Gynacantha ryukyuensis - an exciting duskhawker!

June 16 I visited Cuc Phuong National Park and towards dusk visited a field with several muddy areas along the forest edge where earlier during the day I had seen Gynacantha subinterrupta. I admit it, I was rather jealous of the Gynacantha hyalina recorded in the park by Natalia von Ellenrieder et. al. in their recent publication. So I wanted to see if I could get lucky too.

I noticed a few Gynacantha males that appeared to be G. subinterrupta, hovering in their characteristic way by the forest edge. But when it got really dark I noticed some patrolling Gynacantha along small trails through the grass, just flying up and down. I was able to catch one and was immediately struck by its weird coloration. The thorax was mostly yellow. Moreover, the inferior appendage was whitish, so clearly this was not G. subinterrupta. But also not G. hyalina. So what was it?

It took some searching, but finally it dawned on me that this should be Gynacantha ryukyuensis, a species known from islands between Japan and Taiwan, from Taiwan and from at least Hongkong. But not (yet) from Vietnam.

A beautiful species, Gynacantha ryukyuensis. Yellowish thorax, but with largely sky blue metepimeron. Note the little yellowish squares at the anterior ventral part of segments 4-7.

In dorsal view the deep yellow frons with black T is obvious, as are the greenish eyes (blueish in male G. japonica) 

The appendages, with epiproct less constricted in posterior half compared to G. japonica.

And in lateral view