Silencing of Double-Stranded Ribonuclease Improves Oral RNAi Efficacy in Southern Green Stinkbug Nezara viridula

Variability in RNA-interference (RNAi) efficacy among different insect orders poses a big hurdle in the development of RNAi-based pest control strategies. The activity of double-stranded ribonucleases (dsRNases) in the digestive canal of insects can be one of the critical factors affecting oral RNAi efficacy. Here, the involvement of these dsRNases in the southern green stinkbug Nezara viridula was investigated. First, the full sequence of the only dsRNase (NvdsRNase) in the transcriptome of N. viridula was obtained, followed by an oral feeding bioassay to evaluate the effect of NvdsRNase-silencing on oral RNAi efficacy. The NvdsRNase was first silenced in nymphs by NvdsRNase-dsRNA injections, followed by exposure to an artificial diet containing a lethal αCop-specific dsRNA. A significantly higher mortality was observed in the NvdsRNase-silenced nymphs when placed on the dsαCop-containing diet (65%) than in the dsGFP injected and dsαCop fed control (46.67%). Additionally, an ex vivo dsRNA degradation assay showed a higher stability of dsRNA in the saliva and midgut juice of NvdsRNase-silenced adults. These results provide evidence for the involvement of NvdsRNase in the reduction of oral RNAi efficacy in N. viridula. This information will be useful in further improving potential RNAi-based strategies to control this pest.