Seasonal patterns of host utilization in the multivoltine seed-feeding wasp, Macrodasyceras japonicum (Hymenoptera: Megastigmidae)

Most seed-feeding wasps are considered univoltine in regions that exhibit distinct seasonality, such as temperate regions, because they usually oviposit into seeds before the protective tissues surrounding the seeds harden during seed development. However, one species belonging to the genus Macrodasyceras was reported to be partially bivoltine, although in a temperate region, this could lead to more intense seed utilization than that seen in univoltine species. Such life cycle of seed-feeding wasps would be related to the extent of predispersal seed damage in their host plant species. In this study, we investigated the life cycle of the seed-feeding wasp Macrodasyceras japonicum and its seasonal seed utilization patterns of several fleshy fruited Ilex species in a warm-temperate region of Japan. The observation of periodically sampled fruits and oviposition behavior using reared adults showed that M. japonicum produced at least two generations per year within the seeds of multiple Ilex species and overwintered as adults outside of the fruits. The extent of seed damage caused by the M. japonicum association amounted to ca. 80% in I. pedunculosa, whose seed development phenology was most synchronized with the life cycle of M. japonicum among the host Ilex species. Adults overwintered outside of fruits, likely to avoid being eaten by birds, but risked a large reduction in population size during the winter. However, M. japonicum may overcome this disadvantage through multivoltinism and the ability to use multiple species, which might, in turn, lead to severe predispersal seed damage in the primary host plant species.