How orchid tricks hoverflies

Scientists at the Max Planck Institute for Chemical Ecology in Jena, Germany, have discovered the trick the orchid Epipactis veratrifolia uses to attract pollinating hoverflies. The plant's flower practices a very special mimicry: It produces three chemical substances that are usually emitted as alarm pheromones among aphids.

Hoverfly females smell the alarm and lay their eggs close to the aphids, which are the perfect baby food for their hatching larvae. By mimicking these alarm pheromones, the orchid takes advantage of the hoverfly females, deceiving them into pollinating its flower. The flies even lay their eggs on the flower. However, the hatching larvae are doomed, because no aphids are available in the orchid flower. (Proceedings of the Royal Society B, October 13, 2010)

Eastern marsh helleborine (Epipactis veratrifolia), an orchid species, has successfully lured a hoverfly of the genus Ischiodon by mimicking alarm pheromones usually emitted by aphids.

Even Darwin was a self-admitted orchid lover. Dictionaries describe orchids as exotic ornamentals. Indeed, these plants - more than 30,000 different species are thought to exist - are exotic due their extraordinary and diverse flower morphology. However, they are also exotic from a point of view other than beauty: as crafty imposters in order to achieve reproduction and to make sure that their ovaries are pollinated. Orchids depend on the assistance of pollinators, and like many other flowering plants, attract insects.

Epipactis veratrifolia, an orchid native in South Turkey, the Middle East, and Cyprus, has specialized in hoverflies. Because these insects prefer aphids as food for their larvae, the orchid produces three aphid alarm substances, alpha- and beta-pinene, and beta-myrcene and beta-phellandrene, all of which attract hoverfly females. Interestingly, as the scientists observed, even male hoverflies hang around the orchids, hoping for a chance to copulate with the attracted females.

A bit of nectar as reward