Contact Toxicity of Six Insecticides to the Gypsy Moth (Lepidoptera: Lymantriidae) and Its Parasites Brachymeria intermedia (Hymenoptera: Chalcididae) and Compsilura concinnata (Diptera: Tachinidae)

Abstract

Toxicities of six insecticides to third-instar gypsy moths, Lymantria dispar (L.), the larval parasite, Compsilura concinnata Meigen, and the parasite of pupae, Brachymeria intermedia (Nees), were determined by topical application. Comparisons of parasite and host susceptibilities were made using LD95's based on dosage per individual. Both sexes of the two parasites were more tolerant than the gypsy moth to permethrin (FMC 33297 and SBP 1513), with B. intermedia being the less susceptible of the two species. Both sexes of C. concinnata tolerated higher doses of acephate or carbaryl than did the host, whereas B. intermedia was quite susceptible to these compounds. B. intermedia was more tolerant than the gypsy moth to trichlorfon, while C. concinnata was as susceptible as the host. Fenitrothion was considerably more toxic to both species of parasites than to the host, and Alfacron [S-(6-chloro-2-oxo-oxazolo(4, 5-b) pyridin-3(2 H )-yl methyl) O, O -dimethyl phosphorothioate] also was more toxic to B. intermedia than to the host; Alfacron was not tested against C. concinnata. Female B. intermedia were more tolerant than males to all compounds. C. concinnata, on the other hand, showed no significant differences between sexes in susceptibility to any of the insecticides tested. These results indicate that the decreasing order of potential hazards for field populations of B. intermedia is fenitrothion, Alfacron, carbaryl = acephate, trichlorfon, permethrin; and for C. concinnata, fenitrothion, trichlorfon, permethrin = acephate, carbaryl.