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Examination of commercial Cry1Ac transgenic Bacillus thuringiensis Berliner (Bt) cotton varieties (Bollgard, Monsanto, St. Louis, MO) and an experimental Cry1Ac + Cry2Ab transgenic Bt cotton variety (Bollgard II, Monsanto) for lepidopteran field efficacy was conducted during the 2000 growing season. In addition, a commercially available (Envirologix, Portland, ME) quantification assay (ELISA) was used to measure and profile the expression levels of Cry proteins in two of these varieties 'DP50B, Bollgard'; 'DP50BII, Bollgard II' (Delta & Pine Land, Scott, MS). Populations of beet army worms, Spodoptera exigua (Hübner), and soybean loopers, Pseudoplusia includens (Walker), were significantly lower (P 0.05). Single and dual-toxin genotypes remained superior (P 0.05) impact on Cry1Ac expression in Bollgard II compared with Cry1Ac expression in Bollgard. Furthermore, throughout the season Cry2Ab was present at much higher levels in the plant compared with Cry1Ac for Bollgard II plants. Possible species-specific reasons for increased efficacy of Bollgard II over Bollgard are discussed.
Adamczyk et al. (2001) studied this question.