Ten galls and pseudogalls caused by poplar gall aphids are described, their development discussed, and a key to their identification presented. Nine of these malformations are from Quebec poplars and one from Crystal Springs on Pigeon Lake, Alberta. All of the aphids involved belong to the family Eriosomatidae and sub-family Pemphiginae. Seven species are members of the genus Pemphigus Hartig, and of these P. bursarius (L.) and P. populitransversus Riley are well recognized economic vegetable pests in the United States. A monoecious species P. spirothecae Passerini is reported for the first time in North America. P. monophagus Maxson was collected from balsam poplars in Alberta. Other genera represented are Thecabius Koch (two species) and Asiphum Koch (one species).

Pemphigus spirothecae Passerini, a member of the subfamily Eriosomatinae, was collected in large numbers from spiral galls on lombardy poplars in Quebec during 1972 and 1973. This aphid is well known in Europe but has not been reported previously from North America. It has a monoecious life cycle.

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