A simulation model was used to predict how temperature influences biological control of stable flies (Stomoxys calcitrans (L.)) by the pupal parasitoid Spalangia cameroni. Temperature, which was either constant or fluctuated due to seasonal variation and/or environmental stochasticity, was modeled as a first order autocorrelation process. The simulations showed that stable flies could tolerate a wider temperature interval than expected from their thermal performance curve (TPC). This was attributed to the fact that immature flies develop in manure, which protects them against low air temperatures. In contrast, the parasitoids were found to have a narrower thermal tolerance range than expected from their TPC. This was attributed to the temperature-dependent functional response of S. cameroni, which was a limiting factor for the parasitoid's development and survival when host densities were low at suboptimal temperatures. The effects of seasonal variation on critical thermal limits were studied by means of thermal performance diagrams (TPDs). Fluctuating temperatures narrowed the thermal tolerance range of both species. At constant temperatures, the simulations showed that the optimal temperature for using S. cameroni in control of stable flies is ~20°C and that the parasitoid can persist in environments with yearly average temperatures between 18 and 29°C. However, if temperature variation was taken into consideration, it changed both the optimal temperature and the temperature interval at which biological control will be possible. This indicates that climate change causing increasing temperatures compounded with greater fluctuations may have serious consequences for biological control of pests.