The sub-lethal effects of a neonicotinoid and pyrethroid insecticide on behavior of the ground nesting squash bee Eucera (Peponapis) pruinosa

Insecticides are used to control insect pests, but can also have detrimental effects on beneficial insects like pollinators. The risk that insecticides pose to bees is typically assessed by regulatory agencies based on lethality to honey bees (Apis mellifera). However, it is clear that many of the effects that insecticides have on bees can be sub-lethal, for example influencing foraging behavior. Much of the work on these sub-lethal effects has focused on honey bees or bumble bees, yet wild ground-nesting solitary bees are also exposed to the pesticides used in agricultural management. Many pollinator-dependent crops rely on the services of ground-nesting bees, such as cotton, squash, and blueberries. In particular, squash and pumpkin (Cucurbita sp.) are largely pollinated by the specialist ground-nesting squash bee (E. pruinosa) in the United States, and these bees are regularly exposed insecticides in agroecosystems. We adapted established proboscis extension response (PER) protocols for testing sucrose responsiveness and a y-tube assay to test if field-realistic exposure to two commonly-used insecticides have sub-lethal effects on squash bees (E. pruinosa). Specifically, we experimentally tested if field realistic exposure to the neonicotinoid thiamethoxam or the pyrethroid bifenthrin influenced sucrose responsiveness and preference for floral volatiles of wild caught squash bees (E. pruinosa). We documented differences in sucrose responsiveness and y-tube preference for volatiles with results depending on bee sex and insecticide exposure. Future work will assess additional sub-lethal insecticide effects on the responses of ground-nesting species to better understand the impacts of pesticide stressors on pollinator behavior and health.