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| News :. Smelly flower plays rotten trick on flies
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A Mediterranean flower so accurately mimics the stench of rotting flesh that it lures flies to lay their eggs on it, thereby tricking them into acting as pollinators, Swedish scientists have discovered.
In the latest issue of the journal Nature, Dr Bill Hansson and colleagues of the Swedish University of Agricultural Sciences in Uppsala report a remarkable example of mimicry, a strategy used by several plant species to increase the chances of pollination.
The dead horse arum lily, Helicodiceros muscivorus, is a rather attractive brown flower found on Corsica and other small islands in the Mediterranean. The flower opens for two days, on the first of which it releases an extremely foul odour reminiscent of rotting meat.
Female flies are attracted to the flower because they normally lay their eggs in carrion. When they crawl inside the flower, they become trapped for up to six hours until the male parts of the flower begin to produce pollen. The chamber then opens and, as the fly leaves, it brushes past the pollen and then carries it to other flowers, fertilising them in the process.
After observing the effect the flowers have on the flies, the researchers wanted to know exactly what the flies were responding to. So they exposed fly antennae - which act as the insect's 'nose' - to chemical odourants from both the flower and from rotting meat.
They found no difference in the way the antennae responded to the flower or the meat odour, showing that flies are not able to distinguish between the two. This is despite the fact that the chemical composition of the two odours - made up of several different types of oligosulphides - is slightly different.
To confirm the influence of the oligosulphides on fly behaviour, the researchers impregnated flowers with an artificial form of the odour on the second day of flowering, when there is normally no odour produced. They found that the flower attracted a similar number of flies on both days, showing that the odour is an important component of the mimicry and that their odours attract flies to the flower.
"This plant is a striking example of evolutionary cunning that exploits insects for pollination purposes," Hansson said. Several other plants attract insects which feed or breed in rotten meat, including some species of Stapelia, an African succulent with unusually shaped flowers. But this is the first time scientists have shown that the pollinators find it impossible to tell the real odour from that produced by the flower.
Such swindling of one species by another is also perpetrated by the Ophrys orchid, which has evolved to look like a female bee, and produces a sexual pheromone that tricks the male bee into copulating with it and in the process, pollinating the flower.
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