The tobacco budworm sterile backcross (TBW-BC) was developed before widespread use of pyrethroid insecticides and would potentially be at a disadvantage if released into populations that have been exposed to pyrethroids. Our estimated LD(50) for TBW-BC was about 7,800 times lower than LD(50) values for wild populations of TBW from fields in Mississippi where control failures were reported. We genetically improved TBW-BC by repeatedly backcrossing TBW-BC females to resistant TBW (R-TBW) males and applying selection pressure for resistance to cypermethrin. We increased resistance in our strain of TBW-BC by a factor of 17 million. Our genetically improved resistant TBW-BC (R-TBW-BC) should survive field applications that would kill most wild TBW, including wild TBW from populations where control failures occurred. Our data support the hypothesis that resistance to cypermethrin has a complex genetic basis. Release of R-TBW-BC can not change resistance levels in wild,fertile TBW because introduced resistance alleles would be carried only by individuals that carry the sterility trait. Enhanced resistance of sterile insects would be diluted by outcrossing to wild TBW but could last 3 generations. Use of R-TBW-BC could reduce the cost of TBW-BC release programs.