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This week, researchers led by Johannes Stökl have published a paper in Current Biology describing a flower that uses an unusual smell to attract its pollinators. The Solomon’s Lily, which is a member of the Arum genus – which also contains the largest flower in the world, the Titan Arum – releases a sweet smell that mimics rotting or fermenting fruit to attract Drosophilid fruit flies.
This lily uses what is known as deceptive pollination to trick the flies into pollinating it. Now, many flowers attract their pollinators – like insects, birds, bats, all sorts of animals – with some sort of reward – like a sweet sugary nectar. The pollinator visits the flower, and in the process of feeding on the nectar, pollen gets transferred to them that they then transfer to another plant.
But obviously, it’s quite costly to the plant to produce sweet nectar, so some plants trick their pollinators into pollinating them without giving a reward. They release smells that are similar to the food source, or breeding place of the insect, or sometimes even mimic the pheromones of the female insects to attract the males. And that’s what this lily does – it mimics the smell of something that attracts the fruit flies.
So what the researchers did was that they analysed the volatile compounds released by the lily using Gas Chromatography and Mass spectrometry, and found that 6 of the 13 compounds that make up the smell are also found in rotting fruit and fermentation products like vinegar and wine, that are also very attractive to these fruit flies. Because Drosophilid fruit flies feed on yeasts and breed in rotting fruit, they have evolved to be sensitive to the odour of those things, and to respond to them.
They also carried out functional imaging of the fly ‘smell centre’ – the antennal lobe – and found that the compounds released by the lily activate the same parts of the antennal lobe (which is like the olfactory bulb in our brains) as the smells of rotting fruit – so the lily is exploiting the fact that these flies have evolved to be very sensitive to these particular compounds in order to attract them. So it’s interesting in two ways – from an evolutionary point of view, that the flower has evolved to so closely mimic the smell of rotting fruit, and from the point of view that it has helped to shed a bit more light on the way the fruit fly brain works and responds to particular smells.