Honey bee immune response to sublethal concentrations of clothianidin goes beyond the macronutrients found in artificial diets

Honey bees (Apis mellifera) often encounter a variety of stressors in their environment, including poor nutrition and pesticides. These stressors interact and can be exacerbated in large-scale agroecosystems. We investigated how diets varying in macronutrient ratios can affect nurse bee susceptibility to pesticide stressors. Nurse bees were fed sublethal concentrations of clothianidin (CLO), a neonicotinoid insecticide known to have sublethal and lethal effects on honey bees, after newly emerged bees were given diets varying in proteins and lipids, a natural pollen diet, or no diet. We assessed bee longevity, physiology (hypopharyngeal gland size, abdominal proteins, lipids, and glycogen), enzyme activity levels (glutathione s-transferase, esterase, invertase, acetylcholinesterase, and phenol oxidase), and gene expression related to immunity (P450s (Cyp6A13, Cyp6Aq1, Cyp9q1, Cyp9q2, Cyp9q3, and vitellogenin). Bees given pollen had improved longevity, physiology, enzyme activity, and gene expression related to pesticide detoxification. The artificial diets helped improve bee health and physiology but did little to promote bee detoxification enzymes and genes. There was no effect of the sublethal CLO treatments on its own, but there was an interactive effect between our high CLO treatment and nutrition on bee longevity and vitellogenin expression. Honey bees given pollen upregulated of detoxification genes and had higher enzyme activity related to pesticide metabolism. Our results suggest that macronutrients in artificial diets can help promote bee physiology, but other nutrients in pollen, such as potentially phytochemicals, are more directly linked honey bee tolerance to pesticide stress.