Simulium (Hebridosimulium) adsonense 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 : 76-78

Simulium (Hebridosimulium) adsonense Craig n. sp.

( Figs. 5j , 8f , 10e , 11m , 14e , 17e , 19e , 21e )

Types

Holotype. Adult : female, double pinned. Label data – “ Simulium (Hebridosimulium) adsonense . VANUATU, Santo, Adsone River, S15.55968° E166.96876°, alt. 59m, 15.ix.2004. Coll. D. A. & R. Craig. HOLOTYPE, #16572” ( BPBM). Genitalia in glycerine vial. Pupal cocoon and exuviae as subsidiary material on point; right gill missing . Paratypes. Alcohol material: Pupae: exuviae ( BPBM, DAC). Larvae: later instars ( BPBM, DAC, LCNZ, ROM). Label data as for Holotype, but with “ PARATYPE ” .

Diagnosis

Relatively large species. Adults: black; pleural membrane with distinct yellow hairs; legs markedly bicolourous. Pupa: cuticle medium brown with coarse granules, gill petioles essentially absent, filaments tapered markedly. Larva: head dark brown, anterior cephalic apotome medium brown; hypostomal teeth distinct; abdomen only slightly steatopygous; abdominal dorsolateral tubercles absent.

Description

Adult female (based on 1 reared specimen). Body: head, thorax and abdomen blackish brown; total length 2.6 mm. Head: width 0.85 mm; depth 0.55 mm; postocciput, vertex and frons black, vestiture of sparse, erect, black hairs; frons-head ratio (narrowest width of frons: greatest width of head) 1.0:3.4. Eye: interocular distance 0.16 mm; ommatidia 0.015 mm in diameter; ca 35 rows across and down at mid-eye. Clypeus: 0.24mm wide, concolourous with frons. Antenna: length 0.47 mm; flagellomeres blackish brown, scape and pedicel pale. Mouthparts: 0.4 length of head depth; mandible with ca. 28 fine inner teeth; lacinia with 17 inner teeth and 12 outer teeth; maxillary palpus with total length 0.45 mm, all articles evenly dark brown, proportional length of 3rd, 4th, and 5th articles 1.0:0.8:1.5; sensory vesicle elongate, ca. 0.3 times width of 3rd article, opening 0.8 times as wide as vesicle. Thorax: length 1.3 mm; width 1.1 mm; postpronotal lobes slightly paler than scutum; scutum evenly very dark brownish black, vestiture of sparse silver hairs; scutellum more or less concolourous with scutum, vestiture of long black hairs and pale hairs laterally, apical angle 125°; postnotum concolourous with scutum; pleuron evenly dark brown; pleural membrane slightly paler and with distinct yellow hairs. Wing: length 2.7 mm; width 1.1 mm. Legs: coxae pale brown; fore leg, femur brown, tibia pale proximally, remainder of leg black; mid leg femur brown medially, tibia pale proximally, remainder of leg black; hind leg as for mid leg. Abdomen: anterior light gray, remainder brownish black; vestiture of dense silver hairs, long laterally, with few black hairs; basal scale of golden hairs. Genitalia ( Fig 5j ): median region of sternite VIII moderately depressed and pale posteromedially; hypogynial valves with vestiture of sparse short hairs; medial edges essentially parallel, posterolateral edges concave, membranous apical extensions rounded and simple; genital fork with stem long and markedly narrow, posterolateral arms with medial constriction, anteriorly directed apodeme rounded; anal lobes rounded with sparse longer hairs posteriorly, anterior anterolateral apodeme not well developed, anteromedian concavity distinct with sparse hairs; cercus narrow; spermatheca ovoid, moderately pigmented.

Adult male. Unknown.

Pupa (based on 4 specimens). Body length: 3.0 mm. Gill ( Fig. 10e ): maximum length of female 1.2–1.5 mm, male 1.1 mm; petioles short, branching pattern (2+2)+2+2+2, light brown, thickest proximally, tapered rapidly. Head and anterior thorax with evenly distributed sparse, dark brown, large, irregular granules, cuticle medium brown ( Fig. 8f ). Cocoon: markedly boot shaped, base not flared laterally, anterior collar well raised above substrate; length of female 3.8–3.9 mm long, 1.5–1.7 mm wide; male 2.8–3.0 mm long, 1.4–1.8 mm wide.

Larva (based on 3 mature last-instar larvae). Body ( Fig. 11m ): relatively large; total length 6.9–7.1 mm: females overall grey, males with orange tinge, thorax evenly pigmented, anterior abdominal segments pigmented with intersegmental areas pale, producing banded appearance, posterior abdominal segments evenly pigmented. Head ( Fig. 14e ): both sexes with dark brown pigmentation, lighter anteriorly on frontoclypeal apotome, more so in males; fan stems light brown, triangular region anterior and basal on stem markedly pale, as is region medial of antennal bases and sockets of trichoid sensilla pair 5 and 6, medial of antennal base; head-spot pattern negative, but indistinct; ecdysial lines pale and straight, diverging; width 0.65 mm, length 0.71 mm; distance between antennal bases 0.36 mm; lateral margins of head evenly convex; posterior edge of apotome not emarginate; postocciput finely extended between cervical sclerites and apotome. Antenna: total length 0.83 mm; distal article 0.33 times as long as basal articles, extended barely beyond labral fan stalk, distal article medium brown, distal portion of basal article concolourous, remainder paler. Labral fan: stalk medium brown, anterior palatal bar markedly protruded anteromedially; 37–45 rays, 0.70 mm in length, 10–12 rays less substantial; microtrichia 0.5 times length of ray width, pattern indistinct. Postgenal cleft ( Fig. 17e ): markedly arrowhead shaped, slightly deeper than wide with convex edges; posteroventral elongated muscle spots neutral. Postgenal bridge: 0.6 times as long as cleft depth; genae and postgenae dark brown. Hypostoma ( Fig. 19e ): overall cone-shaped; ratio 5.1; median tooth prominent, lateral teeth smaller and scalloped medially, splayed laterally; sublateral teeth small, well spaced and equal in size; paralateral teeth not obvious; lateral serrations absent; 9–11 substantial hypostomal setae per side. Two substantial hairs situated medially. Mandible ( Fig. 21e ): apical tooth markedly developed; 4–6 spinous teeth, largely covered by subapical teeth; spinous teeth gap small; serration and sensillum distinct; blade region smooth, barely convex. Abdomen: anterior abdomen subequal in width to thorax, expanded gradually posteriorly to 5th abdominal segment then slightly steatopygous. Posterior circlet: directed posteriorly; 175–180 rows of hooks; 29–31 hooks per row (total ca. 5,300).

Additional material examined

Santo, Adsone River , S15.55968° E166.96876°, alt. 59 m, 15.ix.2004. Coll. D. A. & R. Craig. (immature larvae; DAC) .

Etymology

Named after the type locality river, but based on an older spelling, Adson, rather than the modern spelling, Adsone.

Distribution VANUATU: Santo, Adsone River.

Comments

Simulium adsonense is found in Santo only, along with small numbers of S. steatopygium larvae. Association of larvae and pupae of S. adsonense was confirmed by comparison of pupal cuticle ( Fig. 8f ) and gills ( Fig. 10e ) of pharate pupae in the mature last-instar larvae, to the mature pupae. The type locality ( Fig. 24a ) is shallow, with very fast water (respectively ca. 5 cm and 1.8 m /s) on an old concrete causeway. Larvae and pupae were also recovered from a riffle upstream. Larvae exhibit behaviours similar to those of Inseliellum in Polynesia that are adapted to shallow fast water ( Craig 1997), namely, even spacing of larvae and lack of body twisting, so that the ventral surface of the labral fans are directed towards the substrate. The latter behaviour is similar to that observed for larvae of S. paradisium . The number of hooks on the posterior circlet is also higher, again in keeping with adaptation to high-velocity habitats.

With the larva not markedly steatopygous and the pupal cuticle unique, placement of S. adsonense in the steatopygium species group was based solely on the genitalia of the single female adult. The relationship of this species may have to be reconsidered once additional material comes to hand.

Figures

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

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 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.