The genus Trachionus Haliday, 1833 (Hymenoptera, Braconidae, Alysiinae) new for China, with description of four new species

Abstract The genus Trachionus Haliday, 1833 (Hymenoptera, Braconidae, Alysiinae, Dacnusini) is reported for the first time from China. The genus is represented by four new species from Shaanxi province (NW China), which are described and illustrated. An identification key to the species in China is presented, a key to the genera of the Trachionus group and notes on the relationships with other Palaearctic species are added.


Introduction
Trachionus Haliday, 1833 (Hymenoptera, Braconidae, Alysiinae, Dacnusini) is a small Holarctic genus with seven Palaearctic species (four of which reported from the East Palaearctic region) and six Nearctic species. Species of Trachionus are parasitoids of the larvae of the genus Phytobia Lioy, 1864 (Diptera: Agromyzidae) mining in or near the cambium of trees and shrubs (Yu et al. 2012; for a review, see . The most recent key to the Palaearctic species is by Perepechayenko (2000) and a recent key to the Nearctic species is lacking. In the present paper, we describe four species of this genus collected during fieldwork by one of us (JLT); which proved all to be new to science. It is the first report of the genus from China, but the genus is known from neighbouring countries: Russia (including Far East region), Mongolia, Japan and Korea (Yu et al. 2012).

Material and methods
The specimens were collected by hand net during fieldwork in the Qinling Mountains in Shaanxi province (Northwest China). The specimens were collected directly in alcohol and later prepared with the AXA method (van Achterberg 2009: method applying first a mixture of alcohol 96% + xylene, after 24 hours replaced by amylacetate).
Morphological terminology follows van Achterberg (1988van Achterberg ( , 1993, including the abbreviations for the wing venation. Measurements are taken as indicated by van Achterberg (1988): for the length and the width of a body part the maximum length and width is taken, unless otherwise indicated. The length of the mesosoma is measured from the anterior border of the mesoscutum till the apex of the propodeum and of the first tergite from the posterior border of the adductor till the medio-posterior margin of the tergite.

Descriptions
Notes. Up to 1997 the interpretation of the genus Trachionus had been problematical, not the least because of the synonymy with the genus Chelonus by Dalla Torre (1898). It is contradicted by the clear original diagnosis by Haliday (1833): "Areolae cubitales 2; mandibulae hiantes 4-dentes". If the diagnosis of the genus is combined with the diagnosis of the group ("Abdominis segmenta coalita postica retracta. Chelonus") then it is clear that it can only apply to the tribe Dacnusini (because of the exodont mandibles) and to the genus Aenone Curtis, 1837 (because of the Chelonine-like metasoma), a junior homonym and, therefore, unavailable. In 1997 van Achterberg clarified the position of the genus Trachionus and synonymized Trachionus with Symphya Foerster, the oldest available name for the group in current use that time. All four species from China belong to the subgenus Planiricus Perepechayenko (= T. hians-group) because they have the epistomal suture much narrower than the clypeus and the sternaulus is absent or is only anteriorly shallowly developed as punctate area.
Trachionus is similar to two Palaearctic genera, Epimicta Foerster, 1863, andParasymphya Tobias, 1998, because of the presence of the pronotal spine, and the sculpture and shape of the second and third metasomal tergites. These taxa can be separated as follows: 1 Clypeus semi-circular; fourth and fifth tergites of ♀ sculptured and more or less exposed; second tooth of mandible obtuse,   . 4); second and third tergites regularly and rather finely striate, with about 60 striae and moderately shiny (Fig. 5). Similar to T. hians (Nees, 1816), but that species has a strong transverse carina at the propleuron subposteriorly (absent or slightly developed in T. acarinatus); precoxal sulcus and posterior part of notauli wide (medium-sized) and metanotal spine hardly protruding above level of scutellum (protruding far above level of scutellum).
Head. Width of head twice its median length; head dorsally smooth, strongly shiny and largely sparsely setose; antenna with 33 segments, 0.95× as long as forewing, third segment 1.6× as long as fourth segment, length of third, fourth and penultimate segments 2.6×, 1.7× and 1.6× their width, respectively; frons slightly depressed behind antennal sockets and smooth; eye in dorsal view 1.3× as long as temple; temple in dorsal view directly rounded, smooth and near eye sparsely setose; OOL: diameter of ocellus: POL= 3:1:2; face weakly convex, with distinctly longitudinal carina and down- ward pointing setae laterally, largely matt and punctulate; clypeus transverse, with sparse fine punctures and convex; eye glabrous; mandible nearly touching eye, length of malar space 0.1× basal width of mandible; mandible 1.4× as long as its maximum width, largely punctate-rugose medially; mandible weakly widened apically, with long and acute triangular middle tooth, and two wide lateral lobes (Fig. 46); maxillary palp 0.9× height of head.
Colour. Black (including mandible); palpi and legs yellow but tarsi and base of hind coxa darkened; tegulae, pterostigma and forewing veins dark brown; hind wing veins pale brown; forewing membrane slightly infuscate, hind wing nearly pellucid.
Distribution. China (Shaanxi). Etymology. The name is derived from "a" (Greek for "not, without") and "carina" (Latin for "ridge") because of the lacking subposterior transverse carina of the propleuron. Diagnosis. Scutellum largely smooth, at most punctulate and nearly flat; mandible mainly brown, flat, without crest and with small fourth and fifth teeth (Figs 17, 43); temple smooth (Fig. 18); propleuron with transverse carina subposteriorly; sternaulus absent; median groove of mesoscutum and notauli rather narrow posteriorly (Fig. 14); metanotal spine medium-sized, its highest point remaining below level of tips of setae of scutellum (Fig. 21); propodeum angularly lowered posteriorly in lateral view and carina hardly protruding postero-laterally (Fig. 14); transverse carina of propodeum indistinct or absent (Fig. 14); medial third of hind tibia ivory; basal half of second metasomal tergite strongly rugose-striate, with about 30 striae and very shiny, rugae of third tergite with indistinct interspaces. Similar to T. hians, but that species has precoxal sulcus posteriorly and posterior part of notauli wide (rather narrow in T. albitibialis), basal half of hind tibia yellow (ivory) and basal half of second metasomal tergite largely finely aciculate (basal half of second tergite strongly rugose).

Trachionus albitibialis
Description. Holotype, female; body length 3.3 mm, forewing length 3.4 mm. Head. Width of head twice its median length, head dorsally smooth, distinctly shiny and mostly sparsely setose; antenna with 31 (right) or 32 (left) segments, 1.1× longer than forewing, third segment 1.4× as long as fourth segment, length of third, fourth and penultimate segments 2.4×, 1.7× and 1.6× their width, respectively; frons with setae laterally and slightly depressed behind antennal sockets; eye in dorsal view 2.1× as long as temple; temple in dorsal view directly roundly narrowed, smooth and near mandible punctulate and punctate; OOL: diameter of ocellus: POL = 14:4:5; face weakly convex, punctulate, with many upward pointing setae medially and downward pointing setae laterally; clypeus transverse, with fine punctures and convex; eye glabrous; mandible nearly touching eye, length of malar space 0.1× basal width of mandible; mandible 1.3× as long as its maximum width and 1.6× as long as its basal width, mostly smooth, medially rugose; mandible with 4 teeth or lobes, and second one acute, wide triangular; maxillary palp 0.9× as long as height of head.
Metasoma. Length of first tergite 0.8× its apical width, its surface punctate-rugose, with dorsal carinae converging medially and united in distinct median carina (Fig. 15); second tergite rather coarsely rugose-striate; basal half of third tergite coarsely rugosestriate and strongly shiny, rugae of third tergite with indistinct interspaces, apical part of third tergite smooth and shiny; combined length of second and third tergites 0.7× total length of metasoma (Fig. 16); setose part of ovipositor sheath 0.1× as long as fore wing; hypopygium large and apically acute (Fig. 16).
Colour. Black; mandible reddish brown; palpi pale yellow; basal two thirds of hind tibia ivory and apex infuscate, and tarsi largely dark brown; tegula brown; humeral plate and remainder of legs yellow; hypopygium black medially and remainder largely yellowish; pterostigma and most veins dark brown; wing membrane slightly infuscate, but hind wing nearly pellucid.
Distribution. China (Shaanxi). Etymology. The name is derived from "albus" (Latin for "white") and "tibia" (Latin for "shinbone") because of the largely whitish hind tibia. Diagnosis. Scutellum largely smooth, at most punctulate and nearly flat; mandible black, medially with irregular transverse crest and with minute fourth and fifth teeth (Figs 28, 30, 45); temple smooth and medium-sized (Fig. 29); propleuron without transverse carina subposteriorly; sternaulus absent; median groove of mesoscutum and notauli wide posteriorly; metanotal spine medium-sized, its highest point remaining below level of tips of setae of scutellum (Fig. 32); propodeum angularly lowered posteriorly in lateral view and carina hardly protruding postero-laterally (Fig.  25); transverse carina of propodeum coarsely developed and irregular; medial third of hind tibia brownish yellow; basal half of second metasomal tergite coarsely rugosestriate, with about 30 striae and very shiny (Fig. 26); rugae of third tergite with distinct shiny interspaces. Similar to T. hians, but this species has a strong transverse carina at the propleuron subposteriorly (without transverse carina in T. brevisulcatus) and basal half of second metasomal tergite largely finely aciculate (basal half of second tergite moderately striate).
Head. Width of head 2.1× its median length, head dorsally smooth, strongly shiny and largely sparsely setose; antenna with 37 segments,1.2× longer than fore wing, third segment 1.3× as long as fourth segment, length of third, fourth and penultimate segments 2.9×, 2.3× and 1.4× their width, respectively; frons slightly depressed behind antennal sockets and smooth; eye in dorsal view 2.2× as long as temple; temple in dorsal view directly roundly narrowed, smooth and near mandible punctulate; OOL: diameter of ocellus: POL= 10:3:3; face weakly convex, with long downward pointing setae laterally, punctulate and largely smooth; clypeus hemi-circular, smooth with some fine punctures and convex; eye glabrous; mandible nearly touching eye, length of malar space less than 0.1× basal width of mandible; mandible 1.1× as long as its maximum width and 1.2× as long as its basal width, largely rugose medially and basally; mandible with irregular transverse crest, two wide lateral lobes and minute ventral fourth and fifth teeth; maxillary palp as long as height of head.
Metasoma. Length of first tergite 1.1× its apical width, its surface punctate-rugose, with dorsal carinae converging medially and united in distinct median carina (Fig. 26); second tergite strongly rugose; basal half of third metasomal tergite moderately striate and strongly shiny, remainder smooth; combined length of second and third metasomal tergites 0.7× total length of metasoma ; rugae of third metasomal tergite with distinct shiny interspaces; setose part of ovipositor sheath 0.1× as long as fore wing; hypopygium large and apically acute (Fig. 27).
Distribution. China (Shaanxi). Etymology. The name is derived from "brevis" (Latin for "short") and "sulcus" (Latin for "groove") because of the short widened parts of precoxal sulcus and notauli. Diagnosis. Mandible with two wide lateral lobes and one smaller ventral lobe (Fig.  44); sternaulus present as flat punctate area anteriorly (Fig. 35); scutellum coarsely punctate and distinctly convex (Fig. 36); median punctate band of mesoscutum anteriorly as wide as smooth bands next to it (Fig. 36). The new species differs from the similar European T. mandibularis (Nees, 1816) by having the epistomal suture narrow, the sternaulus not impressed (but indicated as a flat punctate area anteriorly) and the mandible distinctly widened ventrally.

Trachionus mandibularoides
Description. Holotype, female; body length 2.2 mm, forewing length 2.7 mm. Head. Width of head 2.5× its median length; dorsally head smooth, strongly shiny and only sparsely setose; antenna incomplete, 20 segments remaining, third segment 1.6× as long as fourth segment, length of third and fourth segments 2.3× and 1.5× their width, respectively; frons narrowly depressed behind antennal sockets and smooth; eye in dorsal view 2.2× longer than temple; temple in dorsal view rounded, shiny and sparsely setose; OOL: diameter of ocellus: POL = 10:3:4; face medio-dorsally somewhat elevated, with upward pointing long setae, with satin sheen and punctulate; clypeus transverse, with some small punctures and convex; epistomal suture narrow; mandible nearly touching eye, length of malar space 0.1× basal width of mandible; mandible 1.3× as long as its maximum width, largely rugose medially; mandible dis-  tinctly widened apically, with long and acute triangular middle tooth, two wide lateral lobes and one smaller lobe ventrally; maxillary palp 0.9× height of head.
Metasoma. Length of first tergite nearly equal to its apical width, its surface longitudinally coarsely striate, with dorsal carinae converging medially and united in distinct median carina (Fig. 37); second and third tergites punctate-striate, but third tergite smooth apically; combined length of second and third metasomal tergites 0.4× total length of metasoma (Figs 37, 42); apically striae of third tergite with distinct shiny interspaces; setose part of ovipositor sheath 0.1× as long as fore wing; hypopygium large and apically acute (Fig. 42).
Distribution. China (Shaanxi). Etymology. The new species is named after T. mandibularis and "oides" (Latin for "similar to"), because of the similar sculpture of the mesosoma.