Scientists from the Max Planck Institute for Chemical Ecology in Jena, Germany, have solved a case of fraud that has been pending for 40 million years. Arum palaestinum, also called the Solomon’s lily, attracts drosophilids (vinegar flies) as pollinators by emitting odor molecules that resemble those produced during alcoholic fermentation of rotting fruit initiated by yeast. The plant accomplishes the illusion of yeast simply by producing six chemicals that – together in a specific mix – create the impression of fermentation in the fly brain. The produced volatiles include two chemicals which are very rarely encountered in plants but are typical of wine and vinegar – actually byproducts of yeast activity. The scientists showed that the lily’s fragrance targets a deeply conserved neuronal pathway specifically tuned to yeast odors. Thus, the Solomon’s Lily is exploiting a million-year-old instinct in flies for its own purposes.
The genus Drosophila – vinegar flies – consists of many species that feed on a variety of sources ranging from fruit to bacterial layers on certain tropical land crab species. For most drosophilids, yeast is the main food. Their antennae and antennal lobes, the
first brain region that receives input from the olfactory sensory neurons, are accordingly specialized in perceiving odor molecules typically emitted by growing yeast. The smallest concentrations are sufficient to lead vinegar flies to their food source.
Many flowering plants depend on insect pollinators; they ensure that offspring are produced and guarantee genetic variability. Flowers use colorful petals and odor bouquets to attract them. Although often pollination service is rewarded with sweet nectar, Arum palaestinum tricks its pollinators. The plant, also called the Solomon’s Lily, produces an odor in its violet-black flowers that to a human nose is most similar to a fruity wine. It was obvious that the plant attracts pollinators with this odor, namely vinegar flies. But unlike other flowers, Arum palaestinum does not give a reward in form of nectar; in fact, flies are trapped in the flower overnight and not released until the next day.