Table Of ContentPROC. 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
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