Macrodasyceras hirsutum Kamijo (Hymenoptera: Torymidae) has been considered to be a specialized seed parasitoid wasp of Ilex integra Thunb. since the description as a new species. A previous study showed that they deposited eggs in seeds of the closely related tree I. latifolia when I. integra was experimentally absent. However, natural occurrence of oviposition into I. latifolia or successful emergence from I. latifolia as adults had not been investigated. Thus, to determine whether M. hirsutum utilizes I. latifolia seeds in the fields, we dissected 536 I. integra seeds and 501 I. latifolia seeds. Macrodasyceras hirsutum larvae were found in 152/307 fertilized seeds of I. integra, while found in 16/285 fertilized seeds of I. latifolia. Additionally, 12 male and 13 female M. hirsutum adults emerged from I. latifolia berries collected from field. The present study confirmed natural occurrence of oviposition by M. hirsutum females in I. latifolia seeds and the emergence of adults from berries.