Bumblebees avoid sucrose solution containing high concentrations of Roundup.

Herbicides are one of the most heavily applied groups of pesticides globally. Whilst research on herbicides in relation to bees is growing, we still have more to learn about how bees may interact with herbicides and the subsequent consequences for bee health. As herbicides are designed to kill the plants they are applied to, bees and other pollinators may interact with them in a different way to other pesticide groups which is important to understand in the context of evaluating hazard and risk. Here, we conducted both a choice and no-choice test, to determine if bumblebees would be deterred from foraging from feeders containing commercial formulations of Roundup (Ultra and Biactive, respectively) compared to controls. We found across both experiments that bees were deterred from foraging where feeders contained above field-realistic concentrations of Roundup formulation, and that on average colonies reduced their consumption from these feeders by ~50% despite lacking other food sources. This demonstrates that, when given no choice, bees can be deterred from sucrose containing Roundup Biactive, although above expected field concentrations, even to their own nutritional detriment. Separately, individual foragers were observed avoiding feeders containing field-realistic levels of Roundup Ultra compared to controls, showing a preference for uncontaminated feed when given a choice. As this was an experimental setup using high concentrations of Roundup with sucrose solution rather than real flowers, more work is needed to understand this phenomenon under field conditions. This work provides useful information and insights for future studies investigating the impacts of glyphosate in the form of both active substance and formulation on bees and could also be useful in identifying future mitigation strategies for field use.