Simulium (Gomphostilbia) varicorne Edwards, 1925

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 : 33-39

33. Simulium (Gomphostilbia) varicorne Edwards, 1925

Simulium varicorne Edwards, 1925: 159 –160 (Male); Edwards, 1934: 126–129 (Male).

Simulium (Gomphostilbia) varicorne: Crosskey, 1973: 425 ; Takaoka & Davies, 1995: 70–72 (Pupa).

This species was originally described from a male collected from Sumatra ( Edwards, 1925). It was recorded from Peninsular Malaysia by Crosskey (1973). The pupa of this species was first described and the male antenna, maxillary palp and genitalia were illustrated based on Peninsular Malaysian specimens by Takaoka and Davies (1995).

The female and larva of this species are here described for the first time and the male and pupa are redescribed.

Female. Body length 2.1–2.2 mm. Head. Slightly narrower than width of thorax. Frons dark brown, not shiny, densely covered with white or yellowish-white scale-like recumbent short hairs except mediolongitudinal portion narrowly bare; frontal ratio 1.3–1.4:1.0:1.6–2.1; frons:head ratio 1.0:4.7–5.2. Fronto-ocular area well developed, narrow, tapered toward apex, directed dorsolaterally. Clypeus dark brown, densely covered with whitish yellow scale-like hairs interspersed with several longer dark hairs on each side. Labrum 0.53–0.59 times as long as clypeus. Antenna ( Fig. 8A ) composed of scape, pedicel and eight flagellomeres, yellow except first flagellomere dark yellow to light brown (though base is yellowish white), third flagellomere light to medium brown and fifth to eighth flagellomeres dark brown. Maxillary palp composed of five segments, light brown except segments 1 and 2 yellowish; proportional lengths of third, fourth, and fifth segments 1.0:1.1–1.2:2.3–2.5; third segment ( Fig. 8B ) somewhat swollen; sensory vesicle ( Fig. 8B ) ellipsoidal, medium-sized (0.25–0.26 times as long as third segment), with medium-sized opening. Maxillary lacinia with 8–10 inner and 13 or 14 outer teeth. Mandible with 19 or 20 inner teeth and two or three weakly developed outer teeth at some distance from tip. Cibarium ( Fig. 8C ) with pair of well-sclerotized triangular projections at posterodorsal margin, which are in front covered by unpigmented transverse thin structure arising from both cornuae. Thorax. Scutum dark brown except anterolateral calli ochreous, shiny when illuminated at certain angles, faintly with three dark narrow vittae (one median and two submedian), and densely covered with white or yellowish-white scale-like recumbent hairs. Scutellum dark brown, covered with yellowish whitish short hairs and light brown long upright hairs along posterior margin. Postnotum dark brown, shiny white pruinose when illuminated at certain angles, and bare. Pleural membrane bare. Katepisternum medium brown, longer than deep, shiny when illuminated at certain angles, moderately covered with fine short hairs. Legs. Foreleg: coxa and trochanter yellow; femur light brown with apical cap medium brown (though extreme tip yellowish) except inner surface widely yellowish; tibia yellowish except subbasal and subapical small portion light brown; tarsus dark brown, with moderate dorsal hair crest; basitarsus moderately dilated, 5.3–5.6 times as long as its greatest width. Midleg: coxa medium brown; trochanter light brown except base yellow; femur light brown with apical cap medium brown (though extreme tip yellowish); tibia yellowish white on basal two-fifths, with light brown subbasal spot, light to medium brown on rest (though extreme tip yellowish); tarsus light to medium brown except little more than basal two-thirds of basitarsus and bases of second and third tarsomeres yellowish white. Hind leg: coxa medium brown; trochanter yellow; femur medium brown, with base whitish yellow and apical cap dark brown (though extreme tip yellowish white); tibia ( Fig. 8D ) white to whitish yellow on basal half or little more, with light-brown subbasal spot, and light brown on one-third of apical half, and dark brown on rest; tibia densely covered with white hairs on basal two-thirds; tarsus light to medium brown except little more than basal two-thirds of basitarsus and little more than basal half of tarsomere 2 yellowish white; basitarsus ( Fig. 8E ) narrow, nearly parallel-sided, 6.36–6.41 times as long as wide, and 0.58 and 0.50–0.55 times as wide as greatest widths of tibia and femur, respectively; calcipala ( Fig. 8E ) slightly longer than width at base, and 0.55 times as wide as greatest width of basitarsus. Pedisulcus ( Fig. 8E ) well developed. Claw ( Fig. 8F ) with large basal tooth 0.44–0.47 times as long as claw. Wing. Length 1.5–1.6 mm. Costa with dark spinules and pale hairs with basal patch of whitish hairs. Subcosta bare (though one female has three hairs on left subcosta). Hair tuft on base of radial vein yellow. Basal portion of radius fully haired; R1 with dark spinules and hairs. 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 tergite of segment 2 yellow to ochreous, moderately covered with whitish short hairs interspersed with dark long hairs; tergites of segments 2 and 6–8 shiny when illuminated at certain angles. Ventral surface of abdomen light to medium brown except segment 2 mostly yellow; sternal plate on segment 7 undeveloped. Terminalia . Sternite 8 ( Fig. 8G ) bare medially, with 8–12 medium-long to long hairs together with two or three slender short hairs on each side. Ovipositor valve ( Fig. 8G ) triangular, thin, membranous, moderately covered with microsetae interspersed with three or four short hairs; inner margins nearly straight or sinuous, somewhat sclerotized, and slightly separated from each other. Genital fork ( Fig. 8H ) of usual inverted-Y form, with slender stem; arms gradually narrowed apically, moderately folded medially, and with triangular lobe directed posteromedially. Paraproct in ventral view ( Fig. 8I ) triangular, with five or six sensilla on darkened anteromedial surface; paraproct in lateral view ( Fig. 8J ) much produced ventrally, 0.6 times as long as wide, with 16–20 medium-long to long hairs on ventral and lateral surfaces. Cercus in lateral view ( Fig. 8J ) short, rounded posteriorly, 0.56 times as long as wide. Spermatheca ( Fig. 8K ) ellipsoidal, 1.6 times as long as its greatest width, well sclerotized even near juncture with duct, and with many longitudinal fissures on outer surface; internal setae absent; both accessory ducts slender, subequal in diameter to major one.

Male. Body length 2.0– 2.4 mm. Head. Somewhat wider than thorax. Upper eye dark brown, consisting of large facets in 11 or 12 vertical columns and 12 horizontal rows. Clypeus dark brown, densely covered with golden yellow scale-like medium-long hairs (mostly directed upward) interspersed with several longer hairs on each side. Antenna ( Fig. 9A ) similar to that of female, though scape, pedicel, second and fourth flagellomeres dark yellow to light brown; first flagellomere elongate, 1.7 times as long as second one. Maxillary palp light brown except segments 1 and 2 yellowish, proportional lengths of third, fourth, and fifth segments 1.0:1.1–1.2:2.1–2.5; third segment ( Fig. 9B ) widened apically; sensory vesicle ( Fig. 9B ) small, ellipsoidal (0.21–0.26 times as long as third segment), and with small opening. Thorax. Nearly as in female except anterolateral calli medium brown. Legs. Color and shape nearly as in female: fore basitarsus moderately dilated, 5.5–5.9 times as long as its greatest width; hind basitarsus ( Fig. 9C ) 5.1–5.3 times as long as wide, and 0.55–0.59 and 0.53–0.55 times as wide as greatest width of tibia and femur, respectively; calcipala ( Fig. 9C ) slightly longer than wide, and 0.4 6–0.48 times as wide as greatest width of basitarsus. Pedisulcus ( Fig. 9C ) well developed. Wing. Length 1.4–1.5 mm; other features as in female. Halter . White except basal stem darkened. Abdomen. Basal scale medium brown, with fringe of yellow hairs. Dorsal surface of abdomen brownish medium to dark brown except tergite of segment 2 ochreous, covered with yellow short hairs intermixed with dark long hairs; segments 2 and 5–8 each with pair of shiny dorsolateral or lateral patches. Genitalia. Coxite in ventral view ( Fig. 9D ) nearly rectangular, 1.3 times as long as its greatest width. Style in ventral view ( Fig. 9D ) bent inward, tapered from base toward apex, and with apical spine; style in ventrolateral view ( Fig. 9E ) 0.95 times length of coxite, much narrowed from base toward near middle, nearly parallel-sided or little widened to apical one-fourth, and then tapered toward apex. Ventral plate in ventral view ( Fig. 9D ) with body transverse, 0.7 times as long as wide, slightly narrowed posteriorly, with anterior margin produced anteromedially, and posterior margin nearly straight, densely covered with microsetae on ventral surface except anterolateral areas bare; basal arms of moderate length, directed forward, and somewhat convergent apically; ventral plate in lateral view ( Fig. 9F ) with body slightly narrowed posteriorly, and arms stout; ventral plate in caudal view ( Fig. 9G ) gently rounded ventrally, moderately covered with microsetae medially on posterior surface. Median sclerite ( Fig. 10F, H ) thin, plate-like. Paramere ( Fig. 9I ) with body narrow and with two distinct hooks directed outward and several hooks directed posterodorsally. Aedeagal membrane ( Fig. 9J ) moderately covered with microsetae. Ventral surface of abdominal segment 10 ( Fig. 9K, L ) without distinct hairs near posterior margin. Cercus ( Fig. 9K, L ) rounded, with 10–12 hairs.

Pupa. Body length 2.2–2.5 mm. Head. Integument yellow, moderately covered with small round tubercles; antennal sheath with outer margin undulate but without any protuberances; frons with three pairs of unbranched long trichomes with uncoiled apices, arising close together, subequal in length to one another ( Fig. 10A ); face with pair of unbranched long trichomes with uncoiled apices ( Fig. 10B ). Thorax. Integument yellow, moderately covered with round tubercles, with three long anterodorsal trichomes with coiled or uncoiled apices (middle and posterior trichomes subequal in length to each other, and much shorter than anterior one) ( Fig. 10C ), two anterolateral trichomes (anterior one medium-long with straight apex, posterior one long with coiled or straight apex) ( Fig. 10D ), one short mediolateral trichome with straight apex ( Fig. 10E ), and three ventrolateral trichomes with straight apices (one medium-long, two short) ( Fig. 10F ) on each side; all trichomes unbranched. Gill ( Fig. 10G ) with eight filaments arranged in two groups (dorsal and ventral) arising from short common basal stalk; dorsal group with two triplets, each of which composed of two paired filaments and one individual filament, or three filaments arising together at same level; two triplets sharing medium-long to long stalk, and each triplet with short to medium-long primary and second stalks; ventral group composed of two paired filaments with long stalk; all filaments subequal in length (1.7–2.0 mm) and thickness to one another; common basal stalk having transparent basal fenestra ventrally (partially broken); cuticle of all filaments with well-defined annular ridges and furrows though becoming less marked apically, densely covered with minute tubercles. Abdomen. Dorsally, all segments transparent except segments 1, 2 and 9 light yellow; segments 1, 2 and 5 each sparsely covered with minute spines; segment 1 with one unbranched slender short hair-like seta on each side; segment 2 with one unbranched slender short hair-like seta and five minute setae submedially on each side; segments 3 and 4 each with four hooked spines and one minute seta on each side; segment 5 with five minute setae on each side; segments 6–9 each with distinct spine-combs in transverse row and comb-like groups of minute spines on each side; segments 6 and 7 each with two minute setae on each side; segment 8 with one minute seta on each side; segment 9 with pair of cone-like terminal hooks ( Fig. 10H ). Ventrally, segment 4 with one hooklet and one minute seta on each side; segment 5 with pair of bifid hooklets and few minute setae on each side; segments 6 and 7 each with pair of bifid inner and unbranched outer hooklets and few minute setae on each side; segments 4–8 each with comb-like groups of minute spines; segment 9 with three pairs of grapnel-like hooklets on each lateral surface. Cocoon. Wall-pocket-shaped, light yellow to dark brown, thinly and moderately woven, slightly extended ventrolaterally; anterodorsal margin not thickly woven; anteroventral tips almost connected in middle to each other in one cocoon; posterior half with floor roughly or moderately woven; individual threads visible or invisible; 1.9–2.5 mm long by 1.0– 1.8 mm wide.

Mature larva. Body length 3.3–3.5 mm. Body color creamy, faintly with bluish green markings: all thoracic and abdominal segments each encircled with broad band, though bands on thoracic segments 2 and 3 disconnected laterally, and that of abdominal segment 8 disconnected ventrally. Head capsule whitish yellow; head spots indistinct. Antenna composed of three segments and apical sensillum, somewhat longer than stem of labral fan; proportional lengths of first, second, and third segments 1.0: 1.0:1.1. Labral fan with 22 or 23 main rays. Mandible ( Fig. 11A ) with three comb-teeth decreasing in length from first to third; mandibular serration composed of two teeth (one medium-sized and one small); major tooth at acute angle against mandible on apical side; supernumerary serrations absent. Hypostoma ( Fig. 11B ) with row of nine apical teeth; median tooth slightly longer than each corner teeth, which are slightly longer than three intermediate teeth on each side; lateral margin serrated apically; three hypostomal bristles per side lying slightly divergent posteriorly from lateral margin. Postgenal cleft ( Fig. 11C ) long, reaching posterior margin of hypostoma. Cervical sclerite composed of two pale small pieces, not fused to occiput, widely separated medially from each other. Thoracic segments 1–3 each with one nipple-like projection submedially on dorsal surface on each side ( Fig. 11D ), and moderately covered with unpigmented minute setae with two to four branches dorsally and dorsolaterally. Abdominal segments 1–5 each with three nipple-like projections (one dorsal, one dorsolateral and one lateral) on each side ( Fig. 11D ); cuticle of all segments moderately to densely covered with similar setae dorsally and dorsolaterally, and cuticle of segments 5–8 also moderately covered dorsally with unbranched flat minute setae each somewhat darkened except apical slender projection unpigmented; last segment densely covered with branched unpigmented setae on each side of anal sclerite. Rectal scales not discernible. Rectal papilla compound, each of three lobes with five or six finger-like secondary lobules. Anal sclerite of usual X-form, with anterior arms 0.7–0.8 times as long as 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 57–59 rows of up to 10 or 11 hooklets per row.

Specimens examined. Four females, four males (all with their associated pupal exuviae and cocoons) (in 80% ethanol) reared from pupae, and three mature larvae, collected from a small stream (width 2–4 m, exposed to the sun, 26.5 ˚C, streambed sandy, elevation 100 m above sea level), Negeri Sembilan, Peninsular Malaysia, 29-XII- 2010, by H. Takaoka, M. Sofian-Azirun & Z. Ya’cob.

Remarks. The female and larva of S. (G.) varicorne are characterized by the small sensory vesicle ( Fig. 8B ) and spermatheca with sclerotized neck ( Fig. 8K ), and the hypostoma with serrated lateral margins ( Fig. 11B ) and body with protuberances on the dorsal and dorsolateral surfaces of abdominal segments 1–5 ( Fig. 11D ), respectively.

The female, male and pupa of S. (G.) varicorne from Peninsular Malaysia are indistinguishable from those recently collected from Sumatra by Ya’cob (unpublished data). However, the larvae from Peninsular Malaysia differ from those from Sumatra in the following characters (those from Sumatra in parentheses): the labral fan with 22 or 23 primary rays (32 primary rays), rectal organ with 5–8 secondary lobules per lobe (9 or 10 secondary lobules) and body color without reddish-brown markings (body with gray markings overlayed with reddish-brown markings: thoracic segment 1 gray encircled with reddish-brown band, though disconnected dorsomedially, abdominal segments 1–8 each encircled with light gray band, though those of segments 6 and 7 disconnected laterally and that of segment 8 disconnected laterally and ventrally, abdominal segments 1–5 each with large reddish-brown band dorsolaterally and segments 1 and 5 also often with another smaller marking ventrolaterally on each side, abdominal segments 6 and 7 each with three reddish-brown markings: two large on each dorsolateral surface and one small ventromedially, though two dorsolateral markings of segment 6 connected in middle to each other in one larva, and abdominal segment 8 with small to large reddish-brown marking on each dorsolateral surface).

Despite the differences in some larval features, both populations from Peninsular Malaysia and Sumatra share the same sequence of the mitochondrial COI gene (Low, unpublished data).

This species is distinguished from five of six related species in the S. chumpornense subgroup by the arrangement of filaments of the dorsal group, which is composed of two triplets ( Fig. 10G ) in this species, but is composed of a main filament and five individual filaments arising from the main filament in S. (G.) chumpornense Takaoka & Kuvangkadilok from Thailand ( Kuvangkadilok and Takaoka, 2000), and a main filament, two paired filaments and three individual filaments arising from the main filament in S. (G.) sumbaense Takaoka & Suana (Takaoka et al., 2018b) , three pairs of filaments in S. (G.) tomae Takaoka from Sulawesi (Takaoka, 2003), eight individual filaments arising from the inflated tubular trunk in S. (G.) kuvangkadilokae Pramual & Tangkawanit from Thailand ( Pramual and Tangkawanit, 2008; Takaoka and Srisuka, 2010), and four filaments in two pairs or two individual and two paired filaments in S. (G.) piroonae Takaoka & Srisuka from Thailand ( Takaoka et al., 2014i).

Figures

FIGURE 8. Female of Simulium (Gomphostilbia) varicorne. (A) Antenna (right side; lateral view). (B) Third maxillary palpal segment with sensory vesicle (right side; front view). (C) Cibarium (front view). (D) Tibia of hind leg (left side; outer view). (E) Basitarsus and second tarsomere of hind leg (left side; outer view). (F) Tarsal claw. (G) Sternite 8 and ovipositor valves (right half; ventral view). (H) Genital fork (ventral view). (I) and (J) Paraprocts and cerci (right side; I, ventral view; J, lateral view). (K) Spermatheca. Scales. 0.05 mm for A, D and E; 0.02 mm for B, C and G–K; 0.01 mm for F.

FIGURE 9. Male of Simulium (Gomphostilbia) varicorne. (A) Antenna (right side; lateral view). (B) Third maxillary palpal segment with sensory vesicle (right side; front 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). (I) Paramere (left side; caudal view). (J) Aedeagal membrane (caudal view). (K) and (L) Abdominal segment 10 and cerci (right side; K, lateral view; L, caudal view). Scales. 0.05 mm for A and C; 0.02 mm for B and D–L.

FIGURE 10. Pupa of Simulium (Gomphostilbia) varicorne. (A) Frontal trichome. (B) Facial trichome. (C)–(F) Thoracic trichomes (C, anterodorsal; D, anterolateral; E, mediolateral; F, ventrolateral). (G) Gill filaments (left side; outer view). (H) Terminal hooks (caudal view). Scales. 0.1 mm for G; 0.02 mm for A–F and H.

FIGURE 11. Larva of Simulium (Gomphostilbia) varicorne. (A) Mandible. (B) Hypostoma. (C) Head capsule (ventral view). (D) Whole body (lateral view). (E) Setae on dorsal surface of abdominal segment 8. Scales. 0.5 mm for D; 0.05 mm for C; 0.02 mm for A, B and E.