http://www.academia.edu/1884569/Akre_et ... _Vespinae_
This is a great review of the North American species of Vespinae. A review of the morphology, biology, and Distributional data of various social wasp genera of the world is included in the introduction of this work as well as habitats, distributional ranges and notes on biology of all North American Vespinae species is provided in this work as well as a key to workers of all species of North American Vespinae. D. alpicola (as D. saxonica Fabricius) was not included in the key in this book as Akre did not find this species to be valid without further investigation.
An updated (2012) key to all North American species of Vespinae (Including D. alpicola) can be found here: http://www.academia.edu/1877231/Kimsey_ ... _Vespidae_