Literature
- Ban-Calefariu, C.M. and Sarospataki M. 2007. Contributions to the knowledge of Bombus and Psithyrus genera (Apoidea: Apidae) in Romania. Travaux du Museum NHN “Grigore Antipa” Vol. L pp. 239–258.
- Banaszak, J. and Dochkova, B. 2014. Bees (Hymenoptera, Apoidea, Apiformes) in the agricultural landscape of Bulgaria: species diversity Journal of Apicultural Science Vol. 58 No. 1 pp. 29-49.
- Leiner, O. 1997. Zur Biologie der Hummeln (Hymenoptera: Apidae) Bayerische Akademie für Naturschutz und Landschaftspflege 21: 83-88.
- Söderman, G. and Leinonen, R. 2003. Suomen Mesipistiäiset ja niiden uhanalaisuus. Tremex Press Oy, Helsinki.
- Wind, P. & Pihl, S. (eds.) 2010. The Danish Red List. - The National Environmental Research Institute, Aarhus University [2004]-. http://redlist.dmu.dk (updated April 2010).