The parasitic wasp species Lariophagus distinguendus (Förster) (Hymenoptera: Pteromalidae) and Anisopteromalus calandrae (Howard) (Pteromalidae) are used for inoculation biological control of the granary weevil Sitophilus granarius (L.) (Coleoptera: Curculionidae) in grain stores in Europe. To assess their suitability for biological control under extreme temperatures in winter and summer, we studied the influence of temperatures on their parasitization behaviour under natural fluctuating temperature conditions in the field and under constant temperature conditions in the laboratory. At low temperatures (≤20°C), L. distinguendus showed a higher parasitization rate than A. calandrae. At high temperatures (≥25°C), A. calandrae performed better than L. distinguendus that was negatively affected already at temperatures above 30°C. These findings suggest a temperature-dependent release of either L. distinguendus or A. calandrae to allow a more efficient application of the wasps in biological control.