PREDICTING INSECTICIDE RESISTANCE - MUTAGENESIS, SELECTION AND RESPONSE

Strategies to manage resistance to a particular insecticide have usual ly been devised after resistance has evolved. If it were possible to p redict likely resistance mechanisms to novel insecticides before they evolved in the field, it might be feasible to have programmes that man age susceptibility. With this approach in mind, single-gene variants o f the Australian sheep blowfly, Lucilia cuprina, resistant to dieldrin , diazinon and malathion, were selected in the laboratory after mutage nesis of susceptible strains. The genetic and molecular bases of resis tance in these variants were identical to those that had previously ev olved in natural populations. Given this predictive capacity for known resistances, the approach was extended to anticipate possible mechani sms of resistance to cyromazine, an insecticide to which L. cuprina po pulations remain susceptible after almost 20 years of exposure. Analys is of the laboratory-generated resistant variants provides an explanat ion for this observation. The variants show low levels of resistance a nd a selective advantage over susceptibles for only a limited concentr ation range. These results are discussed in the context of the choice of insecticides for control purposes and of delivery strategies to min imize the evolution of resistance.