A Systematic Study of RNAi Effects and dsRNA Stability in and , Following Injection and Ingestion of Analogous dsRNAs.

RNA interference (RNAi) effects in insects are highly variable and may be largely dependent upon the stability of introduced double-stranded RNAs to digestion by nucleases. Here, we report a systematic comparison of RNAi effects in susceptible red flour beetle () and recalcitrant pea aphid () following delivery of dsRNAs of identical length targeting expression of V-type ATPase subunit E () and inhibitor of apoptosis () genes. Injection and ingestion of and dsRNAs resulted in up to 100% mortality of larvae and sustained suppression (>80%) of transcript levels. In , injection of but not dsRNA resulted in up to 65% mortality and transient suppression (ca. 40%) of transcript levels. Feeding aphids on dsRNA reduced growth and fecundity although no evidence for gene suppression was obtained. Rapid degradation of dsRNAs by aphid salivary, haemolymph and gut nucleases contrasted with stability in larvae where it appears that exo-nuclease activity is responsible for relatively slow digestion of dsRNAs. This is the first study to directly compare RNAi effects and dsRNA stability in receptive and refractory insect species and provides further evidence that dsRNA susceptibility to nucleases is a key factor in determining RNAi efficiency.