Many papers have been written about caddis cases, treating these movable shelters from the standpoints of choice of materials (Brues 1930, Dodds & Hisaw 1926, Lloyd 1915, Lutz 1930, Simpson 1903), of repair (Marshall & Vorhies 1905), of ontogenetic initiation (Murphy 1919, Copeland & Crowell 1937), and of phylogenetic origin (Milne & Milne, 1938). The last of these references, a paper by Sleight (1913) and the work of Dodds & Hisaw cited above, give some attention to the relation between case-building and the physiology of the larva inhabiting the structure, but much remains to be studied in this connection.

There has been to date, to the knowledge of the writer, no published list of the species of Aphididae common to the Maritime Provinces of Canada. It is proposed in the following contribution to make a beginning to such a list, with the hope that it may prove useful to interested taxonomists.

This list is a record of insects which have been found in or on Douglas fir in the northern Rocky Mountain region by personnel of the Forest Insect Field Laboratory at Coeur d'Alene, Idaho. It comprises insects which feed upon the tree, as well as the parasites and associates of these insects. Of the 153 species listed, 102 were collected by the writer while making a study of the Douglas fir beetle (Dendroctonus pseudotsugae Hopk.). The remainder are listed in the laboratory records and were collected by J. C. Evenden, R. E. Balch, H. J. Rust, and D. DeLeon.