Bacterial Community Structural Dynamics and Predicted Functional Potential in Loxostege sticticalis

Symbiotic bacteria contribute to insect physiology and environmental adaptation, yet their dynamics and potential functions in the major migratory pest Loxostege sticticalis remain poorly understood. We characterized bacterial community composition, diversity, and predicted functional potential across developmental stages, tissues and frass samples, and environmental conditions. In laboratory-reared insects, Enterococcus and Staphylococcus predominated from the second to fifth instars, whose predicted functions emphasized carbohydrate and nucleotide metabolism. Adults were instead dominated by Pseudoalteromonas and Asaia, with predicted profiles showing greater representation of lipid and amino acid metabolism and transport and catabolism. First-instar larvae exhibited an adult-like community structure. Among sample types, Enterococcus predominated in the midgut, whereas Staphylococcus was overrepresented in the epidermis and frass. Epidermal and frass communities emphasized cellular processes and genetic information processing, whereas midgut and other internal tissue communities showed greater predicted potential for membrane transport and metabolism. Wild-caught larvae harbored distinct communities consistently enriched in Stenotrophomonas and Ralstonia, with predicted profiles shifting toward carbohydrate, amino acid, and lipid metabolism and environmental adaptation in later instars. Overall, these findings demonstrate that the symbiotic bacterial communities of L. sticticalis vary markedly with development, tissue niche, and environment, providing a basis for further studies of host–microbe interactions.