Changing Pollinators to Escape Herbivores

Plants need the help of pollinators to reproduce. But some pollinators are also a  threat to plants. For instance once attracted by the flower's scent, moths lay their eggs on the green leaves, and shortly voracious young caterpillars hatch. Scientists at the Max Planck Institute of Chemical Ecology now discovered how tobacco plants successfully solve this dilemma: by reducing the emission of flower scents and changing the flower timing.

In summer 2007, a massive outbreak of tomato hornworms (Manduca quinquemaculata) occurred in tobacco plantations in Utah. The researchers studied the infested plants and noticed that these plants had many flowers that opened after sunrise, although tobacco is typically a night-flowering plant and usually opens its flower buds after sunset. They then compared morning-opening flowers which were only produced by plants that had been attacked by insect larvae and compared them to the usually occurring night-opening flowers.

The researchers found that ‘morning flowers' did not emit the attractant benzyl acetone anymore and also the sugar concentration in the floral nectar was considerably reduced. They also observed that the petals of ‘morning flowers' only opened to a third of the size of ‘night flowers'. With these, the ‘morning flowers' were rendered unnoticeable to moths but more noticeable to other pollinators, particularly to hummingbirds. The researchers discovered that the change in flower phenology, which is elicited by oral secretions (OSs) from feeding larvae, requires jasmonate (JA) signal transduction. JA is a plant hormone that initiates plant defense responses.

The original paper published by Current Biology is available for download at http://dx.doi.org/10.1016/j.cub.2009.11.071