Sub-lethal effects of v-ATPase-A and Snf7 dsRNAs on adult emergence, head capsule width, and dry weight in southern corn rootworm

Southern corn rootworm (SCR), Diabrotica undecimpunctata howardi Barber, is part of the rootworm complex that causes significant damage to corn in the US Corn Belt. RNA interference (RNAi) has been successfully studied in corn rootworm to silence lethal genes. The objective of this study was to evaluate the effect of sublethal exposure to v-ATPase and Snf7 dsRNAs on SCR adult emergence, head capsule width, and dry weight, after neonates’ exposure to LC₅₀s of v-ATPase-A and Snf7 dsRNAs. Neonates were transferred to untreated SCR larval artificial diet or overlaid with LC₅₀ of v-ATPase-A and Snf7 dsRNA/cm² and let fed for three days. Two neonates were transferred to each 50 ml Falcon tubes containing corn plants, in 50 tubes per treatment. The plants were incubated in a chamber at 25^oC and 80% RH until adults emerged. The total number of adults emerged was recorded per treatment and afterwards they were frozen at -20^oC to have head capsule and dry weight measured. Significantly fewer adults emerged from the RNAi treatments. Significant differences were observed between control and RNA treatment on adult head capsule width only for Snf7 dsRNA (control=1.14mm; RNAi= 1.03mm). These results suggest that there is an effect on larva development that substantially reduced adult emergence, but little fitness costs were observed on the adults that emerged after neonate exposure to dsRNA. There is indication that sub-lethal exposure to dsRNA as larvae might affect adult fitness, which should be considered in corn rootworm resistance management.