For better or worse: Pollen protein and lipid content influences honey bee health

         In honey bees (Apis mellifera), there is growing evidence that the impact of multiple stressors, including pesticides, parasites, and pathogens, can be mitigated by high quality nutrition.  Pollen, which is the primary source of protein and lipids in bees’ diets, is particularly critical for generating more resilient phenotypes. We sought to understand the relationship between pollen protein-to-lipid ratios (P:Ls) and honey bee pesticide tolerance. We hypothesized that pollen diets richer in lipids would lead to increased survival in bees exposed to pesticides, as lipids have previously been shown to be important for tolerance under parasite and pathogen pressure.
          To test our hypotheses, we fed age-matched bees pollen diets of different P:Ls by altering a base pollen (with a ratio of 5.5:1) by either adding protein (casein powder) or lipids (canola oil) and simulated chronic pesticide exposure by feeding bees an organophosphate in sucrose. Survival was recorded over a 12 day period. We also tested pollen diets of naturally different P:Ls to determine if results would be consistent in a realistic scenario. Kaplan-meier survival analysis revealed that bees fed lipid-rich pollen diets had longer mean survival times in altered diet trials (1.5-5.5:1) and natural diet trials (1.3-3.2:1). Bees fed lipid-rich altered diets also had upregulation of genes involved in detoxification, immune response, and maturation. Our results indicate that lipid-rich diets lead to increased resilience in bees exposed to a pesticide stressor, and we propose that this may be due to increased lipid metabolism.