Sublethal behavioral impacts of resource limitation and insecticide exposure reinforce negative fitness outcomes for a solitary bee

Contemporary landscapes present numerous challenges for bees and other beneficial insects that play critical functional roles in natural ecosystems and agriculture. Pesticides and the loss of food resources from flowering plants are two stressors known to act together to impair bee fitness. The impact of these stressors on key behaviors like foraging and nesting can limit pollination services and population persistence, making it critical to understand these sublethal effects. We investigated the effects of insecticide exposure and floral resource limitation on the foraging and nesting behavior of the solitary blue orchard bee, Osmia lignaria. Bees in field cages foraged on wildflowers at high or low densities, some treated with the common insecticide, imidacloprid, in a fully crossed design. Both stressors influenced behavior, but they had differential impacts. Bees with limited food resources made fewer, but longer foraging trips and misidentified their nests more often. Insecticide exposure reduced bee foraging activity. Additionally, insecticides interacted with bee age to influence antagonistic behavior among neighboring females, such that insecticide-exposed bees were less antagonistic with age. Our findings point towards mechanisms underlying effects on populations and ecosystem function and reinforce the importance of studying multiple drivers to understand the consequences of anthropogenic change.