Topical Toxicity of Insecticides to Western Corn Rootworm Adults in Nebraska, 1983

Western corn rootworm adults were collected between 18 July and 4 Aug. from corn at 19 geographical sites throughout Nebraska and returned to the laboratory in Lincoln for testing. Mean weights for beetles from each collection site were determined prior to treatment. Unsexed beetles were individually treated by topical application of 1 ul of an acetone solution of the test insecticides to the posterior ventral abdominal area. Beetles were anesthesized with CO2 before treatment. Treatment solutions were prepared with reagent grade acetone using technical grade insecticides. Six to eight dosages, plus an acetone check, were used to determine 2-h LD50 values for all insecticides from all collection sites; two replicates of 10 insects each were used for each dosage rate tested. Insects were declared dead if they could not regain their footing 2 h posttreatment. Dosage-mortality data were calculated in ug/g of insect weight using a probit analysis FORTRAN computer program.