The host quality model for explaining the sex ratio of progeny of hymenopterous parasitoids was tested with Anisopteromalus calandrae (Howard) parasitizing Sitophilus oryzae (L.). The life span of females and males did not show any influence of body size: 15.3 ± 6.14 and 15.9 ± 4.16 d for females of small and large size, and 5.4 ± 1.90 and 6.0 ± 2.30 for males. However the reproduction rate of large females was twice as high as for small females (80.9 ± 5.78 versus 37.4 ± 3.16). Large males mated with twice as many females as did small males (19.2 ± 3.8 versus 8.1 ± 3.8), suggesting that females do not gain greater fitness by being large than males. In a system in which the parasitoid was permitted to search among randomly dispersed host patches, large females showed a higher net reproduction rate than small females. This was not influenced by the size of male the females mated with: 132.8 ± 9.81 and 132.5 ± 7.41 for large females mated with large and small males, respectively, and 70.4 ± 13.72 and 54.07 ± 6.17 for small females mated with large and small males. The size-dependent dispersal ability among host patches of females, which is the active dispersal sex, is another factor that influenced oviposition behavior of A. calandrae, which assigns daughters on large hosts and sons on small hosts.