Stilpon Loew 1859

Genus Stilpon Loew, 1859

Agatachys Meigen, 1830: 343 (as MS name ' Agatachys flavipes ' of Winthem).Type-species: Tachydromia celeripes Meigen, 1830 (= T. graminum Fallén, 1815) [designation by Coquillett, 1910: 504], by monotypy. Suppressed by the I.C.Z.N. (1997: 200 [Opinion 1881]), see Cumming & Evenhuis (1996).

Stilpon Loew, 1859: 34 (as subgenus of Drapetis Meigen). Type-species: Tachydromia graminum Fallén, 1815, by subsequent designation Loew, 1864: 5).

Tetraneurella Dahl, 1909: 362. Type-species: T. beckeri Dahl, 1909 [= Stilpon graminum (Fallén, 1915)], by monotypy.

Pseudostilpon Séguy, 1950: 83. Type-species: Tachydromia paludosa Perris, 1852, by original designation.

Recognition

Stilpon is recognized from other drapetine genera that occur in the Oriental Region by the following combination of features: eyes contiguous on face, frons with sides nearly parallel; antenna with dorsoapical arista-like stylus; wing with cell br much shorter than cell bm, A 1 very weak or absent; abdominal tergites lacking squamiform setae; male terminalia with single rod-shaped ejaculatory apodeme.

Diagnosis

Very small flies, usually 1.0- 1.5 mm (rarely 2.0- 2.5 mm). Eyes contiguous on face. Ommatidia slightly enlarged below antennae. Frons linear to sublinear, narrow to fairly wide. Face strongly convex. Gena barely extended below eye.Ocellar tubercle with 2pairs of bristles.One pair of prominent inclinate vertical bristles. Antennae with pedicel large and globose, bearing long ventral preapical seta; postpedicel small, ovate, with very prominent dorsoapical extension; stylus dorsoapical, long. Palpus elongate-ovate, with distinct apical seta. Thorax blackish brown to yellow in ground-colour. Scutum shiney or tomentose; anepisternum largely shiney. Thoracic bristles mostly only slightly prominent. Metaepimeron large. Halter with knob yellow to black, rarely absent. Wing normally developed or sometimes shortened; nearly hyaline or with distinct pattern; Rs originating halfway along R 1; vein R 2+3 complete or incomplete; cell br short, distinctly less than length of cell bm; crossvein bm-cu nearly transverse; A 1 and crossvein CuA 2 absent. Legs short, often with distinct colour pattern; fore femur thickened; mid femur slender to barely thickened, usually armed with bristles and spinules or spines arranged in specific patterns; fore tibia more or less spindle-like; mid tibia often armed with ventral spinules; hind tibia slender, lacking prominent bristles, rarely with modified posterior apical comb. Abdomen with segments 1-7 lightly sclerotised, rarely segments 1-2 modified; squamiform setae absent. Gland-like intersegmental structures present or absent. Male terminalia asymmetrical, rotated 90° to right. Epandrium completely divided. Left epandrial lamella small and fused to hypandrium. Left surstylus divided into 3 (or 4) lobes; upper lobe with or without surstylar comb. Right epandrial lamella usually large, positioned ventrally. Right surstylus large to moderately large, undivided, sometimes with apical spines. Cerci, including subepandrial sclerite, fused together basally, rarely fused completely into one large lobe, sometimes greatly reduced and bearing apical spines. Phallus elongate, well sclerotised, hair-like or, rarely, straight or very short and rather weakly sclerotised; single rod-shaped ejaculatory apodeme present. Female similar to male except ordinary setation on mid legs and unmodified abdominal segments 1-2; abdomen always without gland-like structures; terminalia short to elongate; tergite 8 not fused laterally with sternite 8; sternite 8 entire, or with apex hinged and partly or completely separated from base. Cercus elongate-ovate or broadly ovate.

Remarks

The species of the genus Stilpon are distributed in the Afrotropical (2 species), Nearctic (13 species), Oriental (26 species) and Palaearctic (12 species) regions, with 54 currently known species (including 5 new species recognised herein from Singapore).

Smith (1965) described the first Oriental species Stilpon divergens. Shamshev & Grootaert (2004b) published 15 new species of Stilpon found in northeastern Thailand above 500 m altitude. Two short papers followed: first with two new species from Cambodia (Shamshev & Grootaert 2006) and second with two new species from southern China (Shamshev et al. 2005). Cumming & Cooper (1992) recognised three informal species groups of Stilpon (S. varipes group, S. graminum group, and S. divergens group), and Shamshev & Grootaert (2004b) added the S. seeluang group.

Species of Stilpon are quite rare at low altitudes in the tropics as is demonstrated here too. On the other hand they are quite common at higher altitudes as is shown by the material collected during the TIGER project in Thailand. In the latter survey project, Stilpon is as common and diverse as Platypalpus and Elaphropeza and many new species await description.

Species of this genus inhabit different biotopes but usually occurring in the low-lying vegetation zones (Collin 1961; Chvála 1975; Cumming & Cooper 1992; Przhiboro & Shamshev 2007).

The key given below is limited to Stilpon from low altitudes including only S. laawae of the 15 species known from northern Thailand (Shamshev & Grootaert 2004b).

Key to species of Stilpon from Singapore

1. Thorax entirely black.............................................................................................................................2

– Thorax at least with yellow pleura........................................................................................................5

2. Wing lacking R 2+3. Palpus brown................................................................... S. nigripennis sp. nov.

– Wing with R 2+3. Palpus yellow..............................................................................................................3

3. R 4+5 strongly curved toward costa in apical part; distance between apices of R 2+3 and R 4+5 about 1.5 times shorter than distance between apices of R 1 and R 2+3. Hind femur (except narrow basal portion) brownish. Male: abdominal tergite 1 produced laterally into small corner-like projection bearing 3 short bristles................................................................................ S. singaporensis sp. nov.

–R 4+5 evenly arcuate; distance between apices of R 2+3 and R 4+5 at least subequal to distance between apices of R 1 and R 2+3. Hind femur wholly yellow. Abdominal tergite 1 unmodified........................4

4. Only tarsomere 5 of all legs black. Male: mid femur with 3 moderately long, ventral, brownish bristles in basal 1/3 (Fig. 203). (Cambodia)............................... S. goesi Shamshev & Grootaert, 2006

– Tarsomere 5 of all legs and tarsomere 1 of hind leg brownish. Male: mid femur with 1 black, posteroventral spine beyond middle and row of 7 spine-like bristles in basal part (Fig. 199). (Cambodia).................................................................... S. angkorensis Shamshev & Grootaert, 2006

5. Hind tibia strongly curved. Halter yellow.......................................................... S. arcuatum sp. nov.

– Hind tibia unmodified. Halter brownish or black.................................................................................6

6. Scutum entirely brown. Hind femur largely brownish...... S. malayensis Shamshev & Grootaert, 2004

– Scutum largely yellow, with brownish patch above wing base. Hind femur at most somewhat brownish in apical part.........................................................................................................................................7

7. Wing finely infuscate; R 4+5 slightly arcuate in apical part. Male: upper lobe of left surstylus lacking surstylar comb (Fig. 211). (Thailand; Singapore)................... S. laawae Shamshev & Grootaert, 2004

– Wing maculate or darker along some veins........................................................................................8

8. Wing maculate; vein R 4+5 strongly curved toward costa in apical part. Male: upper lobe of left surstylus with markedly developed surstylar comb (Fig. 223) (Singapore).................. S. neesoonensis sp. nov.

– Wing broadly brownish infuscate along R 2+3 and CuA 1 (except subapical part). R 4+5 evenly curved toward costa in apical part. Male: upper lobe of left surstylus lacking surstylar comb (Fig. 233) (Singapore)........................................................................................................... S. weilingae sp. nov.