Hyposoter horticola (Gravenhorst)
(Ichneumonoidae: Campoplaginae)
Hyposoter horticola is a parasitoid of checkerspot butterflies in Europe and Asia, though its only certain host is Melitaea cinxia. It is a solitary endoparasitoid, laying eggs in first instar host larvae just before the larvae hatch from the egg. In the Åland Islands there is one generation per year. The immature parasitoid stays within the host larva through out the entire larval development until just prior to pupation in the spring. Hyposoter horticola parasitize about a third of the larvae in virtually all of the local host populations of M. cinxia in Åland. They maintain this remarkably uniform rate of parasitism because they are more dispersive than the host, and because they forage efficiently by learning the locations of multiple host egg clusters befor the hosts are ready to be parasitized.
Mesochorus sp. cf. stigmaticus ( Brischke )
(Ichneumonidae: Mesochorinae)
Wasps in the genus Mesochorus are generally endoparasitic hyperparasitoids. The taxonomy in the genus is not well worked out, but it appears that Mesochorus sp. cf. stigmaticus is associated only with parasitoids of checkerspot butterflies. In the Åland Islands it is associated with M. cinxia, hyperparasitizing about a quarter of the Hyposoter horticola, and occasionally Cotesia melitaearum as well. A female probes second and third instar M. cinxia larvae with her ovipositor, laying eggs in 1st or second instar parasitoid larvae inside. When using Hyposoter horticola it has a single generation per host generation, staying within the parasitoid larva until after the larvae has begun to build a cocoon within the host skin.