RNAi efficiency is limited in larvae of the biting midge Culicoides sonorensis

Broad-spectrum insecticides are not efficient at preventing livestock disease transmission by the biting midge Culicoides sonorensis. Off-target effects and the potential for insecticide resistance development are concerns for the continued use of these chemicals at scale. RNA interference (RNAi) is a potential new control strategy for targeting these insects specifically without affecting non-target species. Insect control by RNAi uses innate cellular mechanisms to degrade physiologically important mRNA transcripts, inducing insect mortality. The efficiency of RNAi can vary widely in insects, and little work has been done to evaluate this mechanism in C. sonorensis. Here, we treated the W8A C. sonorensis cell line and late-stage larvae with double-stranded RNA (dsRNA) and evaluated the dose-response and time course of RNAi action. W8A cells began responding to high doses (10 μg/ml) of dsRNA in as little as 24 h post-treatment, and cells showed a significant decrease in transcript levels with doses as small as 100 ng/ml at 48 h post-treatment. Late-stage larvae showed no significant response to comparable concentrations of dsRNA when compared to cells. This inefficiency may be due to RNA-degrading nucleases (dsRNases) or inefficient uptake of dsRNA in the larval gut. The potential of RNAi as an insect control strategy is promising, but more work is required to fully elucidate the mechanisms that are hindering this strategy in C. sonorensis larvae.