Unintended consequences of antibiotic use in beekeeping: drone health as a potential 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 impact on drone gut microbiota has never been characterized. Additionally, we recently discovered microbial communities in drone reproductive tissues, which could be impacted by OTC exposure. The goal of this study was to determine if OTC has the potential to impact drone development, survival, fecundity, and microbiota composition.

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 conservative field-relevant 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 OTC exposure has the potential to negatively affect drone development, survival, gut microbiota, and sperm viability. These results support our hypothesis that the use of OTC in beekeeping may contribute to reduced male reproductive health. Importantly, this work highlights the need for additional studies, particularly field-based investigations, to better understand the impacts of OTC on drone reproductive health and microbiomes. Such research will be critical for evaluating the broader consequences of antibiotic use in apiculture and for developing sustainable strategies to manage brood diseases.