Larvae of a susceptible strain and a resistant strain of tobacco budworm, Heliothis virescens (F.), were exposed to residues on leaf surfaces of bifenthrin and fenpropathrin and combinations of these two pyrethroids with acephate through five generations. Slight increases in survival were noted for some treatments, but none were accompanied by changes in LD(50) values (ug/larva) of cypermethrin. Survival of the resistant strain treated with fenpropathrin + acephate decreased 43% (mortality increased) in generation 5 as compared to generation 1; and survival in the fenpropathrin treatment decreased 28% in generation 4 as compared to generation 1. LD(50) values of cypermethrin for the fenpropathrin + acephate treatment supported the increased susceptibility of this colony. Selection with the insecticide combinations within colonies created by crossing resistant and susceptible strains showed only small increases in survival through three generations, with no increase in LD(50) values of cypermethrin. Selection of the susceptible female x resistant male colony with bifenthrin + acephate showed a decrease in survival, which was accompanied by a decreased LD(50) value of cypermethrin as compared to the check. The data show the use of both pyrethroids with acephate provides better control of pyrethroid resistant TBW while allowing for a population shift toward susceptibility.