Eotrechus brevipes Andersen, 1982

Polhemus, John T., Tran, A. D. & Polhemus, Dan A., 2009, The Genus Eotrechus (Heteroptera: Gerridae) In Vietnam With Descriptions Of Two New Species, Raffles Bulletin of Zoology 57 (1), pp. 29-37 : 30-32

Eotrechus brevipes Andersen, 1982

( Figs. 1–3 )

Eotrechus brevipes Andersen, 1982: 17–19 , Figs. 13 , 19, 25–27, 32–33 (type locality: Goom, Darjeeling, India); Andersen, 1998: 4–5 (descriptive notes).

Material examined. – INDIA: 1 apterous male, “ N. India: Darjeeling , 7000 ft., 11–20.iii.1924, Maj. R. W.G. Hingston / Everest Exp. Brit. Mus. 1924-386” (paratype, BMNH); 1 macropterous female, “Gopaldhara, Darjeeling, 4720 [not 4729 as in Andersen, 1982]– 6100 ft., on wet ground, 24-7-17, H. Stevens, Brit. Mus. 1922-307” (paratype, BMNH); 1 apterous female, NW Bengal, Rimbik-Srikhola, 2,650m, coll. E. Kucera ˇ, 15–27 May 2006 ( NHMW) . VIETNAM, Lao Cai Prov.: 5 apterous males, 13 apterous females, dry steep rockface, 17 km northwest of Sa Pa , 1,935 m. [6,350 ft.], 22°21'17"N 103°46'28.3"W, 8 Apr.2000, 1115–1300 hrs., CL 4401, coll. J. T . Polhemus, D.A. Polhemus & P. Nguyen ( USNM, JTPC, ZRC) .

Diagnosis. – Size: apterous male, length 7.35, width 2.28; apterous female, length 6.80, width 2.51. Colour as in Andersen (1982).

Body mainly brown, covered with green reflective pubescence. Antennae about 0.7× body length, first antennal segment shorter than head width across eyes. Male fore femur strongly incrassate (slightly less in female) and not spinose; fore tibia slightly curved with a small projection on apex. Abdomen relatively short. Male sternum VII about 1.66× length of two preceding sterna combined, posterior margin emarginated with a broad medial notch (about 1/3 of sternum VII length). Male pygophore with a pair of posterolateral projections, each projection with a finger-like process. Female genital segments concealed, proctiger covered by tergum VIII.

Remarks. – The specimens listed above represent the first record of this species for Vietnam, and represent a range extension of 1,700 kilometres from the original type locality at Darjeeling, India ( Andersen, 1982). This, in combination with other records (see below) implies that the species is distributed along the entire southern margin of the Himalayan uplift from Assam, through Burma and Yunnan, to Vietnam. It has likely been overlooked because of its odd ecological habits, as described in the following section.

Ecological notes. – Eotrechus brevipes is notable among members of the family Gerridae for exhibiting an essentially terrestrial mode of existence. At the Vietnamese locality 17 km northwest of Sa Pa, this species was found inhabiting clumps of grasses and sedges clinging to an exposure of dry, brown bedrock adjacent to a waterfall and associated lateral rheocrenes ( Figs. 1–3 ). Specimens of E. brevipes were found only in this dry setting, where they sheltered at the bases of the vegetation clumps ( Fig. 3 ). If disturbed, they were able to move across the steeply sloping rock face with great rapidity to another patch of sedges or grasses, and were therefore most easily collected by application of a light pyrethrin fog, which slowed their movements and caused them to emerge from their hiding places. The striking color pattern of this species, consisting of longitudinally parallel orange and green stripes, although conspicuous in a collection tray, in fact provides a remarkably effective camouflage amid the green stems and brownish earth of the vegetation clumps in which this species hides. A search of the adjacent wet rheocrenes in closer proximity to the waterfall produced no further captures of E. brevipes ; instead, these wet rheocrenes were inhabited by E. fansipan , new species (see subsequent description). Therefore, it appears that at this single locality, two distinct Eotrechus species were segregating rock face habitats on the basis of moisture regime. The unusual preference of E. brevipes for dry, partially vegetated rock faces may also explain the relative dearth of captures for this species, given that most collectors would not search for water striders in such settings.

Distribution. – India (Sikkim and West Bengal), China (Fukien), and Vietnam (north-western area).

Figures

Figs. 1–3. Type locality for E. fansipan, new species, at a waterfall 17 km. northwest of Sa Pa, Vietnam. Both E. brevipes and E. fansipan, new species, occurred at this location. 1, general view of waterfall and surroundings, showing wet rheocrenes adjacent to the fall itself, on the left side of the photo, which provided habitat for E. fansipan, new species, and dry slopes to the right side of the photo, which provided habitat for E. brevipes. The senior author, standing to the right of the fall, provides scale; 2, lateral view of fall, showing dry bedrock faces in the foreground on which E. brevipes occurred; the photo was taken from near the position of the senior author in Fig. 1; 3, detail of E. brevipes habitat, showing clumps of vegetation scattered on open bedrock. Individuals of E. brevipes sheltered within the vegetation clumps.

Figs. 11–16. Eotrechus pumat, new species, structural details: 11, male foreleg; 12, female abdomen, left lateral view; 13, male proctiger, dorsal view; 14, male terminal abdomen, ventral view; 15, male pygophore, left lateral view; 16, male pygophore, dorsal view.