Chen Ng(Pg61-69)

---

315

THE RAFFLES BULLETIN OF ZOOLOGY 2004

THE RAFFLES BULLETIN OF ZOOLOGY 2004 52(2): 315-346

© National University of Singapore

A REVIEW OF THE GENUS STILPON LOEW, 1859 (EMPIDOIDEA: HYBOTIDAE)

FROM THE ORIENTAL REGION

Igor V. Shamshev

All-Russian Institute of Plant Protection, shosse Podbel’skogo 3, 188620, St.Petersburg – Pushkin, Russia

Present address: Royal Belgian Institute of Natural Sciences, Brussels

Email: [e-mail]

Patrick Grootaert

Department of Entomology, Royal Belgian Institute of Natural Sciences, Rue Vautier 29, B-1000, Brussels, Belgium

Email: [e-mail]

ABSTRACT. – The first comprehensive study of the genus Stilpon Loew in the Oriental region is presented.

Seventeen species are known nowadays from the region, including sixteen new ones. Fifteen species are

separated into three groups: S. graminum group: S. monospinatus, new species (Thailand), S. spinicercus,

new species (Thailand); S. seeluang group (newly recognised): S. crassinervis, new species (Thailand), S.

isaanensis, new species (Thailand), S. laawae, new species (Thailand), S. nhamyaaw, new species (Thailand),

S. seeluang, new species (Thailand), S. taksin, new species (Thailand); S. divergens group: S. khorngkeun,

new species (Thailand), S. lek, new species (Thailand), S. lekkwar, new species (Thailand), S. malayensis,

new species (Singapore), S. nhamdam, new species (Thailand), S. trilobatus, new species (Thailand); two

species have an uncertain group position: S. paradoxus, new species (Thailand), S. yai, new species (Thailand).

A key to all species from the Oriental region is provided. The gland-like structures on the male abdomen are

described for the first time in Stilpon. Phylogenetic relationships within the genus are shortly discussed.

KEY WORDS. – Empidoidea, Hybotidae, Tachydromiinae, Stilpon, new species, Oriental, phylogeny, gland-

like abdominal structures, Thailand, Singapore.

INTRODUCTION

The genus Stilpon Loew, 1859, includes very small predacious

flies inhabiting different biotopes but usually occurring in

the low-lying vegetation zones (Collin, 1961; Chvála, 1975;

Cumming & Cooper, 1992). Stilpon belongs to the subfamily

Tachydromiinae and is a member of an assemblage of the

genera known nowadays as a tribe Drapetini (Chvála, 1975).

Cumming & Cooper (1992) have defined this genus as having

linear to sublinear frons, large antennal pedicel, small

postpedicel with dorsoapical arista and large asymmetrical

male terminalia with a single ejaculatory apodeme. The group

is almost worldwide in the distribution (except Australia),

with about 25 described recent species. However, this number

is attributed mainly to the Palaearctic and Nearctic regions.

A single species of Stilpon has been described from the

Oriental region (Smith, 1965). Additionally, some fossil

species of the genus are known from the Dominican and Baltic

ambers (Meunier, 1908; Cumming & Cooper, 1992; Janzen,

2002).

Stilpon occurs in the same environment as Nanodromia and

can easily be confused with it. Nanodromia Grootaert, 1994,

also a genus of very small flies, was described from Papua

New Guinea. It has the wing cells br and bm equally long,

while the upper cell br is distinctly shorter than the lower

cell bm in Stilpon. Both genera occur together in Thailand.

Stilpon with its 15 species in Thailand is more speciose and

abundant, especially in the Northeast. Nanodromia is less

common since we have seen only 4 species in Thailand so

far (Grootaert & Shamshev, 2004).

The present paper is the first comprehensive study of Stilpon

from the Oriental region. All species, including S. divergens

Smith known from Nepal only (Smith, 1965), are keyed. The

phylogenetic relationships of the new species and the gland-

like structures on the male abdomen are discussed.

MATERIALS AND METHODS

The flies were collected by sweep netting, but most were

collected in Malaise traps. One trap was placed along the

border of a bamboo wood at the Field Research Station (FIRS)

at Na Haeo (Loei province, Northeast Thailand). This trap

was operational during 2.5 years (1999-2001, coll. Verapong

---

316

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

Kiatsoonthorn & P. Grootaert) and the samples were collected

weekly. In addition, some material came from Malaise traps

at the same site, operational in April and May 2003. All

material was stored originally in 70% ethanol.

Holotypes are mostly conserved in the country of origin.

Paratypes are conserved in the zoological collections of

Srinakharinwirot University in Bangkok (SWU), in the

Zoological Reference Collection of the Raffles Museum of

Biodiversity Research, National University of Singapore

(ZRC) and the Royal Belgian Institute of Natural Sciences

(RBINS). Type localities are not designated in the text, but

are the localities of the holotype.

Terms used for adult structures primarily follow those of

McAlpine (1981), although the terminology for the antenna

is taken from Stuckenberg (1999). Homologies for the male

and female terminalia follow Cumming & Cooper (1992) and

Sinclair (2000). To facilitate observations, the terminalia were

macerated in hot 85% lactic acid and immersed in glycerine.

Drawings of morphological features were made with a camera

lucida attached to a compound microscope.

In descriptions and key, right and left side of the male

terminalia are based on the unrotated position viewed

posteriorly, such that in the illustrations the right surstylus

appears on the readers left side and vise versa. All male

terminalia are figured in their unrotated position. When

describing the new species of Stilpon we mainly used the

format applied by Cumming & Cooper (1992). Thus, we

considered that it would be helpful for future comparative

studies of the genus.

SYSTEMATICS

Stilpon Loew, 1859

Agatachys Meigen, 1830. Nomen nudum. Cited as a MS name of

Winthem in specific synonymy under Tachydromia celeripes

Meigen (= graminum Fallén, 1915).

Stilpon Loew, 1859. Subgenus of Drapetis Meigen. Type species:

Tachydromia graminum Fallén, 1815 (des. by Loew, 1864).

Tetraneurella Dahl, 1909. Type species: Tetraneurella beckeri Dahl,

1909 (mon.) (= graminum Fallén, 1915).

Pseudostilpon Séguy, 1950. Type species: Tachydromia paludosa

Perris, 1852 (orig. des.).

Diagnosis. – Very small flies, 1.0-2.5 mm long. Male. Head

dark brown to black in ground-colour. Eyes with ommatrichia,

contiguous in facial part. Ommatidia slightly enlarged below

antennae. Frons linear to sublinear, narrow to fairly wide,

entirely or partially tomentose. Face strongly convex. Gena

barely extended below eye. Ocellar tubercle with 2 pairs of

bristles. One pair of prominent inclinate vertical bristles.

Antennae placed below or near middle of head; scape small;

pedicel large and globose, with long ventral preapical bristle;

postpedicel small, ovate, with well prominent dorsoapical

extension; stylus dorsoapical, long. Palpus elongate-ovate,

with distinct apical seta. Proboscis slightly recurved.

Thorax black brown to yellow in ground-colour. Scutum not

shiny and entirely tomentose or partly or entirely shiny and

lacking tomentum. Postpronotal lobe undifferentiated.

Postalar callus partially differentiated. Thoracic bristles

mostly hardly prominent; acrostichals arranged in 2 complete

or incomplete rows posteriorly or absent; dorsocentrals in 2

or more rows, often undifferentiated from intra-alar setulae,

complete or incomplete posteriorly. Mesopleuron largely

shiny, tomentose along dorsal margin. Metaepimeron large.

Halter with knob yellow to black, rarely absent.

Wing normally developed or sometimes shortened, broad or

narrow; hyaline, more or less infuscate or with distinct pattern.

Microtrichia uniform or lengthened in some parts of wing.

Costal setae short or long. Rs originating halfway along R1.

R2+3 complete or incomplete. Cell br short, distinctly less

than length of cell bm. Crossvein bm-cu nearly transverse.

A1 and crossvein CuA2 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. Hind femur evenly thickened or constricted near

middle, with well prominent anterodorsal bristles. Fore tibia

more or less spindle-like, usually lacking prominent bristles;

Mid tibia often armed with ventral spinules; hind tibia slender,

lacking prominent bristles, rarely with modified posterior

apical comb. Tarsi unmodified, except slightly to moderately

expanded basitarsus.

Abdomen with segments 1-7 lightly sclerotized, subequal in

length or some segments shortened, rarely segments 1-2

modified; segment 8 always short, partially concealed by

segment 7; squamiform lateral setae absent. Gland-like

intersegmental structures present or absent.

Hypopygium asymmetrical, rotated 90

°

 to the right.

Epandrium completely divided. Left epandrial lamella small

and fused to hypandrium, with long or greatly reduced to

absent bristles in apical part. 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. Left cercus usually large,

with or without apical spines. Right cercus undivided or

divided, sometimes with apical spines. Phallus elongate, well

sclerotized, hair-like or, rarely, straight or very short and

rather weakly sclerotized; single rod-shaped ejaculatory

apodeme present.

Female. Similar to male except ordinary setation on mid legs,

unmodified hind femur, wing microtrichia and abdominal

segments 1-2. Abdomen 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. Tergite 9 absent. Sternite

9 reduced to small internal sclerite. Tergite 10 absent. Sternite

---