Labiobaetis mustus ( Kang & Yang, 1996 ) Kang & Yang, 1996

Shi, Weifang & Tong, Xiaoli, 2014, The genus Labiobaetis (Ephemeroptera: Baetidae) in China, with description of a new species, Zootaxa 3815 (3), pp. 397-408 : 403-404

Labiobaetis mustus ( Kang & Yang, 1996) n. comb.

( Figs. 20–23 )

Baetis (Labiobaetis) mustus: Kang & Yang, 1996: 63 ; Pseudocloeon mustum: Soldán & Yang, 2003: 415

Specimens examined (in ethanol). China, Guangdong Province: 4 nymphs, Yingde City, Shimentai Nature Reserve (24.40°N, 113.31°E), 7-vi-2011, and 2 nymphs on slides and 7 nymphs, the same locality but collected on 5-xi-2011, coll. Shi Weifang; Hong Kong: 9 nymphs, Lantau Is., Ling Yan Temple, near Tai O Road, 21-xi-1998, 1 male imago (emerged on 27-xi- 1998 in the lab), coll. Tong Xiaoli; 8 nymphs, Tan Shan River, near Tan Chuk Hanm (22.51°N, 114.18°E), 18-iii-1998, coll. Tong Xiaoli; 10 nymphs and 7 female imagoes (reared from nymphs), Lantou Is., Pui O, the Pumpig Station (22.23°N, 113.96°E, 7m), 22-vi-1999, coll. Tong Xiaoli; Hainan Province: 9 nymphs, Baisha County, Yinggeling National Nature Reserve, Daoyin (18.99°N, 109.58°E), 22-xi- 2005, coll. Yao Haiyuan; 2 nymphs, Wanning City, Nanqiao Town (18.68°N, 110.15°E, alt. 40m), 22-iv-2011, coll. Shi Weifang.

Nymph was adequately described and illustrated by Kang & Yang (1996). The imago stage is described for the first time as follows.

Male imago (in ethanol, genitalia on slide, reared specimen). Body length 4.8 mm. Forewing 4.4 mm. Cerci 8.5 mm. Turbinate eyes orange to orange-red dorsally and well developed; ocelli off-white with red-brown basal rings. Antennae longer than head capsule; flagella grey with off-white basally; pedicels red-brown; and scapes offwhite or cream. Pronotum yellow-brown with purple-brown markings; mesonotum light yellow-brown with brown markings medially and laterally; metanotum yellow-brown; thorax yellow-brown laterally. Forewing hyaline, longitudinal veins and paired marginal intercalaries light yellow; costa with serration; pterostigmal areas with 4-5 slanting veinlets; hind wings hyaline with 2 longitudinal veins and a tiny vestigial costal process ( Fig. 21 ). Legs off-white to cream. Abdominal segment I red-brown, segments II–V (VI) off-white and translucent; segments (VI) VII–X cream to grey-white; terga I–VIII with single purple-brown transverse streak ( Fig. 20 ); terga II–IV with light brown oblique streak laterally. Genital forceps ( Fig. 22 ) off-white, three-segmented; first segment of forceps broad with a small protuberance on inner apical margin, 2nd segment long and slightly expanded on basal half; 3rd segment short and oval; segments 2–3 covered with wrinkles densely; subgenital projection short and prominent medially. Cerci off-white.

Female imago (in alcohol, reared specimen). Body 4.5–5.0 mm. Forewing 4.7–5.5 mm. Cerci 8.8 mm. Female is similar to male except the following characteristics: vertex off-white with 2 longitudinal red-brown streaks submedially; compound eyes black; abdominal segments I–X red-brown, terga II–VIII with two small yellow or pale submedial oblique dashes anteriorly, and two small yellow or pale submedial dots in mid-region; cerci light yellow-brown with red-brown basally.

Distribution. China (Guangdong, Hong Kong, Taiwan).

Remarks. Nymphs of this species are similar to those of Labiobaetis atrebatinus orientalis (Kluge) in color pattern of abdomen, but can be differentiated by abdominal segment I lacking a pair of gills. The male imagoes of L. mustus (Kang & Yang) can be separated from that of L. a. orientalis by (1) the abdominal terga VII–X cream to grey-white; (2) terga I–VIII with single purple-brown transverse streak posteriorly; (3) terga II–IV with light brown oblique streak laterally and (4) unlike the known imagoes of genus Labiobaetis whose hind wing without costal process, this species having a tiny vestigial costal process on costal margin of hind wing ( Fig. 21 ). Both species live among marginal vegetation, but the nymphs of L. mustus are most common in slow-flowing or still water.

Figures

FIGURES 20 – 23. Labiobaetis mustus (Kang & Yang). 20, habitus of male imago (excluding abdominal segment X); 21, hind wing of female imago; 22, genital forceps; 23, habitus of male nymph.