Torsten MEINERS and Monika HILKER
Freie Universität Berlin, Institut für Zoologie, Haderslebenerstr. 9,
D-12163 Berlin, Germany
Eggs of the leaf beetles Galeruca tanaceti (tansy leaf beetle) and Xanthogaleruca luteola (elm leaf beetle) are often heavily attacked by the chalcidoid wasps Oomyzas galerucivorus and O. gallerucae, respectively. The role of chemicals important for successful parasitism in these species was studied. When investigating host location, volatiles of faeces of the elm leaf beetle attracted O. gallerucae, whereas neither undamaged nor damaged elm leaves were attractive. In O. galerucivorus, odour of faeces of the tansy leaf beetle had no effect, but the parasitoids were arrested when they contacted substrates contaminated with faeces. Thus, faeces may contain a contact kairomone important for host finding. Host recognition is indicated by frequent antennal drumming on the egg surface. The (extralchorion was extracted with solvents of different polarities. In both species, a dichloromethane extract was most active. The active extract of the extrachorion of G. tanaceti eggs was fractionated by tic. One tic-fraction was proved to elicit host recognition behavior. The role of chemicals for successful parasitism will be balanced against the possible importance of ohvsical cues.
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