I caught several specimen of these wasps on different dry grassland sites in Eastern Germany. I've got really no idea about the function of the extraordinarily shaped petiolus. It looks like a kind of suit-case handle, but I think it's no deformation.
Hi Sebastian:
Your nice specimen belongs to the family Platygastridae, sometimes incorrectly spelled Platygasteridae (Hymenoptera: Chalcidoidea). The genus is Inostemma. They are parasites of eggs and larvae of cecidomyiid flies. In the female of the genus Inostemma an extraordinarily and long handle-like structure is seen arising on the first abdominal segment and extending forward over the thorax and this acts as a receptacle for the ovipositor. Look at this specimen from Hungary similar to yours but with the horn longer. http://stalemamezivot.blogspot.com.co/2010/09/inostemma.html
Regards,
Luis Miguel Constantino
Dear Luis Miguel,
many thanks for the quick answer! Very fascinating. How much is known about the behavior? Probably not much ... but is there any key literature?
Best regards,
Sebastian
Hello Sebastian:
There is good information about the biology and behaviour of Platygastridae wasps in the Annual Review of Entomology by Austin et. al 2004. He mentions about 87 species of Inostemma. Inostemma are solitary koinobionts in cecidomyiid hosts. These taxa oviposit into eggs or newly emerged larvae, but development is delayed until the host larva is almost fully grown. In at least some cases the parasitoid develops preferentially in particular host tissues, such as brain, nerve cord, and gut. Few species are gregarious within their host, and polyembryony has been confirmed for only one species. For specific taxonomic keys please check the bibliography in this article by Austin et. al. 2004.
Best regards,
Luis Miguel
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