ABSTRACT
In sexually deceptive orchids, the flowers mimic in shape, color, and odor females of their pollinators, thereby attracting males for pollination. There is a strong specialization of the sexually deceptive orchids to male pollinators because sex pheromones in bees are highly species specific. Characteristic variation in the proportions of the chemical compounds of flowers between and within an inflorescence utilizes the learning abilities of the male pollinators, thus raising the chance of more than one flower being visited by the same male bee. As an adaptation to highly specialized pollination mechanisms and rare pollinator visits, orchid flowers are usually long lived. The highly specific Ophrys-pollinator relationship represents the main mechanism of reproductive isolation between the often interfertile Ophrys species and the species-specific scent is mainly responsible for prezygotic isolation. In the Ophrys fusca group, speciation may be brought about by changing the patterns of alkenes, which leads to the attraction of a different pollinator and reproductive isolation.
