Preference-performance hypothesis in host selection by herbivorous insects predicts selective oviposition on plant on which the offspring maximise fitness. The seed parasitoid wasp, Macrodasyceras hirsutum Kamijo (Hymenoptera: Torymidae) selectively lays the eggs into the fertilised seeds of Ilex integra Thunberg (Aquifoliaceae). Only one larva develops in a seed. Therefore, the hypothesis predicts a uniform distribution pattern of wasp eggs among fertilised seeds. Dissection of 531 berries showed that M. hirsutum deposited one to five eggs into a fertilised seed. Iwao's patchiness regression suggested a uniform distribution pattern of M. hirsutum eggs among fertilised seeds at the scales of tree and berry and their random distribution pattern among berries at the tree scale. Destroying the connection of seeds within berries revealed that female wasps randomly selected berries for oviposition in most trees. Generalised linear mixed models showed that the number of fertilised seeds in a berry could not explain the number of eggs in a seed but could explain the number of eggs in a berry. Therefore, this study shows that the wasp females do not distinguish between berries with different numbers of fertilised seeds but distinguish between seeds harbouring different numbers of eggs, which supports the hypothesis.