The overwintering honey bee: Effect of age and climate on the hindgut microbiome- WW/CW samples

Managed honey bee colonies are overwintered in a variety of climates. Successfully overwintered colonies are paramount to spring agricultural pollination demands, which provide nutrients for early-year colony growth. High rates of winter colony loss have prompted investigations into overwintering climate, including indoor climate controlled overwintering. Core to overall colony health, the gut microbiome has largely been ignored in this context. While the gut microbiomes of short-lived workers and long-lived queens have been investigated, that of intermediate-lived, overwintering (diutinus) workers is relatively unknown. We sequenced the hindgut microbiota of overwintering workers from both a warm southern climate and controlled indoor cold climate. A cohort of known chronological age was sampled congruently for comparison. Chronological age was associated with significantly decreased bacterial and fungal load, but the relative structure of the core hindgut microbiome did not change with age. In both climates, the hindgut microbiome was generally stable overwinter. However, collective microbiome changes in the southern climate suggest compromised host physiology. Fungal abundance increased by two orders of magnitude in southern climate hindguts and was positively correlated with non-core, likely opportunistic bacteria. Our results contribute to understanding overwintering honey bee biology and microbial ecology and provide insight into overwintering strategies.