Preliminary results of selection for resistance to v-ATPase-A dsRNA in Diabrotica undecimpunctata howardi Barber

The diabroticite beetles from the genus Diabrotica (Coleoptera: Chrysomelidae) are the main corn pests in the US. The larvae feed on the roots causing damage to the plant structure. New control techniques have been explored such as plants expressing traits associated with RNA interference (RNAi). This research was conducted to select Southern Corn Rootworm (SCR) adults for resistance to V-ATPase-A dsRNA. A SCR colony was established from field collections in Nebraska. One week old adults were exposed to dsRNA on artificial diet three times (244.6 ng dsRNA/cm²) at four day intervals at the F2 generation. At F3, there was no exposure as fewer adults survived at F2 after exposure. Then at F4 and F5, the concentration of exposure was lowered to increase survival in order to perpetuate the colony. After exposure, mortality and fecundity from exposed and non-exposed cages were recorded twice a week, and egg hatch percentage was compared. Higher adult mortality was observed after exposure to RNAi relative to controls at each generation, with no changes in susceptibility detected. However, sublethal effects of exposure were observed at each generation. At F2, control cages produced 774 eggs/10 adults whereas RNAi cages produced only 83 eggs/10 adults. At F4, control cages produced 2,088 and RNAi cages, 631 eggs/10 adults. At F5, control cages produced 2,011 and RNAi females produced 1,042 eggs/10 adults. There was no significant difference in egg hatch percentage from exposed (61%) and non-exposed females (57.7%). These results may inform assessments of resistance risk for RNAi traits and provide insight in the mechanisms of resistance that might evolve.