Two tritrophic systems were experimentally coupled in the present study. One system consisted of a cabbage plant (Brassica oleracea), diamondback moth larvae (Plutella xylostella) and their parasitic wasp (Cotesia plutellae). The other system consisted of a cabbage plant, cabbage butterfly (Pieris rapae) larvae and their parasitic wasp (Cotesia glomerata). First, we demonstrated that parasitism by C. glomerata and C. plutellae increased and decreased, respectively, on plants infested by both herbivore species than on plants infested by their host larvae alone. We then demonstrated that adult Pl. xylostella oviposited preferentially on plants infested with Pi. rapae, whereas adult Pi. rapae revealed no significant preferences between uninfested plants or plants infested with Pl. xylostella. Based on the present results and those of our previous study, we discuss the oviposition preferences of herbivores in tritrophic contexts.