Indirect plant defense is an important component in regulating population dynamics and the structure of numerous communities in different ecosystems. These defenses mainly involve the emission of volatile organic compounds (VOCs) induced after damage by an herbivore. VOCs can play several ecological roles, such as help natural enemies locate prey or hosts, attract or repel other herbivores, mediate communication between neighboring plants and among different parts of the same plant, and affect the behavior of pollinators and seed dispersers. In addition to VOCs, some plants produce extrafloral nectar, which can enhance plant defense, by attracting, retaining, and increasing the efficiency of some natural enemies; however, among the associated costs, these compounds can attract other herbivorous species and exclude some natural enemies due to competition. Many factors can influence the production of indirect defenses by plants, such as the individual species, life stage, density of herbivores, age, abiotic factors, as well as the association of plants with symbiotic microorganisms. The potential of indirect plant defenses to reduce herbivory and increase the plant fitness has been well demonstrated. Indirect plant defenses may have ecological costs but can express phenotypic plasticity, as plants can reduce or increase the production of defenses according to the associated herbivory rate. Such variable expression of characteristics provides a barrier against the evolution of resistance by the associated herbivores. In this article, we intend to provide a review on volatile organic compounds and extrafloral nectar as indirect plant defenses, including some costs and benefits of these defense mechanisms.

间接植物防御是调节种群动态和不同生态系统中众多社区结构的重要组成部分。这些防御措施主要涉及草食动物破坏后诱发的挥发性有机化合物（VOC）的排放。VOC可以发挥多种生态作用，例如帮助天敌找到猎物或宿主，吸引或排斥其他草食动物，介导相邻植物之间以及同一植物不同部分之间的交流，并影响传粉媒介和种子传播者的行为。除挥发性有机化合物外，一些植物还产生花蜜，通过吸引，保留和提高某些天敌的效率，可以增强植物防御能力。但是，在相关费用中，这些化合物可以吸引其他草食物种，并由于竞争而排除一些天敌。许多因素可以影响植物间接防御的产生，例如单个物种，生命阶段，草食动物的密度，年龄，非生物因素以及植物与共生微生物的关联。间接植物防御减少草食动物和增加植物适应性的潜力已得到充分证明。间接植物防御可能具有生态成本，但可以表达表型可塑性，因为植物可以根据相关的草食率降低或增加防御的产生。特征的这种可变表达提供了防止相关的草食动物产生抗性的障碍。在本文中，