Simulium (Hebridosimulium) steatopygium 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 : 65-69

Simulium (Hebridosimulium) steatopygium Craig n. sp.

( Figs. 5i , 6e , 7b , 10b , 11h , 12b , 14a , 17a , 19a , 21a ,)

Types

Holotype. Adult : double-pinned reared male, dried from alcohol. Label data – “ Simulium (Hebridosimulium) steatopygium , VANUATU. Efate, Mele Cascade. S17.67778° E168.25473°, alt. 65m. 6.x.2004. Coll. D. & R. Craig. HOLOTYPE. No. 16610” ( BPBM). Right upper eye and anterior margin region damaged. Pupal exuviae and cocoon as subsidiary material. Cocoon covered with travertine deposits . Paratypes. Adults: double-pinned reared adults, dried from alcohol. Label data – as for Holotype, but with “ PARATYPE ” (1 male, 2 females; BPBM). As for above but date “ 25.vi.1981 ” (3 males, 6 females; ROM). Colours muted in tone. All pinned Paratypes have pupal exuviae and cocoon (some with travertine material) as subsidiary material on points. Alcohol material: label data – as for Holotype (larvae; BPBM, LCNZ, ROM. larvae, pupae, reared males; DAC) .

Diagnosis

Adults: males markedly small; female genital fork stem narrow, hypogynial valves with inner edges straight, anal lobe triangular; male ventral plate keel smaller. Pupa: sparse thoracic granules. Cocoon: smaller and not completely covering female pupa. Larva: head spots and pigmentation forming distinct Eiffel Tower configuration on posteromedial apotome; abdomen markedly steatopygous, dorsolateral tubercles absent.

Description

Adult female (based on numerous reared specimens). Body: head, thorax and abdomen concolourous, very dark brown; total length 2.5–3.6 mm. Head: width 0.8–0.9 mm; depth 0.6–0.7 mm (larger in specimens from Santo); frons and postocciput with vestiture of sparse silvery small hairs; frons-head ratio (narrowest width of frons: greatest width of head) 1.0:3.6. Eye: interocular distance 0.24 mm; ommatidia 0.018 mm in diameter; 45 rows across and 42 down at mid-eye. Clypeus: 0.22–0.25 mm wide; vestiture of dense pale hairs, black ventrally. Antenna: length 0.46–0.54 mm; flagellomeres light brown; scape and pedicel pale. Mouthparts: 0.43 length of head depth; mandible well developed with 18 inner teeth decreased in size proximally; lacinia with 9 inner teeth and 14 outer teeth; maxillary palpus evenly black, proportional length of 3rd, 4th, and 5th articles 1.0:0.6:1.2; sensory vesicle spherical, ca. 0.3 times width of 3rd article, opening 0.8 times width of vesicle. Thorax: length 1.15–1.22 mm; width 0.93–0.96 mm; postpronotal lobes markedly paler than scutum; scutum evenly dark brown, vittae absent, vestiture of sparse, very fine golden hairs; scutellum light brown, vestiture of stiff long black and pale hairs laterally, apical angle 120° (Santo); postnotum concolourous with scutum; pleural membrane pale and with sparse long golden hairs. Wing: length 2.3–2.8 mm; maximum width 1.1–1.2 mm. Legs: fore leg, coxa, trochanter, and proximal femur pale, dark brown distally, proximal tibia yellow, remainder of leg black; mid leg, coxa, trochanter, and proximal femur pale, distal femur black, proximal tibia yellow, remainder of leg black; hind leg as for mid leg except coxa, trochanter, and tarsus yellow, with calcipala and remainder of leg black; some specimens with legs darker overall. Abdomen: overall blackish brown; basal scale brownish black, with fringe of pale hairs; vestiture of evenly distributed short dark and golden hairs, dense laterally. Genitalia ( Fig. 5i ): overall vestiture of coarse black hair; sternite VIII deeply indented, broader anteriorly (Santo), densely pigmented anteriorly, paler posteriorly; hypogynial valves lightly pigmented with sparse vestiture; median edges straight (Efate), slightly concave (Santo), apical membranous extension corrugated (Efate), markedly directed medially and insubstantial (Santo); genital fork with stem narrow, posterolateral arms lightly pigmented, anteriorly directed apodeme rounded; anal lobes with anterolateral apodeme and anteromedian notch small (Efate) or markedly developed (Santo), posteriorly triangular (Efate), or less so (Santo); cercus elongated.

Adult male (based on 4 reared specimens). Body: length 2.4–2.6 mm. Head: width 0.85–0.92 mm; depth 0.58–0.63 mm. Eyes: upper ommatidia orange, 0.042 mm in diameter, ca. 15 across and 13 down; lower ommatidia dark brown, 0.018 mm in diameter, ca. 24 across and down. Clypeus: brown, paler medially; 0.23 times as wide as head; vestiture of long, fine, pale hairs. Antenna: total length 0.52 mm; all pale yellow. Mouthparts: length 0.38 times head depth; mandibles insubstantial, finely tapered with apical hairs; lacinia broad basally, finely tapered apically with terminal hairs; maxillary palpus dark brown, 0.49 mm long, proportional lengths of 3rd, 4th, and 5th articles 1.0:0.9:1.6, 3rd article darker and markedly hairy, sensory vesicle spherical, occupying 0.33 times width of article, opening 0.25 times width of vesicle. Thorax: length 1.0– 1.1 mm; width 0.8 mm; postpronotal lobes and scutum evenly light brown; scutum with 2 barely visible vittae; vestiture of even, small, fine silvery hairs; scutellum pale, apical angle 100°; vestiture of few black hairs laterally, remainder pale; postnotum concolourous with scutum, shiny: pleuron and pleural membrane concolourous with scutum; pleural membrane with hairs, barely visible at 50x magnification. Wing: 2.1–2.2 mm in length, 0.96–1.1 mm at maximum width. Legs: markedly bicolourous, yellow and black; all coxae and trochanters yellow; fore femur light brown, distal region of tibia and all of tarsus black; mid leg as for foreleg; hind leg with femur and tibia pale yellow proximally, black distally, both swollen and flattened, width to length ca. 0.35, tarsomeres black; pretarsal claw with ca. 19 grappling hooks dorsally. Abdomen: dark brown; basal scale well developed and dark, hairs markedly long, fine, pale, extended to beyond 2nd segment; 1st and 2nd segments paler brown, remainder dark brown; vestiture of sparse pale hairs. Genitalia ( Fig.6e ): gonocoxa 1.3 times longer than basal width, brown, with long black hairs on distal half; gonostyle paler, approximately 3.3 times longer than basal width; ventral plate angulate laterally, proximal arms finely tapered, median keel subequal in length to remainder of plate, flattened apically; dorsal sclerite well developed and broadly V-shaped; median sclerite with stem 1.3 times as long as crosspiece length. Cerci: essentially absent.

Pupa (based on 8 specimens — in alcohol). Body length: 2.3–3.0 mm. Gill ( Fig. 10b ): maximum length 1.4 mm, filaments fine, light grey; subequal in length except longer ventral filament and usually slightly shorter dorsal filament; branching pattern (2+2)+2+2+2 arising from petioles, usually 0.25 times length of filament, although rather variable; annulations fine. Head and thorax: cuticle light brown; covered with small granules, variable, from almost absent to evenly dispersed. Cocoon ( Figs. 7b ): distinctly shoe-shaped; opening well defined; in females not completely covering pupa, in males occasionally extended partway along gills; cocoon occasionally flared laterally.

Larva (based on numerous mature last-instar larvae). Body ( Fig. 11h ): total length, male 6.5–6.7 mm, females 6.6–7.8 mm; overall mottled grey, with paler intersegmental regions, producing striped appearance, metathoracic segment pale orange, evenly mottled gray brown (female) more yellowish (male). Head ( Fig. 14a ): overall light brown (darker in Efate specimens), and as wide as long; male width 0.68–0.72 mm; length 0.62–0.71 mm, female width 0.71–0.73 mm, length 0.69–0.81mm; lateral margins of head subparallel to slightly convex; apotome evenly light brown, ecdysial lines straight, diverging posteriorly, maximum width well posterior, broadly rounded inflexion; first and second anterolateral head spots positive, anteromedial and posteromedial head spots positive, posterior ones connected by broad band of similar colour to darker pigmentation on the posteromedial edge of the apotome, producing a distinctive Eiffel Tower configuration, first posterolateral spots positive, second posterolateral spots slightly negative to neutral, all spots surrounded by pale triangular nimbus; head lighter and spots more distinct in Santo larvae; genae anterior of stemmata pale, posterior margin of apotome slightly emarginated; postocciput with narrow extension between cervical sclerites and apotome. Antenna: total length 0.4 mm; distal article 0.3 times as long as basal articles and extended beyond labral fan stalk; basal and distal articles pale brown, median article pale. Labral fan: stalk light brown, anterior palatal bar variously developed; 48–50 rays, 0.80 mm in length; 15–19 rays less substantial; ray width, 0.02 mm; microtrichia with no distinctive pattern, subequal in length to ray width. Postgenal cleft ( Fig. 17a ): broadly V-shaped, slightly concave margins; 1.5 times as deep as wide. Postgenal bridge: 0.5 times as long as cleft depth, paler than genae, which are evenly medium brown; posteroventral elongated lateral muscle scars positive. Hypostoma ( Fig. 19a ): overall broadly cone-shaped; ratio 4.7; median tooth markedly prominent; lateral scalloped medially, slightly directed laterally; three small sublateral teeth; paralateral teeth poorly developed; 3 or 4 small lateral serrations; 11 or 12 substantial hypostomal setae per side. Mandible ( Fig. 21a ): all apical teeth well developed; 4 or 5 spinous teeth, gap absent; serration and sensillum distinct, blade region smooth and slightly convex. Abdomen: thorax and anterior abdomen subequal in width, expanded rapidly laterally at segment VI, markedly steatopygous ( Fig. 12b ); dorsolateral tubercles absent. Posterior circlet: directed posteriorly; 180 rows of hooks; 34–35 hooks per row (total ca. 6,200).

Additional material examined

Santo Apouna Riv. , Camp 2, 450’, 26–27.viii.1971. Coll. G. S. Robinson (larvae, pupae; BM) ; Camp 3, 950’, 11.ix.1971. Coll. G. S. Robinson (larvae, adults; BM) ; 9–11.ix.1971. Coll. G. S. Robinson (adults; BM) . Vonalolu , Adsone Riv., 20 m alt. 23.vi.1981. Coll. D. A. Craig (larvae, pupae, reared adults; DAC) ; 19.ii.1985 Coll. B. S. Batson (larvae, dried; DAC) . Nr. Sareti Village , Vonalolu Str., trib., Adsone Riv., 22–23.iv.1981, alt . 20m, Coll. D. A. Craig (larvae; BM, BP, ANIC, DAC, NZ, PI). Adsone River , S15.55968° E166.96876°, alt . 59m. 23.vi.1981, 15.ix.2004. Coll. D. A. Craig (larvae; DAC) . Sarakata R, UNELCO Hydrostation, S15.43147° E167.11448°, alt. 25 m, 26.viii. 2004. Coll. D. A. & R. Craig (larvae; DAC) . Efate Ewor River , La Cressionnière, S17.71728° E168.56946°, alt. 24m. 16.v.1981. Coll. D. A. Craig (larvae; DAC) . 23.ii.1985. Coll. B. S. Batson (larvae; DAC) . Neslep Riv. , 2 km S of Epao Village. 16.vi.1981. Coll. D. A. Craig (larvae, pupae, reared adults; DAC) . Mele Cascade, west of Port Vila , S17.67778° E168.25473°. alt. 65m. 17.vi.1981, 25.vi.1981, 6.x.2004. (larvae, pupae, pinned reared adults; BM, BPBM, CNCI, DAC, PI) .).?. xi.1981, L. Swillen, (larvae; BM, CNCI, DAC, NZ, PI). 21–23.ii.1985. Coll. B. S. Batson (larvae; DAC) .

Etymology Named after the markedly expanded posterior abdomen of the larva.

Distribution VANUATU: Santo, Efate.

Comments

Widely distributed in Santo, S. steatopygium is by far the most common and numerous species encountered, although less so in Efate. On the basis of larval head pattern, (cf. Figs. 13f , 14a ), this species appears closely related to S jolyi , from which it differs mainly in the more marked steatopygy of the larval abdomen. Female genitalia show minor differences in form between Santo and Efate. As well, pupae show considerable variation in gill-branching pattern, all possible indications that S. steatopygium is a complex of species, in particular the material from Santo.

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 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 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 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 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.