Simulium (Hebridosimulium) pankumuense 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 : 39-44

Simulium (Hebridosimulium) pankumuense Craig , n. sp.

( Figs. 1c , 5c , 7c , 8c , 9d , 11d , 13d , 16d , 18d , 20d )

Types

Holotype. Adult : double-pinned reared male, dried from alcohol. Label data – " S. (H.) pankumuense , Vanuatu, Malekula, Pankumu River, S16.27629º E167.63687º, alt. 15 m, 2.ix.2004. Coll. D. A. & R. Craig. HOLOTYPE. No. 16608”. ( BPBM). Pupal exuviae and cocoon as subsidiary material on point . Paratypes. Adults: double pinned; 2 reared males, 3 females; pupal exuviae and cocoons as subsidiary material on points. Label data – as for Holotype, but with ‘PARATYPE’. Alcohol material: last-instar larvae, pupal exuviae, and reared adults (male and female). Label data – as for Holotype, but with ‘PARATYPE’. (larvae, pupae, adults; BPBM, DAC, LCNZ, ROM) .

Diagnosis

Pupa: cuticular granules absent, petioles of gills elongate. Larva: labral fan stalk clear; head markedly pale anteriorly, darker posteriorly, head-spot pattern mainly negative; genal cleft arrowhead shaped, median and lateral hypostomal teeth well developed; abdominal dorsolateral tubercles present, abdominal posterior circlet directed ventrally.

Description

Adult female (based on 6 reared specimens in alcohol). Body: overall dark brown, head blackish brown, thorax dark brown, abdomen blackish brown; total length 2.3–2.5 mm. Head ( Fig. 1c ): width 0.75–0.79 mm; depth 0.48–0.50 mm; postocciput black, vestiture of dense, black hairs; frons vestiture of smaller fine pale hairs and longer sparser black hairs; frons-head ratio (narrowest width of frons: greatest width of head) 1.0:6.0. Eye: interocular distance 0.13 mm; ommatidia 0.015 mm in diameter; ca. 35 rows across and down at mid eye. Clypeus: 0.21–0.23 mm wide; concolourous with frons; vestiture of dense fine pale hairs and long black hairs ventrally. Antenna: length 0.39–0.41 mm; flagellomeres pale yellow, scape and pedicel markedly pale. Mouthparts: relatively large, 0.4 length of head depth; mandible with 24 inner teeth; lacinia with 11 inner teeth and 13 outer teeth; maxillary palpus with all articles evenly dark brown, proportional length of 3rd, 4th, and 5th articles 1.0:0.9:1.2; sensory vesicle small and spherical, ca. 0.3 times width of 3rd article, opening 0.25 times as wide as vesicle. Thorax: length 1.1–1.3 mm; width 0.83–0.85 mm; postpronotal lobes markedly paler than scutum; scutum evenly dark brown medially, with 2 indistinct lateral vittae in alcohol specimens, vestiture of dense, very fine pale hairs; scutellum more or less concolourous with scutum, vestiture of long black hairs and pale hairs laterally, markedly obtuse; postnotum concolourous with scutum; pleuron evenly dark brown; pleural membrane slightly paler with fine sparse hairs. Wing: length 2.1–2.3 mm; width 1.0– 1.1 mm. Legs: as for male, but darker. Abdomen: overall black; vestiture of dense silver hairs, long laterally, with few black hairs; basal scale black with pale hairs. Genitalia ( Fig. 5c ): similar to those of S. johnfrumi with, however, anterior margin of medial region of sternite VIII not angulate and darker; genital fork stem short and substantial, anteriorly directed apodeme of lateral arm truncated and flattened, spermatheca ovoid, markedly dark.

Adult male (based on 5 reared specimens in alcohol). Body: relatively small, total length 1.9–2.3 mm. Head: width 0.79–8.6 mm; depth 0.57–0.61 mm. Eyes: upper ommatidia dark orange, large, 0.027 mm in diameter, ca. 14 across and down; lower ommatidia brown, 0.017 mm in diameter, ca. 26 across and 27 down. Clypeus: black, pruinose 0.2 times as wide as head; sparse short black hairs laterally. Antenna: total length 0.49–0.54 mm; flagellomeres light yellow, proximal one slightly darker and longer than remainder, scape, pedicel markedly paler. Mouthparts: short, length 0.25 times head depth; mandibles insubstantial, finely tapered with apical hairs; lacinia broad basally, finely tapered apically with terminal hairs, some tooth-like; maxillary palpus dark, 0.45 mm long, proportional lengths of 3rd, 4th, and 5th articles 1.0:0.9:1.6, third article distinctly hairy, sensory vesicle spherical, occupying 0.4 times width of article, opening 0.25 times width of vesicle. Thorax: length 0.8–1.0 mm; width 0.8–0.9 mm; broadest anteriorly; postpronotal lobes slightly paler than evenly medium brown scutum, vestiture of short pale hairs, dense posteriorly; scutellum lighter than scutum, apical angle distinctly obtuse; vestiture of markedly long stiff black hairs, interspersed with paler hairs; postnotum concolourous with scutum: pleuron concolourous with scutum, membrane paler with markedly fine pale hairs. Wing: 1.8–2.0 mm in length, 0.8–1.0 mm at maximum width. Legs: markedly bicolourous; foreleg with coxa, trochanter, femur, and proximal half of tibia pale, remainder black; mid leg coxa brown, trochanter, and proximal half of femur pale, distal half brown, remainder of leg black; hind leg coxa brown, trochanter pale, femur light brown, proximal 2/3 of tibia pale and remainder black, middle portion of tarsus pale, remainder black; pretarsal claws with ca. 21 grappling hooks dorsally. Abdomen: anteriorly yellowish, remainder brownish black, vestiture of dense fine pale hairs; basal scale with markedly long, pale yellowish hairs. Genitalia: essentially as for S. johnfrumi (e.g., Fig. 6b ), ventral plate keel enlarged and flattened apically, ventral plate markedly angulate laterally.

Pupa (based on 12 specimens). Body length, male and female, 2.9 mm in length; dorsal cuticle lacking larger rounded, raised granules, minute granules adjacent to gill base and on posterior thorax, otherwise smooth ( Fig. 8c ). Gill ( Fig. 9d ): dorsal filaments 0.4 times length of longer ventral filaments; branching pattern (2+2)+2)+2+1+1; dorsal filaments with elongated petioles; filaments not markedly tapered, light brown; annulations distinct; maximum length 1.7 mm. Cocoon: not flared laterally, anterior collar distinct, but not markedly so ( Fig. 7c ).

Larva (based on 8 mature last-instar larvae). Body ( Fig.11d ): total length 5.3–5.7 mm, males smaller than females; females mottled light to dark grayish brown, with paler intersegmental regions, males lighter gray and more yellowish orange; prothorax gray, mesothorax pale, metathorax orange, more so in males. Head ( Fig. 13d ): anterior apotome markedly pale; width 0.57–0.58 mm; length 0.65–0.71 mm; distances between antennal bases 0.31–0.38 mm; lateral margins of head slightly convex; ecdysial lines straight, markedly diverged posteriorly, very broadly rounded at maximum width; posterior apotome mottled brown; medial head spots essentially neutral to slightly positive, lateral head spots markedly negative laterally; posterior genae darker brown than posterior apotome, remainder of genae pale; cervical sclerites distinctly separate from evenly curved apotome posterior edge and non-extended postocciput. Antenna: total length 0.35–0.44 mm; distal article 0.25 times as long as basal articles, extended just beyond labral fan stalk; basal article pale, medial and distal articles light brown; distance between antennal bases 0.35mm. Labral fan: stalk markedly clear, posterobasal notch and anterior palatal bar not markedly developed; 38–40 fine pale rays, finely tapered, 0.85 mm in length, 7–9 rays less substantial; microtrichia markedly obvious, subequal in length to ray width, distinctive pattern with 6 or 7 slightly shorter microtrichia between those more substantial. Postgenal cleft ( Fig. 16d ): arrowhead shaped with evenly convex sides, 1.5 times as deep as wide. Postgenal bridge: 0.6 times length of cleft depth; genae pale, posteroventral elongate muscle spot negative. Hypostoma ( Fig. 18d ): ratio 5.2; overall shape domed; median tooth prominent, longer than sharp deltoid lateral teeth; sublateral teeth small but distinct; paralateral teeth absent; 4 or 5 markedly small, low, lateral serrations; only 8 or 9 hypostomal setae per side. Mandible ( Fig. 20d ): all apical teeth well developed; 5 or 6 spinous teeth, gap essentially absent; serration and sensillum cone-shaped, markedly developed; blade smooth, slightly convex. Abdomen: thorax marginally wider than head, anterior abdomen (segments I– IV) narrower, gradually expanding to maximum width at segments VI–VII; expanded gradually to maximum width, markedly callipygous; dorsolateral tubercles present: single diagonal band of muscle markedly pigmented. Posterior circlet: markedly directed ventrally; 134 rows of hooks; 20–21 hooks per row (total ca. 2,700).

Additional material examined

Malekula, Pankumu River , S16.27629º E167.63687º, alt. 15 m. 2.ix.2004. Coll. D. A. & R. Craig (larvae, pupae, reared adults; DAC). Orap River, S15.98335° E167.32998°, alt. 5m. 1.ix.2004. Coll. D. A. & R. Craig (immature larvae; DAC) .

Etymology

Named for the type locality, the Pankumu River , east-central Malekula Island, Vanuatu .

Distribution VANUATU: Malekula.

Comments

A tuberculate Vanuatuan species, S. pankumu is known mainly from a single location, the sizable Pankumu River ( Fig. 23f ). Larvae and pupae were on trailing grass leaves and roots in moderately fast flow (1.1 m / sec). The Orap River, so called, is more of a stream and the few larvae therein were immature and assigned to S. pankumuense , mainly on the basis of abdominal characteristics. Larvae are markedly callipygous and the posterior circlet is directed more ventrally than for other larvae (rf. Fig. 11d ), an orientation previously observed in African simuliid larvae that are phoretic (Crosskey 1990). The number of hooks on the posterior circlet is thought to correlate to water velocity of the habitat (Crosskey 1990, Palmer and Craig 2000); however, S. pankumuense with its relatively low number of hooks, does not show a correlation with the relatively high velocity of the habitat.

Mouthparts of the female adult are moderately substantial and the number of mandibular and lacinial teeth is similar to that of species known to bite, namely S. laciniatum and S. lucyae . The sensory vesicle on the maxillary palpus is, however, small. There are no records of simuliids biting on Malekula, and locals are not aware of biting flies fitting the description of female black flies. Cheesman collected simuliids from Malekula and nearby Achin Island, but makes no mention of any biting simuliids in the vicinity ( Cheesman 1933, 1957a, 1960).

Closely related to S. johnfrumi in genitalic characters, S. pankumuense differs from that and other tuberculate species in lacking pupal cuticular granules ( Fig. 8 ). In the Pankumu River, S. pankumuense larvae occur with those of S. jolyi .

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 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.