Ptilomerinae

Raruanysong, Sajeemat, Vitheepradit, Akekawat & Sites, Robert W., 2014, Key to the species of Ptilomerinae (Hemiptera: Heteroptera: Gerridae) of Thailand and review of the fauna of the Tennaserim Mountain Range, Zootaxa 3852 (1), pp. 101-117 : 103

Subfamily Ptilomerinae

Members of this subfamily are characterized by a body length of 4–20 mm, metacetabular groove dorsally reaching the anterior end of abdominal tergite I, and the length of the foretarsus is at least half of the length of the foretibia ( Chen et al. 2005). These insects are commonly found in montane streams in Thailand where they stride in an upstream direction against the water cuurent (AV pers. obs.). Specifically, species of Pleciobates, Pleciogonus , Ptilomerella , and Rhyacobates generally occur in the fast flowing sections of streams, whereas species of Ptilomera and Rheumatogonus occur in the less turbulent sections of streams in Thailand ( Vitheepradit 2008, Zettel 2009). Moreover, several species of this subfamily are capable of hanging onto emergent rocks in streams and jumping down from those rocks when they are threatened, and a single specimen of Ptilomera tigrina Uhler was found hanging on the rockface of waterfall at the waterline in Kanchanaburi Province (AV pers. obs.).

Key to the genera of Ptilomerinae of Thailand (modified from Chen et al. 2005)

1. Hind femur distinctly longer than middle femur.............................................................. 2

1’. Hind femur subequal to or shorter than middle femur.........................................................3

2. Body large,> 15 mm in length. Hind coxa with prominent distolateral spine................................ Ptilomera

2’. Body small, <8 mm in length. Hind coxa without spine..................................... Ptilomerella akekawati

3. First antennal segment shorter the remaining three antennal segments together ( Fig. 3 ).................. Rheumatogonus

3’. First antennal segment longer or subequal to the three remaining antennal segments together ( Figs. 4–7 )................ 4

4. Mesonotum orange with a broad mid-longitudinal black stripe ( Fig. 4 ).......................... Pleciogonus wongsirii

4'. Mesonotum dark with or without midlongitudinal stripe ( Figs. 5–7 ).............................................. 5

5. Pronotum black laterally with broad triangular orange marking that makes up> half of notum ( Fig. 5 ) (all wing forms). Mesonotum darkly colored with mid-longitudinal orange stripe ( Fig. 5 ) (apterous form only)......... Rhyacobates malaisei

5'. Pronotum mostly black with elongate orange midlongitudinal marking that makes up <half of notum ( Figs. 6, 7 ) (all wing forms). Mesonotum darkly colored without mid-longitudinal orange stripe ( Figs. 6, 7 ) (apterous form only)...... Pleciobates

Figures

FIGURES 3 – 9. Taxa of Ptilomerinae. (3) Rheumatogonus intermedius, (4) Pleciogonus wongsirii, (5) Rhyacobates malaisei, (6) male Pleciobates pachalatkoi, (7) female Pleciobates pachalatkoi, (8) male Ptilomera tigrina, and (9) female Ptilomera tigrina.