Simulium (Gomphostilbia) butwalense Takaoka & Shrestha, 2010

Takaoka, Hiroyuki & Shrestha, Suchitra, 2010, New species of black flies (Diptera: Simuliidae) from Nepal 2731, Zootaxa 2731, pp. 1-62 : 18-21

Simulium (Gomphostilbia) butwalense Takaoka & Shrestha sp. nov.

Description. Male. Body length 2.6 mm. Head. Much wider than thorax. Upper eye consisting of 16 vertical columns and 16 horizontal rows of large facets. Face brownish-black, white pruinose, not shiny. Clypeus brownish-black, white pruinose, not shiny, moderately covered with yellow short to medium-long hairs interspersed with several dark brown simple medium-long hairs along each lateral margin. Antenna composed of scape, pedicel and 9 flagellomeres, dark brownish except scape, pedicel and base of 1st flagellomere yellow though apical portion of pedicel somewhat darkened; 1st flagellomere elongate, 1.58 times as long as 2nd one. Maxillary palp with 5 segments, light brown, proportional lengths of 3rd, 4th, and 5th segments 1.00:1.19:2.77; 3rd segment ( Fig. 9A) widened apically; sensory vesicle ( Fig. 9A) ellipsoidal, small, 0.21 times as long as 3rd segment, and with small opening. Thorax. Brownish-black, whitish-gray pruinose along lateral margins and on anterior and prescutellar areas, covered with yellow scale-like recumbent short hairs (most hairs lost). Scutellum brownish-black (all upright long hairs as well as short hairs lost). Postnotum brownish-black, whitish-gray pruinose and bare. Pleural membrane bare. Katepisternum brownish-black, whitish-gray pruinose, covered with dark short hairs. Legs. Foreleg: coxa and trochanter medium brown; femur medium brown with apical cap dark brown (though extreme tip yellowish); tibia dark brown except base yellow and median large portion on outer surface medium brown; tarsus dark brown, with moderate dorsal hair crest; basitarsus somewhat dilated, 7.29 times as long as its greatest width. Midleg: coxa dark brown; trochanter light to medium brown; femur light to medium brown with apical cap dark brown; tibia dark brown except base narrowly yellow; tarsus dark brown. Hind leg: coxa dark brown; trochanter dark yellow; femur medium brown except base dark yellow to light brown and apical cap dark brown; tibia dark brown except base yellow; tarsus ( Fig. 9B) medium brown except little more than basal 2/3 of basitarsus (though base light brown) and basal 1/2 of 2nd tarsomere yellow; basitarsus ( Fig. 9B) narrow, nearly parallelsided (though slightly tapered from apical 1/3 to apex), 6.25 times as long as wide, and 0.59 and 0.53 times as wide as greatest width of tibia and femur, respectively; calcipala ( Fig. 9B) well developed, 1.30 times as long as wide, and 0.46 times as wide as greatest width of basitarsus; pedisulcus ( Fig. 9B) well developed. Wing. Length 1.6 mm. Costa with dark brown spinules as well as dark brown hairs except basal portion with patch of yellowish hairs. Subcosta without hairs. Hair tuft on stem vein lost. Basal portion of radius fully haired. Basal cell absent. Abdomen. Basal scale dark brown, with fringe of yellow long hairs though basal portions somewhat darkened. Dorsal surface of abdomen medium brown except basal 1/2 of segment 2 yellow, covered with dark brown short to long hairs; segments 2 and 5–8 each with pair of shiny dorsolateral or lateral patches, of which those on segment 2 broadly connected in middle to each other. Genitalia. Coxite in ventral view ( Fig. 9C) nearly rectangular, 1.70 times as long as its greatest width. Style in ventral view ( Fig. 9C) slender, tapered toward apex, markedly curved inward, with apical spine; style in ventrolateral view ( Fig. 9D) somewhat wide basally (0.45 times as wide as its length), moderately tapered toward basal 1/3, then very slightly tapered toward blunt apex; style in medial view ( Fig. 9E) markedly curved mediodorsally. Ventral plate in ventral view ( Fig. 9C) transverse, 0.49 times as long as wide, with anterior margin produced anteromedially, posterior margin somewhat concave medially, posterolateral corners angulate, and densely covered with microsetae on ventral surface except anteromedial portion narrowly bare and lateral portions widely bare; basal arms of moderate length, directed forward though slightly converged apically; ventral plate in lateral view ( Fig. 9F) nearly flat, not produced ventrally; ventral plate in end view ( Fig. 9G) gently curved ventrally, moderately covered with microsetae on ventral 1/2 of posterior surface except both lateral areas mostly bare; ventral margin slightly concave ventromedially. Median sclerite ( Fig. 9F,H) thin, plate-like, wide, connected to anterior 1/5 of ventral plate. Paramere ( Fig. 9I) slender, with 8 small to long distinct hooks and few much smaller ones directed dorsally near apex. Aedeagal membrane densely setose, not sclerotized. Ventral surface of 10th abdominal segment without distinct hairs near posterior margin on each side. Cercus ( Fig. 9J,K) not well defined, with 7 or 9 hairs.

Pupa. Body length 2.8 mm. Head. Integument dark yellow, moderately covered with round small tubercles; antennal sheath without tubercle; frons with 3 pairs of simple very long trichomes with coiled or uncoiled apices ( Fig. 10A), all arising close together, and face with pair of simple very long trichomes ( Fig. 10B) (tip lost, then not known whether apex is coiled or uncoiled). Thorax. Integument dark yellow, sparsely covered with round small tubercles; thorax with 3 very long mediodorsal trichomes with coiled apices ( Fig. 10C) (though 1 of 3 trichomes on right side medium-long and with uncoiled apex— Fig. 10D), 2 anterolateral trichomes (1 very long and with coiled apex, 1 medium-long and with uncoiled apex) ( Fig. 10E), 1 mediumlong simple mediolateral trichome ( Fig. 10F) and 3 simple ventrolateral trichomes (1 long, 2 medium-long) ( Fig. 10G) on each side. Gill ( Fig. 10H,I) composed of 8 thread-like filaments arranged from dorsal to ventral as [2+1+(1+2)]+2 filaments in right gill ( Fig. 10H) or {2+[1+(1+2)]}+2 filaments in left gill ( Fig. 10I) of holotype male pupal exuviae, or [(2+1)+(1+2)]+2 filaments in both right and left gills of female pupal exuviae (arrangement and relative thickness of filaments very similar to those of right gill of holotype male pupal exuviae— Fig. 10H); common basal stalk very short, with round transparent swollen organ ventrally; apical portions of all filaments lost, so their exact lengths unmeasurable (though length of remaining portion of inner filament of vental pair about 1.5 mm); thickness of 8 filaments variable apparently among filaments and also, though slightly, between right and left gills, with inner (or ventral) filament of ventral pair and inner (or ventral) filament of middle pair apparently thicker than other remaining filaments which are subequal in thickness to one another, i.e., proportional thickness of basal portions of 8 filaments from dorsal to ventral 1.00:1.00:1.17:1.17:1.00:1.50:1.17: 1.50 in right gill ( Fig. 10H) and 1.00:1.00:1.00:1.00:1.00:1.33:1.17: 1.50 in left gill ( Fig. 10I); all filaments light yellow, with well-defined annular ridges and furrows on outer surface, and densely covered with minute tubercles. Abdomen. Dorsally, segments 1, 2 and 9 light yellow, without tubercles; other segments almost transparent; segment 1 with 1 medium-long simple seta ( Fig. 10J) on each side; segment 2 with 1 medium-long simple seta and 5 very short setae ( Fig. 10K) submedially on each side; segments 3 and 4 each with 4 hooked spines and 1 very short seta on each side; segment 5 lacking spinecombs; segments 6–9 each with spine-combs in transverse row and comb-like groups of minute spines on each side; segment 9 with pair of distinct triangular terminal hooks when viewed from posteriorly ( Fig. 10L). Ventrally, segment 4 with 1 simple hook and few short setae on each side; segment 5 with pair of bifid hooks submedially and few simple slender short setae on each side; segments 6 and 7 each with pair of bifid inner and simple outer hooks somewhat spaced from each other and few simple slender short setae on each side; segments 4–8 each with comb-like groups of minute spines. Each side of segment 9 with 3 grapnel-shaped hooklets. Cocoon. Wall-pocket shaped, thinly woven, slightly extending ventrolaterally; anterior margin not thickly woven; floor roughly or moderately woven; individual threads invisible; 2.4 mm long by 1.2 mm wide.

Mature larva. Body length 4.0 mm. Body yellowish. Head capsule moderately covered with simple minute setae. Cephalic apotome whitish-yellow on anterior 1/2 and dark yellow on posterior 1/2; spots not well defined though anterior spot of mediolongitudinal spots and posterolateral spots faintly positive. Lateral surface of head capsule mostly dark yellowish except eye-spot region white; 2 large spots and 1 small spot in front of posterior margin on both sides faintly positive, and 2 small spots below eye-spot region on left side faintly positive but those spots on right side indistinct. Ventral surface of head capsule ( Fig. 11A) 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 most of dorsal surface of 1st segment brownish; proportional lengths of 1st, 2nd, and 3rd segments 1.0:1.1:0.8. Labral fan with 29 main rays. Mandible ( Fig. 11B,C) with 2 comb-teeth (though 3rd tooth appearing to be broken and lost in left mandible); 1st tooth much longer than 2nd one; mandibular serrations composed of 2 teeth (1 large and 1 small) (though lost in right mandible); large tooth at acute angle to mandible on apical side. Hypostoma ( Fig. 11D) 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. 11A) long, nearly reaching posterior margin of hypostoma; subesophageal ganglion unpigmented, not visible. Histoblast of pharate pupal gill with 8 thread-like slender filaments, their arrangement being similar to that of right gill of pupa ( Fig. 10H). Thoracic cuticle sparsely covered with fine setae (simple or with 2–8 branches) dorsally. Abdominal cuticle moderately (on segments 1–3) and densely (on segments 4–9) covered with fine setae with 2–9 branches (mostly 6–8 branches) ( Fig. 11E) dorsally, dorsolaterally, and laterally (on segments 5–9); both sides of anal sclerite densely covered with fine similar branched setae as well as colorless simple setae. Rectal scales present. Rectal organ compound, each of 3 lobes with 7 or 8 finger-like secondary lobules. Anal sclerite X-shaped, anterior arms 0.88 times as long as posterior ones; accessory sclerites absent; sensillum absent. Ventral papillae well developed, conical in shape. Posterior circlet with 80 rows of up to 16 hooks per row.

Female: Unkown

Type specimens. Holotype male (together with its associated pupal exuviae and cocoon) (preserved in 80% ethanol), reared from pupa collected from a small, rapid-flowing stream (water temperature 15.0˚C, exposed to the sun, altitude 241 m, 27˚43’90.1” N, 83˚28’17.6” E), Shidhdhababa , near the gate to Palpa, Butwal, Nepal, 25.IX.2009 . Paratypes: 1 female pupal exuviae and 1 mature larva, same date and data as those of the holotype.

Biological notes. The pupa and larva of this new species were collected from grass leaves trailing in water. No other species was collected.

Etymology. The species name butwalense refers to the locality name, Butwal, where this new species was collected.

Remarks. This new species is assigned to the batoense species-group of the subgenus Gomphostilbia in having the antenna with nine flagellomeres, the bare pleural membrane, the haired katepisternum, the slender hind basitarsus ( Fig. 9B) in the male and the eight thread-like filaments ( Fig. 10H,I) in the pupa.

This new species is characterized by the male ventral plate which is not markedly produced ventrally and nearly flat ( Fig. 9G) combined with the relative thickness of the eight pupal gill filaments, of which an inner filament of both ventral and middle pairs are apparently thicker than the other six filaments ( Fig. 10H, I), and the simple triangular terminal hooks ( Fig. 10L). There is no known species which bears a similar combination of the characteristics.