April 21 I was checking for dragonflies inside the forest in Huu Lien Nature Reserve in the afternoon under a cloudy sky. My attention was drawn by a dragonfly cruising up and down a slight opening over the trail. Caught, it appeared to be a female Cordulid. Checking at home it became quickly apparent this is an Idionyx species. Karube (2011) described 3 species for Vietnam, Idionyx victor, I. carinata and I. asahinai. The latter two have the same thoracic markings are my female and the double horn on the vertex points to I. carinata. A further difference with I. asahinai is the facial pattern, with a small yellow spot on the center of the anteclypeus, whereas in I. asahinai the whole labrum is also yellow.
I. carinata is widely distributed in Southern China and apparently also in Northern Vietnam, as Karube mentions specimens from Tam Dao, from Cuc Phuong and also from Cao Bang Province. By the way province is the province west of Lang Son, in which Huu Lien is located.
Fraser (1924) mentions I. optata as very similar to I. carinata, but states for instance that the anal loop of carinata has less cells (4-6 cells in carinata and 12 in optata). However, this was based on only one female and one male specimen. The photo of I. carinata in Karube show around 12 cells in the loop. My specimen also has 12 cells. Of course I will be happy to see a male next time!
|Idionyx carinata, female, scan of dorsal side|
|Same female in ventral view. Note the straight yellow stripe and the extensively yellow metepimeron, yellow extending onto metepisternum.|
|Note the double horn on the vertex and the small yellow spot on the anteclypeus (and extending marginally onto the labrum)|