Effective target genes for RNA interference-based management of the cabbage stem flea beetle

The cabbage stem flea beetle (CSFB, Psylliodes chrysocephala) is a key pest of oilseed rape. The ban on neonicotinoids in the European Union due to environmental concerns and the emergence of pyrethroid-resistant populations have made the control of CSFB extremely challenging. In search of a solution, we recently showed that RNA interference (RNAi) has potential in the management of CSFB. However, the previously tested target genes for RNAi-mediated pest control (subsequently called target genes) exhibited moderate and slow-acting lethal effects. In this study, 27 double-stranded RNAs (dsRNAs) were orally delivered to identify highly effective target genes in CSFB adults by leveraging the findings of a genome-wide RNAi screen in Tribolium castaneum. Our screen using 500 ng dsRNA dose identified 10 moderately lethal (> 50% mortality) and 4 highly target genes (100% mortality in 8-10 days), which mainly included proteasome subunits. RT-qPCR experiments confirmed target gene silencing, and dose-response investigations revealed LD50 values as low as ~20 ng (single exposure, endpoint: 14 days). Four highly lethal dsRNAs also inhibited leaf damage (up to ~75%), and one affected locomotion. The sequences of promising target genes were subjected to in silico target prediction in off-target organisms, e.g. beneficials such as honeybees, to design eco-friendly dsRNAs. Overall, the study provides valuable knowledge for developing dsRNA-based insecticides against CSFB.