Species diagnosis and Bacillus thuringiensis resistance monitoring of Heliothis virescens and Helicoverpa zea (Lepidoptera : noctuidae) field strainsfrom the southern United States using feeding disruption bioassays

Validation of a feeding disruption bioassay for the detection of resistance to Bacillus thuringiensis toxin and species identification is reported usi ng field strains of Heliothis virescens and Helicoverpa zea collected from the southern United States in 1998. Feeding disruption is measured by a lac k of fecal production from lan ne exposed to a diagnostic concentration of CryIAc in a blue indicator diet. The bioassay provided rapid (24 h) diagnos is of the species composition of larvae tested and also monitored for the p resence of resistance in H. virescens. An additional diagnostic concentrati on was established for monitoring resistance in II. tea. A probit model was used to compare the fecal production responses of bisect strains over a ra nge of CryIAc doses. Probability calculations, derived from our assay resul ts, are also presented to aid in the interpretation of future results from field trials. Integration of the feeding disruption bioassay into integrate d pest management programs is discussed.