The Drosophila resistance gene, named Cyp6g1, is part of a large family of genes called the Cytochrome P450 genes that are found in many species, including humans.
Previous studies have implicated some members of this P450 family in pesticide resistance. However the function of the majority of the 90 Drosophila P450 genes is unknown.
CESAR is now analysing these genes to determine their function in Drosophila and in the pest insects, the cotton bollworm (Helicoverpa armigera) and the sheep blowfly responsible for flystrike (Lucilia cuprina).
"Our capacity to control pests would be significantly improved if we understood the defence mechanisms controlled by these genes," says Batterham.
In the Drosophila, Cyp6g1 confers resistance by producing up to 100 times more than the normal level of protein that breaks down DDT and other pesticides. Given the number of P450 genes present in Drosophila, it was unexpected that a single version of one gene could be associated with such widespread resistance, and that this resistance also applied to a wide range of compounds that bear no resemblance to each other in structure or mode of function. These compounds include organochlorines, organophosphorous, carbamate and insect growth regulator insecticides.
"Our research, so far, does not unequivocally demonstrate that Cyp6g1 is the sole culprit for this resistance, but the current evidence leaves little doubt that about its central role," says Batterham.
Species will normally lose mutations that protected it against a particular pesticide once that pesticide ceases to be used. This is because, in the absence of the pesticide, the mutation suddenly confers a disadvantage. In this case, the Drosophila has maintained the resistance gene and is still 'fit'. That is, the mutation does not confer any disadvantage, so it persists in the population.
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Contact: Jason Major
jmajor@unimelb.edu.au
61-3-8344-0181
University of Melbourne
26-Sep-2002