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 we re resistant to malathion were subjected to the release of susceptible males at various ratios. The effects of introducing malathion suscept ible males into the population were monitored by determining the LD50s for 21 day old larvae from each population. F1 hybrid larvae were fou nd to be intermediate in resistance between larvae from the parental s trains, and resistance appeared to be inherited in a codominant fashio n. 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 rat io (including the 20:1 ratio). These results indicated that desirable alleles, such as those for insecticide susceptibility, can be introduc ed into established populations, and that this line of research should be given more emphasis in preventing development of resistance or in ameliorating established resistance.