Taxonomic review of the Palaearctic species of the Cheilosia caerulescens-group (Diptera, Syrphidae)

Abstract The Palaearctic species of the Cheilosia caerulescens group (Diptera: Syrphidae) are revised in this work. The species group belongs to the genus Cheilosia subgenus Taeniocheilosia Oldenberg. One new species is described from north Caucasus, Cheilosia (Taeniocheilosia) circassica sp. n. Cheilosia primulae Hering is established as a junior synonym of Cheilosia laeviventris Loew. Four lectotype designations are made. The species of the Cheilosia caerulescens group are redescribed and illustrated, and a table of diagnostic characters and an identification key to species are provided. MtDNA COI barcodes were generated for several specimens of C. (T.) caerulescens Meigen and other Cheilosia (Taeniocheilosia) and Cheilosia s. str. taxa. Parsimony and maximum likelihood analyses did not place the morphologically similar C. hercyniae Loew in the C. caerulescens group but among other Cheilosia (Taeniocheilosia) taxa. The following eight taxa are included in the Cheilosia (T.) caerulescens group of species: Cheilosia armeniaca Stackelberg, 1960, C. caerulescens caerulescens (Meigen, 1822), C. caerulescens calculosa Skufjin, 1977, C. circassica sp. n., C. herculana Brădescu, 1982, C. kerteszi Szilády, 1938, C. laeviventris Loew, 1857, and C. venosa Loew, 1857.


Introduction
institutions are specified for each species. Identification and location labels are indicated with single quotation marks. Handwritten information on labels is indicated.
Terminology follows Thompson (1999) and Barkalov and Cheng (2004) for most terms. Two of the most characteristic morphological features of Cheilosia taxa, the central area of the face below the antennae that is produced anteriorly, and the distinct lateral narrow area between the face and the eye, have been identified by different terms in various publications. The central area of the face below the antennae that is produced anteriorly is named facial knob by Barkalov and Ståhls (1997), central prominence by Nielsen and Claussen (2001), central knob by Barkalov and Cheng (2004), facial tubercle by Claussen and Ståhls (2007), to name a few. The lateral narrow area between the face and the eye (the elongated tentorial arms) are termed paraface (McAlpine 1981, Thompson 1999, ocular strips (Speight 1987), eye margin Ståhls 1997, Barkalov andCheng 2004), orbital stripes (Thompson 1999, Nielsen andClaussen 2001), facial stripes (Hippa and Ståhls 2005), or parafacialia (Claussen and Ståhls 2007). There is no confusion as to which morphological structures of the Cheilosia flies the different terms refer to, and no clear arguments have been presented for establishing a preference among them. In the present study we use 'facial knob' and 'parafacia'.
The material comprising adult flies consists of dry, pinned specimens from the following museums, institutions and private collections:

Coll. C. Claussen
Private collection of Claus Claussen, Germany Coll. D. Doczkal Private collection of Dieter Doczkal, Germany Coll. T Male genitalia were dissected, macerated in 10% KOH, soaked in water and neutralized with 10% acetic acid, and stored in glycerol in plastic microvials on the same pins as the specimens.
For each species figures are provided for the attributes considered relevant for species recognition. Body length was measured dorsally from the anterior margin of lunula to the tip of the abdomen. Drawings are provided of the male genitalia, the profile of the face and the basoflagellomere for the males; and of the dorsal view of frons and basoflagellomere of the females. The figures of male heads show the distribution of pollinosity and pilosity, in females the distribution of pollinosity. The dorsal aspect of the male head is shown in Fig. 1. Photographs are provided to illustrate selected characters of Cheilosia c. caerulescens, C. laeviventris and C. venosa.
When necessary, a lectotype has been designated and labelled accordingly in order to fix the concept of the taxon in question and to ensure the universal and consistent interpretation of the same.
The distribution given in Peck (1988) is cited with additional data from Marcos García (1985), Brădescu (1991), Maibach et al. (1992), Vujić (1996, and unpublished), Barkalov and Ståhls (1997), Reemer et al. (2009) and Ball et al. (2011). In Peck (1988) and Vujić (1996) the country Yugoslavia is used; in the present paper we indicate in which of the presently existing Balkan countries the species are distributed according to the present political borders. New distributional range data (countries) resulting from the present study are indicated with an asterisk.

Laboratory procedures
DNA was extracted from 1-3 legs of dry pinned or ethanol preserved specimens using the Nucleospin Tissue DNA extraction kit (Machery-Nagel, Düren, Germany) following the manufacturer's protocols and then re-suspended in 50 µl of ultra-pure water.
The universally conserved primers LCO1490 and LCO2198 (Folmer et al. 1994) were used for amplifying and sequencing the 5' end of mtDNA COI. PCR reactions were carried out using GE Ready-to-Go PCR beads in 25 µl reaction aliquots containing 1-2 µl DNA extract, 1 µl of each primer (at 10 pmol/µl) and ultrapure water. Thermocycler conditions were initial denaturing at 95°C 2 min, 29 cycles of 30 s denaturing at 94°C, 30 s annealing at 49°C, 2 min extension at 72°C, followed by a final extension of 8 min at 72°C. Amplified PCR products were visualized on 1.5% agarose gels and treated with Exo-SapIT (USB Affymetrix, Ohio, USA) prior to sequencing. Both PCR primers were used for sequencing. The Big Dye Terminator Cycle Sequencing Kit (version 3.1) (Applied Biosystems, Foster City, CA, USA) was used on an ABI 3730 (Applied Biosystems, Foster City, CA, USA) genetic analyzer at the Sequencing Service Laboratory of the Finnish Institute for Molecular Medicine (FIMM), University of Helsinki. The sequences were edited for base-calling errors and assembled using Sequencher™ (version 4.9) (Gene Codes Corporation, Ann Arbor, MI, USA). All new sequences were submitted to the European Nucleotide Archive database (www.ebi. ac.uk/ena) (see Table 2 for accession numbers).
Parsimony analyses for all sequence datasets were performed in NONA (Goloboff, 1999) spawn with the aid of WINCLADA (Nixon, 2002) using the heuristics search algorithm with 1000 random addition replicates (mult*1000), holding 100 trees per round (hold/100), maxtrees set to 100 000 and applying tree-bisection-reconnection branch swapping. Nodal support for each tree was assessed using non-parametric bootstrap resampling with 1000 replicates using WINCLADA. Maximum Likelihood (ML) analysis was done in MEGA version 6 using the General Time Reversible (GTR) model with gamma distributed rates among sites based on model-testing results as implemented in the software (Tamura et al. 2013). Branch support with 1000 bootstrap replications, and pairwise uncorrected p-distances were also calculated using MEGA.

Taxonomy
The Cheilosia (Taeniocheilosia) caerulescens group of species can be distinguished from all other Cheilosia by the combination of the following characters: eye bare, distinctly darkened cross veins of wing, comparatively broad body, usually bi-colored legs, and characteristics of male genitalia structures: superior lobes with distinct left and right process, apical sclerite of aedeagus elongated in lateral direction (Figs 2-12). The following taxa are included in the Cheilosia (T.) caerulescens group of species: Cheilosia armeniaca Stackelberg, 1960, C. caerulescens caerulescens (Meigen, 1822, C. caerulescens calculosa Skufjin, 1977, C. circassica sp. n., C. herculana Brădescu, 1982, C. kerteszi Szilády, 1938, C. laeviventris Loew, 1857, and C. venosa Loew, 1857. Diagnostic characters separating the species and subspecies of the caerulescens group and Cheilosia hercyniae are summarized in Table 1.

Key to species of Cheilosia (T.) caerulescens group and C. (T.) hercyniae
1 Cell bm and cell cup of wing with distinct areas bare of microtrichia (Fig. 7H) ....2 -Cell bm of wing completely microtrichose (Fig. 10H)  Hind margin of scutellum without black bristles or bristle-like pile. R 4 + 5 of wing distinctly curved ( Fig. 11I; 12B); face with lower part not very prominent ( Fig. 11A and D). Hypopygium Fig. 11F Description. ♂: Face in frontal view slightly divergent from level of antennal insertion to lower mouth edge, covered with very weak narrow strip of pollinosity ( Fig. 2A). Facial knob rounded, not very protruding, shining. Parafacia pollinose in upper part and shining in lower part, in its broadest part nearly 1/2 the width (in its narrowest part about 1/3) of basoflagellomere. Frons slightly swollen, shining, with dense white wavy pile. Frontal angle ≈ 90° (Fig. 1, indicated with letter C). Lunula dark-brown. Antennal pits confluent. Vertical triangle with white pile. Eye-contiguity shorter than length of frons without lunula (A < B, see Fig. 1). Antenna dark-brown, basoflagellomere rounded (Fig. 2B). Arista with very short pile. Scutum, scutellum and pleura shining, with only very pale yellowish (almost whitish) pile, longer pile on pleura and posterior part of scutum distally wavy. Scutum and scutellum completely without black bristles or bristle-like pile. Postalar callus without black bristles. Anepisternum and katepisternum shining, with slight pollinosity, with white pile. Katepisternum with dorsal and ventral hair patches connected. Legs mainly black, knees narrowly yellow, tibiae also narrowly yellow at the extreme tip, 1-3 segments of meso-and 2-3 segments of metatarsi reddish (in the paratype metatarsi black with reddish tips of tarsomeres). Apical half of posterior surface of mesofemur with long light pile. Metafemur with short and long white pile ventrally. Halter yellow. Wing with all cross-veins darkened. Cell bm and cell cup of wing with areas bare of microtrichia. R 4 + 5 of wing not distinctly curved. Abdomen oval, shining, densely punctated. Pile erect and white, longer on the lateral parts and shorter on the central parts of tergites. Sternite I with pollinosity, sternites II-IV shining. Pile erect, white on sternites. Hypopygium as on Fig. 2C

Type locality. Österreich [Austria].
Type material studied. Lectotype, ♂, in MNHN. The original description is for both sexes. Becker (1902: 354) mentions only one male specimen which agrees with the original description and he designates it 'Die Type'. The lectotype bears the following labels: 'Meigen' [handwritten in ink, round greyish collection label]; 'caerulescens' [Meigen's handwriting].
Description. Male: Fig. 4A. Face in anterior view slightly divergent from level of antennal insertion to lower mouth edge, with lower part protruding, with pollinosity laterally and below antenna (Fig. 3A). Facial knob moderate in size, shining. Parafacia rather narrow, in width slightly more than 1/2 the width of basoflagellomere, shining in lower part and with pollinosity on upper part narrowly along the eye. Frons slightly swollen, shining, with white and posteriorly some black pile, yellow pile anteriorly along eye inclined. Frontal angle about 90°. Lunula dark brown. Antennal pits confluent. Vertical triangle with black pile. Eye-contiguity about equal or slightly shorter than the length of frons without lunula. Scape and pedicel dark-brown, basoflagellomere small, dark brown to yellowish brown. Arista rather long, with short pile (Fig. 3C). Scutum shining (with bluish tinge), rather coarsely punctated, with whitish to yellowish erect, rather long pile of about even length, intermixed with black pile of same length or slightly longer. Scutellum with yellowish erect pile of same length as on scutum, margin with some longer black or yellow bristles. Postalar callus with 3-5 black bristles. Anepisternum and katepisternum shining, with very slight pollinosity, and with white long pile. Katepisternum with dorsal and ventral hair patches connected. Wing completely microtrichose, hyaline, crossveins darkened. R 4 + 5 of wing not distinctly curved, angle of R 4 + 5 and M 1 about 90°. Halter yellow. Legs with distal part of femora and tibiae, and basal 1/3-1/2 of tibiae yellowish, tarsi dorsally dark-brown. Mesofemur posteriorly with white pile, metafemur anteroventrally and dorsally with long white pile, and ventrally with shorter (stronger) black pile. Abdomen slightly oval, shining (bluish tinge), with coarse punctation, with long erect yellow pile on tergite I, tergites II-IV with erect yellow pile laterally (longest on tergite II), and somewhat shorter erect yellow and black pile intermixed medially. Yellow pilosity on postero-lateral corners tergites II-IV inclined. Sternite I with pollinosity, sternites II-IV shining, all with long yellowish pile. Hypopygium as in Fig. 3E-G.
Female: Fig. 4D. Face as in the male. Eye-margin width about 1/2 the width of basoflagellomere. Frons coarsely punctuated, with whitish erect pile anteriorly, and with black erect pile on posterior part (Fig. 3B). Whitish pile on anterior part of frons inclined along eye. Vertical triangle with black and white pile. Basoflagellomere rounded, reddish brown to dark-brown (Fig. 3D). Scutum shining, with white pile of even length, with few scattered black pile of about the same length or slightly longer intermixed. Postalar callus with 0-3 black or yellow bristles. Scutellum margin with 2-4 black or yellow bristly-like pile. Metafemur with only yellow pile. Tibiae in basal 1/3 yellow, apically narrowly and obscurely yellow, with broad dark ring, tarsi dorsally brown or yellow, with brown segments 4-5 of protarsi, segment 5 of mesotarsi and segments 3-5 of metatarsi. Abdomen oval. All sternites shining. Otherwise as the male.
Remarks. Color of pile on scutum varies from almost yellow with some black pile to yellow with broad stripe of black pile between wing bases ( Fig. 4B-C). Color of tarsi varies from dark to mainly yellow (especially in female). Some studied females do not have yellow bristles or bristle-like pile on scutellum hind margin. The color of basoflagellomere varies from dark brown to yellowish brown. We treat the taxon as subspecies until evidence to the contrary is presented. Fig. 5 Cheilosia caerulescens calculosa Skufjin, 1977:57. Type locality. 'Lipetzk Region, Galichia Gora reserve' (Russia).
Description. ♂: Face in frontal view slightly divergent from level of antennal insertion to lower mouth edge, slightly elongated, shining with stripe of pollinosity. Facial knob moderate, shining (Fig. 5A). Parafacia shining with slight pollinosity, moderate in width, in broadest part about 2/3 of the width of basoflagellomere. Frons very slightly swollen, shining, with white and posteriorly some black pile. Frontal angle slightly < 90°. Lunula dark-brown. Antennal pits separated. Vertical triangle with black pile. Eye-contiguity approximately equal to length of frons without lunula. Basoflagellomere oval, yellow, arista brownish, almost bare, with very short pile (Fig. 5B). Scutum black, shining with fine punctuation, covered with dense erect bright yellow pile of equal length, with black pile of same length intermixed. Postalar callus with black bristles. Scutellum hind margin with some long fine yellow and black pile. Pleurae with rather dense gray pollinosity and yellow waving on the end pile. Dorsal and ventral hair patch of katepisternum connected. Femora black with yellow extreme tips; mesofemur with long yellow pile on posterior surface of basal 4/5 and black pile of apical 1/5. Pile on anterior surface of metafemur long and yellow in basal 2/3 and short and depressed in apical 1/3. Tibiae yellow with black ring, tarsi yellow with black fifth segment. Halter yellow. Wing completely covered with microtrichia, with brown spot on cross-veins. R 4 +  Fig. 5E-G. Female: Face as in male, parafacia shining, narrow, about 1/3 of width of basoflagellomere. Frons comparatively broad with two furrows (Fig. 5D). Vertical triangle with black pile. Basoflagellomere slightly broader than in male (Fig. 5C). Pilosity of scutum and scutellum as in male, but all bristles on scutellum hind margin yellow. Mesofemur with long yellow pile on posterior surface. Tibiae yellow with rather narrow black ring. Tarsi yellow with darkened 5th segment. Wing and abdomen as in male.
Size. Body length 9-10.2 mm. Additional material studied. Russia 4 ♂, 2 ♀ 'Lipetzk Region, Galichia Gora reserve, 24-28. IV.1966 Description. ♂: Face in frontal view slightly divergent from level of antennal insertion to lower mouth edge, with weak narrow strip of pollinosity (Fig. 6A). Facial knob rounded, not very protruding, shining. Parafacia pollinose in upper part and shining in lower part. Parafacia in its broadest part slightly more than 1/2 the width of basoflagellomere. Frons very slightly swollen, shining, with dense white wavy pile. Frontal angle ≈ 90°. Lunula brown. Antennal pits confluent. Vertical triangle with white pile. Eye-contiguity shorter than the length of frons without lunula. Basoflagellomere yellowish brown, rounded (Fig. 6B). Arista with short pile. Scutum, scutellum and pleura shining, with only very pale yellowish (almost whitish) pile, longer pile on pleura and posterior part of scutum distally wavy. Scutum and scutellum completely without black bristles or bristly like pile. Postalar callus without black bristles. Anepisternum and katepisternum shining, with white pile. Katepisternum with dorsal and ventral hair patches connected. Legs mainly black, knees narrowly yellow, tibiae also narrowly yellow at the extreme tip, 1-3 segments of meso and 2-3 segments of metatarsi yellowish. Apical half of posterior surface of mesofemur with long light pile. Metafemur with short and long white pile ventrally, apicoventrally with a few black pile. Halter yellow. Wing with all cross-veins darkened, completely microtrichose, R 4 + 5 of wing not distinctly curved. Abdomen oval, shining, densely punctated. Pile   5.IX.1980, leg. VL Brădescu', in coll. Claussen. Description. ♂: Face in frontal view slightly divergent from level of antennal insertion to lower mouth edge, shining, with very weak stripe of pollinosity, lower part somewhat protruded (Fig. 7A). Parafacia rather narrow, approximately 1/2 the width of basoflagellomere, shining, with slight pollinosity on upper part. Frons slightly swollen, shining, with white and posteriorly some black, pile. Frontal angle ≈ 90°. Lunula black. Antennal pits confluent. Vertical triangle with black and a few yellow pile. Eye-contiguity slightly shorter than length of frons without lunula. Basoflagellomere small, pale-brown to dark-brown, arista rather long, with short pile (Fig. 7B). Scutum shining, rather coarsely punctated, all covered with whitish pile of even length, also on scutellum. Scutellum margin without stronger bristles. Anepisternum and katepisternum partly shining, with white long pile. Katepisternum with dorsal and ventral pile patches broadly divided posteriorly and narrowly connected anteriorly. Halter brownish. Wing with all cross-veins infuscated. Cell bm and cell cup of wing with obvious bare areas (Fig. 7H). R 4 + 5 of wing not distinctly curved. Postalar callus without black bristles. Legs with distal part of femora and apical 1/3-1/2 and distal 1/6 of tibiae yellowish, tarsi yellow to yellowish brown, pile mainly white. Mesofemur posteriorly with long yellow pile. Metafemur ventrally with short black (rather strong) pile, distally dorsally with yellow pile, its anterior surface with long yellow pile. Abdomen shining, with pollinosity on medial anterior 2/3 of tergite II, and on medial anterior 1/3 of tergite III. Abdomen with white erect pile, longer on the sides and shorter medially. Hypopygium Fig. 7E-F. ♀: Face and parafacia as in the male. Frons shining, coarsely punctated, with white erect pile, and mixed with black erect pile on posterior part. Frontal furrows moderate (Fig. 7D). Lunula dark-brown. Basoflagellomere yellowish brown. Scutum shining, with white pile of even length. Otherwise as the male. Size. Body length 10-11 mm. Additional material studied. No additional material available. Distribution. Romania, Montenegro, FYR Macedonia. Fig. 8 Cheilosia hercyniae Loew, 1857:596;Marcos García 1985:518;Çepelak 1986: 53;Brádescu 1991: 39. Chilosia hercyniae: Becker 1894Sack 1932: 78;Šuster 1959:75;Séguy 1961:40. Nigrocheilosia hercyniae: Vujić 1996 Description. ♂: Face in frontal view moderately divergent from level of antennal insertion to lower mouth edge, with slight to moderate pollinosity, but facial knob shining. Facial knob moderately protruding (Fig. 8A). Parafacia rather broad, approximately 2/3 of width of basoflagellomere, with slight pollinosity in upper part and shining in lower part and with short white pile. Frons moderately swollen, shining, with black pile. Frontal angle slightly > 90°. Lunula reddish brown. Antennal pits separated. Vertical triangle with black pile. Eye-contiguity nearly equal to the length of frons without lunula. First and second antennal segment dark-brown, third segment somewhat quadratic, bright orange with dorsal margin black (Figs 8B,12C). Arista pubescent, with very short pile. Scutum shining (bluish ting), finely punctated, with whitish to yellowish erect, rather long, pile of about even length, intermixed with black pile of same length or slightly longer, also on scutellum, margin with 8-10 longer black bristles. Postalar callus with 3-5 bristles. Anepisternum and katepisternum shining, with slight pollinosity, and with whitish and black, rather long, pile intermixed. Katepisternum with dorsal and ventral hair patches broadly divided. Wing brownish. Wing completely microtrichose. R 4 + 5 of wing not curved. Halter yellow, knob dark-brown. Legs with distal part of femora, tibia with basal 1/3-1/2 and distally narrowly yellow, tarsi dorsally dark-brown. Mesofemur posteriorly with long yellow pile and with some black ones on the tip; metafemur ventrally with short black (rather strong) pile, distally dorsally with longer black and yellow pile, its anterior surface with long yellow pile in basal 2/3 and with black pile in apical 1/3. Abdomen slightly oval, shining tergites I-III with brownish pollinosity medially, tergite IV with stripe of pollinosity antero-medially. Pile yellow, erect on all tergites, tergite IV on postero-lateral corners also with black pile. Pregenital segments with pollinosity, with yellow pile. Sternites pollinose with yellow erect pile, sternite IV also with short appressed black pile medially. Hypopygium as on  ♀: Face and parafacia as in male. Basoflagellomere big, bright orange-yellow, quadratic, with a long (≈ 1/3 of the length of antenna) groove on the inner ventral side (Fig. 8C). Anterior 1/3 of frons very shiny, with fine punctation, and very short pile, posterior 2/3 shining, coarsely punctated, with short yellow and longer black erect pile (Fig. 8D). Scutum shining, rather coarsely punctated, with short erect yellow and slightly longer black pile. Scutellum margin with 4-6 rather strong black bristles. Legs as in the male. Wing yellowish. Abdomen oval, shining, densely punctated, tergite I and antero-medial part of tergite II with pollinosity. Pile erect, yellow on lateral parts, long on lateral part of tergite II, and short, black, appressed pile medially. Sternites with slight pollinosity. Otherwise as the male.

Cheilosia hercyniae Loew
Size. Body length 8-11 mm.  Table 2 for data molecular specimen vouchers also used for morphological study.
Type material studied. Type material could not be located, apparently lost. Description. ♂: Face in frontal view slightly divergent from level of antennal insertion to lower mouth edge, shining with very slight pollinosity, lower part somewhat protruded (Fig. 9A). Facial knob rounded, shining, moderately protruded. Parafacia rather narrow, in the upper part approximately 1/2 the width of basoflagellomere, in lower part slightly narrowed. Parafacia shining, or with slight pollinosity on upper part. Frons slightly swollen, shining, with predominantly yellow and a few black pile. Frontal angle ≈ 90°. Lunula black. Antennal pits separated. Vertical triangle with black and a few yellow pile. Eye-contiguity slightly shorter than length of frons without lunula. Basoflagellomere small, brownish, arista rather long, almost bare (or with very short pile) (Fig. 9B). Scutum shining, rather densely punctated, all covered with erect yellow and black pile of even length, pile becoming slightly longer towards scutellum. Postalar callus with few black bristles. Scutellum with only yellow pile, margin without longer black bristles. Anepisternum and katepisternum with slight pollinosity, with yellow long pile. Ventral and dorsal pile patches on katepisternum narrowly connected posteriorly. Halter yellow. Wing with all cross-veins infuscated, completely covered with microtrichia. R 4 + 5 of wing not curved. Legs dark, with apical (1/8) part of femora, and basal 1/2 and apical 1/6 of tibiae yellowish, tarsi yellow, fifth tarsal segment dorsally blackish or brownish. Mesofemur posteriorly with white pile, metafemur anteroventrally and -dorsally with long white pile, and ventrally with shorter (stronger) black pile. Abdomen shining laterally, mid parts of tergites I-III with pollinosity. Tergites with yellow erect pile, longer on the sides and shorter medi-ally. Sternite I pollinose, other sternites shining, pile yellow, erect. Hypopygium as on Fig. 9E-G.
♀: Face and parafacia as in the male. Frons coarsely punctated, with white erect pile, and also with black erect pile on posterior part (Fig. 9D). Parafacia < 1/2 the width of basoflagellomere. Basoflagellomere reddish (Fig. 9C). Postalar callus with no black bristles. Scutum shining, with yellow and more scattered black pile of even length. Abdomen shining, tergite I and anterio-medial part of tergite II with slight pollinosity. Otherwise as the ♂.

Cheilosia laeviventris Loew
Description. ♂: Face in frontal view moderately divergent from level of antennal insertion to lower mouth edge, with pollinosity, lower part of face clearly protruded (Fig. 10A). Parafacia pollinose, moderate in width, approximately 2/3 of width of basoflagellomere. Frons shining, with black pile. Frontal angle slightly > 90°. Lunula dark-brown to black. Antennal pits separated or very narrowly connected. Vertical triangle with black pile. Eye-contiguity nearly equal to or slightly shorter than length of frons without lunula. Basoflagellomere small, rounded, reddish brown to dark-brown (Fig. 10B). Arista moderately long, with short pilosity. Scutum and scutellum shining, densely punctated, with erect, mixed yellow and black pile, of about equal lengths. Central part of scutum with a rather broad transversal band of black pile. Hind margin of scutellum with black bristles or bristle-like pile. Postalar callus with some black bristles. Pleura slightly pollinose, pile predominantly black or mixed. Katepisternum with dorsal and ventral hair patches only narrowly connected anteriorly. Legs black, knees sometimes very narrowly yellowish. Apical half of posterior surface of mesofemur with long black pile, and basal part of anterior surface of metafemur with short black pile. Wing completely microtrichose, with all crossveins infuscated, R 4 + 5 not distinctly curved (Fig. 10H). Abdomen shining with erect, yellow longer pile on lateral parts of tergites, and erect, black pile on central parts of tergites II-III, IV tergite with depressed pile. Tergite I-II with pollinosity medially on all length of tergite, tergite III with pollinosity only narrowly anteriorly or on all length of tergite. Tergite II often with a patch of black pile laterally. Sternites shining. Hypopygium as on Fig. 10E-G.
Size Description. ♂: Face in anterior view moderately divergent from level of antennal insertion to lower mouth edge, with lower part not very prominent, with band of pollinosity (Fig. 11A). Facial knob prominent (nose-like). Parafacia with pollinosity, on lower part shining patch, slightly more than 1/2 the width of basoflagellomere. Frons shining, rather swollen, with black and white pile. Frontal angle ≈ 90°. Lunula dark-brown to blackish. Antennal pits confluent (occasionally only narrowly confluent). Vertical triangle with black pile. Eye-contiguity nearly equal to length of frons without lunula. Basoflagellomere small, rounded, brown to reddish brown. Arista short, thickened, clearly pubescent (Fig. 11B).
Scutum densely punctated, shining, with long, erect yellow pile, medially a transverse band of predominantly black pile. Scutellum on hind margin without (occasionally with some) black bristles. Postalar callus with two bristles. Pleura pollinose, with long black and yellow pile. Dorsal and ventral pile patches of katepisternum only narrowly connected anteriorly. Legs black, knees sometimes yellow, tibia sometimes black ringed. Apical half of posterior surface of mesofemur and basal part of anterior surface of metafemur with long black pile (Fig. 12A). Halter yellow. Wing with all crossveins infuscated, R 4 + 5 distinctly curved (Figs 11I, 12A). Wing completely microtrichose. Abdomen shining, with pollinosity on middle part of tergites I-III. Tergites with long, erect, yellow pile laterally, and black short erect pile medially. Sternites I pollinose, II-IV shining. Hypopygium as on Fig. 11F-H. ♀: Face shining with fine pollinosity on the sides. Parafacia comparatively narrow, pollinose. Frons moderately broad, shining (Fig. 11D), with yellow and black pile (Fig. 11E). Basoflagellomere, small, rounded, black to brownish, with sensory pit (Fig. 11 C). Arista short, with dense, short pile, almost on whole length of arista. Scutum shining, with long, erect yellow and black pile of equal length. Pleura slightly pollinose. Scutellum margin without black bristles. Otherwise as the ♂.

Molecular COI analyses
Sequences COI barcodes were obtained of 658 bp sequence for 27 Cheilosia specimens and two outgroups (see Table 2), including five barcodes for Cheilosia caerulescens. The pairwise uncorrected p-distances for Cheilosia caerulescens samples ranged between 0-1.3%. COI barcodes were also obtained for representatives of subgenus Taeniocheilosia, and a few samples representing Cheilosia s. str. and sg. Eucartosyrhus Barkalov (Table 2).

Phylogenetic trees
Parsimony analysis of the COI data resulted in two equally parsimonious trees of length 494 steps, with Consistency Index of 0.52 and Retention Index of 0.69, and the strict consensus is presented in Fig. 13. The parsimony analysis of the COI barcode data recovered the subgenus Taeniocheilosia as monophyletic with Cheilosia sibirica as sister group to the other included taxa. Cheilosia (T.) hercyniae was resolved among the other sg. Taeniocheilosia taxa. The obtained ML tree resolved the same topology the as the parsimony analysis (Fig. 14), except for slight change in position for C. hercyniae. In  the parsimony tree Cheilosia (Taeniocheilosia) hercyniae was resolved as sister group to ((C. gagatea Loew, 1857+ C. derasa Rondani, 1857) + (C. pedemontana Rondani, 1857 + C. personata Loew, 1857)), and in the ML tree as sister group to (C. pedemontana + C. personata).

Discussion
The Cheilosia (Taeniocheilosia) caerulescens species group presently comprises eight species. Their distribution is predominantly in the mountainous areas of Europe and Caucasus, but C. caerulescens calculosa is known from chalk slopes at the of the river Don in Lipetsk region (Russia) and C. caerulescens caerulescens is widely distributed in central Europe including both lowland and mountainous areas. The larval host plant is known for C. caerulescens caerulescens, the larvae are phytophagous mining the leaves of species of genus Sempervivum (Aguilar and Coutin 1988, Stuke 2000) and for C. laeviventris (as C. primulae) with larvae reared from Primula auricola (Hering 1944). The taxon has spread in last decades and was reported for the first time for Netherlands by van der Goot in 1989 and in Great Britain in 2008 by Collins and Halstead, and has been listed as a garden pest species in the Netherlands by Reemer (2003).
We consider the C. caerulescens calculosa subspecies as a relict form. According to Skufjin and Kuznetsova (1982) this subspecies "belongs to boreomontane relict forms associated with lower alpine plants growing on poor limestone and marl soils on steep slopes of Central Russian Upland". The larval host plant is unknown for this taxon. In a forthcoming study we aim to resolve the rank of the taxon, specific or subspecific, by obtaining fresh samples of the taxon from the type locality for molecular analysis.
Neither the parsimony analysis nor the ML analysis resolved Cheilosia hercyniae among the included C. caerulescens group species, but among other sg. Taeniocheilosia taxa in congruence with conclusions based on morphological characters. C. hercyniae shares the character of infuscated wing cross-veins and bi-coloured legs with the members of the Cheilosia caerulescens group, but differs from all C. caerulescens group species in having a bright orange-yellow basoflagellomere and hair patches of katepisternum widely separated. In male genitalia C. hercyniae is similar to some sg. Taeniocheilosia species, e.g. Cheilosia pedemontana, C. gagatea and C. faucis (Becker, 1894) in the shape of the superior lobe.
The COI barcode of Cheilosia kerteszi is not full length and is very similar to the COI of the included C. caerulescens samples, but not identical to anyone of them. Identical or near identical COI barcodes of closely related Eristalinae species has also been recorded for Merodon species groups, see e.g. Šašić et al. (2016).
The studied group can be regarded as a morphologically intermediate group between the subgenera Cheilosia (Neochilosia Barkalov) and Cheilosia (Eucartosyrphus Barkalov), as the colour of the legs of its members is similar to that of the latter, but the presence of a large plate on the left process of superior lobe of hypandrium indicates an affiliation of this group to the subgenus Neochilosia.