Effects of Bacillus thuringiensis subsp. kurstaki application on non-target nocturnal macromoth biodiversity in the eastern boreal forest, Canada.

Insect biodiversity is crucial for resilient ecosystems, supporting essential services. Moths play significant roles as herbivores, pollinators, decomposers, and as prey for birds, bats, and predatory invertebrates, emphasizing their conservation importance. However, large-scale studies on the non-target effects of Bacillus thuringiensis subs. kurstaki (Btk) on moth communities are limited, particularly in northern forests where diversity is lower. Btk is commonly used to control pest insect populations, with forest managers in eastern Canada applying it to manage eastern spruce budworm. We established a replicated two-year study in the North American Boreal Forest of western Newfoundland, Canada, using paired Btk-treated and control (untreated) sites. No significant differences in total abundance or richness were found between treated and control sites. In 2021, Hill numbers only differed between our northern treatment and control sites, which may reflect those stands having already received multiple years of treatment compared to just one year in the southern sites. In 2022, control sites showed higher diversity (Shannon and Simpson diversity metrics) compared to treated sites, extending to all locations. Multiple years of Btk treatment led to shifts in community composition and the relative abundance of some common species, without affecting total richness or abundance. Species responses varied, likely due to Btk sensitivity, application timing, and differences in phenology and voltinism, making it difficult to generalize the effects of Btk on moth communities.