Tetracycline Exposure Disrupts Gut Microbiota and Immune–Antioxidant Homeostasis in Honey Bees

Antibiotic exposure can perturb the gut microbiota of honey bees, but its associations with host physiological responses remain incompletely understood. Here, we investigated the effects of tetracycline exposure on survival, locomotor activity, gut bacterial communities, and immune- and antioxidant-related gene expression in Apis mellifera workers maintained under controlled laboratory cage conditions. Tetracycline exposure at 100, 300, and 450 μg/mL reduced worker survival in a concentration-dependent manner, while 100 μg/mL increased daytime locomotor activity without affecting sucrose consumption. Tetracycline also altered gut bacterial community structure, with marked reductions in several core taxa, particularly Snodgrassella and Bartonella, whereas Commensalibacter, Lactobacillus Firm4 and Firm5 increased, especially at the highest concentration. Changes in immune- and antioxidant-related gene expression were more pronounced in the gut than in the head. Moreover, Snodgrassella abundance was positively correlated with Relish expression in the head and with Apidaecin and CAT expression in the gut. These findings demonstrate that tetracycline exposure reduces honey bee survival and is associated with coordinated alterations in gut bacterial communities and host physiological responses.