Thiamethoxam impairs honey bee visual learning, alters decision times, and increases abnormal behaviors

Learning is important for honey bee fitness and the pollination services that they provide. Neonicotinoid pesticides impair learning, fitness, colony health, and pollination, but most studies on how they affect bee learning have focused on olfactory learning. We tested the effects of field realistic doses of 0.8 ng/bee and 1.34 ng/bee of the neonicotinoid pesticide, thiamethoxam (TMX), on bee visual learning. We adapted a T-maze bioassay and classically conditioned bees to associate sugar reward with a simulated flower color (blue or yellow light) in a choice assay. At 1.34 ng/bee, TMX significantly reduced correct choices in the final learning trial as compared to the control treatment. There was no TMX effect in our 1-h memory test. We found stronger effects on decision time and abnormal behaviors. TMX decreased bee decision times, a potential byproduct of induced hyperactivity since bees walked to make choices. Behaviors (falling, trembling, and rapid abnormal movements) were significantly increased by both TMX doses as compared to the control treatment. These results suggest that the effects of neonicotinoids on bee visual learning should be further studied and incorporated into Risk Assessment protocols.