Review of the genus Stigmus Panzer (Hymenoptera, Crabronidae) in China, with description of five new species from the Oriental and Palearctic Regions

Abstract Five new species of the genus Stigmus: S.capoblongus Bashir & Ma, sp. n., S.denticorneus Bashir & Ma, sp. n., S.fronticoncavus Bashir & Ma, sp. n., S.interruptus Bashir & Ma, sp. n. and S.lobomelanicus Bashir & Ma, sp. n. are described and illustrated from China. Also, a key to the species of Stigmus Panzer occurring in China is provided.


Introduction
The genus Stigmus Panzer was erected by Panzer (1804) on the basis of type species Stigmus pendulus Panzer. At present 25 species and 4 subspecies are described worldwide, of which the highest number of species is known from the Nearctic Region (10 species and 2 subspecies), followed by the Palearctic Region (7 species); 4 species and 2 subspecies were found in the Oriental Region (of which 3 species and 2 subspecies were in China), 2 species in Neotropical Region, 1 species in the Palearctic and Oriental Regions, and 1 species in the Nearctic and Neotropical Regions (Morawitz 1864;Tsuneki 1954Tsuneki , 1977Kolesnikov 1977;Allen 1987;Budrys 1987Budrys , 1995Uffen 1997Uffen , 1998Jones 2001;Pulawski 2018). Recently, Stigmus eurasiaticus was well described by Mokrousov from Russia (Mokrousov 2017).
The diagnostic characteristics that differentiate Stigmus from other genera in Pemphredonini are the presence of occipital carina; mandibles in the male bidentate, in the female uni-, bi-, or usually tridentate; vertex micropore field (opaque area) present; labrum subtriangular, pentagonal or trapeziform; face with a shallow scapal basin; interantennal tubercle absent; clypeus of male with silvery dense setae; eyes broadly separated, pitted grooves along orbits narrow or absent; head moderately developed behind eyes; pronotum with a transverse carina; notauli indicated or developed; omaulus well developed (only in S. solskyi A. Morawitz is it invisible against the background of a wrinkled mesopleuron sculpture); no definitive episternal sulcus; stigma large, two submarginal cells; hindwing media diverging before or beyond cua, hindwing median cell normal size; petiole at least twice its diameter; and female pygidial plate present (Valkeila 1956;Krombein 1973;Bohart and Menke 1976;Finnamore 1995).
In the present study, five new species of genus Stigmus Panzer are described and illustrated. A key to the species of the genus Stigmus reported from China is also provided.

Materials and methods
The specimens examined in this study belong to the following institutions: Insect Collections of China Agricultural University, Beijing, P. R. China (CAU); Insect Collections of Yunnan Agricultural University, Kunming, Yunnan, P. R. China (YNAU); and Parasitic Hymenoptera Collection of Zhejiang University, Hangzhou, Zhejiang Province, P. R. China (ZJU).
The specimens were observed and illustrated with the help of an Olympus stereomicroscope (SZ Series, Japan) with an ocular micrometer. For the terminology we mainly followed Bohart and Menke (1976). The abbreviations in the text are as follows: BL, body length; HLD, head length in dorsal view (the distance from frons to occipital margin in the middle); HLF, head length in frontal view (the distance from vertex to clypeal margin in the middle); HW, head width (dorsal view, maximum); EW, eye width (lateral view, maximum); EWd, eye width (frontal view, maximum); TW, gena width (lateral view, maximum); EL, eye length (lateral view, maximum); POD, postocellar distance (distance between inner margins of hind ocelli); OOD, ocellocular distance (distance between outer margin of hind ocellus and nearest inner orbit); OCD, ocello-occipital distance (distance between posterior margin of hind ocellus and occipital margin, dorsal view); PW, petiole width (dorsal view, in the middle); PL, petiole length (lateral view); WTI, maximum width of metasomal tergum I (dorsal view); LTI, maximum length of metasomal tergum I (dorsal view).  , 30.VII.2004 Tsuneki (1954) by frontal furrow weakly impressed, inconspicuously; median and upper frons with fine sparse punctures; admedian line weakly impressed; lateral surface of propodeum shiny and smooth anteriorly and medially, distinctly coriaceous mixed with several longitudinal rugae posteriorly. Closely related to S. quadriceps Tsuneki but differs by free margin of clypeus with two triangular teeth medially; flagellomere beneath fulvous, above, remaining reddish brown to dark brown; scutellum shiny, with fine sparse punctures; petiole subquadrate (non-cylindrical); pronotal collar with strong carinae anteriorly, lateral carina lacking, without antero-lateral corner.

Key to the species of
Description Colour pattern. Clypeus with reddish brown to dark brown band subapically; mandible yellowish except reddish brown apically; palpi ivory; scape beneath ivory, above fulvous; pedicel fulvous; flagellomere beneath fulvous, above I fulvous, remaining reddish brown to dark brown; pronotal lobe white; tegula yellowish; forewing veins brown; fore leg: yellowish to fulvous except outer margin of femur somewhat brown, coxa dark brown largely; mid leg: yellowish to fulvous except outer margin of femur somewhat brown, coxa dark brown largely; hind leg: coxa apically, trochanter, base and apex of femur, tibia largely, tarsi yellowish to fulvous, remainder dark brown; petiole black; gaster dark brown, gastral sterna II-VII posteriorly bright yellow; setae on clypeus silvery and mandible yellow.
Head. Mandible bidentate apically (Fig. 1a). Clypeus nearly flat, with dense tiny punctures, setae on clypeus dense, short; free margin of clypeus slightly produced and with two triangular teeth medially, slightly reflected (Fig. 1a). Scapal hollow half mat, coriaceous, somewhat shallow, provided with a vestigial minute tubercle medially, not spined. Frontal furrow very fine and weakly impressed, inconspicuously, sometimes lacking. Median and upper frons shiny, with fine sparse punctures, gently convex. Ocellar triangle area flat, shiny, impunctate, area near eyes with dense, short, impressed lines, opaque area smaller than hind ocellus. Basal half of vertex shiny, with sparse fine punctures, posterior area half mat, with inconspicuous microsculpture and fine sparse punctures (Fig. 1b). Gena shiny, with several fine punctures dorsally, ventral gena shiny and smooth. Head from above with temples slightly convergent posteriorly. Occipital carina incomplete, not ending in hypostomal carina, suddenly ended at the posterior ridge of stomal hollow, not tooth, much narrowed, no crenulate; inner and outer orbital furrows lacking; flagellomeres without tyloids, normal.
Legs. Normal, outer surface of hind tibia with three long, slender, fulvous to dark brown, spines.
Metasoma. Dorsal surface of petiole subquadrate (cross section), slightly convex and widened toward apex slightly, and with two sturdy, longitudinal median carinae, area between carinae with dense, sturdy, irregular rugae, median and posterior areas with two sturdy, longitudinal, lateral carinae on each side (Fig. 1e). Lateral surface of petiole with a few strong longitudinal carinae (Fig. 1f ). Ventral surface of petiole with 4 sturdy, short, longitudinal carinae posteriorly. Gaster segments shiny, nearly impunctate. Male genitalia (Fig. 1g- , 30.VII.2004. Diagnosis. Distinguished from S. japonicus by combination of characters: in female, free margin of clypeus slightly produced and with two distinct cornuted teeth medially, deeply emarginated in the middle; scrobal suture inconspicuous, just with several longitudinal rugae; lateral surface of petiole with two strong longitudinal carinae; admedian and parapsidal line weakly impressed; posterior surface of propodeum with a shallow narrow median groove, shiny, remaining with contiguous punctures and sparse irregular oblique longitudinal rugae. Closely related to S. quadriceps except antenna dark brown; forewing veins brown; gena with sparse midsize to large punctures dorsally; in male, frontal furrow distinctly impressed on upper frons; free margin of clypeus slightly produced and nearly truncate medially; anterior area of pronotal collar narrowly emarginated in middle, antero-lateral corner lacking; petiole subquadrate (non-cylindrical), slightly convex, not longer than 1 st abdominal tergite. Colour pattern. Clypeus with reddish brown to dark brown band subapically; mandible yellowish except reddish brown apically; labrum dark brown; palpi fulvous; antenna beneath fulvous and dark brown; pronotal lobe ivory; tegula fulvous; forewing veins brown; fore and mid legs: base and apex of femur, tibia, tarsi fulvous, trochanter and remaining femur dark brown; hind leg basal one fourth of tibia and tarsus fulvous, remaining tibia dark brown; petiole black; gaster dark brown; setae on clypeus and mandible yellow.
Legs. Normal, outer surface of hind tibia with three long, slender, fulvous to dark brown, spines.
Metasoma. Dorsal surface of petiole subquadrate (cross section), slightly convex and widened toward apex slightly, with two strong longitudinal carinae, and irregular, strong rugae anteriorly and medially, lateral area with 2 strong longitudinal carinae posteriorly on each side (Fig. 2e). Lateral surface of petiole with a few strong longitudinal carinae (Fig. 2f ). Ventral surface of petiole with a few strong, longitudinal carinae medially and posteriorly. Gastral segments shiny, nearly impunctate, gastral sternum VI with fine, coarse punctures, half mat. Pygidial area shiny, broadly U-shaped, apex rounded, with 2 lines, large punctures and setae medially (Fig. 2g).

Stigmus fronticoncavus
Head. Mandible tridentate apically (Fig. 3a), median tooth larger, outer margin of mandible with a broad triangular tooth nearly apical area (Fig. 3b). Labrum with five lobes, apex with two lateral teeth and round teeth medially (Fig. 3a). Clypeus shiny, impunctate, fairly deeply impressed, setae on clypeus sparse, long; free margin of clypeus not produced, nearly truncate apically, and with two small teeth medially and two blunt teeth laterally, median teeth slightly reflected (Fig. 3a). Scapal hollow shiny, fairly deep and broad, not well outlined, provided with a small round tubercle medially, not spined. Frontal furrow lacking. Median and upper frons shiny, impunc- tate. Ocellar triangle area flat, shiny, impunctate, near eyes area with 3 or 4 short impressed lines, opaque area small. Vertex behind ocelli shiny, impunctate; gena shiny, smooth and impunctate (Fig. 3c). Head from above with temples somewhat roundly convergent posteriorly. Occipital carina incomplete, not ending in hypostomal carina, suddenly ended at the posterior ridge of stomal hollow, forming a blunt tooth, much narrowed, not crenulate. Inner orbital furrow broad, shiny, with inner marginal carina distinct; outer orbital furrow lacking.
Legs. Normal, outer surface of hind tibia with three long, slender, fulvous to dark brown, spines.
Legs. Normal, outer surface of hind tibia with three long, slender, fulvous to dark brown, spines.
Metasoma. Dorsal surface of petiole subquadrate (cross section), strongly convex and widened toward apex slightly, and with two sturdy, longitudinal median carinae, and with irregular strong rugae anteriorly and medially (Fig. 4f ); lateral surface of petiole with a few strong longitudinal carinae medianly and posteriorly (Fig. 4h); ventral surface of petiole with a few strong longitudinal carinae medianly and posteriorly. Metasomal segments shiny, nearly impunctate, gastral sternum VI with fine or coarse punctures, half mat; pygidial area half mat, broadly U-shaped, apex truncate, with longitudinal micro-sculptures, basal area with several large punctures (Fig. 4g).

Distribution. China (Tibet).
Etymology. The name, interruptus, is derived from the Latin word interruptus (= interrupt), referring to the anterior area of the pronotal collar with sturdy carinae, incomplete, narrowly emarginate in the middle. Diagnosis. Differs from S. pendulus by free margin of clypeus strongly produced and truncate medially, frontal furrow lacking, gena with large dense punctures, scutellum with several large punctures, pygidial area broadly triangular, with dense, slender, longitudinal striations; from S. munakatai Tsuneki it differs by setae on clypeus and Colour pattern. Clypeus black; mandible reddish brown to dark brown except black basally and apically; palpi dark brown; scape, pedicel, tegula and flagellomere dark brown to black; pronotal lobe black; forewing veins fulvous to dark brown; fore and mid legs: tibia, tarsi, femur (apex) reddish brown to dark brown, hind tarsus dark brown; petiole and metasoma black; setae on clypeus and mandible golden.
Legs. Normal, outer surface of hind tibia with three long, slender, fulvous to dark brown, spines.