Landscape-associated pesticide contamination shapes pollen provision microbiomes in Osmia cornifrons (Hymenoptera: Megachilidae).

Bees live and forage across a landscape increasingly altered by human activity, collecting pollen, nectar, and an essential microbiome from the local environment as well as chemical contamination from surrounding human activities. The increasing frequency and intensity of antimicrobial chemical use in agricultural systems disrupts the environmental microbial community and has been linked to bee declines. However, it remains largely unknown how pesticides and antimicrobial agents vary across the landscape, and in turn, cascade to alter microbiome assembly in solitary bees. To evaluate landscape-level effects of pesticide contamination on the pollen microbiome of solitary bees, we surveyed Osmia cornifrons (Hymenoptera: Megachilidae Radoszkowski, 1887) pollen provisions across 3 contrasting land use types in central upstate New York: forest, urban, and orchard habitats. Pollen provisions were screened for 94 common pesticides and sequenced to characterize their bacterial community. We found pesticide concentrations and risk varied significantly across land use types and was highest at orchard sites. Microbial communities also differed across landscapes, with increased surrounding forest cover corresponding to higher abundances of Apilactobacillus, a beneficial bee-associated genus in the family Lactobacilliacea. We found a significant correlation between increased pesticide concentration and decreased pollen-associated microbial diversity. These results indicate links between land use, pesticide exposure, and the microbiome of solitary bees.