Cytochrome P450-mediated N-demethylation activity and induction in insecticide-resistant and susceptible western corn rootworm populations (Coleoptera : Chrysomelidae)

Elevated cytochrome P450 monooxygenase-based metabolism is associated with carbaryl and methyl parathion resistance in western corn rootworm (Diabroti ca virgifera virgifera LeConte)) populations in the state of Ncbraska. The objectives of this study were to identify potential differences in cytochro me P450 in resistant and susceptible rootworm populations using the model s ubstrate 4-chloro-N-methyl aniline (4-CNMA and heme staining of microsomal proteins separated by SDS-PACE. Baseline N-demethylation activity correspon ded well with resistance to the N-methyl-substituted insecticide carbaryl a mong study populutions. N-demethylation of 4-CNMA is NADPH dependent and in hibited by the cytochrome P450 inhibitor piperonyl butoxide, which confirms that the reaction is catalyzed by cytochrome P450. Following ingestion of the cytochrome P450 inducer pentamethyl benzene, N-demethylation activity i ncreased signifi- cantly in the more susceptible rootworm populations. Hemo protein staining of microsomal proteins separated by SDS-PAGE identified tw o groups of potential P450 isoforms in the 45- to 53-kDa range which appear more highly expressed (a) in resistant populations and (b) following PMB i nduction. (C) 2000 Academic Press.