Entomopathogenic nematodes (EPNs) are environmentally safe alternative control agents. Nematodes in the Heterorhabditidae and Steinernematidae families are widely used in biological control frameworks, especially for soil-inhabiting insect pests. In this experiment, Heterorhabditis bacteriophora (Poinar, 1976), Steinernema feltiae (Filipjev, 1934) and S. carpocapsae (Weiser, 1955) adapted at high temperature were assessed in order to detect differences in virulence between adapted and non-adapted populations. All species were exposed to 38 degrees C for 2 h. After this treatment, live infective juveniles (IJs) were used to infect to last instar Galleria mellonella (Linnaeus, 1758). larvae at the following doses: 1, 2, 3, 4 and 5 IJs/larva. The LD50 and LD90 were obtained for these species. Non-adapted populations of the nematode species were used as controls for this experiment. The results indicated that differences in S. feltiae and S. carpocapsae virulence between the adapted and non-adapted populations were significant; no significant difference was observed between the adapted and non-adapted H. bacteriophora populations.