Disruption of gut bacterial symbiont homeostasis in Streltzoviella insularis larvae under sublethal chlorantraniliprole exposure.

Chemical insecticides remain a cornerstone of contemporary integrated pest management (IPM). However, the toxicological profile of Streltzoviella insularis, an economically important wood-boring pest, remains insufficiently characterized. In this study, a laboratory rearing system for S. insularis was established using a customized artificial diet, providing a reliable platform for toxicological assays. Bioassays indicated that chlorantraniliprole (CAP) exhibited significantly higher insecticidal activity against fifth-instar larvae than the three other insecticides tested. Focusing on disruption of gut bacterial symbiont homeostasis as a mechanistic entry point, we investigated whether sublethal CAP exposure imposes fitness costs on S. insularis through perturbation of gut symbiotic communities. 16S rRNA amplicon sequencing revealed substantial restructuring of the larval bacterial community under sublethal CAP stress. The abundance of the core genus Enterococcus was significantly reduced, whereas Carnimonas and Levilactobacillus were significantly enriched. These three taxa came to dominate the reshaped gut microbiota, suggesting a potential compensatory functional shift following depletion of core symbionts. Activities of key digestive enzymes, including α-amylase, lipase, and trypsin, were significantly reduced. Substantial fitness costs were observed, including reduced larval and pupal weights, prolonged larval development time, and decreased pupation success, adult emergence, egg hatching, and female fecundity. Collectively, these findings suggest that sublethal CAP exposure is closely associated with gut symbiont dysbiosis in S. insularis, accompanied by impaired digestive function and delayed larval growth and development.