LIBRARY STATE PLANT BOARD March 1949 E-774 United States Department of Agriculture Agricultural Research Administration Bureau of Entomology and Plant Quarantine TESTS OF INSECTICIDES FOR GRASSHOPPER CONTROL, 1947 11 Compiled by J. R. Parker Division of Cereal and Forage Insect Investigations Of the new insecticides tested against grasshoppers in alfalfa in Montana, Arizona, and California in 1946, chlordane, toxaphene (chlorinated camphene), and benzene hexachloride gave the most promising results (Hinman and Cowan I). Additional tests with these and several other new insecticides were made in 1947, and are reported herein. The materials were tested in the laboratory during the winter to select effective dosages which could be used as starting points in field tests during the normal grasshopper season. These results are not to be construed as recommendations for any of the insecticides tested. All of them are more or less toxic to warm-blooded animals. They would therefore have to be used with suitable precautions, which will not be discussed in this paper. SPRAYS AND DUSTS Methods and Conditions Laboratory Tests. --Insecticides were tested in the laboratory during the winter to select minimum effective dosages that could be used in initial field tests during the grasshopper season. All spraying and dusting were done in an open-top sheet-metal drum 28.3 inches in diameter (1/10,000 acre) by 13 inches deep. A false bottom 4 inches from the base of the drum left a treatment chamber 9 inches deep. The inside was lined with wrapping paper, which was replaced after each application of insecti- cide. This drum was mounted on a turntable and revolved at 90 revolutions per minute. 1/ These tests were conducted by F. T. Cowan, E. J. Hinman, J. R. Parker, Lee Seaton, and F. E. Skogg, of Bozeman, Mont.; O. L. Barnes and N. J. Nerney, of Tempe, Ariz; and C. C. Wilson, of Sacramento, Calif. In Arizona and Montana the Division of Grasshopper Control purchased the insecticides and provided equipment for their application. In California the Shell Agricultural Laboratory and the State Department of Agriculture supplied materials and equipment and assisted in field work. APR 1 5 - 2- All sprays were atomized into the chamber from a DeVilbiss hand- atomizer nozzle mounted over the spray chamber. The spray was directed downward toward a point midway between the center and the edge of the drum. Dosages corresponding to various rates per acre were measured to an accuracy within 0.05 ml. At the lowest dosage tested, corresponding to 2 gallons per acre, this measurement was accurate to within 13 percent. All dusts were applied with an improvised duster designed to handle the small amounts of materials used in these tests. Weighed amounts of dust corresponding to the desired rate per acre were used, and although the accuracy was probably not so high as in the spray tests, it was believed to be adequate. Compressed air for both dusting and spraying was supplied by a small motor-driven diaphragm pump connected to the atomizer nozzle or duster through a pressure regulator. A pressure gage was located on the low-pressure side of the regulator. With this apparatus a constant air pressure up to 20 pounds per square inch could be maintained. Soybean plants 3 to 6 inches high in 4- inch flowerpots were used as the test plants. Holes in the false bottom of the drum accommodated the flowerpots so that the tops were nearly level with the bottom of the treatment chamber. The grasshoppers used were mostly late instars or adults of Melanoplus differentialrs which had been reared in the laboratory. In most of the tests the grasshoppers and soybean plants were treated simultaneously, but in some tests they were sprayed separately. The grasshoppers were placed in the chamber along with the soybean plants just before the spray or dust was applied and removed as quickly as possible after treatment. They were then placed with treated or untreated plants in screen cages for observation of mortality and other reactions. Fifteen grasshoppers were placed in each cage, and duplicate cages were used in each test. Field Tests. --Spraying and dusting tests were begun by members of the Bozeman staff in the Salt River Valley, Arizona, on April 10, and continued to May 5. Most of these tests were conducted in medium to heavy stands of irrigated alfalfa. Members of the Tempe staff conducted tests in the same locality throughout the 1947 season. Their work included treat- ment of citrus trees as well as alfalfa. In California most of the tests were conducted in Ladino clover or trap strips of alfalfa during May, June, and July. In Montana all tests were carried out in fields of green alfalfa during July, August, and September. Melanoplus mexicanus (Sauss.) was the most abundant species encountered during the early season in Arizona. Melanoplus differenti- alis (Thos.) and second-generation M. mexicanus were dominant later in the year. Melanoplus differentialis and M. femur- rubrum (Deg.) -3- were the most common species in Montana. The work in California was done with infestations of M. marginatus (Scudd.), Camnula pellucida Scudd., ML differentialis, and M. femur-rubrum. In the early- season tests in Arizona spray applications from the ground were made with a turbine-blower sprayer-duster. This "machine delivered 8 gallons of emulsion spray per acre in 2-rod strips at a ground speed of 5 miles per hour. When concentrated sprays were used, the machine was fitted with a special spray bar that reduced the rate of application to 2.5 gallons per acre. Ground applications by members of the Tempe staff were made with a turbine -blower sprayer-duster, high-pressure power sprayers, or a 6-nozzle power duster. At the Sacramento station emulsions and sus- pensions were applied with a high-pressure power sprayer equipped with a boom, and oil solutions with a sprayer especially designed for discharging finely divided concentrated solutions. Applications of insecticides by airplane were made with a Bureau- owned White Standard biplane equipped with a spinner-disk spray device, and with commercial dusting and spraying planes. Emulsions and oil solutions were in most cases prepared from a concentrated solution of the insecticide in petroleum distillate No. 1 fuel oil. 21 Stocks were prepared so that an easily measured quantity, such as 1 quart, contained 1 pound of insecticide. Solutions were prepared by further dilution of the concentrate with the solvent. For the emulsions an oil- soluble emulsifier (Igepal No. 300) 4/ was added at the rate of 100 ml. (approx- imately 3.4 fluid ounces) per gallon, and the resulting concentrate diluted with water to the desired strength. Water suspensions were made from wettable powders as obtained from manufacturers. All dusts were factory-mixed or diluted from factory-mixed dusts by commercial insecticide companies. The insecticides were first tested on small plots (^ to 2 acres) to determine the most desirable form and rate of application and for comparison with each other. When suitable procedures had been devel- oped, treatments were applied to larger plots under more varied con- ditions. The results of all the tests conducted in Arizona were evaluated by sweeping with an insect net on treated and adjacent untreated plots before and after treatment. The ratio of grasshoppers per sweep on the plots assigned for treatment to those on the check plot would be expected to remain constant except for the effect of the treatment. The percentage 3/ Flashpoints, 100° F. minimum, 165°F. maximum; boiling range 440-560° F.; maximum sulfur 0.5 percent. 4/ A condensation product of ethylene oxide and an alkylated cresol. -4- reduction, or kill, was determined by an adaption of Abbott's formula- - dividing the reduction in this ratio by the ratio obtained before treat- ment and multiplying by 100. The results of the tests in California were evaluated by means of counts of live hoppers per unit area (1 square foot or 1 square yard) before treatment and of dead and live hoppers per unit area after treat- ment. Unless stated otherwise in the text, the kills reported are based on final sweepings or counts made 3 to 4 days after treatment. Chlordane In 1946 chlordane gave excellent results when used as an oil emul- sion but was not tested in oil solutions. In 1947 oil solutions of chlordane were tested first in the laboratory and then in the field to determine whether they were as effective as emulsions. Oil solutions have the advantage of requiring no water. This saves labor, speeds up spraying operations, and eliminates the possibility of using highly alkaline water, which might react unfavorably with the insecticide used. Laboratory Tests. --At the Bozeman station adult grasshoppers (Melanoplus differentialis) and soybean plants were sprayed simultane- ously with chlordane at the rate of 1 pound in 2 gallons of petroleum solvent per acre. Treated grasshoppers and plants were held in screen cages for 24 hours. The average mortality for 10 replicates was 93 percent. The results were considered sufficiently good to warrant using chlordane-oil solutions at this dosage in initial field tests. Field Tests. --The field tests with chlordane were conducted in Arizona, Montana, and California. The details of the tests and the results obtained are summarized in table 1. Chlordane was equally effective in oil solutions and emulsions and in ground and airplane applications. A dosage of 1 pound per acre reduced grasshopper populations 90 to 99 percent in 3 days or less under a wide variety of conditions. A suspension at this dosage gave 90 percent kill in limited tests in Arizona. When compared directly in airplane applications in Arizona, dusts gave 71 percent, solutions 96 percent, and emulsions 98 percent kill. The field tests therefore confirmed the laboratory tests, which showed that 1 pound of chlordane per acre in solution or emulsion was sufficient to give 90 percent or greater reduction in 3 days, and suspen- sions appeared to be almost as effective. Dusts were in general less effective, and when applied to dry vegetation late in the summer failed to give economic control. -5- Chlordane affects grasshoppers within a few hours. Speed of kill and duration of toxicity depend largely upon the dosage. With 1 pound per acre in oil solutions and emulsions the population present during treatment is frequently reduced 90 percent in 1 day and close to 100 percent in 3 days. Under such conditions the killing action after 3 days cannot be measured unless a new population hatches within the field or moves into it from the outside. When only small numbers of late-instar nymphs and adults are found, it is impossible to determine whether they have fed on treated foliage and survived or have only recently moved into the field. The only exact method of determining how long the in- secticide remains effective is to search the treated plots daily for freshly killed grasshoppers. This procedure is time-consuming and frequently impossible because of irrigating, harvesting, or grazing practices. General observations on the residual action of chlordane were made in Arizona and California. In Arizona the 1 -pound dosage continued to kill grasshoppers for 15 to 30 days, but in one test there was no residual effect on grasshoppers that hatched in the plots more than 7 days after treatment. In California an oil solution remained toxic 15 to 17 days. No injury to foliage was observed following the application of chlor- dane dusts or suspensions. Some spotting and wilting of alfalfa foliage was noted where oil solutions were inadvertently applied in dosages heavier than needed. This injury was undoubtedly caused by the solvent. When dosages were evenly distributed over entire plots, foliage injury was insignificant. Toxaphene Tests of toxaphene in 1946 were limited to a few late in the season at dosages of 2 to 8 pounds per acre. The excellent kills obtained indicated that it should be tested extensively in 1947. Laboratory Tests. --Toxaphene at dosages of 0.5 to 4 pounds per acre in 8 gallons of emulsion was used in 10 tests, in which adult grass- hoppers and soybean plants were sprayed together. The 0.5 -pound dosage killed 26 percent of the grasshoppers in 24 hours and 92 per- cent in 48 hours. Dosages of 1 to 4 pounds killed from 58 to 95 percent in 24 hours and 87 to 100 percent in 48 hours. From these tests it was concluded that 1 pound per acre applied as an oil emulsion was close to the minimum effective dosage under laboratory conditions. One pound of toxaphene in 2 gallons of solution per acre was used in 30 tests to compare the effects of spraying grasshoppers and plants separately and together. When sprayed grasshoppers were placed on untreated plants, the mortality averaged 84 percent in 24 hours and 96 percent in 48 hours. When untreated grasshoppers were placed on -6- sprayed plants, the mortality averaged 64 percent in 24 hours and 93 percent in 48 hours. When the grasshoppers and plants were both sprayed, the mortality averaged 98 percent in 24 hours. The high mortality obtained by placing sprayed grasshoppers on untreated plants indicates that toxaphene is very effective as a contact poison. The residual action of toxaphene was investigated by spraying soy- bean plants with an emulsion at a dosage of 2 pounds in 8 gallons and holding the plants for 7 days before allowing untreated grasshoppers to feed on them. In 5 tests the average mortalities 24, 48, and 72 hours after feeding were 24, 58, and 89 percent. When untreated grasshoppers, were placed upon freshly sprayed soybean plants treated at the same rate per acre, the average mortality was 78 percent in 24 hours and 98 percent in 48 hours. Toxaphene applied at 2 pounds per acre in a 10-percent dust was used in 10 tests in which grasshoppers and plants were dusted together. Mortalities averaged 59 percent in 24 hours and 95 percent in 48 hours, and were slightly less than the kills obtained with 1 -pound dosages applied in oil solution or emulsion. The results of the laboratory tests were considered sufficiently good to warrant using toxaphene in preliminary field tests at acre dosages of 1 pound in solution and emulsion sprays and of 2 pounds in dusts. Field Tests. --Field tests with toxaphene were made in Arizona, Montana, and California. The details of the tests are summarized in table 2. Toxaphene was almost equally effective in oil solutions and emulsions and in ground and airplane applications. At a dosage of 1 pound per acre the average kill in 3 days with both formulations was 90 percent, and at 1.5 pounds per acre in an emulsion 90 percent kill was obtained in 1 day and 98 percent in 5 days. Suspensions gave 78 percent kill in 3 days at 1 pound per acre, and 89 and 96 percent at 2 pounds. Dusts were tested at various strengths and dosages, but the highest kill was 89 percent per acre with a 10-percent dust applied at the rate of 2 pounds of toxaphene. Toxaphene was slightly less effective in field tests than in the laboratory. In solution and emulsion the 1.5 -pound dosage gave quicker kill and longer toxic effect than the 1 -pound dosage, and is therefore recommended for best results. To obtain the same kill with suspensions and dusts 2 pounds per acre was necessary. Toxaphene affects grasshoppers within a few hours after treatment. Speed of kill and duration of residual action are nearly the same as re- ported for chlordane. No injury to foliage was noted when dosages were evenly distributed. Excess application of oil solutions occasionally caused some spotting of alfalfa foliage. -7- Benzene Hexachloride Field tests were made with benzene hexachloride in Arizona and Montana. Because of the danger of foliage injury due to the solvent where solutions and emulsions are used, emphasis was placed on testing water suspensions and dusts. Oil solutions were tested only on small acreages in California. The results of these tests are summarized in table 3. All dosages are in terms of the gamma isomer, although the technical benzene hexachloride containing all four isomers was used. Benzene hexachloride, as in 1946, was erratic in performance. In Arizona, in tests on the same day, the kill after 1 day with 0.15 pound of gamma isomer per acre in water suspension was 79 percent whereas with 0.25 pound it was only 61 percent. In 7 tests kills with 0.4 pound in dust ranged from 49 to 99 percent, averaging 87 percent. In Montana average kills after 1 day with 0.3 pound in dust and 0.36 pound in water suspension were 65 and 73 percent. In California kills with only 0.114 pound in water suspensions and 0.15 pound in oil solutions averaged better than 90 percent. In view of the variable results, no statement can be made in regard to minimum dosages needed for consistently high kills. Benzene hexachloride affects grasshoppers within a few hours after treatment and most of the kill occurs within 1 day. There is little or no residual toxicity after 4 to 5 days. No foliage injury was noted with any of the formulations and dosages used in 1947. Hexaethyl Tetraphosphate Hexaethyl tetraphosphate (active ingredient tetraethyl pyrophosphate) was used in 32 laboratory and 22 field tests. It is a liquid which hydro- lyzes rapidly with water. Its chemical character, stability, and insecti- cidal efficiency may vary with the method used in making it. The material tested in the laboratory at Bozeman and in the field in Arizona was labeled "Hexaethyl tetraphosphate, 100 percent." Preparations containing 25 and 50 percent of hexaethyl tetraphosphate were used in California. Laboratory Tests. --Hexaethyl tetraphosphate was used in a prelim- inary series of 10 tests at acre-dosages of 0.5 to 4 pounds in 8 gallons of water. Grasshoppers and food plants were sprayed together. Average kills in 1 day for 2 tests at each dosage were as follows: 0.5 pound, 56 percent; 1 pound, 88 percent; 2, 3, and 4 pounds, 100 percent. In a second series of 10 tests with 1 pound per acre the average kill was 99 percent. In 6 tests in which grasshoppers were sprayed at the 1 -pound rate and placed on untreated foliage, the average kill was 89 percent. In 6 tests in which untreated grasshoppers were placed on foliage treated at the 1 -pound rate, the average kill was only 35 percent. The results of the laboratory tests were considered sufficient to warrant using 1 pound of hexaethyl tetraphosphate in 8 gallons of water per acre in preliminary field tests. They also indicated that it was primarily a contact poison. Field Tests .--Field tests were conducted in Arizona and California. The results of these tests, which are summarized in table 4, failed to support the indications of the laboratory tests. Kills with 1 pound per acre averaged only 35 percent. Most of the grasshoppers v/ere affected within a few minutes after spraying. Many twitched spasmodically and others were unable to jump or walk. Those that recovered behaved normally within a few hours. There was no increase in kill after 1 day. Field tests in California demonstrated that an acre-dosage of 1.35 pounds in 50 gallons of water or 5 gallons of oil was sufficient to obtain kills of 90 percent or better in 1 day. In these tests many grasshoppers were killed in less than 30 minutes. There was no increase in kill after 1 day. No injury to foliage was noted with the formulations and dosages used. Parathion The results of field tests with parathion in Arizona and California are summarized in table 5. Parathion at 0.4 pound per acre as a dust gave consistent kills of 90 percent or better in 3 days. In water- suspension sprays at 0.75 to 15 pounds the kill was 100 percent. Parathion killed very quickly. Dead and dying grasshoppers were noted within 1 hour, and high mortalities were recorded after 4 hours. Killing action continued for at least 5 days. No injury to foliage was noted with the formulations and the dosages used. BAITS New insecticides that had shown promise in grasshopper control when used as sprays and dusts were tested in grasshopper baits in Arizona and Montana during the 1947 field season. Since nearly all tests were comparisons of two or more insecticides, the results are reported under general headings instead of in separate sections on each insecticide. 9- Methods and Conditions All tests were conducted in the field. In Arizona tests were made only on plots; in Montana tests were made on plots and in outdoor screen cages. Uniform procedures were followed in conducting plot tests. Applications were made on 1.25- to 5-acre alfalfa plots at the rate of 10 pounds of dry carrier per acre with a bait broadcaster. When available, green alfalfa 6 to 27 inches tall was selected. Generally six or more tests were made with each bait in each series. Unless otherwise spec- ified, the carrier was a mixture of 3 parts of bran and 1 part of sawdust, by volume, and enough water, usually about 12 gallons, was added to each 100 pounds of carrier to make a moist, crumbly mash. In this report the quantity of a toxicant mentioned is the amount used per 100 pounds of carrier. Counts were made of the grasshoppers taken in sweepings of treated and untreated check areas before and after treatment (usually 3 days). Control results were evaluated by the same method used in tests of sprays and dusts. For cage tests grasshoppers were collected in the field and trans- ferred to screen cages, where they were held overnight without food. Approximately 50 grasshoppers were placed in each cage. In the morning, when temperatures were favorable for feeding, baits were introduced. The bait was scattered evenly over heavy paper cards, which were then laid on the bottoms of the cages. At the end of 3 hours the cards and any remaining bait were removed. The cages were stored out of doors but protected from direct sunlight for 3 days. During this time they were kept supplied with fresh, green food, and dead grasshoppers were re- moved and counted daily. Final counts of dead grasshoppers and of those still alive were made on the third day. New insecticides used in these tests were benzene hexachloride, chlordane, toxaphene, and parathion. Sodium fluosilicate, the standard toxicant in grasshopper baits, was included in most tests as a basis of comparison. Tests in Arizona Comparison of Different Poisons. --Wet baits containing the following quantities of the insecticides in 100 pounds of carrier were first compared in 19 field tests: Sodium fluosilicate 6 pounds, chlordane 0.5 and 1 pound, toxaphene 1 and 2 pounds, and enough benzene hexachloride to make 0.3 pound of the gamma isomer. The five baits containing the new insecti- cides were about equally effective, grasshopper-population reductions ranging from 65 to 71 percent. Baits containing the smaller quantities of chlordane and toxaphene were almost as effective as those containing the larger quantities. The reduction with sodium fluosilicate bait was 53 percent, 12 to 18 percent below the reductions obtained with the new 10- msecticides. In this series the new insecticides were used in the form of wettable powders. In initial tests bait containing 1 pound of toxaphene was as effective as any bait. Further tests demonstrated the superiority of 1 pound of this material over 6 pounds of sodium fluosilicate. In comparison on 5 -acre plots of green alfalfa in mid- July the kill with toxaphene was 77 percent 1 day after treatment and 82 percent in 3 days. With sodium fluosilicate the respective kills were 67 and 72 percent. In 62 direct comparisons during the 1947 season, the average kills in 3 days were 47 percent with 6 pounds of sodium fluosilicate and 60 percent with 1 pound of toxaphene. Sodium fluosilicate, parathion, and benzene hexachloride were compared in wet baits in six additional field tests. Benzene hexachloride and parathion were supplied in the wettable -powder form and sodium fluosilicate as the undiluted powder. The average grasshopper reductions were as follows: Sodium fluosilicate 6 pounds, 66 percent; parathion 1 pound, 70 percent; and benzene hexachloride 0.2 pound gamma, 73 percent. Comparison of Different Quantities of Insecticides in Baits. - - The effectiveness of baits containing 0.1, 0.2, and 0.3 pound of the gamma isomer of benzene hexachloride was compared in 12 field tests. Average grasshopper-population reductions were 78, 79, and 84 per- cent, respectively. These tests indicated that 0.1 pound was about as effective as 0.2 and 0.3 pound. In five other tests with baits containing 0.025, 0.05, and 0.1 pound of the gamma isomer, grasshopper reductions averaged 25, 32, and 57 percent. Reducing the gamma-isomer content of baits below 0.1 pound per 100 pounds of carrier materially reduced their effectiveness. The source of the benzene hexachloride used in this series was a wettable powder containing 5 or 6 percent of the gamma isomer. In early tests 1 and 2 pounds of toxaphene per 100 pounds of carrier were about equally effective in grasshopper baits. In six later tests the amounts were cut to 0.25, 0.5, and 1 pound, and average grasshopper reductions were 39, 46, and 55 percent, respectively. Pending com- pletion of more extensive tests, it is believed undesirable to reduce the concentration below 1 pound per 100 pounds of carrier. The toxaphene used in this series was in wettable-powder form. One -half pound of chlordane was about as effective as 1 pound in tests early in the season. Consequently, in later tests the amounts were reduced to 0.125, 0.25, and 0.5 pound. Average grasshopper reductions were 79, 85, and 90 percent. Differences in mortality from the baits containing the different strengths of chlordane were small, but the trend was toward higher kills with the higher amounts up to 0.5 pound. The chlordane used in this series was a wettable powder. - 11 - Two field tests were made with different quantities of parathion per 100 pounds of carrier--0.125, 0.25, 0.5, and 1 pound. The average re- ductions in grasshopper populations were 71, 77, 81, and 92 percent, respectively. The parathion in this series was a wettable powder. Effectiveness of Baits Containing Different Formulations of Benzene Hexachloride.--In three field tests wet baits containing 0.2 pound of the gamma isomer made from a 50-percent benzene hexachloride wettable powder and from undiluted technical benzene hexachloride (gamma isomer 10 percent) were compared. The technical benzene hexachloride was dis- solved in xylene and emulsified in water before it was mixed with the other bait ingredients. The average reduction in grasshopper population was 84 percent from the bait prepared with the wettable powder and 70 percent from that prepared with the technical benzene hexachloride. In six other field tests the source formulations were two wettable powders, one containing 6 percent and the other 10 percent of the gamma isomer, and an emulsion concentrate containing 9 percent of the gamma isomer. Again all baits contained 0.2 pound of the gamma isomer and all were spread wet. The average reductions in grasshopper populations from these baits were as follows: From 6-percent wettable powder 73 percent, from 10-percent wettable powder 53 percent, and from 9-percent emulsion concentrate 69 percent. In these tests best results were obtained with wettable powders con- taining 5 or 6 percent of the gamma isomer. Comparison of Wet and Dry Baits. --Two wet and two dry baits were compared in eight field tests. Each type of bait was tested with two poisons, 4 pounds of ammonium fluosilicate and 1 pound of toxaphene per 100 pounds of bait. Undiluted technical ammonium fluosilicate powder was used. Technical toxaphene was dissolved in xylene and emulsified in water before being mixed with the other bait ingredients. The carrier was 100-percent bran. In wet baits the water content was 12 to 14 gallons per 100 pounds of carrier, in dry baits approximately 3 gallons. There was little difference in effectiveness between the wet and dry baits, as shown by the following percentage reductions: Average Ammonium fluosilicate Toxaphene both poisons Wet bait 35 47 41 Dry bait 33 43 38 Comparison of Carriers Containing Different Proportions of Bran And Sawdust- -Carrier mixtures containing 1 part of bran to 1 part of sawdust and 3 parts of bran to 1 part of sawdust (all by volume) were tested in 16 field tests. Each mixture was tested with two poisons, sodium fluosilicate and toxaphene. All baits were wet. Average percentage reductions in grasshopper populations were as follows: - 12 Average Sodium fluosilicate Toxaphene both poisons 1:1 Mixture 42 55 49 3:1 Mixture 46 54 50 There was little difference in the effectiveness of baits containing different proportions of bran and sawdust. Tests in Montana Sodium fluosilicate was compared with benzene hexachloride, chlordane, and toxaphene in eight tests on plots of green alfalfa during August. The average kills in 3 days with different poisons were as follows: Sodium fluosilicate Benzene hexachloride (gamma isomer) Chlordane Toxaphene The average mortalities in this series were low, but no more so than usual for sodium fluosilicate bait in alfalfa during late summer in Montana. There was little difference between baits, and all the new insecticides were slightly better than sodium fluosilicate. SUMMARY Laboratory and field tests with the new insecticides for grasshopper control were continued in Montana, Arizona, and California in 1947. In addition to chlordane, toxaphene, and benzene hexachloride, which in 1946 were found to be the most promising, hexaethyl tetraphosphate and parathion were included in the 1947 tests. All these materials were tested as sprays or dusts applied by ground machines and airplanes, and some of them also in grasshopper baits. When applied in sprays or dusts, chlordane and toxaphene caused high mortalities within 24 hours and continued to kill over a period of 1 to 4 weeks. Each of these materials was as effective in oil solution as in emulsion and when applied from the ground as from airplanes. Chlordane at 1 pound per acre in such formulations reduced grasshopper Pounds per 100 Percent pounds of bait 6 mortality 32 0.05 42 .1 44 .3 38 .5 34 1 36 1 38 1.5 38 - 13 populations 90 to 99 percent in 3 days or less. A suspension at this dosage gave 90 percent kill, and dusts averaged 99 percent kill when applied by airplane and 64 percent by ground equipment. Toxaphene solutions and emulsions at 1 pound per acre gave 90 percent kill in 3 days, and emulsions at 1.5 pounds gave 90 percent in 1 day and 98 per- cent in 5 days. Suspensions gave 78 percent kill in 3 days at 1 pound per acre and 89 and 96 percent at 2 pounds. With dusts the highest kill was 89 percent with a 10-percent dust at 2 pounds of toxaphene per acre. Benzene hexachloride was so erratic in performance that it was impossible to select reliable minimum effective dosages; it killed quickly but had no residual toxicity after 5 days. Hexaethyl tetraphosphate at 1 pound per acre gave 99 percent kill in the laboratory but only 35 percent in the field; at 1.35 pounds per acre mortalities in the field ranged from 90 to 100 percent. This material had no killing action after 1 day. Parathion at 0.4 pound per acre in dusts gave consistent kills of 90 percent or higher; in water suspensions at 0.75 to 1.5 pounds per acre mortalities in 3 days were 100 percent. The killing action continued for 5 days. In field tests with baits 0.5 pound of chlordane, 1 pound of toxaphene, 1 pound of parathion, or 0.1 pound of the gamma isomer of benzene hexachloride per 100 pounds of carrier gave 10 to 15 percent higher kills than 6 pounds of sodium fluosilicate. Literature Cited (1) Hinman, E. J., and Cowan, F. T. 1947. New insecticides in grasshopper control. U. S. Bur. Ent. and Plant Quar. E-722, 21 pp. (Processed.) c o o 3 T3 CD (h C a) CJ I (h I V Ih a < cd T3 en a -1 -a o i/i -H !>> 1 rt lO -o J, « a! ■a CD c 3 -c Ih c cd £ E 3 C/3. 14 to ITS co ra ai id co h 0) 0> O) O) c- r- rt -h cm oo oo co oo en m t- t- m m n c o cd 3 o .2 B o 0) Ih 3 7d „ Ih ^ a0 6 ~ CD d 13 M73 . sc ■a in ojojq to M 1-1 f _ 1 ■ o r— | cc — > CO CM ■a c c 0 o ■r-l 3 c 0 ■rH 3 c 0 •rH 0 UJ O 1/5 3 3 +■* •iH e •iH e 3 OWOWQ in 0) 5 0 XJ 0) r c Cd Vh i , 3 H < "S3 CO — cd 0' cd ■"I1 CM 1 i Q co eg R • d (h — ' _ . . a. < a. < n m (D Ih N a. 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