Effects of Insecticide-Induced Reduction in Lepidopteran Larvae on Reproductive Success of Hooded Warblers

Abstract

We examined the effects of an insecticide-induced reduction of lepidopteran larvae due to spraying of Bacillus thuringiensis to eradicate gypsy moths (Lymantria dispar) on the reproduction of Hooded Warblers (Wilsonia citrina). Treatment plots had two applications of Bacillus in 1994. No Bacillus application occurred in 1995. Reductions in lepidopteran larvae were demonstrated by pheromone traps and arthropod samples from oak (Quercus spp.) foliage. We analyzed the following reproductive parameters: nesting success, number of eggs, number of fledglings, egg mass, mass of nestlings at day 5, growth rates, feeding rates, and prey items brought to nestlings. Of these reproductive parameters, three showed both statistical and biological differences. Nesting success was higher in the control than in the treatment zone in 1995, but not in 1994. Nestling masses at day 5 increased over the duration of the breeding season in the treatment zone but not in the control zone. Differences in feeding rates between treatment and control zones occurred only for small clutches. Overall, the reduction of lepidopteran larvae due to Bacillus application appeared to have only minimal effects on reproduction in Hooded Warblers.