INHERITANCE, STABILITY, AND REVERSION OF INSECTICIDE RESISTANCE IN TOBACCO BUDWORM (LEPIDOPTERA, NOCTUIDAE) FIELD POPULATIONS

Responses of an insecticide-resistant strain of tobacco budworm, Helio this virescens (F.), were examined in the laboratory by using three di fferent insecticide bioassays during continuous culture without insect icide selection pressure. Resistance to the pyrethroid cypermethrin an d the carbamate thiodicarb did not revert to susceptiblity until 12 ge nerations in culture- Previous studies indicated that reversion tends to occur much more rapidly in this species. The temporal sequence of r esistance in field populations of H. virescens collected in 1990 and 1 991 was determined by using a spray-chamber bioassay. Resistance to se veral classes of insecticides varied and was often high before and dur ing the cotton growing season. Inheritance of resistance to insecticic les in H. virescens was examined with two different bioassays. Results of bioassays with third instars and adults were similar. Resistance i n reciprocal crosses was intermediate to that of the parent susceptibI e and resistant strains. Codominant mechanisms of resistance to the py rethroid and carbamate insecticides are suggested from the data.