Ovipositional Experience of the Gregarious Parasitoid, Apanteles glomeratus (Hymenoptera : Braconidae), Influencing Her Discrimination of the Host Larvae, Pieris rapae crucivora

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The gregarious parasitoid, Apanteles glomeratus, oviposits in the larvae of Pieris rapae crucivora. We investigated to find how the previous experiences of the wasp in oviposition influence the degree of host discrimination. The oviposition time and the number of eggs laid in a host had a positive correlationship. Therefore oviposition time was used as an index of the number of eggs laid. The wasp could innately discriminate between the parasitized and unparasitied hosts and laid fewer eggs into the former than into the latter. The more the wasps had oviposited in unparasitized hosts just before encountering the parasitized host, the less number of eggs they laid into the latter; moreover they tended to reject the parasitized hosts. The wasp also reduced the number of eggs laid in an unparasitized host when she oviposited in them successively at short intervals. These results indicate that the wasp could estimate the density of unparasitized hosts by the frequency of oviposition and could control the number of eggs laid. These phenomena were explained by the assumption that the wasp, based on the presumed density of the unparasitized hosts, behaves to maximize her own inclusive fitness throughout her life.