Three Antibiotics Exert Differential Effects on the Larval Microbiome and Fitness of Hyphantria cunea

The severe damage caused by the fall webworm Hyphantria cunea is closely related to its internal microbiota. However, due to the widespread use of antibiotics and their environmental persistence, the specific effects of various antibiotics on the microbiome and fitness of H. cunea larvae remain ambiguous. This study investigated the impacts of three antibiotics (tetracycline, rifampicin, and kanamycin) on microbiome assembly, functional traits, and host fitness. Our findings revealed that each antibiotic distinctly altered the microbial community: tetracycline primarily decreased bacterial diversity (e.g., reduced abundance of Actinomycetota) and suppressed host fecundity; kanamycin lowered microbial evenness (e.g., decreased Bacillota) and diminished pupal weight; whereas rifampicin significantly restructured the community (e.g., increased Pseudomonas and decreased Bacillota), enhanced functional traits such as biofilm formation and stress tolerance, and imposed multidimensional adverse effects on fitness (prolonged developmental duration, reduced pupal weight, and decreased hatching rate). Alterations in microbiome diversity, structure, and function were tightly correlated with the differential impacts of antibiotics on host fitness. This research elucidates the mechanisms by which antibiotics disrupt host–microbe interactions in H. cunea, offering a theoretical foundation for understanding antibiotic ecological repercussions and devising microbe-based green pest control strategies.