1. Maine Department of Inland Fisheries and Wildlife, P.O. Box 1298, Bangor, Maine 04401, USA
2. National Institutes of Health, Bethesda, Maryland 20205, USA
3. Present address: Microbiological Associates, Inc., Rockville, Maryland 20850, USA
4. Pennsylvania Cooperative Fish and Wildlife Research Unit, University Park, Pennsylvania 16802, USA
5. School of Forest Resources, The Pennsylvania State University, University Park, Pennsylvania 16802, USA