Characterization of esterases associated with profenofos resistance in the tobacco budworm, Heliothis virescens (F.).

The utility of microplate and electrophoretic assays for detection of biochemical and physiological mechanisms underlying resistance to profenofos in the tobacco budworm, Heliothis virescens (F.), was assessed. Esterase (EST) activities were significantly higher in profenofos-resistant than -susceptible larvae, and activities were highly correlated (r(2) = 0.87) with resistance to profenofos. Both qualitative and quantitative variation was observed in electrophoretic gels stained with alpha- and beta-naphthyl acetates. Staining of ESTs was more intense with resistant larvae than those from a susceptible strain. In addition, a band (designated A') was expressed in larvae from profenofos-resistant strains, but not in larvae from an insecticide-susceptible strain. The frequency of expression of A' increased following selection with profenofos and was detected in 100% of the individuals from a profenofos-selected strain. The appearance of this band coincided with the decreased expression of a second band (designated A). A similar pattern (overexpression of A' and underexpression of A) also was observed in larvae from field-collected strains. Finally, reduction in the activity or the sensitivity of acetylcholinesterase to inhibition by chlorpyrifos oxon was observed in laboratory-selected and field-collected larvae that expressed resistance to profenofos. These results suggest that microplate and electrophoretic assays can be utilized as complementary tools for detecting and monitoring profenofos resistance in H. virescens.