Paul Nelson is used to doing battle with an invasive fruit fly called the spotted wing drosophila, a pest that one year ruined more than half the berries on the Minnesota farm he and his team run.... They used mathematical modeling to show that if they released one modified fruit fly for every four that were not and did that every two weeks, they could collapse a population in about five months.... Scientists have already released genetically modified mosquitoes, for instance, which mate with