Rhyacobates zetteli, Tran, A. D. & Nguyen, X. Q., 2016

Tran, A. D. & Nguyen, X. Q., 2016, Three new species of the water strider genus Rhyacobates Esaki, 1923 (Hemiptera: Gerridae) from Vietnam, Zootaxa 4121 (5), pp. 501-516 : 505-508

Rhyacobates zetteli sp.n.

( Figs. 12–23 )

Material examined. Holotype (apterous female) and allotype (apterous male), Vietnam, Lao Cai Prov., Sa Pa, Hoang Lien N'Park, Nui Xe, Suoi Vang, 22°20.835’N 103°46.446’E, 1366 m asl., coll. Tran A.D., 4 July 2004, TAD0417 ( ZMHU).

Paratypes: VIETNAM: Lao Cai Prov.: 11 males, 13 females (apterous), same locality data as holotype ( ZMHU, ZRC, NHMW); 1 female (macropterous, de-alated), Sa Pa, Hoang Lien N'Park, Nui Xe, a small water flow, 22°21.110’N 103°46.216’E, 1978 m asl., coll. Tran A.D., 4 July 2004, TAD0418 ( ZRC); 1 female (apterous), Sa Pa, Nui Xe, Tram Ton area, feeder stream of Vang stream, 22°20.020’N 103°46.223’E, 1904 m als., coll. Tran A.D. et al., 25 October 2013, TAD1357 ( ZMHU).

Description. Size: males (apterous), length 7.30–7.70 (allotype 7.55), width 2.44–2.67 (allotype 2.54); females, length 9.8–10.6 (holotype 10.5), width 3.04–3.58 (holotype 3.41) (apterous), length 10.3, width 3.36 (macropterous, de-alated).

Colour ( Figs. 12, 13 ): Dorsum of body mainly black or brown, covered with golden and silvery pubescence. Head yellow with 2 (male) or 3 (female) small black markings dorsally. Antennae mainly black, segment 4 with whitish area in distal two-fifths. Pronotum mainly yellow with black outer margin. Pronotum in macropterous form (female) with black anterior margin, anterior part (before pronotal lobe) yellow, pronotal lobe black with thin longitudinal yellow stripe, lateral and posterior margins yellow. Mesonotum in apterous form black with broad yellow median marking from anterior to posterior margins; median marking of females broader than in males. Metanotum with expanded yellow marking (broader in females). Abdominal terga mainly black or brown, with yellow-brown connexiva. Venter of female mainly light yellow, except anterior half of mesosterno-pleuron black or brown, with median light yellow marking confluent with light coloured posterior part. Venter of male, mesosternopleuron mainly black or brown, with long light yellow triangular marking on posterior half, abdominal venter light yellow. All coxae and trochanters yellow. Fore femur yellow with light brown dorsal stripe. Middle and hind femora yellow-brown at basal part, dark brown or black at distal part. All tibiae and tarsi dark brown or black.

Apterous female (holotype): Head width 1.56, interocular width 0.76, eye length (dorsal view) 0.63. Lengths of antennal segments 1–4: 4.02: 1.08: 1.49: 1.12. Pronotum broader than long, length 0.76, width 1.86; mesonotum length 1.51, metanotum length 0.56. All coxae with rings of dark bristle-like hairs at apical margins. Fore trochanter with long hairs on ventral side. Lengths of leg segments (femur: tibia: tarsus 1: tarsus 2): fore leg: 4.48: 4.07: 2.01: 0.98; middle leg: 12.30: 7.65: 4.17: 0.46; hind leg: 12.50: 6.75: 0.22: 0.32. Fore femur slender (width 0.44), with row of 11 long dark bristle-like hairs and scattered soft long hairs on venter, sub-apical part with small tooth-like elevation ( Fig. 14 ). Abdomen ( Figs. 20, 21 ) straight, prolonged, ventral length 5.10. Connexival margin narrow. Each connexival corner of segment 6 with small blunt process ( Fig. 21 ). Abdominal segment 7 prolonged, almost completely enclosing genital segments, tergum 7 medially produced on posterior margin; sternum 7 (length 1.68) slightly more than 1.5 times as long as tergum 7 (length 1.02), posterior margin of sternum 7 bilobate; posterolateral corner of abdominal segment 7 with small blunt process ( Figs. 20, 21 ), sometimes bent inwards thus not visible in lateral view ( Fig. 23 ).

Apterous male (allotype): Head width 1.45, interocular width 0.70, eye length 0.60. Lengths of antennal segments 1–4: 4.02: 1.06: 1.56: 1.11. Pronotum broader than long, length 0.73, width 1.68; mesonotum length 2.08, metanotum length 0.69. Lengths of leg segments: fore leg: 4.41: 3.82: 1.27: 0.91; middle leg: 12.00: 7.10: 3.72: 0.46; hind leg: 11.70: 7.55: 0.21: 0.30. Fore femur with similar pubescence as in apterous female, sub-apical part also with small tooth, width of fore femur 0.51. Middle trochanter with 6–7 spines at distal part, middle femur with spines but not in distinct row ( Fig. 15 ). Other leg structures similar to those of female. Abdomen relatively short, ventral length 2.74. Length of sternum 7: 0.43, posterior margin straight. Genitalia: directed slightly downwards; venter of abdominal segment 8 length (in-situ) 0.24; proctiger relatively widened, with broadly angular lobes laterally ( Fig. 16 ); pygophore of moderate size, apical margin almost straight; paramere relatively long and slender, curved at distal two-thirds, setae not distinct ( Figs. 17, 18 ); endosomal sclerites as in Fig. 19 .

De-alated macropterous female: Head width 1.52, interocular width 0.78, eye length 0.67. Lengths of antennal segments 1–4: 4.12: 1.11: 1.52: 1.22. Pronotum covering most of mesonotum, length 3.23, width (across humeri) 2.71; metanotum length 0.62. Lengths of leg segments: fore leg: 4.31: 4.02: 1.98: 1.03, width of fore femur 0.44; middle leg: 12.30: 7.60: 4.17: 0.48; hind leg: 12.40: 6.60: 0.21: 0.29. Other structural characteristics similar to apterous females.

Macropterous male: unknown.

Etymology. This species is dedicated to Dr. Herbert Zettel (Natural History Museum Vienna) for his great contribution to the knowledge of aquatic bugs of Southeast Asia, and for enthusiastically supporting the first author in the field of water bug research.

Remarks. Rhyacobates zetteli sp.n. differs from all of its congeners in the combination of following characters: the unique dorsal colour pattern of the body ( Figs. 12, 13 ); the abdomen of the female is straight; each connexival corner of segment 6 has a small, blunt process ( Fig. 21 ); abdominal segment 7 of the female is prolonged and in lateral view, tapers apically ( Figs. 21–23 ), the connexival margin of sternum 7 is much shorter than the ventral length ( Figs. 21, 23 ); the connexival corner of sternum 7 of the female is produced into a small blunt process ( Fig. 21 ), the posterior margin of sternum 7 is bilobate, but without a median process ( Fig. 22 ). The shape of the paramere of this new species is similar to that of R. gongvo , but males of the latter can be separated from this new species by other characteristics, i.e., colouration, shape of the proctiger and endosomal structures.

Both new species, Rhyacobates angustus sp.n. and R. zetteli sp.n., are closely related to each other, as both taxa possess the prolonged and rather straight abdomen of the female, the posteromedian process on tergum 7 of the female, and the sub-apical tooth-like elevation on the fore femur of the female. In the subfamily Ptilomerinae , similar modification on the posterior margin of female tergum 7 is previously known only in the genus Stridulobates Zettel & Thirumalai, 2001a (see Zettel & Thirumalai 2001a: Figs. 15, 16 ). However, in species of Stridulobates, tergum 7 of the female is prolonged and covers most of tergum 8, whereas in R. angustus sp.n. and R. zetteli sp.n., tergum 7 is shorter and covers only a small anterior portion of tergum 8. Other characteristics, e.g., the absence of a metanotal process in females, the lack of a "stridulatory device" on the middle trochanter and sterna 2–6 in males, also suggests that R. angustus sp.n. and R. zetteli sp.n. do not belong to Stridulobates. Additionally, males of R. angustus sp.n. and R. zetteli sp.n. clearly differ from males of Stridulobates in the shape of the parameres and structure of endosoma (see Matsuda 1960: Figs. 677, 679; Zettel & Thirumalai 2001a: Figs. 9, 10 ).

Rhyacobates angustus sp.n. and R. zetteli sp.n. can be easily separated from each other by the yellow median markings on the nota, the shape of the male proctiger and paramere, and the structures of female sternum 7. In R. angustus sp.n., yellow markings on the pro- and mesonota are slender (the metanotum of the male is totally black and without yellow marking, the metanotum of the female is with very slender with a yellow median marking; the male proctiger has a rounded lobe on each side) ( Fig. 3 ); the apex of the male paramere is more abruptly narrowed ( Figs. 4, 5 ), sternum 7 of the female has large, sub-triangular connexival processes and a broadly-arched posterior margin ( Figs. 8–10 ). In R. zetteli sp.n., yellow markings on the nota of both sexes are broad; the male proctiger has a broadly angular lobe on each side; the male paramere gradually tapers apically ( Figs. 17, 18 ); sternum 7 of the female has small blunt connexival processes ( Fig. 21 ), the posterior margin of sternum 7 is bilobate ( Fig. 22 ).

Habitats. Most specimens of Rhyacobates zetteli sp.n. were collected in a shaded and fast flowing mountain stream at an elevation of over 1800 m ( Fig. 11 ). They were found skating in schools of numerous individuals: adults and nymphs in a mixture of which the nymphs were predominant. Seasonal fluctuation in population size and ratios of nymphs to adults are still unknown. The individuals of this species were also found often resting on partially submerged rocks in the middle the stream, as do other species of Rhyacobates ( Esaki 1923; Tran & Yang 2006). One macropterous specimen (with a de-alated wing) was found in an unshaded, tiny water flow (locality TAD0418), which continues underground and was ca. 500 m from the main stream (locality TAD0417). None of the specimens found in the main stream were the macropterous form. This observation suggests that this species has good flying ability (probably for dispersal), but upon migrating, the macropterous individuals were likely to have their wings broken off.

Distribution. Vietnam: Lao Cai.

Figures

FIGURES 11 – 13. (11) Habitat of type locality of Rhyacobates zetteli sp. n. (12, 13) Habitus of R. zetteli sp. n. (12) apterous male. (13) apterous female (photographed by Tran Anh Duc).

FIGURES 14 – 23. Morphological features of Rhyacobates zetteli sp. n. (14) right fore leg of female. (15) basal part of right middle leg of male, ventral view. (16) proctiger. (17, 18) left paramere, two different views. (19) endosomal sclerites. (20) body of female, lateral view. (21 – 23) apex of abdomen of female, dorsal, ventral, and lateral views respectively.

FIGURES 1 – 10. Morphological features of Rhyacobates angustus sp. n. (1) right fore leg of female. (2) basal part of right middle leg of male, ventral view. (3) proctiger of male. (4, 5) left paramere, from different views. (6) endosomal sclerites. (7) body of female, lateral view. (8) abdomen of female, dorsal view, (9, 10) apex of abdomen of female, ventral and lateral views.