Function of infochemicals produced at the damage in a tritrophic interaction.

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Cotesia glomerata, a parasitoid of P. rapae larvae, is attracted by a damage made by host larvae and shows intensive searching behavior. The major components of the chemicals produced at the damaged site were fatty acids, palmitic acid and stearic acid. The feeding experiments by Pieris rapae larvae suggested that the fatty acids were feeding attractants of the larvae. Meanwhile, we found that Pieris rapae larvae secreted oily droplets from the dorsal setae. GC-MS analysis showed that palmitic acid and stearic acid were the major components of this secretion.In Hokkaido, we studied oviposition preference of four Pieris butterflies, P. rapae crucivora, P. melete, P. napinesis and P. brassicae, toward six species of food plants in a cage under natural and carried out feeding experiments using larvae of the four Pieris speciesand the six species of plants. The results of the experiments showed that Rorippa sylvestris was relatively intrinsically superior plants for larvae of each species. On the other hand, Arabis pendula was very inferior, even for P. napi, which uses it as a usual food plant. But a oviposition preference test showed ovipositing female butterflies of P. rapae preferred cabbage plants to R. sylvestris and P. melete selected Cardamine leucantha, but did not oviposit on R. sylvestris.In the field condition Cotesia glomerata parasitized P. brassicae larvae. But according to the parasitization experiment, C. glomerata egressed from P. rapae larvae in Hokkaido did not oviposit in larvae of P. brassicae.