Effects of superparasitism, larval competition, and host feeding on offspring fitness in the parasitoid Pimpla nipponica (Hymenoptera: Ichneumonidae)

When females of Pimpla nipponica Uchida, a solitary parasitoid of various lepidopterous pupae, were exposed to hosts for varing periods of time, percentage wasp emergence decreased; the percentage immature wasps dying at the egg or early-instar stages increased with increasing exposure periods. Factors influencing the increased wasp mortality were examined. Larval competition occurred between 24 and 48 h after parasitism when 1st instars fought physically with their mandibles. Also, many parasitoid eggs had melanized wounds, developed abnormally and died, indicating that 1st instars attacked and killed conspecific eggs. Superparasitism did not influence the fitness of emerging wasps. Hosts used for host feeding by female wasps yielded fewer and smaller wasps. Thus, host feeding was the major factor influencing offspring survival and fitness when multiple attacks against a single host occurred. Superparasitism, larval competition, and host feeding in solitary parasitoids are discussed in the context of adaptive superparasitism theories and mass-rearing programs.