Rhopalomyia hirtipomum appears to be anatomically identical to R. pomum but is responsible for a slightly different gall. That of hirtipomum is densely covered with long trichomes, whereas that of R. pomum has short, prostrate, sparse trichomes on the surface. In addition, galls of the former are always monothalamous.

This monothalamous gall (Fig. 9) is globose and quite similar to the monothalamous gall of R. pomum. However, the gall surface is densely clothed with long trichomes, giving it a fuzzy appearance. The gall is generally solitary on either the upper or lower leaf surface, but can occasionally be found in confluent clumps (Fig. 10). Fifty-nine mature galls were measured: the diameter extending from the gall base ranged from 8-15 mm (avg. 12) and the diameter perpendicular to this ranged from 8-13 mm (avg. 11).

Developing galls were first found on October 23, 1969 at Site 1 on A. t. wyomingensis. They appeared as fuzzy swellings with diameters of 1-3 mm on a persistent leaf surface. The long, dense trichomes were white, while the surface of the gall was reddish. Galls had the same appearance on A. t. vaseyana f. xericensis when found at Site 27 on December 29, 1969. At both sites this appearance persisted until March, when growth resumed. As the gall grew, their surface coloration gradually changed to grey. Maximum size of the gall was found to coincide with the presence of pupae and with new stem growth of approximately 2.5 cm in length. Shedding of the galls occured in July and August, at the same time as those of R. pomum.

Rhopalomyia hirtipomum
Apple Gall Midge

This midge induces round, densely hairy, solitary, monothalamous galls on either surface of leaves of Great Basin sagebrush.

Gall surface with long trichomes, surface color not visible...
Gall on Artemisia tridentata...Rhopalomyia hirtipomum Gagné

Galls are ovoid and monothalamous, but several may grow close together on the same leaf. They are smaller than those of R. pomum, with a diameter of 8–15 mm...This gall is probably the one that Felt ascribed to Rhopalomyia navasi Tavares, which makes a somewhat similar gall on terminal or lateral buds on an artemisia in Spain and North Africa.