Simulium (Gomphostilbia) decuplum Takaoka & Davies, 1995

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 : 14-16

13. Simulium (Gomphostilbia) decuplum Takaoka & Davies, 1995

Simulium (Gomphostilbia) decuplum Takaoka & Davies, 1995: 46 –50 (Female, pupa and larva).

This species was described from females, pupae and larvae (Takaoka and Davies, 1995). It is characterized in the female by the elongate sensory vesicle, in the male by abdominal segments 2, 6 and 7 each with a pair of shiny dorsolateral patches, in the pupa by the gill with 10 short slender filaments, and in the larva by the deep postgenal cleft approaching the posterior margin of the hypostoma.

It is widely distributed throughout the mainland of Peninsular Malaysia. The aquatic stages were found in small streams at low to high elevations (159–1,750 m) in Cameron Highlands (Ya’cob et al., 2016b).

This species was recorded from Thailand ( Takaoka and Saito, 1996) and Assam, India ( Borah et al., 2012). Takaoka et al. (2018c) noted that S. (G.) decuplum in Thailand is morphologically and molecularly divided into five new species and that the previous record of S. (G.) decuplum from Thailand by Takaoka and Saito (1996) might have been based on S. (G.) huaikaeoense Takaoka, Srisuka & Low , one of five new species, and true S. (G.) decuplum has not been collected from Thailand. Similarly, the record of this species from Assam, India ( Borah et al., 2012) should be reconfirmed. There is a possibility that the species identified as S. (G.) decuplum in Assam is one of five new species described by Takaoka et al. (2018c).

The male of this species is here described for the first time.

Male. Body length 1.9–2.2 mm. Head. Slightly wider than thorax. Upper eye consisting of 13–15 vertical columns and 14–16 horizontal rows of large facets. Face brownish black. Clypeus brownish black, moderately covered with yellow short hairs interspersed with dark brown longer hairs. Antenna composed of scape, pedicel and nine flagellomeres, dark brown except scape, pedicel and base of first flagellomere yellow, or dark brown except base of first flagellomere yellow; first flagellomere elongate, 1.8 times as long as second one. Maxillary palp with five segments, light brown, proportional lengths of third, fourth, and fifth segments 1.0:1.2:2.4; third segment ( Fig. 1A ) widened apically; sensory vesicle ( Fig. 1A ) globular, small, 0.16 times as long as third segment, and with small opening. Thorax. Brownish black to black, whitish-gray pruinose and shiny along lateral margins and on prescutellar areas, covered with yellow short hairs. Scutellum brownish black, with dark brown upright long hairs and yellow short hairs. Postnotum brownish black to black and bare. Pleural membrane bare. Katepisternum brownish black to black, shiny, covered with dark brown short hairs and yellow fine short hairs. Legs. Foreleg: coxa and trochanter light to medium brown; femur light to medium brown with apical cap dark brown; tibia dark brown except median large portion on outer surface light to medium brown; tarsus brownish black, with moderate dorsal hair crest; basitarsus somewhat dilated, 6.6–6.9 times as long as its greatest width. Midleg: coxa dark brown to brownish black; trochanter medium brown except base light brown; femur medium brown with apical cap dark brown; tibia medium to dark brown except extreme base yellow; tarsus dark brown except basal one-fifth or onefourth of basitarsus dark yellow to light brown. Hind leg: coxa dark brown; trochanter dark yellow to light brown; femur medium brown except basal tip yellow to dark yellow and apical cap dark brown; tibia light to medium brown except basal tip yellow, and subbasal area and apical cap dark brown; tarsus ( Fig. 1B ) dark brown except little more than basal three-fifths of basitarsus (though base light brown) and little less than basal half of second tarsomere yellow to grayish yellow; basitarsus ( Fig. 1B ) narrow, nearly parallel-sided (though somewhat tapered in apical one-third), 5.3–5.6 times as long as wide, and 0.61–0.64 times as wide as greatest width of tibia, which is as wide as femur; calcipala ( Fig. 1B ) well developed, as long as wide, and 0.5 times as wide as greatest width of basitarsus; pedisulcus ( Fig. 1B ) well developed. Wing. Length 1.5–1.6 mm. costa with dark brown spinules and dark brown hairs except basal portion with patch of yellowish hairs. Subcosta without hairs. Hair tuft on base of radius dark brown. Basal portion of radius fully haired. Basal cell absent. Halter . Dull white except basal stem partially darkened. Abdomen. Basal scale medium brown, with fringe of medium-brown long hairs. Dorsal surface of abdomen medium to dark brown except basal half of segment 2 yellow, covered with dark brown short to long hairs; segments 2, 6 and 7 each with pair of shiny dorsolateral patches, when illuminated at certain angles.

Genitalia. Coxite in ventral view ( Fig. 1C ) nearly rectangular, 1.3 times as long as its greatest width. Style in ventral view ( Fig. 1C ) slender, tapered toward apex, markedly curved inward, with apical spine; style in ventrolateral view ( Fig. 1D ) slightly tapered toward basal one-third, moderately tapered to apical one-fourth, then somewhat widened toward blunt apex; style in lateral view with apical one-fourth markedly curved mediodorsally. Ventral plate in ventral view ( Fig. 1C ) transverse, much wider than long, tapered posteriorly, with anterior margin produced anteromedially, posterior margin much concave medially, and densely covered with microsetae on ventral surface except each anterolateral portion bare; basal arms of moderate length, divergent, then parallel-sided; ventral plate in lateral view (Fig. E) nearly flat, not produced ventrally; ventral plate in caudal view ( Fig. 1F ) flat, moderately covered with microsetae except both lateral areas mostly bare; ventral margin slightly concave ventromedially and dorsal margin widely concave. Median sclerite in lateral view ( Fig. 1E ) arising from near anterior tip of ventral plate and directed dorsally; median sclerite in caudal view ( Fig. 1G ) flat, narrowly pigmented mediolongitudinally. Paramere ( Fig. 1H ) slender, with several long distinct hooks and few smaller ones near apex. Aedeagal membrane ( Fig. 1I ) not pigmented, densely covered with short microsetae. Ventral surface of tenth abdominal segment without distinct hairs near posterior margin on each side. Cercus ( Fig. 1J, K ) not well defined, with 9 or 10 hairs.

Specimens examined. Two males reared from pupae collected from a stream (width 0.6 m, water temperature 23.9˚C, partially shaded, elevation 388 m, 04°23’429” N, 101°36’265” E), moderately flowing in a forest, Sungai Koyan , Raub, Pahang, Malaysia, 20-XII-2011, by H. Takaoka, Z. Ya’cob & M. Sofian-Azirun ; 1 male reared from a pupa collected from a fast flowing stream (width 3.1 m, water temperature 23.9˚C, exposed to the sun, elevation 1,315 m, 04°34'573" N, 101°20'430" E), Simpang Pulai , Perak, Malaysia, 19-XII-2011, by H. Takaoka, Z. Ya’cob & M. Sofian-Azirun ; 1 male reared from a pupa collected from a slow flowing stream (width 0.4 m, water temperature 19.4˚C, shaded, elevation 1,033 m, 04°24'672" N, 101°22'213" E), Jalan Tapah , Cameron Highlands, Malaysia, 19-XII-2011, by H. Takaoka, Z. Ya’cob & M. Sofian-Azirun.

Remarks. The male of this species is most similar to that of S. (G.) huaikaeoense Takaoka, Srisuka & Low from Thailand in many characters including the number of upper-eye large facets, relative length of the fore basistarsus against its greatest width, wing length and genitalia.

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.