Simulium (Gomphostilbia) sachini Takaoka & Henry, 2010

Takaoka, Hiroyuki & Shrestha, Suchitra, 2010, New species of black flies (Diptera: Simuliidae) from Nepal 2731, Zootaxa 2731, pp. 1-62 : 27-29

Simulium (Gomphostilbia) sachini Takaoka & Henry, 2010

Simulium (Gomphostilbia) sachini Takaoka & Henry, 2010: 108–110 (pupa only).

Simulium (Gomphostilbia) gombakense (nec Takaoka & Davies, 1995): Shrestha & Takaoka 2009: 254 (pupa, misidentification).

This species was recently described from a unique pupal specimen collected in Darjeeling, India ( Takaoka et al. 2010). As noted under S. (G.) nuwakotense sp. nov., this species seems to be closely related to both S. (G.) nuwakotense sp. nov. and S. (G.) gombakense in having the similar characteristic pupal gills.

In this study, three males reared from pupae collected from Nepal were identified as S. (G.) sachini on the basis of the characteristic configuration of the pupal gill. It should be noted that one of the three specimens examined was the same as previously regarded as S. (G.) gombakense by Shrestha & Takaoka (2009). For this reason, a previous record of S. (G.) gombakense from Nepal should be corrected.

The male and mature larva of S. (G.) sachini are here described for the first time.

Description. Male. Nearly as in male of S. (G.) nuwakotense sp. nov. except following features: Body length 2.5–3.0 mm. Head. Antenna dark brown except scape, basal 1/2 of pedicel and base of 1st flagellomere yellow; 1st flagellomere 1.72 times as long as 2nd one. Maxillary palp: Proportional lengths of 3rd, 4th, and 5th segments 1.00:1.06:2.29; sensory vesicle ellipsoidal, small, 0.24 times as long as 3rd segment. Thorax. Scutum densely covered with golden yellow short hairs. Scutellum with golden yellow short hairs and dark brown upright longer hairs. Legs. Foreleg: basitarsus 7.63–7.78 times as long as its greatest width. Hind leg: basitarsus somewhat swollen, spindle-shaped, 4.05–4.35 times as long as wide, and 0.80–0.84 and 0.80–0.83 times as wide as greatest width of tibia and femur, respectively; calcipala well developed, 1.17 times as long as wide, and 0.33 times as wide as greatest width of basitarsus. Genitalia. Coxite in ventral view nearly rectangular, 1.71 times as long as its greatest width. Style in ventrolateral view 0.86 times as long as coxite. Ventral plate in ventral view transverse, 0.47 times as long as wide. Cercus with 13–15 hairs.

Mature larva. Body length 5.0– 5.3 mm. Body light yellow except dorsal surface of abdominal segments 7 and 8 reddish-brown. Head capsule very sparsely covered with simple minute setae. Cephalic apotome yellow, with faint positive head spots, or somewhat dark yellow on posterior 1/2, thus head spots obscured. Lateral surface of head capsule yellowish or dark yellow except eye-spot region white; spots in front of posterior margin faintly positive; eyebrow indistinct though 1 dark small round spot visible above eye-spot region. Ventral surface of head capsule yellow to dark yellow, with dark brown area on each side of postgenal cleft; elongate spots on each side of postgenal cleft indistinct. Cervical sclerites composed of 2 small light brown rod-like pieces, not fused to occiput, widely separated from each other. Antenna composed of 3 segments and apical sensillum, much longer than stem of labral fan; antenna pale except dorsal surface of basal portion of 1st segment brownish; proportional lengths of 1st, 2nd, and 3rd segments 1.00:0.75– 0.84:0.81–0.84. Labral fan with 25–28 main rays. Mandible ( Fig. 14A) with 3 comb-teeth (plus additional 2 teeth) decreasing in length from 1st to 3rd though 2nd tooth only slightly longer than 3rd one; mandibular serrations composed of 2 teeth (1 large and 1 small); large tooth at acute angle to mandible on apical side. Hypostoma ( Fig. 14B) with row of 9 apical teeth, median tooth and corner teeth prominent; lateral margins smooth; hypostomal bristles 4 or 5 in row, parallel to lateral margin on each side. Postgenal cleft ( Fig. 14C) arrow-head shaped, medium-long, 2.6–3.2 times as long as postgenal bridge; subesophageal ganglion unpigmented, not visible. Pharate pupal gill ( Fig. 14D) with wrinkled enlarged body with 6 short finger-like projections and 8 long slender thread-like filaments. Thoracic cuticle bare. Abdominal cuticle bare except both sides of anal sclerite (down to base of ventral papillae) densely covered with colorless simple setae. Rectal scales appearing to be absent. Rectal organ compound, each of 3 lobes with 9–11 finger-like secondary lobules. Anal sclerite X-shaped, anterior arms nearly as long as posterior ones; accessory sclerites absent; sensillum absent. Ventral papillae well developed, conical in shape. Posterior circlet with 84–88 rows of up to 14 hooks per row.

Specimens examined. One male (together with associated pupal exuviae and cocoon) (preserved in 80% ethanol), reared from pupa collected from a small stream (water temperature 18.5˚C, partially shaded, altitude 1,627 m, 27˚96’12.9” N, 85˚95’66.8” E) moderately flowing along the road, Kodari, Nepal, 16.VII.2009; 1 male (together with associated pupal exuviae and cocoon) (preserved in 80% ethanol), reared from pupa, and 1 mature larva collected from a small water canal (water temperature 20.0˚C, partially shaded, altitude 1,576 m, 27˚95’66.2” N, 85˚95’51.4” E) moderately flowing along the road, Tatopani , Nepal , 16.VII.2009; 1 male (together with associated pupal exuviae and cocoon) (preserved in 80% ethanol), reared from pupa collected from a small stream (altitude 1,600 m), Shivapuri National Park , Nepal , 9.IV.2008 (previously misidentified as S. (G.) gombakense ).

Biological notes. The pupae and larva of S. (G.) sachini were collected from grass leaves trailing in water. Six larvae of S. ( Montisimulium ) sp. and five larvae of S. (Simulium) tuberosum species-group were collected from the same stream in Tatopani.

Remarks. The male of S. (G.) sachini is very similar to that of S. (G.) nuwakotense sp. nov. in many characteristics including the genitalia and color of legs. The hind basitarsus of this species appears to be somewhat wider than that of S. (G.) nuwakotense sp. nov. as shown by its relative widths against the hind tibia and femur (i.e., 0.80–0.84 and 0.80–0.83 versus 0.78 and 0.75 in S. (G.) nuwakotense sp. nov.). The male of S. (G.) sachini is readily distinguished from that of S. (G.) gombakense by the ventral plate with two ventrallyproduced processes (similar to Fig. 12F) as well as the somewhat widened spindle-shaped hind basitarsus (similar to Fig. 12B). The male of S. (G.) gombakense bears the ventral plate with a single ventrally-produced median process and the nearly parallel-sided slender hind basitarsus ( Takaoka 2000).