Chen Ng(Pg61-69)

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Shamshev & Grootaert: A review of the genus Stilpon from the Oriental region

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.

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.

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THE RAFFLES BULLETIN OF ZOOLOGY 2004

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 un-

described 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.

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.

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.

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