Morphophysiological basis of plant defense mechanisms against insect pests

Plants have been interacting with insects for several hundred million years, leading to the development of an intricate and dynamic defense system against insect herbivores. This defense system is further categorized as direct and indirect defense responses based on their expression. Specific or direct defensive responses are mediated by various morphological, biochemical and molecular mechanisms to counteract the effects of herbivore attack while indirect defense is mediated by releasing volatile mixtures to attract natural enemies of plant eating insect herbivores. The structural defense includes both morphological and anatomical traits viz., thorns, spines etc., whereas biochemical mechanisms of defense against the herbivores are wide-ranging, highly dynamic and includes production of different secondary metabolites-terpenes, phenolics and N-containing compounds. The molecular defense mechanisms include intracellular wound signalling viz., systemin signalling and jasmonate regulation of defense responsive genes. The defensive compounds are developed either constitutively or in response to plant damage, affecting insect herbivores’ feeding, development, and survival. In addition, plants also release volatile organic compounds which attract the herbivores’ natural enemies. These strategies either act independently or in conjunction with each other.