A balanced omega-6:3 fatty acid diet can shield honey bee cognition from pesticide impairment

Among the stressors honey bees are exposed to in agricultural settings, poor diet and pesticide exposure are two of the most prevalent and concerning. We tested whether a balanced omega-6:3 fatty acid pollen-substitute diet could increase the resilience of honey bees to the harms of pesticide exposure, focusing on measuring bee survival and olfactory learning. We raised bees on a diet either balanced in omega-6 and omega-3 fatty acids (1:1 ratio) or unbalanced (5:1) for 2 weeks before providing them with either 10 nmol l-1 thiamethoxam (TMX) in 2.0 mol l-1 sucrose solution or a control (pure 2.0 mol l-1 sucrose solution). Using a proboscis extension response (PER) differential conditioning assay, we classically conditioned bees to two odors to assess learning and memory. Bees fed an unbalanced diet and TMX had significantly poorer learning and significantly poorer memory when tested 1 h after the final learning trial. However, bees fed a balanced diet were resilient to the effects of TMX. Balanced-TMX bees had higher survival than unbalanced-TMX bees, suggesting that a balanced diet helped bees exposed to TMX. However, the survival data are complex and may suggest hormesis, in which a short, low dose of pesticide can increase insect survival. Overall, our results suggest that a diet that is balanced in the omega-6:3 fatty acid ratio can increase the resistance of honey bees to a commonly used neonicotinoid pesticide, providing a possible method for enhancing managed colony survival.