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"Bubble Gall" Tephritid - Aciurina trixa - Female
East of Horse Thief Springs, Kingston Range, just south of Inyo County line, San Bernardino County, California, USA
June 2, 2012
This fly was observed sitting and crawling sluggishly on a stem of Ericameria nauseosa (formerly known as Chrysothamnus nauseosus) on a hot afternoon in the desert Kingston Range of far eastern California (SE of Death Valley). It lingered on that plant...and even when it periodically flew to escape my photographic attentions, it would always land again on the same plant. In my experience, that's fairly typical behavior for tephritid females on their host plants. This can be seen to be a female from the elongate, conical "oviscape" (i.e. the visible tip of the abdomen in 2nd and 4th images of this series).

This keyed to Aciurina bigeloviae in the excellent 1993 reference by Foote, Blanc, and Norrbom(1), and everything fit well (e.g. descriptions, wing diagram, location, host plant). Foote et al. mentioned that two other species had been synonymized with A. bigeloviae by Styeyskal in 1984, and that this was the most widespread and commonly encountered species of all the Chrysothamnus-feeding well as the most variable. (In fact, the detailed synonymy and references for A. bigeloviae take up an entire page in their book!)

After I find a name for an insect, I usually search for life history and other info on the web and in books. I soon found that the two species Steyskal had synonymized with A. bigeloviae had been subsequently reinstated as valid species : A. semilucida in a 1996 paper by Geoden & Teerink; and A. trixa, in a 1997 paper by Headrick, Geoden & Teerink (see "Print References" on the Aciurina guide page). So my nicely successful ID was now in question again! :-)

Studying the two papers mentioned above led me to conclude the fly in this post is A. trixa. Headrick, Geoden & Teerink (1997) emphasize that the best way for distinguishing the three species in question here is by their galls. The gall of A. semilucida is "light green, pyriform with an attenuate apex, covered with a uniform light pubescence, and bearing several basal leaves", while the galls of the other two are round. Moreover, the galls of A. bigeloviae have a conspicuously cottony surface, while those of A. trixa are described as having a "waxy" surface. The gall here (see last image in post) fits that of A. trixa (see the images on this web page which were IDed by expert Gary Dodson).

Finally, I consulted the field guide to CA and western galls by Ron Russo(2), and found gall images for A. bigeloviae and A. trixa that reinforced the above. Russo calls A. trixa the "Bubble Gall Tephritid", referring to the (shiny & sticky when fresh) round, glabrous galls.

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