Non-protein amino acids in plant defense against insect herbivores: Representative cases and opportunities for further functional analysis

► Non-protein amino acids have been implicated in plant defense against insect pests. ► Direct toxic effects occur through interference with animal amino acid metabolism.► Nitrogen is stored in a form that is metabolically inaccessible to herbivores. ► Some specialist herbivores have specific detoxification mechanisms. ► Sequenced plant genomes provide opportunities for discovering biosynthetic enzymes.