Performance of Feral and Cry1Ac-Selected Helicoverpa zea (Lepidoptera: Noctuidae) Strains on Transgenic Cottons Expressing One or Two Bacillus thuringiensis ssp. kurstaki Proteins Under Greenhouse Conditions

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 penetra...