Xenanastatus (Hymenoptera, Chalcidoidea, Eupelmidae: Eupelminae)
This week we won’t have much to say about the insect chosen for our weekly series. Xenanastatus sp. is so special that I think the image of this undescribed species stands on its own. It is my favourite insect photo. The family Eupelmidae is a large one with 907 species. Eupelminae, the subfamily of which Xenanastatus is a member, is by far the largest of the 3 subfamilies of Eupelmidae, comprising over 75% of the species in the family. Most Eupelminae are ectoparasitoids of other insects in concealed places or within plant tissue. But to link this behaviour to Xenanastatus would be pure speculation. There are no data on the biology of the genus and its host is unknown. There are data on the geographical distribution of Xenanastatus and comments on its apparent rarity, but that’s about all. Three species have been described in the genus, two from India and one from Australia. As far as its rarity is concerned, the insects of Australia and India have been relatively intensively collected so I will accept the statement made by one of the authors of Xenanastatus species that the genus is very uncommon. We collected the Kenyan specimen at the base of Mumoni forest in eastern Kenya at an elevation of 1045m above sea level. Our collection sites, especially in eastern Kenya, have been well sampled, and we have not seen any other wasp that resembles this specimen. The species is very long and thin. Its length without antennae and ovipositor is approximately 4.8 mm; with antennae and ovipositor about 1 cm.
The geographic distribution of Xenanastatus is interesting in that it is an example of different species of the same genus being collected in widely separated places. We have seen this several times for different genera in Kenya. In the case of Xenanastatus, how is it that species of that genus are found in Africa, Australia and India, each separated from one another by large expanses of ocean? The most likely explanation is that a common ancestor of these three species existed somewhere on the supercontinent Pangaea about 200 million years ago, and that when that continent broke up, sending parts of what are now India, Australia, and Africa in their different directions, each carried population(s) of Xenanastatus along for the ride. Since then, and over such a long time, each population, in adapting to its new environment (or by chance alone) evolved into forms that were related to each other but clearly different enough to warrant separate species status; another example of how continental drift (Alfred Wegener’s brilliant theory) painted the earth with such spectacular diversity.
Credits: Dr Robert Copeland