The ups and downs of insecticide resistance in peach-potato aphids (Myzus persicae) in the UK

The peach-potato aphid, Myzus persicae, provides an excellent demonstration of how genetic and ecological factors can interact to determine the dynamics of resistance and influence success of resistance management. The diversity of resistance mechanisms, based on both enhanced detoxification of insecticides and modifications to their target sites, that this species shows is now well understood at the genotypic, biochemical and molecular levels. These developments have yielded rapid and precise methods for detecting individual mechanisms, and for monitoring frequency changes in the presence and absence of insecticide selection. One factor influencing the prediction of these changes in the UK is the occurrence of prolonged periods of parthenogenesis in M. persicae, which results in non-random associations between particular resistance genes through the absence of genetic recombination. This has important implications for the rate at which resistance genes can accumulate in populations under selection by insecticides, and also for the speed at which they will decline when selection is relaxed. Although it is becoming apparent that resistance can be associated with various fitness costs, the relative contribution of individual resistance genes to these effects is still under investigation. However, the overall effect of the 'ups' and 'downs' of resistance in M, persicae, in the UK at least, has been to help maintain resistance phenotypes at manageable levels in most seasons. Unfortunately, the increasing genetic diversity of resistance in this species is progressively eroding the supply of effective insecticides. This in turn highlights the importance of ensuring sufficient chemical diversity to combat existing resistance mechanisms and to restrict the use of novel insecticides in order to sustain their effectiveness. (C) 2000 Elsevier Science Ltd. All rights reserved.