1. Institute for Biodiversity and Ecosystem Dynamics; University of Amsterdam; P.O. Box 9424 1090 GE Amsterdam The Netherlands
2. Department of Biology; University of Western Ontario; London N6A 5B7 ON Canada
3. Royal Belgian Institute of Natural Sciences; Vautierstraat 29 B-1000 Brussel Belgium
4. Terrestrial Ecology Unit; Biology Department; Ghent University; K. L. Ledeganckstraat 35 B-9000 Gent Belgium
5. Instituto de Ciencias de la Vid y el Vino; 26006 Logroño Spain
6. Laboratory of Agrozoology; Department of Crop Protection; Faculty of Bioscience Engineering; Ghent University; B-9000 Ghent Belgium