1. Dipartimento di Biologia; Università degli Studi di Firenze; Via Madonna del Piano 6 50019 Sesto Firentino (Florence) Italy
2. Department of Entomology; Center for Pollinator Research; Pennsylvania State University; University Park PA 16802 USA
3. School of Biological Sciences; Royal Holloway University of London; Egham TW20 0EX UK