BollgardJ and Bollgard IIJ cottons, along with the conventional sister line, were evaluated in field and greenhouse experiments with respect to efficacy against bollworm in North Carolina in 2000. Field studies were proposed to resolve the question of increased efficacy of Bollgard II over Bollgard on bollworm, as well as to determine survivorship parameters of bollworm on each cotton genotype. The impact of supplemental bollworm control on yield was evaluated at field sites. A greenhouse study was designed to determine the efficacy of three Bacillus thuringiensis Berliner
(B. t.) cotton genotypes on a field-collected bollworm strain and a Cry1Ac-tolerant bollworm strain that had been selected for tolerance to the Cry1Ac toxin in the laboratory for two generations. Results from field studies indicated that although DP50BX (Bollgard II) illustrated no significant effects on larval survival beyond that of DP50B (Bollgard), a significant reduction in the level of fruit damage sustained by DP50 and DP50B was observed for the stacked-gene line. Yield response to supplemental pyrethroid oversprays varied among test sites due to differing bollworm infestation levels and moderate levels of boll rot. Greenhouse study results suggested that DP50BX was equally effective in reducing numbers of both the Cry1Ac-tolerant and susceptible bollworm larvae, as well as surface-damaged and penetrated fruit below that of DP50B.