A green to pink-red pea gall on the midrib or major side vein of Populus tremuloides. The gall is nearly entirely found on the upper side of the leaf, and appears detachable, but its exit hole is found on the lower side at the contact point. Observed from Alaska to Nova Scotia south to New Mexico, fresh between June and August.

This gall is nearly identical to that of Harmandiola tremulae, found on Populus tremula in Europe. It is possible that the same species occurs holarctically on both hosts but no existing literature seems to confirm this.

This gall morphotype can be distinguished from other midge galls on Populus leaves by the following traits:

• Larva concealed within galled tissue, protruding only on the upper side of the leaf
• Thick walled, nearly spherical, large