The 1996 advent of Monsanto's transgenic Bt cotton, commercially available as 'NuCOTN' with the Bollgard Bt gene, provided growers with a new tool for controlling caterpillar pests in cotton. A delta-endotoxin protein (Cry1Ac) from Bacillus thuringiensis Berliner var. kurstaki (Bt) expressed in these transgenic cotton plants is toxic to many lepidopteran larval pests of cotton. Monsanto initially claimed that Bollgard cotton would meet the needs of a high-dose resistance-management strategy by providing an adequately high toxin concentration. Studies confirmed the high-dose toxin level for tobacco budworm, Heliothis virescens F.; however, bollworm, Helicoverpa zea Boddie, was observed to be much less susceptible than tobacco budworm to the Cry1Ac endotoxin. Because a proportion of bollworm larvae were found to survive on Bollgard cotton, the prospect for rapid development of bollworm resistance to Cry1Ac was a general concern. Therefore, development of deployment strategies was necessary to delay resistance.