1. Unité de Bactériologie Moléculaire et Médicale, Institut Pasteur, 75724 Paris Cedex 15, France1;
2. Department of Environmental Science, Policy and Management, Division of Insect Biology, University of California, Berkeley 947202;
3. Département de Parasitologie, Institut de Zoologie, Neuchâtel, Switzerland3; and
4. Institut für Veterinärbakteriologie der Universität Zürich, Zürich, Switzerland4