Habitat preferences and phenology of carrot wasps (Hymenoptera: Gasteruptiidae, Gasteruption) in Central Europe

Gasteruption is a genus of parasitic inquilines of bees and wasps. They are distributed worldwide, with 21 species occurring in Central Europe. The knowledge of the ecology of this genus is not very good, only their host preferences were summarised. We studied the phenology and habitat requirements of this group based on records from museums and private collections. All species occur as adults between May and September with a main fly period from June to August—only Gasteruption merceti activates earlier, in May and June. Gasteruption phragmiticola is the only wetland specialist among all species of the studied region. Gasteruption subtile occurs in forest habitats at higher altitudes, while other species prefer lower altitudes between 100 and 500 m a.s.l. Several species prefer steppic habitats on southern hill slopes (G. diversipes, G. freyi, G. hastator, G. hungaricum, G. paternum). Gasteruption erythrostomum, G. jaculator and G. minutum occur mainly in semi-open or forest habitats. Four species (G. assectator, G. caucasicum, G. nigritarse and G. tournieri) are very common and numerous within the studied region and do not have any specific habitat preferences. All species are dependent on the distribution of their hosts and currently occur in habitats previously uninhabited by them, which was documented especially for G. nigrescens, which spreads to wetland habitats to follow its hosts.

The knowledge on the ecological preferences of all species is the keystone for the conservation of Gasteruption. Many species highly prefer regionally endangered habitat types (steppic grasslands, open sandy habitats, alpine forest margins or wetlands) so their conservation should be connected with the conservation of their habitats. Further, most of these endangered species showed a kind of ecological plasticity in habitat preferences, which is a good news for their conservation.