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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. |
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©National Cotton Council, Memphis TN |
Document last modified Sunday, Dec 6 1998
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