Immature larvae were found at Site 27 on March 8, 1970 coinciding with the first sign of gall development. Pupae were found on May 14, 1969 at Site 1 on A. t. tridentata and at Site 4 on May 29, 1969 on A. t. vaseyana. Adults emerged May 19, 1969 from galls collected on May 14 at Site 1. A pupal exuvium was found at the apex of each gall's hollow portion.

This bud gall (Fig. 23) develops in the spring when plant growth begins. It is green and appears to be made up of a series of fused leaves that form a woody, hollow structure that is open apically. The inner surface of the gall is densely clothed with long trichomes while the outer surface is covered with shorter trichomes. The base of the gall contains a single larval chamber. Some developing galls (Fig. 24) are short and dark reddish. After adults emergence the woody gall dries and persists on the plant for a year or longer.

Eighteen mature galls from A. t. vaseyana and A. t. wyomingensis ranged in length from 10-19 mm (avg. 12). The basal diameter ranged from 4-6 mm (avg. 4). Three galls from A. t. tridentata had had respective lengths of 15, 17, and 25 mm and all with a basal diameter of 3 mm.

- 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^©