A New Species of Megaselia Rondani (Diptera: Phoridae) Reared from a Macrodiplosis Kieffer (Diptera: Cecidomyiidae) Gall on Black Oak

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1 A New Species of Megaselia Rondani (Diptera: Phoridae) Reared from a Macrodiplosis Kieffer (Diptera: Cecidomyiidae) Gall on Black Oak Author(s): Charles S. Eiseman and Emily A. Hartop Source: Proceedings of the Entomological Society of Washington, 117(4): Published By: Entomological Society of Washington DOI: URL: BioOne ( is a nonprofit, online aggregation of core research in the biological, ecological, and environmental sciences. BioOne provides a sustainable online platform for over 170 journals and books published by nonprofit societies, associations, museums, institutions, and presses. Your use of this PDF, the BioOne Web site, and all posted and associated content indicates your acceptance of BioOne s Terms of Use, available at terms_of_use. Usage of BioOne content is strictly limited to personal, educational, and non-commercial use. Commercial inquiries or rights and permissions requests should be directed to the individual publisher as copyright holder. BioOne sees sustainable scholarly publishing as an inherently collaborative enterprise connecting authors, nonprofit publishers, academic institutions, research libraries, and research funders in the common goal of maximizing access to critical research.

2 PROC. ENTOMOL. SOC. WASH. 117(4), 2015, pp A NEW SPECIES OF MEGASELIA RONDANI (DIPTERA: PHORIDAE) REARED FROM A MACRODIPLOSIS KIEFFER (DIPTERA: CECIDOMYIIDAE) GALL ON BLACK OAK CHARLES S. EISEMAN AND EMILY A. HARTOP (CSE) 276 Old Wendell Rd., Northfield, MA 01360, USA ( ceiseman@ gmail.com); (EAH) Natural History Museum of Los Angeles County, 900 Exposition Blvd., Los Angeles, CA 90007, USA ( ehartop@nhm.org) Abstract. Megaselia nantucketensis new species (Phoridae) is described from Nantucket Island, Massachusetts, USA. The single specimen was reared from a leaf gall on black oak (Fagaceae: Quercus velutina Lam.) caused by a species of Macrodiplosis Kieffer (Cecidomyiidae). The larva of this univoltine fly is presumed to be a predator on larvae of the gall midge. Key Words: Nantucket, Quercus ilicifolia, Quercus velutina, Fagaceae, scuttle fly, Platygastridae, Metaclisis floridana, Synopeas DOI: / Megaselia Rondani (Phoridae) is a large fly genus with diverse larval habits including scavenging, predation, parasitism, and herbivory (Disney 1994). Two species, M. chainensis Disney and M. submarginalis (Malloch), have been recorded as specialized predators in galls induced by other insects (Robinson and Brown 1993). Here, we describe a new species from Nantucket, Massachusetts, whose larvae apparently have similar habits. MATERIALS AND METHODS Pouch-shaped leaf galls on black oak (Fagaceae: Quercus velutina Lam.) and scrub oak (Q. ilicifolia Wangenh.) were collected by CSE and J. A. Blyth from 16 to 20 May, 2012, as part of an ongoing survey of gall-making and leaf-mining insects on Nantucket Island, Massachusetts, USA. Specific collection sites were South Valley Road ( , ), Squam Farm ( , ), Coskata Woods ( , ), Dead Horse Valley ( , ), and Madequecham Valley ( , ). Each collection entailed filling one or two 12- or 15-dram plastic vials with galls. As larvae emerged on 22 and 23 May, they were transferred to small jars containing a moistened 1:1 mixture of sand and peat, into which they burrowed. These jars were stored in a refrigerator at 1 3 C from mid-december 2012 to 15 April After removal from refrigeration, lids were removed from the jars, which were placed in sealed plastic bags and were checked daily. Emerging insects were preserved in ethanol. Cecidomyiids (specimens CSE296, CSE320, CSE333) were deposited in the National Museum of Natural History, Smithsonian Institution, Washington, DC. The phorid (LACM ENT ) was slide mounted and

3 464 PROCEEDINGS OF THE ENTOMOLOGICAL SOCIETY OF WASHINGTON deposited in the Natural History Museum of Los Angeles County, Los Angeles, California. Platygastrids (CSE327, CSE362) were deposited in the Museum of Zoology, Lund University, Sweden. RESULTS A total of at least 25 cecidomyiid larvae emerged from the galls collected at South Valley Road, Coskata Woods, and Dead Horse Valley. At least one from each site emerged as an adult Macrodiplosis Kieffer between 17 and 23 April R. J. Gagné examined the specimens (all of which were females) but reported (in litt.) that they cannot be placed to species until an intensive study of eastern oak gall-inducing Macrodiplosis is undertaken. The gall of this species (Fig. 1) closely matches that of M. niveipila (Osten Sacken) (Gagné 1989). Male platygastrid wasps emerged from the Dead Horse Valley and South Valley Road jars on 20 and 28 April 2013, respectively. P. N. Buhl determined the former (from black oak) as Synopeas cf. pubescens (Ashmead) and the latter (from scrub oak) as Metaclisis floridana (Ashmead). There are no previous host records for either species. A single male Megaselia emerged from the Dead Horse Valley jar on 1 May (Fig. 2). EAH determined that it belongs to a new species, which is described below, using the streamlined method introduced by Hartop and Brown (2014). Megaselia nantucketensis, new species (Figs. 3, 4) Diagnosis. Male. In the group II key of Borgmeier (1964), M. nantucketensis keys out to M. cirripes Borgmeier, from which it differs immediately by a number of characters, but most noticeably having unequal supraantennals with the lower SAs 0.6 the length of the upper SAs (subequal on M. cirripes), a long seta at the base of R (minute on M. cirripes), and shorter costal setae at 0.09 mm (0.15 mm on M. cirripes). Description. Male. See Table 1. Distribution. Known from a single location in Nantucket County, Massachusetts, USA. Etymology. Named for Nantucket Island, the type locality. Biology. Univoltine; larva developing in a pouch-shaped leaf gall on black oak caused by a Macrodiplosis species (see discussion). Holotype., USA: MASSACHU- SETTS: Nantucket Co., Dead Horse Valley, , , 18. v.2012, em. 1.v.2013, C. S. Eiseman, ex Macrodiplosis gall on Quercus velutina, # CSE402 (LACM ENT ). DISCUSSION Unfortunately the larva of Megaselia nantucketensis was not observed, so its habits are not known with certainty. They maybelikethoseofm. submarginalis, whichpreyonlarvaeofcontarinia negundinis Gillette (Cecidomyiidae) in similar galls on boxelder (Sapindaceae: Acer negundo L.). The galls of both host midges consist of a pouchlike swelling along the underside of a leaf vein, with a narrow longitudinal opening on the upper surface. This opening allows the female phorid to insert an egg inside the gall. In M. submarginalis, the larva preys on three to six cecidomyiid larvae in its lifetime, then drops to the ground to pupariate, emerging as an adult the following spring (Robinson and Brown 1993). At this point we have no indication that the life history of M. nantucketensis differs. CSE s rearing notes indicate that eight cecidomyiid larvae emerged from the Dead Horse Valley galls on 23 May. It is

4 VOLUME 117, NUMBER Fig. 1. Oak leaf gall of Macrodiplosis sp., similar to the one from which Megaselia nantucketensis was reared. Figs Megaselia nantucketensis, holotype male. 2) habitus; 3) genitalia; 4) wing. possible that one of these was actually the phorid larva and was not recognized as something different; the larvae were transferred to soil without close examination. Another possibility is that the galls were placed directly in the jar of soil after larvae first started emerging in the rearing vial, allowing the phorid larva to enter the soil unnoticed. This was not recorded in CSE s rearing notes but has certainly been done in other rearings. Although M. submarginalis

5 466 PROCEEDINGS OF THE ENTOMOLOGICAL SOCIETY OF WASHINGTON Table 1. Description of male Megaselia nantucketensis. Head SA ratio 0.6 VIF position normal SPS vesicles Palpal setae length long Labellum spinosity spinose Thorax Anepisternum hairs + bristles Relative halter color lighter # NP setae 3 NP cleft Scutellar setae 2+2 Leg ts1 palisade 1-5 t2 palisade 0.93 t3 comb bifurcate t3 setulae PD f3 basal setae AV>B f3 basal setae differentiation Wing Wing Length (mm) 1.5 Subcosta complete R seta long R2+3 present Costal index 0.47 Costal ratios 3.88:2.25:1 Costal setae length (mm) 0.09 Number alular setae 3 Alular setae length (mm) 0.13 Wing color lightly infuscated/clear Genitalia AT length AT>E E setation hairs only Relative posterior setation T6<H;C<E requires three or more cecidomyiid larvae to complete development, M. nantucketensis is substantially smaller (EAH compared the holotypes) and may require fewer. We have considered the possibility that the larva of M. nantucketensis is an internal parasitoid of the Macrodiplosis larva, which is approximately 3.3 mm long when mature, but further observations are clearly needed. The other known phorid predator of gall insects, M. chainensis on the elm cockscomb gall aphid Colopha ulmicola Fitch, pupariates within the host gall (Robinson and Brown 1993). All three phorid species inhabit galls with openings that allow for oviposition as well as emergence of mature larvae or adults, and all three have univoltine life cycles synchronized with those of their hosts. ACKNOWLEDGMENTS We thank Julia A. Blyth, Northfield, MA, for assistance in collecting galls; the Nantucket Conservation Foundation and The Trustees of Reservations for permission to collect on their properties; Brian V. Brown, Natural History Museum of Los Angeles County, Los Angeles, CA, for initial examination of the Megaselia specimen; Raymond J. Gagné, Systematic Entomology Laboratory, Agricultural Research Service, USDA, Washington, DC, for examining the Macrodiplosis specimens; Peter Neerup Buhl, Zoological Museum, Copenhagen, Denmark, for examining the platygastrid specimens; two anonymous reviewers for comments on the manuscript; and the Nantucket Biodiversity Initiative for financial and other support for insect surveys on Nantucket. Literature Cited Borgmeier, T Revision of the North American phorid flies. Part II. The species of the genus Megaselia, subgenus Aphiochaeta. Studia Entomologica, 7: Disney, R. H. L Scuttle Flies: The Phoridae. London, Chapman and Hall. 467 pp. Gagné, R. J The Plant-Feeding Gall Midges of North America. Ithaca, Cornell University Press. 356 pp. Hartop, E. A. and B. V. Brown The tip of the iceberg: a distinctive new spotted-wing Megaselia species (Diptera: Phoridae) from a tropical cloud forest survey and a new, streamlined method for Megaselia descriptions. Biodiversity Data Journal 2: e4093. Robinson, W. H. and B. V. Brown Life history and immature stages of two species of Megaselia (Diptera: Phoridae) predatory on gall-inhabiting insects. Proceedings of the Entomological Society of Washington 95(3):