Holotype : Female (whole body) captured by a sweeping net, at Ban Lek, Fang District, Chiang Mai Province, 20°04'36.3"N, 99°10'53.0"E, 1571 m in elevation, 29 III 2018, by Wichai Srisuka (Site 2). Paratypes: One female and one female (except thorax), same data and date as for the holotype, three females (except thorax), collected at Pratoo Pha, Mueang, Lampang Province (Site 1); three females (except thorax) collected at Ban Romklao Botanic Garden, Chat Trakan, Phitsanulok Province (Site 3).

Female adult: the only species of the S. chumpornense subgroup with antenna with eight flagellomeres, pleural membrane bare, subcosta bare, and hind tibia darkened on apical half, with dark subbasal marking and relatively slender fore basitarsus (6.29–6.38 times as long as its greatest width).

Female (N = 9). Body length 2.3–2.5 mm.

Head. Slightly narrower than thorax. Frons brownish black, dull, densely covered with yellowish-white scale-like recumbent short hairs; frontal ratio 1.35–1.44:1.00:1.71–2.09; frons:head ratio 1.00:4.21–4.66. Fronto-ocular area well developed, directed laterally and slightly upward. Clypeus brownish black, densely covered with yellowish-white scale-like short hairs interspersed with several dark unbranched longer hairs along lateral margin on each side. Labrum 0.65–0.69 times as long as clypeus. Antenna (Fig. 2A) composed of scape, pedicel and eight flagellomeres, dark brown to brownish black except scape, pedicel and base of first flagellomere yellowish white, rest of first flagellomere and third flagellomere medium to dark brown, and second and fourth flagellomeres yellow to dark yellow (sometimes light brown). Maxillary palpus composed of five segments, light brown, proportional lengths of third, fourth and fifth segments 1.00:1.00–1.03:2.34–2.48; third segment (Fig. 2B) somewhat swollen apically; sensory vesicle (Fig. 2B) ellipsoidal, 0.33–0.39 times length of third segment, with medium-sized opening. Maxillary lacinia with 9–12 inner, and 12–14 outer, teeth. Mandible with 20–22 inner teeth and with three or four outer teeth at some distance from apex, though outer teeth very weakly developed in one female. Cibarium (Fig. 2C) with pair of short stout submedian projections directed dorsally on dorsal margin.

Figure 2. 

Female of Simulium khelangense sp. nov. A antenna (left side; dorsal view) B third palpal segment with sensory vesicle (right side; front view) C cibarium D mid tibia (left side; outer view) E hind tibia (left side; outer view) F hind basitarsus and second tarsomere (left side; outer view) G claw of hind tarsus (lateral view) H eighth sternite and ovipositor valves (ventral view) I genital fork (ventral view) J, K paraprocts and cerci (right side; J ventral view K lateral view) L spermatheca. Scale bars: 0.1 mm (D–F); 0.05 mm (A); 0.02 mm (B, C, H–L); 0.01 mm (G).

Thorax. Scutum brownish black (except anterolateral calli ochreous), shiny, gray-pruinose with three longitudinal nonpruinose vittae (one medial and two submedial), densely covered with yellowish-white scale-like recumbent short hairs intermixed with brownish similar hairs. Scutellum dark brown, covered with yellowish-white short hairs and dark brown upright long hairs. Postnotum dark brown, bare, slightly shiny and gray-pruinose when illuminated at certain angle. Pleural membrane bare. Katepisternum dark brown, longer than deep, moderately covered with yellowish fine hairs interspersed with dark brown hairs.

Legs. Foreleg: coxa and trochanter yellowish white; femur medium brown though apical tip yellow; tibia medium brown, except base yellow, and median large portion on outer surface and apex light brown; tarsus brownish black, with moderate dorsal hair crest; basitarsus somewhat dilated, 6.29–6.38 times as long as its greatest width. Midleg: coxa dark brown; trochanter light brown; femur medium to dark brown though apical tip yellow; tibia (Fig. 2D) light brown on basal two-fifths except base yellow and with or without faint subbasal dark marking, and medium to dark brown on apical three-fifths; tarsus light brown except basal three-fourth of basitarsus, basal half of second tarsomere and base of third tarsomere yellowish white. Hind leg: coxa dark brown; trochanter yellowish; femur dark brown with base and apical tip yellowish; tibia (Fig. 2E) dark brown to brownish black on apical half, and yellowish on base, with distinct medium brown subbasal marking (though dark yellow to light brown between subbasal marking and dark apical half, and sometimes subbasal dark marking connected along posterior margin to dark apical half); tibia densely covered with whitish-yellow fine hairs on outer and posterior surface of basal three-fourths; tarsus medium brown except little more than basal two-thirds (though base light brown) of basitarsus and basal half of second tarsomere yellowish white; basitarsus (Fig. 2F) narrow, nearly parallel-sided, 6.55–7.05 times as long as wide, and 0.58–0.61 and 0.48–0.52 times as wide as greatest width of tibia and femur, respectively; calcipala (Fig. 2F) 1.3 times as long as wide, and 0.45–0.47 times as wide as width of basitarsus; pedisulcus (Fig. 2F) well marked. Hind tarsal claw (Fig. 2G) with large basal tooth 0.46–0.47 times length of claw.

Wing. Length 2.0 mm. Costa with dark brown spinules and dark brown hairs except basal portion with patch of white hairs. Subcosta bare. Hair tuft on base of radial vein white. Basal portion of radius fully haired. Basal cell absent.

Halter. White with base of stem darkened.

Abdomen. Basal scale light brown, with fringe of yellowish-white fine hairs. Dorsal surface of abdomen medium brown to brownish black except little less than basal one-half lighter, moderately covered with yellowish-white short hairs interspersed with dark brown long hairs; tergites of segments 2 and 6–8 shiny; sternal plate on segment 7 undeveloped.

Genitalia. Sternite 8 (Fig. 2H) bare medially, with 14–16 long stout hairs and two to five short setae on each side. Ovipositor valves (Fig. 2H) nearly triangular, thin, membranous, each moderately covered with microsetae interspersed with five or six short setae; inner margins slightly sinuous, moderately sclerotized. Genital fork (Fig. 2I) of usual inverted-Y form, with narrow arms; arm folded medially. Paraproct in ventral view (Fig. 2J) rounded outwardly and tapered medially, with 26–31 long hairs on ventral and lateral surfaces, and with five sensilla on anteromedial surface; paraproct in lateral view (Fig. 2K) moderately produced ventrally beyond ventral margin of cercus, 0.58–0.68 times as long as wide. Cercus in lateral view (Fig. 2K) rounded posteriorly, 0.44–0.68 times as long as wide. Spermatheca (Fig. 2L) ellipsoidal, 1.67–1.88 times as long as wide, well sclerotized except duct unsclerotized, and with many fissures on surface; internal setae absent; both accessory tubes slender, slightly larger in diameter than major one.

Male, pupa and larva. Unknown.

The species name khelangense refers to Khelang, an old name of Lampang Province, where this new species was collected.

Thailand (Lampang, Phitsanulok and Chiang Mai).

Females of this new species were captured while attracted to a human, though they have a large claw tooth, a characteristic suggesting that this species is ornithophilic (Adler et al. 2004).

Simulium khelangense sp. nov. is placed in the varicorne species-group in the subgenus Gomphostilbia by having the antenna with eight flagellomeres (Fig. 2A). It is further placed in the chumpornense subgroup by having the pleural membrane bare, and female subcosta lacking hairs ventrally, as defined by Takaoka (2012).

The female of this new species is distinguished from those of S. kuvangkadilokae and S. piroonae of the S. chumpornense subgroup, as noted above. This species is also distinguished from the four other members of the same subgroup: S. chumpornense from Thailand, S. sumbaense Takaoka & Suana from Sumba, Indonesia, S. tomae Takaoka from Sulawesi, Indonesia, and S. varicorne Edwards from Sumatra and Java, Indonesia, and Peninsular Malaysia, by the hind tibia darkened on the apical half (darkened on the apical one-third in the latter four species) (Kuvangkadilok and Takaoka 2000; Takaoka 2003; Takaoka et al. 2018a, b).