Simulium (Hebridosimulium) supercilium 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 : 72-74

Simulium (Hebridosimulium) supercilium Craig. n. sp.

( Figs. 10d , 11k , 14c , 15c , 17c , 19c , 21c )

Types

Holotype. Larva : last-instar male, in alcohol. Label data – “ Simulium (Hebridosimulium) supercilium . Vanuatu, Pentecost, Warbot River. S15.96069° E168.19755°, alt. 25m. 22.ix.2004. Coll. D. A. & R. Craig. HOLOTYPE. No. 16612” ( BPBM) . Paratypes. Larva and pupae: in alcohol. Label data – as for Holotype, but with “ PARATYPE ”. ( BPBM, DAC, LCNZ, ROM) .

Diagnosis

Smaller species. Pupa: thoracic cuticle with sparse, coarse granules. Cocoon: less shoe shaped than other species; anterior collar not raised markedly above substrate; base not flared laterally. Larva: posterior abdomen slightly steatopygous; dorsolateral tubercles absent; head-spot pattern not markedly distinct, males with Eiffel Tower spot pattern, females darker and pattern ill defined; eyebrow stripe dorsal of ocelli marked, ending in distinct small dark head spot; postgenal bridge markedly small, postgenal cleft deep; fewer sublateral setae than in other species of Hebridosimulium .

Description

Adult female. Unknown.

Adult male. Unknown.

Pupa (based on 2 mature specimens). Length 2.9–3.3 mm. Thoracic granules normal. Cocoon covering pupa, base not flared laterally, shoe-shaped. Gills: branching pattern (2+2)+2+2+1+1, maximum length 1.3 mm, petioles short, but variable. ( Fig. 10d ); annulations fine.

Larva (based on 5 mature last-instar larvae). Body ( Fig. 11k ): total length, male 6.1–6.2 mm; female 6.8–7.2mm; females evenly mottled grey-brown, males yellowish grey-brown; expanded gradually posteriorly, very slightly steatopygous, (essentially callipygous in earlier instars). Head ( Fig. 14c ): noticeably longer than wide; female overall medium brown, darker posteriorly, head spots lightly positive, anteromedial spots with paler nimbus, posteromedial spots with darker aureole, male head lighter in colour with head spots forming Eiffel Tower configuration; both sexes with distinct black mark anterior of eyebrow stripe, dorsal of pale ocellar area; head spot ventral of ocelli positive, as are posterolateral spots, surrounded by pale nimbus, producing distinct pattern (lateral head spots not well developed in earlier instars); male head width 0.58–0.63 mm; length 0.74 mm; distance between antennal bases 0.33 mm; female width 0.67–0.73 mm; length 0.75–0.79 mm; distance between antennal bases 0.37 mm; lateral margins of head subparallel; frontoclypeal apotome lateral margins straight, diverging evenly posteriorly, maximum width well posterior; dorsal head spots not distinct, but occasionally in Eiffel Tower configuration; small, distinct black spot anterodorsal of stemmata ( Fig. 15c ); distinct cervical sclerites separated from apotome by extension of postocciput, posterior edge of apotome not eroded. Antenna: distal and medial articles brown, remainder pale; total length 0.42 mm; distal article 0.24 times as long as basal articles, subequal in length to labral fan stalk. Labral fan: anterior palatal bar well developed; stalk lightly pigmented, 37–43 fine rays, 1.4 mm in length, 8 rays less substantial; microtrichia fine, subequal in length to ray width, pattern indistinct, with 3 or 4 slightly shorter microtrichia between longer ones. Postgenal cleft ( Fig. 17c ): deeply V-shaped. Postgenal bridge: yellow; 0.2 times as long as cleft depth; genae evenly pigmented light brown, lateral elongate muscle spots negative. Hypostoma ( Fig. 19c ): overall broadly cone-shaped; ratio 5.3; teeth array smaller and slightly protruding anteriorly; median and lateral teeth not markedly developed, latter smaller than former; sublateral teeth small; paralateral teeth not obvious; lateral serrations poorly developed; 8 or 9 hypostomal setae per side. Mandible ( Fig. 21c : preapical and subapical teeth not well developed; spinous teeth not markedly developed, space absent; serration and sensillum well developed, blade region smooth and convex. Abdomen: expanded gradually to maximum width, dorsolateral tubercles absent, slightly steatopygous posteroventrally. Posterior circlet: directed posteriorly; 160–163 rows of hooks; 23–25 hooks per row (total ca. 3,800).

Additional material examined

Pentecost, Warbot River . S15.96069° E168.19755°, alt. 25m. 22.ix.2004. Coll. D. A. & R. Craig (immature larvae; DAC) .

Etymology

Named for the distinct eyebrow-shaped mark, terminated at a black spot, dorsal to the stemmata in the larvae.

Distribution VANUATU: Pentecost.

Comments

Pentecost is little collected and future surveys of that island are warranted. The nearby island of Maewo, which is also known to support simuliids because of Cheesman’s early collections, is also in need of study. Two other Pentecost rivers (Lonpoa, Oubouen) were examined at the coast, but both lacked simuliids and other macroinvertebrates. The mountainous interior of the island will no doubt be more fruitful.

Found exclusively on trailing vegetation in fast flow ( Fig. 24d ), S. supercilium does not exhibit conspicuous adaptations to life at high velocities. Fan rays are fine in structure, the number of hooks in the posterior circlet is relatively few, and the abdomen is not markedly steatopygous. With adults unknown, the assignment of S. supercilium to the steatopygium species group is based solely on the character states of the immature stages, viz, the small number of hypostomal hairs and number of hooks in the posterior circlet. Nonetheless, S. supercilium would fit almost equally well in the callipygium species group. Does the generalized nature of this species perhaps indicate that it is a basal taxon in Hebridosimulium ?

Figures

FIGURE 10. Pupal gill filaments of Hebridosimulium species (continued). 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 14. Dorsal views of larval heads of Hebridosimulium species. steatopygium species group. Last instars, except d & f, which are penultimate instars. Scale bar = 0.2 mm.

FIGURE 15. Left lateral views of larval heads of Hebridosimulium species. Left labral fan removed for clarity. Last instars except c, which is penultimate. Scale bar = 0.2 mm.

FIGURE 17. Postgenal clefts and hypostoma of larvae of Hebridosimulium species. Last instar except b, d, & f, which are penultimate. Scale bar = 0.1 mm.

FIGURE 19. Hypostomal teeth of larvae of Hebridosimulium species. Last instar, except d & f, which are penultimate. Scale bar = 0.05 mm.

FIGURE 21. Mandibular teeth of larvae of Hebridosimulium species, steatopygium species group. Last instar, except d & f, which are penultimate. Scale bar = 0.025 mm.

FIGURE 24. Habitats of larvae of Hebridosimulium species. a–e. Vanuatu.a. Santo, Adsone River. Type locality of S. adsonense. b. Santo, upper cascade, tributary of Sarakata River. Type locality of S. paradisium. c. Efate, Mele Cascade. Type locality of S. steatopygium. Note travertine terraces. d. South Pentecost, Warbot River. Type locality of S. supercilium. e. Santo, small stream, Millennium Cave region. Typical locality of S. subparadisium. f–i. Fiji. Habitats of S. laciniatum larvae. f. Viti Levu, Abaca Village, above Vereni Falls. Type region. g. Taveuni, Wairiki, Devo Peak, looking down water slide. h. Kadavu, Kadavacoro Village, Wailea Waterfall. i. Vanu Levu, Waisala Rain Forest Reserve, Ravini River.