INDUCTION OF PARASITOID ATTRACTING SYNOMONE IN BRUSSELS-SPROUTS PLANTS BY FEEDING OF PIERIS-BRASSICAE LARVAE - ROLE OF MECHANICAL DAMAGE AND HERBIVORE ELICITOR

Induction of plant defense in response to herbivory includes the emission of synomones that attract the natural enemies of herbivores. We investigated whether mechanical damage to Brussels sprouts leaves (Brassica oleracea var. gemmifera) is sufficient to obtain attraction of the parasitoid Cotesia glomerata or whether feeding by Pieris brassicae caterpillars elicits the release of synomones not produced by mechanically damaged leaves. The response of the parasitoid Cotesia glomerata to different types of simulated herbivory was observed. Flight-chamber dual-choice tests showed that mechanically damaged cabbage leaves were less attractive than herbivore-damaged leaves and mechanically damaged leaves treated with larval regurgitant. Chemical analysis of the headspace of undamaged, artificially damaged, caterpillar-infested, and caterpillar regurgitant-treated leaves showed that the plant responds to damage with an increased release of volatiles. Green-leaf volatiles and several terpenoids are the major components of cabbage leaf headspace. Terpenoids are emitted in analogous amounts in all treatments, including undamaged leaves. On the other hand, if the plant is infested by caterpillars or if caterpillar regurgitant is applied to damaged leaves, the emission of green-leaf volatiles is highly enhanced. Our data are in contrast with the induction of more specific synomones in other plant species, such as Lima bean and corn.