ABSTRACT
Results from 1990 confirm the utility of the adult vial test to accurately measure resistance trends in Heliothis virescens. Resistance levels measured late season indicated that Mississippi, Arkansas, Oklahoma and North Alabama experienced only moderate levels of resistance to pyrethroids, possibly associated with the generally low population pressures in those states. Resistance levels in Texas and Louisiana remained high in 1990, and where high populations were persistent mid to late season and pyrethroid use was frequent, field failures from pyrethroid applications occurred in the later part of the season (generally after Aug. 1). High levels of susceptibility were determined in 1990 for H. virescens in Georgia and for Helicoverpa zea in all states monitored. Currently, target site insensitivity appears to be the major resistance mechanism in field collected strains of H. virescens. In at least one general area where H. virescens populations were persistently high from -mid- to late season and both pyrethroid and alternate class chemicals use was frequent, laboratory and field results indicated that the carbamate and organophosphate alternatives showed definitive signs of decreased efficacy.
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