Reference
Andreas Bertsch, Martin Hrabe de Angelis, Gerhard K.H. Przemeck (2010): A phylogenetic framework for the North American bumblebee species of the subgenus Bombus sensu stricto (Bombus affinis, B. franklini, B. moderatus, B. occidentalis & B. terricola) based on mitochondrial DNA markers. (Hymenoptera: Apidae: Bombus). – Beiträge zur Entomologie = Contributions to Entomology – 60: 229 - 242.