none Entered Effect of different temperature degrees (10, 20 and 30 C) on the developmental stages of the aphid parasitoid Aphidius colemani Vierek (Hymenoptera: Aphidiidae), reared on mealy aphid Hyalopterus pruni (Geoffroy) was studied under laboratory conditions. As temperature increased from 10 to 30[degree]C longevity decreased. Lowest thermal threshold for the development of the parasitoid was 0.40[degree]C for eggs, 2.6[degree]C for larvae and 4.0[degree]C for pupae, while it was 2.8[degree]C for the total developmental duration from (egg to adult). Thermal constant for the development of eggs was 71.93 day degree (DD's), 103.37DD's for larvae, 94.7 DD's for pupae and 258.8 DD's for the total developmental period. The lowest thermal threshold for female longevity was 2.7[degree]C and the thermal constant was 73.63DD's, while the lowest thermal threshold for male longevity was 3.9[degree]C and the thermal constant was 45.67 DD's. Obtained results are essential information for predicting the field population of the parasitoid A. colemani and for its releasing time. Sex ratio (female: male) was 1.71:1 in the field. By rearing the parasitoid for three successive generations in laboratory, the sex ratio was almost 1:1 in the first two generations, but males were relatively higher in the third one (1:1.04) 2014