Bees encounter pesticides across landscapes as they forage for pollen and nectar. Exposure to pesticides has negative effects on wild bees, but little is known about the effects of chronic larval exposure on adult performance. We investigated the effects of larval and adult pesticide exposure on the foraging and reproduction of the solitary bee, Osmia lignaria. We established nesting O. lignaria females in 16 field cages containing wildflowers treated with or without imidacloprid, a neonicotinoid insecticide. As larvae, these parent bees were reared on provisions containing imidacloprid or controls. Larval and adult pesticide exposure directly affected bee nesting activity. Bees exposed to pesticides as adults were less likely to start nesting and produced fewer offspring. Additionally, bees exposed to pesticides as larvae provisioned fewer offspring than unexposed controls. Our research provides experimental evidence of the effects of pesticide exposure on solitary bees across multiple life stages, a critical step in understanding mechanisms underlying pollinator health.
