Simulium asakoae Takaoka and Davies, 1995

Jitklang, Sanae, Kuvangkadilok, Chaliow, Baimai, Visut, Takaoka, Hiroyuki & Adler, Peter H., 2008, Cytogenetics and morphotaxonomy of the Simulium (Gomphostilbia) ceylonicum species group (Diptera: Simuliidae) in Thailand, Zootaxa 1917, pp. 1-28 : 8-14

Simulium asakoae Takaoka and Davies, 1995

(Figs. 6A, 7A, 9A, 11A)

Simulium asakoae Takaoka and Davies, 1995: 55 –60 (female, male, pupa, larva) Simulium sp. ‘C’ Takaoka and Suzuki, 1984: 21 –22 (male)

This species was described from the female, male, pupa, and larva from West Malaysia ( Takaoka and Davies 1995). We redescribe these stages based on material from site 8 to provide a reference for discussing morphological differences and similarities among cytoforms. Our specimens of S. asakoae are morphologically nearly identical to those in the original description, except for differences in several features (e.g., pattern of adult leg color, length of the female sensory vesicle relative to the 3rd maxillary palpal segment, length of the female and male basitarsi against their greatest width, and shape of the pupal terminal hooks).

FIGURE 2. (A) Standard map for IS arm of the Simulium ceylonicum species group. (B) Standard map for IL arm of the Simulium ceylonicum species group. Fixed inversions are underlined; floating inversions are not. A question mark indicates that the breakpoints might not be identical to those of other inversions with the same letter-number designation. a Exact breakpoints of the inversion have not been determined. The approximate breakpoints of IL-2? and IL-3a are indicated as faint lines. C = centromere, NO = nucleolar organizer.

FIGURE 3. Standard map for IIIS arm of the Simulium ceylonicum species group. Fixed inversions are underlined; floating inversions are not. a Exact breakpoints of the inversion have not been determined. The approximate breakpoints of IIIS-3a are indicated as faint lines. Bl = blister marker, C = centromere.

FIGURE 4. (A) Standard map for IIS arm of the Simulium ceylonicum species group. (B) IIS arm of S. trangense n. sp. Fixed inversions are underlined; floating inversions are not. a Exact breakpoints of the inversion have not been determined. The approximate outermost breakpoints of IIS-1 a, 2 a, 3 a, 4 a are indicated as faint lines. BR = ring of Balbiani, C = centromere, db = double bubble.

Diagnosis. The larva is characterized by the combination of a hypostoma shorter than its greatest width, distinct head spots, and greenish transverse bands on abdominal segments I–IV. The pupa is distinguished from that of other cytoforms by having terminal hooks with smooth margins and the gill stalk of the dorsal triplet thinner than that of the middle triplet.

Female. Body length 2.6–2.7 mm. Head. Narrower than thorax. Frons dark brown, moderately covered with whitish-yellow pruinosity, and several dark hairs along lateral margins. Frons: head ratio 1.0: 5.0. Fronto-ocular area well developed. Clypeus dark brown, densely covered with whitish-yellow hairs interspersed with several dark hairs. Antenna composed of scape, pedicel, and 9 flagellomeres, with scape and pedicel and base of 1st flagellomere yellow; remaining flagellomeres brown. Maxillary palp with 5 segments; proportional lengths of 3rd, 4th, and 5th segments 1.0: 1.1: 2.7; sensory vesicle of moderate size, ca. 0.4 x as long as 3rd segment, with round opening distally. Maxillary lacinia with 10 inner and 16 outer teeth. Mandible with ca. 20 inner teeth and 9 outer ones. Thorax. Scutum brown, shiny, with 3 faint, longitudinal vittae, and densely covered with whitish-yellow hairs. Scutellum brown, with long, erect, dark hairs along posterior margin. Postscutellum brown, bare. Pleural membrane bare. Katepisternum dark brown, with hairs. Legs. Foreleg: coxa and trochanter yellow; femur yellowish brown, darkened toward tip; tibia white with distal 1/4 dark brown; outer surface largely white; tarsus dark brown; basitarsus slender, ca. 5.8 x as long as its greatest width. Midleg: coxa brown; trochanter yellow; femur yellowish brown with basal 1/6 paler; tibia yellow on basal 1/3, and dark brown on remainder; tarsus dark brown with basal 1/2 of basitarsus yellow. Hind leg: coxa yellowish brown; trochanter yellow; femur yellow at base, darkened toward tip, and brown on distal 1/4; tibia yellowish white on basal 3/4, and brown on remainder; tarsus brown with basal 3/4 of basitarsus and basal 1/2 of 2nd tarsomere yellowish white; basitarsus slender, parallel sided, ca. 6.4 x as long as wide. Calcipala and pedisulcus well developed. Wing. Length 1.9 mm. Costa with spinules and hairs. Subcosta haired on basal 1/ 2. Hair tuft on stem vein yellow. Base of radius haired. Abdomen. Basal scale yellow, with fringe of yellow hairs. Dorsal surface of abdomen yellowish brown, tergites of segments VI–VIII shiny. Genitalia. Sternite 8 bare medially, with 20 or 21 dark macrosetae on each side. Hypogynial valve densely covered with microsetae; inner margin well sclerotized. Genital fork an inverted Y, with stem slender and well sclerotized. Anal lobe moderately produced ventrally, 0.8 x as long as wide. Cercus 0.7 x as long as wide. Spermatheca ellipsoidal, well sclerotized.

FIGURE 5. (A) Standard map for IIL arm of the Simulium ceylonicum species group. (B) IIL arm of S. trangense n. sp. Fixed inversions are underlined; floating inversions are not. a Exact breakpoints of the inversion have not been determined. The approximate breakpoints of IIL-10a are indicated as faint lines. Arrows indicate breakpoints of IIL-6. C = centromere, D = DNA puff, jg = jagged group, PB = parabalbiani, and S = symmetrical group.

Male. Body length ca. 2.6 mm. Head. 1.1 x wider than thorax. Upper eye with large facets in 13 horizontal rows and in 9 or 10 vertical columns. Clypeus brownish black, densely covered with pale hairs interspersed with several dark hairs. Antenna composed of scape, pedicel and 9 flagellomeres, brownish black except scape, pedicel, and base of 1st flagellomere yellowish brown. Maxillary palp with 5 segments, proportional lengths of 3rd, 4th, and 5th segments 1.0: 1.1: 2.4; sensory vesicle small, round, 0.2 x as long as 3rd segment, opening submedially. Thorax. Scutum brown with 3 faint, longitudinal vittae, and densely covered with yellow recumbent hairs. Scutellum brown with yellow pubescence and several dark hairs. Postscutellum bare. Pleural membrane bare. Katepisternum with hairs. Legs. As in female, except hind tibia and hind basitarsus FIGURE 6. IIIL arm of the Simulium ceylonicum species group in Thailand. (A) S. asakoae (standard map), (B) S. curtatum n. sp., (C) S. nr. asakoae 2, (D) S. nr. asakoae 3, (E) S. nr. asakoae 4, (F) S. inthanonense , (G) S. sheilae , (H) S. trangense n. sp., and (I) S. doisaketense n. sp. C = centromere, m1 = basal marker, and m2= end marker. a Exact breakpoints of the inversion have not been determined.

yellow on basal 1/5 and 1/3, respectively, and dark brown on remainder. Hind basitarsus enlarged, ca. 2.7 x as long as wide. Wing. Length 1.9 mm. Costa with spinules and hairs. Hair at base of costa yellow. Subcosta haired on basal 1/3. Base of radius haired. Hair tuft on stem vein dark yellow. Abdomen. Basal scale brown, with fringe of brown hairs. Segments II and V–VII shiny. Genitalia. Gonocoxite 1.2 x as long as wide. Gonostylus slender, shorter than gonocoxite, gradually tapered toward apex, with apical spinule. Ventral plate in ventral view with body ca. 2.0 x wider than long, with anterior margin slightly convex and posterior margin broadly rounded and slightly concave medially; arms slender, parallel sided, though slightly convergent anteriorly. Paramere with 3 distinct hooks and several smaller hooks. Median sclerite elongated, weakly sclerotized, rounded apically.

Pupa. Body length (excluding gill filaments) 2.5–2.6 mm. Head and thorax. Integument yellow, moderately covered with microtubercules. Head with 4 pairs of trichomes, all long and simple. Thoracic trichomes in 6 pairs (3 anterodorsally, 2 anterolaterally, and 1 posterolaterally), all long and simple. Antennal sheath smooth. Gill ( Fig. 11 A) with 8 filaments, arranged (2 + 1) + (1 + 2) + 2 from dorsal to ventral (sometimes dorsal triplet composed of 3 filaments arising at same level as primary stalk); length of stalk of dorsal triplet ca. 0.60 x as long as that of middle triplet, secondary stalk ca. 1.36 x length of primary stalk in middle triplet, length of stalk of ventralmost filaments ca. 0.5 x shorter than total length of middle triplet, ventralmost filaments ca. 1.2 x thicker than all other filaments, which are subequal in thickness; all filaments directed forward, with numerous transverse ridges. Abdomen. Tergum I with 1 long seta on each side; tergum II with 1 long, simple seta and 5 short setae on each side. Terga III and IV each with 4 hooked spines directed forward and 1 short, spinous seta on each side. Terga VI–VIII each with transverse row of spine combs directed caudad on each side. Tergum IX with pair of terminal hooks, triangular in shape, each with smooth outer margin. Sternum IV with 2 simple hooks and few minute setae on each side; sternum V with pair of bifid hooks on each side; sterna VI and VII each with pair of inner bifid and outer simple hooks on each side; last segment with 3 grapnel-like hooklets on each side. Cocoon. Wall-pocket shaped, densely woven, somewhat extended ventrolaterally, produced as short bulge anterodorsally.

Mature larva (in Carnoy’s fixative). Body length 5.8–6.1 mm. Body yellow with grayish brown transverse band on thoracic segment I, and faint reddish brown band on each of abdominal segments V and VI. Head capsule yellow, slightly darkened along posterior border, with distinct positive spots. Antenna consisting of 3 articles and apical sensillum, longer than stem of labral fan by 1/2 length of distal article; proportional lengths of 3 articles from proximal to distal 1.0: 0.9: 1.0. Labral fan with 47 or 48 primary rays. Mandible with comb-teeth decreasing in size from 1st to 3rd; mandibular sensillum consisting of 1 large and 1 small tooth. Hypostoma with 9 apical teeth; median tooth longest, followed by lateral teeth and sublateral teeth; hypostomal setae 4 per side. Postgenal cleft ( Fig. 9 A) lanceolate, pointed apically, 2.1–2.3 x as long as postgenal bridge. Thoracic cuticle and abdominal cuticle of segments I–IV bare, segments V–VIII typically moderately covered with minute, mostly unbranched setae (rarely 2 branches), or sometimes bare; last segment moderately covered with colorless setae on each side of anal sclerite. Ventral tubercles present. Rectal papilla compound, each of 3 lobes with 8–10 finger-like secondary lobules. Anal sclerite X-shaped, with anterior arm ca. 0.9 x as long as posterior arm. Accessory sclerite absent. Posterior circlet with about 72 rows of 12–14 hooklets per row.

Chromosomes. We analyzed the chromosomes of 322 larvae from 36 sites. The polytene chromosomes stained faintly in all populations, and the centromere regions were condensed. Five of the six chromosome arms had the standard banding sequence, whereas the long arm of chromosome II was fixed for IIL-4 (Fig. 5A). Four unique floating inversions were found: IS-1, IS-2, IS-6 (Fig. 2A), and IIIL-1 (Fig. 6A). B chromosomes occurred in two larvae at site 8. Inversion IIIL-1 was in Hardy-Weinberg equilibrium in three populations: site 4 (χ 2 = 0.34, P> 0.05), site 8 (χ 2 = 0.04, P> 0.05), and site 35 (χ 2 = 0.49, P> 0.05).

Bionomics: Larvae and pupae typically were found on fallen leaves and trailing grasses, rarely on stones or artificial substrates (e.g., plastic) in streams ranging in width from 0.2 to 10.0 m at altitudes from 250 to 1,615 m. They were collected commonly from slow (0.01–0.8 m /s, mean 0.3 m /s), sandy streams with gravels, mostly in northern Thailand ( Table 3 ).

Remarks: Abdominal setae of larvae, which are of taxonomic value in the subgenus Gomphostilbia , are apparently absent in some high-altitude populations (sites 6 and 8) of S. asakoae . A short anterodorsal projection is present on the cocoon in these high-elevation populations (sites 4, 6, and 8); however, we cannot rule out the possibility that the pupae belong to S. inthanonense . The banding sequence in our material matched that in the photocomplement of S. asakoae presented by Kuvangkadilok et al. (2003) and Phasuk (2006) and described by Phasuk et al. (2005).

Figures

FIGURE 9. Postgenal clefts of larvae of 10 cytoforms of the Simulium ceylonicum species group in Thailand. (A) S. asakoae, (B) S. curtatum n. sp., (C) S. nr. asakoae 2, (D) S. nr. asakoae 3, (E) S. nr. asakoae 4, (F) S. sheilae, (G) S. trangense n. sp., (H) S. doisaketense n. sp., (I) S. nr. sheilae 3, and (J) S. inthanonense. Scale bar = 0.1 mm.

FIGURE 11. Gill filaments of 10 cytoforms of the Simulium ceylonicum species group in Thailand. (A) S. asakoae, (B) S. curtatum n. sp., (C) S. nr. asakoae 2, (D) S. nr. asakoae 3, (E) S. nr. asakoae 4, (F) S. sheilae, (G) S. trangense n. sp., (H) S. doisaketense n. sp., (I) S. nr. sheilae 3, and (J) S. inthanonense. Scale bar = 0.1 mm.