In the laboratory study of different pollen densities, caterpillar mortality was significantly greater on the two highest densities of both KnockOut and YieldGard pollen than on nonBt pollen. At the lowest density, larvae survived equally well on Bt and nonBt pollen. Caterpillars that survived exposure to Bt and nonBt pollen appeared to develop similarly into adult butterflies. Milkweeds are found both within and along the margins of corn fields. This field study does not resolve whether or not Bt corn will be a serious threat to monarch butterflies in corn-growing areas.
Much more research needs to be done.
EPA is presently engaged in a comprehensive review of all Bt corn and cotton with the aim of deciding within the next year whether and under what conditions Bt crop registrations should be renewed. Current registrations for Bt corn and cotton expire in 2001. The Union of Concerned Scientists is urging EPA not to reregister any Bt corn until it has a program in place to thoroughly assess ecological risks of Bt crops, including the risk to monarchs and other beneficial insects. In addition, EPA should require farmers to plant buffers of nonBt-corn around Bt fields in the coming year to reduce the amount of toxic pollen blowing beyond transgenic fields. Laura C. Hansen Jesse, John J. Obrycki.