Selection at the diazinon resistance locus in overwintering populations of Lucilia cuprina (the Australian sheep blowfly).

In excess of 70 per cent mortality is observed during the overwintering stage of the life cycle of L. cuprina. The mortality is selective in the absence of a fitness modifier; phenotypes resistant to diazinon overwinter less successfully than susceptibles. In the presence of the modifier the overwintering success of all genotypes is similar. The effect is dominant. Laboratory and field experiments show that selection against resistant individuals increases with time in arrested development. The relevance of these results to the evolution of insecticide resistance is discussed.