Laboratory of Ecological Information, Graduate School of Agriculture, Kyoto University, Kyoto 606-8502, Japan.
Tritrophic interactions mediated by chemicals from host-plant complexes, i.e., those in which carnivores search for herbivorous victims using such chemicals, have been demonstrated in several systems. Under natural conditions, plural tritrophic systems coexist on a plant. Therefore, interactions in one tritrophic system may somehow be affected by chemicals from the other tritrophic systems, and vice versa. This study shows the interactions between two tritrophic systems consisting of two herbivores (Plutella xylostella and Pieris rapae) coexisting on the same plant and their respective parasitic wasps, Cotesia plutella and Cotesia glomerata. We show here that ovipositing P. xylostella females prefer P. rapae-infested plants because such plants constitute space with a low enemy population.