Stilpon crassinervis, Shamshev & Grootaert, 2004

Shamshev, Igor V. & Grootaert, Patrick, 2004, A Review Of The Genus Stilpon Loew, 1859 (Empidoidea: Hybotidae) From The Oriental Region, Raffles Bulletin of Zoology 52 (2), pp. 315-346 : 320-322

Stilpon crassinervis , new species

( Figs. 11-14 )

Material examined. – Holotype - male, THAILAND: Phang-Nga province , Khao Sok, sample n 96035, 6 Apr.1996, coll. P. Grootaert (coll. RBINS).

Paratypes – Pethburi province , Pa Dang, 1 male, 25 Mar.2001 (coll. RBINS) .

Diagnosis. – Species with yellow thorax. Can be readily distinguished from all other species of this group by vein R2+3 flattened at apex.

Description. – Male. Head black in ground-colour, with minute ocellars and short inner verticals. Postpedicel pale yellow, paler than scape and pedicel, nearly 2.0 times longer than wide. Style about 5 times longer than postpedicel. Palpus yellow.

Thorax almost wholly yellow. Scutum entirely tomentose, scutal spots almost invisible, postalar calli dark. Postpronotal bristle hardly prominent. Dorsocentrals in multiple rows, complete posteriorly. Acrostichals 2-serial, complete posteriorly.

Legs with colour pattern: hind femur brownish yellow in apical 2/3; otherwise legs yellow. Hind trochanter lacking spinules. Mid femur ( Fig. 11 ) slender, with 1 long anterior subapical bristle and row of 4 yellow, rather long, ventral bristles. Hind femur (viewed laterally) evenly thickened toward middle, with 1 row of anteroventral bristles becoming longer toward apex of femur (3 subapical bristles longest) and some hardly prominent dorsal bristles in basal part. Mid tibia straight, slender, lacking prominent ventral spinules. Hind tibia slightly arcuate, with more distinctly prominent ventral setulae and unmodified posterior apical comb.

Wing normally developed, covered with uniform microtrichia, finely infuscate, somewhat deeper along longitudinal veins. Costal vein with ordinary short setulae on anterior margin. Vein R2+3 flattened at apex, about 1.5 times longer than Rs. Distance between apices of R2+3 and R4+5 nearly 3.0 times longer than distance between apices of R1 and R2+3. R4+5 and M divergent and evenly arcuate in apical part. Halter with contrast black, elongate knob and pale yellow stem.

Abdomen largely brownish yellow, lacking gland-like structures, with segments 1-2 unmodified, bearing mostly scattered short setulae; tergites 1-2 yellowish, segment 8 with 2 very long and several shorter bristles.

Hypopygium ( Fig. 12 ) brown, small. Hypandrium with 2 long bristles in apical part. Epandrium completely divided. Left epandrial lamella small, fused to hypandrium, with 1 minute bristle in apical part. Left surstylus with upper lobe ( Fig. 13 ) divided; lower part small, slender, lacking surstylar comb, upper part moderately large, subglobular, lacking bristles. Right surstylus ( Fig. 14 ) large, elongate, covered with spinules in apical part. Cerci almost completely fused into one lobe, lacking spines, with several bristles of different length in basal part; left cercus hardly prominent, short, rectangular; right cercus pointed at apex. Phallus short.

Female. Unknown.

Measurements. – Body length 1.5-1.7 mm, wing length 1.1- 1.3 mm.

Etymology. – The name of this species refers to the widening of the tip of vein R4+5.

Phylogenetic relationships. – The relationships of S. crassinervis are unresolved beyond inclusion within the S. seeluang species group. However, the presence of 2 very long bristles on the segment 8 of the male abdomen, the general structure of the male terminalia and, especially, the greatly reduced cerci suggest this species is allied with S. laawae , S. nhamyaaw , and S. taksin .

Distribution and seasonal occurrence. – Thailand. Known from two provinces rather south: Phang-Nga and Petchaburi. Records from the end of March to the beginning of April.

Figures

Figs. 11-14. Stilpon crassinervis, new species, male. 11, mid leg, anterior view, 12, hypopygium, ventral view, 13, upper lobe of left surstylus, dorsal view, 14, right surstylus, dorsal view. Scale bar: 0.1 mm.