Plant defenses against herbivorous insects: A Review

Abstract

There are complex and dynamic interactions, mainly related to food, between plants and insects since hundreds of millions of years ago. Plants have evolved several intricate kinds of defense systems to defend themselves from the herbivores for its survival. Plants lack nervous system like those of animals, but they can readily sense and respond to the insect attack through various signaling pathways in its system which further activates the direct and indirect defenses. Direct defenses include the production of toxins, digestibility reduction of insect, reallocation of resources in plants and morphological defense like thigmonasty, waxy layers on plants, trichomes, tissue toughness etc. Indirect defenses enhance the probability of attracting the natural enemies of herbivores by production of volatiles, the secretion of extra floral nectar, providing nesting spaces to the former. Another strategy of defense without actually having any resistance factor is plant tolerance. In this review, an overview of these defense systems is provided.