Impact of imidacloprid-based chemical control for hemlock woolly adelgid ( <i>Adelges tsugae</i> ) on the eastern red-backed salamander ( <i>Plethodon cinereus</i> )

The hemlock woolly adelgid (HWA; Adelges tsugae) is an invasive insect causing widespread mortality of eastern hemlock ( Tsuga canadensis) across eastern North America, altering forest structure and associated ecosystems. The insecticide imidacloprid is used for HWA control, but its persistence and potential for soil and water contamination raises concern for fossorial species. We used the eastern red-backed salamander (RBS; Plethodon cinereus) as an indicator species to assess how HWA infestation and imidacloprid treatment influence hemlock stands in southwestern Nova Scotia. We conducted line transect surveys across two HWA-infested sites—each containing four treated and four untreated 1 ha stands—and one uninfested control site with four mature hemlock stands. We applied a multi-model Akaike’s information criterion corrected for small sample sizes framework to test the effects of treatment, infestation, and environmental covariates on RBS abundance, body condition, and abundance within a zone of potential residue exposure. Treatment and infestation were the only predictors of abundance: treatment increased abundance, whereas infestation reduced it. Canopy openness, soil pH, and soil moisture did not differ significantly among stands, and none were found to be predictors of body condition or abundance within the zone of potential exposure. These results reinforce the value of integrating chemical control with long-term monitoring while biological control strategies develop.