PROC. ENTOMOL. SOC. WASH. 89(3), 1987, pp. 532-547 CHIROSIA BETULETI (RINGDAHL) (DIPTERA: ANTHOMYIIDAE) A GALL-FORMER ON THE OSTRICH FERN, MATTEUCCIA STRUTHIOPTERIS, WITH NOTES ON OTHER INSECT-FERN ASSOCIATES P. VON Aderkas and B. v. Peterson (PvA) Atlantic Research Laboratory, National Research Council, 1411 Oxford Street, Halifax, Nova Scotia B3H 3Z1, Canada; present address: Canadian Forestry Service? Maritimes, Fredericton, New Brunswick, E3B 5P7, Canada; (BVP) Systematic Entomology Laboratory, BBII, Agricultural Research Service, USDA, % National Museum of Natural History, NHB-168, Washington, D.C. 20560, U.S.A. Abstract.? \.diV\diQ of Chi rosi a bet u I eti cause the formation of cover galls in the vegetative leaves of the ostrich fern, Matteuccia struthiopteris. This is the first record of this antho-myiid fly in North America. Females lay their eggs on the unfurling fronds. Newly emerged fly larvae feed on glandular hairs causing the pinnules to curl around the midrib, and partially or completely loop around the feeding larvae. Fly eggs and larvae have been found contaminating the fiddleheads of this edible fern. Larvae were parasitized by bra-conid wasps of the genus Aphaereta and eulophid wasps of the genera Dimmockia and Elachertus. Larvae of the chloropid fly, Elachiptera costata, were secondary invaders of the vacated galls. Larvae of Chirosia betuleti and Elachiptera costata are described in detail for the first time. Effects of the gall on leaf growth are outlined, and the distribution of the galls in a sampled population is described. A cursory description of a gall caused by the tortricid moth, Olethreutes auricapitana, is given, and a list of the primary insects collected and identified from the fern is also provided. Species of the anthomyiid genus Chirosia ops large clonal populations. Chirosia be-Rondani have been reared from several fern tuleti is closely associated with this fern species. Most descriptions of the life cycles species in eastern Canada, and it is the na-of these flies and their effect on the host ture of this association, as well as the eflfect plant are from the bracken fern, Pteridium it has on the fern plant and population, aquilimim (L.) Kuhn (Meijere, 1911; Cam-which we describe in this paper. We also eron, 1930; Meikle, 1937; Brown and describe the unique immature stages of this McGavin, 1982). Chirosia betuleti (Ring-fly species. During the course of this inves-dahl) is known from the fern genera Pteridi-tigation, a number of other insects were col-um and Athyrium in Europe (Meijere, 1911; lected from Matteuccia struthiopteris or in Seidel, 1957) but has not been recorded pre-association with vacated galls. Principal viously from Matteuccia nor from North among these was the chloropid fly, Ela-America. chiptera costata (Loew), whose larva also is Matteuccia struthiopteris (L.) Todaro, the described below. A list of the other primary ostrich fern, is found along flood plains in insects collected from the fern during this the Northern Hemisphere, where it devel-study is also provided.