Simulium (Hebridosimulium) spiroi Craig, Currie & Hunter, 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 : 79-80

Simulium (Hebridosimulium) spiroi Craig, Currie & Hunter , n. sp.

( Figs. 10f , 11n , 14f , 17f , 19f , 21f )

Types

Holotype. Larva : last instar in alcohol. Label data – “ Simulium (Hebridosimulium) spiroi . VANUATU, Malekula, Wesso River Cascade. S16.37880° E167.76663°, alt. 34 m, 2.ix.2004. Coll. D. A. & R. Craig. HOLOTYPE. No. 16606” ( BPBM) . Paratypes. Larvae: last instars in alcohol ( BPBM, DAC, ROM). Penultimate and earlier instar in alcohol ( BPBM, DAC, LCNZ, ROM). Label data as for Holotype, but with “ PARATYPE ” .

Diagnosis

Larva: head evenly dark brown; body markedly lighter gray, posterolateral diagonal gray stripes on sixth segment. Pupa: gill petioles short.

Description

Adult female. Unknown.

Adult male. Unknown.

Pupa (based on pharate material). Thorax: cuticle with numerous granules present. Gill ( Fig. 10f ): petioles short and thick; branching pattern (2+2) +2 +2 +2, occasionally (2+2) +2 +2 +1+1; filaments noticeably tapered; maximum length 1.4–1.8 mm.

Larva (based on 6 mature last-instar larvae). Body ( Fig. 11n ): total length 6.5–6.9 mm; females evenly pale grey dorsally, males pale yellowish-grey with paler intersegmental regions, difference not marked. Head ( Fig. 14f ): both sexes evenly dark brown including labral fan stalks; dorsal head spots negative, but not distinct; sockets of trichoid sensilla pair 5 and 6 markedly pale, darkly aureolate; width 0.74–0.82 mm; length 0.79–0.82 mm; distance between antennal bases 0.39–0.41 mm; ecdysial lines slightly convex, diverged markedly posteriorly, broadly rounded at maximum width; lateral margins of head convex, especially posteriorly; posterior edge of cephalic apotome slightly emarginate; postocciput with fine medial extension. Antenna: total length 0.36 mm; distal article 0.22 times as long as basal articles; markedly shorter than labral fan stalk; distal article dark brown, remainder pale. Labral fan: stalk heavily pigmented anteriorly, anterior palatal bar noticeable, but not markedly protrusive; 39–43 substantial rays, 0.84 mm in length, medial rays 0.02 mm in width, 8–10 posterolateral rays finer than others; microtrichia substantial, subequal in length to ray width, pattern distinct, with 4 or 5 shorter microtrichia between those longer. Postgenal cleft ( Fig. 17f ): markedly arrowhead shaped; posterior edges parallel, sharply tapered at mid-length to pointed apex, 1.5 times longer than width; postgenal bridge subequal in length to cleft depth; genae evenly pigmented dark brown, paler around stemmata; ventrolateral elongate muscle spots partially negative. Hypostoma ( Fig. 19f ): ratio 4.2; median tooth and lateral teeth prominent, latter slightly scalloped medially occasionally directed more laterally, sublateral teeth distinct; paralateral teeth and lateral serrations not obvious; 11–13 substantial hypostomal setae per side. Mandible ( Fig. 21f ): apical tooth markedly prominent, preapical and subapical teeth not so; spinous teeth small, gap distinct; serration and sensillum robust and fused basally; blade region smooth and slightly convex. Abdomen: thorax and anterior abdominal segments subequal in width, expanded gradually to maximum width, callipygous posteroventrally; colour pale laterally and ventrally, marked diagonal gray banding laterally on sixth segment; posterodorsal tubercles absent. Posterior circlet: directed ventrally; 170–175 rows of hooks, 29–35 hooks per row (total ca. 5,500).

Additional material examined

Last and earlier instar larvae in Carnoy’s fixative. Label data – as for types (larvae; DAC) .

Etymology Dedicated to the memory of Mike “Spiro” Spironello.

Distribution VANUATU: Malekula.

Comments

Known only from the type locality ( Fig. 23c ) on Malekula, larvae of S. spiroi appear to be habitat specialists. They were taken in moderately large numbers only from smooth travertine substrate in fast flow (1.3 m /s; Table 1). However, larvae exhibit little structural adaptation to that habitat beyond the scarcely steatopygous abdomen and a relatively large number of hooks in the posterior circlet. Superficially similar to S. adsonense in possessing a darkly pigmented larval head and lighter coloured body (rf. Figs. 11m, n ), S. spiroi differs in the structure of the pupal gill filaments (cf. Figs. 10e, f ), size and shape of the postgenal cleft, and markedly larger hypostomal teeth. Although grouped together with S. adsonense from Malekula, we are of the opinion that the body shape and the head colour in both species may be independent adaptations to full sunlight in shallow, fast water. Dark pigmentation of larval heads is a known adaptation to full insolation ( Craig 1997) and most likely is protective against UV light ( Donahue & Schindler 1998). Preliminary CO1 mitochondrial DNA analysis indicates that S. spiroi and S. adsonense are not genetically close (A. Cywinska, unpublished data).

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 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 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.