gholamreza Abdi

Insects are major herbivores, exerting significant pressure on plants, which have evolved diverse defense mechanisms despite lacking mobility and an animal-like immune system. While some plant-insect interactions, like 250pollination, are mutualistic, most are antagonistic, with insects feeding on plant tissues and plants responding with morphological barriers and chemical defenses. Herbivorous insects employ various strategies to extract nutrients, but plants counter by producing toxins, protease inhibitors, and volatiles that attract insect predators. Early theories focused on constitutive defenses; compounds produced during normal growth that deter herbivores. However, plants also deploy induced defenses, rapidly modifying their transcriptomes, proteomes, and metabolomes in response to herbivore cues such as compounds in insect saliva or oviposition fluids. These changes involve complex biochemical pathways, including reactive oxygen species (ROS) generation and scavenging enzymes, defense-related phytohormones, and the synthesis of secondary metabolites like terpenes, volatile organic compounds (VOCs), and green leaf volatiles (GLVs). This chapter explores the intricate ways plants perceive and respond to insect herbivory, emphasizing the dynamic and sophisticated nature of these defense systems. Understanding these mechanisms provides valuable insights for developing sustainable pest management strategies and enhancing plant resilience in agricultural ecosystems.