Simulium (Hebridosimulium) callipygium Craig, 2006

Craig, Douglas A., Currie, Douglas C., Hunter, Fiona F. & Spironello, Mike, 2006, A taxonomic revision of the southwestern Pacific subgenus Hebridosimulium (Diptera: Simuliidae: Simulium), Zootaxa 1380 (1), pp. 1-90 : 18-24

Simulium (Hebridosimulium) callipygium Craig n. sp.

Figs (1a, 5a, 6a, 7a, 8a, 9a, 11a, 12a, 13a, 16a, 18a, 20a)

Types

Holotype. Larva : mature last instar in alcohol. Label data – “ Simulium (Hebridosimulium) callipygium . VANUATU, Santo, Sarakata R, UNELCO Hydrostation, S15.43147° E167.11448°, alt. 25 m, 26.viii.2004. Coll. D. A. & R. Craig. HOLOTYPE No. 16605” ( BPBM) . Paratypes. Adults: two double-pinned reared males, dried from alcohol, with pupal exuviae on point. A third with cleared head, genitalia, thorax, pupal exuviae, and cocoon in glycerine vial. Label data as above. ( BPBM). Larvae: mature last and penultimate instars. Label data – as for Holotype, but with “ PARATYPE ” ( DAC, BPBM, LCNZ, ROM). Santo , Nasori / Neavu River, S15.58157° E167.02709°, alt. 43m, 15.ix.2004. Coll. D. A. & R. Craig ( DAC) .

Diagnosis

Relatively small species. Pupa: cuticle pale brown with sparse fine granules; gill filaments tapered evenly. Larva: anterior cephalic apotome markedly pale, darker

posteriorly; hypostomal teeth distinct; abdomen markedly callipygous, posterodorsal tubercles absent, ventral tubercles directed laterally, posterior circlet directed ventrally.

Description

Adult female (based on 2 reared females in alcohol). Body ( Fig. 1a ): head, thorax, and abdomen concolourous, dark brown; total length 1.9 mm. Head: width 0.65 mm; depth 0.51 mm; postocciput very dark brown, vestiture of distinct black hairs; frons concolourous; frons-head ratio (narrowest width of frons: greatest width of head) 1.0:4.1. Eyes: interocular distance 0.14 mm; ommatidia 0.015 mm in diameter; ca. 30 rows across and 40 down at mid-eye. Clypeus: 0.16 mm wide; concolourous with frons; vestiture of dense black and pale hairs. Antenna: length 0.39 mm; flagellomeres very pale brown; scape, pedicel lighter. Mouthparts: 0.3 length of head depth; mandible well developed with 21 finer adoral teeth decreased in size proximally; lacinia with 10 inner teeth and 14 outer teeth; maxillary palpus markedly short, total length 0.41 mm, uniformly brown, proportional length of 3rd, 4th, and 5th articles 1:1:1.2; sensory vesicle spherical, markedly small, ca. 0.2 times width of 3rd article, opening 0.5 times width of vesicle. Thorax: length 0.97 mm, width 0.7 mm; postpronotal lobes and scutum evenly medium brown, vittae not distinct, vestiture of sparse, very fine pale hairs; scutellum pale, apical angle 120°, vestiture of very sparse substantial black hairs and pale hairs laterally; postnotum concolourous with scutum; pleuron and pleural membrane slightly lighter than scutum. Wing: length 1.8 mm; maximum width 0.9 mm. Legs: fore leg; coxa, trochanter, femur, and most of tibia pale yellow, remainder blackish brown; mid leg, as for fore leg, but femur darker; hind leg as for mid leg except femur darker and tarsus yellow, calcipala and remainder black. Abdomen: overall blackish brown, vestiture of evenly distributed short pale hairs; basal scale brownish black, with fringe of pale hairs. Genitalia ( Fig. 5a ): sternite VIII deeply indented, broader anteriorly, median region pale; hypogynial valves lightly pigmented with sparse vestiture; medial margins slightly concave, apical membranous extension simple and broad; genital fork substantial with stem short, lateral arms pigmented, anteriorly directed apodeme pointed; anal lobes with anterolateral apodeme and anteromedian concavity markedly developed, rounded posteriorly; cercus broad; spermatheca slightly ovoid.

Adult male (based on 2 reared specimens in alcohol). Body: overall dark brown to black; total length 2.1 mm. Head: width 0.77 mm; depth 0.55 mm. Eyes: division between upper and lower ommatidia distinct; upper ommatidia dark orange, large, 0.057 mm in diameter, ca. 10 across and 15 down; lower ommatidia brown, 0.019 mm in diameter, ca. 21 across and 30 down. Clypeus: dark brown, pruinose, 0.2 times as wide as head; vestiture of medium and short hairs laterally. Antenna: total length 0.38 mm; flagellomeres light yellow, scape, pedicel, and base of first article slightly darker; first flagellomere slightly longer than remainder. Mouthparts: short, 0.2 length of head depth; mandibles feebly developed, finely tapered with apical hairs; lacinia broad basally, finely tapered apically with terminal hairs, some tooth-like; maxillary palpus dark, 0.51 mm long, proportional lengths of 3rd, 4th, and 5th articles 1:1.4:1.6, third article hairy, sensory vesicle barrel shaped, occupying 0.33 times width of article, opening 0.33 times width of vesicle. Thorax: length 0.8 mm; width 0.77 mm; broadest anteriorly; postpronotal lobes pale; scutum evenly blackish brown; vestiture of short pale hairs; scutellum slightly paler than scutum, apical angle distinctly obtuse; vestiture of long black hairs laterally, interspersed with paler hairs; postnotum concolourous with scutum: pleuron concolourous with scutum. Wing: 1.7 mm in length, 0.9 mm at maximum width. Legs: markedly bicolourous: tarsal and tibial apices dark brownish black, remainder yellow; pretarsal claws with ca. 17 grappling hooks dorsally. Abdomen: anteriorly pale, remainder brownish black, vestiture of dense fine pale hairs; basal scale black with long, pale yellow hairs. Genitalia ( Fig. 6a ): gonocoxa narrow, 1.7 times longer than basal width, basal pigmented band narrow, vestiture of markedly substantial hairs, anterolateral apodeme well developed; gonostyle approximately 3 times longer than basal width, subequal in length to gonocoxite, mediobasal strengthening ridge not marked; ventral plate similar to that of S. laciniatum , small, sloped laterally, proximal arms distinctly curved medially and finely tapered; median keel flattened apically in ventral view, vestiture of small, evenly spaced hairs; dorsal and median sclerite as for S. johnfrumi . Cerci: distinct.

Pupa (based on 10 specimens). Body length: female 2.1–2.9 mm; male 2.2–2.4 mm. Gill ( Fig. 9a ): dark brown, finally tapered, distinctly annulated; maximum length, 1.6 mm; dorsal gill filaments subequal in length; petioles generally subequal in length, middle petiole occasionally longer, filament branching pattern 2+2+2+2+1+1. Head and anterior thorax with sporadically distributed, sparse, brown granules ( Fig. 8a ); thoracic trichomes elongate. Cocoon ( Fig. 7a ): base markedly flared laterally, anterior margin not markedly raised above substrate, both characters variable.

Larva (based on numerous mature last-instar larvae). Body ( Fig. 11a ): relatively small species; total length, female 4.8–5.2 mm, male 3.9–4.6 mm; females grayish, males more yellowish, thorax evenly pigmented, anterior abdominal segments pigmented with intersegmental areas pale, producing marked banded appearance, posterior abdominal segments evenly pigmented. Head ( Fig. 13a ): anterior frontoclypeal apotome markedly pale; labral fan stalks lightly pigmented; female head spot pattern slightly negative, indistinct in darker individuals, ecdysial lines pale and distinct; width 0.49–0.55 mm, length 0.55–0.58 mm; distance between antennal bases 0.28–0.31 mm; male head overall paler than that of female, with positive head spots in Eiffel Tower configuration, distinct in some specimens, width 0.47–0.52 mm, length 0.51–0.66 mm; distance between antennal bases 0.28–0.30 mm; lateral margins of head evenly convex; ecdysial lines slightly concave, broadly rounded at maximum width; posterior edge of apotome not eroded; cervical sclerites distinct; postocciput not extended medially. Antenna: total length 0.36 mm; distal article 0.35 times as long as basal articles, extended slightly beyond labral fan stalk; distal article and basal portion of medial article brown, distal portion of basal article pale, remainder brown. Labral fan: stalk light brown, anterior palatal bar not markedly protruded anteromedially; 38–43 rays, 0.70 mm in length, 9–11 rays less substantial; microtrichia 0.75 times shorter than ray width, pattern of 6 smaller microtrichia between larger ones. Postgenal cleft ( Fig. 16a ): V-shaped, 1.6 times deeper than wide with slightly convex edges; posteroventrally elongate muscle spots light brown. Postgenal bridge: 0.25 times as long as cleft depth; genae and postgenae light brown. Hypostoma ( Fig. 18a ): ratio 4.3; overall shape domed; median tooth prominent, lateral teeth directed laterally, not expanded basally, medial sublateral teeth larger, others smaller; paralateral teeth not apparent; lateral serrations poorly developed; 7–9 hypostomal setae per side. Mandible ( Fig. 20a ): preapical and apical teeth well developed, subapical teeth less so; 7 spinous teeth in distinct row; spinous teeth gap minor; serration and sensillum broadly based; blade region smooth and straight. Abdomen ( Fig. 11a ): anterior abdomen narrower than thorax, expanded gradually posteriorly to 5th abdominal segment, then expanded further laterally ( Fig. 12a ), callipygous posteroventrally; ventral tubercles directed laterally; posterodorsal tubercles absent. Posterior circlet: directed ventrally; 130–135 rows of hooks; 19–23 hooks per row (total ca. 2,700).

Additional material examined

Banks Islands. Vanua Lava , Tahiti River. S13.84454° E167.52212°, alt. 12.5 m, 28.viii.2004. Coll. D. & R. Craig. (larvae. DAC. BPBM) . Nebeseu (?) Str., S13.78245° E167.53139°, alt. 5 m. 29.viii.2004. Coll. D. A. & R. Craig. (larva. DAC) . Santo. Sarakata River , UNELCO Hydrostation. S15.43147° E167.11448°, alt. 25 m, 26.viii.2004. Coll. D. A. & R. Craig. (larvae. DAC) . Millennium Cave Stream, S15.45547° E167.07158°, alt. 192 m. 13.ix.2004. Coll. D. & R. Craig (larvae, pupae. DAC) . Tafwakar Stream , tributary Sarakata River. S15.43839° E167.07425°, alt. 126m. 13.ix.2004. Coll. D. A. & R. Craig (larvae. DAC) . Upper cascade, tributary Sarakata River. S15.43224° E167.07600°, alt. 217 m, 13.ix.2004. Coll. D. A. & R. Craig (larvae. DAC) . Nasori / Neavu River , S15.58157° E167.02709°, alt. 43m, 15.ix.2004. Coll. D. A. & R. Craig. Tributary Rotal River , S15.26410° E167.09851°, alt. 165m, 17.ix.2004. Coll. D. A. & R. Craig (larvae. DAC) .

Etymology Named in reference to the elegant shape of the larval posterior abdomen.

Distribution VANUATU: Vanua Lava (Banks Islands); Santo.

Comments

This species is distributed widely, but in low numbers in streams and rivers ( Fig. 23d ) in Vanua Lava (Banks Islands) and Santo ( Fig 23a ). In dorsal view ( Fig. 12a ), the callipygous posterior abdomen is reminiscent of the amphora shape exhibited by the cascade-dwelling larvae of Inseliellum in Tahiti. Craig and Joy (2000) speculated that the condition is an adaptation for reducing drag in fast water. Velocities recorded (0.8–1.3 m /s) for S. callipygium larvae are in the typical range for Hebridosimulium (see Table 1). Palmer and Craig (2000) suggested a correlation between the number of hooks adorning the posterior circlet and velocity of the habitat, namely that high velocity habitats have larvae with a greater number of hooks. Accordingly, S. callipygium larvae, with the lowest number (2700) of hooks for any larva in Hebridosimulium , do not support this hypothesis.

Simulium callipygium may well be a complex of closely related species. While all larval specimens examined possess, in general, similar morphological characters, there is considerable variation in pupal gill branching pattern and larval head spot pattern.

Larvae from the Banks Islands, while assigned to S. callipygium , are problematic in that the material was all prepenultimate larvae. They are, however, markedly callipygous and have the circlet of hooks directed ventrally. Further examination of additional material may show these to be a separate species.

Figures

FIGURE 1. Typical examples of Hebridosimulium. a. Female Simulium callipygium (Santo). b. Head of male S. laciniatum (Fiji). c. Head of female S. pankumuense (Malekula). Scale bar = 0.5 mm.

FIGURE 5. Hebridosimulium. Female genitalia. a–d callipygium species group, e–j steatopygium species group. e. Adapted from Craig (1987). Scale bar = 0.1 mm. Abbreviations: an lb — anal lobe; cerc — cercus; gen fk — genital fork; hyp vlv — hypogynial valve; spmth — spermatheca.

FIGURE 6. Hebridosimulium. Male genitalia. a–b callipygium species group, c–f steatopygium species group. e. Paramere spines shown in detail. Scale bar = 0.1 mm. Abbreviations: adg mbm — aedeagal membrane; d plt — dorsal plate; goncx — gonocoxite; gonst — gonostyle; m scl — median sclerite; pm th — paramere teeth; v plt — ventral plate.

FIGURE 7. Hebridosimulium. Pupal cocoons. a & b. Lateral and dorsal views. c & d. Lateral view. Scale bar = 0.5 mm.

FIGURE 8. Hebridosimulium. Pupal thoracic cuticle. Scale bar = 0.1 mm.

FIGURE 9. Pupal gill filaments of Hebridosimulium species. Scale bar = 0.2 mm.

FIGURE 11. Left lateral views of Hebridosimulium species larvae. Last-instar larvae, except l & n, which are penultimate. Arrowheads indicate dorsal tubercles. Scale bar = 1.0 mm.

FIGURE 12. Posterior abdomens of larvae of Hebridosimulium. Dorsal views. Scale bar = 0.5 mm.

FIGURE 13. Dorsal views of larval heads of Hebridosimulium species. a–e. callipygium species group, f–h. part of steatopygium species group. Last instars, except f & h, which are penultimate instars. Arrows (b & e) indicate anterior palatal bar. Scale bar = 0.2 mm.

FIGURE 16. Postgenal clefts and hypostoma of larvae of Hebridosimulium species. a–e callipygium species group, d–h steatopygium species group. Last instar, except b, which is penultimate. Scale bar = 0.1 mm.

FIGURE 18. Hypostomal teeth of larvae of Hebridosimulium species. Last instar. Scale bar = 0.05 mm.

FIGURE 20. Mandibular teeth of larvae of Hebridosimulium species. a–e callipygium species group, f–h steatopygium species group. Last instar, except b, which is penultimate. Arrow (e) indicates the blade region; asterisk the spinous teeth gap. Scale bar = 0.025 mm.

FIGURE 23. Habitats of larvae of Hebridosimulium species, Vanuatu. a. Santo, Sarakata River, UNELCO Hydro Station. Type locality of S. callipygium. Note limestone substrate. b. Santo, Upper Sarakata River, Millennium Cave region. Typical habitat of S. callipygium and S. subparadisium. c. Malekula, Wesso River, downstream of cascade. Type locality of S. spiroi. Note travertine substrate. d. Banks Islands, Vanua Lava, Tahiti River. Type locality of S. banksi and S. undulatum. e. Tanna, stream south of Bethel. Type locality of S. johnfrumi. f. Malekula, Pankumu River. Type locality of S. pankumuense. g. Efate, Ewor River, La Cressionnière. Type locality of S. tuberculum. Note the travertine terraces.