Externally, mature galls that contained live puparia usually were subspheroidal. This gall shape also resulted when larval feeding or exit hole construction destroyed the terminal bud at the apex of a gall. Upon death or removal of a larva, or after emergence of the adult, apical growth and internode elongation usually resume and the gall assumes a spindle-shape...
The galls are grey-green when young, sometimes purple tinted, especially when infested by inquilines and certain parasitoids, but turn brown and woody with age. They are covered with a closely appressed whitish tomentum when young and are laterally marked by transverse, scale-like expanded leaf bases bearing sessile leaves and axillary buds that may grow into one or more branches adorning old empty galls. p.28

Unlike other tephritids, galling Artemisia, E. diana has a broad host plant range which includes five species and two varieties of Artemisia. Stoltzfus (1977) lists A. tridentata subsp. tridentata Nutt., A. arbuscula Nutt., A. cana subsp. cana Pursh, A. cana subsp. viscidula (Osterhout), A. nova Nelson, A. tripartita Rydb. and A. tridentata subsp. vaseyana (Rydb.). These species all belong to the tridentate section of Artemisia. Artemisia filifolia Torr. (sand sagebrush) is a new host plant record for E. diana. (pg 02)

[In reference to A. filifolia] The mature gall is a monothalmous, ovoid structure ranging from 39 to 131 mm (average 82 mm) in diameter (fig. 10). The circumference of the galls varies from 17 to 25 mm (average 21 mm). The galls are located at the apical meristem of the lateral branches of the current year's growth. They are uniform in shape, covered by a proliferation of thread-like leaves and are green in color. The size of the gall cavity ranges from 6.5 to 9 mm (average 7.0 mm) in length. There are two distinct tissue layers visible in the gall. The outer layer, which is covered by a proliferation of thread-like leaves, is firm but relatively soft and thin when compared to the inner layer immediately surrounding the cavity. This layer is quite thickened and hard at maturity. (pg 27)