Comparison of efficacy of RNAi mediated by various nanoparticles in the rice striped stem borer (Chilo suppressalis)

RNA interference (RNAi) has proven to be a very promising prospect for insect pest control. However, low RNAi efficacy limits further development of this biotechnology for use on lepidopteran insects, including the rice striped stem borer (SSB) (Chilo suppressalis), one of the major destructive rice pests. In this work, the application of various nanoparticles (NPs) by which double-stranded RNA (dsRNA) could be encapsulated was evaluated as an alternative delivery strategy to potentially increase the bioactivity of dsRNA. Three NPs, chitosan, carbon quantum dot (CQD), and lipofectamine2000, complexed with dsRNA (to target the glyceraldehyde-3-phosphate dehydrogenase gene (G3PDH)) were tested to examine their use in controlling SSB. Relative mRNA expressions were quantified using qPCR to evaluate knockdown efficiency of NP-dsRNA treated larvae, and the correlated dsRNA-mediated SSB larval mortality was tested. Thereafter, the content dynamics of hemolymph dsRNA after ingesting different NP-dsRNA were monitored in vivo; the hemolymph dsRNA content was in ratios of 5.67, 9.43, and 1 with chitosan, CQD, and lipofectamine2000 induced samples, respectively. The results demonstrated that all three tested NPs led to efficient feeding delivery by improving both dsRNA stability and cellular uptake equally. Furthermore, there was a strong correlation (r = 0.9854) between the hemolymph dsRNA contents and the average RNAi depletions in the non-gut tissues of SSB. Overall, our results strongly suggest that due to its strong endosomal escaping ability, CQD was the most efficient carrier for inducing systemic RNAi, and thereby causing effective gene silencing and mortality in SSB.