Single pairs (81) of the tobacco budworm were established from different genotypes in 1983 and 1989-1990. Seventy of these single pairs were for two strains or crosses of the strains for two generations following a selection regime with permethrin. Progeny of 11 single pairs, collected as eggs or larvae from fields across the Lower Rio Grande Valley (LRGV), were treated with cypermethrin. LD_´s of 11, 15, 55 and all 81 single pairs consistently followed a continuum. With one exception there was no significant difference in LD_´s which were adjacent to another and ranked from the lowest to the greatest. The most resistant single pair was the reference strain. The most susceptible single pair was a reference x field cross. A difference of 8,105 was determined for both LD_´s. LD_´s of field collected strains were intermediate to LD_´s of the strains and crosses of strains. A resistance threshold of 0.2 µg pyrethroid/larva is offered.