page_title: Pest (organism)
section_title: Plant defences against pests
hierarchical_section_title: Pest (organism) / Ecology / Plant defences against pests
caption_attribution_description: Vachellia collinsii (formerly Acacia collinsii) in Guanacaste, Costa Rica.
context_page_description: A pest is any animal or plant deleterious to humans or human concerns. The term is particularly used for creatures that damage crops, livestock and forestry, or cause a nuisance to people, especially in their homes. Humans have modified the environment for their own purposes and are intolerant of other creatures occupying the same space when their activities impact adversely on human objectives. Thus, an elephant is unobjectionable in its natural habitat but a pest if it tramples crops.
  Some animals are disliked because they bite or sting; snakes, wasps, ants, bed bugs, fleas and ticks belong in this category. Others enter the home thus invading our own private space; these include houseflies, which land on and contaminate food, beetles which tunnel into the woodwork, and other animals that scuttle about on the floor at night, like cockroaches, rats and mice, which are often associated with insanitary conditions.
  Agricultural and horticultural crops are attacked by a wide variety of pests, the most important being insects, mites, nematodes and gastropod molluscs.
context_section_description: Plants have developed strategies that they use in their own defence, be they thorns (modified stems) or spines (modified leaves), stings, a thick cuticle or waxy deposits, with a second line of defence being toxic or distasteful secondary metabolites. Mechanical injury to the plant tissues allows entry of pathogens and stimulates the plant to mobilise its chemical defences. The plant soon seals off the wound to reduce further damage.
  Plants sometimes take active steps to reduce herbivory. Macaranga triloba for example has adapted its thin-walled stems to create ideal housing for an ant Crematogaster spp., which, in turn, protects the plant from herbivores. In addition to providing housing, the plant also provides the ant with its exclusive food source in the form of food bodies located on the leaf stipules.  Similarly, several Acacia tree species have developed stout spines that are swollen at the base, forming a hollow structure that provides housing for ants which protect the plant. These Acacia trees also produce nectar in nectaries on their leaves as food for the ants.
caption: The large and directly defensive thorn-like stipules of Vachellia collinsii are hollow, offering shelter for ants, which further protect the plant against herbivores.
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