The genus Platypalpus Macquart (Diptera: Hybotidae) from Northeast Thailand with comments on the species groups in the Oriental region

The first records on the genus Platypalpus Macquart from Thailand are presented including 10 species new to science: P. fai sp. nov., P. gaemluang sp. nov., P. hualuang sp. nov., P. isaanensis sp. nov., P. nuadkhao sp. nov., P. phomyaaw sp. nov., P. seedam sp. nov., P. seeluang sp. nov., P. siamensis sp. nov., and P. thaicus sp. nov.. A key to these species is provided. All species of Platypalpus known from the Oriental Region (totally 54) are arranged into the species groups currently established for the genus. Eight species groups are recognized from the Oriental Realm and the distribution of each group is briefly discussed. The P. albiseta‐group is most diverse in the Orient with 16 species recorded. Two species of this group possess a modified structure and vestiture of certain abdominal segments that is the first record of this phenomenon in Platypalpus. Also, within the P. albiseta‐group a complex of closely related species sharing an apomorphous condition of the hypoproct has been recognized. In these species the structure of the hypoproct is likely to deal with clasping during copulation instead of the cerci and epandrial lamellae.


Introduction
Species of the genus Platypalpus Macquart are a marked and a well-known element of main biotopes in almost all biotic realms. The ecological value of this group has been unclear for a long time. However, a number of investigations have shown that adult Platypalpus are important regulators (as very active predators) of the population density of many phytophagous Diptera, including some important pests (Chvála 1975;Stark and Wetzel 1987).
Platypalpus is very rich in species, however, like many other empidoids, the genus has been studied most extensively in the Palaearctic only, especially in Europe (Chvála 1975(Chvála , 1989 including the Mediterranean (Grootaert and Chvála 1992). The European fauna includes about 300 species. Platypalpus is poorly known from the Oriental realm. Smith (1975) listed 30 species, described from India (five species), Sri Lanka (two species), Nepal (eight species), Taiwan (five species), Indonesia (eight species) and the Philippines (two species) only. Later studies dealt with the continental part of China belonging to the Orient (Yang and Yang 1992Saigusa and Yang 2002;. Our paper presents first data on the genus Platypalpus from Thailand and from the Malaysian Peninsula as a whole. Together with descriptions of 10 new species we have attempted to give a preliminary analysis of the species groups of Platypalpus (sensu Chvála, 1975) occurring in the Orient. As a result, eight species groups have been recognized and the patterns of distribution of each group are briefly discussed. The P. albiseta-group has been treated in more detail because the species of this group are more numerous (at least at the present state of our knowledge) in the Orient. Additionally, in the species of the P. albiseta-group presented in this paper we found a number of interesting morphological features that could be helpful in the future analysis of the relationships within the group and the genus on the whole.

Material and methods
The flies were collected at Na Haeo (Thailand, Loei province) in Northeast Thailand (17u309N, 101u049E; altitude 500 m). Malaise traps were operated between 1999 and 2005 at the Field Research Station of Srinakharinwirot University (FIRS, SWU). The Malaise traps were placed in and along a small mixed deciduous forest with dominance of bamboo and under considerable anthropogenic stress. In the ''Material examined'' section of the species descriptions a reference number (in brackets) is given for each Malaise trap site. A detailed description of the site of Na Haeo can be found in Ampornpan and Dhillion (2003) and Grootaert and Verapong (2003).
In addition, some flies were collected by sweep netting and all are stored in 70% ethanol. Homologies for the male terminalia follow Sinclair (2000). To facilitate observations, the terminalia were macerated in 10% KOH and immersed in glycerine. Drawings of morphological features were made with a camera lucida attached to a compound microscope. In descriptions, 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 reader's left side and vice versa. All male terminalia are figured in their unrotated position.
Type material is stored at the Royal Belgian Institute of Natural Sciences (RBINS) and at Srinakharinwirot University. brown spots, sternopleuron, hypopleuron and metapleuron largely brown; tarsomeres 3-5 of all legs darkened, mid femur twice broader than fore femur.

Male
Body length 2.9 mm; wing length 2.9 mm.
Head. Black in ground-colour. Occiput finely greyish pollinose, subshining, with scattered black bristles in upper part, including two hardly prominent verticals, and some pale bristly hairs in lower part. Ocellar tubercle with two very short thin bristles. Frons shining, mostly very narrow, narrower than anterior ocellus, somewhat widened above. Face concolorous with frons. Antenna almost wholly brownish, postpedicel paler at apex; arista missing (2.5 times longer than postpedicel in female). Postpedicel narrow, elongate conical, nearly 5.0 times longer than wide. Palpus wholly yellow, mostly with scattered, short, yellow bristly hairs, bearing one longer brownish subapical bristle.
Thorax. Largely yellow; mesonotum with two triangular brown spots on supra-alar space near scutellum; almost wholly (except for yellowish upper posterior corner) dark brown, hypopleuron largely brown (yellowish to yellowish brown in upper part), metapleuron brown; postnotum with metanotum brownish yellow and metapleuron brown. Mesonotum and sternopleuron shining, otherwise thorax finely pollinose, subshining. Anterior and posterior spiracles brown. Humerus with few minute setulae. Mesonotum with brownish yellow, short, inconspicuous setation including two notopleural (anterior one shorter and thinner), one postalar, and four scutellar (inner ones longer and stronger) bristles; some scattered setulae present behind humerus, on notopleural depression, supra-alar space and postalar callus. Acrostichals lacking. Dorsocentrals arranged in one row, few in number, mostly of subequal length (except for one longer prescutellar pair).
Legs. Almost wholly yellow, only tarsomeres 3-5 somewhat darkened (more distinct on fore leg). Coxae and trochanters with ordinary yellow to brownish yellow setae. Fore femur slender, with a row of brownish yellow, thin, posteroventral bristles (one longest one near middle of femur longer than femur is deep) and a row of yellowish, short (nearly half as long as femur is deep), thin, anteroventral bristles. Fore tibia mostly slender, swollen near tibial gland; mostly clothed with ordinary setulae, with few more prominent, dorsal, brownish setae. Fore tarsus slender, unmodified. Mid femur incrassate, nearly 2.0 times broader than fore femur; with rows of ventral spinules and a row of rather long (nearly as long as femur is deep), brown, posteroventral bristles. Mid tibia with black ventral spinules throughout and hardly prominent flattened apical spur. Hind leg long and slender; hind femur somewhat swollen in apical part anteriorly, bearing a row of short, brownish to brownish yellow, erect, antero-and a row of short, pale, posteroventral bristles.
Arista thick, white pubescent, nearly 2.5 times longer than postpedicel. One long, brownish, basicostal bristle. Otherwise as in male except for sexual differences. Cerci brownish yellow.

Distribution
Thailand.

Remarks
In having the yellow mesonotum with two relatively small brownish spots P. nuadkhao sp. nov. should be compared with P. thaicus sp. nov., P. siamensis sp. nov., and P. isaanensis sp. nov. described in the present paper. P. thaicus sp. nov. and P. siamensis sp. nov. differ from the new species primarily by more slender mid femur (1.5 times broader than fore femur and 2.0 times broader than fore femur, respectively). P. isaanensis sp. nov. appears to be the closest ally to the new species. However, it has shorter postpedicel, a wholly brown sternopleuron and different male terminalia. P. candidiseta (Bezzi) (known from a female taken in Taiwan only) differs from P. nuadkhao sp. nov. by wholly yellow mesonotum and wholly black thoracic pleura (Bezzi 1912). P. nepalensis (Brunetti) (known from Nepal also has mesonotum with two small spots) possesses pale yellowish grey pubescence on the occiput, wholly grey thoracic pleura, uniformly pale brownish yellow legs and rather large male terminalia (Brunetti , 1920. P. sanguinolentus Melander (known after a female taken from Java only) can be readily distinguished from the new species by the wholly yellow mesonotum and black scutellum .

Diagnosis
Mostly yellow (including legs) species; one pair of short verticals; antenna with scape and pedicel brownish, postpedicel brownish yellow, arista white; postpedicel 3.5 times longer than wide; mesonotum with two large, ovate, brownish spots; thoracic pleura partly brown, legs wholly yellow; abdominal sternite 4 with median brown tubercle bearing tuft of brown setae.

Male
Body length 3.1 mm; wing length 3.0 mm.
Thorax. Largely yellow; prothoracic notum with brownish spot; prosternum brownish yellow; sutures of prothoracic sclerites brown in varying extent; mesonotum with two rather large, ovate, brownish spots extending from base of scutellum to level of posterior notopleural bristle; mesopleuron yellowish brown posteriorly and narrowly along suture with sternopleuron; sternopleuron almost wholly (except for yellowish brown upper posterior corner) dark brown; hypopleuron largely brown, somewhat paler along border with sternopleuron and in upper part; pteropleuron brownish yellow anteriorly; metapleuron brown; postnotum with brownish metanotum, metapleuron brownish yellow in lower part. Mesonotum and sternopleuron shining, otherwise thorax finely pollinose, subshining. Anterior and posterior spiracles brown. Humerus with one very short, fine bristle and few minute setulae. Mesonotum with two brown notopleural (anterior one shorter and thinner), one postalar (similar to posterior notopleural), and four scutellar (outer ones very short, thin; inner ones longest among mesonotal bristles, cruciate) bristles; some scattered setulae present behind humerus, on notopleural depression, supra-alar space and postalar callus. Acrostichal and dorsocentral bristles yellowish; the former arranged in two regular rows, lacking on prescutellar depression; the latter arranged in one regular row, rather numerous, short, mostly of equal length (except for two pairs of longer prescutellars) and somewhat longer than acrostichals.
Legs. Wholly yellow with some brownish tinge, coxae rather pale yellow. Coxae and trochanters with ordinary yellow to brownish yellow setae. Fore femur slender, with a row of brownish yellow, thin, posteroventral bristles (one longest one near middle of femur longer than femur is deep) and a row of yellowish, short (nearly half as long as femur is deep), thin, anteroventral bristles. Fore tibia mostly slender, somewhat swollen near tibial gland; clothed with ordinary setulae. Fore tarsus slender, unmodified. Mid femur incrassate, nearly 1.5 times broader than fore femur; with rows of ventral black spinules and a row of long (distinctly longer than femur is deep), brown, posteroventral bristles. Mid tibia with black ventral spinules throughout and hardly prominent flattened apical spur. Hind leg long, slender; hind femur somewhat swollen in apical part anteriorly, bearing a row of short, brownish to brownish yellow, erect, antero-and a row of short, pale, posteroventral bristles.

Female
Unknown.

Distribution
Thailand.
Remarks P. fai sp. nov. can be readily recognized by its peculiar tubercle on sternite 4 of the abdomen. Besides the feature noted, the new species differs from all species described here (and from P. nepalensis as well) by larger brownish scutal spots extending from base of scutellum to level of posterior notopleural bristle. In P. candidiseta and P. sanguinolentus the mesonotum is wholly yellow (Bezzi 1912;.

Male
Body length 2.9 mm; wing length 2.9 mm.
Thorax. Largely yellow; prothoracic notum brownish dorsally, prosternum yellowish brown, sutures of prothoracic sclerites brown in varying extent; sternopleuron almost wholly (except for upper posterior corner) dark brown, hypopleuron largely brown (yellow in upper third), metapleuron brown; postnotum with metanotum brown; metapleuron brown. Mesonotum and sternopleuron shining, otherwise thorax finely pollinose, subshining. Anterior and posterior spiracles brown. Humerus with one minute bristle. Mesonotum with brownish yellow, short, inconspicuous setation including two notopleural (anterior one shorter and thinner), one postalar and two scutellar (missing) bristles; some scattered setulae present behind humerus, on notopleural depression, supraalar space and postalar callus. Acrostichals lacking. Dorsocentrals arranged in one row, few in number, mostly of subequal length (except for one longer prescutellar pair). Legs. Wholly yellow. Coxae and trochanters with ordinary yellow to brownish yellow setae. Fore femur slender, with a row of brownish yellow, thin, posteroventral bristles (one longest one in middle part of femur longer than femur is deep) and a row of yellowish, short (nearly half as long as femur is deep), thin, anteroventral bristles. Fore tibia mostly slender, somewhat swollen near tibial gland; clothed with ordinary setulae. Fore tarsus slender, unmodified. Mid femur incrassate, nearly 2.0 times broader than fore femur; with rows of black, ventral spinules and a row of moderately long (at most as long as femur is deep), brown, posteroventral bristles. Mid tibia with black ventral spinules throughout and short flattened apical spur. Hind leg long, slender; hind femur somewhat swollen in apical part anteriorly, bearing a row of short, brownish to brownish yellow, erect, antero-and a row of short, pale, posteroventral bristles.
Abdomen. Yellowish brown, subshining, mostly with scattered distinct setulae becoming longer and more numerous toward terminalia; sternite 5 with two, sternite 6 with four very long yellowish brown bristles posteriorly.

Female
Unknown.

Distribution
Thailand.

Remarks
In having a wholly yellow mesonotum and, especially, a peculiar structure of the male terminalia, P. phomyaaw sp. nov. is most closely related to P. gaemluang sp. nov. It can be readily distinguished from the latter by partly brownish thoracic pleura and by two and four very long bristles on abdominal sternites 5 and 6, respectively. Two other species with wholly yellow mesonotum are P. candidiseta and P. sanguinolentus (Bezzi 1912;. The former differs from P. phomyaaw sp. nov. by wholly black thoracic pleura. The latter can be readily distinguished from the new species by the wholly black scutellum and largely black thoracic pleura.

Diagnosis
Mostly yellow (including legs) species; one pair of verticals; occiput narrowly densely greyish pollinose behind eyes and in upper part, otherwise subshining, with yellowish spot near mouth-opening laterally; antenna wholly yellowish brown, postpedicel 4.5 times longer than wide, arista 3.0 times longer than postpedicel; mesonotum and mesopleuron wholly yellow.

Male
Body length 3.1 mm; wing length 3.0 mm.

Head
Largely black in ground-colour, with small yellowish spot near mouth-opening laterally, including jowls. Occiput narrowly densely greyish pollinose behind eyes and also in upper half, including vertex and ocellar tubercle, otherwise subshining; clothed with pale bristly hairs of different length, bearing two proclinate, moderately long verticals. Ocellar tubercle lacking bristles (missing?). Frons pollinose, mostly very narrow, narrower than anterior ocellus, somewhat widened above. Face partly concolorous with frons, clypeus shining. Antenna yellowish brown, arista white, thick pubescent. Postpedicel narrow, elongate conical, nearly 4.5 times longer than wide. Arista nearly 3.0 times longer than postpedicel. Palpus wholly yellow, small, mostly with scattered short yellow bristly hairs, bearing one longer, brownish yellow, subapical bristle.
Thorax. Almost wholly yellow; prothoracic notum yellowish brown dorsally; suture between proepisternum and mesopleuron brown. Mesonotum and sternopleuron shining, otherwise thorax finely pollinose, subshining. Anterior and posterior spiracles yellow. Humerus with one minute bristle. Mesonotum with two brownish notopleural (anterior one shorter and thinner), one postalar (similar to posterior notopleural) and two cruciate scutellar bristles; some scattered setulae present behind humerus, on notopleural depression, supra-alar space and postalar callus. Acrostichals lacking. Dorsocentrals inconspicuous, pale yellow, arranged in one regular row, mostly of equal length (except for one pair of longer prescutellars).
Legs. Wholly yellow. Coxae and trochanters with ordinary yellow to brownish yellow setae. Fore femur slender, with a row of brownish yellow, thin, posteroventral bristles (one longest one in middle part of femur longer than femur is deep) and a row of yellowish, thin, anteroventral bristles (nearly as long as femur is deep). Fore tibia mostly slender, somewhat swollen near tibial gland; clothed with ordinary setulae. Fore tarsus slender, unmodified. Mid femur incrassate, nearly 2.0 times broader than fore femur; with rows of ventral, black spinules and a row of long (nearly as long as femur is deep), brown, posteroventral bristles. Mid tibia with black ventral spinules throughout and short, flattened, apical spur. Hind leg long, slender; hind femur somewhat swollen in apical part anteriorly, bearing a row of short, brownish to brownish yellow, erect, antero-and a row of short, pale, posteroventral bristles.
Abdomen. Yellow to brownish yellow, shining, with pale yellow setation. Tergites 1-2 with somewhat longer and numerous setae. Sternites with rather numerous moderately long bristles becoming longer toward terminalia.

Female
Unknown.

Distribution
Thailand.
Remarks P. gaemluang sp. nov. is most closely related to P. phomyaaw sp. nov., as has been also reflected in the key to species. In both species the mesonotum is entirely yellow and the male terminalia have a very similar structure, especially that of the hypoproct. P. phomyaaw sp. nov. can be readily distinguished from P. gaemluang sp. nov. by a peculiar setation of the abdominal sternites 5 and 6 where two and four very long, closely set bristles are present, respectively. Additionally, P. phomyaaw sp. nov. has partly brown thoracic pleura.

Etymology
The name simply refers to the country of origin.

Diagnosis
Mostly yellow (including legs) species; one pair of verticals; antenna wholly yellowish brown, postpedicel 4.0 times longer than wide, arista 2.5 times longer than postpedicel; mesonotum with two brownish spots, mesopleuron partly brownish; anterior spiracle yellow, posterior one brown.
Thorax. Largely yellow; prothoracic notum with brownish spot; prosternum brownish yellow; suture between proepisternum and mesopleuron brown; mesonotum with two small, elongate oval, indistinct, brownish yellow spots above wings; sternopleuron and hypopleuron largely brown to yellowish brown (except for upper part), metapleuron brownish yellow; postnotum with metanotum yellowish brown, metapleuron brown. Mesonotum and sternopleuron shining, otherwise thorax finely pollinose, subshining. Anterior spiracle yellow, posterior one brown. Humerus with one minute bristle. Mesonotum with two brownish notopleural (anterior one shorter and thinner), one postalar (similar to posterior notopleural) and two long scutellar (missing in holotype) bristles; some scattered setulae present behind humerus, on notopleural depression, supraalar space and postalar callus. Acrostichals lacking. Dorsocentrals arranged in one regular row, few in number, short, mostly of equal length (except for two pairs of longer prescutellars).
Legs. Wholly yellow. Coxae and trochanters with ordinary yellow to brownish yellow setae. Fore femur slender, with a row of brownish yellow, thin, posteroventral bristles (one longest one in middle part of femur longer than femur is deep) and a row of yellowish, short, thin, anteroventral bristles (nearly as long as femur is deep). Fore tibia mostly slender, somewhat swollen near tibial gland; clothed with ordinary setulae. Fore tarsus slender, unmodified. Mid femur incrassate, nearly 1.5 times broader than fore femur; with rows of ventral black spinules and a row of long (distinctly longer than femur is deep), brown, posteroventral bristles. Mid tibia with black ventral spinules throughout and hardly prominent, flattened, apical spur. Hind leg long, slender; hind femur somewhat swollen in apical part anteriorly, bearing a row of short, brownish to brownish yellow, erect, anteroand a row of short, pale, posteroventral bristles. Abdomen. With brownish yellow tergites and yellow sternites (except posterior margin of sternite 2), clothed with ordinary scattered setulae becoming on sternites longer toward terminalia.

Female
Unknown.

Distribution
Thailand.

Remarks
In the key to the species given below P. thaicus sp. nov. has been included in a couplet jointed with P. siamensis sp. nov. described below. These two species are extremely similar in their external appearance and the best characters to distinguish them can be found in the male terminalia only. The terminalia of P. thaicus sp. nov. and P. siamensis sp. nov. are strikingly different, especially the structure of the hypoproct. Also, P. thaicus sp. nov. is likely to resemble P. nepalensis . However, some characters noted under the remark to P. nuadkhao sp. nov. indicate that they are two different species.

Etymology
The name ''siamensis'' refers to the ancient name of Thailand.

Diagnosis
Mostly yellow species; one pair of verticals; antenna wholly yellowish brown, postpedicel 4.0 times longer than wide, arista 2.0 times longer than postpedicel; mesonotum with two brownish spots, mesopleuron partly brownish; fore tibia and tarsus somewhat darkened, otherwise legs yellow.

Material examined
Holotype Thorax. Largely yellow; prothoracic notum with brownish spot; suture between proepisternum and mesopleuron brown; mesonotum with two brownish, indistinct, elongate oval spots above wings; sternopleuron and hypopleuron largely (except for apical part) brownish. Mesonotum and sternopleuron shining, otherwise thorax finely pollinose, subshining. Anterior and posterior spiracles brown. Humerus with one very short bristle. Mesonotum with two brownish notopleural (anterior one shorter and thinner), one postalar (similar to posterior notopleural), and four scutellar (outer ones very short, thin; inner ones longest among mesonotal bristles, cruciate) bristles; some scattered setulae present behind humerus, on notopleural depression, supra-alar space and postalar callus. Acrostichals lacking. Dorsocentrals arranged in one regular row, short, mostly of equal length (except for two pairs of longer prescutellars).
Legs. Almost wholly yellow; fore tibia and tarsus somewhat darkened. Coxae and trochanters with ordinary yellow to brownish yellow setae. Fore femur slender, with a row of brownish yellow, thin, posteroventral bristles (one longest one in middle part of femur longer than femur is deep) and a row of yellowish, short, thin, anteroventral bristles. Fore tibia mostly slender, somewhat swollen near tibial gland; clothed with ordinary setulae. Fore tarsus slender, unmodified. Mid femur incrassate, nearly 1.5 times broader than fore femur; with rows of ventral black spinules and a row of long, brown, posteroventral bristles. Mid tibia with black ventral spinules throughout and hardly prominent flattened apical spur. Hind leg long, slender; hind femur bearing a row of short, brownish to brownish yellow, erect, antero-and a row of short, pale, posteroventral bristles.
Wing. Slightly infuscate, with yellowish brown veins, bearing one very long, brownish, basicostal bristle. Vein M1+2 somewhat bowed in apical part but parallel to vein R4+5 near wing-apex. Crossveins m-cu and r-m contiguous. Cell br broader than cell bm. Vein CuA2 somewhat sinuate, recurrent. Vein A1 long. Squama brownish yellow and with long yellow fringes. Halter pale yellow.

Female
Unknown.

Distribution
Thailand.

Remarks
Main distinguishing features of P. siamensis sp. nov. are given in the key and have been discussed under the ''Remarks'' to P. thaicus sp. nov.

Diagnosis
Mostly yellow, including legs, species; one pair of verticals; antenna yellowish brown, arista white, postpedicel 4.0 times longer than wide, arista 2.5 times longer than postpedicel; mesonotum with two brownish spots, sternopleuron and hypopleuron wholly brown to yellowish brown.

Male
Unknown.
Thorax. Largely yellow; prothoracic notum brown; prosternum brownish yellow; suture between proepisternum and mesopleuron brown; mesonotum with two brown, distinct, subtriangular spots above wings; sternopleuron and hypopleuron wholly brown to yellowish brown; mesopleuron brownish yellow in upper part; metapleuron brown; postnotum with metanotum brown. Mesonotum and sternopleuron shining, otherwise thorax finely pollinose, subshining. Anterior and posterior spiracles brown. Humerus with one very short, fine bristle. Mesonotum with two brownish notopleural (anterior one shorter and thinner), one postalar (similar to posterior notopleural), and four scutellar (outer ones very short, thin; inner ones longest among mesonotal bristles, cruciate) bristles; some scattered setulae present behind humerus, on notopleural depression, supra-alar space and postalar callus. Acrostichals lacking. Dorsocentrals arranged in one regular row, few in number, short, mostly of equal length (except for two pairs of longer prescutellars).
Legs. Wholly yellow. Coxae and trochanters with ordinary yellow to brownish yellow setae. Fore femur slender, with a row of brownish yellow, thin, posteroventral bristles (one longest one in middle part of femur longer than femur is deep) and a row of yellowish, short, thin, anteroventral bristles. Fore tibia mostly slender, somewhat swollen near tibial gland; clothed with ordinary setulae. Fore tarsus slender, unmodified. Mid femur incrassate, nearly 2.0 times broader than fore femur; with rows of ventral black spinules and a row of moderately long (as long as femur is deep), brown, posteroventral bristles. Mid tibia with black, ventral spinules throughout and hardly prominent, flattened, apical spur. Hind leg long, slender; hind femur somewhat swollen in apical part anteriorly, bearing a row of short, brownish to brownish yellow, erect, antero-and a row of short, pale, posteroventral bristles.

Distribution
Thailand.
Remarks P. isaanensis sp. nov. is most similar to P. nuadkhao described here. However, P. isaanensis sp. nov. has shorter postpedicel and a different pattern of brownish space on the mesopleuron. Real size of the body of the new species is probably smaller since in both specimens last abdominal segments are entirely extruded.

Diagnosis
A black species with one pair of verticals; antenna brownish, arista white, postpedicel 5.0 times longer than wide, arista nearly 2.5 times longer than postpedicel; mesopleuron largely subshining, sternopleuron shining; legs with yellow femora and brownish tibiae and tarsi.

Male
Unknown.

Female
Body length 2.9 mm; wing length 2.3 mm.
Head. Black in ground-colour, with occiput, ocellar tubercle and frons subshining, face shining. Occiput clothed with dark (mostly in upper part) and pale bristly hairs, bearing two dark moderately long, inclinate verticals. Ocellar tubercle with two moderately long, dark bristles and two minute setulae. Antenna brownish, arista white, thick pubescent. Postpedicel 5.0 times longer than wide. Arista 2.4 times longer than postpedicel and 1.5 times longer than scape, pedicel and postpedicel combined. Palpus wholly yellow, small.
Thorax. Wholly black; humerus, mesonotum and sternopleuron shining, otherwise thorax finely pollinose, subshining. Humerus with one very short bristle and few setulae. Mesonotum with one very short presutural supra-alar, two dark notopleurals (anterior one shorter and thinner), one postalar (similar to posterior notopleural) and four scutellars (outer ones very short, thin; inner ones long, cruciate); some scattered setulae present behind humerus, on notopleural depression, supra-alar space and postalar callus. Acrostichals very short, prominent in anterior part of mesonotum, arranged in two rows, wide apart, few in number. Dorsocentrals arranged in one regular row, divergent in anterior part of mesonotum, mostly very short (two pairs of prescutellars longer).
Legs. Hind coxa brownish basally, femora almost wholly yellow (with brownish tinge dorsally), tibiae brownish (especially fore tibia), tarsi brownish yellow. Fore femur somewhat thickened in basal part; with a row of brownish yellow, thin, posteroventral bristles (two longest ones near middle longer than femur is deep) and a row of pale, short, thin, anteroventral bristles (as long as femur is deep). Fore tibia somewhat swollen in basal part. Mid femur nearly 2.0 times thicker than fore femur; with posteroventral bristles at least as long as femur is deep. Mid tibia with hardly prominent, flattened, apical spur. Hind leg long, slender.
Head. Wholly yellow in ground-colour (ocellar tubercle with slight brownish tinge). Occiput shining, clothed with rather short bristly hairs, with longer setae in lower part laterally, bearing two pairs of brownish verticals. Ocellar tubercle with two short yellowish bristles. Frons pale yellow, widened toward ocellar tubercle, above antennae about 2.0 times broader than anterior ocellus, pollinose. Face below antennae nearly as broad as frons, partly pollinose, clypeus shining. Antenna wholly pale yellow. Postpedicel conical, rather short, about 2.0 times longer than wide. Arista nearly 2.0 times longer than postpedicel. Palpus wholly yellow, short, ovate, with moderately long subapical bristle. Proboscis yellow, long, almost as long as head is high.
Legs. Wholly yellow. Fore femur thickened, with very short antero-and posteroventral bristles. Tarsomeres 3 and 4 of fore tarsus flattened, tarsomere one bearing one long, erect bristle near base. Mid femur incrassate, 1.5 times thicker than fore femur, with two rows of black ventral spinules (posterior ones somewhat longer) and a row of six short, brownish, posteroventral bristles. Mid tibia with short, flattened, apical spur. Hind leg ordinary.

Distribution
Thailand.

Remarks
In having distinct vertical bristles, well-developed humerus, distinct posteroventral bristles on mid femur, polished mesonotum, a hardly prominent spur on the mid tibia, multiserial acrostichal and dorsocentral bristles, a very long proboscis and flattened tarsomeres 3 and 4 of the fore leg, P. hualuang sp. nov. belongs to the P. luteus-group comprising P. luteus (Meigen), P. pallescens Kovalev, P. stroblii (Mik) (all known from Europe only), P. kurilensis Shamshev (Kuril Islands), and P. longirostris (Bezzi) (Taiwan) (Bezzi 1912;Chvála 1989;Grootaert and Chvála 1992;Shamshev 1999). The new species can be readily distinguished from P. longirostris, as well as P. longirostris xanthopus (Bezzi), in the wholly yellow antenna (versus postpedicel wholly black). P. kurilensis differs from P. hualuang sp. nov. by a brownish spot on occiput, shining frons, and black abdomen. Additionally, the new species can be readily distinguished from the European species of this group because P. luteus has one pair of vertical bristles only, P. pallescens has uniformly yellow mesonotum and, finally, P. stroblii possesses a black head.

Etymology
The name ''seeluang'' refers to the yellow colour of the body of this species. ''See luang'' means ''yellow colour'' in Thai.

Diagnosis
Almost wholly (including legs) yellow species; head black, with one pair of vertical bristles, antenna with scape and pedicel brown, postpedicel wholly yellow, arista brown, 1.5 times as long as postpedicel, palpus small, yellow; humerus with one minute bristle, acrostichal and dorsocentral bristles two-serial; tarsomere 5 of fore leg black, tarsomeres 3-5 of mid and hind leg darkened, mid femur with a row of posteroventral bristles, mid tibia with long pointed spur.

Material examined
Holotype
Thorax. Wholly yellow, largely subshining, finely greyish pollinose, sternopleuron shining. Humerus well prominent, with one minute bristle. Mesonotum with black bristles, including two notopleurals (anterior one shorter and thinner), one postalar (shorter than posterior notopleural), and four scutellars (inner ones much longer and stronger); some scattered setulae present behind humerus, in notopleural depression and on supraalar space. Acrostichals very short, arranged in two close, more or less regular rows, distinct throughout. Dorsocentrals subequal in length to acrostichals (except for one pair of longer prescutellars), arranged in two irregular rows. Anterior and posterior spiracles yellow.
Legs. Almost wholly yellow; tarsomere 5 of fore leg wholly black, mid and hind leg with tarsomeres 3-5 becoming gradually darker (from 3rd to 5th). Fore femur incrassate, with moderately long yellow to brownish yellow antero-and posteroventral hair-like setae. Fore tibia spindle-like, with short brownish dorsal bristles and yellow hair-like ventral setae extending on basal tarsomeres. Mid femur incrassate, somewhat thicker, than fore femur, with a row of brownish posteroventral bristles beyond rows of black spinules. Mid tibia with long pointed apical spur. Hind femur with rows of short, yellowish anteroand posteroventral bristles. Hind tibia with some more prominent bristly hairs in apical part.
Wing. Hyaline, with one long black basicostal bristle. Vein M1+2 somewhat bowed in apical part but parallel to R4+5 near wing-apex. Crossveins m-cu and r-m separated. Vein CuA2 straight, at right angle to A1. Squama yellow, pale fringed. Halter pale yellow.

Female
Body length 3.3-3.7 mm; wing length 3.1-3.3 mm. Abdominal tergites 2-5 with brownish rectangular spots separated by yellow median space. Otherwise as in male except for sexual differences. Cerci brown.

Distribution
Thailand.
Remarks P. seeluang sp. nov. is most similar to P. dolichopeza Frey described from the Philippines . However, the new species can be readily distinguished from it by its wholly yellow thorax and many other characters.

Discussion
The Platypalpus species have been divided into several more or less natural groups of species (Chvála 1975) and this classification of the genus is currently commonly accepted. However, the implications of this classification for the oriental species is as yet untested. Our very preliminary analysis shows that most of the Platypalpus species groups defined for the Palaearctic species can be found in the Orient as well (see the checklist). The P. ciliaris-group and the similar P. pallipes-group are represented by five and three species in the Orient, respectively. Almost all species of these groups (except for P. acuminatus Saigusa and Yang, 2002 described from Henan) are known from Nepal and northern India. These groups show quite clear preference to higher altitudes.
The P. albiseta-group is most diverse in the Orient with 16 described species, including those presented here. This is probably not a surprise because the group is especially prolific in the tropical regions (Smith 1969;P. Grootaert, unpublished data). Within the Orient the P. albiseta-group shows the same trend in being richer in species in southern areas: Nepal (one species), Henan (one species), Taiwan (one species), Sri Lanka (two species), Thailand (eight species), and Java (three species). Although, the species of this group appear to be very rare or even absent in southern Thailand and Singapore (Grootaert, P. unpublished data) and they have not been found in India yet.
The P. longicornis-group includes seven species taken from different parts of the region. The P. luteus-group is currently represented by two species in the Orient, including P. longirostris and a species described here from Thailand. The group is small (as we have indicated above) but widely distributed, occurring throughout the Palaearctic including Middle Asia and it is also present in North America (Chvála 1989;Grootaert and Chvála 1992;I. Shamshev, unpublished data).
The P. nigritarsis-group is known from seven regional species. However, contrary to the P. longicornis-group and like the P. ciliaris-and pallipes-groups, the species of the P. nigritarsis-group were only discovered from the northern part of the Orient.
One species of the P. minutus-group (P. dolichopeza) is known from the Philippines (Mindanao) ) and we describe a second species from Thailand in this paper.
The P. pallidiventris-cursitans-group, which is the largest of the Platypalpus species groups, is also found in the Orient, although its presence is probably not so evident as compared with the Palaearctic, where the P. pallidiventris-cursitans-group greatly dominates. Four species agree with the definition of this group and they all were described from Taiwan, Henan, and the Philippines (Mindanao) only.
Finally, nine species of Platypalpus have not been included into any of the groups as currently defined. In all these cases the main problem stems from inadequate original descriptions which lack many important characters. No species belonging to the P. unguiculatus-, brevicornis-, hackmani-or isabellae-groups have been found from the Oriental Realm yet.
It is difficult to discuss the genesis and the relationships of the Oriental species of Platypalpus due to our evidently insufficient knowledge of the group from this realm. Nevertheless, at the specific level, Platypalpus generally appears to demonstrate a high degree of endemism. There are doubtful records of P. albiseta (Panzer) (an uncommon species widely distributed throughout Europe) from Taiwan and Java (Smith 1975) but they are most probably misidentifications as both records are based on the female sex only. Otherwise, so far as is currently known, no species is common between the Oriental and other regions. However, the presence of the different species groups may be evidence of the complexity of the faunistic genesis of Platypalpus in the Orient. The presence and a quite high diversity of the P. albiseta-group in many parts of the realm probably reflects the archaic elements of Platypalpus there. The P. albiseta-group is considered in many respects to be most similar to the presumed basal condition within the genus (Chvála 1975). The resolution of the phylogenetic patterns, including the paleontological data, within the P. albiseta-group could clarify more precisely the relationships between the faunas of the different regions (Kovalev 1978). However, such an analysis has never been conducted. Some morphological features that will be discussed below may suggest that in the Orient the species of the P. albiseta-group have evolved into separate complexes resembling in some respects the species known from Papua New Guinea. The latter represents a separate species group that may be a sister group to the P. albiseta-group (Grootaert 1984;Grootaert and Van de Velde 1988). It is necessary to add that the P. albiseta-group greatly dominates in Africa (Smith 1969;P. Grootaert, unpublished data).
The species of the P. luteus-group are also quite plesiomorphous in many respects. However, the relationships of the group within Platypalpus and its possible centre of origin are not quite clear. The connection of the Palaearctic and Oriental elements of this group occurs through the territories of China and the Russian Far East that also has been recently demonstrated in some species groups of the genus Tachydromia Meigen (Shamshev and Grootaert 2005). Similar connections could be attributed to the species of the P. ciliarisand P. pallipes-groups. Both groups are considered most primitive ones within Platypalpus (Chvála 1975). We hypothesize that the presence of these groups may be a result of the later re-invasion of the Platypalpus species into the region.
The species of the P. pallidiventris-cursitans-group (and some other closely related groups noted above) demonstrate the most derived conditions within Platypalpus. The group is mainly distributed in the Holarctic and its centre of origin was likely to be situated there. The records of the species of the P. pallidiventris-cursitans-group in the Orient appear to reflect the younger elements of the genesis of the Platypalpus fauna.
Generally, the species of the P. albiseta-group treated in this paper could be divided into two complexes, although this subdivision is based on the structure of the male terminalia only. Like other described species, the newly discovered representatives of the P. albisetagroup are very uniform in possessing closely similar external characters.
The first complex of species includes P. nuadkhao sp. nov., P. fai sp. nov., and P. siamensis sp. nov. In these species the terminalia are subglobular, somewhat broader than long, and are rotated about 90u; the hypoproct is enlarged but not extending beyond cerci; the cerci are rather short; the left surstylus is hardly prominent. Almost all these characters (except for the hypoproct) appear to demonstrate apomorphous conditions within the P. albiseta-group. The presence of two spine-like extensions on the hypoproct in P. fai sp. nov. and P. siamensis sp. nov. may suggest closer relationships of these species.
In the species of the second complex, that includes P. phomyaaw sp. nov., P. gaemluang sp. nov., and P. thaicus sp. nov., the terminalia are elongate (especially in P. phomyaaw sp. nov. and P. gaemluang sp. nov.), rotated about 45u, with the hypoproct extending far beyond apices of cerci and overlapping the apical part of the right epandrial lamella, the cerci are long, and the left surstylus is prominent. Almost all these characters (except for the hypoproct) are likely similar to the basal conditions within the P. albiseta-group and the genus on the whole.
The structure of the hypoproct in the second complex deserves a special note. We hypothesize that in these species it may have a clasping function during copulation. If so, this is a unique case within Tachydromiinae and the family as a whole. A clasping function of the hypoproct is known to occur within some families of Diptera (Sinclair 2000). It is evident also that within the P. albiseta-group this condition of the hypoproct is a synapomorphy of the second species complex. It is not clear to us yet whether there is a relation of this species complex with the P. isabellae-group (Grootaert, 1984). The latter is supposed to be a plesiomorphic group within Platypalpus related to the P. albiseta-group. All known species have strong spines on the hypoproct, with slender undifferentiated cerci. So it is possible that an ancestral group of the P. albiseta-group related to the P. isabellae-group developed a mating mechanism where extensions on the hypoproct rather than the cerci played a major role in mating.
Some species of the P. albiseta-group found in Thailand and presented in this paper show peculiar modifications of the abdominal segments. In P. fai sp. nov. the abdominal sternite 4 has a quite large, median tubercle bearing a tuft of short brown setae. Unfortunately, the female of this species has not been found yet. So, it is difficult to say whether this structure on the abdominal sternite 4 is shared by both sexes. In P. phomyaaw sp. nov., a modification of the abdominal setation has been found to occur. In this species abdominal sternites 5 and 6 bear two and four very long and closely set bristles, respectively. Again, in this case the female sex remains unknown, although the feature noted is most likely to be a male secondary sexual character.
Normally, in Platypalpus the sclerites of abdominal segments are of ordinary structure and vestiture, with the sternites being unmodified and clothed with short, scattered bristles becoming longer on the pregenital segments.
As far as we are aware our findings are the first record of abdominal modifications within the genus. It should be noted that the abdominal modifications are quite rare in Hybotidae on the whole, except for the tribe Drapetini. Within Drapetini the different modifications of both vestiture (e.g. scale-like setae in Elaphropeza Macquart and Drapetis Meigen) and the structure (e.g. gland-like structures and tubercles in Stilpon Loew, Nanodromia Grootaert, and Crossopalpus Bigot) are a common feature (Grootaert and Shamshev 2003;Shamshev andGrootaert 2004, 2005).
To conclude, it is evident that a revision of Platypalpus from the Oriental Realm is needed. Many species are presently undescribed and much diversity still probably awaits discovery. Although, the data presented in this study deal with a part of the Orient we have tried to discuss them in a broader context. In most cases our very preliminary conclusions are hypotheses only. But we hope that this study will stimulate further research into the genus Platypalpus from this interesting region, as much remains to be resolved.