not in Young Some biological traits of Lysiphlebus fabarum (Marshal) an important parasitoid of Aphis fabae were studied under laboratory conditions (21 [plus or minus]1[degree]C, a relative humidity of 70 [plus or minus] 5 % and 14:10 L:D h. of photoperiod). Different stages of Aphis fabae and its host plant were used. Average preadult period of male and female adult parasitoids were 13.18 [plus or minus] 0.28 and 13.68 [plus or minus] 0.27 days, respectively. There were no significant differences between male and female wasps longevity ( P>0.05). There was a significant difference between preadult period of female and male parasitoids on different life stages of Aphis fabae ( P 0.05). Diet affected significantly the female parasitoid longevity (P0.05). Longevity was longer when the females were fed on 30% honey solution and the shortest when they had no access to host plant, host, water and honey solution. Sex ratio changed towards males as temperature increased. Data analysis revealed that female parasitoids prefer Aphis fabae over Aphis craccivora Koch and Aphis nerri for oviposition ( P 0.05). The lowest oviposition preference was shown for Aphis nerri. Mean lifetime fertility of Lysiphlebus fabarum was 122 [plus or minus] 27.28 offsprings/female on Aphis fabae. The intrinsic rate of increase(rm), mean generation time, doubling time and rate of increase per week (Rw) were 0.28, 16.31 days, 2.47 days, and 7.11, respectively. Aphis fabae (Aphidoidea): Host, Parasite; Lysiphlebus fabarum (Aphidiidae): Parasite. Animalia, Arthropoda, Insecta, Hemiptera, Homoptera, Sternorrhyncha, Aphidoidea; Animalia, Arthropoda, Insecta, Hymenoptera, Apocrita, Terebrantia, Ichneumonoidea, Aphidiidae. Arthropods; Hymenopterans; Insects; Invertebrates; True Bugs. none