Philoganga vetusta Ris, 1912

I spotted this stunning species in lowland and mountain localities, at Tam Dao and Xuân Son National Parks, in relatively untouched forests but also, sometimes, in degraded secondary forests. 

Male on May 10, 2014, Xuân Son National Park (alt. ca 350 asl)

Another male photographed in natural light (without flash) in June 2012 at Tam Dao, 
in degraded secondary forest at ca 100 asl

"In hand" shots for more details :

Tip of abdomen, male

Immature (?) male, May 10, 2014, Xuân Son National Park

The female is much stouter than the male :

Not fully mature female, Tây Thiên Tam Dao in May 2012, at ca 300 asl

Another female, more yellow on sides of synthorax (also from Tam Dao) :

A third female, photographed on May 10, 2014, from Xuân Son National Park :

 The same female, ovipositing over a small forest stream

Wings, female

Philoganga vetusta is known in southern China (Fujian, Guangdong, Hainan, Hunan), where it is common and widespread, and northern Vietnam.

Remark: The differences between P. vetusta and its close congener P. robusta Navás, 1936 (known from southern China) are relatively minor and non-structural in nature. Nevertheless live male specimens are easily separated in the field since robusta is predominantly dark coloured with greenish blue markings, whereas vetusta is extensively marked with bright orange on the thorax and abdomen (Wilson and Reels, 2001).