Decoupling the effects of nutrition, age and behavioral caste on honey bee physiology and immunity

Nutritional stress, and especially a dearth of pollen, is considered an important factor associated with honey bee colony losses. We used pollen-restricted colonies as a model to study the nutritional stress conditions experienced in colonies within intensively cultivated agricultural areas. This model was complemented by the establishment of an experimental design, which allowed us to uncouple the effect of nutrition, behavior and age in colonies of similar size and demography. We used this system to determine the effect of pollen restriction on workers behavioral development. Then, we analyzed the effect of nutritional stress, behavior and age on the expression of key physiological genes involved in the regulation of division of labor. Finally, we analyzed the effects of these variables on the expression of immune genes and the titers of honey bee viruses. Our results show that pollen restriction led to an increased number of precocious foragers and this behavioral transition was associated with important changes in the expression of nutritionally regulated physiological genes, immunity and viral titers. Vitellogenin (vg) and major royal jelly protein 1 (mrjp1) were the most predictive markers of nutrition and behavior. The expression of immune genes was primarily affected by behavior, with higher levels in foragers. Deformed wing virus (DWV) titers were significantly affected by behavior and nutritional status, with higher titer in foragers and increased levels associated with pollen ingestion. Correlation analyses support the predominant effect of behavior on immunity and susceptibility to viral infection, revealing that both immune genes and DWV exhibited strong negative correlations with genes associated with nursing, but positive correlations with genes associated with foraging. Our results provide valuable insights into the physiological mechanisms by which nutritional stress induce precocious foraging and increased susceptibility to viral infections.