ABSTRACT
Most lepidopteran families appeared in the Jurassic period and co-evolved alongside angiosperms (flowering plants); plants evolved chemical defenses against lepidopteran herbivorous attacks, which was closely followed by biochemical adaptation in herbivores, and the newly evolved detoxification mechanism resulted in the adaptive radiation of lepidopteran lineages. During the long history of the arms race between these adversaries, the larval midgut has been the ‘front line’ of plant chemical defense and larval metabolic counter adaptations, and various unique strategies have developed in both insects and plants. Metabolic reactions such as the detonation of a “mustard bomb” or successful detoxification are often associated with larval digestion and absorption during food intake. In this chapter, recent progress in the understanding of plant–insect interactions, especially direct chemical defense (isothiocyanates, benzoxazinoids, and iridoids) and indirect defense mediated by larval elicitors, are reviewed in the context of the total performance of the larval midgut during mastication/digestion. In addition, the evolutionary background of each system will be discussed.
