West Palaearctic species of the genus Diostracus Loew , 1861 ( Diptera : Dolichopodidae )

A new status (as subgenera of Diostracus Loew, 1861) for Sphyrotarsus Mik, 1874, Lagodechia Negrobov & Tsurikov, 1996 and Ozmena Özdikmen, 2010 stat. nov. is proposed. A new species, Diostracus (Sphyrotarsus) kustovi sp. nov., is described from the Russian Caucasus. The following recombinations (comb. nov.) are also proposed: Diostracus (Sphyrotarsus) argyrostomus (Mik, 1874); D. (S.) caucasicus (Negrobov, 1965); D. (S.) hervebazini (Parent, 1914); D. (S.) hessei (Parent, 1914); D. (S.) hygrophilus (Becker, 1891); D. (S.) leucostomus (Loew, 1861); D. (S.) parenti (Hesse, 1933); D. (Lagodechia) spinulifer Negrobov & Tsurikov, 1988; and D. (Ozmena) stackelbergi (Negrobov, 1965). A key to ten Diostracus species inhabiting the West Palaearctic Region is provided.


Introduction
Until the 1960s the genus Diostracus Loew, 1861, belonging to the subfamily Hydrophorinae, had long been supposed to be Nearctic in distribution, with three known species.In 1968 it was recorded from East Asia for the fi rst time by Takagi (1968).To date, 85 species have been described from a vast territory of the East Palaearctic and Orient, from Buryatia and Sakhalin in the north to Nepal, Bhutan, Assam, NE Myanmar, Yunnan and Taiwan in the south (Grichanov 2003(Grichanov -2013)).Negrobov (1978) placed the genus Asphyrotarsus Oldenberg, 1916 in synonymy with Diostracus, thus recording the genus in the West Palaearctic for the fi rst time.In all, the Palaearctic Region is known to include 21 of the 88 known species of Diostracus (Grichanov et al. 2011b).
The adults are usually found on wet rocks in mountainous areas or on stones in streams and waterfalls at high altitude.A key to Palaearctic species of the genus was provided by Negrobov (1978).A key to 37 Nepalese species was given by Saigusa (1984), who proposed 12 species groups and subgroups.A key to 14 Japanese species was given by Masunaga (2000), who mentioned some more species groups.The last key to males of the 23 known Chinese species was published by Yang et al. (2011).

Material and Methods
The holotype and paratype of the new species as well as other material examined are housed at the Zoological Institute of the Russian Academy of Sciences, St Petersburg (ZIN).
Specimens were studied and photographed with a ZEISS Discovery V-12 stereo microscope and an AxioCam MRc5 camera.Morphological terminology and abbreviations follow Cumming & Wood (2009).The lengths of the podomeres are given in millimetres.Body length is measured from the base of the antenna to the tip of abdominal segment 7. Wing length is measured from the base to the wing apex.Male genitalia were macerated in 10% KOH.The fi gure showing the male genitalia in lateral view is oriented as they appear on the intact specimen, with the morphologically ventral surface of the genitalia facing up, dorsal surface down, anterior end facing right and posterior end facing left.Information on world distribution for known species follows Grichanov (2003Grichanov ( -2013)).

Diagnosis
The genus is very polymorphic and characterized by the following combination of characters: body dark and stout, medium-to large-sized; palpus usually enlarged, loosely applied on proboscis; proboscis bulky; antennal scape glabrous or setose dorsally; arista-like stylus usually dorsal, sometimes basodorsal or subapical to apical; posterior mesonotum fl attened; acrostichal setae absent; 4-6 dorsocentral bristles variable in length; sutural and postsutural, some notopleural, supra-alar and post-alar bristles sometimes absent or reduced; scutellum with 1-2 pairs of strong bristles and with some short lateral setae or hairs, sometimes with three pairs of long bristles; mid and hind coxae without bristle on the outer side; legs often modifi ed; tarsi with more or less modifi ed empodium and claws, usually without pulvilli; wing elongate and wide, sometimes modifi ed in males; costa ended beyond tip of wing; crossvein dm-cu longer than distal section of CuA 1 vein, sometimes strongly sinuate; M 1+2 usually slightly convex anteriorly, often irregularly curved, more or less parallel to R 4+5 , at least partly behind dm-cu.

Remarks
The genus Sphyrotarsus Mik, 1874 includes 5 species from the European Alps, one Caucasian species and one Pamiran species.It was diagnosed by scape glabrous dorsally; tarsi with reduced empodium and without pulvilli; M 1+2 and R 4+5 are not strictly parallel to each other (Parent 1938); scutellum with 3 pairs of bristles (Negrobov 1978).Furthermore, the Pamiran subgenus Takagia Negrobov, 1973 (of Sphyrotarsus), was diagnosed by elongated antennal postpedicel with arista apical, somewhat widened at apex in male; sutural bristle absent; one supra-alar bristle; scutellum with 2 pairs of bristles (Negrobov 1973(Negrobov , 1978)).Nevertheless, all these characters are rather variable and can be found in East Asian species of Diostracus.The monotypic Caucasian genus Lagodechia Negrobov & Tsurikov, 1996 was diagnosed also by variable characters of face, mesonotal setation, wing venation and morphology of abdomen (Negrobov & Tsurikov 1996).In addition, some characters of L. spinulifera were incorrectly described, as follows from the illustrations published by Grichanov et al. (2011a, b).I think the diagnostic characters of these taxa have low generic signifi cance and regard Lagodechia, Sphyrotarsus and Takagia (now Ozmena Özdikmen, 2010) as subgenera of Diostracus.Accepting a new concept of the genus, I associate 97 species with Diostracus, of which 64 occur in the Oriental Region, 30 in the Palaearctic and 3 in the Nearctic Region.The fl ies of the genus are all torrenticolous in habitat.

Diagnosis
At present the nominotypical subgenus differs from other subgenera in having a dorsally setose antennal scape.It is worth noting that many Asian Diostracus species were described with a glabrous scape (e.g., Saigusa 1984Saigusa , 1995;;Saigusa et al. 1997;Yang et al. 2011).

Diagnosis
Describing a new genus, Negrobov & Tsurikov (1996) listed diagnostic characters that can be found in many Diostracus species (e.g., Saigusa 1984Saigusa , 1995;;Saigusa et al. 1997;Yang et al. 2011).The following characters of generic importance were listed in the original description of Lagodechia, but were not obvious on pictures made by O. Selivanova from type material (Grichanov et al. 2011a, b): antennal scape has dorsal projection; distance between scutellum and 1 st tergum is 3 times as long as scutellum.Negrobov & Tsurikov (1996) also found important differences in the female oviscapt of Lagodechia spinulifera and Diostracus subalpinus (Negrobov, 1973).Unfortunately, D. subalpinus (described from the Baikal Lake environs) is the only Diostracus species with illustrated female genitalia.The status of D. subalpinus and D. spinulifer needs further clarifi cation.

Distribution
Georgia.

Diagnosis
The main diagnostic character of the subgenus is the elongate antennal postpedicel in both male and female, and the apical stylus (Negrobov 1973).Nevertheless, some Oriental Diostracus species also have an elongate postpedicel and an apical or subapical stylus (e.g., Saigusa 1984;Yang et al. 2011).
Unfortunately, there are practically no publications with pictures of female antennae in Diostracus species.

Distribution
France, Italy.

Diagnosis
Scutellum with 3 pairs of almost equally long bristles; antennal scape bare above; male and female postpedicel about as long as high, with dorsal stylus; male 2 nd and 3 rd abdominal sterna with strong black spines; male 4 th abdominal sternum with bundle of setae; male with modifi ed legs and simple wings.

Etymology
This species is named after the Russian dipterologist Dr. Semyon Kustov (Krasnodar).

Description
Male LENGTH (mm).Body 9.4, wing 7.8, antenna 1.5, hypopygium 2.25.1A, B).Bluish-greenish black, pollinose; clypeus shining green, weakly pollinose, 1/3 as wide as head; face about 1/5 as wide as head, almost as long as wide; ocellar bristles strong, vertical and postvertical bristles about 1/2 as long as ocellar bristle; postocular ciliation black, strong, nearly as long as postvertical on upper 1/2, fi ner and yellowish below; ventral 1/2 of postcranium clothed with many long yellow hairs, some of which as thick as vertical bristle; antenna with bare vase-like scape; pedicel with ring of short setae; postpedicel as long as high, rounded distally, with middorsal simple arista-like stylus; length (mm) of scape to pedicel to postpedicel to stylus (1 st and 2 nd segments), 0.16-0.11-0.2-0.13-0.85;palpus ovate, 1.6 times as long as wide, 1/3 as long as eye height, slightly dilated at middle; palpus black in ground colour, glittering silvery by pollinosity, bearing short black setae on outer side and along margin; proboscis moderately large for the genus.
ABDOMEN.Black, with washed pollinosity, with short black setae; 1 st tergum with long brownish setae and ciliated with long black bristles on posterior margin; 1 st sternum projected, with shallow transverse furrow anteriorly; 2 nd sternum (Fig. 2) with medial bulb at anterior 1/3, bearing 2 adjacent black spines formed of long glued setae and directed anteriorly; 3 rd sternum (Fig. 2) with twice as large bulb bearing 2 diverging black spines formed of long glued setae and directed anteriorly; 4 th sternum (Fig. 3A) with 2 median bunches of erect brownish setae on low convection, with posterior margin somewhat projecting and covered with short hairs; hypopygium (Fig. 3B) black, moderately large, with posterodorsal portion moderately produced and rounded; hypandrium subtriangular, narrow distally and bifurcated at apex; phallus simple; epandrial lobe short and narrow; surstylus brown, almost semicircular, with short hairs dorsally; cercus distinctly longer than epandrium, slightly swollen at base, band-like, simple, densely ciliated with long yellow setae.

Female
LENGTH (mm).Body 7.0, wing 8.0, antenna 1.4.Similar to male except lacking male secondary sexual characters, otherwise as follows: 6 dorsocentrals of irregular length in left row and 8 dorsocentrals in right row; palpus not glittering silvery; legs and abdominal sterna simple; 6 th and 5 th terga and genital plates densely covered with fi ne long setae; no acanthophorites.

Remarks
Having bulbs on 2nd and 3rd sterna and bearing strong ventral spines or bunches on abdomen, the new species distinctly differs from other species of the subgenus Sphyrotarsus (see key below).D. (L.) spinulifer males also have a setose venter, but not bearing bulbs and thick spines.Some Chinese and Nepalese species of Diostracus were also described with male sterna ornamented with bunches of setae, spines or projections (e.g., Saigusa 1984;Yang et al. 2011), but strongly differing in many other characters.

Ecology
Both types of D. (S.) kustovi were collected together on stones at a stream (S.Kustov, pers. comm.) in high mountains at 2400 m above sea level.

Key to West Palaearctic species of the genus Diostracus (males)
Note: Partially based on previous keys to species of the former genus Sphyrotarsus (Parent 1938;Negrobov 1978).) hervebazini (Parent, 1914)

Discussion
The subgenera of the genus Diostracus are relatively well defi ned in the West Palaearctic Region.In the Nearctic, D. mchughi Harmston, 1966 differs from D. prasinus andD. olga Aldrich, 1911 in its bare antennal scape and can be associated with the subgenus Sphyrotarsus, although bearing only two, rather than three pairs of long setae on the scutellum.The borders of the West Palaearctic subgenera become rather obscure in the East Palaearctic and Orient.Saigusa (1984) supposed that most of the species groups proposed in his paper could be raised to the subgeneric rank if a phylogenetic analysis based on all known species were to be carried out.They could have a common ancestor, which is close to Diostracus or Sphyrotarsus, and their real degree of separation (or similarity) may require molecular investigation.Increased sampling effort should provide specimens that are appropriate for future studies of these fl ies.
Regarding the new species described here, it seems that D. (S.) kustovi sp.nov. is one of the largest hydrophorine species in the Palaearctic Region (see Negrobov 1977Negrobov -1979)).The male body is somewhat longer than the female body (9.4 vs. 7.0 mm), while wings are approximately equal in length in the two sexes (about 8 mm).