1. Laboratory of Infectious Diseases, National Institute of Allergy and Infectious Diseases, Bethesda, Maryland 20205
2. Epidemiology Branch, Rocky Mountain Laboratory, National Institute of Allergy and Infectious Diseases, Hamilton, Montana 59840
3. Insect Pathology Laboratory, Plant Protection Institute, SEA-AR, U.S. Department of Agriculture, Beltsville, Maryland 20705
4. Department of Anatomical Sciences, State University of New York, Stony Brook 11794