Aciurina semilucida (Bates) is a rare, highly localized, tephritid fly forming pubescent, axillary bud galls on branches of Chrysothamnus viscidiflorus (Hooker) Nuttall in southern California. Documentation is provided that the wing patterns of the adults are very strongly sexually dimorphic in southern California, but much less dimorphic in some other parts of its range, e.g. in Idaho, where it previously has been reported only from C. nauseosus [Ericameria nauseosa] (Fallen) Britton.

The gall of A. semilucida is a stunted axillary branch, reminescent of the beaked galls of A. michaeli (Goeden and Teerink 1996a), but not as strongly attenuated or "beaked" apically (Fig. 6E, 6F). As such, they are dark green and subspheroidal when young (Fig. 6B, 6D), elongating and externally becoming pyriform in outline, light green, and pubescent as they grow and mature (Fig. 6E, 6F). They also bear several basally expanded, sessile, linear, smooth- margined leaves, which are shortest apically (Fig. 6E). The gall body is largely composed of whitish, spongy parenchymatous, expanded nodes, and a harder core surrounding the central locule (Fig. 6D, 6E); this description agrees with that of Wang- berg (1981), which stated that, apparently including the epidermis, the galls are composed "of three distinct layers" (Fig. 6E). The gall is uniloculate (monothalmus [sic]) and characteristically contains an ovoidal to pyriform-shaped, central, open chamber within which the larva feeds by scraping away at the inner wall which becomes shallowly pitted (Fig. 6D, 6E). The photographic illustration in Wangberg (1981) shows the surface of the gall of A. semilucida as dull, not shiny, and thus more commensurate with pubescent, and what he termed "smooth." His photograph also better reflects what he described as its "ovoid," but not its alternative "tear-drop" shape. However, the 12 voucher specimens of galls attached to some of his reared specimens of A. semilucida on C. nauseosus from Idaho were, indeed, pubescent, slightly attenuated apicad, and bore shortened, basally expanded leaves more like the California galls described above (Fig. 6E, 6F). The galls of A. semilucida at our study sites externally also closely resembled the whitish gall of a gall midge (Diptera: Cecidomyiidae) also found on C. viscidiflorus, possibly Asphondylia bigeloviae brassicoides (Townsend) as described and illustrated by Gagne (1989).