Response of a mutant strain and crosses of the mutant and laboratory-reared insecticide susceptible "wild" strain of the tobacco budworm, Heliothis virescens (F.), was determined. We wanted to determine if either one or both sexes of mutant could be eliminated by selection regime. The mutant was lethal in homozygous condition and the allele was dominant for black-bodied melanic character. Mutation was maintained in heterozygous status with the "wild" strain. LD₂₀, LD₅₀, and LD₈₀ of methyl parathion to larvae of the mutant and crosses of mutant and the "wild" strain were determined. In the first generation the LD₅₀ of methyl parathion for the heterozygous black-bodied strain was significantly and 22-fold greater than that of "wild" strain. LD₅₀ of insecticide to larvae of reciprocal crosses indicated incomplete dominance or co-dominance of alleles, but no sex linkage. In subsequent three generations percentage black-bodied females and males of selected strain and crosses were compared to same percentages of non-selected strain and crosses. When larvae of both reciprocal crosses were treated with LD₂₀ and LD₅₀ in generation three percentage black-bodied females was reduced 60% and 80%, respectively, compared to the untreated population of the same crosses. When larvae of both reciprocal crosses were treated with LD₈₀ in generation three all black-body males and females were killed. Both sexes of black-bodied strain treated with LD₅₀ and LD₈₀ were reduced 38% and 69%, respectively, in generation three compared to the untreated of the strain. Frequency of black-bodied males of black-bodied strain was reduced 0 to 38% with LD₂₀, LD₅₀ and LD₈₀ in that same generation.