Rhone-Poulenc Ag. Company initiated a program to monitor the insecticidal activity of LARVIN^® brand thiodicarb against susceptible and synthetic pyrethroid resistant populations of Heliothis virescens larvae. Samples of H. virescens eggs were collected from two areas in Louisiana and Texas, where resistance to synthetic pyrethroids exists, and in North Carolina where H. virescens are still susceptible to these insecticides.

Our short exposure results showed no resistance exists against LARVIN^®; however, the Texas and Louisiana populations expressed 14 and 11 fold resistance to Sherpa^® brand Cypermethrin, respectively. Extending the exposure time caused significant improvement in the toxicity of these two insecticides to the three populations. A comparison between the 1989 and 1986 data demonstrated that no major shift has occurred in the toxicity of LARVIN^® to susceptible and synthetic pyrethroid resistant populations of H. virescens larvae.