The performance of two aphid parasitoids, Aphidius colemani Viereck and Aphidius matricariae (Haliday), against Aphis gossypii Glover on greenhouse cucumber (Cucumis sativus L.) and Myzus persicae (Sulzer) on sweet pepper (Capsicum annuum L.) were evaluated at various constant temperatures. Biological parameters of both parasitoids including developmental time, pupal survivorship, percentage of parasitism, and sex ratio of the progeny were studied at 5, 10, 15, 20, 25, 30, and 35 degrees C. At 25 degrees C, an average of 10.0 +/- 1.1 and 9.8 +/- 1.1 d was needed for A. colemani to complete its development from oviposition to adult eclosion on A. gossypii and M. persicae, respectively. The corresponding average times needed for A. matricariae were 11.9 +/- 0.9 and 11.5 +/- 1.1 d, respectively. The lower developmental thresholds for A. colemani reared on A. gossypii and M. persicae were estimated from linear regression equations to be 2.97 and 2.65 degrees C, respectively, whereas these values for A. matricariae were 3.37 and 3.51 degrees C, respectively. Parasitization rate of both parasitoid species, recorded as percent aphids mummified, increased almost linearly with increasing temperature to reach a maximum at 25 degrees C and decreased at 30 degrees C. The optimal temperatures for development of A. colemani and A. matricariae were approximately 30 and 25 degrees C, respectively, and high mortality occurred at higher temperatures. The Lactin 2 and Briere 1 developmental models were accepted based on their excellent goodness-of-fit to the data (residual sum of square and coefficient of determination) and estimable temperature thresholds and are strongly recommended for the description of temperature-dependent development of A. colemani and A. matricariae.