Macrogomphus albardae in Cat Tien*

*This entry was adjusted on December 31, 2019, following the publication in Zootaxa of a paper by Oleg Kosterin, which I had the pleasure of reviewing, on 12 June 2019. The paper addressed the considerable confusion surrounding a group of similar Macrogomphus species, showing, amongst others that Macrogomphus matsukii is a doubtful species and that records of Macrogomphus species identified as such from Cat Tien actually refer to Macrogomphus albardae. M. guilinensis from central and northern Vietnam actually is a junior synonym of the same M. albardae and occurs in a variety of distinct forms. Turns out that the 'matsukii' type gomphids I had been chasing for some time after first seeing them hover in the distance above a river in central Vietnam were conspecific with the species that I knew well from the north, but that based on previous misidentification and confusing literature had identified as M. guilinensis. Anyway, thanks to the careful work by Oleg the situation is now much clearer.

Original text:
James Holden had been reporting Macrogomphus matsukii from Cat Tien NP for a while and I decided to pay him a visit to get to see it in May. Last year I had seen Macrogomphus hovering over a large river at dusk (a habit shared by many gomphids, and certainly M. guilinensis) in Quang Binh Province, but had failed to ascertain beyond reasonable doubt that it was this species. Photos by James from last year had us initially discuss whether it was M. borikhanensis or M. matsukii, because the lateral pattern on the thorax had only two clear stripes. Facial pattern is very much like M. matsukii though. There seems to be some doubt whether these two species may in fact be conspecific anyway.

Commentary December 31, 2019:
Kosterin (2019) shows that the records of M. matsukii on which I based the above knowledge were in fact misidentifications of M. albardae, while M. matsukii remains a sort of phantom species. And he also showed that M. borikhanensis is another junior synonym of M. albardae. So the whole discussion on whether the Cat Tien specimens were one or the other was non-sensical in retrospect.

Below text with portions adjusted on December 31, 2019, in bold:
Just before I went to Cat Tien the rains picked up and the riverbed filled up quickly, so that circumstances had changes considerably when I got there on May 12. Indeed, we saw none, but on the 13th the waters had receded a little and the circumstances the species seems to favor (small trickles over the rocks by the side of the main stream) were restored. And towards dusk: there they were. 3 males hovering over the streams, for a short period joined by a Orientogomphus naninus. That distracted us and therefore I failed to get the stunning pictures I was hoping for. The different individuals had some variability in the extent of the middle lateral stripe, which was absent or represented by a small mark at the dorsal end. Otherwise they seemed perfect for M. albardae.
This is a widespread species, occurring widely in SE Asia. It includes at least the following junior synonyms: M. guilinensis, M. rivularis and M. borikhanensis.

Male Macrogomphus albardae, hovering at dusk over stream