Successful oral RNA interference efficiency in the silkworm Bombyx mori through nanoparticle-shielded dsRNA delivery

Double-stranded RNA (dsRNA) mediated RNA interference (RNAi) is a tool in functional gene study and pest control. However, RNAi efficiency in Lepidoptera is low compared to the RNAi sensitive Coleoptera. Previous studies on RNAi in the silkworm Bombyx mori, the lepidopteran model insect, were performed by injection only. Successful oral RNAi in the silkworm has never been reported yet. This study aims to develop a successful oral dsRNA delivery method to the silkworm larvae. Chitosan is an economical and biodegradable polymer. Chitosan/dsRNA nanoparticles were prepared by self-assembly. These nanoparticles were found to be stable when incubated in the midgut juice of the silkworm larvae, whereas naked dsRNA underwent complete degradation. Chitosan/dsRNA nanoparticles targeting various immune genes in oral administration to the silkworm larvae mediated significant knockdown of gene transcript. This silencing effect resulted in smaller larvae and cocoons when the silkworms were fed with Chitosan/dsRNA nanoparticles targeting BmToll9-2 gene, indicating that immune genes might be used as targets in pest control. Optimization of the chitosan/dsRNA nanoparticles maintained an RNAi effect from 3-5 days. The efficient RNAi was due to the persistence of nanoparticle-shielded dsRNA in the larvae. The above findings contribute to the first oral RNAi report in the silkworm, which facilitates the application of RNAi in insects and oral RNAi in pest control.