Developmental times for the immature stages of four species of endoparasitoids ofHeliothis virescens(F.),Microplitis croceipes(Cresson),M. demolitorWilkinson,Cotesia kazak(Telenga), andHyposoter didymator(Thunberg), were studied at 20, 23, 25, 27, 30, 32, and 35°C. The responses ofM. croceipesandH. didymatorto increases in temperature were significantly different from each other (P0.05;F= 0.58; df = 1, 18). The developmental temperature optima were 33°C forM. croceipes, 31°C forC. kazakandM. demolitor, and 29°C forH. didymator.