1. Swiss Bee Research Centre, Agroscope Liebefeld-Posieux, Schwarzenburgstrasse 161, CH-3003 Berne, Switzerland; Büchi Labortechnik AG, Postfach, CH-9230 Flawil, Switzerland; and ETH Zurich, Institute of Food Science and Nutrition, ETH-Zentrum, Schmelzbergstrasse 9, CH-8092 Zurich, Switzerland