Pemphigus? rileyi n. s.
A spherical, red and yellow gall occurring in clusters, usually on the under side of the leaf, near the petiole. Above there is a conical projection at the top of which is the opening. Thin-walled. About 5 mm. in diameter. On aspen, Populus tremuloides. Rather common.
”- FA Stebbins: (1910) Insect galls of Springfield, Massachusetts, and vicinity©
Reference: https://www.biodiversitylibrary.org/item/71437#page/13/mode/1up