Identification of putative double-stranded RNA-degrading enzymes in the biting midge, Culicoides sonorensis (Diptera: Ceratopogonidae)

The biting midge, Culicoides sonorensis, is a vector of livestock pathogens that are not only detrimental to herd health, but impact animal trade. Broad-spectrum insecticides have typically been used to control these insect pests, but the increasing incidence of insecticide resistance and off-target effects on beneficial insects and aquatic ecosystems are constant worries for commercial livestock farmers. RNA interference (RNAi) offers the potential of a highly specific, environmentally benign control method to supplement those already in place for livestock pests. Unfortunately, the efficiency of RNAi is limited in many insect taxa, including Culicoides, and a better understanding of mechanisms that limit the efficiency of RNAi are needed. In particular, degradation of double-stranded RNAs (dsRNAs) by double-stranded RNases (dsRNases) limits RNAi efficiency in many insect species, though little is known about the contribution of these enzymes to RNAi efficiency in C. sonorensis. Accordingly, we used bioinformatic techniques to identify putative dsRNases in C. sonorensis and are evaluating their expression in different life stages using qRT-PCR. Our efforts provide a foundation for understanding the obstacles limiting RNAi efficiency in dipteran insects as well as for developing strategies to enhance RNAi in C. sonorensis for use in future control strategies.