Revision of the Merodon serrulatus group (Diptera, Syrphidae)

Abstract The phytophagous hoverfly genus Merodon Meigen, 1803 (Diptera, Syrphidae), which comprises more than 160 species distributed in Palaearctic and Afrotropical regions, can be differentiated into multiple groups of species that harbor high levels of hidden diversity. In this work, the serrulatus species group of Merodon is revised, providing an illustrated key to species, a detailed discussion on the taxonomic characters and a morphological diagnosis, including also the first data about the preimaginal morphology of this species group. The study includes characteristics of the 13 species of the M. serrulatus group, along with the available distributional data. Moreover, descriptions are provided for seven new species, namely M. defectus Vujić, Likov & Radenković sp. nov., M. disjunctus Vujić, Likov & Radenković sp. nov., M. medium Vujić, Likov & Radenković sp. nov., M. nigrocapillatus Vujić, Likov & Radenković sp. nov., M. nigropunctum Vujić, Likov & Radenković sp. nov., M. opacus Vujić, Likov & Radenković sp. nov., and M. trianguloculus Vujić, Likov & Radenković sp. nov. In addition, the taxa M. serrulatus (Wiedemann in Meigen, 1822), M. bequaerti Hurkmans, 1993, M. hirsutus Sack, 1913, M. kawamurae Matsumura, 1916, M. sacki (Paramonov, 1936) and M. sophron Hurkmans, 1993 are redefined and redescribed. Following a detailed study of the type material sourced from different entomological collections, the status of all available taxa related to M. serrulatus is revised and a new synonymy is proposed: M. tener Sack, 1913 syn. nov. (junior synonym of M. serrulatus). The identity of M. trizonus (Szilády, 1940) could not be assessed as the type specimens are lost. Thus, the name M. trizonus is considered as nomen dubium. The monophyly and composition of this species group are assessed through Maximum Parsimony and Maximum Likelihood analyses of the mitochondrial COI and nuclear 28S rRNA gene sequences.


Introduction
The phytophagous hoverfly genus Merodon Meigen, 1803 contains more than 160 species distributed across the Palaearctic and Afrotropical regions (Ståhls et al. 2009). Adults mimic bees and bumblebees (Hymenoptera: Apidae) and feed on pollen and nectar from early spring to autumn (Hurkmans 1993;Speight 2018). Based on the immature stages of Merodon found to date, underground storage organs (bulbs, corms and rhizomes) of geophytes of the families Asparagaceae, Amaryllidaceae and Iridaceae are larval microhabitats of this taxon and phytophagy is its feeding mode (Ricarte et al. 2017;Preradović et al. 2018). The immature stages of only eight Merodon species have been described to date (Heiss 1938;Stuckenberg 1956;Ricarte et al. 2008Ricarte et al. , 2017Andrić et al. 2014;Preradović et al. 2018) and a detailed literature review on the immature stages of Merodon, including host plants, has recently been published by Ricarte et al. (2017).
The taxonomic status and identification of many Merodon species requires further investigation, as the genus contains a high number of species groups consisting of morphologically cryptic taxa with very subtle morphological differences. In various recent publications, an integrative taxonomic approach combining morphological and molecular information has been adopted and resulted useful in resolving taxonomic ambiguities in hoverflies, e.g., in Merodon equestris species complex , Merodon avidus complex (Popović et al. 2015;Ačanski et al. 2016), Merodon aureus species group (Šašić et al. 2016), genus Chrysotoxum Meigen, 1803 (Nedeljković et al. 2013(Nedeljković et al. , 2015 and Melanostoma Schiner, 1860 (Haarto and.
In this study, we present a taxonomic review of the serrulatus species group based on a detailed examination of material gathered as a part of our long-term field research in the Palaearctic region, especially in the Mediterranean and the Middle East. Our aims are 1. to review materials stored in several major entomological institutions and private collections holding specimens of this group; 2. to define and describe the taxa within the serrulatus species group, including new species; 3. to infer the phylogenetic relationships among the members of this species group using mtDNA COI gene and the 28S rRNA gene; and 4. to present the first data about the preimaginal morphology of the M. serrulatus species group.

Material examined
Most of the recently collected specimens were sampled by sweep net. Further specimens of the Merodon serrulatus species group were sourced from collections deposited in museums and universities which are listed below. Consisted total of 1,083 specimens collected from 1837 to 2018 across 22 countries (i.e., Algeria, China, Croatia, France, Greece, Israel, Italy, Kazakhstan, Kyrgyzstan, Libya, Montenegro, Morocco, North Macedonia, Portugal, Russia, Spain, Syria, Tajikistan, Tunisia, Turkey, Turkmenistan, and Uzbekistan) were studied for the present study.
The information on labels of the material examined is provided for each studied specimen in the following order: country name, a bullet point (indicating the beginning of a material citation), number and sex of specimen(s), locality data, geographical coordinates, altitude, collection date, collector(s) followed by "leg.", institutional acronym and specimen codes/unique identifiers ("to" indicates range). The specimens are listed alphabetically by country and subsequently by increasing latitude (south to north) within each country. In the quotations of the type specimens' original label data, double quotation marks were used to indicate separate labels, and the slash was adopted to indicate a new line within a label, with additional details and interpretations provided in square brackets, where applicable.

WML
World Museum Liverpool, Liverpool, UK ZHMB Zoological (Zoologisches) Museum of the Humboldt University, Berlin, Germany ZMKU Zoological Museum, State University of Kiev, Kiev, Ukraine ZMUC Zoological Museum, Natural History Museum of Denmark, University of Copenhagen, Copenhagen, Denmark

Taxonomic study of adults
The type material of all described species of the Merodon serrulatus species group were studied, with the exception of the type material of Merodon trizonus (Szilády, 1940) because the type specimens are lost.
To study the male genitalia, dry specimens were relaxed in a closed pot containing water to ensure high humidity levels, and the genitalia were extracted using an insect pin with a hooked tip. Genitalia were cleared by boiling them individually in tubes of water-diluted KOH pellets for 3-5 minutes. This was followed by brief immersion in acetic acid to neutralize the KOH, immersion in ethanol to remove the acid, and storage in microvials containing glycerol. Specimens' measurements were taken in dorsal view with a micrometer and are presented as ranges. Body length was measured from the lunule to the end of the abdomen. Drawings were made using a FSA 25 PE drawing tube attached to a binocular microscope Leica MZ16. Specimens photographs were captured by a Nikon D7100 camera connected to a personal computer, as well as a Leica DFC 320 digital camera attached to a Leica MZ16 binocular microscope. After photographing, CombineZ software (Hadley 2006) was used in order to create composite image with an extended depth of field, created from the in-focus areas of each image. Terminology adopted in the morphological descriptions follows Thompson (1999) and, for male genitalia, Marcos-García et al. (2007), while the term "fossette" follows Doczkal and Pape (2009).
Localities were geo-referenced in Google Earth (Google Inc, California, USA, https://www.google.com/earth; accessed on 10.02.2019). Geographic coordinates of localities were represented in GenGIS (v 2.5.3) (Parks et al. 2013) in order to create distributional maps.

The study of preimaginal morphology
Sampling A targeted search for immature Merodon hoverflies was conducted in the chestnut forest of Agiassos, Lesvos Island (Greece). Abundant population of M. serrulatus and other Merodon species were found at this locality. Searches for larvae were carried out during a field trip from February 27 to March 10 2006, as owing to their biological cycle, these Merodon species would be in immature stages (larvae or pupae) during this period. An area of ca. 3m 2 , where the presence of many bulb species and adults of Merodon were reported the previous year was selected. The whole area was excavated to a depth of approximately 20 cm and the soil was sieved searching for the larvae. Only one larva (third larval stage) was found in the soil surrounding bulbs of different plant genera, such as Fritillaria Tourn. ex L., Gagea Salisb., Muscari Miller, and Ornithogalum L. This solitary larva was kept in a plastic container with the soil in which it had been found at room temperature until it pupated two days later. The adult of M. opacus sp. nov. emerged on 21 March 2006 after spending 17 days in the pupal stage.

Morphological study
The cephalopharyngeal skeleton was removed from the antero-ventral margin of the puparium using entomological pins. After dissection, the cephalopharyngeal skeleton was soaked in 10% KOH and heated for 15 min in order to remove the remaining tissues attached, after which it was soaked for a few minutes in acetic acid followed by 70% ethanol. Once the tissues had been cleared, the skeleton was preserved in glycerin. Debris adhering to the puparial integument was removed with pins and brushes and by placing the specimens in an ultrasonic cleaner for a few minutes. The cleaned specimen was mounted on stubs and was examined with a scanning electron microscope (S3000N Hitachi) at 20 kV using variable-pressure (or low vacuum) mode, as this technique allows a direct evaluation of the specimens without coating the samples with gold. The stereomicroscope Olympus SZX16 (equipped with Olympus U-TVO.5XC-3 camera) was used for the examination and to capture images of the puparium (general view) and the cephalopharyngeal skeleton. Dimension measurements (in mm) were performed on preserved specimens using a Leica MZ9.5 binocular microscope.
The terminology for immature stages adopted here follows Rotheray (1993) and Rotheray and Gilbert (1999), whereas certain characters of the cephalopharyngeal skeleton are determined in line with Hartley (1963), and our morphological character descriptions are based on Merodon puparia descriptions provided by other authors (Heiss 1938;Stuckenberg 1956;Ricarte et al. 2008Ricarte et al. , 2017Preradović et al. 2018). The studied material has been deposited at the University of Alicante, Spain (CEUA).

Molecular analysis
The specimens subjected to molecular analysis are presented in Supplementary file 8: Table 1. DNA voucher specimens were deposited in FSUNS, EMIT, SZMN, and MZH. The genomic DNA of each specimen was extracted from two or three legs using a slightly modified SDS extraction protocol (Chen et al. 2010). For this purpose, the D2-3 region of the nuclear 28S ribosomal RNA gene and the mitochondrial protein-coding cytochrome c oxidase subunit I (COI) gene were amplified. Primer pair F2 and 3DR was used for the amplification of 28S rRNA gene region (Belshaw et al. 2001), whereas C1-J-2183 (alias Jerry) and TL2-N-3014 (alias Pat) primer pair (Simon et al. 1994) was chosen for 3'-end of COI gene, and for 5'-end COI gene, we used LCO1490 and HCO2198 primer pair (Folmer et al. 1994). The PCR reactions were carried out according to Kočiš Tubić et al. (2018). The amplification products were enzymatically purified by Exonuclease I and FastAP Thermosensitive Alkaline Phosphatase enzymes (ThermoScientific, Lithuania) and sequenced using only forward primers on an ABI3730x1 Genetic Analyzer (Applied Biosystems, Foster City, CA, USA) at the Finnish Institute for Molecular Medicine (FIMM), Helsinki, Finland.

Data analysis
In order to establish the systematic position and composition of the Merodon serrulatus group, samples representing the four main Merodon lineages were analyzed following the approaches described by Šašić et al. (2016) and Radenković et al. (2018b), while two further Merodontini species served as outgroups, i.e., Platynochaetus macquarti Loew, 1862 and Eumerus grandis Meigen, 1822 (see Supplementary file 8: Table 1 for GB accession numbers of all analyzed species and outgroups). Alignment of the obtained COI sequences was achieved using the Clustal W algorithm (Thompson et al. 1994) implemented in BioEdit (Hall 1999), while rRNA 28S gene was aligned by the multiple alignment using Fast Fourier Transform (MAFFT) program (Katoh et al. 2005(Katoh et al. , 2009), version 7, which implements iterative refinement methods (Katoh and Standley 2013). The E-INS-i strategy was chosen (Katoh et al. 2009). All sequences in the analyzed twogene dataset (concatenated COI and 28S rRNA gene sequences) were trimmed to equal lengths. Phylogenetic tree construction was performed by conducting Maximum Parsimony (MP) and Maximum Likelihood (ML) analyses. The parsimony analysis was conducted using NONA (Goloboff 1999), spawned with the aid of ASADO, version 1.85 (Nixon 2008), using the heuristic search algorithm (settings: mult*1,000, hold/100, max trees 100,000, TBR branch swapping). GTRGAMMA model was determined as the best choice model for the analysed dataset using MEGA 7 (Kumar et al. 2016). The dataset was divided into two partitions: COI gene and 28S rRNA gene. The ML tree was constructed by RAxML 8.2.8 (Stamatakis 2014) using the CIPRES Science Gateway (Miller et al. 2010) and applying the general time-reversible (GTR) evolutionary model with a gamma distribution (GTRGAMMA) (Rodríguez et al. 1990). Nodal support was estimated using nonparametric bootstrapping with 1,000 replicates for both MP and ML trees, which were rooted on Platynochaetus macquarti.

Merodon serrulatus group
Diagnosis. Member species of the Merodon serrulatus species group exhibit a distinctive and characteristic basolateral protrusion (lateral hump) on the posterior surstyle lobe (Fig. 1A, B: bp, 6: bp, 14C: bp). They are relatively large (11-15 mm) species with a dark scutum and white microtrichose fasciae (at least in females) on the dark olive brown terga 2-4 (as in Fig. 2); tergum 2 usually with a pair of reddish orange lateral maculae. Antennae dark brown (as in Fig. 5).
Intraspecific variability. In most of the taxa in the Merodon serrulatus species group, the length of pile on the metafemur and the presence of microtrichia on the scutum and terga is highly variable among specimens of the same species. The Merodon serrulatus species group consists of 13 species, namely M. bequaerti, M. defectus sp. nov., M. disjunctus sp. nov., M. hirsutus, M. kawamurae, M. medium sp. nov., M. nigrocapillatus sp. nov., M. nigropunctum sp. nov., M. opacus sp. nov., M. sacki, M. serrulatus, M. sophron Hurkmans, 1993, and M. trianguloculus sp. nov. Taxonomy and nomenclature of the species belonging to the Merodon serrulatus species group Hurkmans, 1993 Figs 8A, B, 9A-C, J, 10A, B, 11A-C Diagnosis. Large (8-11.9 mm), dark brown species with pairs of narrow microtrichose fasciae on terga 2-4 in males, in some specimens absent; metafemur with long pile on ventral margin; the longest pile as long as one third to half of width of metafemur (Fig.  8); apical part of anterior surstyle lobe rhomboid shape, covered with dense, short pile, and strong dark brown marginal pile on posterior surstyle lobe ( Fig. 9A: al, J); females with very narrow microtrichose fasciae on terga 2-4 and sparse pilosity on ventral margin of metafemur, only with few longer pile. Similar to Merodon sacki but differs in a less curved metafemur and generally shorter body pile in males, clearly visible on tergum 4 (Fig. 10), and by well separated anterior and posterior surstyle lobe (Fig. 9A), almost fused in M. sacki (Fig. 9D). Related to M. sophron, but differs in more incrassate metafemur (Fig. 8A, D), longer pile on ventral margin of metafemur in both sexes (Fig.    Redescription (based on the type material and additional specimens). Male. Head. Antennae black to dark brown; basoflagellomere 1.7-2.1 times as long as wide, and 2.3 times as long as pedicel, concave dorsally with acute apex; fossette dorsolateral ( Fig.  11); arista dark and thickened at basal one third, covered with dense microtrichia; arista 1.4-1.7 times as long as basoflagellomere (Fig. 11A, B); face and frons black with gray microtrichia, face covered with dense whitish gray, and frons with yellowish gray pile; oral margin shiny with microtrichose lateral areas; lunule shiny black, bare; eye contiguity 10-12 facets long; vertex isosceles, shiny covered with golden microtrichia in front of ocellar triangle; vertex with long, pale whitish yellow pile mixed with black pile on the ocellar triangle; ocellar triangle equilateral; occiput shiny, with gray-yellow pile, covered with a dense, gray microtrichia in ventral half; eyes covered with dense pile.

Merodon bequaerti
Thorax. Scutum and scutellum black with bronze luster, covered with dense, erect, yellow pile; scutum at wing basis with short black pile, in some specimens with fascia of black pile between wing basis; scutum with two or more microtrichose vittae, anteriorly connected and posteriorly reaching the scutellum; posterodorsal part of anterior anepisternum, posterior anepisternum (except anteroventral angle), anterior anepimeron, dorsomedial anepimeron, and posterodorsal and anteroventral parts of katepisternum with long, pale yellow pile and grayish microtrichia; wings entirely covered with microtrichia; wing veins brown; calypteres and halteres pale yellow; legs without spinae or other protuberances; legs mostly black, except brown tarsi ventrally in some specimens; pile on legs pale yellow, except black pile at apical one fourth of metafemur; metafemur curved and incrassate, ca. three times longer than wide; pile on postero-and anteroventral surface long, and ca. one third to half of width of metafemur, slightly longer than pile on dorsal margin (Fig. 8A).
Abdomen. Wide, tapering, 1.2 times longer than mesonotum; terga dark brown to black, with or without pairs of narrow microtrichose fasciae; tergum 2 with orange lateral maculae; pile on terga all yellow, except few black pile on medial part of terga 3 and 4 in some specimens (Fig. 10A, B); sterna dark brown, covered with long whitish/yellow pile.
Male genitalia. Apical part of anterior surstyle lobe rhomboid shape, 1.5 times longer than wide, covered with dense, short pile, and strong dark brown marginal pile ( Female. Similar to the male except for normal sexual dimorphism and for the following characteristics: antennae with rounded tip, basoflagellomere 1.7-1.9 times longer than wide (Fig. 11C); frons with microtrichose vittae along eye margins; frons covered with pilosity of variable color, from mostly gray-yellow until predominantly black; ocellar triangle covered with black pile; ventral margin of metafemur with sparse pilosity, only few pile longer (Fig. 8B); lateral side of terga, anterior two third of tergum 2 and all tergum 5 with yellow pile; terga 2-4 with short adpressed black pile and with very narrow microtrichose fascia.
Ecology. Preferred environment: unimproved montane grassland, including open, grassy areas in pine forest or Mediterranean scrub. Flowers visited: no data. Flight period: February-June.
Thorax. Scutum and scutellum black with bronze luster, covered with dense, erect, yellow pile; scutum at wing basis with short black pile and some black pile between wing basis, from few ones to fascia of black pilosity in some specimens; scutum usually with two or more microtrichose vittae, anteriorly connected and posteriorly reaching the scutellum; scutum dull; posterodorsal part of anterior anepisternum, posterior anepisternum (except anteroventral angle), anterior anepimeron, dorsomedial anepimeron, and posterodorsal and anteroventral parts of katepisternum with long, pale yellow pile and grayish microtrichia; wings entirely covered with microtrichia; wing veins brown; calypteres yellowish; halteres brown-yellow; legs mostly black, except brown tarsi ventrally in some specimens; pile on legs gray-yellow; metafemur moderately in-  crassate, ca. three times longer than wide; pile on postero-and anteroventral surface of medium length; pile on dorsolateral surface dense and length ca. one third to one fourth of width of metafemur (Fig. 13E).
Female. Similar to the male except for normal sexual dimorphism and for the following characteristics: basoflagellomere ca. two times longer than wide (Fig. 12K), fossette dorsal; frons with broad microtrichose vittae along eye margins; frons covered with pilosity of variable color, from mostly gray-yellow to predominantly black; ocellar triangle covered with black pile; terga with whitish pile, except terga 2-5 medially with short black pile; microtrichose fasciae on terga 3 and 4 conspicuous (Fig. 15C).
Distribution. Merodon defectus sp. nov. has been identified in western Turkey (Fig. 7). Ecology. Preferred environment: forest/open ground; thermophilous and evergreen Quercus forest; Castanea forest, dry Pinus forest; unimproved grassland and tracksides; coniferous forest with some yellow flowers along a stream [Reemer and Smit (2007) refer to this last observation as being Merodon alexeji Paramonov, 1925].  Description. Male. Head. Antennae black; basoflagellomere short, 1.2 times as long as wide, and ca. 1.7 times as long as pedicel, and with rounded apex; large fossette dorsomedial and dorsolateral including apex of basoflagellomere (Fig. 12G); arista black and thickened at basal one third, covered with dense microtrichia, 1.5 times as long as basoflagellomere ( Fig. 12G-H); face and frons black with gray microtrichia; face covered with dense whitish gray, while frons with mostly black pile (Fig. 16A); oral margin shiny, with lateral microtrichose area; lunule shiny black, bare; eye dichoptic, separated by distance of 3-5 facets (Fig. 16B); vertex isosceles, covered with dark gray microtrichia and long, black pile; ocellar triangle equilateral; occiput shiny covered with black pile in upper half, ventrally with gray-yellow pile and dense, gray microtrichia; eyes covered with dense pile.
Thorax. Scutum and scutellum dull, with bronze luster, covered with dense, erect, yellowish pile, except posterior half medially with few to many black pile intermixed; in some specimens scutellum with few black pile; scutum with indistinct microtrichose vittae (Fig. 17A); posterodorsal part of anterior anepisternum, posterior anepisternum (except anteroventral angle), anterior anepimeron, dorsomedial anepimeron, and posterodorsal and anteroventral parts of katepisternum with long, dark gray pile and gray-  ish microtrichia; wings entirely covered with microtrichia; wing veins yellow-brown; calypteres and halteres whitish yellow; legs black, except yellow-brown tarsi, tip of femora and basal part of tibiae; pile on legs mostly yellowish; metafemur moderate incrassate, ca. five times longer than wide; pile on postero-and anteroventral surface long, ca. half to two thirds of width of metafemur, as same length as pile dorsally (Fig. 17B).
Abdomen. Tapering, ca. 1.2 times longer than mesonotum; terga dark brown to black, except for a pair of yellow-orange, triangular, lateral maculae on tergum 2; terga 2-4 with conspicuous or with trace of white microtrichose pair of fasciae (variable character); pile on terga mostly yellow, except terga 3 and 4 medially with black pile; sterna dark brown to black, covered with long whitish pile.
Male genitalia. Apical part of anterior surstyle lobe rhomboid in shape, ca. 1.5 times longer than wide, covered with dense, short pile ( Female. Similar to the male except for normal sexual dimorphism and for the following characteristics: basoflagellomere 1.6-1.8 times longer than wide, fossette large, dorsolateral ( Fig. 12I); frons mostly microtrichose and predominantly covered with black pile; ocellar triangle covered with black pile; microtrichose fasciae on terga 3 and 4 conspicuous.
Etymology. The name derives from the Latin adjective disjunctus meaning separated, disconnected which pertains to the dichoptic eyes in the males.
Distribution. Merodon disjunctus sp. nov. has so far only been recorded in Kyrgyzstan and Kazakhstan (Fig. 7).
Ecology. Preferred environment: no data. Flowers visited: no data. Flight period: May-July. Redescription (based on lectotype and additional specimens from the type locality, Syria, and Israel). Male. Head. Antennae black to dark brown; basoflagellomere elongated ca. two times as long as wide, and 2.2-2.5 times as long as pedicel, concave dorsally with acute apex; large fossette dorsolateral and dorsomedial; arista dark and thickened at basal one third, covered with dense microtrichia, 1.6-1.7 times as long as basoflagellomere ; face black with gray microtrichia, covered with whitish pile; frons mostly shiny, with yellowish gray pile; oral margin microtrichose, with small, shiny lateral area; lunule shiny black, bare; eye contiguity 12-14 facets long; vertex isosceles, with long, pale whitish yellow pile, mixed with black pile on the ocellar triangle; ocellar triangle equilateral; occiput with gray-yellow pile; eyes covered with dense pile (Fig. 20A); vertical triangle: eye contiguity: frons = 1.4 : 1 : 2 .
Thorax. Scutum and scutellum black with bronze luster, covered with dense, erect, yellow pile; scutum at wing basis with short black pile; scutum usually with two or more microtrichose vittae, anteriorly connected and posteriorly reaching the scutellum; scutum dull; posterodorsal part of anterior anepisternum, posterior anepisternum (except anteroventral angle), anterior anepimeron, dorsomedial anepimeron, and posterodorsal and anteroventral parts of katepisternum with long, pale yellow pile and grayish microtrichia; wings entirely covered with microtrichia; wing veins brown; calypteres and halteres yellowish; legs mostly black, except brown tarsi ventrally in some specimens; pile on legs pale yellow, except black pile at apical one third of metafemur; metafemur moderately incrassate, ca. three times longer than wide; pile on posteroand anteroventral surface very short; pile on dorsolateral surface long and dense ca. as half of width of metafemur (Fig. 13C).
Male genitalia. Apical part of anterior surstyle lobe rhomboid shape, ca. two times longer than wide, covered with short pile ( Female. Similar to the male except for normal sexual dimorphism and for the following characteristics: antennae with rounded tip, basoflagellomere 1.8-2 times longer than wide, fossette dorsolateral (Fig. 19D); frons with narrow microtrichose vittae along eye margins; frons covered with variable pilosity, from mostly gray-yellow to predominantly black; ocellar triangle covered with black pile; metafemur with shorter pile on dorsolateral surface (Fig. 13D); terga mostly with yellowish pile on tergum 2 and with whitish pile on terga 3-5, except terga 2-4 medially with short black pile; microtrichose fasciae on terga 3 and 4 narrower (Fig. 21F, G).
Ecology. Preferred environment: no data. Diagnosis. Medium sized (7.7-11.2 mm), with olive-brown reflection; antennae reddish brown; body pile predominantly pale, except some black pile on vertex and terga 2-4 medially; basoflagellomere short, ca. 1.2 times as long as wide, with large dorsal to dorsolateral fossette, and short arista ( Fig. 19E-H); tergum 2 with reddish yellow lateral maculae; tergum 3 laterally reddish or brown; metafemur incrassate with long pilosity as long as half of width of metafemur in male and as one third of width of metafemur in female (Fig. 22A Redescription (based on the types of Merodon micromegas and additional material from China). Male. Head. Antennae reddish brown; basoflagellomere short, ca. 1.2 times as long as wide, and ca. two times as long as pedicel, straight dorsally with acute apex; dorsal to dorsolateral fossette large; arista reddish brown and thickened at basal one third, covered with dense microtrichia, ca. 1.3 times as long as basoflagellomere ( Fig. 19E-G); face and frons black with gray microtrichia, face covered with dense whitish, and frons with yellowish white pile; lunule shiny black, bare; vertex isosceles, dull, in front of anterior ocellus covered with dense microtrichia; vertex with long, pale yellow pile, in some specimens mixed with black or dark gray pile on the ocellar triangle; ocellar triangle isosceles; eyes covered with dense pile; occiput with gray-yellow pile, ventrally covered with a dense, gray microtrichia; eye contiguity ca. ten facets long; vertical triangle: eye contiguity: frons = 2.5 : 1 : 2.5.
Thorax. Scutum and scutellum black with bronze luster, covered with dense, erect yellow pile; scutum usually with indistinct microtrichose vittae; posterodorsal part of anterior anepisternum, posterior anepisternum (except anteroventral angle), anterior anepimeron, dorsomedial anepimeron, and posterodorsal and anteroventral parts of katepisternum with long, dense pale yellow pile and grayish microtrichia; wings entirely covered with microtrichia; wing veins reddish brown; calypteres and halteres pale yellow; legs mostly black, except tip of femora and basal part of tibiae and brown tarsi ventrally; pile on legs pale yellow; metafemur incrassate and curved, ca. three times longer than wide; long pile on postero-and anteroventral surface ca. as half of width of metafemur, approximately the same length as pile on dorsal surface (Fig. 22A).
Abdomen. Broad, tapering, 1.2 times longer than mesonotum; terga dark, except for a pair of reddish yellow, triangular, lateral maculae on tergum 2 (and in some specimen on 3); terga 2-4 each with a pair of white microtrichose, wide, usually oblique fasciae; pile on terga all yellow, except black pile on tergum 3 medially, and on tergum 2 posteriorly and tergum 4 anteriorly in some specimens (Fig. 23E); sterna dark brown, covered with long whitish yellow pile.
Male genitalia. Apical part of anterior surstyle lobe rhomboid shape, covered with dense, short pile (   Female. Similar to the male except for normal sexual dimorphism and for the following characteristics: antennae with rounded tip, fossette dorsolateral (Fig. 19D); frons microtrichose, covered with mostly gray-yellow pile; ocellar triangle covered with black pile; long pile on postero-and anteroventral surface ca. as half of width of metafemur (Fig. 22B); microtrichose fasciae on terga 2-4 narrower (Fig. 23F).
Distribution. Merodon kawamurae is known from Japan and China (Fig. 7). This is the only species of the genus Merodon in eastern Palaearctic.
Ecology. Preferred environment: no data. Flowers visited: no data. Flight period: April-May.
Type material. Merodon kawamurae was described after an unknown number of specimens from Kumamoto, Kyushu, Japan, leg. Kawamura. Matsumura's type material is held at the Hokkaido University, Department for Systematic Entomology, at Sapporo, Japan, but the type material was inaccessible for this study.
Merodon micromegas Lectotype [designated by Hurkmans (1993  Description. Male. Head. Antennae black to dark brown; basoflagellomere elongated ca. 2.2 times as long as wide, and ca. 2.5 times as long as pedicel, concave dorsally with acute apex; dorsolateral fossette narrow; arista dark and thickened at basal one third, covered with dense microtrichia, ca. 1.5 times as long as basoflagellomere (Fig. 19I); face and frons black with gray microtrichia, face covered with dense whitish gray, and frons with yellowish gray pile; oral margin microtrichose with shiny lateral areas; lunule shiny black, bare; vertex shiny black, except microtrichose area in front of anterior ocellus; vertex isosceles, with long, pale whitish yellow pile, mixed with few black pile on the ocellar triangle; ocellar triangle equilateral; eyes covered with dense pile; occiput with gray-yellow pile, ventrally covered with a dense, gray microtrichia; eye contiguity 10-12 facets long; vertical triangle: eye contiguity: frons = 1.2 : 1 : 2.
Thorax. Scutum and scutellum black with bronze luster, covered with dense, erect, yellow pile, except sides of scutum at wing basis with patch of short black pile and fascia of black pile between wing basis; scutum with two or more microtrichose vittae, anteriorly connected and posteriorly reaching the scutellum; scutum dull; posterodorsal part of anterior anepisternum, posterior anepisternum (except anteroventral angle), anterior anepimeron, dorsomedial anepimeron, and posterodorsal and anteroventral parts of katepisternum with long, pale yellow pile and grayish microtrichia; wings entirely covered with microtrichia; wing veins brown; calypteres and halteres yellowish; legs mostly black, except brown tarsi ventrally in some specimens; pile on legs pale yellow, except few black pile in apical fifth of metafemur in some specimens; metafemur incrassate, ca. three times longer than wide; pile on postero-and anteroventral surface short, except few sparse pile approximately the same length as pile on dorsal surface (Fig. 22C).
Female. Similar to the male except for normal sexual dimorphism and for the following characteristics: antennae with rounded tip, basoflagellomere ca. two times longer than wide, (Fig. 19J); frons with broad microtrichose vittae along eye margins; frons covered with pilosity of variable color, from mostly gray-yellow until predominately black pile; ocellar triangle covered with black pile; metafemur incrassate, pile on postero-and anteroventral surface short (Fig. 22D); terga pale yellow pilose at lateral sides, anterior two thirds of tergum 2 and all terga 4 and 5; terga 2 and 3 medially with short adpressed black pile; microtrichose fasciae on terga 3 and 4 broad (Fig. 24B).
Etymology. Medium (middle, center) refers to the species' distribution, being the only taxon of the group found on Crete, in the middle of Mediterranean Sea.
Distribution. Merodon medium sp. nov. is endemic to the Greek island of Crete (Fig. 7).
Description. Male. Head. Antennae black; basoflagellomere short, 1.3 times as long as wide, and ca. two times as long as pedicel, with rounded apex; fossette dorsolateral; arista black and thickened at basal one third, covered with dense microtrichia, ca. two times as long as basoflagellomere (Fig. 28C); face and frons black with gray microtrichia, face covered with dense whitish gray or mixed black and whitish gray, and frons mostly with black pile; oral margin shiny, with lateral microtrichose area; lunule shiny black, bare; vertex isosceles, shiny black, except in front of anterior ocellus covered with microtrichia; vertex with long, black pile; ocellar triangle equilateral; eyes covered with dense whitish pile; occiput shiny covered with black pile in upper half, ventrally with gray-yellow pile and dense, gray microtrichia; eye dichoptic, separated by distance of three facets (Fig. 27A).
Thorax. Scutum and scutellum black, shiny, covered with dense, erect, black pile; scutum without microtrichose vittae (Fig. 26A); posterodorsal part of anterior anepisternum, posterior anepisternum (except anteroventral angle), anterior anepimeron, dorsomedial anepimeron, and posterodorsal and anteroventral parts of katepisternum with long, dark gray or black pile and grayish microtrichia; wings entirely covered with microtrichia, except bare area at basal one third; wing veins dark brown; calypteres gray; halteres blackish; legs black (Fig. 26B); pile on legs mostly black or dark gray; metafemur curved and medium incrassate, ca. four times longer than wide; pile on postero-and anteroventral surface ca. one third to half of width of metafemur, slightly shorter than pile dorsally.
Abdomen. Tapering, 1.2 times longer than mesonotum; terga completely dark; terga 3 and 4 without, or with indistinct pair of white microtrichose fasciae; pile on terga mostly black, except anteromedial part of tergum 2 partly covered with whitish pile (Fig. 26A); sterna dark brown to black, covered with long black and whitish pile.
Female. Similar to the male except for normal sexual dimorphism and for the following characteristics: basoflagellomere 1.5 times longer than wide, fossette narrow (Fig. 28D); pile on face of variable color, from black to whitish; frons mostly microtrichose, covered with black pile; ocellar triangle covered with black pile; microtrichose fasciae on terga 2-4 narrow (Fig. 26C); thorax on lateral sides with variable pilosity color, from black to whitish.
Etymology. The name nigrocapillatus is derived from Latin adjective niger meaning black, dark and Latin noun capillatus meaning long-haired, referring to the long, black body pile of this species.
Description. Male. Head. Antennae black to dark brown; basoflagellomere narrow and elongated, 1.8 times as long as wide, and 2.5 times as long as pedicel, with rounded tip; large fossette dorsomedial and dorsolateral (Fig. 28A, B); arista dark and thickened at basal one third, covered with dense microtrichia; arista long, ca. two times as long as basoflagellomere (Fig. 28A, B); face and frons black covered with whitish pile; face covered with indistinct whitish gray microtrichia; frons with dense whitish microtrichia; lunule shiny black, bare; vertex isosceles, with long whitish pile and black pilosity on the ocellar triangle; ocellar triangle equilateral; eyes covered with long, dense, whitish pile (Fig. 27B); occiput with whitish pile, covered with a dense, silver microtrichia along eye margin; eye contiguity short, approximately five facets long; vertical triangle: eye contiguity: frons = 4.5 : 1 : 4.5.
Thorax. Scutum and scutellum black with bluish luster, covered with dense, erect, white pile including wing basis; posterior half of scutum with square shaped area of black pile medially; scutum with indistinct microtrichose vittae; posterodorsal part of anterior anepisternum, posterior anepisternum (except anteroventral angle), anterior anepimeron, dorsomedial anepimeron, and posterodorsal and anteroventral parts of katepisternum with long, whitish pile and grayish microtrichia; wings entirely covered with microtrichia; wing veins dark brown; wing with distinct dark area in apical half (Fig. 29C); calypteres whitish; halteres yellowish, with darker capitulum; legs mostly black, except dark brown tarsi ventrally; pile on legs mostly whitish mixed with black ones on femora; metafemur moderately incrassate, ca. three times longer than wide; pile on postero-and anteroventral surface very long, and ca. two thirds of width of metafemur, approximately the same length as pile on dorsal surface.  Abdomen. Tapering, 1.2 times longer than mesonotum; terga dark brown to black; terga 2-4 each with a pair of white microtrichose, wide, oblique fasciae (on tergum 2 triangular); pile on terga long, whitish laterally and at microtrichose fasciae, medially black (Fig. 29A); sterna dark brown, covered with long whitish pile.
Female. Unknown. Etymology. The word nigropunctum is derived from the Latin words niger (black, dark whitish) and punctum (dot/spot) referring to the dark macula on the wing as an important diagnostic character of this new species.
Description. Male. Head. Antennae black to dark brown; basoflagellomere elongated 1.8-2 times as long as wide, and 2.3 times as long as pedicel, concave dorsally with acute apex; large fossette dorsomedial and dorsolateral ( Fig. 12A-C); arista dark and thickened at basal one third, covered with dense microtrichia, 1.5 times as long as basoflagellomere; face and frons black with gray microtrichia, face covered with dense whitish gray, and frons with yellowish gray pile; oral margin microtrichose with shiny lateral areas; lunule shiny black, bare; vertex covered with microtrichia (Fig. 20C); vertex isosceles, with long, pale whitish yellow pile, in some cases mixed with few black pile on the ocellar triangle; ocellar triangle equilateral; eyes covered with dense pile; occiput with gray-yellow pile, covered with a dense, gray microtrichia; eye contiguity ca. 10-12 facets long; vertical triangle: eye contiguity: frons = 1.2 : 1 : 2.
Thorax. Scutum and scutellum black with bronze luster, covered with dense, erect, yellow pile; scutum at wing basis with short black pile; scutum with two or more microtrichose vittae, anteriorly connected and posteriorly reaching the scutellum; scutum dull; posterodorsal part of anterior anepisternum, posterior anepisternum (except anteroventral angle), anterior anepimeron, dorsomedial anepimeron, and posterodorsal and anteroventral parts of katepisternum with long, pale yellow pile and grayish microtrichia; wings entirely covered with microtrichia; wing veins brown; calypteres yellowish; halteres yellowish, in some specimens with darker capitulum; legs mostly black, except brown tarsi ventrally in some specimens; pile on legs pale yellow; metafemur moderately incrassate, 3.5 times longer than wide; pile on postero-and anteroventral surface very short with few sparse pile, and ca. as one fourth of width of metafemur, approximately the same length as pile on dorsal surface (Fig. 13A).
Female. Similar to the male except for normal sexual dimorphism and for the following characteristics: antennae with rounded tip, basoflagellomere ca. two times longer than wide, fossette dorsal (Fig. 12D-F); frons with broad microtrichose vittae along eye margins; frons covered with pilosity of variable color, from mostly gray-yellow to predominantly black; ocellar triangle covered with black pile; terga pale pilose, in some specimens terga 2-4 medially with short adpressed black pile; microtrichose fasciae on terga 3 and 4 narrower (Fig. 21B, D).
Morphological description of the puparium (Fig. 31A). Length: 7.5 mm, width: 4 mm; light brown in color; sub-cylindrical; rough integument with larval segmentation persisting as transverse folds and wrinkles; integument covered with small domes and spicules; pronounced segmental sensilla, bearing seta. The dorsal surface of the prothorax with a pair of anterior spiracles, which are more than two times longer than broad at the base, sclerotized, cylindrical in shape, brown in color, apex with two linear spiracular openings (Fig. 32B). On the anal segment, two different pairs of lappets present: the ventro-lateral pair represented by fleshy papilla with one sensilla bearing a seta and the dorso-lateral pair with a very poorly developed basal papilla, apically divided bearing one sensilla with a long seta on top of each division. Cephalopharyngeal skeleton (Fig. 31B). Robust mandibles with dark highly sclerotized hooks, without accessory teeth, fused to the external mandibular lobes; the dorsal cornu narrowed, representing almost the whole length of the ventral cornu. Clypeal sclerite sclerotized, tentorium and intermediate sclerites highly sclerotized and apparently fused; ventral cornu elongated and narrow in profile view, wider and more heavily sclerotized at the posterior end, forming the grinding mill of pestle and mortar construction at the posterior end of the cibarium; cibarium at the base, with a clearly sclerotized end. Posterior respiratory process (Fig. 32A). Brownish, wider than long, very short (barely visible from dorsal view), button shape, base only slightly wider than apex; dorsal and lateral surface covered by a barely visible ornamentation resembling a network. The outline of the spiracular plate sub-elliptical and barely irregular. Spiracular plate with four pairs of sinuous spiracular openings (clearly separated from each other) around two central scars, first pair clearly shorter than the others; three or four very small circular nodules on each side of the surface of spiracular plate in the area of spiracular openings; four pairs of branched inter-spiracular setae emerging on the outward edges of the spiracular plate. Pupal spiracles (Fig. 32C). Sclerotized, brownish in color, stout, cylindrical in shape, almost as long as broad, slightly tapered, with not heavily rounded prominence at the end (length 0.3 mm) separated by a distance of ca. five times their length. Upper two-thirds of the lateral sides (except for the granularly surfaced apex) covered with irregularly-spaced, oval-shaped domed tubercles, leaving a more or less triangular central area free of tubercles on both ventral and dorsal surfaces; 3-7 radially-arranged spiracular openings on each tubercle. The whole spiracle surface (from the base to the apex) reticulated with a polygonal pattern, more irregular on ventral side, with polygons being noticeably smaller in the apical part. Etymology. Latin adjective opacus (opaque, not transparent), pertains to the dark tergum 2, without reddish yellow lateral maculae.

Merodon sacki
Redescription (based on holotype and additional material from the type area, Spain). Male. Head. Antennae black to dark brown; basoflagellomere ca. two times as long as wide, and ca. two times as long as pedicel, concave dorsally; large fossette dorsolateral; arista dark and thickened at basal one third, covered with dense microtrichia, 1.6 times as long as basoflagellomere (Fig. 11D-F); face and frons black with gray microtrichia, face covered with dense whitish gray, and frons with yellowish gray pile; oral margin microtrichose with shiny lateral areas; lunule shiny black, bare; vertex covered with golden microtrichia around ocellar triangle; vertex isosceles, with long, pale whitish yellow pile mixed with black pile on the ocellar triangle; ocellar triangle equilateral; eyes covered with dense pile; occiput with gray-yellow pile, covered with a dense, gray microtrichia; eye contiguity 10-14 facets long.
Thorax. Scutum and scutellum black with bronze luster, covered with dense, erect, yellow pile; scutum at wing basis with short black pile; scutum with two or more microtrichose vittae, anteriorly connected and posteriorly reaching the scutellum; scutum dull; posterodorsal part of anterior anepisternum, posterior anepisternum (except anteroventral angle), anterior anepimeron, dorsomedial anepimeron, and posterodorsal and anteroventral parts of katepisternum with long, pale yellow pile and grayish microtrichia; wings entirely covered with microtrichia; wing veins brown; calypteres and halteres pale yellowish; legs mostly black, except brown tarsi ventrally in some specimens; pile on legs pale yellow, except black pile at apical one fourth of metafemur; metafemur curved and incrassate, approximately three to four times longer than wide; pile on postero-and anteroventral surface long, and ca. half of width of metafemur (Fig. 8C).
Redescription (based on the types and specimens from the type area of nominal taxon, Iberian Peninsula; variability includes populations from all of the range). Male. Head. Antennae black to dark brown; basoflagellomere ( Fig. 3A-C, G-J) elongated, 1.7-2.2 times as long as wide, and 2.5-3 times as long as pedicel, concave dorsally, tapering to the apex; dorsolateral and dorsomedial (if present) fossette large with vari-able shape (see variability) (as on Fig. 3); arista dark and thickened at basal one third, covered with dense microtrichia; arista short, 1.2-1.5 times as long as basoflagellomere (Fig. 3); face and frons black with gray microtrichia, face covered with dense whitish, and frons with yellowish gray pile; oral margin shiny, with small lateral microtrichose area; lunule shiny black, bare; eye contiguity 8-10 facets long; vertex isosceles, shiny black, except in front of anterior ocellus, covered with microtrichia; vertex with long, pale whitish yellow pile, in some cases mixed with few black pile on the ocellar triangle; ocellar triangle from equilateral to isosceles (see variability); occiput with gray-yellow pile, ventrally covered with a dense, gray microtrichia; eyes covered with dense whitish pile (Fig. 5A, B); ratio of length of vertical triangle: eye contiguity: frons = 3 : 1 : 3.
Thorax. Scutum and scutellum black with bronze luster, covered with dense, erect, usually yellow pile; scutum at wing basis in some specimens and populations with patch of black pile, or with fascia of black pile between wing basis; scutum usually with two or four microtrichose vittae (see variability), anteriorly connected and posteriorly reaching the scutellum ( Fig. 2A); anterior half of scutum from dull until shiny black (see variability); posterodorsal part of anterior anepisternum, posterior anepisternum (except anteroventral angle), anterior anepimeron, dorsomedial anepimeron, and posterodorsal and anteroventral parts of katepisternum with long, dense pale yellow pile and grayish microtrichia; wings entirely covered with microtrichia; wing veins brown; calypteres pale yellow; halteres yellow, in some cases with dark capitulum; legs (Fig. 4) without spinae or other protuberances; legs mostly black, except brown tarsi ventrally in some specimens; pile on legs pale yellow, except black pile at apical one third of metafemur in some populations (see variability); metafemur moderately incrassate, ca. three times longer than wide; long pile on postero-and anteroventral surface sparse, and ca. one third to one fourth (see variability) of width of metafemur, approximately the same length as pile on dorsal surface (Fig. 4).
Abdomen. Tapering posteriorly, ca. 1.2 times longer than mesonotum; terga dark brown to black, except for a pair of pale yellow-orange, triangular, lateral maculae on tergum 2 (in some specimens less visible: see variability); terga 3 and 4 each with a pairs of white microtrichose, oblique fasciae (on tergum 2 triangular); color of pile on terga variable, from all yellow to specimens with many black pile on terga 2-4 (see variability) (Fig. 2C, D); sterna dark brown, covered with long whitish yellow pile.
Female. Similar to the male except for normal sexual dimorphism and for the following characteristics: antennae with rounded tip, basoflagellomere ca. two times longer than wide, fossette dorsal (Fig. 3D-F); frons with microtrichose vittae along eye margins variable in shape and size (see variability); frons covered with variable color of pilosity, from mostly gray-yellow until predominately black (see variability) (Fig. 5C,  D); ocellar triangle covered with black pile; lateral side of terga, anterior two third of tergum 2 and all tergum 5 with yellow pile; central part of terga 2-4 with short adpressed black pile; microtrichose fasciae on terga 3 and 4 conspicuous (Fig. 2D).
Variability. There is some intra-and interpopulation variability in the morphological characters of Merodon serrulatus, which are summarized in Table 1.
Distribution. As shown in Fig. 7, this Merodon taxon is characterized by the greatest range, extending from Iberian Peninsula in the south-west, through Greece and eastern Turkey to the south, and eastward to Siberia and Mongolia (Doczkal pers. comm.).
Redescription (based on the material from type locality, Middle Atlas, Azrou). Male. Head. Antennae black to dark brown; basoflagellomere elongated, ca. 1.8 times as long as wide, and ca. 2.5 times as long as pedicel, concave dorsally with acute apex; fossette dorsolateral; arista dark and thickened at basal one third, covered with dense microtrichia, ca. 1.8 times as long as basoflagellomere (Fig. 11G, H); face and frons black with gray microtrichia, face covered with dense whitish, and frons with yellowish gray pile; oral margin shiny, with small lateral microtrichose area; lunule shiny black, bare; vertex shiny black, except in front of anterior ocellus, covered with microtrichia; vertex isosceles, with long, pale whitish yellow pile, mixed with black pile on the ocellar triangle; ocellar triangle isosceles; eyes covered with dense pile; occiput with gray-yellow pile, ventrally covered with a dense, gray microtrichia; eye contiguity 8-11 facets long; vertical triangle: eye contiguity: frons = 3 : 1 : 3.
Thorax. Scutum and scutellum black with bronze luster, covered with dense, erect, usually yellow pile; sides of scutum at wing basis with patch of black pile or fascia of short black pile and few black pile between wing basis; scutum with two microtrichose vittae, anteriorly connected and posteriorly reaching the scutellum; anterior half of scutum dull; posterodorsal part of anterior anepisternum, posterior anepisternum (except anteroventral angle), anterior anepimeron, dorsomedial anepimeron, and posterodorsal and anteroventral parts of katepisternum with long, dense pale yellow pile and grayish microtrichia; wings entirely covered with microtrichia; wing veins brown; calypteres and halteres pale yellow; legs mostly black, except brown tarsi ventrally in some specimens; pile on legs pale yellow; metafemur moderately incrassate, ca. three times longer than wide; pile on postero-and anteroventral surface medium long, and ca. as one third of width of metafemur, approximately the same length as pile on dorsal surface (Fig. 8D).
Abdomen. Tapering, 1.2 times longer than mesonotum; terga dark, except for a pair of pale yellow-orange, triangular, lateral maculae on tergum 2; terga 3 and 4 each with a pair of white microtrichose and oblique fasciae (on tergum 2 triangular); pile on terga all yellow; sterna dark brown, covered with long whitish yellow pile.
Female. Similar to the male except for normal sexual dimorphism and for the following characteristics: antennae with rounded tip, basoflagellomere ca. two times longer than wide (Fig. 11I); frons with broad microtrichose vittae along eye margins; frons covered with variable pilosity, from mostly gray-yellow until predominantly black; ocellar triangle covered with black pile; lateral side of terga, anterior two thirds of tergum 2 and all of tergum 5 with yellow pile; terga 2-4 with short adpressed black pile.
Description. Male. Head. Antennae black to dark brown; basoflagellomere rounded, 1.6-1.8 times as long as wide, and ca. 2.3 times as long as pedicel; large fossette dorsomedial and dorsolateral; arista brown and thickened at basal one third, covered with dense microtrichia, ca. 1.8 times as long as basoflagellomere (Fig. 33A, B); face and frons black with gray microtrichia, face covered with dense whitish gray, and frons with yellowish gray pile; oral margin shiny with microtrichose lateral areas; lunule shiny black, bare; vertex covered with gray microtrichia; vertex isosceles, with long, pale whitish yellow pile mixed with black pile on the ocellar triangle; ocellar triangle equilateral; eyes covered with dense pile; occiput with gray-yellow pile, covered with a dense, gray microtrichia; eye contiguity 8-12 facets long.
Thorax. Scutum and scutellum black with bronze luster, covered with dense, erect, yellow pile; scutum with conspicuous silver microtrichose ornamentation (Fig. 23A); posterodorsal part of anterior anepisternum, posterior anepisternum (except anteroventral angle), anterior anepimeron, dorsomedial anepimeron, and posterodorsal and anteroventral parts of katepisternum with long, pale yellow pile and grayish microtrichia; wings entirely covered with microtrichia; wing veins brown; calypteres and halteres pale yellow; legs mostly black, except yellowish tip of femora, basal and apical part of tibiae and brown tarsi ventrally; pile on legs pale yellow; metafemur moderately incrassate, ca. four times longer than wide; pile on metafemur long, and ca. half to two thirds of width of metafemur.
Female. Similar to the male except for normal sexual dimorphism and for the following characteristics: basoflagellomere ca. 1.8 times longer than wide, fossette dorsolateral (Fig. 33C); frons with microtrichose vittae along eye margins; frons covered with mostly gray-yellow pile mixed with black ones; ocellar triangle covered with black pile; ventral margin of metafemur with sparse pilosity, only individual pile longer; lateral side of terga, anterior two third of tergum 2 and all tergum 5 with whitish pile; terga 2-4 with short adpressed black pile medially; microtrichose fasciae on terga 3 and 4 narrower (Fig. 23D).
Etymology. The name trianguloculus derives from the Latin adjective triangulus (triangular) and Latin noun loculus (spot) and describes the distinctive triangular silver pollinose fasciae on the abdomen.

Merodon trizonus (Szilády, 1940) nomen dubium
Remarks. The identity of Merodon trizonus remains unclear. The species was described based on two male and two female syntypes labelled "La Calle [el Kala], Algeria" and "Ain Draham, Tunisia", which were not examined. Originally, the syntypes were located in the Hungarian National Museum in Budapest, but the Diptera collection was destroyed by a fire in 1956. The description of Szilády (1940) is incomplete and based on a few differences from the related species M. hirsutus. The types of M. trizonus are assumed lost and the description is insufficiently accurate to associate name to one of these species. Currently, two species from the M. serrulatus species group, to which M. hirsutus belongs, occur in northern Africa, namely M. bequaerti and M. sophron. Therefore, we propose to leave the name Merodon trizonus (Szilády, 1940) as nomen dubium.   26A, B); terga 2-4 bare or with indistinct microtrichose fasciae (Fig. 26A); distribution: Tajikistan (Fig. 7) ................Merodon nigrocapillatus sp. nov. -Species with olive-brown reflection, predominantly covered with pale yellow pile; terga 2-4 with conspicuous lateral microtrichose fasciae (Fig. 15A); distribution: Kyrgyzstan and Kazakhstan (Fig. 7) .Merodon disjunctus sp. nov. 6

Molecular inference
The final aligned and pruned dataset including two-gene data matrix (COI+28S rRNA) comprised 1,859 nucleotide characters (421 parsimony informative sites) pertaining to 81 specimens (79 in-group specimens of the studied genus Merodon lineages along with two outgroups). The final number of aligned sites for COI gene (concatenated 3' and 5' fragments of the gene) included 1,273 nucleotides, while 586 nucleotide characters (with gaps) were included in analyses for the D2−3 region of the 28S rRNA gene.
Both obtained phylogenetic trees (Maximum Parsimony, Fig. 36 and Maximum Likelihood, Supplementary file 7: Figure 7) resolved the four previously described lineages as clades, while the M. serrulatus species group was recovered as monophyletic within the Merodon avidus-nigritarsis lineage (MP = 54, ML = 75). Within the serrulatus species group, specimens belonging to M. nigrocapillatus sp. nov., M. medium sp. nov., M. bequaerti and M. sacki were clearly grouped together with high bootstrap support (MP = 100, ML = 100; MP = 100, ML = 100; MP = 97, ML = 94; MP = 100, ML = 100, respectively). The single sequenced specimen of M. sophron was resolved as sister taxon of M. bequaerti. Unfortunately, although morphologically differentiated, specimens identified as M. defectus sp. nov. clustered with M. serrulatus in a clade without support, but also with M. opacus sp. nov. in another clade without support. These three species together with M. sacki were resolved in a group with high support value. High level of inter-population molecular variability within M. serrulatus species was also detected.  Likov et al. (2019) reported the monophyly of the Merodon avidus-nigritarsis lineage. Within this lineage, the Merodon serrulatus species group is supported in our phylogenetic analyses.

Taxon delimitation and integrative taxonomy
The M. serrulatus species group comprises six already described species (Merodon bequaerti, M. hirsutus, M. kawamurae, M. sacki, M. serrulatus, and M. sophron) and seven new species described here. Based on the present results, six species of this group, namely M. disjunctus sp. nov., M. kawamurae, M. medium sp. nov., M. nigrocapillatus sp. nov., M. nigropunctum sp. nov., and M. trianguloculus sp. nov., are delimited on differences of morphological characters. Moreover, two pairs of very similar species can be separated from other species of the group by some distinct characters, but the distinction between the species in each pair is based on characters with more subtle differences. These two pairs are M. bequaerti / M. sacki, with the metafemur incrassate and long pile on postero-and anteroventral surface of the metafemur, and M. hirsutus / M. opacus sp. nov., with tergum 2 dark, without yellow-orange lateral maculae in both sexes.
The remaining three species within the M. serrulatus species group are morphologically very similar to each other. Merodon defectus sp. nov. has subtle, but stable differences in structures of the male genitalia serving as diagnostic characters (lateral hump on posterior surstyle lobe reduced). Closely related and very similar, M. serrulatus and M. sophron are distinguished by molecular data, in addition to a clear morphological diagnostic character in males (presence or absence of medial antennal fossette).
In the present study we applied this integrative approach, i.e., to combine morphology, genetic data, and distribution, to support the taxonomic status and systematic decisions made for the M. serrulatus species group. For example, the species M. sophron and M. serrulatus, although morphologically similar, are conspicuously separated from each other based on molecular data. The same situation is found between M. bequaerti and M. sacki. In contrast, the morphologically distinct species M. defectus sp. nov., M. serrulatus, and M. opacus sp. nov. cluster together in the molecular analysis. Discord-ance between morphological and molecular data has been observed in some previous studies concerning closely related taxa within the family Syrphidae (e.g., Ståhls et al. 2009;Francuski et al. 2014;Haarto and Ståhls 2014), as well as in recently conducted studies on Merodon species groups ). In the present study the molecular data for M. defectus sp. nov. show some interpopulation differentiation: while the specimens from Bozdag (Turkey) were resolved in the same cluster with M. opacus sp. nov., the specimens of M. defectus sp. nov. from Isparta (Turkey) and M. serrulatus were resolved in another cluster. Unfortunately, these two clades do not have support and the whole cluster, including M. sacki, could be resolved in a large polytomy when collapsing nodes without high support. Different molecular profile of different populations of one species was also detected by Likov et al. (2019). The suggested reasons for the low COI divergence between these species are retained polymorphism or mitochondrial introgression between the taxa, as it has been hypothesized in previous studies (e.g., Ståhls et al. 2009;Francuski et al. 2014;Haarto and Ståhls 2014).
It is important to do further taxonomic research with the populations of Merodon serrulatus with high inter-population morphological and genetic variability. These populations may be also geographically isolated and are posited to exhibit low genetic flow. The very wide distributional range of M. serrulatus, extending from Iberian Peninsula to Mongolia, is highly unusual in the genus Merodon, thus exemplifying a complex population structure that might contain evolutionary units at different levels of speciation.

Immature stages
One of the main reasons for the gap in extant knowledge on the immature stages of Merodon species is the difficulty of finding specimens in the field, since host plants, the larval food-plants and the breeding and oviposition sites, have not been recorded for the great majority of Merodon species (Hurkmans 1993;Rotheray 1993;Speight 2018). The description of the puparium of Merodon opacus sp. nov. in this work is based on a single specimen reared from the larva found in the soil near the bulbs of Fritillaria, Gagea, Muscari, and Ornithogalum. In extant studies, the immature stages of Merodon species were linked to bulbous geophytes, mostly belonging to plant families Asparagaceae (Ricarte et al. 2008;Andrić et al. 2014;Preradović et al. 2018), Iridaceae (Stuckenberg 1956) and Amaryllidaceae (Heiss 1938;Ricarte et al. 2017).
The morphology of the puparium of M. opacus sp. nov. shows similarities with the puparium of M. avidus in terms of the morphology of the posterior respiratory process (prp) and ornamentation of pupal spiracles (Preradović et al. 2018). In fact, these species share the button-shaped prp and the poorly defined outline of the spiracular plate, whereas the spiracular openings of M. opacus sp. nov. are less convoluted than those in M. avidus. The pupal spiracles are stout in shape (almost as long as broad) and are clearly shorter than in M. avidus, but share the reticulated ornamentation (polygonal pattern).
A single larva of Merodon opacus sp. nov. was found in the ground surrounded with bulbs of different plant genera (Fritillaria, Gagea, Muscari, Ornithogalum). Recent larval records suggest that groups of related Merodon species could have the same plant genus as a host. These close relationships could be suspected between: M. constans species group and Galanthus L. (Amaryllidaceae) [Popov and Mishustin (pers. comm) confirmed that eight species of the constans species group feed on bulbs of eleven snowdrop species], M. aureus species group and Crocus L. (Iridaceae) [Speight 2018;Popov pers. comm.], and M. geniculatus species group and Narcissus L. (Amaryllidaceae) [i.e., M. eques (Fabricius, 1805) (see Pehlivan and Akbulut 1991), M. geniculatus Strobl, 1909 (see Ricarte et al. 2017), and M. neofasciatus (see Vujić et al. 2018]. Based on these findings, we suggest that the host plant for the members of the M. serrulatus species group should be a plant genus present on its large range, extending from North Africa, throughout the entire Palaearctic region to Japan. Two bulb genera with native ranges (WCSP 2019) fitting this distribution, Gagea and Fritillaria (Liliaceae), might be the larval food-plants. Future research in this field could thus focus on more detailed field work in areas characterized by numerous populations of species from the M. serrulatus species group.

Distribution and species diversity
Being distributed from the Iberian Peninsula in the south-west, along the Mediterranean and Balkan Peninsula, through Turkey and southern Russia to Siberia and Mongolia in the north-east, Merodon serrulatus is the species of the genus Merodon with the largest distributional range. Other species of the M. serrulatus species group can be found at the edges of this distributional range, albeit with a much more restricted distribution. For example, M. sacki has been found in southern Spain, M. medium sp. nov. is endemic to Crete Island, whereas M. defectus sp. nov. and M. opacus sp. nov. have been recorded in western Turkey, with the latter species also being found on Lesvos Island, and M. hirsutus found in south-eastern Turkey, Israel and Syria. The M. serrulatus species group includes two North-African species, i.e., M. sophron restricted to Morocco, and M. bequaerti more widely distributed along the Mediterranean coast of the African continent. Only one species of the group, M. kawamurae, is found in the Far East of the Palearctic region, i.e., in central and south-eastern China and Japan. It is worth noting that four of the seven newly described species are distributed in Central Asia, the central and somewhat isolated part of the distribution range of the M. serrulatus species group. Merodon disjunctus sp. nov. is found in Kyrgyzstan and Kazakhstan, M. nigrocapillatus sp. nov. has been collected in Tajikistan, whereas M. nigropunctum sp. nov. and M. trianguloculus sp. nov. are found in Uzbekistan and Turkmenistan, respectively.
The genus Merodon is known to be widespread in regions such as the Mediterranean Basin, with high diversity of geophytes, whereby underground storage organs serve as larval food sources for Merodon species (Ricarte et al. 2008(Ricarte et al. , 2017. Such potential for the development of a high diversity of Merodon taxa might explain their current geographical distributions . The highest number of Merodon species and the greatest endemicity level in the Mediterranean Basin was noted for the Anatolian region , which represents the main center of Merodon diversity within the Palaearctic region, along with the Iberian Peninsula (Marcos-García et al. 2007). The high number of endemic species in the eastern Mediterranean Basin has been suggested to be related to the intense orogenic activity favoring isolation and allopatric speciation . The biologically diverse Anatolian region, characterized by a rich geological history, comprises of an extensive system of high mountain chains and closed basins, thus providing a wide range of habitats. Throughout history, different parts of this topographically complex area, connecting diverse geographic regions of Asia and Europe, have served not only as natural barriers but also as highly important refugia and corridors providing passages for species spreading .
Central Asia is characterized by many mountains exceeding 6,500 m in elevation, as well as by major desert basins, which have thus far remained understudied. This is particularly the case for the alpine areas, and especially in terms of the invertebrate fauna (CEPF 2017). The very diverse flora of this region harbors a large number of endemics, including many bulbous plants (CEPF 2017) which can support high diversity of Merodon taxa, including the four endemic species of the M. serrulatus species group described here. Major mountain ranges located in Central Asia represent an extensive zone for faunistic evolution and differentiation, not only ecologically, but also orographically and biogeographically (Mani 1968). Heterogeneous topography with various isolated habitats along altitudinal gradients fosters high rates of speciation, species diversity and endemism. Climatic fluctuations and tectonic processes throughout the complex geological history of this region have contributed to its unique climate and have promoted high levels of floristic diversification and alpine endemism, while also affecting the distributions and structure of many taxa (e.g., Djamali et al. 2012;Zinenko et al. 2015). Having a long history as the crossroads between east and west, this region has historically been subjected to high levels of anthropogenic disturbance that continue to the present day, and populations of many species have declined due to habitat modifications (Djamali et al. 2012;CEPF 2017). The results yielded by the present study confirm previous conclusions emphasizing the importance of such underexplored regions as centers of endemicity, hosting habitats potentially harboring hidden diversity within the genus Merodon