Pollen protein and lipid content influence resilience to insecticides in honey bees (Apis mellifera)

In honey bees (Apis mellifera), there is growing evidence that the impacts of multiple stressors can be mitigated by quality nutrition. Pollen, which is the primary source of protein and lipids in bee diets, is particularly critical for generating more resilient phenotypes. Here, we evaluated the relationship between pollen protein to lipid (P:L) ratio and honey bee insecticide resilience. We hypothesized that pollen diets richer in lipids would lead to increased survival in bees exposed to insecticides, as pollen-derived lipids have previously been shown to improve bee resilience to pathogens and parasites. Furthermore, lipid metabolic processes are altered in bees exposed to insecticides. We fed age-matched bees pollen diets of different P:L ratios by altering a base pollen by either adding protein (casein powder) or lipid (canola oil) and simulating chronic insecticide exposure by feeding bees an organophosphate (chlorpyrifos). We also tested pollen diets of naturally different P:L ratios to determine whether the results were consistent. Linear regression analysis revealed that mean survival time for bees fed altered diets was best explained by protein concentration (P=0.04, adjusted R²=0.92), and that mean survival time for bees fed natural diets was best explained by the P:L ratio (P=0.008, adjusted R²=0.93). Our results indicate that higher dietary P:L ratios have a negative effect on bee physiology when combined with insecticide exposure, while lower P:L ratios have a positive effect. These results suggest that protein and lipid intake differentially influence insecticide response in bees, laying the groundwork for future studies of metabolic processes and development of improved diets.