Institute of Plant Sciences, Applied Entomology, Swiss Federal Institute of Technology (ETH), Clausiusstrasse 25/NW, CH 8092 Zurich, Switzerland.
Brussels sprouts plants (Brassica oleracea var. gemmifera) attacked by Pieris brassicae caterpillars release volatiles that attract natural enemies of the herbivores, the parasitoid Cotesia glomerata, to the damaged plant. Non infested leaves of caterpillar infested plants emit a volatile bouquet similar to that of infested leaves which attract parasitoids in a two choice wind tunnel bioassay. Systemically induced volatiles are emitted in detectable quantities only after three days of caterpillar continuous feeding and only upon recent mechanical damage of the non-infested leaf. The volatile emission decreases to non detectable quantities in the three days following termination of caterpillar feeding. GC-MS and behavioural results suggest that green leaves volatiles and several monoterpenoids are accumulated in non infested leaves of infested plants before a possible herbivore attack. If no attack occurs, no volatile emission will take place. Herbivore induced synomones in cabbage appear to produced through mechanisms which differ from other known tritrophic systems.