P450 MONOOXYGENASES ARE AN IMPORTANT MECHANISM OF PERMETHRIN RESISTANCE IN CULEX-QUINQUEFASCIATUS SAY LARVAE

Culex quinquefasciatus Say from Saudi Arabia (JPal-per) showed high le vels of resistance (2,500-fold) to permethrin. A major contribution of cytochrome P450 monooxygenases as a mechanism of resistance was sugge sted by the large synergistic effects of oxidase inhibitors such as 2- propynyl 2,3,6-trichlorophenyl ether (PTPE) and piperonyl butoxide (PB O) on the toxicity of permethrin in the resistant strain, Contents of cytochrome P450 and b(5) were about 2.5 times higher in the JPal-per s train than those in the susceptible strain, P450 monooxygenase in the microsomes of gut and other parts of the body metabolized permethrin t o 4'-HO-permethrin and other metabolites, Degradation of permethrin by microsomal P450 enzymes was much greater in the resistant JPal-per st rain and was inhibited by PBO and PTPE, In addition to a kdr type mech anism which seems to work in the larvae, cytochrome P450 monooxygenase is clearly shown to play an important role as a mechanism of permethr in resistance in JPal-per strain larvae. (C) 1998 Wiley-Liss, Inc.