Can Costs of Pesticide Exposure for Bumblebees Be Balanced by Benefits from a Mass-Flowering Crop?

Mass-flowering crops provide forage for bees but also contain pesticides. Such pesticide exposure can harm bees, but our understanding of how this cost is balanced by forage benefits is limited. To provide insights into benefits and costs, we placed bumblebee colonies in 18 landscapes with conventional red clover fields treated with the neonicotinoid thiacloprid (flowers + pesticide), untreated organic red clover fields (flowers), or landscapes lacking clover fields (controls). Colonies grew heavier near thiacloprid-treated clover compared to controls lacking clover, while colonies near untreated clover did not differ from colonies in neither of the other landscape types. Thiacloprid treatment effectively controlled pests and increased bumblebee crop visitation. However, colony production of queens and males did not differ among landscape types. In conclusion, thiacloprid application in clover appears to be of low risk for bumblebees. More generally, neonicotinoids may not be equally harmful when used in flowering crops and effective low-risk pest control in such crops could potentially benefit bumblebees and crop pollination.