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 emiss ion of synomones that attract the natural enemies of herbivores. We in vestigated whether mechanical damage to Brussels sprouts leaves (Brass ica oleracea var. gemmifera) is sufficient to obtain attraction of the parasitoid Cotesia glomerata or whether feeding by Pieris brassicae c aterpillars elicits the release of synomones not produced by mechanica lly damaged leaves. The response of the parasitoid Cotesia glomerata t o 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 damage d leaves treated with larval regurgitant. Chemical analysis of the hea dspace of undamaged, artificially damaged, caterpillar-infested, and c aterpillar regurgitant-treated leaves showed that the plant responds t o damage with an increased release of volatiles. Green-leaf volatiles and several terpenoids are the major components of cabbage leaf headsp ace. Terpenoids are emitted in analogous amounts in all treatments, in cluding undamaged leaves. On the other hand, if the plant is infested by caterpillars or if caterpillar regurgitant is applied to damaged le aves, the emission of green-leaf volatiles is highly enhanced. Our dat a are in contrast with the induction of more specific synomones in oth er plant species, such as Lima bean and corn.