Identification of ()-8-Heptadecene and -Pentadecane as Electrophysiologically Active Compounds in and Its Pollinator.

Sexually deceptive orchids typically depend on specific insect species for pollination, which are lured by sex pheromone mimicry. European orchids often exploit specific species of wasps or bees with carboxylic acid derivatives. Here, we identify the specific semiochemicals present in , and in females of one of its pollinator species, . Headspace volatile samples and solvent extracts were analysed by GC-MS and semiochemicals were structurally elucidated by microderivatisation experiments and synthesis. ()-8-Heptadecene and -pentadecane were confirmed as present in both and female extracts, with both compounds being found to be electrophysiologically active to pollinators. The identified semiochemicals were compared with previously identified pollinator attractants, such as ()-9 and ()-12-C-C alkenes in and ()-9-octadecenal, octadecanal, ethyl linoleate and ethyl oleate in , to provide further insights into the biosynthesis of semiochemicals in this genus. We propose that all these currently identified semiochemicals can be formed biosynthetically from the same activated carboxylic acid precursors, after a sequence of elongation and decarbonylation reactions in and , while in , possibly by decarbonylation without preceding elongation.