Stilpon arcuatum, Grootaert & Shamshev, 2012

Grootaert, Patrick & Shamshev, Igor V., 2012, The fast-running flies (Diptera, Hybotidae, Tachydromiinae) of Singapore and adjacent regions, European Journal of Taxonomy 5, pp. 1-162 : 127-129

Stilpon arcuatum sp. nov.

Figs 204-206

Diagnosis

Species with entirely yellow thorax; legs largely brownish yellow, hind tibia modified, strongly curved and largely thickened towards apex; wing distinctly maculate, broadly brownish infuscate on middle leaving apical and basal parts hyaline, halter yellow.

Description

Male LENGTH. Body 1.2 mm, wing 1.1 mm.

HEAD. Black. Two moderately long, fine vertical bristles present. Frons linear with sides nearly parallel, broad, entirely tomentose. Ocellar tubercle with minute setulae. Antenna with scape and pedicel brownish yellow, postpedicel pale yellow. Palpus brownish yellow, with moderately long, brownish subapical bristle.

THORAX. Yellow in ground-colour with some brownish tinge (especially sutures); scutum entirely tomentose. Postpronotal bristle moderately long, inclinate. Dorsocentral and acrostichal bristles undifferentiated, scutum more or less evenly covered with uniform setulae.

LEGS. With fore and mid femora apically, hind femur entirely, fore and hind tibiae entirely, mid tibia basally, fore tarsus entirely, mid and hind tarsomere 5 brownish yellow, otherwise yellow. Coxae with unmodified setation; hind trochanter lacking spinules. Fore femur markedly thickened, with row of moderately long brown anteroventral and row of minute posteroventral bristles. Fore tibia spindle-like, with unmodified setation. Mid femur slender, with 4 moderately long ventral bristles basally and 1 long, subapical bristle anteriorly. Mid tibia lacking ventral spinules (ventral setulae slightly stronger apically) and prominent bristles. Hind femur (viewed laterally) evenly thickened towards middle, with 1 complete row of short anteroventral bristles, several similar setae on basal part anteriorly and several dorsal erect bristles near base. Hind tibia strongly curved and largely thickened towards apex, bearing longer than on other parts ventral setulae, with unmodified posterior apical comb. Fore and mid tarsi slender, hind tarsomere 1 slightly thickened.

WING. Normally developed, covered with uniform microtrichia; distinctly maculate, broadly brownish infuscate on middle leaving apical and basal parts hyaline. Costal vein with short setulae along anterior margin. R 1, R 2+3 (in less degree), R 4+5 and M 1+2 thickened. R 2+3 long, nearly 2.0 times as long as Rs, sinuate, meeting costa beyond middle of wing. Distance between apices of R 2+3 and R 4+5 subequal to distance between apices of R 1 and R 2+3 (22/18). R 4+5 evenly curved towards costa in apical part. R 4+5 and M 1+2 slightly divergent before wing apex. Halter entirely yellow.

ABDOMEN. Tergites 1 and 2 unmodified. Segment 8 with several unmodified setae of different lengths (2-3 long). Sternites brownish yellow, with scattered minute, brownish setulae. Gland-like structure present between tergites 2 and 3 and 3 and 4.

TERMINALIA. Yellowish brown ( Figs 204-206 ). Cerci narrowly fused, short, lacking spines; right cercus pointed, with several setae of different lengths; left cercus ( Fig. 206 ) bilobed, with right lobe bearing 1 very long and several short setae. Epandrium completely divided. Right surstylus with several long submarginal setae dorsally, lacking spines. Left epandrial lamella fused to hypandrium, with 2 minute setulae in apical part. Left surstylus ( Fig. 205 ) with upper lobe divided; lower part lacking surstylar comb, upper part elongate oval. Hypandrium with 2 long bristles in apical part. Phallus short.

Female

Unknown.

Material examined

Holotype ♂ SINGAPORE: Kranji (KNT01), 12 May 2009, mangrove, Mal. (reg. 29052, leg. P.G.; in ZRC).

Etymology

The name ' arcuatum ' alludes to the bent hind femora and tibia of this new species.

Distribution

Singapore.

Habitat and seasonal occurrence

This species occurs in mangrove, with a single record from May.

Remarks

The new species can be readily distinguished from all other species of Stilpon described from the Oriental Region by a combination of characters that has been given in the diagnosis. It should be noted that in this species the structure of the hind tibia is unique within the genus.

Figures

Figs 204-206. Stilpon arcuatum sp. nov., ♂ terminalia. 204. epandrium with cerci, dorsal view. 205. left surstylus, lateral view. 206. left cercus, lateral view.