Sunday, 6 October 2013

Agriocnemis pygmaea and Agriocnemis femina, a story of posterior lobes

October 5 we decided to go to Van Long once more, for both birds and odonata. It was a good day for Agriocnemis and I was lucky enough to find a field in the afternoon with many hundreds of both A. femina and A. pygmaea. Here a few of the photos. But before going into that, let's take a look at the prothorax, more specifically for posterior lobe, as it holds the key to the identification of the females. A. femina has a distinct posterior lobe, that can easily be seen in hand. The lobe of A. pygmaea is very much reduced in size and does not protude. Interestingly, in the males it is reversed. Both males have a distinct posterior lobe, bot that of A. pygmaea stands up almost vertically. This is not so important, as the caudal appendages are already such a clear clue.
The prothorax of A. femina has from the early stages darker markings that are another identification trait. For the males the shape and extent of the orange on the abdomen tip also helps, but this disappears with age. A. pygmaeae has on average thinner antehumeral stripes, but this is not always the case, and the blackish mark on the postgena (the back of the eyes) is generally vague in A. pygmaea and clear-cut in A. femina.

Standard adult Agriocnemis femina, male

A. femina, immature male

Another immature male

And yet another

Prothorax of A. femina, note flat posterior lobe

Prothorax of A. pygmaea, note upright posterior lobe

Agriocnemis pygmaea, male

Another male, note pattern on S8 and shape appendages

Female Agriocnemis femina, note dark markings on prothorax and clear posterior lobe

Dorsal view of prothorax of A. femina, female, with clear posterior lobe
Lateral view of prothorax of A. femina female, showing large posterior lobe

Dorsal view of A. pygmaea female prothorax, showing reduced posterior lobe

Similar in lateral view, showing almost not posterior lobe

Agriocnemis pygmaea, female, note posterior lobe

Another female

And another female

Copula of A. pygmaea. Apart from the appendages, visible, the lobe of the prothorax of the male is a give-away!

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