1.   But because any pesticide spurs the emergence of resistant insects, some scientists say tougher bugs are inevitable in the long run.

2.   Environmentalists believe it could accelerate the evolution of resistant insects, harm consumer health and, perhaps most important, alter corn at its center of origin forever.

3.   If resistance to Bt is not to spread, a resistant insect has to be overwhelmingly likely to mate with an insect that is not resistant to Bt.

4.   Some studies have shown that continuous exposure to Bt quickly creates resistant insects, thus destroying the effectiveness of the pesticide.

5.   So far, there has been no evidence of resistant insects, although some insects have shown a temporary tolerance to the toxin, agency scientists said Wednesday.

6.   The EPA said Tuesday it is acting to ensure that farmers comply with planting restrictions designed to prevent the development of insects resistant to the toxin.