Rhopalomyia calvipomum
Plum Gall Midge

This midge induces ovoid monothalamous leaf galls that protrude mostly from the lower surface of leaves of Great Basin sagebrush.

This species is most similar to R. pomum and R. hirtipomum. All three species form the same general type of gall, but that of R. calvipomum is naked.

The mature gall (Figure 8) is globose to irregularly elongate and is similar to that of R. pomum in shape and by having small brown spots on the surface. It differs by being firmer and having a smooth surface that lacks trichomes.

One hundred fifty mature galls were measured: the diameter extending from the gall base ranged from 9-26 mm (avg. 15) and the diameter of the greatest width perpendicular to the previous measurement ranged from 8-20 mm (avg. 13).

Developing galls were evident on March 23, 1970 at Site 21. They appeared as a reddish or violet-colored swelling of a persistent leaf. Galls fall from the plant in July and August, as do those of R. pomum.

Gall on leaves...
Gall globular to lobed, soft, spongy...
Gall surface bare...Rhopalomyia calvipomum Gagné

Galls are irregularly lobed and polythalamous to globular and monothalamous, smaller than those of R. pomum, with a diameter of 8–20 mm...Host: A. tridentata.