Tests of insecticides for grasshopper control, 1948 and 1949

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Title:
Tests of insecticides for grasshopper control, 1948 and 1949
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27 p. : ; 27 cm.
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English
Creator:
Parker, J. R
United States -- Bureau of Entomology and Plant Quarantine
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U.S. Department of Agriculture, Agricultural Research Administration, Bureau of Entomology and Plant Quarantine
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Washington, D.C
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Insecticides -- Testing   ( lcsh )
Grasshoppers -- Control   ( lcsh )
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federal government publication   ( marcgt )
bibliography   ( marcgt )
non-fiction   ( marcgt )

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Bibliography:
Includes bibliographical references (p. 23).
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Also available in electronic format.
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compiled by J.R. Parker.
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Caption title.
General Note:
"E-807."
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"July 1950."

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University of Florida
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Full Text



July 1950 E-807

United States Department of Agriculture
Agricultural Research Administration
Bureau of Entomology and Plant Quarantine



TESTS OF INSECTICIDES FOR GRASSHOPPER CONTROL, 1948 and 19491/

Compiled by J. R. Parker
Division of Cereal and Forage Insect Investigations


Reports have been published on tests of insecticides for grasshopper control conducted in 1946 (Hinman and Cowan 2) and 1947 (Parker 3). This paper presents the results of similar tesTs made in 1948 andT949. They should not be construed as recommendations of the insecticides for general use. All the insecticides 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 report.

SPRAYS AND DUSTS

Conditions and Methods

Members of the Bozeman, Mont., and Tempe, Ariz., stations
cooperated in conducting tests in Arizona during April and early May in 1948 and 1949. Tempe staff members continued tests in Arizona during the summers of both years and Bozeman staff members continued tests in north- central Montana during the summer of 1948 and in southeastern Montana during the summer of 1949. Several tests were conducted in western Kansas in 1948 by a member of the Manhattan, Kans., station. Other experiments conducted cooperatively with members of the Department of Entomology of the Kansas Agricultural Station have been reported elsewhere (1950, Butcher, Wilbur, and Dahm 1) and will not be discussed in this report.
In Arizona most of the tests were made in tall (15-30 inches) irrigated alfalfa in 1948 and in short (2-14 inches) irrigated alfalfa and range grass (14-18 inches) in 1949. Dominant grasshopper species in alfalfa were


j1j These tests were conducted by F. T. Cowan, E. J. Hinman, J. R. Parker, Lee Seaton, and F. E. Skoog, of Bozeman, Mont.; 0. L. Barnes, N. J. Nerney, 1. R. Laird, and F. M. Svoboda, of Tempe, Ariz.; and F. D. Butcher of Manhattan, Kans. The Division of Grasshopper Control supplied insecticides and equipment, and paid the salaries of temporary field aide s.






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Melanoplus mexicanus (Sauss.) and M. differentialis (Thos.). Boopedon nubilum (Say) was most abundant in range grass.
In Montana tests were conducted in weedy grain stubble (5-12 inches) and roadside vegetation (6-20 inches) in 1948 and in dry, short (6-14 inches) range grass in 1949. Melanoplus bivittatus (Say) was dominant in grain stubble and roadsides.
Twenty-one species of grasshoppers were collected from range grass plots. Five of them- -Ageneotettix deorum (Scudder), Arphia pseudonietana (Thos.), M. mexicanus, Opeia obscura (Scudder), and Phoetaliotes nebrascensis (Thos.) --comprised 75 to 80 percent of the total population.
Oil solutions were made by dissolving the technical grade of the
insecticide in kerosene. Stocks were prepared so that an easily measured quantity, such as 1 quart, contained 1 pound of insecticide. The desired volume of spray per acre was obtained by further dilution of the concentrate with the solvent. Emulsions were prepared by diluting commercial or laboratory-made emulsifiable concentrates with water. The laboratory concentrate was made by adding 100 ml. (approximately 3. 4 ounces) of a commercial emulsifier (Igepal 300 ~) to each gallon of kerosene solution concentrate. Water suspensions were made from wettable powders as obtained from manufacturers. Dusts were factory-mixed or diluted from factory-mixed dusts by commercial insecticide companies.
Spray applications from the ground were made with a turbine-blower sprayer and a low-pressure boom-type sprayer. The volume of spray ranged from 1 to 8 gallons per acre with the turbine blower but was generally slightly less than 2 gallons. With the low-pressure sprayer it was 7.5 gallons. Dust applications from the ground were made with a turbine-blower duster and a 6-nozzle power duster equipped with a canvas trailer. The quantity of mixed dust applied per acre varied from 10 to 30 pounds but was usually 20 pounds. The percentage of technical insecticide in mixed dust varied from 2 to 7.5 percent. In this paper dosages of sprays or dusts are stated as pounds of technical insecticide per acre. Tests in previous years indicated that within reasonable limits the efficiency of any given dosage of active ingredient per acre in dust mixtures was not affected by various degrees of dilution. Air plane applications of sprays and dusts were made by commercial croptreating services employing standard equipment or with Bureau-owned aircraft. Volume rates per acre were approximately the same as with the turbine blower in ground applications.
Plot size varied slightly but was generally 1 1/4 acres for ground application and 10 acres for airplane treatment.


3A condensation product of ethylene oxide and alkylated cresol.








The results of all tests were evaluated by sweeping with an insect net on treated and adjacent untreated plots before arnd after treatment. The ratio of grasshoppers per sweep on the plots assigned for treatment to those on the check pi ..ts would be expected '.rcmairi coflst; .I E~x( 2't for the effect of the treatment. The percentag., reduction, or kill, was determined by an adaptation of Abbott's formula- -dividing the reduction in this ratio by the ratio obtained before treatment and multiplying by 100. Unless otherwise stated in the text, the kills reported are based on final sweepings made 3 to 4 days after treatment.
Detailed data on crops treated, size of plots, grasshoppers per square yard, dates of treatment, temperatures, methods of application, formulations, rates per acre, number of tests, and average percentage reductions or kills are given in the tables at the end of this report.
The conditions and methods pertaining to tests in Kansas are not described in the foregoing statements but are given later in the text.

Objectives

In 1948 the main objective was to obtain more information on chlordane and toxaphene. These two insecticides had performed better than other new chemicals in previous tests and had been recommended for general use in grasshopper control. Reports of occasional failures stressed the need for further testing. Tests were planned to compare the effectiveness of chlordane and toxaphene applied as solutions, emulsions, water suspensions, and dusts. Their effectiveness during different seasons of the year and under different crop conditions was given particular attention. Other objectives were to continue the testing of benzene hexachloride and parathion, both of which had shown some promise in previous work, and to make initial tests of several new compounds.
In 1949 the primary objective was to determine minimum effective
acre-dosages of chlordane and toxaphene in short alfalfa and open stands of range grass. Tests of these insecticides in 1946, 1947, and 1948 were confined mainly to tall (15-30 inches) dense alfalfa. Under these conditions acre-dosages of 1 pound of chlordane or 1 1/2 pounds of toxaphene were usually needed to obtain 90 to 100 percent control in 3 days. Reports of work done in Canada and Illinois indicated that satisfactory control in those areas was obtained with lower acre-dosages. In previous tests conducted by the Bozeman and Tempe stations, there were a few instances when acre-dosages of less than 1 pound of chlordane or 1 1/2 pounds of toxaphene gave better than 90 percent control in short vegetation but sufficient data were not obtained to warrant recommending the lower dosages for general use. Most of the tests in 1949 were therefo~re carried out in short (2-14 inches alfalfa and open stands of ran,,, grass. The latter habitat was included because of the exten- .. Lc range grasshopper outbreak in Montana and Wyoming and the fact that some spraying of rangeland might be needed if baiting did niot give satisfactory control.





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The effect of time of day on insecticide treatments made with
ground equipment was also studied. This was considered important because it might determine the periods during the day when spraying and dusting equipment could be operated most successfully.
Another objective was to obtain more information on parathion and tetraethyl pyrophosphate. The quick, high kills obtained with these insecticides in 1948 and the fact that they break down rapidly after application suggested they might have a place in controlling grasshoppers in crops where the use of insecticides having longer killing action present hazards to human health.
Aldrin, dieldrin, and heptachlor were included in the 1949 program because of their high toxicity to grasshoppers at low acre-dosages in preliminary tests during 1948.

Chlordane

The results of the tests made in Arizona and Montana in 1948 and 1949 are given in table 1.

Arizona 1948. --Chlordane emulsions, solutions, suspensions, and dusts were applied by airplane and turbine blower to tall (10-28 inches) alfalfa during April, May, and June. Dosages of 1 pound per acre in sprays and 1.5 pounds in dusts gave average kills of 96 percent. Turbine-blower and airplane applications were equally effective. Residual action during this period prevented reinfestation of plots for 2 to 3 weeks. Dust applied with a power duster to short (3-10 inches) alfalfa and alfalfa stubble during May and June gave as good initial kills within 3 to 4 days (99 percent) with 1 pound per acre as with 1.5 pounds. Residual action after 1 week was greater with 1.5 pounds than with 1 pound.
Chlordane was less effective when applied during July, August, and September than in April, May, and June. Emulsions applied to tall alfalfa at 1 pound per acre gave an average kill of 76 percent in the summer as compared with 96 percent in the spring. Dust applied to short alfalfa at 1.5 pounds per acre gave an average kill of 74 percent in the summer as compared with 99 percent at both 1.5 and 1 pound in the spring. Residual action was considerably reduced during the summer and seldom lasted more than I week.

Montana 1948. --Chlordane formulations and dosages similar to those used on alfalfa in Arizona during the spring were applied with a turbine blower to weedy grain stubble and roadsides in Montana during the summer. The results were similar to those obtained with the same materials used in the summer in Arizona. Average kills in Montana were as follows: I pound in emulsion, 68 percent; 1 pound in suspension, 76 percent; 1.5 pounds in dust, 74 percent. Results in late summer after






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a new growth of succulent weeds appeared in the stubble were much better than during midsummer when dry, mature weeds were the dominant vegetation.

Kansas 1948. --In western Kansas chlordane applied to weedy roatsides at the rate of 1 pound per acre in emulsion was equally effe(stive in June and August. Average kills were 84 perceive. Combination sprays of chlordane and 2, 4-D were used successfully in the same area. Chlordane emulsifiable concentrate was added to the 2,4-D (ester) spray to provide 1 pound of chlordane per acre. In applications with ground equipment to control weeds along roadsides and ditchbanks kills of grasshoppers averaged 90 percent. In airplane treatments to destroy sagebrush kills of grasshoppers averaged 98 percent. Weed and sagebrush control with the combination spray was as good as with 2,4-D used alone.

Arizona 1949. --Chlordane solutions, emulsions, and suspensions applied to short (1-14 inches) irrigated alfalfa during spring and early summer were nearly equal in effectiveness at dosages of 0.5, 0.75, and
1 pound per acre. Kills with all formulations and dosages were better than 90 percent. In tests conducted in 1946 (1) the 0.5-pound dosage failed to control grasshoppers in tali (15-30 inches) irrigated alfalfa; the average kill with emulsions was 48 percent for 0.5 pound as compared with 92 percent for 1 pound. Differences in height and density of vegetation appear to be the main reasons for the better results secured in 1949. Grasshopper species and stages of development were similar during both years. Morning and afternoon applications of chlordane sprays with the turbine blower on short alfalfa between June 24 and July 8 were equally effective. An average kill of 96 percent was obtained in 15 tests in which application was made between 8:40 and 10: 20 a.m., and in 15 tests in which matched dosages and formulations were applied between 2:15 and 5: 10 p. m. Chlordane dust applied with ground equipment to short (2-7 inches) irrigated alfalfa during May and June at 1 pound of chlordane per acre gave an average reduction of only 61 percent as compared with 90 percent or better with the same dosage in sprays.
Chlordane sprays applied during August with the turbine blower to
range grass in southeastern Arizona were 11 to 17 percent less effective than similar sprays applied during July to short alfalfa in the Salt River Valley. The kill obtained with emulsion at 1 pound per acre was 80 percent in range grass and 97 percent in alfalfa.

Montana 1949. --Results with chlordane emulsion applied to short,
dry range grass during July and August at 1.0 pou;-d per acre were almost identical with those obtained in range grass in Arizona during the same period but the average kill was 13 percent less than the 94 percent kill









aY. ( t i,Jdane suspension was also apm ed : m e grass In 11 "**n n oa tests arid was slightly inferit c 1 t<. c lide aInuisi:s. Ii with 0.5 pound per acre in emulsion and suspension were less than with
1 pound.

Toxaphene

Th( result, of the tests a ide ^t" c in 1948 and 1949 are given in table 2.

Arizona 1948. --Toxaphene sprays at J.5 p(,unds per acre and du-;t %t
2 pounds applied by airplane and turbine blower to tall (8-28 inches) alfalfa during April, May, and June were nearly equal in effectiveness. Average kills ranged from 88 to 98 percent. Residual effectiveness continued for
2 to 3 weeks. Toxaphene was less effective when applied in July and August than in April, May, and June. In July and August average kills with 1.5 pounds per acre in emulsion and 1.5 and 2 pounds in dusts ranged from 76 to 83 percent. Residual action seldom continued beyond 1 week.

Montana 1948. --Toxaphenc formulations and dosages similar to those used in alfalfa in Arizona were applied with a turbine blower to weedy grain stubble in Montana durin, '.. 1 -rrn.e The results of the summer tests in both States were much alike. A-verage kills in Montana were as follows: 1.5 pounds in emulsion, 91 percent; 1.5 pounds in suspension, 85 percent; 2 pounds in dust, (:2 percent. Kills in general were slightly less than with the same formulations a.d agess used in alfalfa in Arizona during the spring.

Arizona 1949. --Toxaphene solution, m ,Ision, and suspension sprays applied .vith a turbine blower '4 ,hort (1 4 inches) alfalfa during spring and early summer at dosages, ft and I. p,)o~rds per acre gi. v above 90 percent. Residuai :. on conti (, 2 to 3 weeks. during i same period dust appl iedi %:vti. a newer d iu. ,er at the rate of 1 5 pounds of toxaphene pert acre :. l< of 87 percent. Residual
action was less than with a .s. L 1.o and afternoon applications
were ,qually effective ,ag s 0f pound of toxaph .,. in r
*rd 1.5 pounds in dust w- rt: ff-ci ;ve in 194 :s 1.5 and 2 ,ounmid 1048. The better kills obhtairid i:1 '949 w ,I L O ': d e >,, the al:.1fa being only 1 to 14 in. r : : t us. A .er Similar tests in other yt-.it H. A L 1t < c)nducted i, tall, d~ 1 inches) alfalfa which, in i0 instarces, completely shaded the ground.
Applications o(i rat:1 : A: Ai .q-, were less effective than similar treatment on :.a a :. the spring and early summer.
Oil solutions and C: 'ased noticeable spotting of alfalfa foliage
in s e ; 1 nint.-. In 3 1 : r with 1 .5 pounds per acre than with 1 )cound.










Montana 1949. --Toxaphene emulsions and suspensions applied with a turbine blower on short dry range grass during July and August gave nearly equal average kills at dosages of 1 and 1 5 pounds per acre. The kill with 0.75 pound in emulsion was 76 percent as compared with 83 percent with 1 pound and 84 percent with 1.5 pounds.

Benzene Hexachloride

All data on tests with benzene hexachloride are contained in table 3.

Discussion

Arizona 1948. -Benzene hexachloride applied to alfalfa in dusts and in emulsions at The rate of 0. 4 pound of the gamma isomer per acre gave results that were erratic and generally unsatisfactory. Average kills were as follows: dust applied by turbine blower in April, 35 percent; dust applied by power duster, 98 percent in May and 49 percent during July, August, and September; emulsion applied by low-pressure power sprayer in July, 63 percent. There was little residual killing action later than 1 day after treatment.

Montana 1948. -Benzene hexachioride dust applied by turbine blower to weedy stubble at the rate of 0.4 pound of gamma isomer per acre failed to give satisfactory control. Average kills were 61 percent during July and August and 74 percent in September.
None of the benzene hexachloride formulations and dosages used in either Arizona or Montana caused noticeable injury to vegetation.

Parathion

Detailed data pertaining to tests with parathion are contained in table 4.

Discussion

Arizona 1948. -Parathion dust was applied by power duster to alfalfa during May and again in July at 0.2 and 0.4 pound per acre. Both dosages gave excellent control. Average kills with 0.2 per acre were 99 percent in May and 91 percent in July.

Montana 1948.--Parathion dust was applied by turbine blower to weedy grain stubble and roadside vegetation at 0.4 pound per acre. Average kills were 81 percent in midsummer and 91 percent in late summer.







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Arizona 1949. --Parathion suspensions were applied by turbine
blower to short alfalfa during July at 0.2, 0.3, and 0.4 pound per acre. Average kills with all dosages were 97 percent or better. Dust was applied with the power duster to short alfalfa during May and June at
0.3 and 0.4 pound per acre. In 6 trials at 0.3 pound per acre the average kill was 90 percent as compared with only 81 percent in 2 trials at 0.4 pound. The 9 percent higher kill obtained with the smaller dosage was perhaps due to the .,-nall number of trials at the higher dosage.

Montana 1949. --Suspensions applied by turbine blower to short, dry range grass during July and August at 0.2 and 0.4 pound per acre gave average kills of 83 and 90 percent.
In all tests with parathion in both Arizona and Montana grasshoppers were visibly affected within an hou.L- after treatment and maximum results were obtained in 24 hours. The kills reported are for 1 day instead of the usual 3 to 4 day period. There was practically no residual action after 1 day.
None of the parathion applications caused any noticeable injury to vegetation in Arizona or Montana.

Aldrin

Detailed data on the tests with aldrin are given in table 5.

Discussion

Montana 1948. --In preliminary tests of aldrin conducted in weedy
grain stubble during September dusts applied with the turbine blower at
0.2 and 0.4 pound per acre gave average kills of 83 and 90 percent.

Arizona 19 49: --Solutions, emulsions, and suspensions applied with the turbine blower to short alfalfa during April, May, June, and July at dosages of 0.125 and 0.25 pound of aldrin per acre gave average kills of over 90 percent. Dust applied with a power duster at 0.25 pound of aldrin per acre gave an average kill of 78 percent.

Montana 1949. --Ernulsions applied with the turbine blower to short, dry range grass during July and August at 0.1 and 0.2 pound of aldrin per acre gave average kills of 75 and 83 percent.
None of the aldrin formulations and dosages used in either Arizona or Montana caused any noticeable injury to alfalfa or range grass.
Residual killing action with aldrin continued for 1 to 2 weeks. It was more pronounced at the higher dosages and during cool weather. Residual kills were less with dusts than with sprays.






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Heptachior, Dieldrin, and Tetraefhyl Pyrophosphate

Montana 1949. --Emulsions of heptachlor (12 tests) and dieldrin (10 tests) were sprayed on 1 1/4-acre plots of range grass (20 to 50 hoppers per square yard) at 0.1 and 0.2 pound per acre. Tetraethyl pyrophosphate was used at 0.1 pound per acre in a water solution. Applications were made by turbine blower between July 13 and August 26 (temperature range 610-980 F.). There was little difference in kill between 0.1 and 0.2 pound per acre of heptachlor or between the same quantities of dieldrin. Kills with all the materials and dosages fell within the range of 81 to 90 percent. Kills with heptachlor and dieldrin were as quick as with chlordane or toxaphene, and residual action was about the same. Killing action with tetraethyl pyrophosphate was generally complete in 2 hours and there was practically no residual kill after that time. None of the materials caused any noticeable injury to alfalfa or range grass.

BAITS

Conditions and Methods

In 1948 all tests in Arizona were made by members of the Tempe station. Experimental plots were in irrigated alfalfa 4 to 18 inches high. Plots were usually 1 1/4 acres in size but in one series 10-acre plots were used. Grasshopper populations ranged from 10 to 50 per square yard. Melanoplus mexicanus and M. differentialis were the dominant species. Wet baits were used in all tests. The carrier mixture contained 3 parts of bran and 1 part of sawdust, by volume. Approximately 12 gallons of water was added to 100 pounds of carrier to make a moist, crumbly mash. Toxicants formulated from wettable powders or emulsion concentrates were first suspended or emulsified in water and then mixed with the carrier. The concentrations of toxicant specified in the following discussion represent the quantity of technical insecticide used per 100 pounds of dry carrier. Bait containing 6 pounds of sodium fluosilicate was included in all series of tests as a basis for comparison. Sodium fluosilicate powder and the carrier were mixed before water was added. Applications were made with a power-operated bait broadcaster at the rate of 10 pounds of dry carrier (about 20 pounds wet weight) per acre. Counts were made of the grasshoppers taken in net sweepings of treated and untreated plots before and after treatment (usually 3 days). The results were evaluated by the same method used in tests of sprays and dusts. Except as noted in the text, six or more tests were made with each bait in each series of tests.
In 1949 members of the Bozeman and Tempe stations cooperated in conducting bait tests in Arizona during April and early May. Members of the Tempe station continued tests in Arizona during the rest of the






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season. Conditions and methods were in general the same as those prevailing and used in 1948. Major attention was given to testing bran baits impregnated with chlorinated hydrocarbons and applied dry or wet. Dry bait was prepared by dissolving the desired quantity of toxicant in enough kerosene to make 0.5 gallon of solution, which was then sprayed on 100 pounds of coarse bran. Wet bait was made by mixing equal volumes-of impregnated dry bran and sawdust and then moistening the mixture with enough water to make a crumbly mash. Dry baits were applied with a turbine blower and wet baits with a power-operated bait b ro(a dcaster.
Members of the Bozeman station conducted field-plot and cage tests in north-central Montana in 1948 and in southeastern Montana in 1949. Differences from the conditions and methods noted for the Arizona tests are indicated in the sections of the text which describe the Montana tests.
All series of bait tests included comparisons of several insecticides. The results are therefore reported under topic headings instead of in separate sections on each toxicant.

Objectives

In tests conducted during 1947 sodium fluosilicate, then the standard grasshopper bait toxicant, was not so effective as chlordane, toxaphene, parathion, or benzene hexachloride. Tests in 1948 were designed to provide further comparisons of these and other new insecticides with sodium fluosilicate and to determine the most effective dosages and formulations for use in wet baits.
In 1949 special attention was given to testing baits made by impregnating coarse bran with chlorinated hydrocarbons in oil solution. This was done because of their possible use in large range grasshopper control programs with aircraft bait applications. The particular advantage of dry baits for such work is that the per-alcre rate of application is only one-fofirfh the weight of wet bait containing the same quantities of bran and toxicant. Field tests with impregnated bran were designed to compare different proportions of toxicant, dry and wet treatments, rates of application, freshly mixed and stored bait, and morning and afternoon bait applications. Cage tests were included to determine the acceptance of impregnated bran by different species of grasshoppers, the number of flakes eaten, and the number of flakes required to kill.

Tests in Arizona, 1948

Effectiveness of Toxicants at Different Concentrations. --In tests conducted during April and May baits containing 0.5 pound of chlordane, I pound of toxaphene, or benzene hexachloride at 0. 3 pound of the gamma isomer were as effective as higher concentrations. These rates were










compared with lower concentrations between June 14 and October 19. Parathion was included in the later tests, the results of which are given below:

Toxicant per 100 pounds Average Toxicant per 100 pounds Average
of carrier (pounds) kill () of carrier (pounds) kill()

Chlordane Toxaphene
0.125 67 0.25 50
.25 77 .5 69
.375 81 .75 68
.5 88 1.0 80
Sodium fluosilicate 67 Sodium fluosilicate 60

Benzene hexachioride
(gamma isomer) Parathion
0.025 12 0.125 66
.05 17 .25 80
.1 66 .5 88
.2 69 .75 86
.3 73 1.0 88
Sodium fluosilicate 55 Sodium fluosilicate 58

In these tests 0.5 pound of chlordane and 1 pound of toxaphene were more effective than lower concentrations. Approximately equal kills were obtained with parathion at 0.5, 0.75, and 1 pound. Lower rates were less effective. There was little difference in the effectiveness of benzene hexachloride with the 0. 1- to 0. 3-pound range of the gamma isomer but lower quantities gave much lower kills. Chlordane at 0.25 to 0.5 pound, toxaphene at 0.5 and 1 pound, parathion at 0.125 to 1 pound, and benzene hexachloride at 0.1 to 0 3 pound of the gamma isomer were all more effective than sodium fluosilicate at 6 pounds.

Effectiveness of Different Formulations at the Same Concentrations. The effectiveness of different benzene hexachloride formulations containing the same amount of the gamma isomer (0.2 pound per 100 pound of bait carrier) was compared in a series of field tests from April 7-19. Formulations made from wettable powders containing 6 and 12 percent of the gamma isomer and from an emulsifiable concentrate containing 11 percent gave average grasshopper reductions of 58, 57, and 66 percent, respectively. Thtse results indicate that the emulsifiable concentrate may be slightly more effective than wettable powders for use in baits.
In a series of Ipsts made between May 12 and 24 a bait containing 0.5 pound of technical chlordane in wettable powder was compared with a bait containing the"same amount of chlordane in emulsifiable concentrate.






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The bait prepared with the wettable powder gave an average grasshopper reduction of 73 percent; that with the emulsifiable concentrate, 70 percent. Apparently the two materials were equally effective as sources of chlordane for use in baits.
Toxaphene was also tested in wettable-powder form and as an emulsifiable concentrate. The rate of application was 1 pound of toxaphene per 100 pounds of carrier. The wettable powder contained 25 percent of toxaphene and the emulsifiable concentrate 8 pounds of toxaphene per gallon. The baits in which these materials were used were applied between May 12 and 24. The bait prepared with the wettable powder gave an average grasshopper reduction of 57 percent; that with the emulsifiable concentrate, 69 percent.

Comparison of Toxaphene and Sodium Fluosilicate Baits on Large
Plots. --Baits containing 1 pound of toxaphene were compared with baits containing 6 pounds of sodium fluosilicate. Five tests were made on 10-acre plots between April 9 and June 21. The carrier was a mixture containing 1 part of bran and 1 part of sawdust, by volume. The average reduction of grasshoppers was 78 percent with toxaphene and 60 percent with sodium fluosilicate.

Comparison of Chlordane, Toxaphene, and Sodium Fluosilicate Baits on Small Plots. --A number of comparable tests were made on 1 1/4-acre plots to compare the effectiveness of baits made with different materials. In 23 tests in alfalfa the average kill of grasshoppers 3 to 4 days after treatment was 70 percent with 1 pound of toxaphene per 100 pounds of carrier compared with 59 percent with 6 pounds of sodium fluosilicate. In 24 tests 0.5 pound of chlordane gave an average kill of 74 percent compared with 61 percent with 6 pounds of sodium fluosilicate. In 12 tests average kills with chlordane at 0.5 pound and toxaphene at 1 pound were both 69 percent.

Speed of Killing Action. --In tests made during 1948 baits containing parathion, chlordane, or benzene hexachloride reduced grasshopper populations more rapidly than did baits containing sodium fluosilicate or toxaphene. If it is assumed that the maximum grasshopper reduction is reached 3 days after bait application, then the reduction obtained within
1 day after application was 68 percent with sodium fluosilicate (41 tests), 76 percent with toxaphene (35 tests), 92 percent with chlordane (30 tests), and benzene hexachloride (24 tests), and 98 percent with parathion (18 tests).






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Tests in Montana, 1948

Field Tests of Toxicants. -Wet baits were applied on half-acre plots in short alfalfa and green barley. Melanoplus bivittatus, in late instar and early adult stages, was the dominant grasshopper. Populations ranged from 25 to 50 per square yard. All kills were relatively low because of invasion from highly populated untreated vegetation before the 3-day counts were made. Each test was replicated 5 to 6 times. The insecticide carrier consisted of 2 parts by volume of sawdust and 1 part of bran. Wettable-powder formulations were mixed with the sawdust and bran, which was then moistened with water. Emulsion concentrate formulations were diluted with water and then added to the sawdust and bran. Kills with 0.5 and 1 pound of chlordane from emulsion concentrate were 64 and 73 percent as compared with 74 and 70 percent from wettable powder. Kills with 1 and 1. 5 pounds of toxaphene from emulsion concentrate were 52 and 59 percent as compared with 65 and 59 percent from wettable powder. Increasing the dosages of chlordane from 0.5 to 1 pound and of toxaphene from 1 to 1.5 pounds did not materially change the average kills. Wettable powders were slightly more effective than emulsion concentrates. Kills with 0.3 pound of the gamma isomer of benzene hexachloride were similar with all formulations used; these included wettable powders and emulsion concentrates containing mixed isomers or only pure gamma. All kills were within the range of 47 to 54 percent. Kills with parathion at 0.2 and 0.4 pound were 47 and 49 percent. With 6 pounds of sodium fluosilicate the average kill was 41 percent.

Cage Tests of Toxicants. -Melanoplus bivittatus, late instar and early adult, were collected late in the afternoon and held overnight in cages without food. The next morning they were allowed to feed on bait for 3 hours. The bait was then removed and the grasshoppers were held on untreated green sweet clover for 3 days. Dead grasshoppers were removed and counted 3, 24, and 72 hours after the baits were offered. Paired cages, each containing 50 to 75 grasshoppers, were used in each replicate. All tests included at least 7 replicates. Wettable-powder formulations were mixed with bran, which was then moistened with water. Emulsion concentrates were diluted with water and added to the bran. Stated concentrations represent the quantity of insecticide added to 100 pounds of dry bran. The insecticides tested, the concentrations used, and average kills obtained in 72 hours were as follows:





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Toxicant per 100
pounds of carrier Toxicant per 100 Average kill (%)
(wettable powder, Average pounds of carrier Wettable Emulsion
pounds) kill (16) (pounds) powder concentrates

Chlordane Aldrin
0.25 76 0.2 81 85
.5 85 .4 85 91
1.0 89
Benzene hexachloride:
Heptachlor Pure gamma
0.1 80 0.2 77 77
.2 81 .3 72 79
1.0 91
Parathion
0.2 80 Mixed isomers
.4 86 0.2 78 76
.3 77 79
Toxaphene 1.0 91
0.5 67
.75 72
1.0 80
1.5 81

The lowest concentrations used that did not show marked differences from the kills obtained with higher rates were as follows: Chlordane 0.5 pound, toxaphene 1 pound, aldrin 0.2 pound, heptachlor 0.1 pound, parathion 0.2 pound, benzene hexachloride gamma isomer 1 pound. All these concentrations gave as good or better kills than 6 pounds of sodium fluosilicate (76 percent). Since the concentrations listed for aldrin, heptachlor, and parathion were the lowest ones tested, smaller quantities might have been equally effective. When equal quantities of gamma isomer were used, kills with benzene hexachlride were almost identical regardless of the formulations, which included wettable powders and emulsion concentrates containing mixed isomers and others containing only pure gamma.
Benzene hexachloride and parathion killed quicker than any of the other toxicants. Sodium fluosilicate required the longest time to kill.
Results of the cage tests in Montana were much the same as those obtained with the same insecticides in field tests in Arizona.

Tests in Arizona, 1949

Comparison of Toxicants in Dry Bran Baits. --Dry bran baits containing chlorinated hydrocarbons and a wet bait containing sodium fluosilicate were compared in 3 series of tests on 1 1/4-acre plots--8 replicates in







-15


short, green alfalfa during April; 6 replicates in similar vegetation during June; and 6 replicates in short, dry alfalfa during October. The dry baits were applied at 5 pounds per acre and the wet bait at 20 pounds per acre(5 pounds mill- run bran plus sawdust and water). The results were as follows:

Pounds of toxicant per Percent reduction Toxicant 100 pounds of bran April June October

Chlordane 0. 5 46 47 85
Toxaphene .75 50 44 92
1.0 51 58 83
Aldrin .1 42 59 92
.2 41 62 91
Heptachlor .1 60 86
Sodium fluosilicate 49 62 64

Average kills with toxaphene 1 pound, aldrin 0.1 pound, and heptachlor 0.1 pound, were nearly equal and slightly higher than with 0.5 pound of chlordane. Kills with 1 pound of toxaphene were 14 percent higher than with 0.75 pound in the June series and 9 percent lower in October. Differences in average kills with 0.1 and 0.2 pound of aldrin were less than 4 percent in all series. Kills with the wet bait containing sodium fluosilicate were about the same as with dry baits during April and June but were 19 to 28 percent less than with dry baits in October. Kills with all dry baits were much higher in October when alfalfa was dry, than in April and June, when the alfalfa was green.

Comparison of Dry Bran Baits Applied At Different Rates Per Acre. -Dry bran baits containing different quantities of chlordane or toxaphene were compared at rates of 5 and 10 pounds per acre and with sodium fluosilicate wet bait at 20 pounds per acre (5 pounds mill-run bran plus sawdust and water) in 12 tests in green to drying alfalfa (3-10 inches) during May and July. Grasshopper populations ranged from 6 to 30 per square yard. The results were as follows:

Pounds of toxicant per Pounds of bait Percent Toxicant 100 pounds of bran per acre reduction

Chlordane 0.5 5 64
10 68
1 10 78
Toxaphene 1 5 67
10 77
2 10 79
Sodium fluosilicate 20 50






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When 10 instead of 5 pounds of bait was uaed per acre the average kill was raised 4 percent with 0.5 pound chlordane and 10 percent with 1 pound of toxaphene. When the chlordane concentration was increased from 0.5 to 1 pound and the toxaphene concentration from 1 to 2 pounds and the bait was used at 10 pounds per acre the average kills were increased 10 and 2 percent. At both 5 and 10 pounds of bait per acre kills with 0.5 and 1 pound of chlordane were almost the same as with 1 and 2 pounds of toxr, hene. Kills with wet bait containing sodium fluosilicate were decidedly inferior to chlordane and toxaphene baits at all toxicant concentrations and rates of bait application.
Greater differences in kills between the lower and higher quantities of bait per acre might have occurred if grasshopper populations had been higher.

Comparison of Impregnated Bran Wet Baits Applied at Different Rates Per Acre. --Impregnated bran wet baits were compared at different rates per acre and with sodium fluosilicate wet bait at 20 pounds (5 pounds mill-run bran plus sawdust and water) in 6 tests in green alfalfa (6 to 12 inches high) during May. Grasshopper populations ranged from 20 to 30 per square yard. Impregnated bran wet bait consisted of equal parts by volume of sawdust and dry bran bait containing chlordane 0.5 pound or toxaphene 1 pound per 100 pounds of dry bran. Water was added to make a crumbly mash. The impregnated bran content (dry weight) was approximately one-fourth the weight of the finished wet bait. The results were as follows:

Pounds of toxicant per Pounds of wet Percent Toxicant 100 pounds of bran bait per acre reduction

Chlordane 0.5 20 69
40 84
Toxaphene 1 20 78
40 81
Sodium. fluosilicate 20 41

Chlordane-impregnated wet bait was 15 percent more effective at 40 pounds per acre than at 20 pounds. With toxaphene the increased kill with 40 pounds was only 3 percent. At the 40-pound rate of application the 0.5 pound of chlordane bait was as effective as 1 pound of toxaphene but at the 20-pound rate the toxaphene bait gave a slightly higher kill. Kills with sodium fluosilicate wet bait at 20 pounds per acre were considerably less than with chlordane or toxaphene baits at the same rate of application.






17


Comparison of Chlordane -Impregnated Bran Baits Applied Dry and Wet At Different Rates: --Dry bran bait impregnated with chlordane was compared with similar bait applied wet and with sodium fluosilicate wet bait in 4 tests in green to dry alfalfa (3-8 inches) during September. Grasshopper populations ranged from 15 to 25 adults per square yard. The results were as follows:

Pounds of toxicant per Pounds of bait Percent Toxicant 100 pounds of bran per acre reduction

Chlordane 0.5,. 5 dry 93
20 wet 87
10 dry 93
40 wet 90
1.0 10 dry 94
40 wet 90
Sodium fluosilicate 20 wet 72

Kills were not materially improved in the grasshopper population encountered by increasing the chlordane or by using 10 pounds of dry bait or 40 pounds of wet bait per acre instead of 5 or 20 pounds. Greater differences in kills might have occurred in heavier infestations. Experience gained in 1949 range grasshopper control programs indicated that more than 5 pounds of dry bait per acre is needed to control populations which exceed 50 adult grasshoppers per square yard. Kills with sodium fluosilicate wet bait were much lower than with chlordane -impregnated dry or wet baits containing the same quantity of bran.

Comparison of Stored and FreshlyMixed Chlordane -Impregnated
Dry Bran Bait. --Stored and freshly mixed dry bran bait containing 0. 5 pound of chlordane per 100 pounds of bran was applied on drying alfalfa in 6 tests during August when air temperatures ranged from. 900 to 1010 F. The stored bait was prepared 110 days and the fresh bait 1 to 3 days before it was used. Average kills were 85 percent with the fresh bait and 88 percent with the old. The results indicate that storage of chlordane -impregnated dry bran bait for over 3 1/2 months in a warm climate did not reduce its toxicity or attractiveness to grasshoppers.

Comparison of Morning and Afternoon Applications of Impregnated Bran Baits. --In each series of bait tests conducted in alfalfa from May 4 to November 3 half of the tests were made in the morning and half in the afternoon. Morning applications were made between 7:20 and 11:00 a.m. at air temperatures ranging from 60 0 to 940 F. ; afternoon applications were made between 1: 40 and 5: 00 p.m. at temperatures of 770 to 1100 F. In 78 matched tests with dry baits composed of coarse










bran impregnated with dane, toxaphenc, adrin or ht.pta. tl)r average kills were 72 perc( nt for morning treatments and 78 perc ert for those made in the afternoon. In 18 matched tests with we aic omposed of coarse bran impregnated with oil solutions of chlo d nE toxaphene plus sawdust ,nJ water, average kills were 84 per nt morning tests and 79 percent for afternoon applications. These ,ufferences were not constant throughout the entire season. During May morning and afternoon applications of dry bait were equally effect'-: i t '-nrroon applications of wet baits were better than morning tr atm, tj,. :'ring June, July, and August afternoon applications of dry baits were more effective than morning treatments and wet baits were equally effective in the morning and afternoon. During September and October rn ning and a: r 1: a wet or di'y, w ere about a
effect in v la. ude' ACzonIa condit1ins owing
in alf faa It a; ecti a throughout the day without much d fference in kills between morning and afternoon applications.

Dry Bran Bait Tests in Range Grass. --Chlordane- and toxapheneimpregnated dry baits and sodium fluosilicate wet baits were used in four tests in green range grass (3-15 inches) during August. Boopedon nubilum was the dominant species in three tests and Melanoplus lakinus (Scudder) in the other. Populations ranged from 10 to 20 per square yard. Dry bran baits containing chlordane 0.5 pound, or toxapbene 1 p< und, were applied at 10 pounds per acre. Sodium fluosilicate wet bait was used at 20 pounds per acre. In the three tests in which B. nubil Cm was dominant kills were 53 percent with chlordane, 38 percent with toxaphene, and 52 percent with sodium fluosilicate. In the one test in which M. lakinus was dominant, kills were 87 percent with chlorda n 75 percent wi'h toxaphene, and 60 percent with sodium flucsilicate. None of the baits gave economic control of B. nubilum. Toxaphene and sodium fluosilicate baits failed to control this grasshopper in limited tests on rage grass in 1948. Field observations indicate that it sometimnes take: bait rt adily arid at other times only sparingly

Tc 's in Montana, 1949

In-prgnate Bran r, 1 7(sts in Range Grass. --Impregnated dry bran baits < ntainrr ch-orda'E were compared at different rates per acre and with toxapfhun. d 'y bait. Wet baits containing chlordane or sodium fLusilicate were .;o in 1 l-d in the tests. All tests were replicated
9 times in .ge g (6- 10 inches). Gra shop. were rno s ly in late nyr pha' inM.ars and ranged from 25 to 35 per square yard. Agenetettih. deorurn, Drepam opterna ferroraturm, ..cudder), Boopedon nubilurn, Ha.r t-' ax tritasciatus (Say), Metator pardalinus (Sauss.), Phottat- b'i n, n-,is, Mermiria maculipennis jmacclungi Rehn,







19


Melanoplus mexicanus, and M. bivittatus made up 89 percent of the population. Twelve other species were present. The results were as follows:

Pounds of toxicant per Pounds of bait Percent Toxicant 100 pounds of bran per acre reduction

Ch~ordane 0.5 3 -dry 67
-5 -dry s0
7 -dry 60
-20 -wet 71
Toxaphene 110 5 -dry 60
Sodium fluosilicate -20 -wet 70

Increasing the rate of application of chlordane -imnpregnated dry bait
from 3 to 5 or 7 pounds per acre did not result in higher kills. Chlordane at 0.5 pound and toxaphene at 1 pound were equally effective in dry bran baits applied at 5 pounds per acre. Chlordane -impregnated wet bait was 11 percent more effective than dry bait containing the same quantity of toxicant and applied at the same rate of bran. Sodium fluosilicate wet bait, contrary to the results in Arizona tests, gave as good kills as the chlordane -impregnated wet bait and better kills than with the dry baits. Results with all baits were unfavorably influenced by rapid invasion of the 1 1/4-acre plots by grasshoppers from untreated range and by the presence of several species of grasshoppers which ate bait only sparingly.

Effects of Sunlight, High Temperatures, and Storage Upon the
Toxicity of Dry Bran Bait. --It was surmised that the toxicity of dry bran bait containing chlordane or toxaphene might be considerably reduced after a few hours' exposure to direct sunlight on hot,. bare ground. To gain information on this point, flakes of bait scattered thinly in the lids of paper cartons were exposed to direct sunlight on bare gound for single or cumulative exposures of 2, 4, 5, 26, and 52 hours. Exposures were generally made between 9 a. m. and 5 p. m. when soil surface temperatures ranged from 1100 to 1400 F.
The toxicities of the exposed arnd unexposed baits were compared by offering the bait in quantity to mixed species of grasshoppers in screen cages and by feeding flakes to individual specimens of adult 'Melanoplus mexicanus. The baits contained 0.75 pound of chlordane or 1 pound of toxaphene per 100 pounds of bran.
Contrary to expectations there was no appreciable break-down in the toxicity of chlordane and toxaphene dry bran bait from 2- to 52-hour exposures to sunlight and high temperatures. Baits exposed for 52 hours killed as many grasshoppers as freshly mixed bait.






-20


In other cage tests stored dry chlordane and toxaphene dry bran baits from 6 to 12 months old were compared with freshly mixed bait. No significant differences in toxicity were noted. These results are similar to those obtained in comparing stored and freshly mixed bait in field tests in Arizona.

Acceptance of Dry Bran Bait by Range Grasshoppers and the Number of Flakes Required o Kill Those That Fed. --Shortly after control operations against range grasshoppers in southeastern Montana were started, it was noticed that certain species were surviving in greater numbers than others. It was not known whether these species simply refused to eat bait or whether they ate the bait but did not obtain a lethal dose of poison. In order to answer these questions, tests were conducted in which individual grasshoppers of the more common range species were offered one or more flakes of bait and records were kept of the kills obtained when known numbers of flakes were eaten.
Baits containing 0.75 pound of chlordane or 1 pound of toxaphene per 100 pounds of d~y bran were used. Uniformly sized flakes were obtained by using bait which passed through an 8-mesh screen and was retained on a 12-inch screen.
Grasshoppers were collected in the evening and held overnight in screen cages. The next morning individual grasshoppers were placed in small glass dishes containing one or more flakes of bait. The dishes were covered and the grasshoppers observed for 3 hours. Grasshoppers
failing to eat all the flakes offered in 3 hours were discarded; those which had eaten a known number of flakes were transferred to individual screen cages containing green food and held for 3 days. Grasshoppers which had not fed on bait were held in similar cages for the same length of time ajchecks but in only one instance was there any mortality in the check cages.
There were wide differences in the acceptance of the bait by the different species of grasshoppers. Trachyrhachis kiowa (Thos) and peia obscura refused to eat any bait; Phlibostroma quadrimaculatum (Thos.), Amphitornus coloradus (Thos.), and Metator pardalinus ate very little. Six other species--Aulocara elliotti (Thos.), Drepanopterna femoratum, Phoetaliotes nebrascensis, Boopedon nubilum, and Melanoplus mexicanus--ate bait readily.
Of those species which ate bait, one flake of either bait was sufficient to cause death in 3 days in most of the individual tests and the eating of additional flakes did not strikingly increase the percentage of grasshoppers killed. With B. nubilum, two or three flakes gave better kills than one. The lower kills of this species can be partly explained by the unusually large size of the females. Two flakes killed 80 percent of the males but only 15 percent of the females.







-21


Number of Flakes of Dry Bait Eaten by Individual Grasshoppers. -In connection with the range grasshopper control campaign in southeastern Montana it became important to know how many flakes of dry bait one grasshopper would eat at one feeding and whether the number eaten could be reduced by increasing the quantity of toxicant. Five founds of mediumsized flakes of bran per acre provide approximately 1,000 flakes per square yard. Field observations indicated that this was not enough bait to control unusually high infestations which, in some instances, ran as high as several hundred grasshoppers per square yard. Some doubt existed as to whether it would be better to increase the quantity of bran per acre or to increase the toxicant per 100 pounds of bran. The latter course would be the least expensive because it would not increase the quantity of bran per acre or the flying time in airplane baiting. It was thought that the number of flakes eaten per grasshopper might be greatly reduced by increasing the poison per 100 pounds of bait carrier considerably above the minimum quantity required to kill by eating only a few flakes of bait.
Tests to answer the above questions were conducted by placing
individual grasshoppers in covered glass dishes and feeding them flakes of bait as long as they would eat. The flakes of bran used passed through an 8-mesh screen and were retained on a 12-mesh screen. Grasshoppers used in the tests were held overnight in screen cages without food. Those that did not readily accept the first flakes of bait offered were discarded.
All species of grasshoppers tested-- 'Melanoplus feniur-rubrum. (Deg.), M. bivittatus, M. mexicanus, and Phoetaliotes nebrascensis--ate a surprisingly large number of flakes regardless of the quantity of toxicant in the bait. The average number of flakes consumed by M. femur-rubrum, the smallest grasshopper used, was 12.5 and for M. bivittatus, the largest species tested, was 26. The average for intermediate -sized species was approximately 15 flakes per grasshopper. One specimen of M. mexicanus ate 38 flakes of bait containing 4 pounds of chlordane per 100 pounds of bran within a 2-hour period. This was the largest number of flakes eaten by a single grasshopper. Another M. mexicanus ate 20 flakes in 15 minutes. Fifty grasshoppers per square yard feeding at the same rate would consume all the bait applied if dosages of 5 pounds per acre were used. Feeding continued until the grasshoppers were visibly affected by the poison, which generally occurred within 2 hours or less.
Recognized effective quantities of toxicants per 100 pounds of bran are as follows: Chlordane 0.75 pound, toxaphene 1 pound, aldrin 0.1 pound. Increasing these quantities to 4 pounds of chlordane, 4 pounds of toxaphene, and I pound of aldrin did not decrease the number of flakes eaten. It therefore seems clear that repellent action is not increased by increasing the dosages of these insecticides. The tests indicate that





22


increasing the quantity of bran per acre is more effective in obtaining control of heavy infestations than increasing the quantity of toxicant per 100 pounds of bran.

SUMMARY

Satisfactory control of grasshoppers in short, green alfalfa was obtained with the following insecticides and minimum acre-dosages: Chlordane spray 0.5 pound, dust 1 pound; toxaphene spray 1 pound, dust 1.5 pounds; aldrin spray 0.125 pound, dust 0.25 pound; parathion suspension spray 0.2 pound, dust 0.3 pound. Kills at these dosages approximated 90 percent in 3 days.
To secure control in tall, dense alfalfa, weedy grain stubble, and drying range grass it was necessary to use the following dosages: Chlordane spray 1 pound, dust 1.5 pounds; toxaphene spray 1.5 pounds, dust 2 pounds; parathion spray and dust 0.4 pound; aidrin spray 0.25 pound.- dust 0.4.
Oil solution, emulsion, and water -suspension formulations of chlordane, toxaphene, and aldrin were about equally effective.
Dieldrin, heptachlor, and tetraethyl pyrophosphate used at 0.1 pound per acre were equally effective against grasshoppers in range grass. Kills ranged from 80 to 90 percent.
Benzene hexachloride was used at 0.4 pound of the gamma isomer in emulsion spray and dust. Kills were occasionally good but usually poor.
All insecticides were less effective when applied to mature or dry vegetation during the summer, than when used on succulent vegetation in the spring or fall.
Residual kills with chlordane, toxaphene, aldrin, dieldrin, and
heptachlor continued for 1 to 3 weeks; residual kills with benzene hexachloride, parathion, and tetraethyl pyrophosphate after one day were of no consequence as compared with 1 day for tetraethyl pyrophosphate and 5 days for benzene hexachloride and parathion.
The following bait toxicants and minimum rates per 100 pounds of carrier gave as good and usually much higher kills in field tests than
6 pounds of sodium fluosilicate: Chlordane 0.5 pound, toxaphene 1 pound, aldrin, dieldrin, and heptachlor 0.1 pound, and benzene hexachioride at
0.25 pound of the gamna, isomer.
Toxicants in oil solution, emulsion, and water suspension showed no consistent outstanding differences in kills. Toxicants in oil solutions were the easiest to use in making dry baits; emulsions were more convenient for making wet bait.
The following baits containing chlorinated hydrocarbons were more effective than wet bait with sodium fluosilicate as the toxicant: Mixture of mill-run bran and sawdust moistened with water containing the toxicant in emulsion or water suspension and applied wet; coarse bran impregnated






-23


with the toxicant in oil solution plus an equal volume of sawdust, water to make a crumbly mash, and applied wet; coarse bran impregnated with
-the toxicant in oil solution, and applied dry. The dry bait is easier to prepare, can be stored for months without loss of effectiveness, and is particularly well suited for distribution by aircraft because the acre-rate of application is only one-fourth the weight of wet bait containing the same quantities of bran and toxicant.
Increasing acre-rates of bait application from 5 to 10 pounds with dry bait and from 20 to 40 pounds with wet bait did not consistently increase the kills with the grasshopper populations (10-50 per square yard) encountered in the tests. Experience gained in range grasshopper control programs indicated that more than 5 pounds of dry bait is needed to control populations exceeding 50 per square yard.
The relative effectiveness of morning and afternoon bait applications in alfalfa varied with the seasons of the year but differences were not great enough to warrant limiting baiting operations to any particular time of day.
Most species of grasshoppers ate impregnated dry bran readily but
some range species fed on it only sparingly and a few not at all. Species that accepted the bait readily ate from 1 to 38 flakes at one feeding although only 1 flake was needed to kill. Increasing the toxicant to four times the minimum effective dosage did not decrease the number of flakes eaten.

LITERATURE CITED

(1) Butcher, F. D., Wilbur, D. A., and Dahm, P. A.
1950. A comparison of the grasshopper killing effectiveness of
chlordane, toxaphene, parathion and compound 118
sprays and sodium fluosilicate bait in Kansas in 1948.
Kans. Ent. Soc. Jour. 23: 1-26.

(2) Hinman, E. J., and Cowan, F. T.
1947. New Insecticides in grasshopper control. U. S. Bur. Ent.
and Plant Quar. E-722, 21 pp. Lprocessedj.

(3) Parker, J. R.
1949. Tests of insecticides for grasshopper control, 1947.
U. S. Bur. Ent. and Plant Quar. E-774, 18 pp.
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