Symbiotic bacteria participate in pectinolytic metabolism to enhance larval growth in Zeugodacus cucurbitae.

BACKGROUND: Symbiotic microbes play a pivotal role in the feeding processes of phytophagous insects, and symbiosis has been established as a key strategy for certain species to acquire pectinases. However, whether symbiotic bacteria play a role in the pectinolytic metabolism of Zeugodacus cucurbitae remains unclear. RESULTS: Removal of symbiotic bacteria via egg sterilization significantly reduced larval food consumption, growth, and pectinase activity (P < 0.05), highlighting that the microbiota was required for Z. cucurbitae larval growth under feeding on host plants. Microbial community analysis identified Klebsiella spp. as persistent colonizers of larval feeding wounds, exhibiting recycling between host tissues and plant substrates. Functional assays demonstrated that Klebsiella strains (CpL20, CpL49, CpL63, and CpL64) formed distinct hydrolysis zones on pectin medium and degraded pectin via high enzymatic activity (495.98-830.54 μ/mL). Reintroduction of Klebsiella spp. restored larval growth in sterile treatment groups, confirming their metabolic contribution. CONCLUSION: Our results suggest that Klebsiella spp. circulate between the feeding environment and larval tissues, participating in the pectinolytic metabolism to utilize the host plant efficiently, thereby facilitating larval growth and development. This study provides a foundation for understanding the role of symbiotic bacteria in pectinolytic metabolism during the ecological adaptation of phytophagous insects and offers new insights into the environmentally friendly management of Z. cucurbitae in agricultural settings. © 2025 The Author(s). Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.