20 0 0年 ,美国种植 Bt棉超过总面积的 50 % ,主要抗烟芽夜蛾 ,还要特别注意其它害虫的暴发。如 90 %棉铃虫最终可以得到控制 ,但需要 5或 6天 ,此时幼虫正在取食造成为害。1 999年 ,路易斯安那州 6 4 %的棉田种植了 Bt棉 ( 1 997年为 3 0 % ) ,以便根除该州北部地区的棉铃象鼻 In the United States, Bt cotton is more than 50% of the total area planted in the year 2000, mainly against N. litura, with special attention to the outbreak of other pests. For example, 90% cotton bollworms can eventually be brought under control but take 5 or 6 days when the larvae are feeding to cause harm. In 1999, Bt cotton was planted in 64% of cotton fields in Louisiana (30% in 1997) in order to eradicate the cotton boll trunk in the northern part of the state