1. U.S. Geological Survey, 345 Middlefield Road, Mail Stop 439, Menlo Park, California 94025, Department of Entomology, Soils, and Plant Sciences, 270 Poole Agricultural Center, Clemson University, Clemson, South Carolina 29634-0315, and the Department of Geological Sciences, University of Saskatchewan, 114 Science Place, Saskatoon, SK S7N 5E2 Canada