Herbivore-induced plant volatiles enhance the ability of parasitic wasps to find hosts on a plant

We previously reported that cabbage plants emitted volatiles in response to herbivory by diamondback moth (DBM) larvae and that a cocktail of four induced volatile compounds (n‐heptanal, sabinene, α‐pinene and (Z)‐3‐hexenyl acetate) attracted Cotesia vestalis, a wasp parasitoid of DBM larvae (Shiojiri et al., PLOS ONE, 2010). Here, we describe the behaviour of the wasp in response to exposure to the cocktail and a solvent (control) on crucifer plants (Brassica rapa) with DBM larvae. Wasps showed longer residence and search times on plants with the cocktail than they did on control plants. Further, both wasp–host encounters and oviposition frequencies were significantly higher on plants associated with the cocktail and the rates of parasitism on plants with the cocktail increased due to longer residence and increased searching activity by the parasitoid on the plant. These results indicate that the host‐searching activity of the parasitoid C. vestalis is enhanced on host‐infested plants by the DBM‐induced plant volatiles.