Gut-microbiota reshaping by environmental oxytetracycline residues threatens life-history traits in a polyphagous fruit fly.

The persistence and overuse of oxytetracycline (OTC) have been associated with environmental contamination, ecological toxicity, and the emergence of antimicrobial resistance. Beyond its direct antimicrobial activity, environmental residues of OTC may disrupt non-target organisms by affecting life-history traits. In this study, the oriental fruit fly (Bactrocera dorsalis) was chronically exposed to OTC to assess gut microbiota shifts and associated life-history responses. Our results demonstrated that environmental OTC residues prolonged larval development, reduced pupal weight, and suppressed ovarian maturation in B. dorsalis. Microbiome analysis revealed that OTC exposure decreased beneficial bacteria while increasing opportunistic taxa, with multiple opportunistic taxa enriched under OTC exposure. Such OTC-induced microbial compositional changes might be associated with reduced availability of specific amino acids, which may contribute to cascading effects on pupal mass and ovarian development. Importantly, both lactic acid bacteria (Lactiplantibacillus plantarum and Levilactobacillus brevis) replenishment and amino acids (leucine, isoleucine, and glutamic acid) supplementation significantly alleviated OTC-induced impairments. Overall, our findings demonstrate that residual OTC exposure reshapes gut microbiota composition and metabolic function. Finally, we propose a conceptual framework illustrating how OTC-driven microbiota reorganization may be associated with cross-kingdom effects on insect life-history traits, providing insight into the ecological risks of environmental antibiotic residues.