Recovery of nontarget Lepidoptera on Vancouver Island, Canada: One and four years after a gypsy moth eradication program

Abstract

The gypsy moth (Lymantria dispar) is a destructive defoliator that is not established in British Columbia, Canada, because of successful eradication programs involving the microbial insecticide Bacillus thuringiensis var. kurstaki (Btk). In 1999, three aerial applications of Btk were made over two areas, totaling 12,805 ha, on southern Vancouver Island, Canada. The impacts of these Btk applications on nontarget Lepidoptera were studied from 1999 to 2004 on Garry oak (Quercus garryana) and common snowberry (Symphoricarpos albus). In 1999, lepidopteran larvae were collected from S. albus foliage at 24 urban parks and from Q. garryana foliage at 28 oak-dominated habitats. The initial impacts (i.e., 1999 data) were published previously, and the present paper is a continuation of the same study. We tested two hypotheses: Reductions of nontarget Lepidoptera would be more severe at 12 to 13 months postspray than at one to two months postspray, and recovery would be significant, though not necessarily complete, at four years postspray. The total number of nontarget Lepidoptera on S. albus and Q. garryana was significantly reduced in the treatment sites in each year of the study: the reduction was greatest in 2000. Relative to the reference sites, each of 11 species that were initially reduced by the Btk applications showed an increase in the treatment sites between 2000 and 2003, by which time only four species remained significantly reduced in the treatment sites. The uncommon species were significantly reduced in 1999 and 2000 but not in 2003, indicating that some recovery had occurred. Limitations and economic implications of the present study are discussed.