Simulated Climate Warming Influenced Colony Microclimatic Conditions and Gut Bacterial Abundance of Honeybee Subspecies Apis mellifera ligustica and A. mellifera sinisxinyuan

Ectothermic organisms including insects are highly vulnerable to climate warming which not only influences their biology, ecology and physiology but also affects their symbiotic gut microbiota. This study determined the impact of ambient (control) and simulated warmer (heating) climatic conditions on the microclimate of brood nest and gut bacterial abundance of two Apis mellifera subspecies i.e. A. mellifera ligustica and A. mellifera sinisxinyuan. For both subspecies, brood nest temperature and relative humidity under the heating treatment were significantly different (p≤0.001) than those under the control treatment. Quantitative PCR data revealed that the abundance of gut bacteria (16S rRNA gene copy numbers) of A. mellifera ligustica and A. mellifera sinisxinyuan larvae was significantly higher (P≤0.05), 1.73 and 5.32 fold higher respectively, during the heating treatment than those in control conditions. Although gut bacterial abundance of A. mellifera ligustica (1.67 × 10⁷ copies g⁻¹ fw) and A. mellifera sinisxinyuan (1.7 × 10⁷ copies g⁻¹ fw) larvae was similar during the control treatment, A. mellifera sinisxinyuan larvae exhibited three times greater gut bacterial abundance than A. mellifera ligustica during the heating treatment. Similarly, adult A. mellifera sinisxinyuan bees harboured significantly greater bacterial abundance during the heating treatment than control. These findings elucidate that climate warming may significantly affect the honeybee colony microclimate and their gut bacterial abundance. However, further studies are needed to better understand how gut microbial community may influence the learning, physiological and behavioural mechanisms of the host bees in a climate warming scenario.