Toxicity to the cotton bollworm, Helicoverpa armigera, of some Cry1Ac toxins expressed in cotton in India

Bacillus thuringiensis (Bt) transgenic cotton, grown over about 3.8 million hectare in 2006 in India, is essentially a mosaic of different cry1 genes, predominantly based on Monsanto's 531 event carrying the cry1Ac gene, and to some extent JK AgriGenetics's event 1 with native modified cry1Ac, Nath Seeds's GFM event with fusion genes of cry1Ab and cry1Ac, and cry1Ab and cry1C in single-stacked hybrids, and the Monsanto's 15985 event with two cry1Ac and cry2Ab genes. In view of different cry1Ac genes used for transformation, toxicity (96 h LC50) of some Cry1Ac proteins to the neonates of the cotton bollworm, Helicoverpa armigera, varied, with a range of 0.158–5.42 μg/g for BGSC Cry1Ac (23 populations), 0.076–5.76 μg/g for JK Cry1Ac (24 populations) and 0.0085–0.822 μg/g for MVP Cry1Ac (21 populations). There are significant differences in the toxicity of these Cry1Ac proteins; despite the use of genetically diverse insect populations, suggesting a need of evolving a consensus on Cry1Ac resistance monitoring of the larvae of H. armigera.