Target gene selection for RNAi-based biopesticides against the hawthorn spider mite, Amphitetranychus viennensis (Acari: Tetranychidae)

RNA interference (RNAi), a species-specific control alternative, represents the next generation pest management strategy, which has been deregulated and commercialized in the US and Canada. An economically important arthropod pest for fruit trees and woody ornamental plants, the hawthorn spider mite, Amphitetranychus viennensis Zacher, has been controlled predominated by chemical pesticides. To address the emerging pesticide resistance issues in A. viennensis, we initiated a project to develop RNAi-based biopesticides. In this study, we 1) optimized a dietary RNAi system, and 2) screened for the candidate target genes using the newly developed oral delivery system through leaf disc. The five candidate genes include two housekeeping genes (V- type proton ATPase subunit A, V-ATPase A and Glyceraldehyde 3-phosphate dehydrogenase, GAPDH) and three genes associated with development (DEAD Box RNA Helicase, Belle; Farnesoic acid O-methyltransferase, FaMet; and CREB-binding protein, CBP). Suppression of expression levels were confirmed for all candidates under dsRNA treatments. As for the mortality, housekeeping genes, not surprisingly, were better candidates than development-related genes. Specifically, V-ATPase A and GAPDH accounted for 91% and 82% mortalities, respectively, while FaMet and CBP caused about 70% mortalities, respectively.  Belle, however, had no significant biological impacts on A. viennensis. These combined efforts not only provide an effective oral delivery method for pesticidal dsRNAs, but also identify potential target genes for RNAi-based biopesticides in A. viennensis.