We reared the resistant Heliothis virescens larvae collected from Hebert, Louisiana in 1990 for five generations without exposure to insecticides and found a significant decline in resistance to Larvin^®. However, removing the insecticide selection pressure for five generations did not alter the high level of knockdown and metabolic resistance to Sherpa^®. These results indicate that the mechanism responsible for resistance to Larvin^® is not as stable as the one causing metabolic and knockdown resistance to Sherpa^®.

Subjecting another sample of the resistant larvae to the selection pressure of Larvin^® for five generations did not increase resistance to this compound and had no significant impact on the high level of resistance to Sherpa^®.

The results of contact toxicity studies suggest that resistant larvae are able to metabolize and/or excrete Larvin^® better than susceptible larvae. Larvin^® was almost equitoxic to the acetylcholinesterase enzymes separated front the heads of susceptible or resistant larvae.