Molecular Mechanisms of Cytochrome P450 Monooxygenase-Mediated Pyrethroid Resistance in the House Fly, Musca domestica (L.)
Type of DegreeDissertation
Entomology and Plant Pathology
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A wild-type pyrethroid resistant house fly strain, ALHF, was collected from a poultry farm in Alabama after control failure with permethrin (a pyrethroid insecticide). It was further selected with permethrin for 6 generations in the laboratory and obtained a very high level of resistance to permethrin. When ALHF was treated with piperonyl butoxide (PBO), an inhibitor of cytochrome P450s, the permethrin resistance in ALHF was reduced dramatically from 1,800- to 100-fold, indicating that P450-mediated detoxification is one of the important mechanisms involved in permethrin resistance in ALHF. In order to characterize P450 genes that are involved in the permethrin resistance of ALHF, I isolated 19 P450 cDNA fragments from ALHF using PCR strategies. This preliminary study provided a framework for conducting the whole project to investigate the importance of P450 genes in permethrin resistance in ALHF. To characterize the functional importance of these P450 genes in resistance, I examined the expression profiles of these 19 P450 genes between resistant and susceptible house flies. Six of them were constitutively overexpressed in ALHF compared with a susceptible strain, CS, suggesting that multiple genes are involved in the increased detoxification of permethrin in ALHF. To test my hypothesis that insecticide resistant insects may be uniquely resistant to insecticides due to an ability of up-regulation of P450s when challenged with insecticides, I examined P450 gene expression in response to insecticide stimulation. Among these 6 overexpressed P450 genes, 3 of them were further induced by the permethrin stimulation in ALHF, indicating that these 3 genes may play an important role in resistance. Tissue specific analysis indicated that these constitutively expressed and permethrin induced P450 genes were overexpressed in the abdomen tissue, in which the primary detoxification organs of insects are located. This finding strongly suggests the importance of these genes in increased insecticide detoxification in ALHF. Genetic linkage analyses were further conducted to determine the causal link between these constitutively expressed and permethrin induced P450 genes and insecticide resistance. Five of these genes were mapped on autosome 5, which is correlated with the linkage of resistance in ALHF. Taken together, my research provides the first evidence that multiple P450 genes are up-regulated in insecticide resistant house flies through both constitutively overexpression and induction mechanisms, which increase overall expression levels of the P450 genes and the level of detoxification of insecticides in resistant house flies.