Wednesday, 4 June 2014

Drepanosticta hongkongensis

May 25 I went to Ba Vi to look for the promising Drepanosticta there. I reported on it last year, when I saw them in May on a visit to Vietnam and found only one male in July after we moved here. Based on the close-ups of that time I wrote that surely this was an unidentified species. Indeed, looking at the photos, it is uncanny to see the lobe on the superior appendage, which does not fit closely allied species. But on the 25th I saw several males and also looked at them in close-up. I am sure it is the same species as I saw last year, but none had the lobe! Which pointed me straightaway to D. brownelli or D. hongkongensis. (I do not know why the specimen last year was different, some defect or damage? Also, at the time I described blue on the pronotum. Again, no sign of that now.) Keith Wilson has published on both species and pointed out the differences between them. In the appendages these are virtually absent and also the penile organ is difficult to use for identification. I found the flagella rather variable in the small sample I looked at, so I worry about the usefulness of that character. Brownelli has pale anterior lobe to the prothorax and abdomen is 37-43 mm, hongkongensis has blackish anterior lobe and has abdomen 31-36 mm. The Ba Vi specimens are about 39mm in abdominal length and has cream-white anterior lobe. This seems a clear case of D. brownelli. However, segments 8-10 in brownelli have grayish white dorsum, in hongkongensis bright cyan blue. Hey, the Ba Vi specimen are also bright blue. Nevertheless, I would say that just the color of the dorsum of S8-10 is a little to go by to claim it as a different species. because of this, I considered it D. brownelli. Keith Wilson however commented as follows:

"Colour and size are not always reliable characters in establishing a species’ taxonomic status but in the case of Drepanosticta brownelli and Drepanosticta hongkongensis both are useful aids. D. brownelli is a relatively large species, with male abdomen and caudal appendages ranging from 37-42 mm as compared to the smaller D. hongkongensis which ranges from 31-36 mm. The dorsum of D. brownelli’s abdominal segments 8-10 are predominantly coloured very pale whitish-blue or pale greyish-white whereas the caudal, dorsal patches of D. hongkongensis are colured bright cyan blue. The distinguishing morphological feature is the acutely reflexed horn-like processes of the penile organ found in D. brownelli, (best viewed laterally),  contrasting with the smoothly curved horn-like processes of D. hongkongensis [see Wilson, 1997: The Platystictidae of Hong Kong and Guangdong, with descriptions of a new genus and two new species (Zygoptera). Odonatologica 21(1): 59-63]. The colour and shape of the penile organ in your photos indicate D. hongkongensis."

Drepanosticta hongkongensis, male. Note that due to flash the dorsum of S8-10 is lighter than in reality. The white on the thorax is some kind of defect.

Another male, abdomen tip lighter than in real life

Appendages in dorsal view

In dorso-lateral view

In lateral view
And in ventro-lateral view

Penis in lateral view

In ventral view

Close-up showing cream anterior lobe of prothorax

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