The responses of an insecticide-resistant strain of the tobacco budworm, Heliothis virescens (F.), were examined in the laboratory using two insecticide bioassays during continuous culture without insecticide selection pressure. Resistance to the pyrethroid cypermethrin and the carbamate thiodicarb did not revert to susceptiblity until 12 generations in culture. The temporal sequence of resistance in field-collected H. virescens in 1990 and 1991 was examined using a spray table bioassay. Resistance to four classes of insecticides was variable but present, often at high levels, prior to and during the cotton growing season. The inheritance of resistance in H. virescens to insecticides was examined using two bioassays. Bioassays were conducted on 3rd instars and adults, and results were similar for both life stages. Resistance in reciprocal crosses was intermediate to that of the parent susceptible and resistant strains. Codominant mechanisms of resistance to the pyrethroid and carbamate insecticides are suggested from the data.