Aciagrion migratum - no Prodasineura after all

On December 1 in Huu Lien I noticed a thin damsel hovering over the stream like Prodasineura autumnalis tends to do. At first I therefore suggested it might be something similar, but Rory Dow pointed out it had to be a Coenagrionid (thanks Rory) related to Ischnura, on behalf of the spine on the sternum of S8. That pointed me to Aciagrion and then I remembered that Aciagrion migratum passes through the winter as imago, but only gets its blueish color in spring. How exciting, the second record for Vietnam, but undoubtedly it is just under recorded.

Aciagrion migratum, female winter type

The same female

And in hand 

Close-up of the ovipositor and S8, showing clearly the apical spine on the sternum