Tetracycline changes the microbial assembly of Hyphantria cunea and reduces its fitness.

The strong environmental adaptability of the fall webworm Hyphantria cunea is closely linked to its internal microbiota. However, with the widespread usage and environmental residuals of antibiotics, their effects on the microbiome and fitness of H. cunea remain unknown. In this study, we found that tetracycline significantly decreased bacterial diversity in H. cunea, evident in a notable reduction in both the number of bacterial species and their relative abundance. Furthermore, the bacterial community structure was influenced by tetracycline, resulting in an increase in the relative abundance of Firmicutes and a decrease in the relative abundances of Proteobacteria, Bacteroidota, and others. Additionally, the potentially tetracycline-resistant bacterial genus ZOR0006 became dominant after tetracycline ingestion. The tetracycline also led to significant alterations in the function of the bacterial community, particularly in defense mechanisms, cell motility, energy production, and conversion. Corresponding to the changes in the microbiota, tetracycline significantly reduced the fitness of H. cunea, mainly manifested as an extension of the developmental duration and a decrease in the survival rate. These findings elucidate the effects of tetracycline on the microbial assembly and fitness of H. cunea, providing an important reference for a deeper understanding of the complex roles of antibiotics in ecological environments.