As more farmers plant crops genetically engineered to be bug-resistant, the market for insecticides and weed-killers is falling. Cotton farmers have cut the amount of insecticide they apply to their fields by 12 percent, or about 2 million pounds, since bug-resistant cotton plants hit the fields three years ago, according to the National Center for Food and Agriculture Policy, a think tank in D.C. But while American farmers have flocked to gene-altered crops, Europeans are still wary of them, concerned that genetic engineering might have unintended consequences for human health and wildlife. Pres. Clinton this week is expected to warn Europe that it needs to curb its “hysteria” over exports of genetically modified crops from the U.S.