Five polymorphic microsatellite loci were isolated from Cotesia melitaearum (Wilkinson) and three from Hyposoter horticola (Gravenhost). Both of these parasitic Hymenoptera use the butterfly Melitaea cinxia (Linnaeus) exclusively as their host in the Aland islands in SW Finland. Allelic diversity and heterozygosity were quantified in samples from the Aland islands and other localities around Europe. In addition, microsatellite loci for C. melitaearum were tested in five other Cotesia species: C. acuminata (Reinhard), C. bignellii (Marshall), C. congregata (Say), C. cynthiae (Nixon) and C. koebelei (Riley) from several different host species in Europe and Asia. Techniques; Genetic techniques; Biochemistry; Genetics; Parasites diseases and disorders; Parasites; Insect parasites; Hosts; Insect hosts; Land zones; Palaearctic region; Eurasia Melitaea cinxia (Nymphalidae); Hymenopteran parasites; Cotesia & Hyposoter; Parasite microsatellite loci characterization; Europe; Hymenopteran parasite microsatellite loci characterization Cotesia melitaearum (Braconidae ); Hyposoter horticola (Ichneumonidae ); Population genetics techniques; Nucleic acids; DNA; Molecular genetics; Microsatellite loci; Population genetics; Lepidopteran hosts; Melitaea cinxia; Parasite microsatellite loci characterization; Europe; Microsatellite loci characterization, lepidopteran host none