Stress response of the honey bee exposed to warming, starvation and neonicotinoids

Honey bees are the world's most important crop pollinators, but their populations have recently shown significant declines, likely due to multiple stressors. Bees and other insects rely on heat shock proteins (HSP) and antioxidant defense systems to buffer against potentially noxious effects coming from challenges such as rising temperatures, starvation, and pesticide exposure. Nevertheless, our understanding of how combined stressors impact honey bee physiology, and the extent to which HSPs and antioxidants can protect against biomolecular damage, remains incomplete. In our study, we examined the isolated and combined effects of three stressors (temperature increase, starvation, and exposure to the neonicotinoid insecticide imidacloprid at two realistic doses) on HSP levels, total antioxidant capacity, and antioxidant protective effect against lipid oxidative damage in Apis mellifera ligustica, using a full factorial experimental design. We found a positive relationship between lipid peroxidation and total antioxidant capacity throughout all conditions tested, indicating a limited capacity of antioxidants to protect against oxidative damage. Moreover, when bees were exposed to starvation or increased temperature alone, the antioxidant protective effect against lipid peroxidation was improved, but when both stressors were present together such an antioxidant protective effect was reduced, suggesting an antagonist effect of combined exposure to heat and starvation. These findings provide evidence that exposure to multiple stressors may produce sublethal effects by overwhelming antioxidant defenses. We discuss potential implications of these results for the management of honey bee colonies, particularly in the context of global environmental change, to ensure the health of honey bees and protect the essential ecosystem services they provide.