Female. Body length 3.4 mm, fore wing length 3.8 mm.

Head. Rather large, oval in frontal view, with antennal sockets high above middle level of eyes; transverse in dorsal view, 1.6× as wide as long and as wide as mesoscutum, with short white setae all over, including eyes. Ocelli in a very low triangle, the posterior transverse tangent to the anterior ocellus cutting the posterior pair. POL:OD:OOL=7.1:5.0:6.0. Vertex shiny but densely and shallowly punctate, strongly convex, and sharply constricted to occiput; frons virtually without sculpture; face shiny but shallowly rugose, slightly convex, upper half with indistinct median longitudinal carina which is triangularly widened downwards and forms a subtriangular shiny area; width of face 0.6× as high as eye and clypeus combined (19.8:32.2); eyes very large, inner margin of eyes slightly constricted at antennal sockets, widening upwards and downwards, 1.7× as high as wide (30.0:17.9); temple and gena also shiny but shallowly rugose, densely setose. Mouth opening wide, clypeus feebly rugose; tentorial pits of moderate size, distance between tentorial pits 3.6× as long as distance from pit to eye margin (11.0:3.1); malar space very short, 0.2× as long as eye height. Antennae normal, long, with the preapical segment about 2.3× as long as wide; flagellomeres long, thick, with bristly setosity, all flagellomeres with placodes arranged regularly in 2 ranks; apical segment longer than preapical one. Flagellomere proportion: 2 L/W=2.6, 8 L/W=2.6, 14 L/W=2.2; L 2/14=1.4; W 2/14=1.2.

Mesosoma. Pronotum shiny but sparsely punctate, with a strongly indicated, foveate, ventral furrow laterally. Mesoscutum shiny, evenly and densely punctate, with sparse short setae all over; notauli not impressed. Disc of scutellum shiny, also evenly punctate, its rugose (punctate) tip at middle widely interrupting the posterior, polished band of scutellum, with sparse short setae. Lateral part of the polished band at least distinctly convex anteriorly. Anterior margin of the postscutellum closely applied to the posterior margin of the scutellum so that, laterally, the phragma of scutellum is completely hidden. Scutellar sulcus deep, with few strong longitudinal short carinae, its width 1.3× as long as scutellum (25.0:20.0). Propodeum short, with a strong median keel, shiny beside the median keel on posterior half and anteriorly just behind anterior margin; the area behind the anterior polished area and posterolaterally strongly setigerous punctate; spiracles enclosed by strong costulae. Mesopleuron polished posteriorly and above precoxal sulcus polished; precoxal sulcus long, broad, shallow, punctate.

Wings. Forewing with vein r-m reduced to a hyaline point; areolet 3-sided; vein r (1st abscissa of radius) arising from distal 1/2 of pterostigma, far behind the middle, very obliquely placed on the pterostigma; meeting vein 2-SR at a 150 degree angle. Vein 1-R1 (metacarp) with distal end sharply defined, 5.5× as long as its distance from the apex of the marginal cell and 1.1× as long as pterostigma; pterostigma 3.3× as long as wide; r:2-SR:length of pterostigma=14.5:6.0:40.0. Width of 1st discal cell:height of 1st discal cell =31.5:38.0; 1-CU1:2-CU1:m-cu=13.0:12.5:12.5. Hind wing narrow, with edge of vannal lobe beyond its widest part very slightly concave and without trace of a fringe of setae.

Legs. Long. Hind coxa large, flattened on outer side, closely covered with deep punctures, the interspaces very shiny, hardly reaching past posterior margin of T3. Hind tibia swollen toward apex and 0.9× as long as hind tarsus (70.0:80.0). Inner hind tibial spur much longer than outer one, about 0.7× as long as hind basitarsus (23.0:33.0); fourth tarsal segment shorter than fifth tarsal segment (9.0:12.0); apical segment of the front tarsus without a spine. Tarsal claws long, simple.

Metasoma. Shorter than mesosoma. T1 strongly sclerotised, slightly widened posteriorly, with a complete deep and broad median groove which bifurcates apically into two strongly foveate grooves, with smooth surface but setigerous punctate distal to the middle, 1.4× as long as its width and 1.2× as long as T2. T2 with a polished elongated, narrow, parallel-sided median field that is separated from the strongly striate-rugose lateral surface by two broad, deeply foveate grooves; 0. 7× as long as its greatest width and 1.2× as long as T3. T3 as heavily sclerotised as T2, the two tergites together forming a sculptured carapace, beneath which the more apical tergites are completely or partially hidden. T3 subrectangular, with middle of anterior margin slightly arched; very shiny, with surface aciculate, coarsely laterally and weakly medially; the weak but distinct polished median field slightly widened posteriorly and open apically; separated from T2 by a deep foveate groove that is margined along posterior edge of T2. Tergites posterior to T3 membranous, smooth and shiny with very few fine setae. Ovipositor sheath thin and decurved, with sparse long setae posteriorly, without trace of apical, modified setae. Hypopygium large, evenly sclerotised, smooth and without setae, slightly surpassing the last tergite.

Colour. Body bright yellow to black; head brown, except the yellow mouthparts; mesosoma black, but brownish. Flagellum yellowish brown at basal half and darkened to brown apically, scape and pedicel bright yellow, even with antennal socket lightened to yellowish apically. Apex of mandible brown; palpi whitish yellow. Tegula yellow. Fore and mid legs bright yellow. Hind coxa, trochanter and femur also bright yellowish, except the extreme apex of coxa and distal 1/4 of femur brown; hind tibia and tarsi brown except the area distal to the extreme base to the middle of the tibia, the base of basitarsus and the tibial spurs whitish yellow. T1 bright yellow, somewhat transparent, T2 and T3 black, the other tergites and ovipositor sheaths light brown, with posterior margin of tergites more or less transparent, whitish. Wings hyaline but forewing with a faint apical spot; veins brown, vein 1-R1 (metacarp) lightened to yellow, pterostigma evenly brown with extreme base yellowish.

Variation. Body length 2.7–4.2mm, sometimes few tergites posterior to T3 with pale colour. Some individuals from Hainan with pale-colored head and some other individuals with T1 darkened posteriorly.

Same as female.

Unknown.

Holotype: ♀, Mt. Diaoluo (109°53'E, 18°39'N ~ 109°58'E, 18°42'N), Lingshui, Hainan, 2006. VII. 16–17, Liu Jingxian, No. 200802405. Paratype: 1♀, Mt. Diaoluo (109°53'E, 18°39'N ~ 109°58'E, 18°42'N), Lingshui, Hainan, 2006. VII. 16–17, Weng Liqiong, No. 200802525; 4♂♂, Mt. Diaoluo (109°53'E, 18°39'N ~ 109°58'E, 18°42'N), Lingshui, Hainan, 2006. VII. 16–17, Liu Jingxian, No. 200802161, 200802163, 200802289, 200802419; 1♀, Mt. Jianfengling (108°48'E, 18°41'N ~ 108°49'E, 18°42'N), Ledong, Hainan, 2007. VI. 5–7, Xiao Bin, No. 200806874; 2♀♀, Tianchi, Mt. Jianfengling (108°48'E, 18°41'N ~ 108°49'E, 18°42'N), Ledong, Hainan, 2007. X. 22–23, Liu Jingxian, No. 200810501, 200810789; 1♀, Hongmao, Mt. Yinggeling (109°31'E, N19°04'N), Baisha, Hainan, 2007. V. 23–25, Zeng Jie, No. 200804476; 1♀1♂, Mt. Yinggeling (109°31'E, N19°04'N), Baisha, Hainan, 2007. X. 18, Liu Jingxian, No. 200709927, 200709723; 1♀, Mt. Yinggeling (109°11'E, 18°49'N ~ 109°34'E, 19°08'N), Baisha, Hainan, 2008. XI. 17, Wang Manman, No. 200805450; 1♂, Mt. Bawangling (109°02'E, 19°05'N ~ 109°04'E, 19°08'N), Changjiang, Hainan, 2008. XI. 26, Wang Manman, No. 200805645; 1♀, Mt. Chebaling (114°14'E, 24°43'N ~ 114°16'E, 24°44'N), Shixing, Guangdong, 2003. VIII. 21, Xu Zaifu, No. 20052280; 1♀, Mt. Nanling (112°59'E, 24°53'N ~ 113°05'E, 24°56'N), Ruyuan, Guangdong, 2004. VIII. 4, Xu Zaifu, No. 20049754; 1♀, Mt. Jiuwandashan (108°12'E, 24°52'N ~ 108°32'E, 25°03'N), Pingying, Guangxi, 2003. VII. 30, Wang Yiping, No. 20037539; 1♀, Shiwandashan Forest Park (107°53'E, 21°53'N ~ 107°55'E, 24°55'N, 310m), Guangxi, 2001. XI. 29, Ma Yun, No. 20021577; 1♀, Letu (117°13'E, 24°53'N ~ 117°14'E, 24°54'N), Nanjing, Fujian, 1991. V. 23, Liu Changming, No. 20006068; 1♀, Xianrending, West Mt. Tianmu (119°23'E, 30°20'N ~ 119°24'E, 30°20'N), Linan, Zhejiang, 1999. VI. 30, Zhao Mingshui, No. 996522; 2♀♀, Mt. Gutian (118°07'E, 29°14'N ~ 118°10'E, 29°16'N), Kaihua, Zhejiang, 2005. VII. 3, Zhang Hongying, No. 200616206, 200617220.

The specific name “bifurcifossa” derives from the Latin adjective “bifurcus” and noun “fossa”, referring to median groove of T1 bifurcate apically.

China (Zhejiang, Fujian, Guangdong, Guangxi, Hainan).

This species is similar to Diolcogaster eclectes (Nixon, 1965), but can be distinguished by the almost smooth surface of T3 beside the median field (the latter has T3 sculptured except for a median, polished area) and the ovipositor sheath without a modified apical seta (the latter with one).