This gall develops from the buds forming on new stem growth. It has a broad base made up of several whorls of fused and stunted leaves subtended by a pair of normal ephemeral leaves (Fig. 25). The outermost leaves are as wide as long while the inner leaves are oblong. The gall is green and normally covered with trichomes. The sclerenchymatous larval capsules in the mature gall are located at the bases of the innermost leaves at the stem apex. These galls are commonly found in clusters on a single branch.

Fifty mature galls had a width (diameter at widest point) ranging from 5-12 mm (avg. 9) and a height (base of gall to leaf apices) ranging from 5-12 mm (avg. 8). There are 1-8 sclerenchymatous capsules per gall.

The developing galls, containing early instar larvae, differ from mature galls only in size. The gall usually attains maximum size by winter although some growth may occur in the following spring. After midge emergence the galls begin to dry and within a year the leaves are lost but the galls persist indefinitely as dark, woody bodies on branch tips of the plants.

Rhopalomyia cramboides Gagné

Outer whorls of gall leaves as wide as long, inner whorl with more linear leaves
Adults emerge in spring. New galls develop on new stem growth.

Host: A. tridentata
Distr: Idaho