Trade-off among life-history traits has been a central subject in the research of evolutionary ecology and biology. A major trade-off concerned is found in the relationship between reproduction and life expectancy but the trade-off between the two may depend on the environment such as food availability In parasitoids, cost of reproduction has been examined only for a few species. The solitary pupal parasitoid wasp Itoplectis naranyae (Hymenoptera: Ichneumonidae) is a typical host-feeder, and host-feeding in this parasitoid is known to relate to egg production. Here, we first examined whether cost of reproduction occurs in I. naranyae by comparing the longevity between females with and without host provision. Because I. naranyae use hosts both for oviposition (reproduction) and for food source, we then compared egg production among females when different food sources (host blood, sucrose or water only) were given. Host provision strongly affected the longevity of females. Wasp life-span was shortened when hosts had been given, suggesting the cost of reproduction in regard to oviposition. Cost of reproduction also tended to depend on the size of females; larger females suffered a greater cost. Females fed on host blood carried much more eggs than those fed on sucrose or water only. When sugar source is lacking or only water was given, they showed 'egg resorption'. Feb 2012 noneaafc0