Stenochironomus okialbus Sasa, 1990

Song, Chao, Zhu, Bin-Qing, Moubayed-Breil, Joel, Lei, Teng & Qi, Xin, 2022, Taxonomic study on the genus Stenochironomus Kieffer from the Baishanzu Nature Reserve, China (Diptera, Chironomidae), ZooKeys 1104, pp. 93-113 : 93

Stenochironomus okialbus Sasa, 1990

Figs 9 , 10

Stenochironomus okialbus Sasa, 1990: 122, fig. 10.

Material examined.

3 male adults, collected by light trap in Zhejiang Province, Lishui City, Qingyuan County, Baishanzu National Nature Reserve , 27.76°N, 119.31°E, 11-12.VIII.2020, leg. Song C.

Diagnostic characters.

Stenochironomus okialbus differs from other related species by a combination of characters: wing with dark markings in the middle and apex; superior volsella short and small, spatulate, with four or five long setae; inferior volsella elongate, with 2-4 long setae and a slender terminal spine; posterior margin of tergite IX with 8-10 setae and eight spines.

Description.

Male imago (N = 3). Total length 2.94-3.98, 3.62 mm. Wing length 1.80-1.85 mm. Total length / wing length 1.85-2.20, Wing length / length of pro-femur 178-1.88.

Coloration (Fig. 8 ). Body almost pale yellowish or white, except postnotum with spot area and tergite IV-VII brown; wing with dark pigmentation on median and apical parts; all legs pale yellow with dark knees and apex of tibia.

Head. AR 1.10-1.25, 1.12, ultimate flagellomere 430-660, 580 µm long. Temporal with 12-16, 14 setae, including 7-8, 7 inner verticals, 4-7, 6 outer verticals and 1-2, 2 postorbitals. Clypeus with 12-20, 17 setae. Tentorium 155-220, 190 μm long, 30-53, 44 μm wide. Palpomere lengths (μm): 33-48, 37; 40-65, 55; 123-195, 170; 85-125, 116; 130-218, 194. Palpomere ratio (5th /3rd) 1.05-1.21, 1.13.

Thorax. Dorsocentrals 14-21, 18; acrostichals 9-12, 11; prealars 5-6, 6; Scutellum with 7-12 setae in two rows.

Wings. VR 1.06-1.10, 1.08. Brachiolum with 1-2, 2 setae. Distribution of setae on veins: R, 20-29, 25; R1, 21-39, 31; R4+5, 49-53, 51. Squama with 10-18, 14 setae. Anal lobe normally developed.

Legs. Fore leg: width at apex of tibia 53-63, 58 μm, tibia with blunt scale 35-50, 44 µm long. Mid leg: width at apex of tibia 53-70, 61 μm, tibia with two apical spurs 43-53, 48 and 45-58, 52 µm long. Hind leg: width at apex of tibia 58-73, 64 μm, tibia with two apical spurs 45-55, 51 and 45-56, 52 µm long. Lengths (in μm) and proportions of legs as in Table 6 .

Hypopygium (Fig. 10 ). Anal point 110-125, 118 μm long, 43-60; wide, 52 µm width at base, 18-20, 18 µm at apex; slightly swollen and rounded apically. Tergite IX with 19-25, 22 long setae on median part; posterior margin of tergite IX with 6 strong setae and 3 spines. Laterosternite IX with 3-4, 4 setae. Transverse sternapodeme 35-48, 41 μm long; phallapodeme 85-95, 89 μm long. Gonocoxite 138-175, 159 μm long. Gonostylus 185-200, 196 μm long. Superior volsella short, 25-30, 28 μm long, 23-25, 24 μm wide, with 4-5 long setae. Inferior volsella linearly elongate, 183-220, 208 μm long, with 2-3 long setae and 1 stout terminal spine. HR 0.74-0.86, 0.81; HV 1.58-1.97, 1.84.

Remarks.

The morphological characters of the Chinese specimens fit well with the original description and illustrations provided by Sasa (1990): wing with two spotted areas; narrow dark rings on knee points; anal point slightly swollen and rounded. However, some relevant differentiating characters were observed within the examined specimens: the inferior volsella have only two or three long setae, while it bears four in the Japanese specimens; average values of the AR 1.10-1.25 are lower than 1.37-1.41 in the Japanese species.

According to the molecular data, specimen (LC462365) of Stenochironomus okialbus , shows a large genetic distance to other specimens (up to 14%); as the specimen is not accessible it should be rechecked. The K2P distance between Japanese and Chinese specimens is 1.7%, which well supports them as the same species.

Distribution.

Oriental China (Zhejiang) and Japan.

Figures

Figure 8. Male adult (holotype) of Stenochironomus baishanzuensis Song & Qi, sp. nov. A hypopygium in dorsal view B hypopygium in ventral view C superior volsella.

Figure 9. Male adult of Stenochironomus okialbus (in lateral view): new record to China

Figure 10. Male adult of Stenochironomus okialbus. A hypopygium in dorsal view B hypopygium in ventral view C superior volsella.