Orchid mimics the smell of aphids to attract hoverflies

Scientists have discovered how a plant species attract hoverflies by mimicking chemicals released by aphids.

The report, which appears in the journal Proceedings of the Royal Society B, claims a species of orchid (Epipactis veratrifolia) produces chemicals that are ‘remarkably similar’ to aphid attack pheromones.

Epipactis veratrifolia was shown to release chemicals that mimic aphid pheromones.

Research was carried out by the Max Planck Institute, Germany and the University of Ulm, Israel, using samples collected from Enot Tsukim Nature Reserve, Israel. Epipactis veratrifolia can be found throughout the Middle East and its range extends eastwards to the Himalayas and southwards to Ethiopia.

Attack pheromones are released by aphids when they are in danger and certain species of hoverfly can recognise these pheromones and use them to locate aphids. By mimicking aphid pheromones, the orchid deceives hoverflies to pollinate the flower without offering the usual ‘reward’ of sugar-rich nectar.

The findings demonstrate, for the first time, mimicry of aphid attack pheromones – chemicals used for communication- by a plant species and, as such, represent a new pollination strategy.

The discovery

Scientists were first alerted to the mimicry when they realised hoverflies would lay eggs in flowers that did not contain any aphids.

In a normal system, hoverflies, attracted by the smell of aphids, enter the orchid flower in order to lay eggs, which feed on the aphids after they hatch into larvae.

The presence of eggs in orchid flowers that did not contain aphids, led researchers to reason the orchid was mimicking aphid pheromones.

Bill Hanson, Director at the Max Planck Institute, explains, “We assume that the insects are not only deceived by the aphid alarm pheromones, but also fall for the aphid-like dark warts in the orchid’s flower”.

Pheromones are chemicals used by aphids to communicate.

A three step experiment

Researchers used three methods to demonstrate the mimicry.

  • Chemical analysis, often used in forensic science, compared chemicals released by the orchid and aphid.
  • Behavioural studies showed the orchids scent induced egg laying in hoverflies.
  • Measuring electrical signals in hoverflies antennae demonstrated which chemicals were recognised.

Evolution

There are over thirty thousand species of orchid, ten thousand of which have evolved deceptive mechanisms for pollination. The current study speculates that production of a pheromone mimic first evolved to deter aphids from entering the flower and only later became important in attracting pollinators.

The original article can be found here .

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