Reproduction and host-feeding in the solitary parasitoid waspPimpla nipponica(Hymenoptera: Ichneumonidae)

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Abstract
Many parasitoid wasps feed on host body fluids in order to achieve maximal lifetime reproduction, a phenomenon termed “host-feeding”. This study examines egg morphology, embryonic development, ovarian dynamics and lifetime oviposition of the parasitoid wasp Pimpla nipponica, which uses the host as adult food, and highlights the contribution of host-feeding to female reproductive success. Females emerge without mature eggs and produce relatively large yolk-rich eggs at a constant rate throughout the remainder of life, indicating that P. nipponica is a synovigenic parasitoid. Females have relatively few number of ovarioles, and the lateral oviducts are narrow, suggesting low potential fecundity at any one time. In fact, dissection revealed that females have only 4–6 eggs at any one time throughout their lifetime. Eggs do not increase in volume in hosts during development and hatch successfully in Ringer solution, indicating that P. nipponica produces anhydropic eggs. Although females produce about 20 eggs during the earlier stage of life without host-feeding, they are unable to lay eggs during the later stage without host food, indicating that host-feeding is essential for maximal lifetime reproduction. Females prevented from host-feeding live as long as those allowed to host-feed, suggesting that host-feeding contributes to egg production, other than to maintenance. Associations between parasitoid life histories and the contribution of host-feeding to reproduction are discussed.