Properties of a cytochrome P-450-dependent epoxidase in aldrin-resistant western corn rootworms, Diabrotica virgifera virgifera LeConte

A highly active cytochrome P-450-dependent aldrin epoxidase has been found in cell-free midgut fractions from western corn rootworms (Coleoptera: Chrysomelidae) resistant to cyclodiene insecticides. Optimal in vitro assay conditions for the epoxidase are pH 7.4, 31°C, 10 min of incubation, and a substrate concentration of 0.05 mM. The enzyme is concentrated in the microsomal fraction of midgut tissue, NADPH dependent, and susceptible to established cytochrome P-450 inhibitors such as piperonyl butoxide and 1-phenylimidazole. In rootworm adults, most enzyme activity occurs in gut tissue with much lower amounts in fat body and the remaining carcass. Whole body activity of the enzyme changes markedly throughout development, and is at least 24 times and 6 times more active in adults than in pupae and larvae, respectively. The possible roles of the epoxidase in dietary relationships and aldrin resistance of the rootworms are discussed.