Expression Profiles of Chitin Deacetylase Genes and Functional Characterization of Key Genes in Spodoptera frugiperda

Chitin deacetylase (CDA) are critical enzyme involved in the growth and molting of insects. Targeting CDA offers a novel approach for developing environmentally friendly, control strategies against the fall armyworm, Spodoptera frugiperda (S. frugiperda). In this study, we performed functional characterization of CDA genes in this agriculturally important pest. A total of seven CDA genes, designated SfCDA1–7, were identified. Quantitative real-time PCR (qRT-PCR) was used to systematically profile the expression patterns of these SfCDA genes across different developmental stages and tissues. The results showed relatively high transcript levels during the third and fifth instar larval stages, with predominant localization in the integument and midgut. Based on these findings, double-stranded RNA (dsRNA) targeting each SfCDA gene was designed, synthesized, and injected into larvae to achieve RNA interference-mediated gene silencing. Knockdown of each SfCDA gene via injection revealed that silencing SfCDA2, SfCDA3, and SfCDA6 resulted in mortality rates of 16%, 13% and 60%, respectively, whereas knockdown of the remaining genes induced no significant larval mortality. SfCDA6 exhibited the most pronounced effect. Subsequently, nanoparticle-mediated feeding was employed to silence SfCDA6, which led to severe molting defects during the late sixth-instar larva-to-pupa transition, characterized by body shrinkage, developmental arrest, and eventual death, with a mortality rate of 53%. Therefore, SfCDA6 represents a highly promising molecular target for controlling S. frugiperda via RNAi-mediated knockdown. This study clarifies the biological functions of chitin deacetylase genes in S. frugiperda molting and development, and identifies SfCDA6 as a novel potential target for RNAi-based pest management.