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Mechanism of Resistance and Cross Resistance in a Laboratory, Spinosad-Selected Strain of the Tobacco Budworm and Resistance in Laboratory-Selected Cotton Bollworms

Hugh P. Young, Woodward D. Bailey, R. Michael Roe, Takao Iwasa, Thomas C. Sparks, Gary D. Thompson and Gerald B. Watson


 
ABSTRACT

A laboratory strain of the tobacco budworm, Heliothis virescens, was selected for high levels of resistance to spinosad, the active ingredient in Tracer®. Resistance relative to the parental strain was estimated at 1,068, 314-, and >163-fold by topical, diet, and injected routes of exposure, respectively. Experiments to determine the mechanism of resistance have shown that reduced or delayed penetration of the cuticle, metabolism, or excretion are not significantly different in the resistant strain. Neurophysiological preparations show 1.9- and 1.8-fold reductions of spinosad A-induced inward currents in the resistant strain when spinosad A is applied at in vitro concentrations of 10 -8 and 10 -7 M, respectively, suggesting that the selected strain may have decreased neural sensitivity to spinosad A. Reduced inward currents in the resistant strain may or may not be related to the mode of action of the spinosyns. In a further effort to elucidate the mechanism of resistance several pesticides were bioassayed for cross resistance. No cross resistance was found based on comparisons of the LC50s to permethrin, profenofos, indoxacarb, emamectin benzoate, or acetamiprid, suggesting that the mechanism of resistance in the laboratory selected strain is unique as is the mode of action of the spinosyns. Finally, a laboratory strain of the cotton bollworm, Helicoverpa zea, was selected with spinosad (Tracer®) in artificial diet for 6 generations, resulting in a strain that was 5-fold less susceptible to topically applied technical spinosad.





Reprinted from Proceedings of the 2001 Beltwide Cotton Conferences pp. 1167 - 1170
©National Cotton Council, Memphis TN

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Document last modified XXXXXX, XXX XX 2001