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

菜青虫幼虫的寄生蜂团状绒茧蜂，为寄主幼虫的危害所引诱，表现出强烈的捕食行为。受损地点产生的化学物质的主要成分是脂肪酸、棕榈酸和硬脂酸。菜粉蝶幼虫的取食实验表明，脂肪酸是菜粉蝶幼虫的取食引诱剂。同时，我们发现菜粉蝶幼虫从背部刚毛分泌油性液滴。GC-MS分析表明，棕榈酸和硬脂酸是该分泌物的主要成分。在北海道，我们研究了4种菜粉蝶在自然条件下对6种食用植物的产卵选择性，并用4种菜粉蝶幼虫和6种植物进行了取食试验。试验结果表明，对每种幼虫而言，刺梨是相对优势的植物。另一方面，阿拉比斯秋葵的地位非常低，即使对于通常用作食用植物的甘蓝型油菜来说也是如此。产卵喜好试验表明，菜青虫产卵雌蝶对菜青虫有较好的产卵选择性，白粉蝶选择豆蔻菜蛾，但不对菜青虫产卵。田间条件下，菜粉蝶寄生菜青虫幼虫。但根据寄生实验，从北海道菜青虫幼虫中排出的团头虫在菜青虫幼虫体内没有产卵。

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.