Effects of a Microbial Insecticide, Bacillus thuringiensis kurstaki, on nontarget Lepidoptera in a Spruce Budworm-infested Forest

Abstract

Species in a guild of nontarget leaf-feeding Lepidoptera on tobacco brush, Ceanothus velutinus Dougl. were monitored in the field to assess ecological effects of one application of the microbial pest control agent, Bacillus thuringiensis Berliner var. kurstaki (BTK). The Lepidoptera were sampled to compare species richness, species evenness, species diversity, larval abundance, and a dominance index between an untreated and BTK treated site over a period of two years. The guild of leaf-feeding Lepidoptera on C. velutinus consisted of 32 species. No statistically significant differences were observed in overall species richness, although the number of species in the untreated site was 30% higher two weeks after treatment. However, species richness among uncommon species was significantly reduced in the treated site.