1. Department of Ecology and Evolutionary Biology, University of Colorado, Boulder, CO 80309, USA
2. Department of Bioagricultural Sciences and Pest Management and Graduate Degree Program in Ecology, Colorado State University, Fort Collins, CO 80523-1177, USA
3. UMR Centre de Biologie et Gestion des Populations, INRA, 34988 Montferrier sur Lez, France