A new internal marking technique using the rare stable isotope ⁴⁴Ca was developed for the gregarious endoparasitoid Cotesia glomerata, which parasitizes Pieris brassicae larvae. The isotope was enriched in parasitoids through the food chain, i.e. ⁴⁴Ca was enriched in plants and transferred to the parasitoids via their host larvae feeding on the enriched plants. Adult female parasitoids could then transfer the ⁴⁴Ca marker through oviposition to a new generation of host larvae. Enrichment of ⁴⁴Ca is traced by analysis of individuals using inductively coupled plasma mass spectrometry (ICPMS) with a dynamic reaction cell (DRC). This new marking technique with ⁴⁴Ca was shown to be applicable under greenhouse and field conditions to trace dispersal of the parasitoid and parasitism in mark-release studies.