Butaya auko Yakovlev sp. nov.

(Figs 7, 15, 17)

Type material. Holotype: male, Vietnam, Gia Lai Prov., Kon Ka Kin N.[ational] P.[ark], K’Bang distr., Dak Roong Comm., top of mountain pass, N14º4286’; E108º36’, 16− 17.03.2012, H – 1210 m, leg. V. Zolotuhin (ZISP); Paratypes: 2 males, same data and locality (RYB).

Description. Antennae bipectinate from base, distal third of antenna simple, filiform. Thorax covered with light-yellow hairs. Upper surface of abdomen covered with black hairs, apex of abdomen with light-yellow hairs. Forewing length 15–16 mm. Forewing light-yellow with slightly developed silver-grey area in cubital area. Edge light-yellow, lighter than background. Fringe light-yellow. Hindwing light-yellow, lighter than forewing, without pattern. Fringe light-yellow.

Male genitalia. Uncus rather long, with pyramidal apex. Tegumen medium-sized. Branches of gnathos completely reduced. Valvae narrow, medium-sized, lanceolate. Costal edge of valva nearly even, lowers edge with deep incisures in middle third. Juxta stout, saddle-like, with two pairs of stout lateral dorsally directed processes. One pair of small, thin, apex acute. Second pair long, band-like with semispherical apices. Saccus conic, directed back, medium-sized. Aedeagus with medium thickness, short, slightly narrowed in middle ⅓. Lateral surface of vesica with long sclerite.

Female unknown.

Diagnosis. The new species is easily distinguished from the single known species of the genus, B. gracilis Yakovlev, 2004 (Yunnan, China) by the following characters: the comparatively small size, narrower valvae, the deep incisions on the lower edge of the valva, and the much narrower aedeagus.

Etymology. Named after Au Ko, a mythological character, mountain fairy, goddess, and mother of the Vietnamese civilization.