D3198: RNA interference-mediated knockdown of genes implicated in ecdysteroid synthesis impairs molting in the potato psyllid Bactericera cockerelli (Insecta: Hemiptera)

RNA-mediated interference (RNAi) offers a promising biopesticide technology for controlling the potato psyllid Bactericera cockerelli (Sulc.) (Triozidae) because of sequence-specificity and potential for systemic gene silencing. In this study, dsRNA-silencing of three strategically-selected target genes, A, C, and D known to be essential for the synthesis and regulation of ecdysteroids, were evaluated for knockdown and corresponding phenotype in 3rd instar nymphs using oral delivery of individual dsRNAs and in all possible combinations of two or three. Knockdown was quantified by real-time quantitative PCR (qPCR) to determine fold-change in gene expression. Knockdown of target D, at 27-46%, resulted in 50% mortality 10-days post-ingestion-access period (IAP). In addition, three phenotypes characterized here for the first time, INCOMEC, PREMEC, and SWOLLEN, were observed, collectively related to the impairment of ecdysis in immature and reared adult psyllids. Psyllid mortality reached 65% when dsRNA-D was ‘stacked’ with dsRNA-C, 10-d post-IAP. Knockdown of C, at 38-60%, resulted in 53% mortality 10-d post-IAP, and was associated with mortality and INCOMEC and SWOLLEN phenotypes. The INCOMEC mutants survived for several days but were unable to fly or mate whereas SWOLLEN and PREMEC phenotypes were lethal. Knockdown for target A was not observed in any of the 10 replicated experiments. Results indicated a significant increase in RNAi penetrance was achieved by strategically combining dsRNAs to multiple target genes associated with the same or interacting pathway, and avoidance of targets with predicted apparent compensatory effects.