Cotton is one of the most important crops of southern Tamaulipas, Mexico. In the last two years the crop area reached 55,000 ha. The tobacco budworm (Heliothis virescens), cotton boll weevil (Anthonomus grandis), and lately the beet armyworm (Spodoptera exigua), are the most important pests of this area. Lately, a tendency of the tobacco budworm population towards resistance has been noticed, especially to pyrethroids.

In 1991 the level of resistance to permethrin was 1.9x and 2.7x in 1994. The levels for cypermethrin were 1.1x in 1991 and 8.4x in 1994. Deltamethrin levels were 3.8x and 8.6x respectively. The LD₅₀ for methyl parathion was lower than the susceptible strain. In the case of profenofos a lower value was observed between 1991 and 1994.