1. Biology Department University of York PO Box 373 York YO10 5YW UK
2. Food and Environment Research Agency Sand Hutton York YO41 1LZ UK
3. Institute for Bee Research Fiedrich‐Engels‐Str. 32 Hohen Neuendorf 16540 Germany
4. Institute of Microbiology and Epizootics Freie Universität Berlin Robert‐von‐Ostertag‐Str. 7–13 Berlin 14163 Germany