This study assessed the biological characteristics of Cotesia flavipes (Cameron) (Hymenoptera: Braconidae) with different densities of female parasitoids with Diatraea saccharalis (Fabricius) (Lepidoptera: Crambidae) caterpillars. Third instar caterpillars of D. saccharalis were exposed to C. flavipes females at parasitoid to host ratios of 1:1, 3:1, 6:1, 9:1, and 12:1, with 5 replications. The parasitism of C. flavipes was 90% at 3:1 ratio, and the emergence was 100% for all densities. The life cycle of C. flavipes ranged from 18.17 ± 0.26 to 18.93 ± 0.50 d with the densities of 12:1 and 1:1 parasitoid to host. The higher progeny of C. flavipes (87.38 ± 2.07 and 67.18 ± 2.57 individuals per D. saccharalis caterpillar) were obtained at the densities of 3:1 and 6:1, respectively. The sex ratio of parasitoid per D. saccharalis caterpillar ranged from 0.12 ± 0.05 to 0.66 ± 0.02 between the parasitoid to host densities of 12:1 and 3:1, respectively. The density of 3:1 C. flavipes females per D. saccharalis caterpillar was found to be optimal for propagation of the parasitoid.