Functional responses and superparasitism by the indigenous parasitoid wasp Lysiphlebus testaceipes Cresson (Hymenoptera: Aphidiidae) and the introduced parasitoid Aphidius colemani Viereck (Hymenoptera: Aphidiidae) on the greenbug, Schizaphis graminum Rondani (Homoptera: Aphididae), were measured at four temperatures (14, 18, 22, and 26°C) during a 24-h period (12:12 L:D). At each temperature, 5–75 greenbugs were exposed to individual wasp mating pairs for 24 h. At all experimental temperatures, functional responses for both wasps most closely fit the type III model. Instantaneous attack rates (a) for A. colemani were not significantly different among experimental temperatures. However, for L. testaceipes, the estimate for a at 14°C was significantly lower than estimates at 22 and 26°C when data were fit to a type II functional response model. When data were fit to a type III functional response model for L. testaceipes, the estimate for a at 14°C was significantly lower than estimates at 18, 22, and 26°C. Superparasitism for both wasps was often less than expected if superparasitism were a random occurrence, suggesting that these parasitoids may be able to sense when the host has been previously parasitized. A. colemani achieved higher parasitism rates than L. testaceipes at lower temperatures. This observations suggests that A. colemani may be an effective addition to the parasitoid guild for biological control of the greenbug during cooler periods in the Southern Great Plains.