Honey bees are critical pollinators for many crops. As with many wildlife species, losses in honey bees have been increasing in recent decades, likely due to multiple interacting factors. This study explored the interactions among potential drivers of honey bee colony overwinter mortality: infection by a gut parasite and gut microbiome structure. The gut microbiome promotes host health in a variety of ways, including stimulating the host immune response and aiding in nutrient metabolism. Therefore, gut microbiome variation may ultimately lead to differences in pathogen infection intensity and host physiology. Nosema ceranae and Nosema apis are microsporidian parasites that infect the honey bee midgut, and could potentially interact with the honey bee gut microbiome. The honey bee gut bacteria may influence Nosema spp. infection by altering host resistance. Conversely, the presence of Nosema spp. may disrupt the gut microbiome, which could also impact host physiology. This study investigated gut microbiome structure, Nosema spp. infection intensity, and worker physiology as potential predictors of hive survival or failure by sampling hives during the fall and then re-sampling the surviving hives in the subsequent spring.
Results/Conclusions
N. apis levels were below the threshold of detection in the majority of the sampled hives; therefore, N. apis was excluded from further analyses. N. ceranae was present in all hives. N. ceranae infection intensity did not vary significantly between the fall and spring, nor did it differ in the fall between colonies that ultimately failed or survived. Gut microbiome community structure differed significantly in relative abundance and species identity between season and based on hive location. Measures of gut microbiome alpha diversity in the fall were associated with overwinter survival. Specifically, hives that survived the winter had a higher effective number of species, phylogenetic diversity, and species richness than hives that failed. There did not appear to be a correlation between the gut microbiome structure and Nosema ceranae infection intensity. Overall, we did not find clear evidence that Nosema infection was related to overwinter survival; however, our findings suggest properties of the gut microbiome may be indicators of overwinter survival.