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RNA interference (RNAi) is a promising technology for the development of next‐generation insect pest control products. Though RNAi is efficient and systemic in coleopteran insects, it is inefficient and variable in lepidopteron insects. In this study, we explored the possibility of improving RNAi in the fall armyworm (FAW),Spodoptera frugiperdaby conjugating double‐stranded RNA (dsRNA) with biodegradable chitosan (Chi). dsRNA conjugated with chitosan was protected from degradation by endonucleases present in Sf9 cell‐conditioned medium, hemolymph, and midgut lumen contents collected from the FAW larvae. Chi–dsRNA complexes showed reduced accumulation in the endosomes of Sf9 cells and FAW tissues. Exposing chitosan formulated dsRNA in Sf9 cells and the tissues induced a significant knockdown of endogenous genes. Chi–dsIAP fed to FAW larvae induced knockdown ofiapgene, growth retardation, and mortality. Processing of dsRNA into small interfering RNA was detected with chitosan‐conjugated³²P‐UTP‐labeled ds green fluorescent protein in Sf9 cells and FAW larval tissues. Overall, these data suggest that dsRNA conjugated with chitosan helps dsRNA escape from the endosomes and improves RNAi efficiency in FAW cells and tissues.

RNA interference (RNAi) is a valuable method for understanding the gene function and holds great potential for insect pest management. While RNAi is efficient and systemic in coleopteran insects, RNAi is inefficient in lepidopteran insects. In this study, we explored the possibility of improving RNAi in the fall armyworm (FAW),Spodoptera frugiperdacells by formulating dsRNA with Cellfectin II (CFII) transfection reagent. The CFII formulated dsRNA was protected from degradation by endonucleases present in Sf9 cells conditioned medium, hemolymph and midgut lumen contents collected from the FAW larvae. Lipid formulated dsRNA also showed reduced accumulation in the endosomes of Sf9 cells and FAW tissues. Exposing Sf9 cells and tissues to CFII formulated dsRNA caused a significant knockdown of endogenous genes. CFII formulated dsIAP fed to FAW larvae induced knockdown ofiapgene, growth retardation and mortality. Processing of dsRNA into siRNA was detected in Sf9 cells andSpodoptera frugiperdalarvae treated with CFII conjugated³²P‐UTP labeled dsGFP. Overall, the present study concluded that delivering dsRNA formulated with CFII transfection reagent helps dsRNA escapes from the endosomal accumulation and improved RNAi efficiency in the FAW cells and tissues.

Apoptosis has been widely studied from mammals to insects. Inhibitor of apoptosis (IAP) protein is a negative regulator of apoptosis. Recent studies suggest thatiapgenes could be excellent targets for RNA interference (RNAi)‐mediated control of insect pests. However, not much is known aboutiapgenes in one of the well‐known insect model species,Tribolium castaneum. The orthologues of fiveiapgenes were identified inT. castaneumby searching its genome at NCBI (https://www.ncbi.nlm.nih.gov/) and UniProt (https://www.uniprot.org/) databases usingDrosophila melanogasterandAedes aegyptiIAP protein sequences as queries. RNAi assays were performed inT. castaneumcell line (TcA) and larvae. The knockdown ofiap1gene induced a distinct apoptotic phenotype in TcA cells and induced 91% mortality inT. castaneumlarvae. Whereas, knockdown ofiap5resulted in a decrease in cell proliferation in TcA cells and developmental defects inT. castaneumlarvae which led to 100% mortality. Knockdown of the other threeiapgenes identified did not cause a significant effect on cells or insects. These data increase our understanding ofiapgenes in insects and provide opportunities for developingiap1andiap5as targets for RNAi‐based insect pest control.