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.

Responses of nontarget lepidoptera to foray 48B® Bacillus thuringiensis var. kurstaki on Vancouver Island, British Columbia, Canada

“…However, a concurrent study of birds [12] using 21 of the Garry oak sites showed no impact of Btk spraying on the relative abundance of most (41 of 42) adult birds. These reductions may have been harmful to other animals that depend on immature lepidopterans as a food source during the spring.…”

“…Garry oak study sites were selected in seminatural parks and private estates according to the criteria reported by Sopuck et al [12]. Twenty-eight Garry oak sites were sampled: 13 were located within the larger (12,203-ha) spray zone in Greater Victoria, and 1 site was within the smaller (602-ha) separate spray zone in Brentwood Bay (BC, Canada).…”

“…kurstaki is toxic to only certain species of Lepidoptera that have a high midgut pH level that is capable of activating Btk toxins. their utility as biological control agents [10], or their importance as a food source for insectivores [11,12]. Although Btk formulations are less hazardous than the previously used broad-spectrum insecticides (i.e., carbaryl, acephate, and diflubenzuron), their environmental impacts should not be ignored.…”

Monitoring native non-target Lepidoptera for three years following a high dose and volume application ofBacillus thuringiensissubsp.kurstaki

“…Although the entire Lepidoptera guild on R. cereum, and two species within the guild-Gelechia ribesella Chambers (Gelechiidae) and Euhyponomeutoides gracilariella Busck (Yponomeutidae)-appeared to recover within 2 years of treatment, there are concerns that recovery may take longer if Btk is applied at a higher dose and volume. There is also concern that a temporary reduction of Lepidoptera may be harmful to other ecosystem components since Lepidoptera function as pollinators, herbivores, and a food source for insectivores (Hammond and Miller, 1998;Holmes, 1998;Norton et al, 2001;Sopuck et al, 2002;Boulton, 2004). Thus, we initiated the study reported here to assess the effects of an experimental high dose and volume (60 BIU ha 7 1 in 4.8 L ha 7 1 ) application of Btk on nontarget Lepidoptera.…”

Short communication. First field assessment of Bacillus thuringiensis subsp. kurstaki aerial application on the colony performance of Apis mellifera L. (Hymenoptera: Apidae)

“…There is a lack of studies developed to evaluate the impact of Btk aerial application on A. mellifera, although there are some studies developed to evaluate the impact on many groups of animals, such as non-target Lepidoptera (Boulton, 2004), non-target soil organisms (Addison & Barker, 2006) and songbirds (Sopuck et al, 2002). The effect on bees have been developed in some f ield and laboratory studies, although the majority of the experiments tested the toxicology of Btk used in genetically modif ied crops (O'Callaghan et al, 2005;Duan et al, 2008).…”