How sexually deceptive orchids lure and trap pollinators

A study led by The University of Western Australia and The Australian National University has found a particular orchid species is able to lure male flies to facilitate pollination by emitting chemical compounds that match the female flies’ sex pheromones. 

The greenhood orchid (Pterostylis species) lures the male fungus gnat and traps it in its flowers, and the fly’s only escape is through a corridor where it brushes past the flower’s anther, collecting pollen on its thorax.

Published in Current Biology, the study is the first time it has been identified that the greenhood orchid, highly prevalent in Australia, produces a unique set of compounds to attract pollinators. 

“We were curious to learn more about the relationship between the greenhood orchid and the fungus gnat fly and how they interacted."              Tobias Hayashi

Lead Researcher Tobias Hayashi, who completed the study through UWA and The Australian National University, said pollination of the greenhood orchids had long remained a mystery.

“It was only recently that it was confirmed that the fungus gnat was the sole pollinator of this species of orchid,” Mr Hayashi said.

“We were curious to learn more about the relationship between the greenhood orchid and the fungus gnat fly and how they interacted.

“Initially, in the study, we were focused on the orchids, but this is also the first time a sex pheromone has been documented for these fungus gnats.

“When we looked at two closely related greenhood orchid species we found that they had different chemistry. This suggests to us that they may cleverly produce different chemicals to attract different types of pollinators.”

Dr Gavin Flematti from the UWA School of Molecular Sciences said the findings had important implications for understanding the evolution of orchids.

“The chemical compound used by both the orchid and fungus gnat is quite unusual,” Dr Flematti said. 

“This is an example of our biodiversity in Australia where we have found another set of unique compounds involved in orchid signalling to achieve pollination, and helps expand our knowledge of these unique systems.”