Synergistic control of Spodoptera frugiperda based on nanoparticle-mediated dsRNA and insecticide

RNAi is currently the most promising gene silencing-based biotechnology for pest control. However, double-stranded RNA (dsRNA) is easily degraded in the environment, resulting in poor stability and ineffectiveness. In this study, we designed a nanoparticle chitosan-polyethylene glycol-carboxyl (CS-PEG-COOH), which can spontaneously assemble with dsRNA to form a dsRNA/CS-PEG-COOH complex. Atomic force microscopy (AFM) and transmission electron microscopy (TEM) revealed the complex size being 543.66 nm. CS-PEG-COOH was able to prevent dsRNA from being degraded by midgut fluid or RNase A, thereby significantly improving the dsRNA stability under various environmental conditions. CS-PEG-COOH gradually released dsRNA at pH > 8. Cy3 fluorescent labeling confirmed that CS-PEG-COOH significantly enhanced the delivery of dsRNA to insects, and was water-washing resistant on plants. Subsequently, ds VGSC fragments were expressed in E. coli using selected VGSC fragments. Their silencing efficiency was significantly enhance by CS-PEG-COOH. Feeding Spodoptera frugiperda the nanocomposite in combination with metaflumizone caused down-regulation of genes related to cuticle synthesis, cell metabolism, and drug metabolism. Metaflumizone/ds VGSC /CS-PEG-COOH significantly enhanced pest control effect by inhibiting insect growth and development.