Evaluation of B. T. Cotton Deployment Strategies and Efficacy against Pink Bollworm in Arizona

A multi- agency team in Arizona in 1997 evaluated B.t. cotton deployment strategies in a large field trial; conducted statewide monitoring of pink bollworm (PBW) susceptibility to the Cry1Ac endotoxin, and established a Rapid Response Team that investigated claims of unacceptable performance of B.t. cotton. Though needing further evaluation, in-field refuges of one row of non-B.t. cotton for each five rows of B.t. cotton showed promise as an alternative to the current recommendation of external refuges for planting B.t. cotton. Preliminary results of statewide monitoring showed that four field populations were more susceptible to Cry1Ac than were two reference susceptible laboratory strains. A strain of PBW previously reported to be resistant to CrylAc was confirmed to be significantly less susceptible to this toxin than were the two susceptible laboratory strains or the four field populations tested. The Rapid Response Team, based at the Arizona Cotton Growers Association, investigated nine reports of unusual larval survivorship in B.t. cotton. Only one of these, which has been placed in culture, was confirmed to have resulted in substantial numbers of large larvae surviving in bolls of putatively B.t. cotton. Further investigations of this population and the plants from which it was derived are underway.