Efficacy of Bollgard (DP50B) and Bollgard II (DP50BX) cottons that express either one or two Bacillus thuringiensis Berliner proteins, respectively, along with the conventional sister genotype (DP50), was determined for a feral strain of bollworm, Helicoverpa zea (Boddie), and a Cry1Ac-selected bollworm strain in 1999. In 2000, a greenhouse study was designed to compare the efficacy of three transgenic cottons expressing either the Cry1Ac endotoxin alone (DP50B), the Cry2Ab endotoxin alone (DP50X), or both the CrylAc and Cry2Ab endotoxins (DP50BX) against a feral and a Cry1Ac-selected bollworm strain. Results from the 1999 greenhouse study evaluating both a feral and a Cry1Ac-selected bollworm strain demonstrated that when averaged across bollworm strains, the Bollgard II genotype significantly reduced larval survival and fruit penetration by bollworm compared to the Bollgard variety. Also, the Cry1Ac-selected bollworm strain displayed increased larval survival, superficial fruit damage, and fruit penetration compared to the feral strain when averaged across genotypes. In the 2000 study, the Bollgard II genotype significantly reduced fruit penetration by bollworm below that of the Bollgard variety when averaged across strains; however, the single Cry2Ab-producing genotype performed similarly to both Bollgard and Bollgard II with respect to fruit penetration. The Cry1Ac-selected bollworm strain exhibited significantly greater larval survival and superficial fruit damage on the Bollgard variety compared to the feral strain, but no differences among larval strains were evident for other genotypes. Also, when averaged across genotypes, the Cry1Ac-selected bollworm strain penetrated a higher proportion of cotton fruit compared to the feral strain. These results suggest that commercialization of Bollgard II cottons would significantly reduce bollworm survival and damage compared to that experienced by current Bollgard varieties. Bollgard II plantings also should have a positive impact on Bt resistance management of bollworm.
Estimated Frequency of Nonrecessive Bt Resistance Genes in Bollworm, Helicoverpa zea (Boddie) (Lepidoptera: Noctuidae) in Eastern North Carolina
