Simulium (Gomphostilbia) fuscidorsum Takaoka

Takaoka, Hiroyuki, Sofian-Azirun, Mohd, Ya’Cob, Zubaidah, Chen, Chee Dhang, Lau, Koon Weng & Pham, Xuan Da, 2015, The black flies (Diptera: Simuliidae) from Thua Thien Hue and Lam Dong Provinces, Vietnam, Zootaxa 3961 (1), pp. 1-96 : 13-17

Simulium (Gomphostilbia) fuscidorsum Takaoka & Ya’cob sp. nov.

( Figs. 4 A–5L)

Female (dissected from pupal case). Body length 3.0 mm. Head. Slightly narrower than thorax. Frons brownishblack, shiny when illuminated at certain angles, densely covered with whitish-yellow scale-like recumbent short hairs interspersed with few dark longer hairs along each lateral margin; frontal ratio 1.8:1.0:2.8; frons:head ratio 1.0:5.2. Fronto-ocular area well developed, narrow, directed dorsolaterally. Clypeus dark brown, densely covered with whitish-yellow hairs interspersed with dark longer hairs on each side. Labrum 0.6 times length of clypeus. Antenna composed of scape, pedicel and nine flagellomeres, dark brown except scape, pedicel and base of first flagellomere yellow. Maxillary palp composed of five segments, light brown except third segment dark brown, proportional lengths of third, fourth, and fifth segments 1.0:1.1:2.7; third segment ( Fig. 4 A) somewhat enlarged; sensory vesicle ( Fig. 4 A) elongate, 0.57 times length of third segment and with medium-sized opening. Maxillary lacinia with 13 or 14 inner and 18 outer teeth. Mandible with 30 inner and four or five outer teeth (outer teeth at some distance from tip of mandible). Cibarium ( Fig. 4 B) with strongly sclerotized dorsal margin having short plate produced forward, and with somewhat sclerotized mediolongitudinal ridge, of which apex has two small narrow projections. Thorax. Scutum brownish-black except anterolateral calli ochreous, shiny when illuminated at certain angles, densely covered with yellow scale-like recumbent hairs except three narrow vittae (one median and two submedian), which are covered with dark brown short hairs (both ends of these vittae not reaching anterior and posterior margins of scutum). Scutellum ochreous, covered with yellow short hairs and dark-brown long upright hairs along posterior margin. Postnotum brownish-black, shiny and white pruinose when illuminated at certain angles and bare. Pleural membrane bare. Katepisternum longer than deep, brownish-black, shiny when illuminated at certain angles, moderately covered with short hairs. Legs (Color pigmentation, in particular, that of femora and tibiae probably incomplete). Foreleg: coxa yellow; trochanter light brown; femur yellow with apical cap light to medium brown; tibia whitish to yellowish-white except apical cap blackish, densely covered with whitish short hairs (brightly shiny when illuminated) on outer surface of basal three-fourths; tarsus black, with moderate dorsal hair crest; basitarsus somewhat dilated, 6.1 times as long as its greatest width. Midleg: coxa medium brown; trochanter light brown on inner surface and dark yellow on outer surface; femur yellow except apical cap light to medium brown; tibia ( Fig. 4 C) yellowish-white on basal half and blackish on apical half (though near border not well pigmented), and with whitish-yellow short hairs (brightly shiny when illuminated) on outer and posterior surfaces of basal three-fourths; tarsus blackish except basal half of basitarsus dark yellow to light brown. Hind leg: coxa light to medium brown (though posterior portion not well pigmented); trochanter yellow; femur yellow except apical cap medium to dark brown (though appearing yellow on basal one-third and darkened on apical two-thirds due to presence of thick dark hairs on outer surface of apical two-thirds); tibia ( Fig. 4 D) yellowish-white except apical one-fourth dark brown to black, densely covered with whitish-yellow short hairs (brightly shiny when illuminated) on outer and posterior surfaces of basal three-fourths; tarsus dark brown to black except little more than basal half of basitarsus (though base light brown) yellow; basitarsus ( Fig. 4 E) narrow, nearly parallel-sided; calcipala (Fig, 4E) well developed, nearly as long as wide; pedisulcus ( Fig. 4 E) well developed; claw ( Fig. 4 F) with large basal tooth 0.5 times length of calw. Wing. Length not measurable. Costa with dark brown spinules and light brown hairs except basal patch of golden-yellow hairs. Subcosta haired. Hair tuft on base of radial vein composed of golden-yellow hairs and dark brown ones. Basal portion of radius fully haired. Basal cell absent. Halter . Clear white except basal portion darkened. Abdomen. Basal scale yellowish, with fringe of yellowish-white hairs. Dorsal surface of abdomen light to medium brown except that of segment 2 yellow (though narrowly darkened along posterior margin), moderately covered with whitish-yellow short hairs mixed with light to dark brown short to long hairs; tergites of segments 2 and 6–8 shiny when illuminated at certain angles. Ventral surface of segments 2–4 yellow, those of other segments dark yellow to light brown except middle portion of sternite 8 medium brown; sternal plate on segment 7 undeveloped. Genitalia. Sternite 8 ( Fig. 4 G) bare medially, with 22–24 medium-long to long hairs together with one or two slender short hairs on each side. Ovipositor valves ( Fig. 4 G) tongue-like, thin, membranous, moderately covered with microsetae interspersed with three short hairs; inner margins gently concave, moderately sclerotized, and somewhat separated from each other. Genital fork ( Fig. 4 H) of usual inverted-Y form, with slender stem; arms of moderate width, moderately folded medially, without posteromedial lobe or projection. Paraproct in ventral view ( Fig. 4 I) nearly triangular, with anterior corner unpigmented, with five or six sensilla on anteromedial surface; paraproct in lateral view ( Fig. 4 J) somewhat produced ventrally, 0.6 times as long as wide, with 28–30 medium-long to long hairs on ventral and lateral surfaces. Cercus in lateral view ( Fig. 4 J) short, rounded posteriorly, 0.45 times as long as wide. Spermatheca ( Fig. 4 K) ellipsoidal, 1.7 times as long as greatest width, well sclerotized except duct and small area near juncture with duct unsclerotized, and with many fissures on outer surface; internal setae absent; both accessory ducts slender, slightly wider in diameter than major one.

Male. Unknown.

Pupa. Body length 3.4 mm. Head. Integument ochreous, moderately covered with small round tubercles; antennal sheath without protuberances; frons with three pairs of unbranched long trichomes with coiled or uncoiled apices ( Fig. 5 A); face with pair of unbranched medium-long trichomes with coiled apices ( Fig. 5 B); three frontal trichomes on each side arising close together, subequal in length to one another and much longer than facial one. Thorax. Integument ochreous except narrow mediolongitudinal portion darkened, moderately covered with small round tubercles, with three anterodorsal trichomes with coiled apices (anterior one longest, two middle ones long) ( Fig. 5 C), two anterolateral trichomes (one long with coiled apex, one medium-long with uncoiled apex) ( Fig. 5 D), one medium-long mediolateral trichome with coiled or uncoiled apex ( Fig. 5 E), and three ventrolateral trichomes with uncoiled apices (one long, two short) ( Fig. 5 F) on each side; all trichomes unbranched. Gill ( Fig. 5 G) composed of eight slender thread-like filaments, arranged as [(2+1)+(1+2)]+2 filaments from dorsal to ventral; common basal stalk long, 1.2 times length of interspiracular trunk, having somewhat swollen basal fenestra at base; dorsal and middle triplets sharing long common stalk 0.8–0.9 times length of common basal stalk; dorsal triplet with short primary stalk and medium-long secondary stalk; middle triplet directed forward, with long primary and secondary stalks; stalk of ventral pair directed somewhat downward, then forward, long, 2.4–2.6 times length of common basal stalk; stalk of ventral pair 0.9 times as thick as common stalk of dorsal and middle triplets, which is 0.8 times as thick as common basal stalk; all filaments light brown, gradually tapered toward apices; lengths of filaments measured from base of gill to apices of filaments, which are intact, are as follows: one filament of dorsal triplet 3.6 mm long, one filament of middle triplet 3.8 mm long; one filament of ventral pair 4.2 mm long; filaments of dorsal and middle triplets subequal in length and thickness to one another, and appearing to be slightly shorter and thinner than ventral paired filaments; cuticle of all filaments with well-developed annular ridges and furrows, which are almost indistinct along some apical portions of all filaments, densely covered with minute tubercles, relatively larger ones on ridges. Abdomen. Dorsally, segments 1–5 grayish light-brown (though segment 5 less distinct), segment 9 yellowish, other segments unpigmented; segment 1 with one unbranched slender medium-long hair-like seta on each side; segment 2 with one unbranched slender short hair-like seta and four short somewhat spinous setae submedially near posterior margin on each side; segments 3 and 4 each with four hooked spines and one short somewhat spinous seta near posterior margin on each side; segments 5–8 each with two unbranched short setae near posterior margin on each side; segments 6–9 each with spine-combs in transverse row and comb-like groups of minute spines near anterior margin; segment 9 with pair of triangular terminal hooks, of which outer margins somewhat undulated ( Fig. 5 H). Ventrally, segment 4 with two unbranched hooks and few unbranched short setae on each side; segment 5 with pair of bifid hooks submedially and few unbranched short slender setae on each side; segments 6 and 7 each with pair of bifid inner and unbranched outer hooks somewhat spaced from each other and few unbranched short slender setae on each side; segments 4–8 each with comb-like groups of minute spines. Each side of segment 9 with three grapnel-shaped hooklets. Cocoon ( Fig. 5 I). Wall-pocket-shaped, moderately woven, widely extended ventrolaterally; anterior margin somewhat thickly woven, with long anterodorsal projection gently curved downward; posterior half with floor roughly woven; individual threads partially visible; 4.2 mm long by 3.5 mm wide.

Mature larva. Body length 6.1 mm. Body light ochreous except abdominal segments 1–3 grayish-green, abdominal segments 5 and 9 each with reddish-brown transverse band dorsally, and abdominal segments 6–8 each with reddish-brown areas dorsolaterally. Cephalic apotome dull yellowish though whitish on little less than anterior half, and moderately covered with unpigmented minute setae; head spots indistinct or faintly negative. Lateral surface of head capsule yellowish except eye-spot region whitish; eyebrow somewhat darkened on posterior half, two relatively large spots and one small spot near posterior margin faintly positive; one or two small spots below eye-spot region indistinct. Ventral surface of head capsule yellowish except darkened area near posterior margin on each side of postgenal cleft; one elongate spot and one round spot on each side of postgenal cleft faintly positive. Antenna composed of three segments and apical sensillum, somewhat longer than stem of labral fan; length ratio of three segments (from base to tip) 1.00:0.82:0.96. Labral fan with 42 or 43 main rays. Mandible ( Fig. 5 J) with three comb-teeth decreasing in length from first to third; serrations composed of two teeth (one medium-sized, one small); major tooth at acute angle against mandible on apical side; supernumerary serrations absent. Hypostoma ( Fig. 5 K) with row of nine apical teeth, of which median tooth slightly longer than each corner tooth; lateral margin smooth; four hypostomal bristles per side lying parallel to lateral margin. Postgenal cleft ( Fig. 5 L) medium-long, 1.21 times length of postgenal bridge. Cervical sclerites composed of two pale small pieces, not fused to occiput, widely separated medially from each other. Cuticle of thorax almost bare. Cuticle of abdomen sparsely covered with unbranched colorless minute setae dorsally and dorsolaterally except last segment moderately covered with unbranched colorless setae on each side of anal sclerite down to ventral papillae. Rectal scales not discerned. Rectal organ compound, each of three lobes with eight or nine finger-like secondary lobules. Anal sclerite of usual X-form, with anterior arms nearly 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 87 rows of hooklets with up to 15 hooklets per row.

Type material. HOLOTYPE: Pharate female, dissected from pupal case collected from a small stream (width 0.4 m, depth 10 cm, bottom muddy, water temperature 15.0˚C, partially shaded, altitude 1,722 m, 12˚06’06.888” N/ 108˚22’02.797” E) slowly flowing in a swampy area, Dinh Kno, Lac Duong, Lam Dong Province, southern Vietnam, 23-IV-2014, by H. Takaoka, M. Sofian-Azirun, Z. Ya’cob, C.D. Chen & K.W. Lau. PARATYPE: One mature larva, same data as those of the holotype.

Biological notes. The pupa and larva of this new species were collected from grass leaves trailing in the water. Associated species were S. (N.) phami Takaoka, Sofian-Azirun & Ya’cob and S. (S.) congi sp. nov.

Etymology. The species name fuscidorsum refers to the darkened dorsal surface of the pupal abdominal segments 1–5. The Latin adjective ‘ fuscus’ means ‘dark-colored’.

Remarks. This new species cannot be reliably assigned to any species-group of the subgenus Gomphostilbia , defined by Takaoka (2012), due to the lack of information of the male ventral plate and hind basitarsi, but it is temporarily placed in the S. asakoae species-group based on the enlarged female sensory vesicle ( Fig. 4 A), pupal gill with an elongated common basal stalk ( Fig. 5 G), and medium-sized larval postgenal cleft ( Fig. 5 L), similar to those of S. (G.) sofiani Takaoka & Hashim described from Peninsular Malaysia, which is one of the members of the S. asakoae species-group ( Takaoka et al. 2011a; Takaoka 2012).

The pupa of this new species is distinctive among species of the S. asakoae species-group and other speciesgroups of the subgenus Gomphostilbia by having the gill with an elongate common basal stalk ( Fig. 5 G), combined with the cocoon with an anterodorsal projection ( Fig. 5 I). The pupae of S. (G.) chiangdaoense from Thailand and S. (G.) yunnanense Chen & Zhang from China, both of the S. asakoae species-group, have a similar combination of the characteristics but the arrangement of their gill filaments is quite different, e.g., dorsal and middle triplets have short primary and secondary stalks; in addition, the female sensory vesicles of these two species are much shorter than that of this new species ( Takaoka and Srisuka 2009; Chen and Zhang 2004)..

The pupa of S. (S.) sofiani has a similar arrangement of gill filaments but its cocoon lacks an anterodorsal projection ( Takaoka et al. 2011a).

The pupa of S. (S.) fuscidorsum sp. nov. is also characterized by having the darkened dorsal surfaces of the abdominal segments 1–5, a character not occurring in the S. asakoae species-group and other species-groups of the subgenus Gomphostilbia except S. (G.) asakoae , originally described from Peninsular Malaysia, which has the darkened dorsal surface on abdominal segments 1 and 2 ( Takaoka et al. 2013a).

Figures

FIGURE 4. Female of Simulium (Gomphostilbia) fuscidorsum sp. nov. A, third segment of maxillary palp (left side; front view); B, cibarium (front view); C, tibia of midleg (left side; outer view); D, tibia of hind leg (left side; outer view); E, basitarsus and second tarsomere of hind leg (left side; outer view); F, claw; G, sternite 8 and ovipositor valve (right half; ventral view); H genital fork (ventral view); I & J, paraprocts and cerci (right side; I, ventral view; J, lateral view); K, spermatheca. Scale bars. 0.1 mm for C – E; 0.02 mm for A, B and G – K; 0.01 mm for F.

FIGURE 5. Pupa and mature larva of Simulium (Gomphostilbia) fuscidorsum sp. nov. A – I, pupa; J – L, larva. A, frontal trichome; B, facial trichome; C – F, thoracic trichomes (C, anterodorsal; D, anterolateral; E, mediolateral; F, ventrolateral); G, gill filaments (right side; outer view); H, terminal hooks (caudal view); I, cocoon (dorsal view); J, mandible; K, hypostoma (ventral view); L, head capsule with postgenal cleft (ventral view). Scale bars. 1.0 mm for I; 0.2 mm for G; 0.1 mm for L; 0.04 mm for A – F; 0.02 mm for H, J and K.