1. Department of Zoology, NJ-15, University of Washington, Seattle, Washington 98195, USA
2. Present address: Organizacion para Estudios Tropicales, Apartado 676-2050, San Pedro de Montes de Oca, Costa Rica
3. College of Veterinary Medicine, Department of Infectious Diseases, University of Florida, Gainesville, Florida 32611-0880, USA
4. Department of Zoology, 223 Bartram Hall, University of Florida, Gainesville, Florida 32611, USA