Monday, 16 September 2013

Macrogomphus

On July 24 we were walking along a slow stream in open area (paddies) in Ba Be National Park when I noticed a large gomphid ovipositing on the muddy bank. I caught it and took some photos before releasing it again. At the time I did not realise it was a Macrogomphus. A week later, on August 2, we were walking in a completely different setting at a very different location, now in the village outside Cuc Phuong National Park, when I spotted a large gomphid sitting on an overhead wire. It was well out of reach, but with a tele lens I was able to take a few shots before it moved off. This again was a Macrogomphus, this time a male.

To my knowledge only two Macrogomphus have been recorded in Vietnam, M. rivularis and M. annulatus. The former species was described in 1914 by Foerster and apparently has not been recorded since. Although I have some pages of the article by Foerster, the relevant pages are missing. M. annulatus In surrounding countries several additional Macrogomphus species have been recorded. Asahina for instance mentions M. borikhanensis, M. thoracicus and M. matsukii from Thailand. Basically Macrogomphus has two groups, species similar in relation to the dorsum of the thorax. Those with ante-humeral stripes fall into the quadratus group, as do these specimens. The other group has large squares on the dorsum, like M. kerri and M. caudatus.

Of the possible quadratus group species, M. annulatus has the abdominal segments 3-8 all ringed completely, both in male and female. M. borikhanensis has a much darker thoracic pattern, with narrower yellow markings and the caudal appendages for the male are quite different, with the ventral branch very large, extending beyond the upper branches in ventral view. Moreover, the vertex is all black. M. matsukii also has complete rings, both in male and female, different caudal appendages and more extensive light markings on the face.

In fact both specimens are very similar to M. guilinensis as described by Chao (male) and Wilson (female). This species has incomplete rings, a yellow spot on the vertex, small conical caudal appendages with simple valvula vulvae (female), or upper appendages with outer branch longer than interior, and angled inferior appendages (with a "heel"). Also in ventral view, the inferior appendages extent laterally beyond the superior appendages. I am not aware of other records of Macrogomphus guilinensis in Vietnam and with M. rivularis unknown, I welcome comments on the identity of these specimens, but as M. guilinensis occurs in Guangxi, it is likely that it may also occur in North Vietnam.

The female Macrogomphus from Ba Be

The dorsum of the thorax and frons. In fact the seperation in the middle of the yellow stripe on the frons is different from the drawing in Wilson. Tricky.

The ventral side of the tip of the abdomen, showing the vulvar lamina

The dorso-lateral view of the tip of the abdomen, showing the caudal appendages
The male from Cuc Phuong, high and dry on the wire. The thoracic and abdominal pattern very similar to that of the Ba Be female.

The view from below of wings and caudal appendages, see the close-ups

Close-up of the caudal appendages of the male, showing the inferior appendages protruding laterally beyond the superior appendages and the larger outer branch of the superior appendages

A slightly different angle
 I welcome any comments and insights! Or, if you have the complete article on M. rivularis, let me know.

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