1Inst. for Organic Chemistry, Univ. Hamburg, Martin-Luther-King-Platz 6, 20146 Hamburg, Germany.
2Dept. of Evolutionary Biology, Althanstraße 14, 1090 Vienna, Austria.
Flowers of Ophrys-orchids mimic receptive females of usually one
pollinator species, only. Males of this species are attracted primarily by the flower odour and
transfer the pollinia during so-called "pseudocopulations" with the flowers. We investigated
the pairs Ophrys sphegodes (orchid) / Andrena nigroaenea (bee),
Ophrys panattensis (orchid) / Osmia rufa (bee) and Ophrys speculum
(orchid) / Camsposcolia ciliata (wasp) with respect to volatiles produced both by
the plants and by the females of the pollinators and which may be attractant for the males
of the pollinators. Coupled gas chromatography and electroantennography was used for
tracing candidate compounds. Identification was carried out by GC/MS. Field bioassays
were performed with extracts of flowers or insects and with synthetic compounds. While a
blend of saturated and unsaturated straight chain hydrocarbons
(C20-C29) proved to be strongly attractive to males of
A. nigroaenea (see ref.), males of O. rufa respond to a mixture of
saturated and unsaturated fatty acids. In contrast to these bouquets which require a pattern
recognition at the receptor site, 9-hydroxy decanoic acid is the decisive compound to attract
C. ciliata males. After pollination or after copulation, the attractiveness of flowers or
nsects is strongly reduced. The chemical background of this phenomenon will be presented.
F.P. Schiestl, M. Ayasse, H.F. Paulus, C. Löfstedt, B.S. Hansson, F. Ibarra,
W. Francke, 1999, Nature 399, 421-422.