Screening of 57 Candidate Double-Stranded RNAs for Insecticidal Activity Against the Pest Termite Reticulitermes flavipes (Isoptera: Rhinotermitidae)

RNA interference insecticides have received increasing attention in recent years due to their classification as a reduced-risk biopesticide and their proposed faster path to registration compared with conventional synthetic insecticides. The goal of this study was to synthesize and compare efficacy of 62 double-stranded RNAs (dsRNAs) from 31 target genes against the pest termite species, Reticulitermes flavipes (Kollar) (Isoptera: Rhinotermitidae). Fifty-seven dsRNAs of ~125 base pairs each were successfully synthesized. First-tier screens using a combination immersion/feeding assay revealed 10 top candidates and also that dsRNAs coming from synthesis reactions with 80–90× yields were the most effective. Follow-up studies using uptake enhancers in combination with top candidate dsRNAs were unsuccessful. Subsequent concentration range feeding assays on the top candidates revealed two lead termiticidal dsRNAs (3ʹ Hexamerin-2 and 3ʹ Glycosyl Hydrolase Family [GHF] 9-2 cellulase) and another that enhanced feeding (5ʹ GHF9-2 cellulase). Testing a matrix of combinations of these three dsRNAs revealed ultimately that the most consistently effective dsRNA combination was the 3ʹ Hexamerin-2 + 3ʹ GHF9-2 cellulase dsRNA combination. These results provide new information on candidate termiticidal dsRNAs and some apparent factors that have a bearing on their efficacy. Despite these successes, further research and development will be necessary to move dsRNA termiticides from pest management theory to real-world application.