage Seedpod Weevil In laboratory tests at Sumner, Wash., 10 peroent DDT dust showed no toxicity to the cabbage seedpod weevil ( Ceutorhynchus ass^ills (Payk.)). A bait spray containing 6 pounds of the 10 percent DDT -pyrophylllte mix- ture and 45 pounds of sugar In 100 gallons of water was also ineffective. - 5 - Sweetpotato Weevil Laboratory teste at Opelousas, La., indicate that DDT is toxic, to the sweetpotato weevil ( Cylas formicarius elegantulus (Summers)) hut not so toxic as potassium f luosilicate. The 10 percent DDT gave mortalities ranging from 82 to 98 percent, as compared with 98 to 100 percent with undiluted potassium f luosilicate and 80 percent vith undiluted calcium arsenate . Pea Aphid In the laboratory tests in I9U3 DDT showed a toxicity to the pea aphid ( Macro siphum plBi (Kalt.)) comparable to that obtained with rotenone dust mixtures. Results of field experiments at Madison, Wis., did not substantiate these consistent laboratory results. For example, in one experiment the application of 5 percent DDT dust with a power duster at the rate of 35 pounds per acre, followed by heavy rains, resulted in 99 percent control after 7 days, as compared with 88 percent for a 0.5 percent rotenone dust containing 2 percent of a light mineral oil. In this experiment the average yields of shelled peas per acre in five quarter -acre plots were 1,517, 859, and lj-95 pounds, for the DDT, rotenone, and check treatments, respectively. In a second experiment, also followed by rains, a 5 percent DDT dust gave less outstanding results than those obtained with several dosages and strengths of rotenone dust mixtures. In a third experiment, under wet conditions but accompanied by very little precipitation, both the 5- and 10-percent strengths of DDT were less effective than a dust containing 0.75 percent of rotenone and 2 percent of a light mineral oil. Onion Thrips At Twin Falls, Idaho, in an experiment conducted in cooperation with the Idaho Agricultural Experiment Station, a 5 percent DDT dust, applied to table onions at the rate of 25 pounds per acre with a power duster equipped with a 20-foot muslin hood, gave 69 percent control of the onion thrips ( Thrips tabaci Lind.). This figure was based upon the number of thrips surviving in the dusted plots after four applications as compared with those surviving in the undusted plots. In another experiment in which the material was applied with a hand duster the control was 63 per- cent. The DDT dust yielded greater control than a spray containing k pounds of 10 percent DDT per 100 gallons of water, and applied with a traction sprayer under 350 pounds pressure at the rate of approximately 100 gallons per acre. This dust also gave greater control than a spray containing 1 quart of nicotine sulfate and 3 quarts of corn sirup per 100 gallons of water. On the other hand, in California a 10 percent DDT dust gave no better control than a spray containing 1 quart of nicotine sulfate, k pounds of sugar, and 8 ounces of a spreading agent per 100 gallons, and this nicotine spray did not yield so good a result as a DDT spray containing 6 pints of a 10 percent DDT emulsion per 100 gallons of water. The emulsion was prepared by dissolving undiluted DDT in toluene and adding an emulsifying agent and water. In small-plot exper- iments at Beltsville, Md., the performance of DDT has conformed in general with the results of the field experiments in Idaho and California. - 6 - Beet Leafhopper In 11 replicates of a field experiment with the "beet leafhopper (Eutettix tenellus (Bak.)) on sugar "beets at Twin Falls, Idaho, the appli- cation of 115 pounds per acre of 5 percent DDT dust resulted in an average reduction in populations of 95 percent after 3 days and 89 percent after 10 days. A spray containing k pounds of 10 percent DDT applied at 200 gallons per acre did not give so great a reduction. Squash Bug In small field tests in California, only 12 adult squash hugs ( Anasa tristis (Deg.)) survived 13 days after the last of two applica- tions of a 10 percent DDT dust mixture. In comparahle untreated plots the survivors included 221 adults, 20 eggs, and 7 nymphs. Harlequin Bug The harlequin hug ( Murgantia histrlonica (Halm)) was confined in field cages on cahhage at Hendersonville, N. C. A 10 percent DDT dust killed only 6k percent of the adult hugs in 3 days. In small tests at Alhamhra, Calif., a 2.5 percent DDT dust killed 35 percent in 3 days and 86 percent in 5 days. Wireworms At Walla Walla, Wash., where the sugar -heet wireworm ( Limoniu s califronicus Mann.) and the Pacific Coast wireworm (L. canus Lee . ) were used in lahoratory tests, the indications are that long periods of time are required to kill wireworms with DDT and that this material does not act as a repellent. The wireworms killed hy DDT appear to he desiccated, as though affected hy a strong alkali or exposed to drying, whereas those killed hy funigants are usually found to he stiff and "bloated. In one series of experiments "begun in May and repeated in July and August 19^, DDT was thoroughly mixed with the top 9 inches of garden soil and wireworms were caged within the treated soil. The wireworm mortalities at the end of 5 weeks' exposure to different dosages of DDT were as follows: Pounds per acre Present mortality 27 16 63 32 69 1*8 85 320 98 The surviving wireworms, many of which were inactive, were placed on moist blotting paper in salve tins and ohserved for an additional 5 weeks. The mortality at the end of the 10 weeks was 99 percent for the l6-pound dosage and 100 percent for the others. No data are availahle on the effect these dosages of DDT will have on subsequent plant growth. - 7 - Horcrvorms on tobacco In field experiments at Florence, S. C, and Oxford, N. C, the application of either a 5 or a 10 percent DOT mixture did not give a satisfactory reduction of the tobacco hornvorm ( Protoparce sexta ( Johan. ) ) . In laboratory tests at Oxford the fifth instar of the tobacco hornworme was not affected by the 10-percent mixture, but the same instar of the tomato hornvorm (P. qulnquemaculata (Haw.)) succumbed readily. In comparable tests with third instars of the two species, 100 percent mortality of the tomato hornworm was obtained in 2k hours in each of seven replicates, whereas the mortality of the tobacco hornworm averaged 12 percent in 24 hours and 35 percent in 96 hours. There was very little feeding of either species on the treated foliage. Tobacco Budworm In a field experiment at Florence, S. C, a 10 percent DOT dust mixture applied in the buds of the plants by different methods gave from 88 to 100 percent kill of the tobaoco budworm ( Hellothis vireBcens (F . ) ) in k days. Tobacco Flea Beetle In a field experiment at Oxford, N. C, a 5 percent DDT dust gave 66 percent control of the tobacco flea beetle ( Epitrix hlrtlpennls (Mslsh.)) 3/ based on a comparison of the number of beetles surviving on treated and untreated plots following the first application, and 59 percent following the second application. In this experiment three 60 percent cryolite dusts, each in a different diluent, gave control ranging from 39 to 5^ percent. Tobacco Moth and Cigarette Beetle In laboratory experiments at Richmond, Ya., undiluted DDT was used in an acetone-oil solution. The solution was atomized into a modified Peet- Grady chamber. The test insects were adults of the tobacco moth ( Ephestla e lute 11a (Hbn. ) ) and the cigarette beetle ( Lasloderma serrlcorne (F . ) ) . A 5 percent DOT-oil solution, used at the rate of 100 cc. per 1,000 cu.ft., resulted in 97 percent kill of the tobacco moth in 3 days and 71 percent kill of the cigarette beetle in 5 days. A 15-percent solution resulted in kills of 98 and 90 percent of the moths and beetles, whereas pyrethrum-oil spray containing 0.2 percent of pyrethrins gave mortalities of 100 and kS percent of the moth and the beetle, respectively. A 10 percent DDT dust mixture, prepared by miTing pyrophyllite with an oil solution of DDT and then blowing it into the dust chamber at the rate of 3 ounces per 1,000 cubic feet, killed 1*8 percent of the tobacco moths and 93 percent of the cigarette beetles. A 15-percent solution of DDT in oil sprayed on packages of cigarettes did not prevent them from becoming infested during an exposure of 30 days to the cigarette beetle and the tobacco moth. 3/Heretof ore erroneously identified as Epitrix parvula F. - 8 - Plant Tolerance UNIVERSITY OF FLORIDA I3IIIDIIIIIIIIIIIIIIIIIIIIII1IIIIIIIIIII 3 1262 09230 4152 No exhaustive tests have been conducted on the tolerance of plants to DDT dust or spray mixtures or solutions. However, the vork that has "been done with DDT dusts indicates that tomatoes, potatoes, cabbage, turnips, onions, beans, peas, and tobacco are tolerant to lov strengths and reasonable dosages of this material, and that some injury to squash or other cucurbits may be expected when this material is applied in dust form at low concentrations.