Herbivore-species-specific interactions between crucifer plants and parasitic wasps (Hymenoptera: Braconidae) that are mediated by infochemicals present in areas damaged by herbivores

We compared the host-searching behavior of two parasitoid species, Cotesia plutellae and C. glomerata on their respective host-infested leaf in the laboratory. We observed the host-searching behavior of C. plutellae on a cabbage plant infested by the host larvae Plutella xylostella, and found that the wasps showed their antennal-searching behavior only on the host-infested site. The plants and the regurgitant of the host larvae were both involved in the production of the infochemicals that promoted the antennal-searching behavior in C. plutellae. The searching time of C. plutellae on a piece of cabbage leaf infested by host larvae was significantly longer than that on a piece infested by nonhost (Pieris rapae) larvae and that on the artificially damaged piece. The same pattern in the searching time by C. plutellae was also observed when we used Japanese radish plants and Rorippa indica plants. Likewise, the searching time of C. glomerata on the host (P. rapae)-infested piece of cabbage or Japanese radish was significantly longer than that on the piece infested by nonhost (P. xylostella) larvae. Thus, the two wasp species could detect infestation of these plant species by their respective host through antennal contact.