Expression of the Cytochrome P450 Gene CYP6A1 in the Housefly, Musca domestica

Cytochrome P450 enzymes play a major role in the metabolic resistance of insects to a variety of insecticides. A house fly P450 gene named CYP6A1 has a high level of constitutive expression in an insecticide-resistant strain (Rutgers) when compared to a susceptible strain (sbo), suggesting that it may be involved in metabolic resistance. We have compared the levels of CYP6A1 mRNA in fifteen strains of the house fly and show that expression of the CYP6A1 gene is not always elevated in strains (such as R-Fc) known to possess a metabolic resistance mechanism. The CYP6A1 gene is rapidly inducible by phenobarbital given in the drinking water of adult flies of both resistant and susceptible flies. Other chemicals such as DDT and dieldrin, known to induce P450 activities in house flies, did not induce CYP6A1 . These results show that metabolic resistance in the house fly must involve the regulation of expression of more than one P450 gene, and that the induction mechanism of P450 genes by xenobiotics, including insecticides, is selective for some P450 genes.