Field Assessment of the Effects of a Microbial Pest Control Agent on Nontarget Lepidoptera

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Abstract
Species in a guild of nontarget leaf-feeding Lepidoptera on Garry oak, Quercus garryana Dougl., were monitored in the field for a period of 3 yr (1986–1988) to assess the ecological effects of three applications of the microbial pest control agent, Bacillus thuringiensis Berliner var. kursraki within a single-season application (spring 1986). The target species for the B. thuringiensis kursraki application was the gypsy moth, Lymanrria dispar (L.), in a large-scale eradication program in Lane County, Oreg. Species richness in the guild of leaf-feeding Lepidoptera on Garry oak was significantly reduced in the treated plots during all 3 yr of the study. Also, the total number of individual nontarget Lepidoptera was significantly reduced in treated plots during the first 2 yr but not in the third. These data suggest that certain nontarget species of Lepidoptera may be ecologically “at risk” in large-scale pest control programs based on B. thuringiensis kurstaki . Variables such as phenology, voltinism, and plot size are discussed regarding the degrees of risk and type of species that may be most affected by largescale microbial pest control agent control and eradication programs.

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