November 1951 E-825 United States Department of Agriculture Agricultural Research Administration Bureau of Entomology and Plant Quarantine FIELD-PLOT TESTS OF INSECTICIDES AGAINST THE EGYPTIAN ALFALFA WEEVIL ON ALFALFA IN SOUTHERN ARIZONA, 1950 By E. E. Russell— and O. L. Barnes Division of Cereal and Forage Insect Investigations-^ In 1950 heavy infestations of the Egyptian alfalfa weevil ( Hypera brunneipennis (Boh.)), in alfalfa near Tempe, Ariz., were treated experi- mentally with DDT, methoxychlor, toxaphene, chlordane, aldrin, lindane, and benzene hexachloride. This species was first observed in Arizona in 1939 by Wehrle (2) and later studied and described by McDuffie (1_). Sprays were applied from March 2 to 10 against the larvae and over- wintering adults with 3-gallon hand compression sprayers at the rate of 10 gallons per acre on 1/40 -acre plots of first-crop alfalfa 10 to 14 inches high. They were made by diluting the required quantities of emulsion concentrates with water. The DDT concentrate was a commercial product containing 34.3 per- cent (3 pounds per gallon) of technical DDT, but information on the other ingredients was not obtained. The methoxychlor concentrate, also a commercial product, contained 25 percent (2 pounds per gallon) of technical methoxychlor, 72 percent of petroleum hydrocarbon, and 3 percent of inert ingredients. The toxaphene and chlordane concentrates were prepared at the lab- oratory by adding 4 pounds of technical toxaphene or chlordane and 100 ml. of Igepal CTA Extra High Concentration (emulsifier) to enough diesel oil or kerosene to make 1 gallon of concentrate. The aldrin concentrate was an experimental formulation prepared by the manufacturer. It contained 45 percent (4 pounds per gallon) of tech- nical aldrin, 10 percent of Atlox 1045 -A (emulsifier), and 45 percent of equal parts of kerosene and xylene. The lindane concentrate was a commercial product containing 20 per- cent (1.6 pounds per gallon) of the gamma isomer of benzene hexachloride in a light-oil solvent provided with an emulsifying agent. V Retired August 31, 1950. 2/ N. J. Nerney assisted with the insecticide applications, - 2 - Dusts were applied from March 24 to April 3 against the larvae and new-generation adults with a multiple-nozzle power duster at the rate of 10 or 20 pounds per acre, depending on the concentration, on 1/4-acre plots of second-crop alfalfa 10 to 20 inches high. The benzene hexa- chloride dusts were made up at the laboratory from a 50 -percent wettable powder containing 6 percent of the gamma isomer. All the other dusts were ready mixed. They were diluted with pyrophyllite and each con- tained 5 percent of celite. The lindane dust containing 1 percent of the gamma isomer of benzene hexachloride was obtained by mixing 4 pounds of a 25-percent wettable powder in 96 pounds of inert diluents. During the test period the maximum daily temperatures ranged from 63° to 95° and the minimum from 37° to 57° F., and the total rainfall was only 0.2 inch. Populations of larvae and adults of the weevil were sampled with a 15-inch insect net before treatment and at 2- to 6-day intervals afterward. Control was based on the number of specimens per net stroke in collections on treated plots as compared with the number on untreated plots in the same field. Data on the treatments and their effectiveness against larvae and adults are summarized in table 1. The emulsion sprays reduced larval populations 98 to 99 percent in 2 days and 99 to 100 percent in 4 and 6 days. Three days after treatment the dusts were as effective as the sprays. However, after 5 days DDT at 0.5 and 1 pound and methoxychlor at 1 pound per acre were slightly less effective than at the higher dosages tested. The overwintering adults were highly susceptible to the sprays. All sprays except those containing lindane gave 98 to 100 percent reduc- tion in 2 and 4 days, and lindane gave more than 99 percent in 6 days. The dusts were much less effective against newly emerged adults of the 1950 generation than were the sprays containing the same insecticides against the overwintering adults of the 1949 generation. The difference in effectiveness of the insecticides against the over- wintering and the new-generation adults probably was not due to the form in which the materials were applied, because in cage tests conducted from March 31 to April 13 dusts used at dosages similar to those in the field tests gave 94 to 100 percent kill of new-generation adults in 3 days. Furthermore, it has already been noted that dusts and sprays were about equally effective against weevil larvae. Most of the overwintering adults presumably were on the plants and were hit by the sprays, whereas many of the new-generation adults did not emerge until after treatment, by which time the residues had lost much of their toxicity. On untreated plots populations of overwintering adults remained fairly stable or decreased after treatment, whereas those of spring-emerging adults increased 100 to 600 percent within 3 to 5 days after the time of treat- ment. It was also noted that reductions of new-generation adults were invariably greater 3 days after the application than 5 days thereafter. 3- o > CD CD i— H ctj <*h i—i ctj G ctj •iH +-> a tuo W 0) x: o to 3 X 03 TJ G cd CD as > ctj 10 g •rH ctj tuo a to cu -a •■h o •rH -T-» CJ CD CO g ■H 10 o •rH -h crj > CO to CD c £ X] i i a: cd cd tuO ^1 to -t-> 3 X < Percent reduction after -- co r>> cd X CO to~ r>> x" co CTJ x CM Number per net stroke before treatment 0) aj > U cd Percent reduction after- - CO cd XI co co >> aJ CO a X! CM Number per net stroke before treatment Number of tests Active ingredient, pounds per acre CD X •rH CJ CD co G i— < CD CO o o o CO CO CD o T— 1 o T-l o r— I CO co >1 4 4- ctj CD CO CO 00 o ^ X CO CD CO CO o T-H CO in CO 4 4- 4- >> co CO CO CO o lO ctj ■CO CO CD CO o CO X) 00 LO O CO ^ »-H CM LO CO CO CO CO CO CO 00 CO CM CO LO CM T-H CM CM rH rC CD " c g O Q. t 2 Q ^ oS2.h 0J C CTJ rH XI co >>, a LO CO CTJ X oo LOOOOOOOOrHO "tf t> LO CO CO "^ CO 00 COOOCOOOr-COCMCOLOO CMrH COCOCOCOLOOO-^CO"* coco COrHOr-H'^OOOtMrH rH rH rH CM rH CO CM I I I I I I I I I I oo'*co^cococo , * l coco LO rH CM rH rH LO CM CM o o co' co* +■ + 4- C0C0rHt>COC0eMC0COC0 coco C0C0COC0I>C0C0C0C0C0 coco 4- 4- 4 4- COCOt-COLOcOCOCOCOCO coco cocococococococococo coco ffllfiHO)^iflOt"CNH CMO COOOOOrHCOCOOOLOOO'^ -^ ^ Tf ^ CO -* "tf CM I> o LO co H « 9 Q o i-H rG o >> X o rG H-> CD c ctJ CD "tf CM CM rH rH e o X rH O X! Xl G rC -rH U J 0) X •rH rH o r-H rG a CTJ X CU CO CD CTJ N G G CTJ CD DJO cq CO r-H X CTJ G o •rH H-> CTJ Sh CD G CD tuo I CD G H-> CO G •rH CTJ CJO CTJ CO H-> CO X X G CTJ tuo c •H rH CD rH CD > o H-> CO c •rH CTJ tuo CTJ XI CD •rH r-H a a CTJ CO >» CTJ a CO UNIVERSITY OF FLORIDA 3 1262 09239 6083