[The author mistakenly described this gall as being induced by Aciurina ferruginea, and his description perfectly matches what is now known as Aciurina michaeli] It is monothalamous, smooth, pear-shaped and occurs at the axillary buds on the current year's growth. A few modified leaves usually arise from the gall surface. The color of galls is green, becoming pale green to yellow with age. Some may have pinkish hues. Twenty-five mature galls collected near the Craters of the Moon National Monument, Butte County, in 1975 ranged from 8.5 to 16.0 mm (x = 12.9 mm) in length and 4.5 to 8.0 mm (x = 6.4 mm) in width. The young gall resembles the mature gall in form. The stem and most of the leaves that would normally arise from the axillary bud are incorporated as gall tissue. A few unmodified leaves may remain and grow from the surface. In some instances stem growth occurs from the gall and many leaves will develop from such a stem above the gall. Larval feeding appears to be the stimulus for A. ferruginea [A. michaeli] gall growth. Growth continues up to the pupal stage. If a larva dies early in development, the gall ceases growth. A mature gall shows evidence of desiccation. Following emergence of the gall-inhabitant the gall desiccates rapidly and will abscise from the host plant. No portions of the host plant's foliage appear suitable for gall growth as long as growing stems are present. Galls are usually concentrated on the lower half of branches rather than toward the tips.

Aciurina michaeli
Beaked-gall Tephritid

This fly induces monothalamous, pear shaped, smooth bud galls on the current year's growth of rubber rabbitbrush and yellow rabbitbrush.