1Institute of Organic Chemistry, Technical University Braunschweig, Hagenring 30, 38106 Braunschweig, Germany.
2Instiute of Zoology, Free University Berlin, Haderslebener Str. 9, 12163 Berlin, Germany.
The role of volatiles involved in the host finding process of the parasitoid Oomyzus galerucae that attacks the eggs of Xanthogaleruca luteola were studied. Olfactometer bioassays showed that neither volatiles from the eggs of Xanthogaleruca luteola nor from its host plant Ulmus campestris attract parasitoids. Damaged plants were also not attractive whereas volatiles from feed-damaged plants onto which host eggs had been deposited acted as attractants. This result suggests that it is the deposition of eggs rather then the feeding that initiates the release of attractive volatiles. Headsapce samples of differently treated leaves were analysed by GC/MS. Best results were obtained by incubation of undamaged elm twigs with jasmonic acid. This treatment renders the foremost unattractive elm leaves attractive. A complex blend of mono- and sesquiterpenes is released from the plant.