Simulium (Chirostilbia) obesum Vulcano

(Figs. 7, 22, 47, 48, 88–90, 112, 128, 143, 164, 165, 186, 200, 212, 225, 252)

This is an uncommon zoophilic species from south-eastern Brazil.

Simulium obesum Vulcano, 1959: 351. HOLOTYPE ♂ (reared), BRAZIL: São Paulo State, Serra da Bocaina, Fazenda da Bonito, São José do Barreiro; 1–30.i.1959, (Vulcano, M.A.) (MZUSP).

Female. General body colour dark brown. Body length (specimen pinned) 4.2 mm (n=1), wing length 3.1 mm (n=1), wing width 1.6 mm (n=1).

Head— dichoptic with dark red eyes and nudiocular area developed (Fig. 7). Frons, clypeus and occiput dark brown to black, with silvery grey pruinosity; clypeus and frons covered with dark erect setae. Mouthparts dark brown to black. Antennae with scape and pedicel brown, remaining segments pale brown. Cibarium without teeth and with sclerotised cornuae (Fig. 22).

Thorax— scutum black covered by evenly arranged, recumbent, golden setae interspersed with black setae. Scutal pattern varying with illumination. With anterior illumination, scutum greyish black with 1+1 wide sublateral grey pruinose areas in central region; humeri brownish, weakly pruinose; lateral and posterior margins greyish black (Fig. 47). With posterior illumination, thorax greyish black with median, black area on anterior margin giving rise to fine black vitta in anterior third of scutum and 1+1 submedian circular lighter areas on anterior margin; humeri silver pruinose; lateral and posterior margins greyish black (Fig. 48). Scutellum dark brown with recumbent golden setae interspersed with long black bristles. Postnotum dark brown with silver pruinosity. Pleura dark brown to black with silver pruinosity. Costa of wing with sparse distribution of spines and setae. Subcosta with line of setae nearly to apical third. Radius with line of setae intermixed with spines; basal section of Radius with setae. Basal tuft of long, dark setae. Leg coloration and proportions as in Figs. 88–90. Fore leg with coxa trochanter, femur and tibia brown [external surface of tibiae appear white in slide mounted specimens]; distal articulation of tibia and tarsi dark brown to black. Mid and hind legs dark brown with basal half of tibia, basal three fourths of basitarsus and basal half of second tarsomere yellowish. Claws curved, each with distinct basal tooth. Halteres cream with brown bases.

Abdomen— tergites I–IV velvet black, tergites VI–IX shiny black. Tergal plates developed; sternal plates undeveloped. Sternites greyish black; genitalia black. Eighth sternite sclerotised with irregularly distributed setae on posterior margin; gonapophyses subtriangular, protruding posteriorly, with inner half sclerotised and fine setae basally (Fig. 112). Cercus hemispherical, covered with long, brown setae; paraproct subrectangular with ventral extension subtriangular and twice as long as cercus, sclerotised, covered with prominent brown setae centrally and highly setose apically (Fig. 128). Genital fork stout, sclerotised; anterior and posterior processes poorly developed (Fig. 143). Spermatheca globular, without external sculpturing and with internal spicules irregularly arranged; area of insertion of spermathecal duct membranous.

Male. General body colour black. Body length (specimen pinned) 2.8 mm (n=1), wing length 2.9 mm (n=1), wing width 1.4 mm (n=1).

Head— holoptic with dark red eyes. Remainder of head coloration as in female.

Thorax— scutum covered with golden, recumbent hairs. Scutal pattern varies with light incidence: with anterior light source velvet black with 1+1 lateral silver pruinose areas on anterior margin (Fig. 164). With light source posterior to specimen thorax black (Fig. 165). Humeri, lateral and posterior margins black. Scutellum black with recumbent golden hairs interspersed with long erect and black hairs on posterior margin. Postnotum dark brown.

Abdomen— tergites I–IX black. Silver pruinosity on lateral margin of tergite II; basal fringe with long, brown hairs. Genitalia black; tergal plates developed, sternal plates undeveloped. Gonocoxite subrectangular; gonostyle trapezoidal, nearly same length as gonocoxite, with small spiniform setae apically; gonocoxite and gonostyle covered with long setae (Fig. 186). Ventral plate weakly sclerotised, subtriangular with main body well developed, rounded centrally, setose; basal arms short (Fig. 200). Median sclerite long, pear-shaped with distinct apical incision (Fig. 212). Paramere with developed and sclerotised basal process and several stout teeth apically (Fig. 225).

Pupa. Gill length 1.6–1.8 mm (n=2) [Other measurements not given because of lack of material.]

Cocoon— shoe-shaped as in Fig. 238, dark brown and knobbled, composed of thick, coalesced fibres posteriorly and distinct fenestrations anteriorly, with reinforced rim to anterior aperture, margin of aperture elevated.

Gill— dark brown with more than 120 forwardly-directed arranged in vertical plane. Gill with main trunk short, giving rise to five primary branches that divide at different heights into numerous secondary branches (Fig. 252). Primary branches fairly stout basally and narrower towards apex, rounded distally, covered with small spicules, edges crenate; of different lengths.

Head— frontoclypeus with 2+2 long bifid to multi-branched frontal and 1+1 long bifid to multi-branched facial trichomes; frontoclypeus with distinct group of platelets mesally, 1+1 dorso-laterally and 3–4 platelets in one group laterally in frontal region, respectively; tubercles rounded, densely distributed over entire frontal and facial region.

Thorax— with numerous long bifid to trifid trichomes near margin of dorsal cleft, approximately three long bifid and 1+1 long simple trichomes on ventral region; tubercles mostly rounded, more densely distributed near base of gill and dorsal cleft.

Abdomen— [Based on the original description because of lack of material] tergites I and II sclerotised with few setae; tergite III with row of spiniform setae; tergite IV with 2+2 hooks in row; tergites V–IX with spine combs on anterior margin; tergite IX with 1+1 apical spines. Sternites V–VI with 2+2 bifid hooks; sternite VII with 1+1 bifid hooks.

Larva. A description of the larva has been recently given by Pepinelli et al. (2006).