Abstract The aphid parasitoids, Aphidius colemnai Viereck and A. matricariae (Haliday) (Hymenoptera: Braconidae: Aphidiinae) have high potential as the most effective biological control agents for controlling the cotton aphis Aphis gossypii Glover (Hemiptera: Aphididae). In this investigation, the effect of five constant temperatures (10, 15, 20, 25 and 30 °C) on the reproductive parameters was studied at 65 ±5% relative humidity and a photoperiod of 16L: 8 D hours In this study, the newly laid (one- day old) eggs were reared on third instar nymphs of cotton aphid, and the pupal and adult stages of the parasitoids were recorded daily, until the last individual was found dead. The experiments were carried out with 15 replications at each temperature. The results revealed that the gross fecundity and fertility rates were significantly different at all tested temperatures for both species (P