Field and laboratory evaluations of transgenic cottons expressing one or two Bacillus thuringiensis var. kurstaki Berliner proteins for management of noctuid (Lepidoptera) pests

Field studies were conducted from 1999 to 2001 to evaluate the efficacy of the transgenic cotton, Gossypium hirsutum (L.), genotype, Bollgard H (Monsanto 15985), which expresses two Bacillus thuringiensis Berliner (Bt) proteins (CrylAc + Cry2Ab) that are active against lepidopterous pests. Bollgard H was compared with Bollgard (DP50B), which expresses only one Bt protein (CrylAc), and, in all tests, the conventional variety, DP50, was used as a non-Bt control. Larval populations of the bollworm, Helicoverpa zea (Boddie), and the soybean looper, Pseudoplusia includens (Walker), were significantly lower in Bollgard II than in Bollgard and conventional cotton, and the proportion of fruit damaged by H. zea was also lower. Fall armyworm, Spodoptera frugiperda (J. E. Smith), populations were lower in Bollgard H than in Bollgard, although not significantly. Field tests were supplemented with laboratory bioassays in 2001 to compare mortality of S. frugiperda, and beet armyworms, Spodoptera exigua (Hubner), feeding on these genotypes. Mortality of both species was significantly greater on Bollgard H plant material than on either Bollgard or conventional cotton. This study demonstrated that the dual-toxin Bollgard H genotype is highly effective against lepidopterous pests that are not adequately controlled by the current single-toxin Bollgard varieties. If toxin expression in future Bollgard H varieties remains consistent with that of Monsanto 15985, supplemental insecticides will be reduced, and may be eliminated for lepidopterous pests in South Carolina.