The use of pyrethroid insecticides on Helicoverpa armigera susceptible crops has been restricted to only 6 weeks each summer since 1983, when resistance to pyrethroids was diagnosed. The long term management of resistance in H.armigera is based on the hypothesis that after pyrethroid spraying ceases, resistance will decrease, partly due to dilution by susceptible immigrants from unsprayed refugia. The long term liability of the strategy will be favoured by the refugia remaining uncontaminated by resistant H.armigera. Success of the strategy will be enhanced if resistant individuals have a higher overwintering mortality than susceptibles. Project DAN 36 L aimed to test these assumptions by determining the frequency of pyrethroid resistant H.armigera from areas where insecticide use was infrequent and to test the resistance status of the overwintering and spring populations of H.armigera . This project was a collaborative effort between researchers from NSW Agriculture & Fisheries and CSIRO Division of Entomology.