Chronic exposure to a neonicotinoid pesticide alters the interactions between bumblebees and wild plants

Summary Insect pollinators are essential for both the production of a large proportion of world crops and the health of natural ecosystems. As important pollinators, bumblebees must learn to forage on flowers to feed both themselves and provision their colonies. Increased use of pesticides has caused concern over sublethal effects on bees, such as impacts on reproduction or learning ability. However, little is known about how sublethal exposure to field‐realistic levels of pesticide might affect the ability of bees to visit and manipulate flowers. We observed the behaviour of individual bumblebees from colonies chronically exposed to a neonicotinoid pesticide (10 ppb thiamethoxam) or control solutions foraging for the first time on an array of morphologically complex wildflowers (Lotus corniculatus and Trifolium repens) in an outdoor flight arena. We found that more bees released from pesticide‐treated colonies became foragers, and that they visited more L. corniculatus flowers than controls. Interestingly, bees exposed to pesticide collected pollen more often than controls, but control bees learnt to handle flowers efficiently after fewer learning visits than bees exposed to pesticide. There were also different initial floral preferences of our treatment groups; control bees visited a higher proportion of T. repens flowers, and bees exposed to pesticide were more likely to choose L. corniculatus on their first visit. Our results suggest that the foraging behaviour of bumblebees on real flowers can be altered by sublethal exposure to field‐realistic levels of pesticide. This has implications for the foraging success and persistence of bumblebee colonies, but perhaps more importantly for the interactions between wild plants and flower‐visiting insects and ability of bees to deliver the crucial pollination services to plants necessary for ecosystem functioning. Lay Summary