The significance of background odour for an egg parasitoid to detect plants with host eggs.
Scots pine has been shown to produce a volatile bouquet that attracts egg parasitoids in response to oviposition of the herbivorous sawfly Diprion pini. Previous analyses of headspace volatiles of oviposition-induced pine twigs revealed only quantitative changes; in particular, the sesquiterpene (E)-beta-farnesene was emitted in significantly higher quantities by oviposition-induced pine. Here we investigated whether (E)-beta-farnesene attracted the egg parasitoid Chrysonotomyia ruforum. We tested the behavioural response of C. ruforum females to different concentrations of (E)-beta-farnesene. Egg parasitoids did not respond to this sesquiterpene at either concentration tested. However, they did respond significantly to (E)-beta-farnesene when this compound was offered in combination with the volatile blend emitted from pine twigs without eggs. This response was dependent on the applied concentration of (E)-beta-farnesene. Further bioassays with other components [(E)-beta-caryophyllene, delta-cadinene] of the odour blend of pine were conducted in combination with the volatile blend from egg-free pine as background odour. None of the compounds tested against the background of odour from an egg-free pine twig were attractive to the egg parasitoid. These results suggest that the egg parasitoids responded specifically to (E)-beta-farnesene, but only when this compound was experienced in the 'right' context, i.e. when contrasted with a background odour of non-oviposition-induced pine volatiles.
Mumm
Roland
R
Institute of Biology, Freie Universität Berlin, Haderslebener Strasse 9, D-12163 Berlin, Germany.
Hilker
Monika
M
D000818:Animals; D005260:Female; D006790:Host-Parasite Interactions / Q000502:physiology; D006927:Hymenoptera / Q000502:physiology*; D009812:Odorants; D010058:Oviposition; D010063:Ovum / Q000502:physiology*; D041605:Pinus sylvestris / Q000378:metabolism / Q000469:parasitology / Q000502:physiology*; D012717:Sesquiterpenes / Q000378:metabolism*; D014835:Volatilization
D012717:Sesquiterpenes; C062671:beta-farnesene