Plants also adopt an olfactory strategy of attraction. In fact, the scent that we appreciate as we approach the petals of certain flowers is a more or less complex mixture of low molecular weight volatile organic compounds and constitutes a fundamental chemical message for pollinators. Plants emit this call to warn them that there is nectar waiting for them in return for transporting pollen, but also to show their geographical position.
In addition, the scent is also a selectivity factor: the more the scent is composed of multiple aromas, the more pollinators will like the flower and, conversely, the less aromas are released, the fewer insects will be attracted to the flower. However, not all pollinating insects are in search of sweet nectar. A unique example is the strategy adopted by the titan aro plant; this particular plant from the Araceae family develops a large inflorescence that releases an unpleasant odour in order to attract and be pollinated by meat flies and carrion-eating beetles.
Another interesting strategy is that of certain plants that can generate heat. This phenomenon, called thermogenesis, is an effective method of attraction but very expensive for the plant; some species of night-flowering plants (such as Victoria Amazonica) use heat to attract insects in search of a warm refuge, involving them in the pollination process. A different strategy is adopted by Amorphophallus Titanum, a plant that spreads its scent over great distances due to the flower's higher than atmospheric temperature.
The most unique attraction strategy was brought to light by the studies of Dominic Clarke et al. in 2013. His research showed that there is a complicated communication system based on the differences in electrical potential between the flower and its pollinator. These studies showed that flying insects, including pollinators, usually have a positive electrical potential, while flowers often show a negative potential. This difference in potential generates an electric field between flowers and insects that favours the adhesion of pollen to the insect fur. Clarke also discovered that pollinators can detect and learn to use floral electric fields to assess the magnitude of flower rewards. Flowers vary their electric potential depending on how much pollen they have on their stamens, allowing pollinators to recognise and select the flowers that are richest in nectar and pollen. These studies show that electrical fields are also an important way of communication between plant and pollinator. The interesting feature of this electrical language is its speed: the time scale at which information is exchanged is in the order of milliseconds.
These types of flower signals can act individually or in complementarity. When these three levels of communication are combined into a single signal that can be received by several of the pollinator's sensors, the pollinator will have greater perceptual certainty in selecting which flowers to visit.
This silent conversation between plants and pollinators developed over millennia has led to deep bonds that provide an alternative example of the struggle for survival where mutual aid takes the place of overwhelm!