Key to species of Vietnamese Triancyra species

1. Occipital carina complete (Fig. 4a)....................................................................... 2

-. Occipital carina absent medio-dorsally.................................................................... 3

2. Distance between posterior ocelli distinctly greater (1.9–2×) than ocellar-ocular distance (Fig. 5b); mesosoma covered with whitish setae (Fig. 5d); first metasomal tergite with lateral carina extending to spiracle; tergites 1–3 smooth, with only some punctures on tergite 3 anteriorly (Fig. 5e).............................................. Triancyra mystaxa sp. nov.

- Distance between posterior ocelli slightly longer (1.2×) than ocellar-ocular distance (Fig. 4a); mesosoma covered with golden setae (Fig. 4b); first metasomal tergite with lateral carina not extending to spiracle; tergites 1–3 sparsely to moderately densely punctate (Fig. 4c)....................................................... Triancyra graptothoracalis Wang & Hu

3. Ground colour black with yellow markings (Fig. 1a); clypeus with basal deep groove, apical margin pointed (Fig. 1b); first metasomal tergite shorter than its apical width (Fig. 1c).................................... Triancyra acuta sp. nov.

-. Ground colour yellow with black markings; clypeus without basal groove, apical margin truncate or slightly concave (Figs. 2b, 3a); first tergite metasomal slightly to distinctly longer than its apical width (Figs 2c, 3c)............................ 4

4. Scutellum with V-shaped striation (Fig. 3d); metasomal tergite 3 onwards with longitudinal median brown to black marks (Fig. 3c)...................................................................... Triancyra cucphuongensis sp. nov.

-. Scutellum with transverse striations; metasomal tergites with basal and apical transverse black marks, without any longitudinal median brown/black marks (Fig. 2c)................................................. Triancyra aurea Wang & Hu