Strains of the tobacco budworm, Heliothis virescens (F.), collected in Mississippi, Louisiana, and Texas were evaluated in bioassays to four classes of insecticides and a synergist. The temporal development of resistance showed few relationships of cross resistance among different classes of insecticides in Mississippi populations. High levels of resistance were found to cypermethrin and endosulfan in populations from Mississippi, Louisiana, and Texas. Significant level of resistance were also shown to carbamate and organophosphorus insecticides, although levels were generally not as high to these classes of insecticides. Tests using piperonyl butoxide showed synergism of cypermethrin and indicated metabolic resistance in several strains from Louisiana and Texas. Multiple resistance appears to be more wide-spread than previously reported and metabolic resistance to pyrethoids appears to be increasing.