1. Department of Behavioral Physiology and Sociobiology; University of Würzburg, Biozentrum; Am Hubland 97074 Würzburg Germany
2. INRA UR 406, Abeilles et Environnement; Site Agroparc 84914 Avignon France
3. Department of Chemistry; Simon Fraser University; Burnaby BC Canada V5A 1S6