Hyposoter distriangulum Chen, Huang & Hsu sp. nov.

Type series. Holotype. Taiwan: 1 male, 550 m alt., Mt. Kantoushan, Dongshan District, Tainan City. 13. i. 2015. (Y. F. Hsu) reared from Artona flavipuncta. emgd. 27. i. 2015 (HSUM 15 A4). Paratypes. Taiwan: 3 males, 1 female, same data as holotype (1 male, 1 female prepared for SEM) (HSUM 15 A4); 1 male, 550 m alt., same locality as holotype, 12. ii. 2015. (Y. F. Hsu) reared from Artona flavipuncta. emgd. 21. iii 2015 (HSUM 15 B7); 1 male, 550 m alt., same locality as holotype, 2. iii. 2015. (Y. F. Hsu) reared from Artona flavipuncta. emgd. 11. iii 2015 (HSUM 15 C1); 3 females, Lookout forest trail, Heshe, Shinyi Township, Nantou City. 21. ix. 2016 (C. J. Chang, W. J. Lin and Y. M. Hsu) reared from Alpinia kawakamii. emgd. 30. x. 2016 (HSUM 16 J19); 1 male, Lookout forest trail, Heshe, Shinyi Township, Nantou City. 19. x. 2016. (C. J. Chang, W. J. Lin and Y. M. Hsu) reared from Alpinia kawakamii. emgd. 15. xi. 2016 (HSUM 16 K11).

Description. Body length, 5.2–6.5 mm (n = 9).

Head (Figs 1–4, 22). Head black except mandible and palps yellowish white; face square, 1 × width, surface polished, entirely covered with punctures. Clypeus 0.25 × width, covered with punctures, without clypeal suture. Malar space 0.9 × basal width of mandible (Fig 1). Lateral ocelli, without adjacent with eye, postocellar line1 × as long as diameter of posterior ocellus, oculo-ocellar line 0.9 × diameter of posterior ocellus (Fig 22). Antenna black, with 33 flagellomeres, 1.2 × fore wing length, length of first flagellomere 1.5 × that of second flagellomere.

Mesosoma (Figs 5, 17). Mesosoma covered with hairs. Pronotum with epomia and shallow groove, groove without hairs. Mesoscutum without notauli. Scutellum triangular, covered with hairs. Epicnemium with wrinkles. Mesopleuron with hair, speculunm polished without hair, mesepleural fovea weak. Metapleuron hairy, with a pit between lower and upper division. Propodeum with weak carina, median longitudinal carina merged into a carina, basal area absent or forming a very tiny triangular area in the anterior end, areola pentagonal with width 1.5 × as long as length, apical transverse carina between areola and apical area very weak.

Wings. Fore wing (Fig 23) approximately 3.8 mm. Areolet quadrangular, petiolate. CI, 0.85; DI, 0.5; MI, 0.47; SDI, 1.75.

Legs (Figs 6–11, 17). Legs yellowish brown, hind coxa black (Fig 21). Longer tibial spur 4 × the shorter one on median legs (Fig 17), 2 × that on hind legs.

Metasoma (Figs 12–14, 15–16, 18–20). Metasoma compressed, petiolate. PI, 2.0; DMI, 1.3. First tergite with a lateral pit in front of its spiracle, polished and smooth, posterior part of first tergite with sparse hairs (Figs 13–14). Anterior end of tergo-sternal suture with a short series of hairs. Second to eighth tergites covered with hairs. Ovipositor sheath ca. 0.5 mm, 0.5 × anterior part covered with hairs (Figs 19–20).

Coloration (Fig. 21). Body black, except following part: mandible, maxillary palpus and labial palpus yellowish white. 0.2 × posterior part of second tergite and 0.7 × anterior part of third tergite yellowish brown. Second and third sternites yellowish brown.

Cocoon (Figs 24–25). Ellipsoid in shape, 6.3–8.1 mm in length, 2.6–3.1 mm in diameter (n=9), brown.

Distribution. Southern and central Taiwan (Tainan and Nantou).

Bionomics. Host is Artona flavipuncta (Lepidoptera: Zygaenidae) (Fig. 26). Full grown wasp larva makes a cocoon tightly attached inside the host body. Emergence hole made by Hyposoter distriangulum is located on the meso-dorsal part of prothorax and mesothorax of the host.

Etymology. The specific name distriangulum is a combination of “dis-” and “triangulum”, referring to the vestigial triangular basal area of propodeum.

Remarks. In this genus, eight species have been recorded from China, Japan and Taiwan (Walker 1874; Kokujev 1915; Matsumura 1926; Sonan 1929; Chiu et al. 1984; He et al. 1996; Shao 2009; Konishi 2016). Among them, H. distriangulum sp. nov. is similar to H. vierecki Townes, Momoi & Townes, 1965 from Japan, H. posticae (Sonan, 1929) and H. taihorinensis from Taiwan (Uchida, 1932). The body size of samples of H. distriangulum examined in the present study ranges from 5.5 mm to 6.5 mm (n=9). The body size of H. vierecki Townes, Momoi & Townes, 1965, H. posticae (Sonan, 1929) and H. taihorinensis (Uchida, 1932) fall into this range, which is smaller than the other five species (body size over 7 mm). H. distriangulum sp. nov. differs from H. vierecki, H. posticae and H. taihorinensis by the following diagnostic characters: (1) Base and apex of both femur and tibia of hind legs are black in H. posticae. Femur of hind legs are orange-red and apex of tibia black in H. vierecki. Hind legs are dark maroon in H. taihorinensis. By contrast, in H. distriangulum both femur and tibia of hind legs are all red tinged with orange. (2) The abdomen is red in H. taihorinensis, and black in H. vierecki and H. posticae. In H. distriangulum, it is black with posterior part of second tergite and anterior part of third tergite dark brown; a pale patch is present in anterior half ventrally. (3) There is a prominent triangular basal area on propodeum in H. vierecki, but the basal area in H. distriangulum is vestigial with a tiny triangular remnant at the anterior end. This basal area on propodeum is completely missing in H. posticae and H. taihorinensis.