Isoplastus bimaculatus Kieffer [=Tanypus nebulosus Meigen] by original designation.

Holotype male (HNU: Cdbs60), China: Hubei Province, Huanggang City, Yingshan County, Dabie Mountain, Longtan Gorge, light trap, 31.0867°N, 115.8138°E, 486.71 m a. s. l., 7. IX. 2022, Zigang Xu.

The new species is named “excavata” derived from the Latin term “excavatus”, meaning concave, which aptly describes the inward concave shape of tergite IX’s posterior edge.

The distinguishing characteristics of this new species are the presence of two prominent longitudinal thick spots positioned in the middle of tergites II to IV, and the wing with brown markings on the distal end of Cu₁ and basal part of cell an. Additionally, the tergites from V to IX display a distinctive brown hue, adding to their identification. The posterior edge of tergite IX is concave in shape, and the anal point is absent. The gonostylus is prominently curved at a right angle.

Adult male (N = 1)

Total length 4.69 mm, thorax length 1.45 mm, wing length 2.66 mm, TL/WL 1.76, WL/Pfe 2.19.

Coloration (Fig. 1D). The head and thorax are uniformly dark brown. The femur of the legs is also dark brown, while the remaining parts of the legs are yellow. The wings exhibit two significant gray spots positioned near the Cu₁ and An veins. There is a longitudinal color spot present in the middle of tergites II to IV, the tergites V to IX and hypopygium are all brown in coloration.

Head (Fig. 1A). Antenna (Fig. 1B) with 13 flagellomeres, with an antennal ratio (AR) measuring 2.24. The flagellomeres taper towards their ends and ultimate flagellomere with a single apical seta. Temporal setae 24, comprising 8 inner verticals, 12 outer verticals, and 16 postorbitals. Tentorial length 234 µm, width 43 µm. Stipes length 192 µm, width 82 µm. Clypeus with 16 setae. Length of palpomeres (in µm): 69; 100; 161; 210; 342. Length ratio of palpomeres 5/3: 2.13.

Thorax (Fig. 1F). Antepronotals with 9 setae, the acrostichals and dorsocentrals arranged in multiple columns, acrostichals with 41 setae, dorsocentrals with 62 setae. Postnotals with 6 setae, humerals with 8 setae, prealars with 32 setae. Scutal tubercle present and obvious, scutellars with 32 setae.

Wing (Fig. 1C). The wing membrane area hairy, distinctive gray spots present near Cu₁ and An veins, the arculus hook-like shape, and the anal lobe mainly developed. VR: 0.91, brachiolum with 3 setae, veins with many setae, squama with 34 setae. Costal extension 128 µm.

Legs. The fore tibia possesses a single spur measuring 85 µm in length and features 15 side teeth. The width of the fore tibia at its apex is 84 µm, and the fore tibial comb consists of 5 setae (Fig. 1G). Two spurs of mid tibia are observed, measuring 87 µm and 51 µm long, bearing 16 and 11 lateral teeth, respectively, and has a width at the apex of 73 µm. The hind tibia exhibits two spurs, measuring 75 µm and 45 µm, with 18 and 12 lateral teeth, respectively. The hind tibial comb composed of 10 setae, with the longest seta 73 µm and the shortest 45 µm. The width of the hind tibia at its apex is recorded as 80 µm. The lengths and proportions of each leg are shown in Table 1.

Hypopygium (Fig. 1G, H). The anal point absent. The phallapodeme, although short, measures at a clearly discernible length of 69 µm. The gonocoxite showcases a cylindrical shape and spans 206 µm in length. The gonostylus (Fig. 1K) is 125 µm long and exhibits a curved inward shape at approximately two-thirds of its length. It displays protrusions on both the inside and outside, gradually narrowing towards the tip. The megaseta is 16 µm long. The inferior volsella unconspicuous, along the inside of gonocoxite, and contains concentrated long inner microhairs. HR: 1.64, HV: 3.74.

This new species is similar to M. kibunensis (Tokunaga) because their anal point is absent and the inferior volella is undeveloped, but can be distinguished by AR 2.24, wing with brown markings on distal end of Cu₁ and basal part of cell an, otherwise unmarked, and a concave rear edge line of tergite IX, while AR 1.7–1.9, wing with brown markings on distal end of Cu₁, M₃₊₄ and M₁₊₂. The pairwise distance based on the COI sequence of M. kibunensis and M. excavata sp. nov. is 0.105–0.107, further distinguishing them from each other.

Hubei Province, Oriental China.

Holotype, male (HNU: Cdbs7602), China: Hubei Province, Huanggang City, Yingshan County, Dabie Mountain, Longtan Gorge, 31.0867°N, 115.8138°E, 486.71 m a. s. l., 8. VI. 2022, light trap, leg. Zigang Xu. Paratypes: 3 males (HNU: Cdbs7601, Cdbs7603, Cdbs7604), same as holotype; 3 males (HNU: Cdbs8901, Cdbs8902, Cdbs8903), Hubei Province, Huanggang City, Yingshan County, Dabie Mountain, Wujiashan National Forest Park, 31.1047°N, 115.7913°E, 931.91 m a. s. l., 9. VI. 2022, light trap, leg. Zigang Xu.

The name of this new species is derived from the Latin words “quartri” and “macula”, meaning “four” and “spot”, “stain” or “mark”, respectively. The name specifically pertains to the presence of four distinctive black spots found on the tergites of this species.

This species has two short longitudinal striped spots on each side of tergites II to V, as well as two elliptical spots in the center. Wing with brown markings on apical of Cu1, M3+4 and basal part of cell an. Additionally, tergite IX with a triangular anal point beyond the margin of tergite IX. Lastly, the gonostylus is curved inward at two-thirds of its length, and the apex is markedly tapered.

Adult males (N = 7)

Total length: 4.49–5.55, 5.02 mm, Wing length 2.72–3.27, 2.99 mm, TL/WL 1.65–1.76, 1.71, WL/Pfe 2.08–2.59, 2.34.

Coloration (Fig. 2D). The head and thorax of this species are uniformly brown. The femurs of all legs are also brown, while the other sections display a yellow coloration. The wings are adorned with various color spots. Notably, there is a longitudinal color band on both sides of tergites II to V, accompanied by two elliptical spots at the center. Tergites VI to VII exhibit a dark brown hue, while tergites VIII to IX and the hypopygium are brown in color.

Head (Fig. 2A). Antenna with 13 flagellomeres (Fig. 2B), AR: 2.01–2.05, 2.03, The end of flagellomere narrow, with approximately one-third of the end easily foldable, and the ultimate flagellomere possessing a single apical seta. Temporal setae 20–22, 21. The inner verticals and outer verticals are arranged in two or three columns, with 4–8, 6 inner verticals, 10–16, 13 outer verticals, and 12–18, 15 postorbitals. Tentorial length 250–258, 254 µm, width 36–43, 40 µm. Stipes length 271–303, 287 µm, width 62–95, 78 µm. Clypeus with 16–18, 17 setae. Length of palpomeres (in µm): 67–78, 72; 91–105, 98; 173–190, 182; 241–279, 260; 334–378, 356. Length ratio of palpomeres 5/3: 1.93–1.99, 1.96.

Thorax (Fig. 2F). Thorax length 1.36–1.73, 1.55 mm, antepronotals with 12–12, 12 setae. The acrostichals and dorsocentrals are arranged in multiple columns, acrostichals with 40–60, 50 setae, dorsocentrals with 60–80, 70 setae. Anepisternals with 2–3, 3 setae, postnotals with 4–6, 5 setae, humerals with 8–14, 11 setae, prealars with 22–26, 24 setae. Scutal tubercle was present and obvious, scutellars with 32–40, 36 setae.

Wing (Fig. 2C). The wing membrane area is hairy, Cu₁ and An with obvious gray spots around the veins, arculus hook-shaped, and anal lobes particularly developed. VR: 0.91–0.96, 0.94, brachiolum with 3 setae, R₁ with 30–40, 35 setae, R with 40–60, 50 setae, R₄₊₅ with 50–60, 55 setae, squama with 54–60, 57 setae. Costal extension 157–160, 158 µm.

Legs. The fore tibia possesses a single spur measuring 85–112, 98 µm in length and features 19–20, 20 side teeth. The width of the fore tibia at its apex is 79–86, 82 µm, and fore tibial comb consists of 5–6 setae (Fig. 2G). Two spurs on mid tibia are observed, measuring 87–95, 91 µm and 50–56, 53 µm long, bearing 18–20, 19 and 11–16, 14 lateral teeth, respectively, and has a width at the apex of 75–81, 78 µm. The hind tibia exhibits two spurs, measuring 88–96, 92 µm and 49–53, 51 µm, with 19–21, 20 and 15–17, 16 lateral teeth, respectively. The hind tibial comb is composed of 13–15,14 setae, with the longest comb seta 73–81, 77 µm and the shortest 40 –46, 43 µm. The width of the hind tibia at its apex is recorded as 76–86, 81 µm. The lengths and proportions of each leg are shown in Table 2.

Hypopygium (Fig. 2H–K). The anal point is small, forming an obtuse triangle. Phallapodeme short and obvious, 72–81, 77 µm long. Gonocoxite cylindrical shape, 253–265, 259 µm long. Gonostylus (Fig. 2K) 126–146, 136 µm long, curved inward at two-thirds of its length and possessing protrusions both on the inner and outer sides, the inner protrusion was located at a quarter of the apex of the gonostylus, while the outer protrusion was located halfway along the apex. Tergite IX with 16–20, 18 setae, megaseta 16–17 µm long. Inferior volsella small and protuberant. HR: 1.91–2.09, 2.00. HV: 3.56–3.94, 3.75.

This new species can be identified by the presence of two short longitudinal color bands on the sides of tergites II to V, along with two elliptical spots in the middle. These distinctive characteristics set it apart from other species within the genus. However, the abdominal spots of this species may sometimes be indistinct and appear blurry. In tergites III to V, these spots may be partially obscured by brown spots, but tergite II consistently displays four clearly visible elliptical spots. The overall shape of this new species is similar to that of M. kibunensis, and it shares the same gonostylus morphology. However, M. kibunensis lacks an inferior volsella and anal point, while this new species possesses a protrusion on the inferior volsella. The shape of the inferior volsella is comparable to that of M. excavata sp. nov., but this new species can still be differentiated by the presence of color spots on the tergites, the presence of the anal point, and a higher HR value (1.91–2.09) compared to M. excavata sp. nov. Based on COI sequences, the pairwise distances between M. quadrimacula and M. kibunensis, and between M. quadrimacula and M. excavata, are 0.119–0.125 and 0.131, respectively, further setting it apart from them.

Hubei Province, Oriental China.