Cotesia melitaearum (Wilkinson)
This wasp is a parasitoid of several species of checkerspot butterflies in Europe and Asia. In the Åland islands in Finland there are two forms, one that parasitizes the Glanville fritillary, Melitaea cinxia, and another that parasitized the Heath fritillary, Melitaea athalia. It is a gregarious endoparasitoid, laying one to about 40 eggs inside a host larva, depending on the size of the host. In Åland it has two or sometimes three generations per year, and spend the winter as a larva inside of the host larva. The C. melitaearum that parasitizes M. cinxia in Åland has a metapopulation structure. Currently there are few small local populations.
Gelis agilis (Fabricius)
Wasp in the genus Gelis are wingless generalist ectoparasitoids. In the Åland Islands Gelis agilis and several related species are hyperparasitoids of Cotesia melitaearum pupae. The female punctures the silken cocoon and lay a single egg on the developing wasp inside. Gelis have other hosts in Åland (though the species are not known), and can be extremely abundant, aggregating where there is a high density of C. melitaearum cocoons.