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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: shamshev@mail.ru
Patrick Grootaert
Department of Entomology, Royal Belgian Institute of Natural Sciences, Rue Vautier 29, B-1000, Brussels, Belgium
Email: Patrick.Grootaert@naturalsciences.be
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
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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