Honey bees overwintering in a southern climate: longitudinal effects of diet and queen age on colony-level molecular physiology and performance

Authors: Ricigliano, Vincent; Mott, Brendon; FLOYD, AMY - University Of Arizona; Copeland, Duan; Carroll, Mark; Anderson, Kirk

Submitted to: Scientific Reports
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/28/2018
Publication Date: 7/11/2018
Citation: Ricigliano, V.A., Mott, B.M., Floyd, A.S., Copeland, D.C., Carroll, M.J., Anderson, K.E. 2018. Honey bees overwintering in a southern climate: longitudinal effects of diet and queen age on colony-level molecular physiology and performance. Scientific Reports. https://doi:10.1038/s41598-018-28732-z.
DOI: https://doi.org/10.1038/s41598-018-28732-z

Interpretive Summary: In this study, we monitored colony performance and group-level molecular physiology of honey bee colonies in the Imperial Valley of California. This landscape is agriculturally intensive with warm winters and low diversity and abundance of natural forage that necessitates supplemental feeding. We manipulated two factors, queen age and supplemental feed composition of 285 colonies across three apiary sites during a 7 month period from July 2016 through January 2017. We found that brood production by young queens was significantly greater than that of old queens, and was augmented by feeding colonies supplemental pollen. In contrast to northern climates, immune gene expression increased or remained stable. The potential costs associated with immune gene expression and continuous brood production in southern climates may offset by the comparatively reduced stresses incurred by younger queens. More generally, we report the first comprehensive study of southern overwintering, with novel insights into colony performance detailing the molecular economy of nutritional resources. We emphasize the utility of colony-level, molecular profiling to identify factors influencing honey bee health and physiology on a large scale. We report for the first time colony-level expression analyses of three recently identified homologs of vitellogenin (vg), a storage glycol-lipoprotein central to colony nutritional state, immunity, oxidative stress resistance and life span regulation. We propose that pooled sample expression analyses of these gene transcripts are promising biomarkers for future large-scale studies of honey bee health and physiology in diverse environments and contexts.

Technical Abstract: Honey bee colony nutritional ecology relies on the acquisition and assimilation of floral resources across a landscape with changing forage conditions. Here, we examined the impact of pollen diet and queen age on colony health across extended periods of reduced forage in a southern climate. We measured conventional hive metrics as well as colony-level gene expression of eight immune-related genes and three recently identified homologs of vitellogenin (vg), a storage glycolipoprotein central to colony nutritional state, immunity, oxidative stress resistance and life span regulation. Across three apiary sites, concurrent longitudinal changes in colony-level gene expression and nutritional state reflected the production of diutinus (winter) bees physiologically altered for long-term nutrient storage. Brood production by young queens was significantly greater than that of old queens, and was augmented by feeding colonies supplemental pollen. A feeding regimen of natural pollen resulted in a non-significant increase in brood production and gene expression putatively associated with improved nutritional status. Expression analyses of the newly identified vg homologs vg-like-A, -B, and -C revealed distinct patterns that correlated with colony performance, phenology, and immune-related gene transcript levels. Our findings provide new insights into dynamics underlying managed colony performance on a large scale. Colony-level, molecular physiological profiling is a promising approach to effectively identify factors influencing honey bee health in future landscape and nutrition studies.