The synthetic pyrethroids continue to provide effective control of most major cotton pests in the western U.S. However, there are isolated areas where field control of the pink bollworm has been difficult to achieve and laboratory results have verified resistance levels of up to 20-fold when compared with a susceptible laboratory strain. The relative susceptibility of different geographic populations of pink bollworm in the West is directly correlated with insecticide - use patterns in the areas.

The other major pest for which the synthetic pyrethroids are used is the tobacco budworm. Populations of this pest have been fairly light during the past several years and no field failures in control have been noted, Monitoring for resistance at the end of each growing season in Arizona has shown no change in the tolerance level of this pest to the pyrethroids. Laboratory studies have shown however, that under severe selection pressure high levels of resistance can be developed.