Evaluation of RNA Interference for Control of the Grape Mealybug (Hemiptera: Pseudococcidae).

The grape mealybug (Ehrhorn, 1900) (Hemiptera: Pseudococcidae) is a significant pest of grapevines ( spp.) and a vector of disease-causing grape viruses, linked to its feeding on phloem sap. The management of this pest is constrained by the lack of naturally occurring resistance traits in . Here, we obtained proof of concept that RNA interference (RNAi) using double-stranded RNA (dsRNA) molecules against essential genes for phloem sap feeding can depress insect survival. The genes of interest code for an aquaporin () and a sucrase () that are required for osmoregulation in related phloem sap-feeding hemipteran insects (aphids and whiteflies). In parallel, we investigated the grape mealybug genes coding non-specific nucleases (), which reduce RNAi efficacy by degrading administered dsRNA. Homologs of and with experimentally validated function in aphids, together with , were identified in the published transcriptome of the citrus mealybug by phylogenetic analysis, and sequences of the candidate genes were obtained for by PCR with degenerate primers. Using this first sequence information for , dsRNA was prepared and administered to the insects via an artificial diet. The treatment comprising dsRNA against , and significantly increased insect mortality over three days, relative to dsRNA-free controls. The dsRNA constructs for and were predicted, from sequence analysis to have some activity against other mealybugs, but none of the three dsRNA constructs have predicted activity against aphids. This study provides the basis to develop in planta RNAi strategies against and other mealybug pests of grapevines.