The new species belongs to Dibrachys s. str., and the mainly differences with Dibrachys microgastri (Bouché) as follows: Dibrachys liaoi sp. n. slightly blue-greenish, clypeal margin with two sharp teeth, Fu₁ to Fu₄ length slight longer than its width respectively, Fu₅ and Fu₆ quadrate, gaster 1.8× as long as broad; but in Dibrachys microgastri (Bouché), body yellow-green, clypeal margin with two blunt teeth, Fu₁ to Fu₅ quadrate, Fu₆ transverse, gaster 2× as long as broad.

Holotype. Female. Body (Figs 29, 30) length 2.2 mm. Head and mesosoma dark green, with metallic reflection; gaster brown and with metallic reflection basally. Antennae dark brown except scape and pedicel yellowish brown; mandible brown; legs yellowish brown except coxae brown; fore wing slightly infumate, wing venation yellowish brown.

Head in frontal view (Fig. 31), width 1.24× height; frons with dense reticulation; lower face flat, reticulation on lower face same as that on frons; eye height 0.7× head height, eyes separated by 1.09× eye height; antennal scrobe deep, extending upwards but not reaching anterior ocellus. Antennal insertion on lower ocular line, distance from upper margin of torulus to lower margin of anterior ocellus 2.35× distance from lower margin of torulus to clypeal margin; clypeus with longitudinal sculpture, only small area smooth; clypeal margin protruded, emarginate in middle with two sharp teeth; oral fossa width 0.46× head width. Head in lateral view, malar sulcus inconspicuous, eye height 3.3× malar space. Antennal scape 0.81× as long as eye height, not reaching lower margin of anterior ocellus; length of pedicel and flagellum combined shorter than head width (0.84×); pedicel in lateral view 2.6× as long as broad; anelli transverse; Fu₁ to Fu₄ slightly longer than broad respectively, Fu₅ and Fu₆ quadrate; each funicular segment with one row of longitudinal sensilla; clava slightly clavate, 2.43× as long as broad, micropilosity only limited to apex of third clava segment. Head in dorsal view 1.89× as wide as long; vertex convex, occipital carina strong; eye length 2× temple length; POL 1.64× OOL.

Head 1.31× as broad as thorax. Mesosoma 1.38 × as long as broad. Pronotum with raised reticulation, pronotal collar slightly narrower than mesoscutum (0.86×); middle length of pronotum almost 1/9 as long as length of mesoscutum; collar not margined anteriorly, posterior margin of collar with a smooth band. Mesoscutum 1.86× as broad as long, with regular and dense reticulation; notauli incomplete and unconspicuous. Scutellum convex, 1.09× as broad as long, frenal line absent; reticulation same as on mesoscutum but slightly large on posterior part of scutellum. Propodeum (Fig. 32) medially ½ as long as scutellum; plica complete; median carina incomplete, occasionally with one or two short longitudinal ridge which interrupted in the middle; nucha short and smooth, separated with middle part of propodeum by a transverse shallow depression; spiracles elongate, 2× as long as broad, separated by the width of spiracles from hind margin of metanotum; area below spiracles with finely reticulation. Fore wing 2.25× as long as broad, without marginal fringe; basal vein with sparse setae, basal cell bare; speculum only stretched to 1/3 base of marginal vein; upper surface of costal cell bare, lower surface with a one complete row of setae and distal 1/3 with some scattered setae; submarginal vein 2.33× as long as marginal vein; marginal vein 1.67× as long as postmarginal vein; stigmal vein as long as postmarginal vein, slightly curved.

Petiole invisible dorsally. Gaster (Fig. 29) long ovate, 1.8× as long as broad, 1.3× as broad as thorax width; surface of each tergite coriaceous; Gt₁ covering 1/3 length of gaster, posterior margin of Gt₁ cambered, median with an obvious hollow; following tergites with posterior margin straight; gaster terminal acute.

Male. Body length 2.1 mm; head and thorax blue-green; antenna light brownish except clava slightly dark, other segments yellow; legs yellow to yellowish brown except coxae concolorous with body; fore wing yellowish brown; gaster brown, with a yellow transverse bright ribbon at 1/3 base of gaster.

Holotype: China: ♀, Beijing: Miyun Reservoir, 40.29°N, 116.50°E, 18.VII.1983, ex. pupae of Dendrolimus tabulaeformis, leg. Ju-Wen Wu. Paratypes: China: 1♂, 2♀, same data as holotype; 2♀, Beijing: Miyun Reservoir, 20.VII.1983, ex. pupae of Dendrolimus tabulaeformis, leg. Ju-Wen Wu; 5♀, Beijing: Huairou, 15.VI.1982, ex. Illiberis pruni, leg. Mr. Jin; 1♀, Beijing: Songshan, 26.VIII.1984, ex. Illiberis pruni; 4♀, Beijing: Changping, 15.VI.1981, ex. Locastra muscosalis, leg. Zhen-Hua Liu; 1♀, Beijing: Yuanmingyuan Imperial Garden, 18.VII.1984, ex. larvae of Lymantria dispar, leg. Mu-Zong Cheng; 6♀, Beijing: Yuanmingyuan Imperial Garden, 2.VI.1984, ex. larvae of Lymantria dispar, leg. Ding-Xi Liao; 4♂, 5♀, Beijing: Mentougou, late July of 1983, ex. Prothesia similes xanthocampa, leg. Sui-Hua Zhao; 1♀, Beijing: Qingbaichang, leg. Ding-Xi Liao.

In memory of professor Ding-xi Liao in China.

Larvae of Illiberis pruni Dyar, Illiberis nigra Leech (Lepidoptera: Zygaenidae), Lymantria dispar (L.) (Lepidoptera: Noctuoidea) and Porthesia similis (Fueszly) (Lepidoptera: Lymantridae), pupae of Dendrolimus tabulaeformis Tsai et Liu, Dendrolimus superans (Butler) (Lepidoptera: Lasiocampidae), Illiberis ulmivora Graeser, Pseudopanolis flavimacula Inaba (Lepidoptera: Noctuidae), Rogas dendrolimi (Matsumura) (Hymenoptera: Braconidae) and Tenthredinidae sp..

China (Liaoning, Beijing, Hebei, Shanxi, Shandong, Gansu, Qinghai).