Rice leaf folder Cnaphalocrocis medinalis is one of the most serious pests of rice in rice-planting regions worldwide. DsRNA-degrading nucleases (dsRNases) are important factors in reducing the efficiency of RNA interference (RNAi) in different insects. In this study, a dsRNase gene from C. medinalis (CmdsRNase) was cloned and characterized. The CmdsRNase cDNA was 1395 bp in length, encoding 464 amino acids. The CmdsRNase zymoprotein contains a signal peptide and an endonuclease NS domain that comprises six active sites, three substrate-binding sites, and one Mg²⁺-binding site. The mature CmdsRNase forms a homodimer with a total of 16 α-helices and 20 β-pleated sheets. Homology and phylogenetic analyses revealed that CmdsRNase is closely related to dsRNase2 in Ostrinia nubilalis. Expression pattern analysis by droplet digital PCR indicated that the expression levels of CmdsRNase varied throughout the developmental stages of C. medinalis and in different adult tissues, with the highest expression levels in the fourth-instar larvae and the hemolymph. CmdsRNase can degrade dsRNA to reduce the efficiency of RNAi in C. medinalis. Co-silencing of CmCHS (chitin synthase from C. medinalis) and CmdsRNase affected significantly the growth and development of C. medinalis and thus improved RNAi efficacy, which increased by 27.17%. These findings will be helpful for green control of C. medinalis and other lepidopteran pests by RNAi.

The rice leaf folder, Cnaphalocrocis medinalis is a major pest of rice and is difficult to control. UDP-N-acetylglucosamine pyrophosphorylase (UAP) is a key enzyme in the chitin synthesis pathway in insects. In this study, the UAP gene from C. medinalis (CmUAP) was cloned and characterized. The cDNA of CmUAP is 1788 bp in length, containing an open reading frame of 1464 nucleotides that encodes 487 amino acids. Homology and phylogenetic analyses of the predicted protein indicated that CmUAP shared 91.79%, 87.89%, and 82.75% identities with UAPs of Glyphodes pyloalis, Ostrinia furnacalis, and Heortia vitessoides, respectively. Expression pattern analyses by droplet digital PCR demonstrated that CmUAP was expressed at all developmental stages and in 12 tissues of C. medinalis adults. Silencing of CmUAP by injection of double-stranded RNA specific to CmUAP caused death, slow growth, reduced feeding and excretion, and weight loss in C. medinalis larvae; meanwhile, severe developmental disorders were observed. The findings suggest that CmUAP is essential for the growth and development of C. medinalis, and that targeting the CmUAP gene through RNAi technology can be used for biological control of this insect.