This midge was reared in May, 1913, by Mr, P. H. Timberlake from a pubescent, variable, conical, stem gall on rabbit brush, Chrysothamnus graveolens [Ericameria nauseosa], collected in the vicinity of Murray, Utah. The species approaches closely R. utahensis, from which it may be most easily separated by its decidedly smaller size, the fewer antennal segments and particularly by the peculiar type of gall.
Gall. — A variable, conical outgrowth of the stem with a height of about 4 mm. and a basal diameter of 2 to 3 mm. The gall contains basally, an oval, thin-walled cell with a length of 2.75 mm. and a diameter of 1.75 mm., the hollow, distal portion being filled with a slender, thread-like growth of delicate cells placed end to end and forming a rounded or, in some cases, nearly truncate plug.

Rhopalomyia chrysothamni
Stem-gall Midge

This midge induces small, conical-tubular monothalamous galls that project out at right angles to the stems of rubber rabbitbrush.

Conical swellings of same texture as stem and with cottony fibers filling exit...Rhopalomyia chrysothamni Felt
Host: C. nauseosus. Distr.: Utah