Thursday, 10 July 2014

Philoganga robusta

The genus Philoganga is represented in northern Vietnam by the magnificent Philoganga vetusta, the Ochre Titan. This species characteristically develops bright orange-red dorsum to the first segments of the abdomen and to the flanks of the synthorax. In southern China there are two species. Next to the Ochre Titan, there is another species, Philoganga robusta. Wilson and Reels reviewed many of the records and looked at many specimens and concluded that the structural differences between these two species are difficult to ascertain and inconsistent. However, life insects are easily separated because, as they write (2003): The differences between vetusta and robusta are relatively minor and non-structural in nature. Nevertheless life male specimens are easily separated in the field since robusta is predominantly dark colored with greenish blue markings, whereas vetusta is extensively marked with bright orange on the thorax and abdomen. Now, already in Tam Dao both Sebastien and myself encountered a large whitish Philoganga without any orange. However, the dorsum of the abdomen of this insect was not dark, and showed also some orange (see that post). We considered it maybe an aberration. However, on June 23 I encountered a male in Pia Oac Nature Reserve that displayed the typical coloration of P. robusta. If lack of structural characteristics, but color is the identifying feature, there should be no objection to identifying this specimen as P. robusta. More research may be needed and copula looked for, but until then we should assume that just as in southern China, both species occur in northern Vietnam. The other option is that these are in fact two forms of the same species, in which case P. vetusta is the  senior synonym.

Note the dark dorsum, especially noticeable on S2, whitish flanks marked with blueish. The legs appear to have some orange.

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