ORIGINAL ABSTRACT

Wild pollinator declines are increasingly linked to pesticide exposure, yet it is unclear how intraspecific differences contribute to observed variation in sensitivity, and the role gut microbes play in the sensitivity of wild bees is largely unexplored. Here, we investigate site-level differences in survival and microbiome structure of a wild bumble bee exposed to multiple pesticides, both individually and in combination. We collected wild Bombus vosnesenskii foragers (N = 175) from an alpine meadow, a valley lake shoreline and a suburban park and maintained them on a diet containing a herbicide (glyphosate), a fungicide (tebuconazole), an insecticide (imidacloprid) or a combination of these chemicals. Alpine bees had the highest overall survival, followed by shoreline bees then suburban bees. This was in part explained by body size differences across sites and the presence of conopid parasitoids at two of the sites. Notably, site of origin impacted bee survival on the herbicide, fungicide and combination treatment. We did not find evidence of gut microbiome differences across pesticide treatment, nor a site-by-treatment interaction. Regardless, the survival differences we observed emphasize the importance of considering population of origin when studying pesticide toxicity of wild bees.