PROC. ENTOMOL. SOC. WASH. 99(3), 1997, pp. 487-489 GALL MIDGE FORMS GALLS ON FRUIT FLY GALLS (DIPTERA: CECIDOMYIIDAE, TEPHRITIDAE) David H. Headrick and Richard D. Goeden CA Department of Entomology, University of California, Riverside, 92521, U.S.A. — Abstract. 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 ofA. 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 uni- voltine. 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 depen- dent on the presence of a tephritid gall. Key Words: Gall formers, gall midge, Cecidomyiidae, Tephritidae, Aciurina, trixa, Rho- palomyia, bigeloviae Aciurina trixa Curran forms axillary bud USDA). This species was originally de- galls on branches of its only known host scribed from a large woolly gall up to 12 mm plant, Chrysothamnus nauseosus (Fallen) long, typical of that made by another Britton, in western United States; but, the species ofAciurina (Gagne 1986). Dodson morphology of its gall varies strikingly and George (1986) and Headrick et al. within its range. In Idaho, at least three gall (1997) have clarified the status ofAciurina morphs ofA. trixa were reported by Wang- species on C. nauseosus, and this woolly berg (1981); in southern California, we rec- gall is now attributed to the tephritid, A. ognize two gall morphs for A. trixa on C. bigeloviae (Cockerell). We have examined nauseosus (Headrick et al. 1997). such woolly galls from various collections On one of the two gall forms in southern (Washington State University, Pullman; California (Fig. lA), we observed that its University of Idaho, Moscow; G. Dodson, exterior sometimes was covered by small personal collection) and they do, indeed, nodules at different densities among differ- bear R. bigeloviae galls. None of the other ent locations. Upon dissection, each of gall types, as described by Wangberg these nodules was found to contain a small (1981), examined from museum collections cecidomyiid identified for us as Rhopalo- throughout western U.S., including the myia bigeloviae (Cockerell) by Raymond J. smaller resinous gall of A. trixa found in Gagne (Systematic Entomology Labora- California hosted this gall midge (Headrick tory, Agricultural Research Service, et al. 1997). 488 PROCEEDINGS OF THE ENTOMOLOGICAL SOCIETY OF WASHINGTON Fig. 1. (A) The fully formed gall ofAciurina trixa on Chrysothamniis naitseosus; (B) detail of the cecido- myiid, Rhopalomyia bigeloviae, galls on anA. trixa gall; (C) saggital section ofA. trixa and R. bigeloviaegalls; (D) detail of the R. bigeloviae gall with cecidomyiid larva within; (E) the exposed pupa of R. bigeloviae; (F) an adult female ofR. bigeloviae. In southern California, the midge galls midge gall takes on the surface character- become visible in early spring (March) and istics of the host gall. In southern Califor- grow very rapidly (Fig. IB), as do other nia, the midge larvae feed within their gall Rhopalomyia spp. galls (Gagne 1989). The locules as the tephritid larva continues to gall in saggital section is layered exactly develop in its own, much larger, separate like the tissues comprising the parent A. locule (Fig. 1 C, D). Midge development trixa gall, including the smooth, waxy, out- proceeds rapidly and both the tephritid and er layer. On the cottony galls ofA. bigelov- midge co-occur as late-instar larvae, and iae, the midge galls also bear the thick to- pupate at about the same time. The midge mentum of the host fruit fly gall, thus, the pupa forms inside its gall locule, but the VOLUME 99, NUMBER 3 489 waxy apex ofits gall sometimes splits, part- may otherwise reveal not a budding leaf, ly exposing the pupa within (Fig. E). The but rather a de—veloping cecidomyiid gall! gall midge adult emerges in April (Fig. F), Dedication. We would like to dedicate but the fate of this generation remains un- this paper to Raymond J. Gagne in honor known. We know that A. trixa is univoltine ofhis recent retirement from the Systematic on C. nauseosus, with the gall dying after Entomology Laboratory, U.S. Department emergence of the fruit fly adult. Thus, the of Agriculture. current season's tephritid galls are no longer Literature Cited suitable for oviposition by the midge. The options for the adult female gall midge fol- Fernandez, G. W. and P. W. Price. 1994. Life history, courtship, andmatingbehaviorofthegall-forming lowing emergence include, but are not re- Acimina trixa (Diptera: Tephritidae) on Chiyso- stricted to, oviposition into the primordial thanmus nauseosus hololeucus (Asteraceae). Pro- tephritid gall tissues or the axillary bud ceedings of the Entomological Society of Wash- galls of the host plant or oviposition on an- ington 96: 301-307. other part of the host plant, thus cycling Gagne, Raymond. J. 1989. The plant-feeding gall midges of North America. Comstock Publishing between alternate gall types. The latter ap- Associates, Cornell University Press, Ithaca and pears likely as this has been reported for London. 356 pp. other species in this genus (Gagne 1989). Goeden, R. D., D. H. Headrick, and J. A. Teerink. There is as yet no indication that the ceci- 1995. Life history and description of immature stages of Valentibulla californica (Coquillett) domyiid affects the growth and develop- (Diptera: Tephritidae) on Chrysothamnus nauseo- ment of the tephritid and the relationship sus (Pallas) Britton in southern California. Pro- thus appears unequal, with the cecidomyiid ceedings of the Entomological Society of Wash- dependent on the tephritid during this part ington 97: 548-560. of its life cycle. Headrick, D. H., R. D. Goeden, and J. A. Teerink. This is the first known description and l1i9f9e7.hiTsatoxroynoomny oCfhiA-cyisuortihnaomntiriixsa Cnuarursaenosaunsd iitns illustration of a cecidomyiid gall being southern California; with notes on A. bigeloviae formed upon a tephritid gall. Tephritids are (Cockerell). ProceedingsoftheEntomologicalSo- known to be inquilines ofcecidomyiid galls ciety ofWashington 99: 415-428. (Jones et al. 1983), but this is the most in- Jones, R. G., R. J. Gagne, and W. E Barr. 1983. A systematic and biological study ofthe gall midges timate association between gall-forming (Cecidomyiidae) of Artemisia tridentata Nuttall flies of these two families known to us. (Compositae) in Idaho. Contributions of the Some workers may not have previously American Entomological Institute 21(2): 1-79. recognized this phenomenon and interpret- Wangberg, J. K. 1981. Gall-forming habits ofAciuri- na species (Diptera: Tephritidae) on Rabbitbrush ed the growths on tephritid galls as devel- (Compositae: Chrysothamnusspp.) in Idaho.Jour- oping leaves (Fernandez and Price 1994). nal ofthe Kansas Entomological Society 54: 711- This does happen, but closer inspection 732.