eLife http://dx.doi.org/10.7554/eLife.15039 (2016)

It has been known for hundreds of years that floral scent is related to pollination, but Alexander Haverkamp and colleagues from the Max Planck Institute for Chemical Ecology in Jena have now shown that it is not a simple case of attraction. The researchers studied wild tobacco, Nicotiana attenuate, which is pollinated by the hawkmoth Manduca sexta and whose flowers emit a fairly simple scent dominated by benzyl acetone (BA). Using RNAi, the researchers silenced the production of BA to compare emitting and non-emitting plants.

Credit: © JEFF SMITH/ALAMY STOCK PHOTO

Somewhat surprisingly, odourless flowers were not ‘invisible’ to the moths, which showed no preference for visiting either type of flower both in tent and wind-tunnel tests. However, the odoured plants were pollinated more efficiently than those emitting no BA. Closer investigation revealed that the hawkmoths remained on scented flowers for longer and were more persistent at attempting to insert their proboscis into the bloom.

The researchers identified cells on the very tips of the proboscis as responsible for sensing BA and showed that the behaviour of the moth was affected only once the proboscis had entered the flower. Rather than being a long-range signal (which could also attract nectar thieves, herbivores and female moths looking for sites to lay their eggs), BA is a local signal indicating the presence of ample nectar and so encouraging the moth to remain longer on the flower, thereby increasing the likelihood of pollination.