RNA interference in <i>Bactericera cockerelli</i> (Hemiptera: Triozidae) by silencing single or stacked genes encoding a proton pump essential to global biological processes

"Candidatus" Liberibacter spp. infect crop plants and the psyllid vector, and at least 2 species have been shown to be susceptible to RNAi. Here, the knockdown efficacy was analyzed of 4 genes essential for insect physiological processes, vacuolar ATPase (V-ATPase) subunit genes A, B, D, and E, for potential biopesticide activity against the potato psyllid, Bactericera cockerelli Šulc (Hemiptera: Triozidae). Adults and third instar psyllids were given a 48-h ingestion-access period (IAP) on either single or stacked dsRNAs to compare knockdown effects. While adults showed no significant mortality, 10-d post IAP on the individual dsRNAs, mortality was significantly greater post-IAP on the stacked dsRNAs compared to negative controls. Oviposition of dsRNA-treated females was reduced by 50% to 70%, however, there was no significant difference between the single and stacked dsRNA treatments. Adult and third instar psyllids exhibited 58% and 45% mortality, respectively, post-IAP on the 4 stacked dsRNAs. In contrast, only third instar nymphs showed significant mortality after individual dsRNAs targeting V-ATPase subunits, at 42% for subunit A and 35% for subunits D and E. In general, gene silencing was more robust in potato psyllid nymphs compared to the adults. Although gene knockdown was moderately lower following an IAP on dsRNAs delivered singly, IAP on stacked dsRNAs resulted in equal or greater mortality in both psyllid life stages. These findings highlight the potential for delivering multiple dsRNAs to suppress genes involved in essential cellular processes and enhance RNAi efficacy in insects.