Adaptive superparasitism theory is based on the assumption that a female parasitoid superparasitizes not because she fails to recognize prior parasitism of a host but because she decides to do so to increase her fitness. This theory suggests that recognition of prior parasitism is always advantageous, but it does not necessarily result in rejection of a parasitized host. The solitary parasitoid Pimpla nipponica Uchida readily superparasitizes when unparasitized hosts are scarce. Tests were conducted to examine whether P nipponica positively superparasitized, even after it recognized prior parasitism. Direct observations of its oviposition behavior revealed that P nipponica responded differently to unparasitized and parasitized hosts when ovipositing. The female drilled into parasitized hosts repeatedly to find a suitable egg-allocation site in the hosts. Also, the female probed parasitized hosts repeatedly with its ovipositor inserted in the hosts. These repeated drilling and probing actions were seldom observed on unparasitized hosts. Repeated drilling and probing actions were not associated with larvicide because no larva of the first female was killed by a superparasitizing female. The results indicated that superparasitism in P nipponica did not result from a failure to recognize a host being parasitized, but resulted from its positive decision to superparasitize.
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