Winter Storms Within: Climate-Driven Stressors Undermine Honey Bee Gut Microbiome

Climate change is intensifying winters in temperate regions, posing a serious threat to Apis mellifera health. The gut microbiome, a distinct community of core bacterial species, is central to overwintering success by supporting immune function, nutrient assimilation, and pathogen resistance, but is highly sensitive to environmental stressors such as cold temperatures and dietary shifts. Stress-induced perturbations can reshape the composition and relative abundance of the gut microbiome in honey bees, leading to adverse effects on host health, physiological functions, and overwinter survival. Cold temperatures and additional stressors further destabilize the microbiome, compounding these effects. This review is the first to synthesize current knowledge on how extrinsic factors, such as diet, antibiotics, and pathogens, and intrinsic factors, including age and strain, influence the composition and function of the honey bee gut microbiota during the overwintering period. Given the increasing severity of winter conditions under climate change, a deeper understanding of microbiome–host–environment interactions is essential for improving honey bee resilience. By integrating evidence on the microbiome’s roles in nutrient utilization, immune modulation, and pathogen defense, this review outlines a framework to guide future research aimed at sustaining pollinator health and nutrition in a changing global climate.