NOTES ON SE ASIAN WATER BUGS, WITH DESCRIPTIONS OF TWO NEW SPECIES OF TIMASIUS DISTANT (HEMIPTERA: GERROMORPHA)

Pingping CHEN¹, Nico NIESER² & C. LEKPRAYOON³ ¹c/o National Museum of Natural History, Naturalis, Leiden, The Netherlands ²Tiel, The Netherlands ³Dept. of Biology, Faculty of Sciences, Chulalongkorn University, Bangkok, Thailand. NOTES ON SE ASIAN WATER BUGS, WITH DESCRIPTIONS OF TWO NEW SPECIES OF TIMASIUS DISTANT (HEMIPTERA: GERROMORPHA) Chen, P.-p., N. Nieser & C. Lekprayoon, 2006. Notes on SE Asian water bugs, with descriptions of two new species of Timasius Distant (Hemiptera: Gerromorpha). Tijdschrift voor Entomologie 149: blz. 55-66, figs. 1-22, table 1. [issn 0040-7496]. Published 1 June 2006. Two new species of Timasius (Hebridae) are described: T. nilsi sp. n. from Vietnam, and T. chesadai sp. n. from Thailand. The males of two species of Gerridae, Amemboa (Amemboides) ptychoconnexiva Polhemus & Andersen, 1984, and Metrocoris shepardi Chen & Zettel, 1999 are described for the first time. Correspondence: Dr. P.-p. Chen, c/o Dept. of Entomology, National Museum of Natural History, Naturalis, P.O. Box 9517, 2300 RA Leiden, The Netherlands. E-mail: P.Chen@minlnv.nl N. Nieser, Htg. Eduardstr. 16, 4001 RG Tiel, The Netherlands C. Lekprayoon, Dept. of Biology, Faculty of Sciences, Chulalongkorn University, Bangkok, Thailand. Key words. Hebridae, Gerridae, Timasius, Amemboa, Metrocoris, new species, Thailand, Vietnam. This study is part of the results of several expeditions by the National Museum of Natural History Naturalis to Vietnam in 2001, by the first author to Thailand in 2001, and by the Chulalongkorn University in Thailand in 2002. Among the samples, one undescribed species of the genus Timasius Distant, 1909 (Hebridae) and the male of Amemboa (Amemboides) ptychoconnexiva Polhemus & Andersen, 1984 (Gerridae) were discovered from Thua Thien Hue, Phong Dien Natural Reserve, Vietnam. The latter was described by Polhemus & Andersen (1984) from a single female. A similar situation applies to Metrocoris shepardi Chen & Zettel, 1999 (Gerridae), of which the description was based on a number of female specimens collected from Phu Hin Rong Kla National Park, Thailand. Since the genital structure of males is important for reliable identification in Gerridae, the descriptions of the males of these two species are given. In addition, Timasius chesadai sp.n. was found in Kanchanaburi, Thailand, during studies associated with the brt project of Thailand, carried out by the Department of Biology, Faculty of Sciences, Chulalongkorn University. All four species treated in this paper are typical elements of the Oriental fauna. The genus Timasius is a group of interesting semiaquatic bugs inhabiting rocky streams in mountains, of which the substrate can be very different, i.e. soil, litter, plants, rocks etc. covered by a thin film of water (Andersen 1981). He also pointed out that the locomotion structures of Timasius, in particular the long and powerful claws, are well suited for walking and climbing on rocks (Andersen 1981). Our personal observations fit his description well. In Thailand, we collected these insects around big rocks in streams or on the banks of the streams. Sometimes the specimens became evident by moving around the rock, and sometimes they were caught by sweeping the net without seeing them, indicating reaction to disturbance. This latter method often resulted in the capture of one or two specimens. In Taiwan, T. lundbladi Miyamoto, 1965, one of the most common bugs in the central part of the island, was easily found under small rocky stones in streams (personal observation P.-p. Chen). However, it is indeed in general very difficult to find them in the field as has been 55

T JD H F V E M L E, V LUME 149, 2006 mentioned in the literature (Andersen 1981, Zettel 2004), consequently they are rare in museum collections. Timasius was revised by Andersen (1981). A number of species were described later from Taiwan (Zettel 1998a), India (Zettel 2000) and Borneo (Zettel & Chen 2000). All these species belong to other species-groups than the new species described below. Recently Zettel (2004) revised the T. chinai species group to which T. nilsi sp.n. belongs. So far the genus Timasius counts 30 described species ranging from India to the west of Wallace s Line and Dickersons Line (Zettel 2004). This is further corroborated because no species of Timasius were found in the samples from the recent expeditions to Lanyu Island, between Taiwan and Luzon. However, the knowledge of Hebridae remains comparatively poor, and although new species have been found continuously, more extensive field work is absolutely required for a better understanding of this group. We describe here two new species of Timasius from Thailand and Vietnam, making the total species number of Timasius now 32. The genus Amemboa (Eotrechinae) was revised by Polhemus & Andersen (1984), treating 23 species. Subsequently, six additional species and one subspecies were described from continental Southeast Asia, and one species from Borneo (Zettel 1995, 1998b, 2002, Zettel & Chen 1996, 1997), bringing the total number of described species to 30. The genus Metrocoris (Halobatinae) was revised by Chen & Nieser (1993), with many new species subsequently described (Chen 1994, 1995, Chen & Nieser 1996, Zettel & Chen 1996, Polhemus 1998, Chen & Zettel 1999). At present, sixty Metrocoris species are known excluding a number of undescribed species found in continental Southeast Asia and the Philippines. During the preparation of this work, the following collections were consulted: ccbc P.-p. Chen Collection, Beijing, China. nctn N. Nieser Collection, Tiel, The Netherlands. rmnh National Museum of Natural History, Leiden, The Netherlands. mcbt Museum of Chulalongkorn University, Bangkok, Thailand. Measurements of specimens are in millimeters. The body length is measured from the anterior margin of the rostrum to the abdominal end in dorsal view. The length of thorax and abdominal segments are along the median line from the anterior to the posterior margin. Hebridae Timasius nilsi sp. n. (figs. 1, 3, 6, 7, 9 10, 11) Type material. Holotype, macropterous male (rmnh): vietnam, Thua Thien Hue Province, 40 km W of Hue, Phong Dien Natural Reserve, 60m asl., at light, 22.iii-7.iv.2001, leg. J. van Tol. Paratype: macropterous male, same data as holotype (nctn). Type locality. Thua Thien Hue Province, Vietnam. Description Dimensions, macropterous male. Body length 2.90-3.00; humeral width of pronotum 1.08 (fig.1). Colour. Dark brown with scattered long erect golden setae. Head in dorsal view blackish, apices of antennal tubercles and posterior margin brown. Pronotum brownish, pronotal lobe lighter with blackish pits. Mesoscutellum brownish. Metanotal elevation blackish. Hemielytra medium to dark brown, proximally each with a pair of elongate sordid white pruinose patches, basal veins blackish, along Sc+R and M+Cu with silvery hairs which are denser distally; distal part of hemielytra with a large, ill defined, irregular sordid white pruinose patch. Connexiva medium brown. Thoracic sterna black with longitudinal carinae light brown; abdominal venter blackish with connexiva light brown and genital segments medium to dark brown. Antennae and legs pale, yellowish to light brown. Structural characteristics. Width of eye (0.14) slightly over one half the interocular distance (0.23); head without paired dorsal carinae. Buccula (fig. 3) with two, somewhat semicircular depressions, posterior margin emarginate with its dorsal process short and broad, ventral process narrow and reaching distinctly beyond dorsal process. Antennae (2.22) 0.75 times as long as body (2.95). Pronotum with a pair of vague median carinae which are absent on pronotal lobe. Median length of scutellum and metanotal elevation together (0.49) 0.80 times the median length of pronotum (0.61); metanotal elevation with distinct median keel and acute apex (fig. 6). Head, pronotum, scutellum and metanotal elevation with widely scattered erect bristle-like hairs. Hind femur (1.34) distinctly longer than the humeral width of pronotum (1.08). Wings barely surpassing end of abdomen. Venter not modified ventrally, segment eight (figs. 7, 9) slightly tumid ventrally. Proctiger (fig. 11) nearly symmetrical, rectangular with lateral processes basally, on each side with two groups of bristles, one of about four on basal process and one of about eight near apex. Parameres (figs. 10, 11) only slightly asymmetrical. 56

Chen et al.: Asian water bugs Fig. 1. Timasius nilsi, holotype, male, body length 3,00 mm. Biological note The specimens were attracted to light from a rocky stream. Distribution Only known from the type locality: Thua Thien Hue Province, Vietnam. Etymology This species is named in honour of the late Prof. Dr. Nils Møller Andersen, for his invaluable contribution to the knowledge of semiaquatic bugs, and here referring particularly to his excellent work on Hebridae in 1981, which laid the foundation for the modern systematics of this group. Comparative notes This species belongs to the Timasius chinai-group of Andersen (1981) which was revised by Zettel (2004). This author presents two keys to species: one based on external characteristics present in both sexes and one based on characteristics of the male. In both these keys T. nilsi runs to T. yangae Zettel, from West Malaysia. Differences can be found in the buccula (fig. 3), which in T. yangae has a more pronounced dorsal process separated from the ventral process by a wider emargination, and in the metanotal elevation which in T. nilsi has a more pronounced spiniform process than in T. yangae. The males of both T. yangae and T. nilsi have proctigers with subparallel sides (fig. 11) which separates them from other species of 57

T JD H F V EntoM L E, V LUME 149, 2006 Fig. 2. Timasius chesadai, holotype, male, body length 2.59 mm. the T. chinai-group, in which species have caudally convergent proctiger or have convex lateral margins. The proctiger of T. nilsi has well developed narrow lateral processes, whereas in T. yangae the lateral processes are much shorter, broader and somewhat ear-like. The parameres of T. yangae are much more produced distally giving them a more elongate shape than the parameres of T. nilsi (fig. 11). Timasius chesadai sp. n. (figs. 2, 4, 5, 8, 12) Type material. Holotype, macropterous male (mcbt): thailand, Kanchanaburi, Hua Pak Kok, 180 m asl., ii.2002, leg. S. Mongchoichana & S. Leepitakrat. Type locality. Kanchanaburi Province, Thailand. 58

Chen et al.: Asian water bugs Description Dimensions, macropterous male (unique specimen). Body length 2.59; humeral width of pronotum 1.09. Colour. Dark brown to blackish, with scattered long erect golden setae. Head in dorsal view black except posterior margin with two small triangular brownish markings; clypeus, apices of antennal tubercles and eyes castaneous. Pronotum medium brown with blackish pits, anterior part of pronotum darker. Mesoscutellum medium brown. Metanotal elevation dark brown. Hemielytra blackish, proximally each with a pair of elongate white pruinose patches, basal veins black, Sc+R vein densely beset with appressed golden bristles; distal part of hemielytra with a brownish spot. Connexiva medium brownish. Prosternum brownish, meso- and metasternum blackish except for acetabula and caudal point of longitudinal carinae brownish; abdominal venter blackish with connexiva medium brown, and genital segments medium to dark brown. Antennae light brown, distal part of segment 4 pale; rostrum yellowish. Legs pale yellowish, femora distally and tibiae proximally light brown. Structural characteristics. Width of eye (0.14) two third the interocular distance (0.21); head without paired dorsal carinae. Buccula (fig. 4) with two semicircular depressions; posterior margin emarginate with its dorsal process distinct and curved ventrad, ventral process reduced to a rounded ventrocaudal angle of the buccula. Antennae (1.56) 0.60 times as long as body (2.59). Paired median carinae of pronotum distinct in anterior half and obliterated on pronotal lobe. Median length of scutellum and metanotal elevation together (0.38) 0.66 times median length of pronotum (0.58); metanotal elevation with distinct median keel; apex not spiniform (fig. 5). Head, pronotum, scutellum and metanotal elevation with widely scattered erect bristle-like hairs. Hind femur (0.88) distinctly shorter than the humeral width of pronotum (1.09). Wings barely surpassing end of abdomen. Venter not modified ventrally, segment eight slightly tumid ventrally. Male (fig. 12). Proctiger symmetrical, domeshaped, on each side with a group of about 12 bristles near apex, caudal margin with a row of about eight bristles. Parameres symmetrical. Distribution Only known from the type locality: Kanchanaburi Province, Thailand Etymology This species is named in honour of Associate Prof. Dr. Chesada Kasemset of the istrd, Chiang Mai University, for his great support and efforts to promote scientific research in Thailand. Comparative notes The genus Timasius has been divided into seven species groups (Andersen 1981, Zettel & Chen 2000). Timasius chasadai is intermediate between the T. chinai and T. livens-species groups, but it seems closer to the T. livens-group, notably by the following characteristics: short and broad body shape, high and comparatively short bucculae, distinct carinae anteriorly on pronotum, median length of metanotal elevation 0.66 times its basal width, apex of metanotal elevation not spiniform and hind femur distinctly shorter than humeral width of pronotum. The male genitalia (fig. 12) agree with the T.chinaigroup by the shape of the parameres and absence of the caudolateral processes on the pygophore. As there are still a number of undescribed species of Timasius from Thailand in collections, in our opinion it is premature to erect new species groups or to lump existing groups. Timasius chesadai differs from all described species of Timasius by the shape of the posterior margin of the buccula and the shape of the parameres, notably the proximal fingerlike process of paramere (fig. 12) in combination with a simple symmetrical proctiger. Gerridae Amemboa (Amemboides) ptychoconnexiva Polhemus & Andersen (figs. 13-16) Amemboa (Amemboides) ptychoconnexiva Polhemus & Andersen, 1984: 106-107 (description,vietnam). Material examined. vietnam: Thua Thien Hue Prov. 40 km W Hue, Phong Dien Natural Reserve, Ô Lau river & Khe Cá Lóc tributary, 5.iv.2001, 16 31 15 N, 107 12 45 E, leg. J. van Tol, 1, 2 (rmnh, 1 nctn). The description of this species was based on a single female by Polhemus & Andersen (1984). We provide here the description of the male, and additional description to the female. Description Dimensions, male (fig. 13). Slightly smaller than the female, length 3.45, maximum width 1.20. Colour. The same as in female holotype (see Polhemus & Andersen 1984). Structural characteristics. Head width 0.82 across eyes. Mesosternum about 6.5 times as long as metasternum (1.34/0.20). Antennae (4.51) distinctly longer than entire body (3.45); length of antennal segments 1-4: 0.90, 0.82, 1.21, 1.58. Fore femur 4.4 times as long as wide (1.32/0.30). Middle femur (3.50) only slightly longer than body length (3.45); 59

T JD H F V EntoM L E, V LUME 149, 2006 3 9 0,25 mm 4 5 6 7 0,5 mm 10 11 0,5 mm 0,1 mm 0,1 mm 0,1 mm 12 8 Figs. 3-12. Timasius spp.; 3, 5, 7, 9, 10, 11, T. nilsi, holotype; 4, 6, 8, 12, T. chesadai holotype. 3-4, Buccula, in lateral view scale 0.25 mm); 5-6, elevation on metanotum, in lateral view (scale 0.25 mm); 7-8, abdominal segment 8, in lateral view (scale fig.7 = 0.25 mm, fig. 8 = 0.1 mm); 9, abdominal segment 8, in ventral view(scale 0.1 mm; 10, left paramere, in dorsal view (scale 0.1 mm); 11-12, dorsal view of abdominal end (pressed), showing parameres and proctiger (scale 0.5 mm). 60

Chen et al.: Asian water bugs Table 1. Length of leg segments of Gerromorpha in mm. femur tibia tars-1 tars-2 claw Gerridae* Amemboa ptychoconnexiva fore leg 1.32 1.32 0.10 0.21 middle leg 3.50 2.08 0.48 0.37 hind leg 2.92 1.30 0.22 0.30 Amemboa ptychoconnexiva fore leg 1.52 1.51 0.14 0.28 middle leg 3.90 2.35 0.55 0.41 hind leg 3.22 1.52 0.29 0.31 Metrocoris shepardi * fore leg 2.40 2.25 0.16 0.82 middle leg 6.75 4.54 1.81 0.30 hind leg 6.55 3.67 0.40 0.33 Hebridae Timasius anderseni * fore leg 0.84 0.89 0.29-0.13 middle leg 0.94 1.07 0.31-0.14 hind leg 1.39 1.58 0.44-0.13 Timasius chesadai fore leg 0.60 0.63 0.22-0.09 middle leg 0.76 0.69 0.21-0.09 hind leg 0.88 0.96 0.30-0.11 * In Gerridae the claws are usually very small and have not been measured. In Timasius the first tarsal segment is very small, tars1 represents actually the combined segments1+2. In Metrocoris the suture between segments of the hind tarsus is hardly visible, tars1 represents the combined segments 1+2. length of leg segments see table 1. Body length (3.45) about 14 times the pregenital abdominal venter (0.25). Sternum 7 (0.075) slightly longer than sterna 5+6 together (0.063). Genital segments (0.32) on ventral midline longer than pregenital abdomen (0.25). Genital segments small and simple; pygophore (fig. 15) ovate, with a triangular-shaped posterior margin; proctiger (fig. 14) with a short blunt process on each side; paramere (fig. 16) slender, sinuate, with a curved apex, most of the sensory hairs were rubbed off in this individual species. Phallotheca moderately sclerotized at basal half, dorsal and lateral sclerites long, apical sclerites large and slightly sclerotized, ventral sclerites short. Female. The examined females are somewhat larger than the holotype, length 3.70-3.85, maximum width 1.40-1.50. The colour agrees with the original description except that the silvery pubescence in the light median stripe on pro- and mesonotum is reduced to a few scattered silvery hairs in two specimens studied (in the male the distinct silvery pubescence is present). The antennae (4.93) are distinctly longer than the body (3.78), which is much longer than those given for the holotype (3.73). The mean length of the antennal segments 1-4 of the examined specimens: 1.12, 0.88, 1.23, 1.64. Fore femur (1.52) 5.3 times as long as wide (0.29). The connexiva are distally somewhat variable, in one specimen they are distally folded over each other as in the holotype; in another specimen they are distally turned much less strongly inward and not reaching each other by a distance of nearly 0.1 mm. Distribution Only reported from Vietnam so far. Comparative notes Male structures are similar to those of A. perlata Polhemus & Andersen, 1984. The pregenital venter of male is shorter, 0.19 times body length in A. perlata, 0.07 times body length in A. ptychoconnexiva. The genitalia in general are similar to A. perlata, but distinctly different in details: the proctiger of A. ptychoconnexiva (fig. 14) is not only slightly broader than that in A. perlata, but also has the lateral process pointed in a different direction; the pygophore 61

T JD H F V EntoM L E, V LUME 149, 2006 Fig. 13. Amemboa (Amemboides) ptychoconnexiva Polhemus & Andersen, 1984, apterous male, body length 3.46 mm. of A. ptychoconnexiva (fig. 15) with a triangularshaped posterior margin, also which differs from A. perlata (Polhemus & Andersen, 1984: fig. 104). The paramere of A. ptychoconnexiva (fig. 16) is more slender at the base and has a more distinctly sinuate shape than that in A. perlata (Polhemus & Andersen, 1984: fig. 106). In their revisionary work of 1984, Polhemus & Andersen mentioned: The infolded angles of the connexiva are unique. The specimens we have seen possess both folded and unfolded connexiva corners. Since A. perlata has the same structure in posterior connexiva corners (Polhemus & Andersen, 1984: fig 107) as in A. ptychoconnexiva, we presume that it might be possible that A. perlata can fold this structure as well. In addition, Polhemus & Andersen (1984) gave the 2nd and 4th antennal segments of the holotype (female) an equal length of 0.80, which is obviously an error, as in all species of Amemboa the 4th antennal segment is always distinctly longer than the second one. 62

Chen et al.: Asian water bugs Metrocoris shepardi Chen & Zettel, 1999 (figs. 17-22) Metrocoris shepardi Chen & Zettel, 1999: 19-21 (description, Thailand, Phitsanulok Prov.). Material examined: thailand: Phitsanulok Prov., Phu Hin Rong Kla National Park, stream, 1100 m, 06.iii.2001, leg. P.-p. Chen, W. Wattanachaiyingcharoen & S. Piyapichart, C0111, 9 14 (ccbc, nctn, rmnh). Description Dimensions (apterous ). Body length 5.35, maximum width 2.55. Colour. Body yellowish, prominently darkened by the strongly developed black markings. Interocular dark mark W-shaped, bifid posteriorly, with lateral arms reaching inner margin of eye, internal margin of eye with a narrow dark line. Antennal segments dark brown to blackish, but basal 1 /6 of first segment yellowish. Dark markings on dorsal part of thorax blackish. Pronotum blackish at basal half (fig. 17). Width of sublateral stripes of mesonotum as thick as the yellowish part, not confluent with posterior oblique dark band; longitudinal dark strip of mesopleura blackish and thick, running through its length. Metanotum blackish, with two hook-shaped yellowish marks; metacetabula strip black and broad, running through its length. Dorsal dark stripes of fore femur (fig. 18) not confluent into dark apex; external face of fore tibia dark, but ventral face yellowish subbasally. Abdomen blackish dorsally, tergites II-III blackish, tergites IV-VI and genital segments blackish with brownish posterior margin; tergite VII and VIII yellowish with two lateral dark spots anteriorly. Venter yellowish except: external side of fore coxal cleft dark; anterior margin of mesosternum with a pair of blackish short stripes at external side of fore trochanters; along external side of coxal cleft blackish. Structural characteristics. Head (fig. 17) width 1.65 across eyes; width of eye 0.52 about the same as its posterior width; posterior half of eye covering anterior 3/5 of propleura. Length of antennal segments 1-4 : 2.4 0 : 1.05 : 0.90 : 0.58, longer than body length without genital segments (4.35) in ventral view. Pronotum (fig. 17) bulbous, broader than width of head. Fore femur incrassate, ratio length/width about 3.6 (2.50/0.70), inner side of fore femur with an apical indentation, provided with an broad tooth; inner side of fore tibia straight with a small tooth subapically (fig. 18). Middle femur (6.80) longer than hind femur (6.60), length of hind trochanter 0.64. Male genitalia. Segment VIII large, trapezoidal (L/W = 0.60/0.90 in dorsal view, with an median keel ventrally and a tuft of long hair at each side (fig. 20). Pygophore (figs. 19) subovate in lateral view, not raised upwards posteriorly (L/W = 1.19/1.00 ventrally), with a patch of long setae at each side (fig. 20). Proctiger relatively small (L/W = 0.30/0.38 dorsally). Paramere (Fig. 21) very stout, curved upwards, extending distinctly beyond genital segments, caudal face concave along its length, apex moderately sharp in lateral view. Structure of phallus (fig. 22): basal apparatus strongly sclerotized at lateral corner as the consequence of having stout paramere; the phallotheca scoop shaped, opening dorsally and weakly hardened laterally and medioventrally; membranous conjunctivum with a cord-shaped structure along ventral side of vesica; vesica large and not strongly darkened; vesical sclerites: dorsal sclerite long and recurved basally, apical accessory sclerites indistinct, lateral sclerites straight, ventral sclerites long and sclerotized more strongly than the other sclerites; three pairs of additional lateral sclerites less sclerotized. In everted endosoma the lower pair of sclerites curving backwards, lying between basal and ventral lobe, indicating a support function. Female. Abdominal tergite VII modified, each posterolateral corner with one finger-like projection. For further description and diagnostic illustration see Chen & Zettel, 1999. Macropterous form: unknown. Biological notes Collected in a heavily shaded narrow mountainous stream with a rocky bottom, hardly disturbed by human activities. Distribution Only found at the type locality in Phitsanulok Province, northern Thailand. Remark This species was originally described on the basis of apterous females by Chen & Zettel (1999), where they mentioned: This species seems superficially close to species of the M. compar group. However, the bilobed abdominal sternite VII is a strong argument for classing M. shepardi sp.n. in the M. bilobatus group. A final conclusion about the phylogenetic position of M. shepardi must wait till male individuals are found and a cladistic analysis of the Metrocoris species groups is carried out. After checking male specimens of M. shepardi, some similarity of male genital structure was found between M. shepardi and M. bilobatoides Chen & Nieser, 1993, e.g., the structure of pygophore, stout paramere, and general structure of vesica. However, its phylogenetic position will be treated in a future study. In the paper of Chen & Zettel (1999), the type locality of this species was given as Thailand: Petchabun Prov.,... according to the attached sample label. However, Phu Hin Rong Kla national park is under the administration of Phitsanulok Province. 63

T JD H F V EntoM L E, V LUME 149, 2006 14 15 16 6,3x10=0,25mm 0,25 mm Figs. 14-16. Amemboa (Amemboides) ptychoconnexiva. 14, Dorsal view of proctiger (scale = 0.25 mm); 15, dorsolateral view of pygophore (scale = 0.25 mm); 16, external view of left paramere (scale = 0.1 mm). 17-18. Metrocoris shepardi. 17, dorsal view of head and pronotum (scale = 1 mm); 18, dorsal view of left fore leg (scale = 1 mm). 0,1 mm 17 1 mm 18 1 mm Acknowledgements This paper includes results of the expeditions organised by Naturalis and the Institute of Ecology and Biological Resources (Hanoi) to Vietnam. We thank the trf/biotec Program for Biodiversity Research and Training Grant (Thailand), to support the project of Diversity of aquatic and semiaquatic bugs (Suborder Heteroptera) at Thong Pah Phum forest area (Project number brt-r-144018) to the third author, which led to the discovery of a number of interesting Hemiptera from Thailand. Our sincere thanks are due to J. van Tol (rmnh), S. Mongchoichana and S. Leepitakrat (mcbt) for collecting and offering the aquatic bugs for studying. We also thank Jan van Tol for critical review and linguistic corrections to the manuscript. References Andersen, N.M., 1981. Semiaquatic bugs: phylogeny and classification of the Hebridae (Heteroptera: Gerromorpha) with revisions of Timasius, Neotimasius and Hyrcanus. Systematic Entomology 6: 377-412. Chen, P.-p., 1994. An overview of of Chinese Metrocoris Mayr, with descriptions of three new species (Hemiptera: Gerridae). Entomologia Sinica 1(2): 124-134. Chen, P.-p., 1995. A new species of Metrocoris Mayr from Yunnan, China (Insecta: Heteroptera: Gerridae). Annalen des Historischen Museums in Wien 97B: 155-158. Chen, P.-p. & N. Nieser, 1993. A taxonomic revision of the Oriental water strider genus Metrocoris Mayr (Hemiptera, Gerridae). Part I. Steenstrupia, 19 (1): 1-43, part II. 19(2): 45-82. Chen, P-p. & N. Nieser, 1996. A new species of Metrocoris Mayr (Heteroptera: Gerridae) from Sangihe Island, 64

Chen et al.: Asian water bugs 19 Figs. 19-22. Metrocoris shepardi. 19, Lateral view of pygophore and proctiger (scale = 0.5 mm); 20, ventral view of abdominal end (scale = 1 mm); 21, External view of left paramere (scale = 0.1 mm); 22, male genitalia, in dorsolateral view, lateral sclerites at right side not illustrated (scale = 0.5 mm). 20 0,5 mm 21 1 mm 0,1 mm 22 0,5 mm Indonesia. Entomologische Berichten, Amsterdam, 56(4): 72-75. Chen, P.-p. & H. Zettel, 1999. Five new species of Halobatinae genus Metrocoris Mayr, 1865 (Insecta: Hemiptera: Gerridae) from continental Asia. Annalen des Naturhistorischen Museums in Wien 101 B: 13-32. Miyamoto, S., 1965. Hebridae in Formosa (Hemiptera). Shiboldia (Biol.) 3(3): 281-290. Polhemus, D.A., 1998. Two new species of water striders (Heteroptera: Gerridae) from The Philippines. Proceedings of the Entomological Society of Washington 100(2): 261-268. Polhemus, J.T. & N.M. Andersen, 1984. A revision of Amemboa Esaki with notes on the phylogeny and ecological evolution of eotrechine water striders (Insecta, Hemiptera, Gerridae). Steenstrupia 10(3): 65-111. Zettel, H., 1995. Zwei neue Amemboa Esaki, 1925, aus Borneo und Vietnam (Heteroptera: Gerridae). Annales Historico-Naturales Musei Nationalis Hungarici 87: 63-66. Zettel, H., 1998a. A remarkable new Timasius Distant 1909 (Heteroptera: Hebridae) from Taiwan. Linzer Biologische Beiträge 30: 601-604. Zettel, H., 1998b. Faunistical notes on Amemboa Esaki (Heteroptera: Gerridae) from Laos and Vietnam, with description of a new species. Acta Zoologica Cracoviensia 41: 169-172. Zettel, H., 1999. An illustrated key to the genera of Hebridae (Gerromorpha) in Thailand. Amemboa 3: 22-26. Zettel, H., 2000. Neue und wenig bekannte Hebridae (Insecta: Heteropter) aus Süd-Indien mit Neubeschreibungen von sechs Arten aus den Gattungen Hyrcanus Distant, 1910, Timasius Distant, 1909 und Hebrus 65

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