RNA Interference Targeting MaCht-2 Induces Severe Molting Defects and Lethality in Monochamus alternatus

Monochamus alternatus, the principal vector of pine wilt disease, poses a serious threat to pine forest ecosystems, and the identification of effective molecular targets is important for the development of environmentally friendly control strategies. In this study, a Group VII chitinase gene, MaCht-2, was identified in M. alternatus, and its developmental expression pattern, RNA interference (RNAi) efficiency, and RNAi-induced phenotypes were investigated using quantitative PCR, dsRNA injection, and transmission electron microscopy. MaCht-2 was highly expressed from the fifth-instar larval stage to the pupal stage, indicating a role in molting and metamorphosis. Silencing of MaCht-2 caused severe developmental defects across multiple life stages, including incomplete ecdysis, pupation failure, adult deformities, impaired locomotion, and high mortality. In third-instar larvae, injection of 5 μg of dsRNA resulted in mortality exceeding 50%. Ultrastructural analysis further showed that MaCht-2 silencing disrupted normal cuticle organization, causing thinning, wrinkling, and disordered lamellar structure. Compared with previously studied chitin-related genes, MaCht-2 produced stronger lethality and more stable RNAi effects. These results indicate that MaCht-2 is essential for normal development of M. alternatus and represents a promising target for RNAi-based pest management.