Plant Volatiles Yielding New Ways to Exploit Plant Defence

When plants are damaged, they produce semiochemicals which can act as repellents for herbivorous pests and as attractants for organisms antagonistic to these pests, e.g., predators and parasitic wasps. Plants can also produce signals that warn other plants of impending attack. From this range of phenomena, it is possible to identify new ways to control pests. Although, in the past, we have needed to deploy such approaches by applying slow-release formulations of semiochemicals to crop plants, we can now use the plants themselves as a source of these semiochemicals. This may be achieved by using inducing agents, or a new range of natural product plant activators, to ‘switch on’ plant defence prior to attack. This paper considers the identification of new plant activators. In addition, practical use of plants releasing semiochemicals to ward off pest attack, to ensnare the attackers, and to attract beneficial insects that will attack the pests, is demonstrated by use of the stimulo-deterrent diversionary (‘push-pull’) strategy that has been developed for management of stem-borer moths in Africa.