Simulium (Gomphostilbia) trangense Jitklang, Kuvangkadilok, Baimai, Takaoka & Adler, 2008

Takaoka, Hiroyuki, Ya’Cob, Zubaidah & Sofian-Azirun, Mohd, 2018, Classification, annotated list and keys for the black flies (Diptera: Simuliidae) of Peninsular Malaysia, Zootaxa 4498 (1), pp. 1-65 : 21-27

25. Simulium (Gomphostilbia) trangense Jitklang, Kuvangkadilok, Baimai, Takaoka & Adler, 2008

Simulium (Gomphostilbia) trangense Jitklang et al., 2008: 19 –20 (Female, male, pupa and larva).

This species was briefly described from females, males, pupae and larvae collected from southern parts of Thailand ( Jitklang et al., 2008).

The aquatic stages are widely distributed in small to medium sized streams at low to medium elevations in the mainland of Peninsular Malaysia, Langkawi Island , Pangkor Island and Tioman Island.

The female, male, pupa and larva are redescribed.

Female. Body length 1.7–1.8 mm. Head. Somewhat narrower than width of thorax. Frons brownish black, slightly shiny when illuminated at certain angles, densely covered with whitish yellow scale-like recumbent short hairs interspersed with few dark simple longer hairs along each lateral margin; frontal ratio 1.7–2.0:1.0:2.5–2.7; frons-head ratio 1.0:4.2–5.0. Fronto-ocular area well developed, narrow, directed dorsolaterally. Clypeus dark brown, densely covered with yellow short scale-like hairs interspersed with several dark longer hairs on each side. Labrum 0.54–0.62 times as long as clypeus. Antenna composed of scape, pedicel and nine flagellomeres, medium to dark brown except scape, pedicel, and base of first flagellomere whitish yellow. Maxillary palp composed of five segments, light to medium brown, proportional lengths of third, fourth, and fifth segments 1.0: 1.0:2.4–2.6; third segment ( Fig. 3A ) swollen; sensory vesicle ( Fig. 3A ) elongate (0.55–0.59 times as long as third segment), with medium-sized opening. Maxillary lacinia with 7 or 8 inner and 11 outer teeth. Mandible with 20 inner teeth and 9 or 10 outer teeth. Cibarium ( Fig. 3B ) medially forming sclerotized plate folded forward from posterior margin, with moderately sclerotized medial longitudinal ridge. Thorax. Scutum brownish black except anterolateral calli ochreous, thinly gray-pruinose, shiny when illuminated at certain angles, densely covered with whitish yellow scale-like recumbent short hairs, and also with brown similar short hairs on median and submedian longitudinal vittae. Scutellum dark brown, shiny when illuminated at certain angles, covered with dark brown short hairs and dark brown upright longer hairs along posterior margin. Postnotum dark brown, shiny when illuminated at certain angles, and bare. Pleural membrane bare. Katepisternum dark brown to brownish black, longer than deep, shiny when illuminated at certain angles, moderately covered with fine short hairs. Legs. Foreleg: coxa whitish yellow; trochanter light brown except base whitish yellow; femur light to medium brown; tibia white except little more than apical one-fourth brownish black, with whitish sheen on outer surface of basal three-fourths; tarsus brownish black, with moderate dorsal hair crest; basitarsus moderately dilated, 5.0–5.2 times as long as its greatest width. Midleg: coxa dark brown except posterior surface brownish black; trochanter light brown except basal half whitish yellow; femur medium to dark brown; tibia medium to dark brown except little more than basal one-third whitish, covered with whitish fine hairs on basal two-thirds and white sheen on posterior surface of basal two-thirds when illuminated at certain angles; tarsus dark brown except basal two-fifths of basitarsus yellow though its border not well defined. Hind leg: coxa medium brown; trochanter whitish yellow; femur medium brown with extreme base whitish yellow and apical cap dark brown; tibia ( Fig. 3C ) light to dark brown except little more than basal two-fifths whitish, covered with whitish fine hairs on outer and posterior surfaces of basal three-fourths and white sheen on posterior surface of basal three-fourths when illuminated at certain angles; tarsus dark brown except little more than basal threefifths of basitarsus (though base light brown) and basal half of second tarsomere white; basitarsus ( Fig. 3D ) narrow, nearly parallel-sided, 5.5–5.9 times as long as wide, and 0.7–0.8 and 0.6–0.7 times as wide as greatest widths of tibia and femur, respectively; calcipala ( Fig. 3D ) nearly as long as width at base, and half as wide as greatest width of basitarsus. Pedisulcus ( Fig. 3D ) well defined. Claw ( Fig. 3E ) with large basal tooth 0.42–0.45 times as long as claw.

Wing. Length 1.5–1.6 mm. Costa with dark brown spinules and grayish to light brown hairs intermixed with subbasal patch of yellow hairs. Subcosta with light brown hairs except near apex bare. Hair tuft on base of radial vein dark brown. Basal portion of radius fully haired; R1 with dark spinules and hairs; R2 with hairs only. Basal cell absent.

Halter . White except basal stem darkened. Abdomen. Basal scale light brown, with fringe of whitish yellow hairs. Dorsal surface of abdomen dark brown to brownish black except basal half to four-fifths of segment 2 whitish yellow, moderately covered with dark short to long hairs; tergites of segments 2 and 6–9 shiny when illuminated at certain angles. Ventral surface of segment 2 whitish yellow except narrow area along posterior margin light brown, and those of other segments medium to dark brown; sternal plate on segment 7 undeveloped. Terminalia . Sternite 8 ( Fig. 3F ) bare medially, with 12–15 medium-long to long hairs together with few slender short hairs on each side. Ovipositor valves ( Fig. 3F ) triangular (though posteromedial corners rounded), thin, membranous, moderately covered with microsetae interspersed with 1–3 short hairs; inner margins slightly concave, somewhat sclerotized, and somewhat separated from each other. Genital fork ( Fig. 3G ) of usual inverted-Y form, with slender stem; arms of moderate width, moderately folded medially; lateral plate of each arm with thin lobe directed posteromedially. Paraproct in ventral view ( Fig. 3H ) nearly triangular, with 4–6 sensilla on anteromedial surface; paraproct in lateral view ( Fig. 3I ) somewhat produced ventrally, 0.7 times as long as wide, with 18–25 medium-long to long hairs on ventral and lateral surfaces. Cercus in lateral view ( Fig. 1I ) short, rounded posteriorly, 0.4 times as long as wide. Spermatheca ( Fig. 3J ) oblong, 1.7 times as long as its greatest width, well sclerotized except duct and small area near juncture with duct unsclerotized, and with many fissures on surface; internal setae absent; both accessory ducts slender, subequal in diameter to major one.

Male. Body length 2.0– 2.1 mm. Head. Nearly as wide as thorax. Upper eye medium brown, consisting of 10 vertical columns and 12 horizontal rows of large facets. Face dark brown, grayish-white pruinose. Clypeus brownish black, whitish pruinose, densely covered with golden-yellow scale-like medium-long hairs (mostly directed upward) interspersed with several light-brown simple longer hairs. Antenna composed of scape, pedicel and nine flagellomeres, dark brown except scape and pedicel and base of first flagellomere yellow; first flagellomere elongate, 1.6–1.7 times as long as second one. Maxillary palp light to medium brown, with five segments, proportional lengths of third, fourth, and fifth segments 1.0: 1.2:2.8–3.0; third segment ( Fig. 4A ) slightly widened apically; sensory vesicle ( Fig. 4A ) globular, small, 0.16–0.18 times length of third segment, and with small opening. Thorax. Scutum dark brown to black, shiny and thinly grayish-white pruinose on each shoulder, on broad area along each lateral margin and on prescutellar area when illuminated at certain angles; scutum densely covered with golden-yellow recumbent short hairs. Scutellum dark brown, with dark brown short hairs and dark brown long upright hairs along posterior margin. Postnotum dark brown and bare. Pleural membrane bare. Katepisternum dark brown, moderately covered with fine hairs. Legs. Foreleg: coxa yellow; trochanter light brown except base yellow; femur light brown with apical cap medium brown; tibia whitish except apical one-fourth or little more medium brown, and with white sheen on outer surface of basal three-fourths; tarsus dark brown; basitarsus moderately dilated, 6.3–6.6 times as long as its greatest width. Midleg: coxa dark brown except posterior surface brownish black; trochanter light brown except base yellow; femur light brown except apical cap medium brown (though apical extreme light brown); tibia dark brown except basal one-third or little more whitish; tarsus dark brown except basal one-third of basitarsus yellow to dark yellow (though its border not well defined). Hind leg: coxa medium brown; trochanter whitish yellow; femur medium brown with base whitish yellow and apical cap dark brown (though apical extreme light brown); tibia ( Fig. 4B ) dark brown to brownish black except basal onethird whitish; tarsus ( Fig. 4C ) dark brown except basal two-fifths or little more of basitarsus (though base darkened) and basal half of second tarsomere yellowish; basitarsus ( Fig. 4C ) enlarged, wedge-shaped, 3.5–3.9 times as long as wide, and 0.9–1.0 and 1.0–1.2 times as wide as greatest width of tibia and femur, respectively; calcipala ( Fig. 4C ) slightly shorter than basal width, and 0.3 times as wide as greatest width of basitarsus. Pedisulcus ( Fig. 4C ) well defined. Wing. Length 1.6 mm; other characters as in female except subcosta without hairs. Abdomen. Basal scale medium brown, with fringe of light-brown hairs. Dorsal surface of abdomen medium brown to brownish black, moderately covered with dark brown short to long hairs; segments 2 and 5–8 each with pair of shiny dorsolateral or lateral patches; ventral surface of segment 2 white, and those of other segments light brown to dark brown. Genitalia. Coxite in ventral view ( Fig. 4D ) nearly rectangular, though much narrowed posteriorly, 1.9 times as long as its greatest width. Style in ventral view ( Fig. 4D ) bent inward, nearly parallelsided, rounded apically and with apical spine; style in medial view 0.8 times length of coxite, gently bent inward, nearly parallel-sided, with apical spine; style in ventrolateral view ( Fig. 4 Fe) tapered very slightly from base toward apex. Ventral plate in ventral view ( Fig. 4D ) with body transverse, 0.6 times as long as wide, with posterior half or little more markedly narrower than basal width, with anterior margin produced anteromedially, and posterior margin slightly convex medially, densely covered with microsetae on ventral surface; basal arms of moderate length, directed forward, then slightly convergent apically; ventral plate in lateral view ( Fig. 4F ) moderately produced ventrally; ventral plate in caudal view ( Fig. 4G ) produced ventrally (height:width ratio 0.5), ventral margin slightly rounded ventrally or nearly straight, densely covered with microsetae on posterior surface. Median sclerite ( Fig. 4F, H ) thin, plate-like, wide. Parameres of moderate size, each with three long and one medium-long stout hooks and several shorter ones. Aedeagal membrane sparsely setose, dorsal plate not well defined. Ventral surface of abdominal segment 10 slightly sclerotized, and without distinct hairs near posterior margin. Cercus small, rounded, encircled with 13 hairs.

Pupa. Body length 2.0– 2.3 mm. Head. Integument light yellow, moderately covered with small round tubercles; antennal sheath without any protuberances; face with pair of unbranched long trichomes with coiled or uncoiled apices, and frons with three pairs of unbranched long trichomes with coiled or uncoiled apices; three frontal trichomes on each side arising close together, subequal in length to one another and slightly longer than facial one. Thorax. Integument yellow, moderately covered with round tubercles except posterior half somewhat sparsely covered with tubercles, with three long dorsomedial trichomes with coiled apices, two long anterolateral trichomes (one with coiled apex, one with uncoiled apex), one medium-long mediolateral trichome with uncoiled apex, and three ventrolateral trichomes with uncoiled apices (one medium-long, two short) on each side; all trichomes unbranched. Gill ( Fig. 5A ) composed of eight slender thread-like filaments, arranged in [(2+1) (or 1+2)+(1+2)]+2 from dorsal to ventral, with medium-long common basal stalk having somewhat swollen basal fenestra at base; common basal stalk 0.7–0.8 times length of interspiracular trunk; dorsal and middle triplets sharing short stalk; dorsal triplet composed of one individual and two paired filaments with short primary and secondary stalks; middle triplet composed of one individual and two paired filaments with medium-long primary stalk and short secondary stalk; ventral paired filaments with medium-long stalk which is 1.1–1.5 times length of common basal stalk and 0.8–1.1 times length of interspiracular trunk; stalk of ventral pair 1.1–1.2 times as thick as primary stalk of middle triplet, 1.2–1.3 times as thick as primary stalk of dorsal triplet, and 0.8–0.9 times as thick as common stalk of middle and dorsal triplets; primary stalk of dorsal triplet lying against stalk of ventral pair at angle of 80–100 degrees when viewed laterally; all filaments grayish light-brown, gradually tapered toward apex; three filaments of dorsal triplet subequal in length (1.8–2.0 mm long including their own stalks and basal common stalk) and thickness to one another; three filaments of middle triplet subequal in length (2.0– 2.3 mm long including their own stalks and basal common stalk) and thickness to one another (though individual filament always slightly thicker than paired filaments); two filaments of ventral pair subequal in length (2.3–2.6 mm long including their own stalk and common basal stalk) and thickness to each other, and 1.5 times as thick as those of six other filaments when compared basally; cuticle of all filaments with weakly-defined annular ridges and furrows along basal one-third or to two-thirds and nearly smooth on rest, densely covered with minute tubercles. Abdomen. Dorsally, segments 1 and 2 not pigmented and without tubercles; segment 1 with one unbranched slender mediumlong hair-like seta on each side; segment 2 with one unbranched slender medium-long hair-like seta and five short somewhat spinous setae submedially on each side; segments 3 and 4 each with four hooked spines and one short somewhat spinous seta on each side; segment 5 lacking spine-combs; 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 flat terminal hooks, of which outer margin is 3.4–3.6 times length of inner margin and crenulated ( Fig. 5B ). Ventrally, segment 4 with one unbranched hook and few slender short setae on each side; segment 5 with pair of bifid or trifid hooks submedially and few slender short setae on each side; segments 6 and 7 each with pair of bifid inner and unbranched hooks somewhat spaced from each other and few unbranched slender short setae on each side; segments 4–8 with comblike groups of minute spines. Each side of segment 9 with three grapnel-shaped hooklets. Cocoon. Wall pocketshaped, thinly and moderately or somewhat roughly woven, extended ventrolaterally; anterior margin thickly woven or not, with dorsal portion slightly produced anteriorly when viewed dorsally; posterior half with floor roughly or moderately woven; individual threads visible; 2.4–3.0 mm long by 1.4–1.7 mm wide.

Mature larva. Body length 4.0– 4.4 mm. Body creamy except dorsal surface of thorax light whitish-grayish, part of proleg light grayish, ventral surface of thoracic segments 2 and 3 grayish-ochreous, abdominal segments 1– 4 encircled with grayish broad band, and dorsal surface of other abdominal segments light grayish; body with purplish- or reddish-brown markings: thoracic segment 1 encircled with broad transverse band (though disconnected ventromedially), abdominal segment 2 with dorsolateral spot (often divided into two spots) on each side, segments 3 and 4 each encircled with broad band (though disconnected dorsomedially and ventral portion not so marked), abdominal segments 5–8 each with broad transverse band on dorsal and dorsolateral surfaces (though those on segments 6 and 7 (or also 8) often disconnected dorsomedially), abdominal segment 7 with transverse band on ventral surface. Cephalic apotome yellow, and moderately covered with unbranched minute setae; head spots faintly positive. Lateral surface of head capsule yellow except eye-spot region whitish, and sparsely covered with unbranched minute setae; two relatively large spots and two small spots near posterior margin, as well as one small spot below eye-spot region, faintly positive. Ventral surface of head capsule yellow except darkened area near posterior margin on each side of postgenal cleft, and sparsely covered with simple minute setae; one elongate spot and one round spot on each side of postgenal cleft faintly positive. Antenna composed of three articles and apical sensillum, somewhat longer than stem of labral fan; proportional lengths of first, second, and third segments 1.0: 0.8:0.9–1.1. Labral fan with 33–35 main rays. Mandible with three comb-teeth, of which first tooth is longest and second is subequal to or slightly longer than third; mandibular serration composed of two teeth (one mediumsized, one small); major tooth at acute angle against mandible on apical side; supernumerary serrations absent. Hypostoma ( Fig. 5E ) with row of nine apical teeth; median tooth most prominent, followed by each corner tooth and 3 intermediate teeth on each side subequal in size to one another and shortest of all; lateral margin smooth; four to six hypostomal bristles per side lying parallel to lateral margin. Postgenal cleft ( Fig. 5E ) long, 11.3–15.3 times length of postgenal bridge. Cervical sclerites light yellow, small, rod-like, not fused to occiput, widely separated medially from each other. Thoracic cuticle bare. Abdominal cuticle almost bare except few posterior segments moderately covered with unbranched and branched (with 2–4 branches) setae dorsally and dorsolaterally and last segment densely covered with unbranched colorless setae on each side of anal sclerite. Rectal scales absent. Rectal papilla compound, each of three lobes with five or six finger-like secondary lobules. Anal sclerite of usual X-form, with anterior arms as long as or little longer than posterior ones, broadly sclerotized at base; accessory sclerite absent. Last abdominal segment expanded ventrolaterally forming double bulges on each side, visible as large conical ventral papilla when viewed from side. Posterior circlet with 90 rows of up to 13 hooklets per row.

Specimens examined: Three females, five males (with associated pupal exuviae and cocoons) (preserved in 80% ethanol) reared from pupae, one pupa and five mature larvae collected from a lowland stream in Langkawi Island, Malaysia, 29.X.2011, by H. Takaoka, M. Sofian-Azirun & Z. Ya’cob.

Remarks. The male, pupa and larvae of this species are slightly different morphologically from those originally described from Thailand (shown in parentheses) by Jitklang et al. (2008) as follows: male upper-eye facets 10 vertical columns and 12 horizontal rows (9 or 10 vertical columns and 11 horizontal rows), the primary stalk of the dorsal triplet against that of the ventral pair of filaments lying at an angle of 80–100 degrees (at an angle of over 90 degrees), and larval postgenal cleft long but not reaching the posterior margin of the hypostoma ( Fig. 5E ) (long, almost reaching the posterior margin of the hypostoma).

This species is similar to S. (G.) sheilae but is distinguished by the following characters (characters of S. (G.) sheilae in parentheses): the common basal stalk of the pupal gill medium-long (short), terminal hooks wide, platelike, with outer margin crenulated ( Fig. 5B ) (triangular, with outer margin smooth or slightly undulate, Fig. 5C, D ), and the larval postgenal cleft not reaching the posterior margin of the hypostoma ( Fig. 5E ) (reaching the postgenal margin of the hypostoma, Fig. 5F ), and thoracic segment 1 encircled by a reddish-brown band (lacking such a reddish-brown marking).

The males and pupae collected from Bentong, Peninsular Malaysia are slightly different from those from Langkawi Island . The yellow portion of the male hind tibia is slightly narrower. In the pupa, the surface of the gill filaments is almost smooth, lacking annular ridges and furrows, and the dorsal and middle triplets of the filaments bear rather longer secondary stalks. The gill filaments of pupae collected from Tioman Island have a similar smooth surface. In addition, the ratio of the sensory vesicle against the third maxillary palpal segment of the male from Tioman Island is somewhat bigger than that from Langkawi Island (0.24 versus 0.16–0.18). Further studies are needed to clarify whether these morphological differences between populations are due to intraspecific or interspecific variations.

This species is distinguished from other members of the S. ceylonicum species-group using keys provided by Takaoka et al. (2014g).

Figures

FIGURE 1. Male of Simulium (Gomphostilbia) decuplum. (A) Third maxillary palpal segment with sensory vesicle (right side; front view). (B) Basitarsus and second tarsomere of hind leg (left side; outer view). (C) Coxites, styles and ventral plate (ventral view). (D) Style (right side; ventrolateral view). (E) Ventral plate with median sclerite (lateral view). (F) Ventral plate (caudal view). (G) Median sclerite (caudal view). (H) Paramere (left side: caudal view). (I) Aedeagal membrane (caudal view). (J) and (K) Abdominal segment 10 and cerci (right side; J, lateral view: K, caudal view). Scales. 0.05 mm for B; 0.02 mm for A and C– K.

FIGURE 3. Female of Simulium (Gomphostilbia) trangense. (A) Third maxillary palpal segment with sensory vesicle (right side; front view). (B) Cibarium (front view). (C) Tibia of hind leg (left side; outer view). (D) Basitarsus and second tarsomere of hind leg (left side; outer view). (E) Tarsal claw. (F) Sternite 8 and ovipositor valve (right half; ventral view). (G) Genital fork (ventral view). (H) and (I) Paraprocts and cerci (right side; H, ventral view; I, lateral view). (J) Spermatheca. Scales. 0.1 mm for B and C; 0.02 mm for A, B and F–J; 0.01 mm for E.

FIGURE 4. Male of Simulium (Gomphostilbia) trangense. (A) Third maxillary palpal segment with sensory vesicle (right side; front view). (B) Tibia of hind leg (left side; outer view). (C) Basitarsus and second tarsomere of hind leg (left side; outer view). (D) Coxites, styles and ventral plate (ventral view). (E) Style (right side; ventrolateral view). (F) Ventral plate with median sclerite (lateral view). (G) Ventral plate (caudal view). (H) Median sclerite (caudal view). Scales. 0.1 mm for B and C; 0.02 mm for A and D–H.

FIGURE 5. Pupa and larva of Simulium (Gomphostilbia) trangense and S. (G.) sheilae. (A) Pupal gill filaments of S. (G.) trangense (left side; outer view). (B)–(D) Pupal terminal hooks (caudal view; B, S. (G.) trangense; C and D, S. (G.) sheilae). (E) and (F) Larval head capsules (ventral view; E, S. (G.) trangense; F, S. (G.) sheilae). Scales. 0.1 mm for A; 0.05mm for E and F; 0.02 mm for B–D.