Studies were conducted to assess the insecticidal activity of thiodicarb and several other insecticides against susceptible and resistant strains of Spodoptera frugipercia (J.E. Smith) and Heliothis virescens (Fabricious). No resistance or cross-resistance was detected against thiodicarb. Also, subjecting susceptible and a synthetic pyrethroid resistant strains of H. virescens to the selection pressure of thiodicarb failed to induce any resistance to this insecticide. The results of this study suggest that thiodicarb will be a useful component of any resistance management program designed for H. virescens control.