Smells Like Bee Spirit

Is there anything orchids won't do to get pollinated? The latest discovery is a flower that smells like a stressed bee to attract bee-eating hornets.

According to a paper published in the latest issue of Current Biology (volume 19, pages 1368-1372), about one-third of the world's 30,000 orchid species deceive their pollinating insects. The flowers trick the pollinators into visiting by imitating flowers that do deliver, or by smelling like a potential mate.

The plant doesn't waste energy producing nectar, and the insect leaves empty footed but carrying some precious pollen to the next flower. Remember that cross-fertilisation is the engine of evolution.

Now there is a new twist on this theme. Dendrobium sinense, from China (as its species name suggests), is pollinated by a hornet that sniffs out something called '(Z)-11-eiconsen-1-ol', better know as the smell of a stressed bee. This pheromone is produced by Asian and European honey bees and has never before been found in a flower.

The orchid flowers are white with a red centre (see above) and offer no reward to the hornet other than the perfume of an unhappy bee.

The researchers from Germany and China - Jennifer Brodmann, Robert Twele, Wittko Francke, Luo Yi-bo, Song Xi-qiang and Manfred Ayasse - set up dummy bees impregnated with the floral scent to show that the smell was in fact attractive to the hornets.

There may be other species with the same pollination trick. Another wasp-pollinated orchid, Steveniella satyrioides, is the next to be studied. The scientists wonder whether mimicking the scent of prey may be common in those wasp-pollinated orchids that offer no food reward.

Other than revealing another fascinating orchid pollination story, this discovery may be useful in developing a safe system for trapping hornets that frustrate beekeepers.

Image: Dendrobium sinense and its pollinating hornet, Vespa bicolor, with a pollen mass on its back. This picture is from Daily Mail on-line and the scientific paper can be purchased from Current Biology.