Nontarget impacts of insecticide-based population control of eastern spruce budworm (Lepidoptera: Tortricidae) on nontarget caterpillar communities and parasitism

Abstract

Narrow-spectrum insecticides are currently used to control populations of spruce budworm, Choristoneura fumiferana Clemens (Lepidoptera: Tortricidae), in eastern Canada. However, these could have nontarget impacts on other caterpillars – some of which may serve as alternative or alternate hosts to key parasitoids – that are also susceptible to control tactics. This study was conducted to determine how the insecticides, Bacillus thuringiensis variety kurstaki (Btk) and tebufenozide, used to control spruce budworm populations, impact caterpillar communities and associated parasitism rates. Post-treatment field sampling of caterpillars was conducted in 2018 and 2019 in New Brunswick, Canada, at sites treated with either Btk or tebufenozide and at control sites. Caterpillar species richness and abundance, community structure, and parasitism rates were assessed using molecular analyses for 659 collected caterpillars. We found that insecticide applications had no significant impact on abundance, species richness, or parasitism rate relative to the measurements made in the control sites. Nonetheless, a significantly higher caterpillar abundance and lower parasitism rate occurred in Btk-treated sites than in tebufenozide-treated sites. Overall, however, Btk and tebufenozide treatments did not negatively affect the non-budworm caterpillar community under the present conditions of low caterpillar densities, suggesting that parasitoids have alternative and alternate hosts after treatments that target the spruce budworm.

Effects ofBacillus thuringiensissubsp.kurstakiapplication on non-target nocturnal macromoth biodiversity in the eastern boreal forest, Canada

“…We found that the overall abundance of macromoths did not differ between Btk treated and control (untreated) sites. These findings are consistent with Glaus et al (2023), who employed similar Btk application rates. However, while both of our studies found that the overall abundance of non-target Lepidoptera did not differ between Btk-treated areas and non-treated areas, our present study found, although not always significant, there is evidence of interspecific variation in treatment effects.…”