The effects of host density and temperature on the functional response of the bethylid parasitoidCephalonomia waterstoni(Gahan) attacking fourth-instar rusty grain beetle,Cryptolestes ferrugineus(Stephens) were examined. Five temperatures and six host densities were used. A type II functional response model was fit separately to each temperature. The maximum attack rate ranged from 7.5 larvae/12 h at 25°C, to 2.9 larvae/12 h at 38°C. Handling time and instantaneous search rate varied with temperature. A new functional response equation was developed in which handling time is a quadratic function of temperature. This equation explained 83% of the variation in attack rate. Although instantaneous search rate was also affected by temperature, it was sufficient to make only handling time a function of temperature because the two parameters were highly correlated.