Pollinator attraction in a sexually deceptive orchid by means of unconventional chemicals

Abstract

Ophrys flowers mimic virgin females of their pollinators, and thereby attract males for pollination. Stimulated by scent, the males attempt to copulate with flower labella and thereby ensure pollination. Here, we show for the first time, to our knowledge, that pollinator attraction in sexually deceptive orchids may be based on a few specific chemical compounds. Ophrys speculum flowers produce many volatiles, including trace amounts of (omega-1)-hydroxy and (omega-1)-oxo acids, especially 9-hydroxydecanoic acid. These compounds, which are novel in plants, prove to be the major components of the female sex pheromone in the scoliid wasp Campsoscolia ciliata, and stimulate male copulatory behaviour in this pollinator species. The specificity of the signal depends primarily on the structure and enantiomeric composition of the oxygenated acids, which is the same in wasps and in the orchids. The overall composition of the blend differs significantly between the orchid and its pollinator and is of secondary importance. 9-Hydroxydecanoic acid is a rarely occurring compound that until now has been identified only in honeybees. Contrary to the standard hypothesis that Ophrys flowers produce only 'second-class attractivity compounds' and are neglected once the pollinator females are present, we show that flowers are more attractive to the males than are their own females.

Floral colour signal increases short-range detectability of a sexually deceptive orchid to its bee pollinator

“…They produce the behaviourally active components of the sex pheromone of receptive females of the imitated insect species to attract males and elicit mating behaviour. During the subsequent copulation attempt, the so-called pseudocopulation, the pollinaria become attached to the male's body and pollen is transferred upon visitation of subsequent flowers (Kullenberg, 1961;Ayasse et al, 2003;Schiestl et al, 2004;Schiestl, 2005). Pollinator attraction in these orchids is very specific as only males of the target species are attracted while other flower visitors do not respond to the odour bouquet.…”

Does Selection on Floral Odor Promote Differentiation Among Populations and Species of the Sexually Deceptive Orchid Genus Ophrys?

“…The specific pollinator responses of Andrena nigroaenea and A. flavipes to the closely related and sympatric O. fusca and O. bilunulata, respectively (Schiestl and Ayasse 2002), are mediated by different relative amounts of alkenes. By contrast, in the floral odor of the more distantly related O. speculum, highly specific oxygenated carboxylic acids attract scoliid wasps as pollinators (Ayasse et al 2003).…”

“…However, floral odor is the primary signal for pollinator attraction. Floral odor extracts and synthetic blends of those odors can induce attraction and copulatory behavior in patrolling male hymenoptera with only crude visual or tactile cues (Kullenberg and Bergströ m 1976;Borg-Karlson 1990;Schiestl et al 1999;Ayasse et al 2000Ayasse et al , 2003. It is also the floral odor traits that are responsible for maintaining species boundaries through the attraction of a single or very few pollinator species (Paulus and Gack 1990a;Schiestl and Ayasse 2002).…”

“…Using this method, the orchid chemical mimicry has been characterized in several cases (Schiestl et al 1999Ayasse et al 2003). The floral odor of Ophrys sphegodes subsp.…”

The orchid Ophrys speculum Link (Orchidaceae) in Croatia

“…(DELFORGE 2006). The species is pollinated by the wasp Dasyscolia ciliata (Scoliidae, Hymenoptera) and this relationship is highly species-specific (POUYANNE 1917, AYASSE et al 2003, BAUMANN et al 2006, PAULUS 2007. It has been found that the western variant is pollinated by D. ciliata ssp.…”