The U.S. Department of Agriculture frequently approves the use of new genetically engineered crops based on unsupported claims and shoddy studies by seed companies, say many scientists who have studied the approval process. The USDA, the primary agency responsible for assuring the ecological safety of such plants, has not rejected a single application for a genetically modified crop. A growing number of studies suggest that genetically modified crops could lead to rapid evolution of pesticide-resistant insects and superweeds, create new plant diseases, and harm insects that are beneficial to agriculture. But the USDA has set no scientific standards for proving the environmental safety of a plant and it asks only that petitioners explain why the new plant is likely or unlikely to pose a number of broadly defined risks. Even some scientists at seed companies acknowledge that they could have done a more thorough job of providing data to regulators.