Responses of songbirds to aerial spraying of the microbial insecticide Bacillus thuringiensis var. kurstaki (Foray 48B®) on Vancouver Island, British Columbia, Canada

Abstract

Use of bacterial insecticides containing Bacillus thuringiensis var. kurstaki (Btk) is gaining popularity as an environmentally safe control measure against lepidopteran pests, but indirect effects on nontarget organisms through reduced prey base have received little attention. Aerial spraying of Btk (Foray 48B) over a 12,803-ha area on southeastern Vancouver Island (BC, Canada) in May to June 1999 as part of a gypsy moth (Lymantria dispar) control program provided us with an opportunity to examine the responses of songbirds to spray application. To obtain an estimate of species richness and relative abundance, we conducted standard songbird point-count surveys in Garry oak (Quercus garryana)-dominated habitats in Btk-sprayed and unsprayed areas in April to June 1999 and, one year after spraying, in 2000. These surveys revealed no patterns consistent with adverse effects of spraying on the relative abundance of adult birds or singing males for any of the species, whether examined individually or when combined into foraging guilds. An exception was the spotted towhee (Pipilo maculatus), which in 1999, but not in 2000, occurred at significantly lower numbers in sprayed plots after Btk treatment. Intensive searches of plots in sprayed and unsprayed areas revealed no differences in the numbers of songbird broods between the two areas for any of the species examined.

Dissecting the Environmental Consequences of Bacillus thuringiensis Application for Natural Ecosystems

“…On the other hand, Bt var. kurstaki -mediated L. dispar control did not affect the diversity of songbird species or the number of chicks in each species with the exception of Pipilo maculatus, for which a significant decrease in the offspring number was shown [ 189 ].…”