The Authors refer to experiments and research done in Central Italy on the efficacy and effects of mass releases of the larval parasitoid, Copidosoma koehleri Blanchard, on potato tuber moth larvae [Phthorimaea operculella (Zeller)]. Furthermore, data were also collected on naturally occurring parasitoids. Data were collected between June and September 1999 with release plots in an open field and one release in a storage facility. The results showed a modest percentage of parasitized larvae by C. koehleri (max. 3%) in the open field plots, whereas, in the storage building this was even less, reaching just 1% parasitism. Indigenous parasitoids found in the study area were the following: Diadegma pulchripes Kokujev (Ichneumonidae), Pnigalio pectinicornis L. and Sympiesis viridula Thomson (Eulophidae). It is to be noted that D. pulchripes were at a higher density when compared to the other two parasitoid species. The latter ones, known as parasitoids of other lepidopteran larvae [e.g. Phyllonorycter cerasicolella (Herrich-Schaffer) and Ostrinia nubilalis (Hubner)], were new findings for Ph. operculella. However, keeping in mind their low incidence, they must be considered as only occasional parasitoids of potato tuber moth. Altogether, indigenous parasitoids reached a maximum of 23% parasitism in the first week of June. Animals and man; Control; Biological control; Parasites diseases and disorders; Parasites; Insect parasites; Hosts; Insect hosts; Land zones; Palaearctic region; Eurasia; Europe Phthorimaea operculella (Gelechiidae); Control by; Copidosoma koehleri (Hymenoptera); Hymenopteran parasites; Native & exotic parasites prevalence; Italy; Umbria; Castelgiorgio; Native & exotic hymenopteran parasites prevalence Hymenoptera; Lepidopteran hosts; Phyllonorycter cerasicolella; Native & exotic parasites prevalence; Italy; Umbria; Castelgiorgio; Native & exotic species prevalence in lepidopteran host Copidosoma koehleri (Encyrtidae); Control of; Phyllonorycter cerasicolella (Lepidoptera); Lepidopteran hosts; Phyllonorycter cerasicolella; Biocontrol efficacy vs native hymenopteran parasites; Italy; Umbria; Castelgiorgio; Lepidopteran host biocontrol efficacy vs native hymenopteran parasites none