(Figs. 1–3, 8, 9)

Type material. Holotype: male, Malaysia, Borneo, Sabah, Mt. Trusmadi, 20–25.viii.2016, H.L. Han & H. Geng, genit. prep. hhl-3598-1, coll. NEFU. Paratypes: 6 males, Malaysia, Borneo, Sabah, Mt. Trusmadi, 24.iv–2.v.2016, H.L. Han, coll. NEFU; 2 males, same data as holotype, coll. NEFU; 1 male, same collecting site as holotype, 1–6.x.2018, H.L. Han, genit. prep. hhl-4342-1, coll. NEFU.

Diagnosis. Superficially C. fibigeri is similar to C. honeyi (Fig. 4, 11), but can be separated from this species by the following characters: in C. fibigeri the ground colour of the forewing is light whitish-yellow, slightly mixed with brownish-yellow in outer part of wing (in C. honeyi the ground colour of the forewing is whitish yellow, blurred); the basal patch of the forewing in costal area is broader than that in C. honeyi; the costal patch of in medial area in C. fibigeri is broader and square-shaped (in C. honeyi it is smaller and less expressed); the reniform spot in C. fibigeri is whitish-yellow, rather large and oblate (in C. honeyi it is white, small and indistinct); the hindwing in C. fibigeri is greyish-yellow (in C. honeyi the hindwing is grey); the discal spot is brown, expressed as a small dot (in C. honeyi the hindwing is darker brown, the discal spot is bigger, diffused, band-shaped). In the male genitalia, the valvae are strongly asymmetrical (in C. honeyi they are slightly asymmetrical (Fig. 9); the process of the sacculus in C. fibigeri is conical thorn-like but in C. honeyi it is absent; the saccus in C. fibigeri is narrow and long, but in C. honeyi it is broad and 2X shorter; the anellus plate is irregularly trapezoid, with a small apical extension (in C. honeyi it is long, spatulate, and with a rounded apical extension); in C. fibigeri the aedeagus is bent curved at a right angle while in C. honeyi the aedeagus is smoothly curved.

Description. Adult (Figs 1–3). Wingspan 9.5–11.0 mm. Head. light brownish yellow. Thorax. Whitish-yellow; tegulae whitish-yellow; patagia dark brown. Forewing light whitish yellow to yellow mixed with brown scales; basal line very thin, indistinct; antemedial line light orange, waved, with 3—4 blackish brown small dots; median line light orange, smoothly curved, with over 10 blackish- brown small dots; postmedial line light orange, oblique, formed with several blackish brown small dots, folows to M 3, then incurved to inner margin; subterminal line somewhat darker, blackish brown, roundedat M 3 -Cu 1, light orange mixed with smoky brown in costal area, close to postmedial line down of M 3; terminal line blackish-brown; fringe smoky brown, mixed with some yellow and orange; reniform spot bright whitish yellow, rather large and oblate; costal area darker than ground colour; basal patch cylindrical, blackish-brown; medial patch in costal area large, square, thick; terminal area blackish brown. Hindwing greyish-yellow; discal spot brown, as small dot; outer margin of wing weakly incurved, angulate at Cu 2; fringe slightly lighter than ground colour, in basal part yellowish. Abdomen. Whitish yellow to brownish yellow, with tuft of yellow hairs at terminus. Male genitalia (Figs 9, 10). Tegumen fused with anellus plate, forming a circular ring in upper part. Vinculum asymmetrical, broader than tegumen, equal to tegumen in length. Saccus narrow, long, Y-shaped, deviated left. Valvae asymmetrical, extended apically, right valva (from dissection perspective) longer and broader than left one; process of sacculus conical spine-like process, extending downward near basal part of valva left process larger than right one; ampulla bilobed, asymmetrical, its left lobe tongue-like, setose, right lobe 1.5 X as broad as left one, apically rounded, with small, thorn-like, dorsal extension; digitus as long as valva, on right valva digitus is larger and broader than on left valva. Juxta large, sclerotized, its left part quadrangular, right part triangle. Anellus plate irregularly trapezoidal, with small apical extension. Aedeagus bentat a right angle, tapered apically. Vesica with small, short basal cornutus. Female genitalia. Unknown.

Distribution. The species is distributed in East Malaysia: Borneo, Sabah (Trusmadi Mountain). Costasensora fibigeri inhabits montane meadows and open hills with woody shrubs and herbaceous plants in the zone of tropical rainforest. Probably several generations over the year. Specimens were captured at UV light in April, August and October.

Etymology. The species name “ fibigeri ” is dedicated to the late Dr. Michael Fibiger who was an author, first explorer and developer of the classification of the family Micronoctuidae.