Reference

Andreas Bertsch, Horst Schweer (2012): Cephalic labial gland secretions of males as species recognition signals in bumblebees: are there really geographical variations in the secretions of the Bombus terrestris subspecies? (Hymenoptera: Apidae: Bombus). – Beiträge zur Entomologie = Contributions to Entomology – 62: 103 - 124.