Impacts of systemic insecticide exposure on the movement ecology of bumble bee queens

Background/Question/Methods

Bumble bees are an important group of pollinators of both wild plants and crops. While foraging for pollen and nectar bumble bees can be exposed to insecticides, such as neonicotinoids, which have previously been shown to have sublethal effects. Such reported negative effects have resulted in increased regulation on neonicotinoid usage, and in some jurisdictions, their use has been banned. However, a new class of insecticides that are poised to replace neonicotinoids may also have negative impacts on pollinators. Diamides are a class of pesticides that are a popular candidate for replacement of neonicotinoids, but their effects on the behaviour of bees have not yet been assessed. Despite the apparent lower toxicity of diamides compared to neonicotinoids, the mode of action of diamides (e.g., cyantraniliprole), that targets bee muscles, could cause greater negative impacts on bumble bee flight performance compared to neonicotinoids (e.g., imidacloprid). Here we tested the impacts of both classes of insecticide relative to a control group on bumble bee (Bombus impatiens) queen movement using an autonomous radio-tracking array of 43 radio towers to track the movement of 75 radio-tagged queens.

Results/Conclusions

Control queens completed both exploratory flights across the field site and exhibited more directed flights towards high resources areas (i.e., high floral abundance, candidate overwintering sites). Control queens also had the fewest and most direct flight paths. Queens exposed to a neonicotinoid performed more flights with longer flight paths, and showed a relatively random distribution in activity. Lastly, queens exposed to the diamide had the shortest flight path, the fewest exploratory flights, and were concentrated in select areas, particularly those with high resources or adjacent to the release site. We confirm that neonicotinoids impair the ability for queens to re-located resources and overall reduce flight efficiency. By contrast, diamides may be impairing the muscle function of queens resulting in them trying to maximize their efforts in high resource areas near the release site. Although comparisons of lethal endpoints suggest that diamides are less toxic to bees compared to neonicotinoids, our findings demonstrate impaired flight ability for queens, which may limit their effectiveness as pollinators, ability to find a mate, or likelihood of overwinter survival. Our study describes the first relationship between an increasingly popular pesticide and pollinator flight behaviour that will be important consideration for sustainable agriculture and biological conservation.