Simulium (Asiosimulium) suchitrae Takaoka, 2010

Takaoka, Hiroyuki & Shrestha, Suchitra, 2010, New species of black flies (Diptera: Simuliidae) from Nepal 2731, Zootaxa 2731, pp. 1-62 : 4-8

Simulium (Asiosimulium) suchitrae Takaoka sp. nov.

Description. Female. Body length 2.3 mm. Head. Slightly narrower than thorax. Frons brownish-black, thinly whitish-gray pruinose and slightly shiny at certain angle of light, moderately covered with yellow hairs (except median longitudinal portion narrowly bare, and narrow area between antennal sockets bare) interspersed with several dark longer and stouter hairs along each lateral margin; median suture on lower portion absent; frontal ratio 1.56:1.00:1.97. Frons-head ratio 1.00:4.23. Fronto-ocular area ( Fig. 1A) well developed, triangular, directed laterally and somewhat upward. Clypeus brownish-black, thinly whitish-gray pruinose and slightly shiny at certain angle of light, moderately covered with yellow hairs (except narrow portions near upper and lower margins bare) intermixed with dark longer and stouter hairs. Labrum 0.91 times as long as clypeus. Antenna composed of scape, pedicel and 9 flagellomeres, light to medium brown, except scape, pedicel, and anterior surface of 1st to 3rd flagellomeres dull yellow. Maxillary palp consisting of 5 segments, medium brown except 3rd segment blackish-brown, proportional lengths of 3rd, 4th, and 5th segments 1.00:0.86:1.48; 3rd segment ( Fig. 1B,C) not enlarged; sensory vesicle ( Fig. 1B,C) roughly ellipsoidal, 0.30 times as long as 3rd segment, with large opening apically. Lacinia with 9 or 10 inner and 11 outer teeth. Mandible with 25 inner and 14 outer teeth. Cibarium ( Fig. 1D) moderately concave posterodorsally and with 69 spinous processes elaborately arranged in narrow space between inner and outer walls, somewhat apart from posterodorsal margin; these processes arising from inner wall. Thorax. Scutum brownish-black, slightly to moderately shiny at certain angle of light, thinly gray pruinose on prescutellar area and densely covered with yellowish-white short hairs mixed with dark brown short hairs on anterior surface, and interspersed with several dark brown upright long hairs on prescutellar area. Scutellum medium brown, with many dark upright long hairs as well as yellowish-white short hairs. Postnotum dark brown, slightly shiny at certain angle of light, bare. Pleural membrane bare. Katepisternum longer than deep, brownish-black, shiny in light and bare. Legs. Entirely medium brown to brownish-black except some parts of all trochanters and extreme base of mid and hind tibiae dark yellow to light brown. Fore basitarsus moderately dilated, 6.91 times as long as its greatest width, and with moderate dorsal hair crest. Hind basitarsus ( Fig. 1E) nearly parallel-sided though somewhat tapered near both ends, 6.69 times as long as its greatest width, 0.73 and 0.64 times as wide as greatest widths of tibia and femur, respectively; calcipala developed, short, 0.63 times as long as its width at base, and 0.50 times as wide as greatest width of basitarsus; pedisulcus developed. All claws ( Fig. 1F) with large basal tooth 0.44 times as long as claw. Wing. Length 2.5 mm. Costa with 2 parallel rows of dark short spines as well as dark hairs. Subcosta with dark hairs except near apex bare. Hair tuft on stem vein dark. Basal portion of radius fully haired. R 1 with dark spinules and hairs. R 2 with dark hairs only. Basal cell and basal median cell absent. Abdomen. Basal scale dark brown, with fringe of yellowish-white long hairs. Dorsal and lateral surfaces of abdomen brownish-black to black, moderately covered with dark short hairs mixed with yellowish-white short hairs on tergite 2 and on each lateral surface of segments 2–4; tergites 2 and 6–8 shiny, although tergites 3–5 somewhat shiny at certain angle of light; ventral surface of abdomen brownish-black to black; segment 7 with large sternal plate medially. Genitalia. Sternite 8 ( Fig. 1G) wide, bare medially but furnished with 13 or 14 short to medium-long hairs on each side. Ovipositor valve ( Fig. 1G) nearly triangular, thin, membranous except inner margin narrowly sclerotized, densely covered with microsetae interspersed with 6 or 7 short hairs; inner margins nearly straight, moderately separated from each other. Genital fork ( Fig. 1H) inverted-Y-shaped, with well sclerotized, basally widened stem; each arm of moderate width, thin except basal and subapical portions well sclerotized, and coiled near apex. Paraproct in ventral view ( Fig. 1I) subquadrate, with distinct process produced ventrally along anteromedial margin, with 7 or 8 spinous colorless sensilla on anteromedial surface; paraproct in lateral view ( Fig. 1J) much wider than long, with 20 short to medium-long hairs on lateral and ventral surfaces. Cercus in ventral view ( Fig. 1I) 0.8 times as long as paraproct, with numerous short and medium-long hairs; cercus in lateral view ( Fig. 1J) rounded posteriorly, 0.71 times as long as its width at base. Spermatheca ( Fig. 1K) pear-like, strongly sclerotized except duct unsclerotized, without distinct reticulate surface pattern; internal setae not discernible; accessory ducts subequal in diameter to each other and slightly larger than main duct.

Male. Unknown.

Pupa. Body length 3.5 mm. Head. Integument dark yellow, without tubercle; face with 1 simple mediumlong trichome on each side, and frons with 1 (left side) or 2 (right side) simple medium-long trichomes on each side; antennal sheath without any projection and tubercle. Thorax. Integument dark yellow, bare except dorsal surface of posterior 1/2 sparsely or moderately covered with tubercles, and small area at base of gill densely covered with tubercles ( Fig. 2A); thorax on each side with 9 simple trichomes (2 mediodorsally, 2 anterolaterally, 2 mediolaterally and 3 ventrolaterally), all medium-long except 1 of 2 anterolateral trichomes and all 3 ventrolateral trichomes short. Gill ( Fig. 2A) of arborescent type, composed of 28 short slender thread-like filaments arranged from dorsal to ventral as {[(2+2)+(2+1+1)+2+2]+[4+(1+1+2)]}+(2+2)+(2+2) on left side, and {[2+2+2+2+(2+2)]+[4+(1+1+2)]}+(2+2)+(2+2) on right side; all filaments light to medium brown, variable in length ranging from 0.5 mm (1 filament of dorsal group) to 1.2 mm (1 filament of ventral group), with annular furrows (no distinct ridges) and densely covered with minute tubercles; gill with enlarged transparent bulbous organ basally. Abdomen. Dorsally, all segments nearly transparent except segment 9 yellowish; segment 1 smooth (without tubercle), with 1 short slender seta on each side; segment 2 with 1 short slender seta, 5 very short spinous setae and 1 very short minute seta on each side; segments 3 and 4 each with 4 stout hooks and 1 very short spinous or minute seta on each side; segments 5–9 each with comblike groups of minute spines though very sparsely on segment 5 and without spine-combs on each side; segment 9 with pair of small cone-shaped terminal hooks ( Fig. 2B). Laterally, segments 2–4 each with 3 very short spinous setae on each side; segment 9 with 2 grapnel-shaped hooklets on each side. Ventrally, all segments nearly transparent except segment 9 yellowish; segmens 5–7 each with pair of simple stout hooks on each side; segments 4–8 each with comb-like groups of minute spines and on each side. Cocoon ( Fig. 2C). Wall-pocket shaped, tightly woven, with anterodorsal margin thickly woven, and slightly extended ventrolaterally: individual threads invisible; 3.0 mm long by 2.0 mm wide.

Mature larva. Body length 6.1 mm. Body grayish. Cephalic apotome whitish-yellow on anterior 2/5 or little more, dark yellow to light brown on posterior 3/5 or little less, and dark brown along posterior margin; head spots distinct, dark brown except anterior spot of posterolateral spots on each side indistinct; posterior spot of posterolateral spots on each side merged in dark brown background and posterior spot of mediolongitudinal spots connected posteriorly to dark brown area along posterior margin. Lateral surface of head capsule yellow except area above and posterior to eye-spot region light to medium brown, with distinct dark brown spots, i.e., 2 large spots and 1 small spot in front of posterior margin and 3 isolated small spots below eye-spot region. Ventral surface of head capsule yellow except central portion and posterior portion along posterior margin widely light to medium brown, with distinct dark brown elongate and round spots on each side of postgenal cleft though round spots appear to be merged into medium brown background. Cervical sclerites composed of 2 dark brown small elliptical pieces, not fused to occiput, widely separated medially from each other. Antenna consisting of 3 segments and apical sensillum, subequal to or little longer than stem of labral fan; proportional lengths of 1st, 2nd, and 3rd segments 1.00:1.36:0.69. Labral fan with 30 main rays. Mandible ( Fig. 3A) with mandibular serration consisting of 1 large tooth (1 small tooth probably lost on left side) (either 1 or 2 teeth apparently lost on right side); large tooth at right angle to mandible on apical side; comb-teeth composed of 3 teeth decreasing in size from 1st to 3rd; supernumerary serrations absent. Hypostoma ( Fig. 3B) with 9 apical teeth in row; median and corner teeth well developed; lateral serration weakly developed anteriorly; 9 hypostomal bristles per side, lying slightly divergent posteriorly from lateral margin. Postgenal cleft ( Fig. 3C) deep, reaching posterior margin of hypostoma. Thoracic and abdominal cuticle bare except both sides of anal sclerite moderately covered with simple colorless setae. Rectal scales not discernible. Rectal organ compound, each of 3 lobes with 13–17 finger-like secondary lobules. Anal sclerite X-shaped, with anterior arms 0.94 times as long as posterior ones; anterior arms broadened, and space between arms widely sclerotized basally; 8 sensilla just posterior to basal juncture area; accessory sclerite absent. Last abdominal segment somewhat expanded ventrally forming ventral bulge, visible as very small ventral papilla when viewed from side. Posterior circlet with 90 rows of up to 16 hooklets per row.

Type specimens. Holotype female (with associated pupal exuviae and cocoon) (preserved in 80% ethanol), reared from a pupa collected from a small stream slowly flowing on rocks (water temperature 15˚C, shaded, altitude 1,826 m, 28˚57’61.5” N, 83˚51’02.0” E) near Titar , Mustang, Nepal, 23.IX.2009 . Paratype: 1 mature larva, same data as those of holotype.

Biological notes. The pupa and larva of this new species were collected with larvae of S. (Montisimulium) dattai Takaoka & Somboon.

Etymology. The specific name suchitrae is in honor of Miss Suchitra Shrestha, junior author, who collected this new species, together with many other new species in her recent field surveys in Nepal.

Remarks. This new species is assigned to the subgenus Simulium (Asiosimulium) defined by Takaoka & Choochote (2005a) in that it has a combination of the following characteristics: numerous spinous processes on the cibarium ( Fig. 1D), hairs on the basal portion of the radial vein, and a large basal tooth of the claw ( Fig. 1F) in the female, gill filaments of arborescent type ( Fig. 2A), dorsal surface of abdominal segments 5–9 without spine-combs, ventral surface of abdominal segments 5–7 each with pair of simple hooks on each side and lateral surface of abdominal segment 9 with grapnel-shaped hooklets in the pupa, and deep postgenal cleft ( Fig. 3C) in the larva.

This is the third species of the subgenus Simulium (Asiosimulium) and represents a new record of this subgenus from Nepal. This subgenus was so far represented by only two species, i.e., S. (A.) oblongum Takaoka & Choochote and S. (A.) wanchaii Takaoka & Choochote , both of which were described from Thailand ( Takaoka & Choochote 2005a, 2006).

The female of S. (A.) suchitrae sp. nov. is distinguished from those of the two known species by the genital fork without any projection ( Fig. 1H), the short cercus (much shorter than its basal width) ( Fig. 1I,J) and a pear-like spermatheca ( Fig. 1K). The pupa of this new species is distinguished from that of S. (A.) oblongum by the frons lacking any tubercle. The pupa as well as the male and larva of S. (A.) wanchaii is not known.

The pupa of this new species is most distinctive in having a large transparent bulbous organ at the base of the gill ( Fig. 2A), which occurs very rarely in the Oriental species of black flies. Until now, only two species of the multistriatum species-group of the subgenus Simulium (Simulium) , i.e., S. (S.) rotifilis Chen & Zhang from China ( Chen & Zhang 1998) and S. (S.) bullatum Takaoka & Choochote from Thailand ( Takaoka & Choochote 2005b), have been reported to bear such a large bulbous organ.