Plant Defences Against Herbivore and Insect Attack

The story of Adam and Eve links eating a forbidden fruit with death in the cycle of human existence (Genesis 3:1– 24). Indeed, to avoid poisoning, herbivores and omnivores such as humans must be cautious in choosing which plants and plant parts to eat. A prevailing hypothesis is that the nearly ubiquitous antiherbivore metabolites in plants were selected by coevolution with herbivores. Likewise, the ability of a herbivore to detoxify or tolerate toxins of food plants is essential for the herbivore’s survival. Plants may largely escape herbivory if they are imbued with an especially toxic cocktail, although the plants must also have mechanisms for protection from their own toxins. Other defences, such as thorns and tough or unpalatable tissues, and recruitment of parasitoids and predators that attack herbivores, all work in conjunction and synergy with chemical defences. Plants survive only if they are able at least partly to deter or avoid herbivory. Without defences, plants would be driven to extinction, with the consequent extinction of myriad herbivores, predators, parasites and saprotrophs. Thus, the familiar species of our biosphere and the fossil record of longstanding associations of plants with animals indicate a dynamic balance struck between plants and those that eat them.