Schmutterer, H. 1956 Zur Morphologie, Systematik und Bionomie der Physokermes - Arten an Fichte (Homopt. Cocc.). [About the morphology, systematics and bionomy of Physokermes - species on spruce (Homopt. Cocc.)]. Zeitschrift für Angewandte Entomologie 39: 445-466.

Notes: Reviews structure, differentiation, biology, and feeding bahavior of P. piceae Schrk. and hemicryphus Dalm.