The genus Cotesia (Hymenoptera: Braconidae: Microgastrinae) comprises koinobiont endoparasitoid wasps specialized in lepidopteran hosts. This research aimed to investigate the potential to identify Cotesia species associated with hosts from the tribe Melitaeini based on their fore wing morphology. Additionally, the intraspecific diversification within the C. melitaearum aggregation was explored. Parasitoids were reared from twelve broods of Melitaea didyma, M. ornata, M. phoebe and Euphydrias aurinia, collected primarily in Serbia, as well as in Croatia and Spain. Emerged parasitoids were identified as C. bignellii, C. hispanica, C. lycophron and C. melitaearum agg. The females' fore wings were analyzed using geometric morphometrics to evaluate the interspecific and intraspecific morphological variation. The results of this study revealed significant differences in the forewing shape among the Cotesia species. The Principal Component Analysis (PCA) identified four distinct species, supporting species-level differentiation based on identification keys. Cotesia hispanica was distinguished by the slight widening and elongation of the distal part of its wings. The evidence suggests the existence of a potential biotype within the C. melitaearum aggregation, which may represent a distinct subgroup, requiring further investigation. This study enhances the identification of morphologically similar species within the highly diverse genus Cotesia based on forewing morphology, particularly those utilizing Melitaeini caterpillars as hosts.