Stilpon yai, 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 : 339-341

Stilpon yai , new species

( Figs. 76-79 )

Material examined. – Holotype - male, THAILAND: Loei Province, Na Haeo, Chang Tok , riverbed, sample n 21047, 9 May.2001, coll. P. Grootaert (coll. RBINS).

Diagnosis. – Readily distinguished from other species known from Oriental region by its large size, veins R4+5 and M parallel and straight in apical part, male mid femur with 3 black antero- and 2 longer posteroventral spines in basal half.

Description. – Male. Head black in ground-colour, with minute anterior ocellars, somewhat longer posterior ocellars and long inner verticals. Antenna and palpus brownish yellow. Postpedicel nearly 1.5 times longer than wide. Style nearly 8 times longer than postpedicel.

Thorax dark brown. Scutum entirely tomentose. Postpronotal bristle long, inclinate. Dorsocentrals in multiple rows, complete posteriorly. Acrostichals 2-serial, complete posteriorly.

Legs with colour pattern: hind femur brownish in apical 1/ 2; fore tibia, fore and mid tarsi, mid femur at apex, mid and hind coxae brownish yellow. Mid coxa with 2 brown bristles on outer side. Hind trochanter lacking spinules. Mid femur ( Fig. 76 ) slender, with 3 short black antero- and 2 longer posteroventral spines in basal 1/2, bearing 2 long yellow bristles in extreme base. Hind femur (viewed laterally) more or less evenly thickened, with row of anterodorsal bristles becoming longer toward apex and row of prominent dorsal bristles. Fore tibia lacking prominent ventral bristles. Mid tibia with ordinary setation, lacking ventral spinules. Hind tibia unmodified.

Wing normally developed, covered with uniform microtrichia; more or less uniformly, rather deep infuscate. Costal vein with long setulae along anterior margin. Vein R2+3 about 2.5 times longer than Rs. Distance between apices of R2+3 and R4+5 1.5 times longer than distance between apices of R1 and R2+3. R4+5 and M parallel and straight in apical part. Halter with elongate, contrast black knob and pale stem.

Abdomen largely dirty yellow, bearing mostly scattered dark setulae which are longer on pregenital segments, with all tergites (except segment 8) of subequal in length, tergites 1- 2 unmodified. Hardly prominent gland-like structures present between tergites 6-5, 5-4, 4-3 and 3-2. Segment 8 with moderately long bristles.

Hypopygium ( Fig. 77 ) brown, large. Hypandrium with 2 short bristles in apical part. Epandrium completely divided. Left epandrial lamella small, fused to hypandrium, with 2 short bristles in apical part. Left surstylus with upper lobe ( Fig. 78 ) largely divided; lower part with greatly developed surstylar comb, upper part digitiform, fused with lower part basally. Right surstylus ( Fig. 79 ) moderately large, sublinear, more or less rounded at apex, bearing numerous bristles of different length, lacking spines. Left cercus unbranched, short, fairly broad, rounded at apex, lacking spines and ventral bristle, with 2 very long left marginal bristles in basal part. Right cercus unbranched, short, rectangular, lacking spines. Phallus short.

Female. Unknown.

Measurements. – Body length 2.5 mm, wing length 2.2 mm.

Etymology. – In reference to the largest size of this species

among all others found until now from the Oriental region, “yai” means big in Thai.

Phylogenetic relationships. – The relationships of S. yai are unresolved. The main problem originates because of unknown female of this species. The presence of 2 long marginal bristles in basal part of cercus may indicate S. yai is closer related to some species of the S. divergens species group. However, it has no a long ventral bristle on the left cercus, whereas the presence of this bristle appears to support a monophyly of this group. The structure of the phallus resembles that in the S. graminum and S. seeluang species groups. However, this character is insufficiently studied in many other Stilpon species. S. yai has setose left cercus and 2 distinct bristles in apical part of the left epandrial lamella. So, it cannot be included in the S. graminum or S. seeluang species groups, respectively. S. yai shares the same condition of the left surstylus as in S. paradoxus (upper part largely separated). Additionally, in S. yai the right surstylus appears to be enlarged and cerci might exhibit some tendency to be completely fused (presumably, the conditions toward those found in S. paradoxus ). However, the last two arguments are hypotheses only. Whereas the condition of the left surstylus noted is a too weak argumentation to discuss some relationships between these two species at present. Like some North American species, S. yai has the elongate costal setulae. But, again, this is probably a quite homoplastic character because the lack of the scutal tomentum supports well the monophyly of these Nearctic species.

Distribution and seasonal occurrence. – Thailand. Known from one locality. The only record is from the beginning of May. Collected from riverbed.

Figures

Figs. 76-79. Stilpon yai, new species, male. 76, mid leg, anterior view, 77, hypopygium, ventral view, 78, upper lobe of left surstylus, dorsal view, 79, right epandrial lamella and right surstylus, dorsal view. Scale bar: 0.1 mm.