This species and R. tumidicaulis are the only ones responsible for stem galls on A. tridentata.

Immature larvae were found June 5, 1969 at Site 24, coinciding with the first sign of gall development. Adults emerged in the field on July 23, 1969 at Site 23, and at Site 24 sometime prior to August 8, 1969.

The mature gall is a slight swelling of the vegetative stem and is covered by long white trichomes (Fig. 41). Its sclerenchymatous larval capsules are found between the woody tissues and the outer layers of stem tissue. The galled stem may be slightly bent or, if larvae are near the apex of the gall, it may be stunted.

Forty mature galls from Sites 23 and 24 were measured with the length of the stem surface covered by long trichomes ranging from 4-19 mm (avg. 9). The length of the trichomes ranged from approximately 1 to 2 mm. The galls contained from 1-7 larval chambers (avg. 2).

Developing galls were first observed in early June and found to differ from mature galls only in size. Galls were mature in mid-July when the larvae and pupae were well encapsulated within the stem and normal ephemeral leaves were mature. The old galls persisted on the plant for a year or more.

- Robert G. Jones, Raymond J. Gagné, William F. Barr: (1983) Biology and taxonomy of the Rhopalomyia Gall Midges (Diptera: Cecidomyiidae) of Artemisia tridentata Nuttall (Compositae) in Idaho^©