Malostenopsocus lacteus sp. nov.

(Figs. 1–3)

Diagnosis. This species is characterized by the light-colored body and the indistinctly sclerotized female subgenital plate.

Female. Measurements. Body length 3.27 mm, length from postclypeus to wing tip 5.91 mm. IO: 0.56 mm, d: 0.19 mm, IO/d = 2.95, f1: 0.66 mm, f2: 0.63 mm, f3: 0.57 mm, FWL: 4.67 mm, FWW: 1.73 mm, HWL: 3.04 mm, HWW: 1.03 mm, t1: 0.47 mm, t2: 0.12 mm.

Coloration (in alcohol). Head (Figs. 1 b–d) whitish, middle of vertex brown, ecdysial line brown, ocellar area dark brown, middle of front with a brown marking. Antennal scape yellowish white, pedicel and flagellum brown. Mouthpart yellowish white, but labrum yellowish brown and tip of maxillary palpi brown. Prothorax yellowish white, meso- and metathorax dorsally brown, laterally mostly yellowish white. Legs with yellowish white coxae and trochanters, femora and tarsomere 1 mostly yellowish white with brown apex, tibiae and tarsomere 2 brown. Forewing (Fig. 1 e) transparent and immaculate, wing margin mostly pale brown; costal vein from base to pterostigma and R yellowish white, M+CuA and A pale brown, other veins brown; basal membranous region with setae (Fig. 2). Hind wing (Fig. 1 f) transparent; costal vein and R yellowish white; other part of wing margin, M+CuA, and A yellowish brown; other veins brown. Abdomen yellowish white.

Genitalia (Fig. 3 a) feebly sclerotized. Epiproct (Fig. 3 b) subtrapezoid. Paraproct with 28 trichobothrias. Subgenital plate (Fig. 3 c) without distinctly sclerotized region. Gonapophyses (Fig. 3 d) slightly sclerotized, external valve subtrapezoid, dorsal and ventral valve blade-shaped.

Male. Unknown.

Type material. Holotype female, Laos: Oudomxai, near Muang Xai, 880 m, 24.III.2016, Xingyue Liu (CAU).

Distribution. Laos (Oudomxai).

Etymology. The specific name “ lacteus ” refers to the type female with light-colored body.

Remarks. This new species differs from all other species of Malostenopsocus by the yellowish white costal vein and the indistinctly sclerotized region of the female subgenital plate. It is the first record of the genus Malostenopsocus from Indochina Peninsula. Another record of this genus from Southeast Asia is from Malaysia (Yoshizawa et al. 2014).