Reduction of malathion resistance in caged almond moth, Cadra cautella (Walker) (Lepidoptera: Pyralidae), populations by the introduction of susceptible males

Caged populations of the almond moth, Cadra cautella (Walker), that were resistant to malathion were subjected to the release of susceptible males at various ratios. The effects of introducing malathion susceptible males into the population were monitored by determining the LD₅₀s for 21 day old larvae from each population. F₁ hybrid larvae were found to be intermediate in resistance between larvae from the parental strains, and resistance appeared to be inherited in a codominant fashion. Populations which received only a single release of males were, in general, more malathion susceptible the greater the introduction ratio (except at a ratio of 20:1). Larger populations subjected to repeated introductions of susceptible males showed a clear trend of decreasing larval survival after malathion treatment with increasing release ratio (including the 20:1 ratio). These results indicated that desirable alleles, such as those for insecticide susceptibility, can be introduced into established populations, and that this line of research should be given more emphasis in preventing development of resistance or in ameliorating established resistance.