In the Midwest, neat rows of modified corn and soybeans are free of unruly patches of milkweed. The crops are resistant to the herbicide Roundup. But the destruction of milkweed may have an unintended consequence: the end of annual migrations of the Monarch butterflies, a phenomenon dear to lovers of nature. The Monarch is so beloved one entomologist calls it "the Bambi of the insect world." Andrew Pollack covers the business and science of biotechnology for the New York Times.