A system was developed to provide the parasitic wasp Ephedrus persicae Froggatt (Hymenoptera: Braconidae: Aphidiinae), which attacks the rosy apple aphid Dysaphis plantaginea (Passerini) (Homoptera: Aphididae), with the alternative host Dysaphis sorbi Kaltenbach (Homoptera: Aphididae) in apple orchards. Rowan trees (Sorbus aucuparia L.) arranged along the side of an unsprayed orchard were artificially infested in late February 2002 with eggs of D. sorbi. Colonies of D. sorbi successfully developed from the introduced eggs and persisted on several trees until the end of June. The only primary parasitoid species emerging from a sample of mummified aphids collected in spring from the infested rowan trees was the braconid wasp species E. persicae. In a host-switching experiment, nymphs of D. plantaginea proved suitable for female parasitoids originating from mummified D. sorbi. A series of mummies collected from the rowan trees in early summer contained diapausing parasitoids and hyperparasitoids that only hatched in April of the following spring. These observations suggest the possibility of establishing a local population of E. persicae in apple orchards, so that D. plantaginea can be readily attacked by diapause-emerging parasitoids in early spring. Ephedrus persicae (Aphidiidae) : Parasite Dysaphis plantaginea (Aphidoidea) : Host Dysaphis sorbi (Aphidoidea) : Host Animals and man; Control; Biological control; Parasites diseases and disorders; Parasites; Insect parasites; Hosts; Insect hosts; Habitat; Man made habitat; Land zones; Palaearctic region; Eurasia; Europe Dysaphis plantaginea; Dysaphis sorbi; Control by; Ephedrus persicae (Hymenoptera); Hymenopteran parasites; In field production of parasitoids using substitute host; Ephedrus persicae; Cultivated land habitat; Apple orchard; Belgium; Baraque de Fraiture, Vielsalm Ephedrus persicae; Control of; Dysaphis (Hemiptera); Hemipteran hosts; In field production of parasitoids using substitute host; Dysaphis plantaginea & Dysaphis sorbi; Cultivated land habitat; Apple orchard; Belgium; Baraque de Fraiture, Vielsalm none