Stilpon paradoxus, 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 : 337-339

Stilpon paradoxus , new species

( Figs. 69-75 )

Material examined. – Holotype - male, THAILAND: Loei province, Na Haeo , riverbanks in gallery forest at FIRS, sample n 2020, 24 May.2000, coll. P. Grootaert ( SWU).

Paratypes – 6 males, 6 females, same data as in holotype ; 2 males, 5 females, Na Haeo, sample n 99016, 10 Feb.1999, coll. P. Grootaert. ( SWU, ZRC, RBINS) .

Diagnosis. – Species with black brown thorax, differing from all other species from Oriental region by a set of unique characters of male, including constriction in middle hind femur, spur-like posterior apical comb on hind tibia, modified abdominal tergites 1-2, completely fused cerci; female habitually very similar to S. lek but with shortened terminalia.

Description. – Male. Head black in ground-colour, with minute anterior and posterior ocellars and long cruciate inner verticals. Antenna brownish yellow (in darker specimens postpedicel and style darker). Postpedicel nearly 2.0 times

longer than wide. Style about 5 times longer than postpedicel. Palpus pale.

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

Legs with colour pattern: hind coxa in extreme base; mid femur in apical 1/3, hind femur in apical 2/3 and tarsomere 5 of all legs brownish; fore tibia and fore tarsomere 1 with brownish tinge; otherwise legs yellow. Hind trochanter lacking spinules. Mid femur ( Fig. 69, 70 ) slender, with 1 long anterior subapical bristle, 1 long yellow basal bristle, 8 black spinules in basal 1/3 and 2 posteroventral spinules in middle. Hind femur (viewed laterally) constricted and bent near middle, broader in apical half; with row of 8 fairly long (scarcely longer than femur is deep) anteroventral bristles in apical part, row of 5-6 dorsal bristles in basal part and 3-4 dorsal spinules just beyond midpoint of femur. Fore tibia lacking prominent bristles. Mid tibia straight, rather slender, with rows of ventral spinules and 1 longer subapical spinule. Hind tibia ( Fig. 71 ) with posterior apical comb greatly modified, long, spur-like.

Wing ( Fig. 72 ) normally developed, covered with uniform microtrichia; almost uniformly infuscate, somewhat deeper along longitudinal veins. Costal vein with ordinary short setulae on anterior margin. Vein R2+3 about 3 times longer than Rs. Distance between apices of R2+3 and R4+5 nearly 1.3 times longer than distance between apices of R1 and R2+3. R4+5 and M divergent and slightly arcuate in apical part. Halter with contrast black, elongate knob and pale yellow stem.

Abdomen with hardly prominent gland-like structures at least between tergites 3-4 and 4-5. Tergite 1 ( Fig. 84 ) produced laterally into projection bearing 3 spine-like black bristles of different length and resting into a shallow sclerotized excavation on tergite 2; tergite 3 with posteromarginal spinules; tergites 4-6 with minute posteromarginal setulae; tergite 7 with short ordinary bristles, segment 8 with short bristles. Sternites bearing ordinary bristles becoming more numerous and stronger toward hypopygium.

Hypopygium ( Fig. 73, 74 ) dark brown, large. Hypandrium with 2 strong bristles in apical part. Epandrium completely divided. Left epandrial lamella small, fused to hypandrium, bearing 2 long bristles in apical part. Left surstylus with upper lobe largely divided; lower part with markedly developed narrow surstylar comb, upper part long, slender, fused with lower part basally. Right surstylus large, elongate oval, lacking spines. Cerci completely fused into one large lobe, which is subequal in size and similar in shape to right surstylus, lacking spines, ventral and marginal bristles. Phallus ( Fig. 75 ) elongate, straight, strongly sclerotized.

Female. In most respects identical to male. Mid femur with 1 row of yellow ventral bristles becoming longer toward base of femur, longest bristle longer than femur is broad. Hind femur slender, with ordinary setation. Mid tibia lacking spinules. Hind tibia with short posterior apical comb. Halter with brownish knob. Abdomen lacking gland-like structures and with unmodified tergites 1-2. Terminalia shortened. Segment 8 normally sclerotized. Proximal margin of sternite 8 without 2 anteriorly directed rods. Apex of sternite 8 partially separated from base. Sternite 10 uniformly sclerotized, not fused with ventroapical margin of tergite 8. Cercus elongate oval, brownish yellow, clothed in setulae of different length.

Measurements. – Body length 1.5-1.8 mm, wing length 1.2.- 1.3 mm.

Etymology. – In reference to a unique set of characters which this species possesses.

Phylogenetic relationships. – The relationships of S. paradoxus are unresolved. In this species the female terminalia are shortened and, thus, it appears to be more closely related to the S. graminum and S. seeluang groups. In S. paradoxus the upper lobe of the left surstylus is almost completely divided that could also support this conclusion. However, the phylogenetic value of such condition is not quite clear at present. It should be noted that within a S. graminum + S. seeluang clade most of the known species have a completely divided upper lobe of the left surstylus ( S. spinicercus , S. monospinatus , the S. graminum species complex and the entire S. seeluang species group). Although, the upper lobe of the left surstylus is undivided in the S. nubilus species complex. S. paradoxus has the surstylar comb and the gland-like structures on the male abdomen. However, the first character is very homoplastic within the genus, whereas the second one is likely to be plesiomorphous. In the shape of the male hind femur (constricted and bent near middle) this species resembles some North American species, e.g. S. curvipes Melander or S. varipes Loew (Cumming & Cooper, 1992). However, this appears to be due to the homoplastic nature of this character rather than an evidence of some direct relationships. Besides of the characters noted, S. paradoxus possesses a set of unique features, which place them aside of all other Stilpon species. In this species the male abdominal segments 1-2 are greatly modified. Together they appear to form a special device of uncertain functional value. The male terminalia are also very peculiar. The cerci are completely fused into a large lobe, which is strictly similar in size and shape to the right surstylus. The right epandrial lamella is small and it is distinctly smaller than the left epandrial lamella (in Tachydromiinae normally vise versa). The phallus is elongate, straight, thick and strongly sclerotized (elongate, hair-like and curved in the S. divergens species group, very short and rather weakly sclerotized in the S. graminum and S. seeluang groups). Unfortunately, at the present state of our knowledge of the genus, almost all these characters are usefulness for the discussion some relationships of this species. Some of them are insufficiently studied in the Drapetini on the whole (e.g., aedeagal complex). The phylogenetic value of others may be clarified when new undescribed species are discovered.

Distribution and seasonal occurrence. – Thailand. Known from one locality only. Records are from the first decade of February to late May. Collected on riverbanks in gallery forest.

Figures

Figs. 69-72. Stilpon paradoxus, new species, male. 69, mid leg, anterior view, 70, mid femur, posterior view, 71, apical part of hind tibia, dorsal view, 72, wing, dorsal view. Scale bar: 0.1 mm.

Figs. 73-75. Stilpon paradoxus, new species, male. 73, hypopygium, ventral view, 74, same, left lateral view, 75, phallus, dorsal view; hypd – hypandrium, rt epan lam – right epandrial lamella, rt sur – right surstylus, u lb – upper lobe of left surstylus. Scale bar: 0.1 mm.

Figs. 80-84. Details of male abdomen, dorsal view. 80, Stilpon lek, new species, 81, Stilpon lekkwar, new species, 82, Stilpon trilobatus, new species, 83, Stilpon malayensis, new species, 84, Stilpon paradoxus, new species; T – tergite. Scale bar: 0.1 mm.