Tramea virginia (Rambur, 1842)

Tramea virginia is a quite large libellulid characterized by very large basal patches to hind wings (obvious even in flight). This late season species can be seen (in my area) from August to November-December.

This male visually track a prey.

Tramea typically have bases of hind-wing more or less broadly marked with a large or irregular opaque spot. In fly, this creates the impression of them carrying bags; hence they are commonly known as “saddlebags gliders”!

A male viewed from above, showing well its famous “saddlebags”. This shot has been taken in mid-November with my old megazoom camera bridge (an interesting concept for a “polyvalent naturalist”, but once you have tasted a DSLR camera, you forget it quickly... Nevertheless, if sharpness is the least of your concerns, it remains a great tool). 

Another male, posed upon release. I didn’t choose the best support. Tramea loves twigs, not leaves! But a leaf is a more comfortable place for recovering...

Tom Kompier recently found the wind blown vagrant T. transmarina euryale at the marsh of Van Long in northern Vietnam (Ninh Binh Province). This is the first record of this species for the country. The most obvious differences between transmarina euryale and virginia concern the hindwings markings (notably reduced in transmarina, extending distally to distal end of discoidal cell and involving nearly whole of anal loop in virginia) and the secondary genitalia (hamules slightly overlapping the genital lobe in transmarina, markedly longer than lobe in virginia). The latter feature is obvious even on perched individuals – if you have binoculars!

Close-up on the secondary genitalia. 
Note the very long hamulus, greatly overlapping the genital lobe - three years ago I thought these things were penis and testicles :))

Tip of abdomen, male, lateral and dorsal views. 
Cerci very long, as long as the last three segments of abdomen.

The female is similar to male in head/thoracic colour pattern. Apart sexual characters, the most obvious differences between sexes are the colour of abdomen (amber-brown in the female, bright brick-red in the male; the last three segments are black in both sexes) and the basal marking on hind-wing (amber-yellow reticulation in the female, red in the male).
Anal appendages nearly as long as in the male, black, straight, very narrow.

The female above was caught as she was flying above a recently harvested rice field, in company of many Pantala flavescens. Both are great gliders! 
Many Tramea species engage migratory flight, but not to the same extent as seen in Pantala ; during the flight of the latter a good proportion of specimens of Tramea are to be seen accompanying them. All Tramea spp. appear to be physically adapted for gliding flight, and thus potentially for migration, by virtue of their broadly expanded hind wings, and extreme vagrancy (Michael L. May, 2012).

What the heck is that? If you answer “her eggs”, it is time to immerse yourself in the anatomy of Odonata! No, these bugs are water mites larvae. For more details about these ectoparasites, click here (an excellent post on Jim Johnson’s blog).

Female, posed upon release. Again, not the best support!

Spot in hind-wing very large, extending distally to distal end of discoidal cell and involving nearly whole of anal loop. Within this mark, the reticulation is amber-yellow in the female (left), bright red in the male (right), well defined against the dark background.

 Vulvar scales of great size, deeply cleft into two keeled processes, rounded at apices.

T. virginia is known from India, Myanmar, Bangladesh, Nepal, China, Taiwan, Japan, Korea and Vietnam. There is a single old record from Thailand.
I spotted it at ponds, marshes, often in human altered habitats. It is probably a fairly common species, but surprisingly I had few photo opportunities.

Due to its strong migrating power, Tramea basilaris is likely to appear as vagrant in Vietnam (apparently already recorded).

Aucun commentaire:

Enregistrer un commentaire