Gene silencing through RNAi in the red palm weevil Rhynchophorus ferrugineus and the red flour beetle Tribolium castaneum

Gene silencing induced by RNA interference (RNAi) is a powerful technique not only for gene function analysis, but also for potential control of insect pests. The red palm weevil (Rhynchophorus ferrugineus Oliver, Coleoptera: Curculionidae) is considered one of the most devastating pests of several palm species globally. Conventional pest management strategies (e.g. pesticides, parasitoids, heat treatment) are not effective at controlling this pest species. Thus, there is an urgent need to develop alternative approaches, having low environmental impact, to control this insect pest. The potential of RNAi as a future control strategy for R. ferrugineus was investigated through targeting three different genes encoding key enzymes (α-amylase, V-ATPase) and the Ecdysone receptor. The efficiency of gene-silencing, and subsequent effects on insect mortality, was evaluated through delivery of the dsRNA using two different methods, injection and ingestion. Similar studies were also carried out with the red flour beetle (Tribolium castaneum Herbst, Coleoptera: Tenebrionidae) as a model system. Although R. ferrugineus and T. castaneum belong to the same order, the two insects showed species- and delivery-specific responses with major differences observed in the levels of gene knockdown and mortality, both of which were greater when the dsRNA was delivered via injection. The results showed that α-amylase and Ecdysone receptor genes were significantly down-regulated in R. ferrugineus. Significant differences between the genes tested and the doses provided were observed with an inverse dose-dependent effect. In T. castaneum expression of genes encoding V-ATPase and the Ecdysone receptor, were reduced following delivery of dsRNA. This study demonstrates the potential of RNAi as a technology able to inform new strategies for future control of R. ferrugineus.