A cecidomyiid gall midge, Rhopalomyia bigeloviae (Cockerell), was reared from galls formed on galls of the tephritid, Aciurina trixa Curran, on Chrysothamnus nauseosus (Pallas) Britton in southern California. Only one of the two A. trixa gall types in southern California hosted the gall midge. Rhopalomyia bigeloviae galls were originally discovered in Colorado on the large cottony galls of A. bigeloviae, a species closely related to A. trixa, that forms galls on C. nauseosus outside of California. The midge galls are similar to the host tephritid galls externally, i.e. either smooth or cottony. The number of midge galls per tephritid gall varies, but they can, in some cases, cover the entire surface of the tephritid gall. The gall midge is probably bivoltine, and the tephritid host is univoltine. Gall midge galls first become visible in early spring (March). Adults emerge later in the spring. The fate of these adults remains unknown, but females may oviposit into other parts of the host plant to form a second generation of cecidomyiid galls not dependent on the presence of a tephritid gall.
On one of the two gall forms in southern California (Fig. lA), we observed that its exterior sometimes was covered by small nodules at different densities among different locations. Upon dissection, each of these nodules was found to contain a small cecidomyiid identified for us as Rhopalomyia bigeloviae (Cockerell) by Raymond J. Gagne (Systematic Entomology Laboratory, Agricultural Research Service, USDA). This species was originally described from a large woolly gall up to 12 mm long, typical of that made by another species of Aciurina (Gagne 1986). Dodson and George (1986) and Headrick et al. (1997) have clarified the status of Aciurina species on C. nauseosus, and this woolly gall is now attributed to the tephritid, A. bigeloviae (Cockerell). We have examined such woolly galls from various collections (Washington State University, Pullman; University of Idaho, Moscow; G. Dodson, personal collection) and they do, indeed, bear R. bigeloviae galls. None of the other gall types, as described by Wangberg (1981), examined from museum collections throughout western U.S., including the smaller resinous gall of A. trixa found in California hosted this gall midge (Headrick et al. 1997).
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