Declining honey bee populations have highlighted the importance of wild and managed non-Apis bees as pollinators in agricultural systems. However, the degree to which insecticide exposure could negate the benefits of non-Apis pollinators in agricultural systems remains poorly understood. In particular, insecticide-contaminated soils represent a likely, yet largely unstudied, route of exposure to non-Apis bees because most species either nest underground or use soil as a nesting material. Our objective was to determine the lethal and sub-lethal consequences of exposure to field-realistic concentrations of insecticide-contaminated soil for non-Apis bees that contact soil during their life cycle. Using Megachile rotundata as surrogate species, we reared bees from larvae to adults while exposing them to soil treated with the neonicotinoid insecticide imidacloprid. We assessed the effects of this exposure by quantifying pre-emergence mortality, post-wintering developmental rates, adult body size and weight, body lipid concentrations, and bilateral wing asymmetry (a proxy for developmental stress). Preliminary results suggest that imidacloprid in soil may impact post-wintering development, pre-emergence mortality, and bilateral wing assymetry, but not adult body size or body lipid concentrations. Our findings suggest that concentrations of imidacloprid found in soils may have lethal and sublethal consequences for non-apis bees that contanct soil during nesting. We conclude that insecticide risk assessments and regulations aimed at promoting non-Apis bee conservation in agroecosystems should consider contact with insecticide-contamined soil as a relavent and impactful exposure route.
