Tissue distribution of microsomal cytochrome P-450 monooxygenases and their inducibility by phenobarbital in the insecticide resistant LPR strain of house fly, Musca domestica L.

Cytochrome P-450s, cytochrome b5, P-450 reductase, and four P-450 monooxygenase activities were abundant in proximal intestine (PI), Malpighian tubules (MT), and fat bodies (FB) in the insecticide resistant (LPR) strain of house fly. Insecticide resistance in LPR flies was associated with increases in P-450 monooxygenase activities in nearly all of these tissues relative to an insecticide susceptible strain. Cytochrome P-450lpr was present in all tissues and at higher levels in LPR than in susceptible flies suggesting that the role of P-450lpr in monooxygenase-mediated insecticide resistance is not due to its higher levels in a single tissue. However, it appears that fat bodies may have a major role in resistance due to their relatively large size and the abundance of P-450lpr in this tissue. Total cytochrome P-450s, cytochrome P-450lpr and P-450 monooxygenase activities were generally refractory to phenobarbital (PB) induction in LPR. This contrasts with a previous report in susceptible house flies showing that P-450 monooxygenases were induced by PB. It appears that total P-450s, cytochrome P-450lpr and monooxygenase activities were expressed at constitutive high levels in several tissues of LPR house flies.