Biema Huo & Zhao gen. nov., a new flower fly genus (Diptera, Syrphidae) from China

. A new flower fly genus (Diptera, Syrphidae), Biema Huo & Zhao gen. nov. from China is described based on two new species: Biema wanglangensis Huo & Zhao gen. et sp. nov. (designated as type-species) and Biema qilianensis Huo & Liu gen. et sp. nov. The new genus can easily be distinguished by the following morphological features: head, mesonotum and scutellum black; postpronotum without pile; metasternum not reduced, posterior margin shallowly concave; katepisternum only with ventral pile patches; alula narrow, as wide as basal width of cell c; male postabdomen conspicuously more swollen than other segments, surstylus and postgonite complex, phallus unsegmented. The results of


Introduction
Among the most species-rich dipteran families, Syrphidae Latreille, 1802 (Insecta, Diptera) is wellknown by nature enthusiasts and researchers because they provide several crucial ecosystem services (Dunn et al. 2020). Commonly known as flower or hover flies, syrphids are important pollinators, biological control agents of pests and recyclers of organic matter (Morales & Wolff 2010;Inouye et al. 2015;Arcaya et al. 2017;Moerkens et al. 2021). The family is currently divided into four subfamilies and 15 tribes (Mengual et al. 2015;Young et al. 2016).
The first scientific reference on the Chinese hover fly fauna was given by Sack (1922). To date, about 900 species of Syrphidae in 120 genera have been recorded in China (Huo 2020), but a better understanding of the Chinese syrphid fauna is needed.
The old concept of the tribe Bacchini Bigot, 1883 has recently been extensively discussed (Huo 2014;Thompson & Skevington 2014). The tribe as defined by Vockeroth (1992) for those syrphines with an unsegmented phallus is now divided into two tribes, i.e., Bacchini and Melanostomini Williston, 1885 (Mengual 2020). So far, two genera of Melanostomini have been recorded in China, i.e., Melanostoma Schiner, 1860 with eight species, and Xanthandrus Verrall, 1901 with three species (Cheng et al. 1998; Thompson & Rotheray 1998;Huo et al. 2007;Huo 2014). In the present work, the current knowledge on Chinese hover flies is expanded with the addition of a new genus and two new species belonging to Melanostomini. Moreover, an identification key to genera of Bacchini and Melanostomini recorded from China is also provided.

Collecting sites
Field work was carried out between 2016 and 2018 in the Wanglang National Nature Reserve, Sichuan Province, China. The reserve, located between 103º55′−104º10′ E and 32º49′−33º02′ N, belongs to the Palaearctic Region (Procheş & Ramdhani 2012) and was established in 1963 for giant panda protection. It has a total area of about 322.97 km 2 , an elevation between 2300−4980 m and the average elevation is 3200 m. Collected specimens possess a distinctive and apomorphic combination of characters that identify them as a member of the bacchines sensu lato, but not concordant with any of the known genera (Vockeroth 1992). In 2021, we did another expedition to the Qilian Mountain National Park (2600−3248 m above sea level), Qinghai Province, China. The Qilian Mountain National Park also belongs to the Palaearctic Region and has a total area of 50 200 km 2 with a complex ecosystem of mountain forests, temperate desert grasslands, alpine meadows, and glacial snow-capped mountains. More unknown specimens, similar to the previous specimens collected from Sichuan Province in appearance, were collected. Figure 1 shows the location of the sampling site and it was created with the help of SimpleMappr (Shorthouse 2010).

Morphological examination
All specimens were generally pinned directly or stored in ethanol after collecting by hand net, then stored at Shaanxi University of Technology, Hanzhong, China (SNUT) and at the Zoologisches Forschungsmuseum Alexander Koenig, Bonn, Germany (ZFMK). The male genitalia were extracted using an insect pin with a hooked tip. Genitalia were cleared by boiling in tubes of water-diluted KOH pellets for 5 min and brief immersion in glacial acetic acid to neutralize the alkaline, then rinsed twice in ethanol to remove the acid before storage in microvials containing glycerol. Morphological terminology follows Thompson (1999). Body length is measured from the frontal prominence excluding antenna to the apex of the abdomen, wing length from the base to its apex, all presented in millimeters.

DNA extraction, sequencing and assembly
The mitochondrial cytochrome c oxidase subunit I (COI) gene has frequently been employed as a molecular marker for phylogenetic studies on Syrphidae, and it has been shown to be informative for both generic and species level studies (Radenković et al. 2020;Young et al. 2020). Thus, we generated the complete COI sequences of these two unknown taxa and compared the obtained sequences with all available sequences of other species from Bacchini and Melanostomini to test their systematic status. The genomic DNA extraction of Biema wanglangensis Huo & Zhao gen. et sp. nov. and Biema qilianensis Huo & Liu gen. et sp. nov. was done using the DNEasy kit (Qiagen, Hilden, Germany). One paired-end sequencing library (2 ×150 base pairs, bp) with insert sizes of 350 bp was constructed with VAHTS Universal DNA Library Prep Kit for Illumina V2 kit (Vazyme, Nanning, China) and sequenced on the Illumina HiSeq 4000 platform. The generated reads were filtered by the software fastp ver. 0.20.1 (Chen et al. 2018). After removing unpaired reads, adapter sequences, low-quality reads, and duplicated reads, the complete mitochondrial COI gene sequences of B. wanglangensis and B. qilianensis were assembled and annotated using the software Geneious R11 (Biomatters, New Zealand) (Kearse et al. 2012). The new generated mitogenomic data are submitted to GenBank (https://www.ncbi.nlm.nih.gov/) with the accession number starting with ON067497 and ON067496, respectively.

Molecular analysis
The genetic distances between species of Bacchini and Melanostomini were calculated with the software MEGA ver. 7 under a K2P model based on the COI dataset (Kimura 1980). For the General Mixed Yule-Coalescent Model (GMYC) analysis (Fujisawa & Barraclough 2013), an ultrametric tree was reconstructed by Beast ver. 2.6.2 (Bouckaert et al. 2014) using the GTR + Γ + I model, a relaxed clock lognormal and Birth-death process, the resulting ultrametric tree was used for GMYC analyses on the web interface (http://species.h-its.org/gmyc) under the single-threshold method to generate the putative species. For the java Molecular Operational Taxonomic Units (jMOTU) analysis, the low BLAST identity filter was set to 97 and percentage of minimum sequence length to 95 in jMOTU ver. 4.1 (Jones et al. 2011). The automatic barcode gap discovery (ABGD) analysis (Puillandre et al. 2012) was performed on the web interface (https://bioinfo.mnhn.fr/abi/public/abgd/abgdweb.html) under Kimura (K80) TS/TV ver. 2.0 model with default parameters except the values of steps = 50, relative gap width (X) = 0.5. To infer the phylogenetic status of Biema Huo & Zhao gen. nov., we reconstructed the phylogenetic tree using the concatenated sequences data of COI sequences from 68 species of Bacchini and Melanostomini, and two species of genus Episyrphus Matsumura & Adachi, 1917 were used as outgroups. MAFFT ver. 7.429 was applied for sequences alignment with the E-INS-I strategy (Katoh & Standley 2013), and the aligned data matrix were trimmed by the software TrimAI ver. 1.2 (Capella-Gutiérrez et al. 2009). Phylogeny estimation was performed using Maximum Likelihood (ML) and Bayesian inference (BI) methods. PartitionFinder2 ver. 2.1.1 (Lanfear et al. 2017) was used to estimate the best substitution model and partitioning scheme selection for tree building. MrBayes ver. 3.2.7 (Ronquist et al. 2012) were used for Bayesian inference (BI) tree building, four simultaneous Markov chains were run for 10 million generations, with tree sampling occurring every 1000 generations and a burn-in of 25% of trees. Maximum Likelihood tree were reconstructed using IQ-tree ver. 2.0.3 (Nguyen et al. 2015) with 1000 bootstrap replicates.

Diagnosis
Biema gen. nov. can be distinguished by the following morphological features: head deeply concave posteriorly with a concealed postpronotum; postpronotum without pile; head, mesonotum and scutellum black; metasternum not reduced, with posterior margin shallowly concave similar to that in Platycheirus Le Peletier & Serville, 1828; alula narrow, as wide as basal width of cell c; male postabdomen conspicuous more swollen than other segments, surstylus and postgonite complex, phallus unsegmented. In the identification key to bacchine and melanostomine groups by Thompson & Skevington (2014), the new genus keys out to couplet 2. Further, males of Biema key out to Baccha Fabricius, 1805 based on its short pilose antennal arista, unmodified hind tibia, distinct facial tubercle and bare metathoracic pleuron. Our new genus can be easily distinguished from Baccha by the incomplete postmetacoxal bridge (complete postmetacoxal bridge in Baccha) and by the sparse but present scutellar fringe (absent in Baccha). Females of Biema, with a parallel-sided abdomen, key out to couplet 11 and are morphologically related to Platycheirus, Argentinomyia Lynch-Arribálzaga, 1891 and Melanostoma.

Etymology
The new genus is named after the Biema Zang people, who live where the type specimens were collected.

Description
Small sized flies. Head hemispherical. Eye bare. Vertex, frons and face black, densely white pollinose obscures ground colour. Facial tubercle rounded and produced, bare and shinning. Arista extremely short pilose. Antennal sockets confluent. Scutellum black, row of short bristles on posterior margin and one pair of bristles elongated in the middle. Katepisternum only with ventral patches. Metasternum not reduced, posterior margin shallowly concave similar to that in Platycheirus. Legs slender, not modified, hide-coxa without tuft of pile on anteromedial corner. Wing membrane entirely microtrichose. Vein R 4+5 straight; spurious vein rudimentary; crossvein r-m slightly inclined, located before basal ⅓ of cell dm; alula narrow, as wide as width of cell c. Male abdomen nearly parallel-sided, slightly constricted at tergite 2 posterior margin, broadened from tergite 3 and widest part at end of tergite 4, postabdomen conspicuous more swollen than other segments. Tergite 2 slightly longer than tergite 3, and tergite 3 slightly longer than tergite 4. Abdomen blackish brown with yellow maculae or fasciae. Male surstylus and postgonite complex, phallus unsegmented.

Biology and distribution
Biema gen. nov. occurs in forest areas, at or above 2300 m altitude in China (Sichuan, Qinghai) ( Fig. 1).

Diagnosis
Mesonotum sparsely light yellow pollinose, only thickened on lateral sides before transverse suture; pleuron and scutellum sparsely pollinose; male tergite 4 with dark brown or yellow broad median fascia; female tergites 3 and 4 with yellow fasciae, not extended to the anterior margin; female tergites 5 to 7 with yellow maculae basolaterally.

Etymology
The specific name is derived from the locality where type specimens were collected.
Head (8)(9)11). Hemispherical, deeply concave posteriorly with a concealed postpronotum. Eye bare, with eye contiguity longer than frons. Vertex slightly convex, black, yellow pilose and pollinose. Ocellar triangle equilateral, located at the anterior half of vertex. Occiput densely yellow pilose and pollinose on dorsal and upper half of lateral portions, yellowish white pilose and pollinose on lower half, obscures ground colour. Frons densely white pollinose obscures ground colour, short light pile along the margins. Lunule narrow, light yellowish brown. Face almost vertical in lateral view, facial tubercle rounded and produced, anterior margin of oral open not pointed. Face black and densely white to light yellow pollinose obscures ground colour, facial tubercle and lateral oral margins shiny black and bare. Face short light pilose laterally. Gena densely light yellowish white pilose and pollinose. Antennal sockets confluent. Antenna light yellow; basoflagellomere dark brown dorsally; arista dark brown with extremely short pile, thickened basally.
tHorax (Figs 2-3). Black. Mesonotum metallic golden green, with subappressed short yellow pile; sparsely light yellow pollinose, thickened on lateral sides before transverse suture. Postpronotum light yellow pollinose. Scutellum shining black, metallic green, with subappressed short yellow pile, row of light yellow bristle-like pile on posterior margin and two pile elongated in middle. Subscutellar fringe short and sparse, absent medially. Pleuron shining black, light yellow pollinose. Posterior convex part of anepisternum and anterior anepimeron sparsely short yellow pilose. Katepisterum sparsely short yellow pilose, only with ventral pile patches. Metasternum not reduced, posterior margin shallowly concave similar to that in Platycheirus, yellow, bare.
Wing (Figs 2-3, 14). Transparent, stigma light yellow, membrane entirely microtrichose. Vein R 4+5 straight, spurious vein rudimentary, corssvein r-m slightly inclined, located before the basal ⅓ of cell dm. Vein M 1 bent basally and formed s-shaped slightly. Vein M 1 and vein dm-cu parallel with wing margin. Alula narrow, as wide as basal width of cell c. Calypters narrow, yellowish white. Halters yellowish white, except yellowish green apically.
abdoMen (Figs 2-3, 12). Male abdomen parallel-sided, slightly constricted at tergite 2 posterior margin, broadened from tergite 3 and widest part at end of tergite 4, postabdomen conspicuous more swollen than other segments. Tergite 2 slightly longer than tergite 3, and tergite 3 slightly longer than tergite 4. Abdomen blackish brown, yellowish white to yellow laterally; tergite 2 with two triangular yellow markings merged into yellow lateral margin and broadly separated on inner end; tergite 3 with broad median yellow fascia, sometime interrupted medially; tergite 4 with dark broad median brown fascia, sometimes absent. Terminalia yellowish brown. Tergites with light yellow pile on lateral margin, appressed black pile medially. Sternites light pilose; sternites 1 and 2 yellowish white, 3 and 4 brownish yellow. MaLe terMinaLia (Figs 15-23). Dark brown. Cercus small, weakly sclerotized, with yellow pile. Epandrium nearly quadrilateral in lateral view, broad slightly longer than high, basal margin broader than apical margin. Surstylus triangular in dorsal view, broadened basally, then gradually narrowed ventrad, with apex acute, and bent posterodorsally; in posterior view expanded into broad triangle towards middle line along posterior margin of epandrium, with pile on inner margin. Hypandrium circular and expanded basally, with transparent circular membrane area on postmedial portion ventrally, without lingula. Postgonite divided into dorsal and ventral branches, dorsal branch broadly striped, transparent on margins, with circular apex, bent posteroventrally in middle right angled. Ventral branch narrowly striped, expanded posteroventrally. Phallus unsegmented, with 2 ridges dorsally, apical end of ridges pointed.
Legs. Tarsi with black pile dorsally.

Immature stages
Unknown.

Diagnosis
Mesonotum densely pollinose, anterior area with one pair of inconspicuous submedial pollinose vittae extended posteriad of transverse suture; scutellum densely pollinose; male tergite 4 without macula or with a small yellow macula/fascia anteromedially; female tergites 2 to 7 with broad yellow fasciae, extended to the anterior margin of tergites.

Etymology
The specific name is derived from the locality where the type specimens were collected. Legs. Light yellow to yellowish white; two apical tarsomeres of mid-tarsi light brown; hind-tibiae, hindtarsi and apical ½ to ⅔ of hind-femora black to blackish brown, hind-knees and apical of hind-tibiae light yellow. Yellow pilose.

Holotype
Wing (Fig. 31) bent basally and formed s-shaped slightly, Vein M 1 and vein dm-cu parallel with wing margin. Alula narrow, as wide as basal width of cell c. Calypters narrow, yellowish white. Halters yellowish white, except yellowish green apically. abdoMen (Fig. 29). Male abdomen parallel-sided, slightly constricted at tergite 2 posterior margin, broadened from tergite 3 and the widest part at the end of tergite 4, postabdomen conspicuous more swollen than other segments. Tergite 2 slightly longer than tergite 3, and tergite 3 slightly longer than tergite 4. Abdomen blackish brown, yellowish white to yellow laterally; tergite 2 with two triangular yellow markings merged into yellow lateral margin and broadly separated on inner end; tergite 3 with yellow broad median fascia, sometime interrupted medially; tergite 4 without macula, sometime with median small yellow macula or fascia anteriorly. Terminalia yellowish brown. Tergites with light yellow pile on lateral margin and appressed black pile medially. Sternites light pilose; sternites 1 and 2 yellowish white, 3 and 4 brownish yellow.
MaLe terMinaLia (Figs 32-41). Yellowish brown. Cercus small, weakly sclerotized, yellowish brown with yellow pile. Epandrium nearly quadrilateral in lateral view, slightly longer than high, with the dorsal margin slightly convex. Surstylus elongated, slightly expanded inwards basodorsally, narrowly stripelike in lateral view, dorsal and ventral margins at basal ⅔ nearly parallel, apical ⅓ bent posterodorsally, ventral margin with circularly concave, apical with two triangular dentate-shaped point, inner surface with short brown setae. Hypandrium rounded and enlarged, with short brown setae posteroventrally and concave posteromedial margin. Postgonite bluntly basodorsally with a prominent tooth in lateral view, posterior part divided into dorsal and ventral branches, dorsal branch blunt and broad apically, ventral branch slightly sharp apically with dentate-shaped towards midline. Phallus unsegmented, in lateral view bluntly rounded apically, in dorsal view enlarged medially, arc-shaped laterally, two dentateshaped apically, arc-shaped between dentate-shape.
Head (Fig. 26). Vertex and frons densely gray yellow pollinose and yellow pilose, with a blackish brown spot in the front of lunule. Antenna dark brown.
Legs. Tarsi with black pile dorsally. abdoMen (Fig. 30). Abdomen parallel-sided, blackish brown, yellowish laterally. Tergite 1 yellow or dark brown. Tergite 2 with lateral yellow spots medially, separated at the inner ends and merged into lateral yellow. Tergites 3 to 7 with broad yellow fasciae, anterior border of fasciae contacts anterior margin of tergites, covering about ⅔ of tergites 3 and 4, about ½ of tergites 5 to 7. Sternites yellow with light pile. Remainder similar to male.

Immature stages
Unknown.

Molecular analyses
The mtDNA COI dataset comprised 1539 nucleotides with 552 variable and 426 parsimony informative sites for 68 Bacchini and Melanostomini taxa and two outgroups. Biema wanglangensis gen. et sp. nov. was found to have a 2.93% sequence divergence from Biema qilianensis gen. et sp. nov., and averaged 11.54% divergent from other species of Bacchini and Melanostomini (Supp. file 1: Table S1). Based on the COI gene, all three species delimitation methods consistently supported our morphological results and the newly described species Biema wanglangensis and Biema qilianensis were well supported as two distinct and separate taxa (Fig. 43). Both the consensus trees inferred using BI and ML analyses produced an identical topological structure, where the placement of Biema gen. nov. was clearly distinct from other taxa and recovered as a highly supported monophyletic clade within tribe Melanostomini (PP = 100, BS = 100), but the phylogenetic relationships amongst genera Biema, Melanostoma and Argentinomyia are unclear.

Discussion
The discovery of a new flower fly genus, Biema gen. nov., with two new species presented in this study increases the knowledge not only of the Chinese syrphids, but also gives valuable data on Bacchini and Melanostomini species in the Palaearctic Region.
Based on the key of Vockeroth (1992), Biema gen. nov. belongs to the old concept of the tribe Bacchini with the following synapomorphies: head, mesonotum and scutellum black; deeply concave posteriorly with a concealed postpronotum; postpronotum bare; and phallus unsegmented. Further, in the Palaearctic key of genera by Thompson & Rotheray (1998), Biema keys out to couplet 52 and runs close to Melanostoma, Platycheirus and Xanthandrus, but Biema has an entire metasternum (greatly reduced in the species of Melanostoma found in China), only ventral pile patches on katepisternum (pile patches broadly separated posteriorly on katepisternum in Xanthandrus), narrow alula as broad as costal cell (broader in Platycheirus). In addition, as mentioned in the diagnosis, males of Biema can key out to the group of genera with petiolate abdomens (Thompson & Skevington 2014), and it is easy to distinguish from Baccha, Spazigaster Rondani, 1843 and Leucopodella Hull, 1949 by its short pilose antennal arista, unmodified hind tibia, distinct facial tubercle, bare metathoracic pleuron, and complete postmetacoxal bridge.
In our inferred topologies based on the COI gene, Biema gen. nov. is resolved within the tribe Melanostomini and clearly distinct from other congeners, but the phylogenetic relationships amongst the genera Biema, Melanostoma and Argentinomyia are not fully resolved. Although the accurate taxonomic status of these three genera needs to be revised by further works with extended species sampling and morphological or molecular data, the genus Biema can be well distinguished from Melanostoma and Argentinomyia based on morphological characters. The differences between Biema and Melanostoma were described above; moreover, Argentinomyia is mainly distributed in the Neotropical Region and can be distinguished from Biema by the following morphological features: scape elongate, about twice as long as pedicel; antennal pits separated; subscutellar fringe complete; wing membrane broadly bare basally (cells r and bm bare), microtrichose apically; alula broad; regular-sized terminalia with triangular to rectangular superior lobes, or irregular in shape.
Regarding the two new species, Biema wanglangensis gen. et sp. nov. and Biema qilianensis gen. et sp. nov., diagnostic characters are found in the male genitalia (especially the hypandrium, surstylus, postgonite and apical end of phallus) and the abdominal pattern. In addition to the adult morphological analysis, we used COI sequences to test the delimitation of species of Biema gen. nov. within the tribes of Bacchini and Melanostomini, all three species delimitation approaches (ABGD, GMYC and jMOTU) also recognized the newly proposed two species of Biema as two separate groups from other studied taxa.