Life history data for Aphidius gifuensis (Ashmead) and Myzus persicae (Sulzer) were collected in the laboratory. To consider both sexes and variable developmental rates among individuals, the raw data were analyzed using the age-stage, two-sex life table. The intrinsic rate of increase (r) for A. gifuensis is 0.264 d−1. The mean parasitism rate is 92.3 aphids per female. The intrinsic rate of increase for M. persicae is 0.252 d−1. For applying the female age-specific life table to a female population, we prove that the relationship between the mean female fecundity (F) and the net reproductive rate (R0) is R0 = saF, where sa is the preadult survival rate. When the female age-specific life table is applied to two-sex populations, the relationship between F and R0 is R0 = sawF, where sa is the preadult survival rate of females, and w is the female proportion in offspring. This is valid when w is a constant for the age-specific fecundity (mx) of all ages. Because sexing preadult individuals is difficult, and obtaining a constant sex ratio in offspring is uncertain, determining preadult mortality of the individual sexes may be problematical. As a result, calculations of the age-specific survival rate (lx) and fecundity and population parameters may be adversely affected. Moreover, if lx and mx are constructed based on adult age, they may also cause errors in population parameters. Because the application of female age-specific life table to stage-structured bisexual population results in inaccuracies, we recommend that the age-stage, two-sex life table should be used in insect demographic studies.