In southern Alberta there are several species of aphids that produce galls on poplar trees (Harper, 1959). These aphids are all in the subfamily Eriosomatinae and in the genera Pemphigus Hartig, Thecabius Koch, and Mordwilkoja Del. G. Two of the species are of economic importance, Pemphigus betae Doane, a pest of sugar beets in Alberta and parts of United States (Harper, 1957; Maxson, 1916; Parker, 1915), and Pemphigus populitransversus Riley, a serious pest of crucifers in Texas (Wene and White, 1953). Both species overwinter on poplar as eggs. In spring the fundatrix emerges from the egg and feeds on the poplar leaf, initiating a gall in which the winged fundatrigeniae are produced. During the summer the fundatrigeniae migrate to the secondary host where they produce the wingless alienicolae; in the fall these in turn produce the winged sexuparae, which migrate to the poplars where they produce the wingless sexuales. The female sexuales, after mating, deposit eggs on the poplars to complete the life cycle (Harper, 1957; Jones and Gillette, 1918; Parker, 1914).