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

Bacillus thuringiensis subs. kurstaki ( Btk ) is a widely used bio-lepidoptericide for controlling pest insect populations. Currently, as part of a large-scale eastern spruce budworm management strategy, forest managers are treating forest stands with high insect densities to curtail the damage and spread of this forest pest. While moths serve vital roles as herbivores, pollinators, and as a food source for many migratory birds and bats, there is a dearth of large-scale studies on the non-target effects of Btk on moth assemblages, particularly in northern forests where diversity is relatively low.

We established a replicated field study to evaluate the effects of Btk on non-target nocturnal macromoth communities in the eastern boreal forest of western Newfoundland, Canada over two years.

We found no significant differences in total abundance or richness between treated and control sites. In 2022, control sites had significantly higher diversity (i.e. Hill numbers for Shannon and Simpson diversity metrics) compared to treatment sites. In 2021, differences in Hill numbers were only observed between north controls and treatments.

After multiple years of treatment, there were shifts in the community composition and relative abundance of certain common species, but without significant changes in species richness or total abundance between control and treatment groups. The response of species is idiosyncratic, likely influenced by differences in phenology and voltinism.