Herbivore feeding preference corroborates optimal defense theory for specialized metabolites within plants

Significance The “optimal defense theory” is a long-standing theoretical framework that is still controversially discussed. The central hypothesis of the optimal defense theory predicts that plant defenses are concentrated at the highest level in tissues and in organs that are the most valuable for survival and fitness. In this paper, we use the herbivore-deterrent defense compounds glucosinolates in the reference plant Arabidopsis thaliana as a model to test this central aspect of the optimal defense theory. We eliminated the gradient of glucosinolate distribution across tissues by the mutation of genes encoding transporters and thereby altered the feeding preference of the African cotton leafworm, Spodoptera littoralis , which is a devastating pest of many economically important crop plants including cotton, tomato, and maize.