D3227: Increasing RNAi penetrance in an RNAi recalcitrant pest Bactericera cockerelli by targeting a process or pathway instead of a single gene

Environmental RNAi has emerged as a potentially lucrative alternative to chemical pesticides for controlling insect plant pests and/or vectors of plant pathogens and therefore can be exploited to control the psyllid vectors, the causal agents of citrus greening and zebra chip of potato disease, respectively. Psyllids respond moderately to RNAi, with sub-optimal gene knockdown, making such low RNAi penetrance of a single gene potentially inadequate to produce the anticipated, detrimental phenotype. In this study, an alternative approach was evaluated in which multiple genes from a single biological process, the vacuolar ATPase complex, were subject to knockdown. The hypothesis was that silencing of multiple genes from the same process might achieve additive phenotype. Results indicated that potato psyllid adults required a longer dsRNA ingestion-access period (IAP) than the third instar to achieve comparable knockdown and mortality. Ingestion-access to the ‘stacked’ dsRNAs resulted in 23-28% and 16-28% knockdown in immature and adult psyllids, respectively, compared to ingestion of single dsRNAs, which resulted in 42-58% and 23-41% knockdown in the respective instars. The immature and adults showed 52% and 46% mortality, respectively. Post-IAP of any single dsRNA exhibited no mortality in adults. The phenotypes associated with stacked compared to single dsRNA ingestion-access indicate a positive, additive effect of RNAi. Co-delivery of groups of dsRNAs targeting genes essential for a crucial biochemical process demonstrates the possibilities for achieving psyllid control when knockdown targets are integral to a global process or a pathway, instead of restricting targets to a single gene.