Plants can use volatile organic compounds released from herbivore-infested neighbours to anticipate future enemy pressure and adjust their defensive phenotype accordingly. The most likely explanation for the evolution of this phenomenon is that plants use volatile signals for within-plant signalling, that is, to mount a systemic response to local damage in as yet undamaged parts. The benefits of this within-plant signalling are obvious and the same remains true for the receivers of cues that allow them to anticipate upcoming enemy attack. By contrast, no study has demonstrated that the emitting plant benefits from warning its neighbours. The question remains open whether this signalling phenomenon represents communication or, rather, eavesdropping.

Key concepts:

• Plants are sessile organisms and require phenotypic plasticity to cope with a rapidly changing and in part unpredictable environment.
  
• Plants express induced systemic resistance to herbivores and pathogens.
  
• Plants can anticipate future enemy attack by perceiving cues that are released from damaged neighbours.
  
• Volatile organic compounds play multiple roles in the resistance of plants to pathogens and herbivores.
  
• Communication is defined differently, making it difficult to clearly apply the term ‘plant communication’ to signalling between plants.
  
• Volatile organic compounds serve as signals exchanged among plants and carnivores and likely also serve as plant hormones.