Unintended Consequences of Antibiotic Use in Beekeeping: Drone Health as a Hidden Vulnerability

Background Declines in honey bee queen quality and variability in drone (male) reproductive performance are contributing factors to colony losses reported by beekeepers. While the causes of reduced reproductive fitness remain unclear, recent evidence implicates agrichemical exposure. Oxytetracycline (OTC), an antibiotic used in apiculture for over 70 years to treat brood diseases, is classified as an endocrine-disrupting compound due to its inhibition of mitochondrial function in reproductive cells. In other animals, OTC exposure has been associated with impaired reproductive development, reduced sperm viability, and broader reproductive dysfunction. Although the effects of OTC on worker bee gut microbiota and physiology are well documented, its influence on drone gut microbiota remains poorly characterized. Additionally, our recent discovery of microbial communities in drone reproductive tissues raises new questions about the potential role of these microbiota in drone fertility. Results Using an in vitro rearing system, we found that larval OTC exposure delays drone development, reduces survival, and results in detectable residues in the gut and reproductive tissues of newly emerged adults. In mature drones, oral exposure to field-realistic OTC concentrations significantly reduced gut bacterial abundance and diversity, although reproductive tissue-associated microbiota appeared largely unaffected. In vitro assays further revealed that OTC is highly toxic to drone sperm at environmentally relevant concentrations. Conclusion Our findings demonstrate that antibiotic exposure negatively impacts drone development, survival, gut microbiota, and sperm viability. These results suggest that the use of OTC in beekeeping may contribute to reduced male reproductive health and, ultimately, colony failure. This work highlights the urgent need for alternative strategies to manage brood diseases and underscores the importance of further research into the effects of antibiotics on drone microbiomes and reproductive fitness.