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).

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The scanning electron microscope reveals that the egg of Pollenia rudis (Fabricius) is structurally suitable for a plastron method of respiration.

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