Holotype, ♀ (ZUH), “S. China: Hunan, nr Zhangjiajie, Badagong Mts, Bamaoxi, 2–3.VI.2009, 540 m, Xi-Ying Li, RMNH’09”. Paratypes (91 ♀ + 18 ♂; RMNH, ZUH): 28 ♀ + 2 ♂ with same data; 47 ♀ + 7 ♂, id., but Longtanping, 4-5.VI.2009, 550 m; 1 ♀ + 2 ♂, id., but Tian Ping Mt, 9–13.VII.2009, 550 m; 13 ♀ + 1 ♂, “S. China: Hunan, nr Suining, Huangsang N. R., Shaoyang, 12-13.VI.2009, 1000 m, Xi-Ying Li, RMNH’09”; 1 ♀ + 6 ♂, “S. China: Hunan, nr Chengbu, Nan Mt., Shaoyang, 1500 m, 10-11.VI.2009, Xi-Ying Li, RMNH’09”; 1 ♀, “S. China: Hunan, Changsha, garden Hunan Agr. Univ., 80 m, 31.V.2009, Xi-Ying Li, RMNH’09”.

Antenna with 23–27 segments and 1.1–1.3 times as long as fore wing; setose part of ovipositor sheath 0.06 times as long as fore wing and about half as long as first tergite (Fig. 145); clypeus truncate ventrally with a lamelliform rim and hypocly-peal depression distinct but rather narrow clypeus ventrally (Fig. 151); segments of labial palp moniliform, strongly narrowed basally (Fig. 155); medio-posterior depression of mesoscutum absent; propodeum and mesopleuron black or dark brown; propodeum less steep posteriorly than of Opius pallipes; vein r of fore wing distinct; second submarginal cell of fore wing more widened basally than in Opius pallipes (Fig. 146); vein CU1b of fore wing narrowly developed (Fig. 146); hind femur yellowish-brown dorso-apically hind tibia apically and tarsus usually infuscate.

Holotype, ♀, length of body 1.9 mm, of fore wing 2.2 mm.

Head. Antenna with 25 segments and 1.2 times as long as fore wing; length of third segment 1.1 times fourth segment, length of third, fourth and penultimate segments 4.2, 3.8, and 2.3 times their width, respectively (Fig. 156); length of maxillary palp 0.9 times height of head; labial palp segments petiolate, moniliform (Fig. 155); occipital carina moderately far removed hypostomal carina (Fig. 153) and dorsally absent; hypostomal carina narrow; length of eye in dorsal view 1.5 times temple; frons slightly convex and glabrous, smooth; face smooth, medially weakly elevated; width of clypeus 1.8 times its maximum height, clypeus flattened, largely smooth and its ventral margin thin and straight (Fig. 151); hypoclypeal depression slit-like, rather narrow (Fig. 151); malar suture present; mandible moderately widened basally, with short and weakly protruding ventral carina (Fig. 153).

Mesosoma. Length of mesosoma 1.4 times its height; dorsal pronope distinct, but rather small, round (Fig. 148); pronotal side mainly smooth, but medial groove faintly crenulate and posterior groove absent (Fig. 145); epicnemial area smooth dorsally; precoxal sulcus only medially shallowly impressed, smooth as rest of mesopleuron (Fig. 145); pleural sulcus smooth; notauli absent on disc, only anteriorly indicated by some rugulae (Fig. 147); mesoscutum glabrous except for a few setae; medio-posterior depression of mesoscutum absent; scutellar sulcus moderately crenulate; scutellum smooth and flat; surface of propodeum largely smooth, but medio-posteriorly rugulose (Fig. 148).

Wings. Fore wing (Fig. 146): pterostigma comparatively wide elliptical; 1-R1 reaching wing apex and 1.3 times as long as pterostigma; r:3-SR:SR1 = 1:21:48; 2-SR:3-SR:r-m = 12:21:6; 1-M straight; SR1 nearly straight; m-cu moderately postfurcal; cu-a postfurcal and 1-CU1 widened; first subdiscal cell narrowly open, CU1b minute. Hind wing (Fig. 146): M+CU:1-M:1r-m = 15:16:10; cu-a straight; m-cu absent.

Legs. Length of femur, tibia and basitarsus of hind leg 5.0, 9.6 and 4.8 times as long as wide, respectively; hind femur with long setae and of tibia medium-sized (Fig. 150).

Metasoma. Length of first tergite 1.1 times its apical width, its surface distinctly convex medially and with some rugae, but largely smooth and dorsal carinae developed in its anterior 0.7, parallel or nearly so medially (Fig. 148); second and following tergites smooth; length of ventrally visible setose part of ovipositor sheath 0.06 times fore wing and 0.2 times hind tibia (Figs 145, 154).

Colour. Black; antenna (but scapus laterally and ventrally and pedicellus ventrally yellowish), mesopleuron, first tergite, second tergite subposteriorly, third tergite medially, apical half of fourth tergite, most of following tergites and ovipositor sheath dark brown; second-fourth tergites membranous and pale yellowish posteriorly; clypeus, mandible, tegulae, propleuron and remainder of metasoma largely yellowish-brown; palpi and legs pale yellowish, but apex of middle and hind tibia, hind tarsus and telotarsi more or less infuscate; pterostigma and veins mainly brown; wing membrane hyaline.

Molecular data. COI, 16S, 28S (CVA 4242 (♀) and 4247 (♂)).

Variation. Length of body 1.5-1.9 mm, of fore wing 1.9-2.3 mm; antenna of female with 23 (2), 24 (17), 25 (42), 26 (15) or 27 (3) segments and 1.1-1.3 times as long as fore wing and 1.5-1.6 times body, of male with 23 (2), 24 (6), 25 (3) or 26 (1) segments and 1.2-1.3 times as long as fore wing; first tergite largely smooth or largely rugose-reticulate; side of pronotum black to largely yellowish-brown; mesopleuron and first tergite medio-posteriorly sometimes largely orange-brown; rarely first tergite and metapleuron entirely yellowish-brown; second tergite sometimes brown or partly dark brown; palpi of males less moniliform than of females; clypeus yellowish-brown to largely dark brown; sometimes legs completely pale yellow.

*China (Hunan).

Unknown, but Wen et al. (2002) reported Liriomyza species (Agromyzidae) as hosts of their specimens that may belong to this species (see below).

Name derived from “monilis” (Latin for “string of beads”) and “palpus” (Latin for “feeler”), because of the petiolate labial palp segments.

Very similar to Opius pallipes Wesmael, 1835 (Figs 413-416) but the new species has the third labial palp segment bead-like petiolate (gradually narrowed and normal shaped in Opius pallipes), the hypoclypeal depression medium-sized (minute), the ventral margin of the clypeus straight (slightly convex), the propleuron usually yellowish-brown (black); the hind femur of female narrow and pale yellowish (moderately wide and yellowish-brown), the first subdiscal cell of fore wing rather robust (comparatively slender), the antenna of the male 1.2-1.3 times as long as body (1.4-1.6 times), the second metasomal tergite of female yellowish-brown (usually dark brown) and there are differences in DNA sequences (COI, 16S). Most likely the Opius pallipes reported from South China (Wen et al. 2002, Fischer 2004) belongs to Opius monilipalpis sp. n. We have seen a female from North China (RMNH: Shandong, Anqiu, Suotou Mt., 31.VII.2009, c. 120 m) with normal third segment of labial palp (as in Opius pallipes) and third antennal segment about 4 times as long as wide, but with a medium-sized hypoclypeal depression and the propleuron entirely and the first tergite medio-posteriorly brownish. It may be a species closely related to Opius pallipes Wesmael and Opius moniliformis sp. n. It is not the very similar East Palaearctic Opius extusus Papp, 1981, because the female of Opius extusus has the antenna twice as long as its body.

The new species runs in the key by Chen and Weng (2005) to Phaedrotoma postuma (Chen & Weng, 2005) comb. n. Opius monilipalpis differs by having the mandible abruptly narrowed subbasally and assymmetical (gradually narrowed and nearly symmetrical in Phaedrotoma postuma), length of the mesosoma 1.4 times its height (1.2 times), the width of clypeus 1.8 times its maximum height (3 times), the pterostigma comparatively wide elliptical (narrow elliptical) and the length of the maxillary palp 0.9 times height of head (1.1–1.2 times).