Molecular mimicry and sexual deception

by Zoë Tulip

Pollination of the spider orchid Caldenia crebra by the Thynnine wasp Campylothynnus flavopictus

A team of chemists and biologists at both the ANU and the University of Western Australia (UWA) have been investigating and discovering what draws pollinators (such as wasps) to orchids.

The team of ANU and UWA researchers found the chemistry generated by a certain kind of orchid in order to attract particular pollinators is very specific. They also discovered new chemical compounds never before found in plants, as well as some that are brand new to science altogether.

The process involved working out what chemicals were being produced by Caladenia crebra – a spider orchid - to attract the Campylothynnus Flavopictus, a species of wasp.

The challenge was mostly in how best to measure the minute amounts of chemicals produced by the plant. For the plants, these chemicals act as a kind of pseudo-pheromone.  So in other words, they “smell” like a female wasp in order to attract the male wasps, and in turn aid the process of pollination.

By actively imitating the smell of female pollinators, the orchids attract the male wasps who then instinctively try to fly away with the part of the orchid plant imitating a female wasp, which is the typical behavior. The mechanical movement of the effort to fly away with the “female” results in pollen attaching to the wasp, which can then be transferred to another plant. 

Earlier research looked at the male wasp antennae as clues as to what chemicals might be at play. However, this method didn’t work with the specific spider orchid and wasp these researchers were looking at.

So instead, they looked closely at the chemistry by using chromatography – a way to separate different chemical compounds from each other - and mass spectrometry, a way of identifying different chemicals found within the pheromone sample. For comparison, the samples were taken from both the plant, and from the female wasp. To verify that they had identified the new pheromones correctly, the researchers tested mixtures of the identified chemicals found in these pseudo-pheromones on dummy female wasps.

The result revealed chemical combinations never before found within plants, including some that were beforehand unknown to science.

Another unexpected result was the discovery that there is in fact diversity within the pseudo-pheromones between orchids. Pseudo-pheromones are also found in other plants such as daisies, but orchids appear to have developed the most complex array of these chemicals.

Pseudo-pheromone research originated as an idea to attract pest insects into pheromone traps. These traps are generally the main goal/focus of commercial ecology, putting orchid ecology in a unique field by itself. The Peakall Lab at the ANU are the known experts on pseudo-pheromones outside of pest control.

The paper on the specific orchid/pollinator combination is called “The Spider Orchid Caladenia crebra produces Sulfurous Pheromone Mimics to Attract its Male Wasp Pollinator” and can be found here

An earlier paper by these authors was the lead-up to the findings of the later one.

The research is part of a cross-institutional long-term genetics investigation program.

Updated:  25 November 2017/Responsible Officer:  Director RSB/Page Contact:  Webmaster RSB