1. Department of Ecology and Evolution, University of Lausanne, CH-1015 Lausanne, Switzerland;
2. INRA/Agrocampus Ouest/Univ. Rennes 1, UMR 1099 BiO3P (Biology of Organisms and Populations applied to Plant Protection), Domaine de la Motte, 35653 Le Rheu, France;
3. University Rennes 1/CNRS, UMR 6553 ECOBIO, Campus de Beaulieu, 35042 Rennes Cedex, France