Pemphigus populi-ramulorum Riley.

[Drawings of this gall appear on page 17 of the pdf]

While this species was described from material collected on Populus balsamifera it occurs commonly on Populus deltoides in localities outside the range of the balsam poplar. This species resembles quite closely both P. p.-caulis and P. p.- globuli.

This aphid is frequently encountered in Utah and is particularly interesting because of the gall it produces on the young twig bark of poplars, especially Populus balsamifera. Collections made at Leeds, both from twig galls and from galls below the bases of the leaves on the petiole, indicate that this one species produces two types of galls. This is a rather uncommon occurrence among gall-forming aphids. The openings to the leaf galls are often slightly beaked, and the mouth does not always open along the same axis, which gives variation in appearance to the openings of different galls.

In Utah this species has been collected from Benjamin, Benson, Farmington, Holliday, Hooper, Leeds, Provo, St. George, Santa Clara, and Zion National Park.

- Asa Maxson, George Knowlton: (1929) The tribe Pemphigini (Aphididae) in Utah^©