1. Crop BioProtection Research Unit, National Center for Agricultural Utilization Research, Agricultural Research Service, U.S. Department of Agriculture, 1815 North University Street, Peoria, Illinois 61604, Department of Botany, North Carolina State University, Campus Box 7612, Raleigh, North Carolina, 27695-7612, and Department of Agronomy and Horticulture, University of NebraskaLincoln, Lincoln, Nebraska 68583