EXPRESSION OF PYRETHROID RESISTANCE IN ADULT HELICOVERPA-ARMIGERA (LEPIDOPTERA, NOCTUIDAE) AND SELECTIVE MORTALITY IN FIELD POPULATIONS

Pyrethroid resistance was examined in adult Helicoverpa armigera (Hubner) in both laboratory and field selected strains. A series of F1 and backcrosses was made between a susceptible and an isofemale resistant strain. Dose-responses were obtained using contact with a treated surface inside a scintillation vial. Inheritance of resistance was consistent with an incompletely dominant major gene and resistance factors were greater than 100-fold. Piperonyl butoxide synergized the effects of the synthetic pyrethroid, fenvalerate, 1000-fold and eliminated resistance entirely. Field trials examined the mortality of resistant and susceptible adults exposed to commercial application rates of synthetic pyrethroids. Adults were immobilized and placed in cotton fields prior to aerial applications of insecticide. Survival of resistant adults was significantly greater than susceptible ones in both trials. It was concluded that selective mortality in the adult life-stage contributes to the evolution of pyrethroid resistance.