The Effect of Host Aggregation on Parasitism by Trichogramma papilionis NAGARKATTI (Hymenoptera : Trichogrammatidae), an Egg Parasitoid of Papilio xuthus LINNE (Lepidoptera : Papilionidae)

Field experiments were conducted to determine what effect grouping eggs of Papilio xuthus LINNE, which lays eggs singly, would have on parasitism by Trichogramma papilionis NAGARKATTI. Host clusters of different sizes artificially placed on leaves of potted citrus trees were located in a Latin square and exposed to the natural or released population of the parasitoid. The experiments indicated that if P. xuthus were to deposit eggs in clusters, rather than singly, it would suffer less parasitism by T. papilionis and the parasitoid would produce less progeny. The possible mechanisms are discussed in relation to the chance of detection of a large host cluster by the parasitoid, the frequency of encounters of host clusters with parasitoids, and the egg-laying potential of the parasitoid. We conclude that T. papilionis is well-adapted to the egg-laying habit of its host.