Differential Toxicity of Insecticides to the Cabbage Aphid and Two Associated Entomophagous Insect Species1

Abstract

Ten insecticides were applied as sprays to cole crops, and the effects upon population levels of the cabbage aphid, Brevicoryne brassicae (L.), its principal parasite, Diaeretiella rapae (McIntosh), and coccinellids, Hippodamia spp., were measured. Demeton and endosulfan appeared to have a considerable selective advantage, being more toxic to the aphids than to the beneficial species. Phosdrin®(a mixture of the alpha isomer of 2-carbomethoxy-l-methylvinyl dimethyl phosphate (not less than 60%) and related compounds (not more than 40%)) and Zectran® (4-dimethylamino-3,5-xylyl methylcarbamate) were highly destructive to the mobile stages of the parasites and coccinellids, but were of low toxicity to the late larval and pupal stages of the parasite within aphid mummies. DDT, dimethoate, ethion, and phosphamidon showed evidence of low toxicity to D. rapae stages within mummified aphids and to D. rapae adults.