Sunday, 16 August 2015

Nychogomphus flavicaudus - New for Vietnam

It always pays to wade into rivers towards dusk and look for gomphids in spring and early summer. There are many species that only appear close to dusk and either patrol or hover over the water. On June 17 I therefore waded into a river close to Cao Bang City and noticed several medium-sized gomphids hovering over the water. But the current was strong, so it took quite a while before I finally was able to net first one and then a second. In hand it was immediately obvious this was an exciting species, because of the shape and colour of the appendages.

Basically it was very similar to a species I had seen earlier at Cat Tien National Park, Nychogomphus duaricus. Although that is much further south, this species has also been recorded from Yunnan in China. But checking Chao it dawned on me that this was in fact Nychogomphus flavicaudus, a species thought to be endemic to Hainan.

Having said that, these species are extremely similar, so I will not be surprised if DNA-analysis would indicate they are in fact the same species, or subspecies. The most noticeable differences are 1) the antehumeral pattern (a humeral spot and a separated humeral line or series of small spots forming a broken humeral line in N. duaricus and only an antehumeral spot in N. flavicaudus) and the size (abdomen around 36mm and hindwing around 27mm in N. duaricus, abdomen around 40mm (total body length 54mm) and hindwing 33mm in N. flavicaudus). It must be noted that Asahina (1986) points out that specimens of N. duaricus from Malaysia also miss the antehumeral line. But if we follow current practice, then the specimens from Cao Bang must be considered N. flavicaudus.

This brings the number of Nychogomphus species in Vietnam to three. The other is N. lui (see Sebastien's site. I have not been lucky enough to bump into this species that inhabits large rivers and occurs in the suburbs of Hanoi).

Top 2 specimens are N. flavicaudus from Cao Bang. Bottom specimen is much smaller N. duaricus from Cat Tien. Shape of appendages is virtually the same between the two species. Tips of superiors are somewhat more flattened in N. flavicaudus specimens, but not to the same degree in both, so the consistency of this trait is questionable.
Male Nychogomphus flavicaudus. Note the antehumeral spot, but complete lack of antehumeral stripe.
Appendages in dorsal view
Appendages in lateral view
Facial pattern similar to N. duaricus, but extent of yellow patches somewhat reduced

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