Susceptibility of southern and western corn rootworms adult and larva to v-ATPase-A and Snf7 dsRNAs

RNA interference (RNAi) functions by silencing the expression of essential genes and has been considered to be a promising pest control corn rootworms, given its high specificity for the target pest. This study was conducted to compare the susceptibility of adults and larvae of southern (SCR) and western corn rootworm (WCR) to v-ATPase-A and Snf7 dsRNAs. For the bioassays, 48 well plates were used and six dsRNA concentrations plus control were tested. Both adults and larvae were exposed using similar exposure methods and concentrations. One adult was placed in each well containing two artificial diet pellets (4 mm diameter, 2 mm height) each overlaid with 3 µl of dsRNA solution. Two SCR neonates were placed in each well using the same conditions as adults, or one WCR neonate was placed in well containing 200 µl of artificial diet overlaid with 40 µl of dsRNA. Diet plates were changed every other day, except for WCR larva bioassays. Mortality was recorded after 12 days for larvae and 14 days for adults. The LC₅₀s calculated indicated that adults were less susceptible for both v-ATPase-A and Snf7 dsRNAs (33.3 and 13.2 for SCR, 657.3 and 60.2 ng/cm² for WCR, respectively), as compared to neonates (8.0 and 2.6 for SCR, 1.70 and 1.54 ng/cm² for WCR, respectively). These results show that although adults are more tolerant than larvae, dsRNAs potentially affect rootworm adults, and because corn they feed on corn silk and pollen which may express significant levels of dsRNA, there may be substantial impact on rootworm adults.