UC San Diego

Pesticides can harm honey bee health and foraging behavior, even when bees are exposed to sublethal doses. We tested the effect of imidacloprid, a common neonicotinoid pesticide, on honey bee avoidance of danger during foraging in indoor and outdoor feeder choice trials. Danger stimuli consisted of honey bee sting gland alarm pheromone or live praying mantises. In outdoor foraging experiments in which bees chose between two feeders, bees fed repeatedly upon sucrose solution containing a high but field-realistic concentration of 40 μg/L imidacloprid. However, there was no effect of pesticide treatment. Neither pesticide nor control bees demonstrated significant avoidance of the live mantis (P≥0.63 for non pesticide bees and P≥0.42 for pesticide bees). In contrast, control bees avoided the alarm pheromone feeder in all three consecutive choices (P≤0.01). Pesticide-treated bees avoided the alarm pheromone feeder only on their second choice (P=0.004). There was no significant overall effect of pesticide treatment in this experiment. In indoor trials designed to mimic outdoor foraging under controlled conditions, bees exposed to 1 ng or 2.16 ng of imidacloprid spent 16-26% less time on the side of the indoor arena with alarm pheromone as compared to control bees. These trials possibly presented a different context: bees attempting to escape rather than forage. Overall, our results do not provide strong support for the hypothesis that imidacloprid alters bee decision-making about danger in the context of foraging, though the indoor trials suggest a new avenue of investigation into the effects of imidacloprid on honey bee escape behavior.