Key for European species of the Cheilosia proxima group (Diptera, Syrphidae) with a description of a new species

Abstract A new hoverfly species, Cheilosia barbafacies Vujić & Radenković sp. n. (Diptera, Syrphidae), is described and distinguished from the closely related species Cheilosia pascuorum Becker, 1894, based on material collected from the mountains of the Balkan Peninsula. Diagnostic characteristics and an identification key for the members of the proxima group of Cheilosia s. str., including the new taxon, are provided.

introduction Cheilosia Meigen, 1822 is the largest Palaearctic hoverfly (Diptera, Syrphidae) genus with nearly 300 species listed by Peck (1988), and 439 described species worldwide (Thompson et al. 2010). Its distribution extends to the Nearctic (more than 80 species), Oriental (about 50 species) and northern part of the Neotropical regions (one species from Chiapas, Mexico, and another one from Guatemala) (Ståhls et al. 2004; Thompson et al. 2010).
All known species undergo larval development in specific plants or fungi, although some species feed on a wide range of plants. There is only one known exception, the species of the subgenus Neocheilosia Barkalov, 1983, which feed on sap and cambium of coniferous trees. One of the most serious pests of genus Cheilosia, is the species C. vulpina (Meigen, 1822) that infested 50% of artichoke (Cynara scolymus) crops in Northern France during the 1980s (Rotheray and Gilbert 2011). Although larvae of species from the proxima group are mostly undescribed, except C. proxima (Zetterstedt, 1843) and C. vulpina, they were observed from different plants by several authors. Very often these larvae mine stems, roots or rhizomes, or, rarely, graze roots externally, as observed in larva of C. proxima found on Cirsium palustre Gilbert 2011). C. gigantea (Zetterstedt, 1838) was reported from Rumex sp.; C. pascuorum Becker, 1894 is an internal feeder in Cynoglossum officinale; C. proxima (Zetterstedt, 1843) was collected from Cirsium palustre and C. oleraceum; C. rufimana (Becker, 1894) was observed ovipositing on Polygonum bistorta, while C. velutina Loew, 1840 mines the stems of Cirsium palustre and the rhizome of Scrophularia nodosa (Speight 2012). While phytophagous hoverflies can cause economic damage by attacking cultivated plants, they can also be used beneficially to control weeds. Examples of this are C. psilopthalma (Becker, 1894) andC. urbana (Meigen, 1822), which have been found to be efficient biological control agents for Hieracium spp., and which are sufficiently host-specific for release in New Zealand where no native Hieracium species exist (Grosskopf et al. 2002).
After detailed analysis of published material under the name Cheilosia pascuorum Becker, 1894 from the Balkan Peninsula (Vujić 1996), one new morphologically cryptic species was discovered and is described in the present text. This new cryptic species belongs to the proxima group of Cheilosia s. str., together with the other Palaearctic species C. balkana, C. gigantea, C. ingerae, C. pascuorum, C. proxima, C. rufimana, C. velutina, and C. vulpina (see Table 1 for distribution). Nielsen and Claussen (2001) presented an identification key and diagnostic characters for the Fennoscandian species of the proxima species group which is here adapted and expanded. In addition, relationships between this species group and related species are discussed.

Methods
The characters used in the key, descriptions, and drawings employ the terminology established by McAlpine (1981); the male genitalia characters are defined by Claussen (1998) and Nielsen and Claussen (2001).
The specimens under study were collected by sweep netting. To study male genitalia, specimens were relaxed and the genitalia were extracted using an insect pin with a hooked tip.
Genitalia were cleared by boiling individually in tubes of water-diluted KOH pellets for 5 min. This was followed by brief immersion in acetic acid to neutralize the KOH and immersion in ethanol to remove the acid. Samples were stored in microvials containing glycerol. Drawings were made with an FSA 25 PE drawing tube attached to a binocular microscope. Measurements were taken with an eye piece graticule or micrometer. Proxima species group Diagnosis. Eyes pale haired; antennal pits separated; vertex grey dusted; central prominence rounded and more protruding than lateral corner of subcranial cavity, in lateral view; face at the level of central prominence less wide than half width of head. Probasisternum of protorax not fused with adjacent sclerites; anterior anepisternum bare; scutellum with black, exceptionally yellow, marginal setae; katepisternum with upper and lower hair patches connected or narrowly divided, entirely dusted; legs predominantly black, except tibiae usually paler on both ends; front coxa without lateral tooth; last tarsomere of front leg unmodified; in females, some hairs on hind tibiae longer, at least more than half of its width. Sternites of abdomen entirely grey dusted; male genitalia: gonostylus with a characteristic dorsal lobe (Figs 1, 2), neither S-shaped ( Fig.  3A) nor sickle-shaped (Fig. 4D, 4E).
Abdomen: Tergites shining, except the whole tergite 2 and dull central area on tergites 2 and 3, which extends from anterior margin of tergite 2 to basal 6/7 of tergite 3, leaving the posterior margin of tergite 3 shining; tergites covered with erected, pale hairs, except few black hairs on posterior half of tergite 4 and on pregenital segments. Sternites grey dusted covered with pale hairs.
FEMALE (Figs 6A, 6B, 7, 9B, 10, 11B). Similar to the male, except for normal sexual dimorphism and the following characters: pile is general shorter and more extensively pale, and legs less dark, basal 1/4 of femora, basal 1/3 and apical 1/4 of tibiae pale; frons with two lateral channels, shiny, except dusted antero-lateral corners (Fig.   Figure 7. Cheilosia barbafacies sp. n., female, tip of wing (x indicates the meeting point of vein M 1 and vein R 4+5 ). Scale in mm. 6B), covered with pale hairs, except a few black hairs around ocellar triangle and above antennae; thorax pale haired, except for a few black hairs on post-alar calli and near wing base; tibiae of fore and middle legs pale, except dark central ring; basal tarsi of fore and middle legs pale; tergites covered with long and erect hairs, except adpressed hairs on central part of tergites 1-4.
Etymology. The specific epithet is derived from the Latin nouns (in apposition) of feminine gender in the nominative case: "barba" (beard) and "facies" (face). The name indicates the presence of long hairs on the face. Distribution (Fig. 13). Cheilosia barbafacies sp. n. is found in two Dinaric mountains in the central part of the Balkan Peninsula, in Durmitor (Montenegro) and Jahorina (Bosnia-Herzegovina), while the related species, C. pascuorum, has a wider range extending from the Alps, across the Balkan Peninsula, to Romania and the European part of Russia (Speight 2012). Both species appear sympatrically within one refuge area rich in endemics and relict species (Durmitor mountain, gorge of river Sušica and glacial lakes Škrčka jezera) (Šimić 1987(Šimić , Vujić 1996. Discussion. Although C. barbafacies has long facial hairs, it is closely related to C. pascuorum with a non-hairy face. Species with long facial hairs were assigned to "group B" of Sack (1928)(1929)(1930)(1931)(1932), based on Becker's (1894) revision of the genus. Also recent authors (e.g. Bartsch et al. 2009) still use this old name ("group B") in their keys for practical reasons. In his recent classification of the genus, Barkalov (2002) included taxa with long facial hairs in seven out of his thirteen subgenera, i.e. subgenera Cheiloisa s. str., Convocheila Barkalov, 2002, Endoiasimyia Bigot, 1882, Floccocheila Barkalov, 2002, Hiatomyia Shannon, 1922, Neocheilosia Barkalov, 1983and Taeniochilosia Oldenberg, 1916. Phylogenetic analysis of the relationship between the genus Cheilosia and the  tribe Rhingiini, based on mtDNA COI gene sequence (Ståhls et al. 2004), revealed that Cheilosia species with this character state can be found in eight clades (see Fig. 1 in Ståhls et al. 2004). It seems clear that the length of the facial pilosity is not a synapomorphic character of any species group, and might evolve several times within the genus Cheilosia.
In Bartsch et al. (2009), specimens of C. barbafacies key out to C. vulpina (group B), and in Van Veen (2004), males and females with dark-brown antennae can be identified as C. vulpina, while specimens with reddish antennae are C. barbata. For the separation of C. barbafacies from C. barbata, diagnostic characters of the proxima group can be used, and the distinction between C. vulpina and C. barbafacies sp. n. is presented in the following key.
Some females of C. barbafacies sp. n. are similar to females of C. redi, and they can be separated by the following characters: C. barbafacies sp. n.: vein M1 meeting vein R 4+5 with an obtuse angle ( Fig. 7: x); hairs on scutum and tergites long and erected (Fig. 9B); hind tibia on posterodorsal surface with few longer hairs ( Fig. 10: y).
C. redi: vein M1 meeting vein R 4+5 with an acute angle; hairs on scutum and tergites shorter and significantly adpressed; hind tibia on posterodorsal surface without long hairs.  Female: vein M1 meeting vein R 4+5 at an obtuse angle ( Fig. 7: x)  Basal 2/3 of hind femur with the anterodorsal hair fringe longer than the anteroventral hair fringe; genitalia with the dorsal lobe of gonostylus with a more or less distinct hook on its dorsal margin (Fig. 3D) ...... C. proxima (Zetterstedt, 1843) -Basal 2/3 of hind femur with the anterodorsal hair fringe as long as or shorter than the anteroventral hair fringe; genitalia with the dorsal lobe of gonostylus simple (Fig. 3E)  Face in lateral view usually concave between central prominence and upper mouth edge (but not distinctly so in all specimens); in dorsal view central prominence of the face not occupying the whole width of the face; occiput behind the upper corners of the eye often completely grey dusted; lunula generally yellowish; scutum with fine punctures, at least anterior half with erect or semi-erect, predominately pale, short hairs, not longer than diameter of hind tibiae, with some longer hairs often intermixed laterally and in front of scutellum .. Vein M1 meeting vein R 4+5 at an obtuse angle (as in Fig 7); arista bare (as in Fig. 4B of Serbia (Genetic resources of agroecosystems in Vojvodina and sustainable agriculture). We also thank Edward Petri and Mike Taylor for kindly improving the English language of this text.