Abstract
Mechanisms of resistance to oregano phosphorus, carbamate, and cyclodicne insecticides were investigated in adult tobacco bud worms, Heliothis virescens (F.). Comparative studies on profenofos toxicity with or without synergists failed to demonstrate that enhanced metabolism was a major mechanism of resistance to this insecticide. Percentage of survival of several partially resistant tobacco bud worm populations at diagnostic concentrations of profenofos and methomyl was highly correlated, suggesting the same mechanism confers resistance to these insecticides. Differences between resistant and susceptible tobacco bud worms in inhibition of acetylcholinesterase by tetrachlorvinfos (7-fold), methomyl (7.6-fold), and carbaryl (4-fold) indicated that target-site insensitivity was a major mechanism of resistance to oregano phosphorus and carbamate insecticides. The high correlation of survival of field tobacco bud worm populations exposed to diagnostic concentrations of endosulfan and dieldrin suggested that the same mechanism (target-site) conferred resistance to both insecticides. Measurements of penetration of radiolabeled profenofos indicated that a decrease in insecticide uptake may be an additional resistance factor in the tobacco bud worm. Because target-site resistance to insecticides is expressed in both larvae and adults, monitoring for resistance in adults is appropriate with these insecticides.
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