Simulium (Gomphostilbia) rhopaloides Craig, Englund & Takaoka

Craig, D. A., Englund, R. A. & Takaoka, H., 2006, Simuliidae (Diptera) of the Solomon Islands: new records and species, ecology, and biogeography, Zootaxa 1328, pp. 1-26 : 12-14

Simulium (Gomphostilbia) rhopaloides Craig, Englund & Takaoka n. sp.

( Fig. 7 )

Types

Holotype. Larva: early­last instar on slide. Label data “ Simulium (Gomphostilbia) rhopaloides . Solomon Islands, Guadalcanal, Charovuga River upstream of Gold Ridge Mine, S9.59936º E160.12402º, alt 540m. 27.vii. 2005. Coll. R. Englund. HOLOTYPE. No. 16626 ( BPBM).

Paratypes. Larvae: seven early last and penultimate instars in alcohol. Label data—as for Holotype, but with “ PARATYPE ” ( BPBM).

Diagnosis

Pupa: Gill filaments modified into single club­like structure with 2 fine nontapered filaments. Larva: anterior cephalic apotome markedly pale, light brown elsewhere; antennae extended well beyond labral fan stalk, hypostomal margins smooth; mandible serration and sensillum forming acute angle with mandible; ventral tubercles present, but not markedly developed.

Description

Adult female: Unknown.

Adult male: Unknown.

Pupa (based on poorly developed pharate pupal gill). Gill with club­like structure and 2 fine filaments ( Fig. 7 b).

Larva (based on early last­instar larvae). Body: total length 5.3 mm, overall greyish, thorax evenly pigmented, paler dorsally, posterior abdomen darker dorsally, pale ventrally ( Fig. 7 a). Head ( Fig. 7 e): lateral margins convex; anterior frontoclypeal apotome markedly pale, lighter brown elsewhere; antero­ and posteromedial head spots positive and distinct, anterolateral head spots positive and distinct, posterolateral head spots positive and surrounded by diffuse light brown; ecdysial lines pale and distinct, broadly rounded posteriorly; fan stalks translucent; width 0.51 mm, length 0.61 mm; distance between antennal bases 0.25 mm; cervical sclerites distinct; postocciput not extended medially. Antennae: total length 0.41 mm; proportions of articles 1.0:1.0:1.1; distal article extended half length beyond labral fan stalk; distal article and proximal portion of medial article brown, distal portion of basal article pale, remainder distinctly brown. Labral fan: stalk with anterior palatal bar not markedly protruded; 43 rays, 0.55 mm in length, 5 rays less substantial; microtrichia 1.75 times longer than ray width, distinct pattern of 5 or 6 smaller microtrichia between larger ones. Hypostoma ( Fig. 7 c): median tooth and lateral teeth equally developed, not prominent, lateral teeth broadly based, sublateral teeth distinct, but not markedly so; paralateral teeth poorly developed; 1 lateral serration poorly developed, otherwise smooth; 8 hypostomal setae per side. Postgenal cleft ( Fig. 7 f): arrowheadshaped, 1.5 times deeper than wide, posterior margins vertical for half of depth, remainder V­shaped with slightly rounded margins; posteroventrally elongate muscle spots light brown. Postgenal bridge: 0.3 times as long as cleft depth; genae and postgenae markedly light brown. Mandible ( Fig. 7 d): preapical and apical teeth well developed but not markedly, subapical teeth less so; 7 and more spinous teeth decreased in size markedly; sensillum markedly developed and forming acute angle with anterior blade of mandible, serration single, distinct, but not well developed. Abdomen: anterior abdomen narrower than thorax, expanded smoothly posteriorly to 5th abdominal segment, then expanded markedly smoothly. Anal sclerite ( Fig. 7 g): rectal scales well developed; anterior arms slightly longer than ventral arms, central junction broad. Posterior proleg circlet of hooks: 118 rows of hooks; 15­16 hooks per row (total ca. 1,800).

Etymology

The name is in reference to the club­like pupal gill.

Comments

Larval characteristics clearly place this material in Gomphostilbia . The pupal gill is, however, unusual with a club­like structure and only two fine filaments ( Fig. 7 b)—a unique arrangement for that subgenus. There are, however, gills with some thickened filaments in the sherwoodi species group (e.g., S. (G.) kerei and S. (G.) pangunaense ) and the batoense species group ( S. (G.) padangense ), albeit the number of slender filaments is four in the former two species and seven in the last. Elsewhere in Gomphostilbia , four gill filaments are also found in S. (G.) palauense , S. (G.) mogii , S. (G.) gimpuense , and S. (G.) brevilabrum . We consider the gill of S. (G.) rhopaloides the extreme of such examples and within the sherwoodi species group.

All types are deposited in the Bishop Museum.

Although Guadalcanal is the largest and most geographically complex of the Solomon Islands, it was not emphasized during the present survey, and was little sampled. Because few roads extend into the backcountry, with the notable exception of the Gold Ridge Mine area, gaining access to higher­elevation stream areas is problematic. However, we were able to sample upstream of the influence of the large Gold Ridge Mine on the Charovuga River ( Fig. 11 e), at elevations above 500 m. There the Charovuga River is moderately sized, but heavily sedimented in places because of many small­scale gold diggings being done by squatters. However, the river has numerous tributaries and cascades feeding it at this elevation, many of which appear to run through undisturbed forest. Water temperatures were 23.5ºC and aquatic habitats were highly varied, ranging from small seeps and cascades to riffles and pools. Simulium (G.) rhopaloides larvae were collected from rocks in small riffles in the main portion of the river.

Figures

FIGURE 7. Simulium (G.) rhopaloides n. sp. Guadalcanal. Early last instar larva, Holotype. a, left lateral view. b, pharate pupal gill. c, hypostomal teeth. d, mandible teeth, sensillum, and serrations. e, dorsal view of head. f, hypostoma and postgenal cleft. g, anal sclerite and circlet of hooks.

FIGURE 11. Localities of new Simuliidae material from the Solomon Islands. a, Stream near Ringgi, Kolumbangara, New Georgia Islands. b, Upper Sakumbare River, New Georgia, New Georgia Islands. c, Upper Toropi River, Rendova, New Georgia Islands (J. Polhemus in background). d, Garana River (3 km inland), Santa Isabel. e, Charovuga River, Guadalcanal. f, Aluta River, cascade, Malaita (R. Englund in background). g, Puepue River, Makira.