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

Nutritional stress, especially a dearth of pollen, has been linked to honey bee colony losses. Colony-level experiments are critical for understanding how nutritional stress affects individual honey bee physiology and pushes honey bee colonies to collapse. In this study, we investigated the impact of pollen restriction and amino acid supplementation on key markers of honey bee physiology, main elements of the immune system, and predominant honey bee viruses. We first evaluated the effect of pollen deprivation on behavioral development. Then, we used quantitative PCR to determine the expression of molecular markers of physiological status, immune genes and honey bee viruses. Our results showed that pollen deprivation results in accelerated behavioral development, and this behavioral transition has a major effect on gene expression. In particular, we found that vitellogenin (vg) and royal jelly major protein 1 (mrjp1), were significantly associated with nursing, pollen ingestion, and older age. On the other hand, genes involved in hormonal regulation, including insulin-like peptides (ilp1 and ilp2) and methyl farnesoate epoxidase (mfe), exhibited higher expression levels in young foragers. We also found a strong effect of behavior on the expression of all immune genes, with higher expression levels in foragers. Our results also show higher Deformed wing virus (DWV) titers associated with foraging and pollen ingestion. Finally, we show that amino acid supplementation induced delayed foraging and increased Vg, mrjp1 levels. However, in colonies having moderate Varroa infestation levels, amino acid supplementation was also associated with higher DWV titers.