Kraft Foods announced a nationwide recall on Friday of Taco Bell-brand taco shells found to contain small amounts of a genetically modified corn variety not approved for human consumption because it may cause allergies. The corn, known as StarLink, has been approved as animal feed, but in an effort to reassure the public, the manufacturer of the corn, Aventis Corp., announced today that it will suspend sales of the variety unless the U.S. EPA approves its use in human food. The recall is likely to put pressure on the biotech industry and the government to more tightly regulate genetically modified crops. Rep. Dennis J. Kucinich (D-Ohio) is sponsoring a bill that would require stricter safety testing and mandatory labeling. But some experts are saying that accurate labeling would be difficult, since it is hard to keep genetically modified crops from contaminating and being mixed with other crops. Meanwhile, enviros are criticizing a new preliminary report released by the U.S. EPA that claims genetically modified corn is unlikely to pose a serious threat to monarch butterflies, despite recent high-profile studies that have found pollen from the corn plants can kill monarch caterpillars.