Lygistorrhina chaoi (after Papp, 2002)
L. chaoi is an easily recognisable species. It belongs to that species-group of the true Lygistorrhina, where flagellomeres yellow-black patterned, namely L. cincticornis EDWARDS, 1926 (Borneo), L. pictipennis OKADA, 1937 (Japan), as well as L. legrandi MATILE, 1990 in the Afrotropical Region. The 5th to 8th and 11th to 13th flagellomeres are black in this species, which separate it from the related ones. Also the male genitalia (tergite 9, gonostylus) bear distinctive features.
Male. Head: Frons and thorax dull dark brown (blackish), abdomen subshiny with basal (cranial) lateral small round lights pots on T2 to T6 (on T6 minute, indistinct). Eyes with evenly distributed short hairs; also mid ocellus present. Scape, pedicel and four basal flagellomeres yellow, 5th to 8th flagellomeres black, 9th and 10th flagellomeres yellow, 11th to 13th flagellomeres black again and apical (14th and 15th) flagellomeres yellow again.
Legs dirty yellow. Apical 2/5 of mid and hind femur dark brown. Coxae and trochanters dark brown. Tibial setulae in well-ordered rows. Tibial spurs 1:2:2, mid tibial spurs subequal. Fore claws 0.7 mm long, thin, sharp, curved arched with a ca. 0.025 mm long ventrobasal second apex.
Wing light brownish with brown veins. Sc rather strong, ends free. R1 reaching near middle of wing, R5 joins C far from apex of wing, costal vein distinct and abruptly ends at 3/4 of the section between R5 and M1. M1-M2 fork nearly complete, their stalk present as colourless fold only. M3+4 (cf. KRZEMINSKI & EVENHUIS 2000) distinct even below section of R1. Cu1 not reaching wing margin, apical part perpendicular to alar margin. Cu2 straight, distinct almost to the curved part of Cu1. A1 almost parallel to hind margin of wing, short, shorter than down-curved section of Cu1. Wing patterned, 4 brown spots as follow: 1) apical 3-shaped spot from below the apex of R5 leaving the subcostal area light, continued narrowed to M1 forming a wide band along M1 continued in ml cell more proximally than its R5 part and terminating below M2, leaving m, apical part light. 2) Second spot covers ml at the area of the M1, M2 bases, continued in m2 somewhat lower than M3+ 4 and follows M3+ 4 widely to the wing apex, main part in m2. 3) Third spot along Cu-s and widens on the down-curved part of Cu1. 4) Fourth spot present as a round one in Cu cell (at about the middle). Halter 0.53 mm long, pale yellow.
Genitalia. Gonostylus yellow, contrasting gonocoxites. Gonostylus (Figs 2-3) with a subapical medial blunt, more or less globular tooth, lacking in a number of Lygistorrhina species, large and pointed in L. carayoni MATILE, 1986. Caudally to this took a thicker short black thorn present. Tergite 9 club-shaped with rounded basal and caudal edges, caudal apex with dense short black thornlets, like in carayoni. Tergite 9 dorsally with long setae, 2 pairs of them in apical quarter rather long. Sternite 8 short liguliform. Phallus short and hidden, as in its congeners. Tergite 9 completely covers the short pale cerci, which bear some minute black thornlets apically.
Measurements in mm: body length not precisely measurable (abdomen down-curved), ca. 3.75, wing length 3.12, wing breadth ca. 1.00, length of proboscis 2.30, length of fore tibia 1.45, length of fore metatarsus 1.80.