Dr. Jonathan Gershenzon, Director of Max Planck Institute for Chemical Ecology

Biochemistry on six legs: How insects resist plant toxins

Plants contain thousands of chemical compounds purported to be anti-herbivore defenses. Yet, in natural communities nearly every plant is attacked by some species of insect that feeds on it without apparent ill effects. In recent years, we have learned that the ability of insect herbivores to metabolize plant defense compounds is widespread. In fact, the chemical diversity of insect metabolites of plant defenses rivals the chemical diversity of the defenses themselves. Nevertheless, it is still unclear which metabolic processes are true detoxification reactions that benefit insects.

I will discuss some highlights of our recent work on insect detoxification of glucosinolates, the plant defenses responsible for the flavor of mustards and cabbages. These sulfur-rich defenses are activated on plant damage by glucose cleavage and rearrangement to poisonous products. Herbivorous insects deal with glucosinolate defenses in several different ways with varying consequences for their growth and survival. Glucosinolates can be detoxified by converting the parent protoxin to a non-hydrolyzable derivative, by diverting the hydrolysis reaction, or by waiting for the toxic hydrolysis products to form and then metabolizing them.

Under selection pressure, insect herbivores have developed many ways to circumvent the toxic arsenal of their host plants. More knowledge of these adaptations will increase our understanding of what plant defenses are most effective, what the limits are to an insect’s host range, and which insects are likely to become pests on a plant, as well as leading to new approaches to controlling pest insects in agriculture and forestry by targeting their detoxification systems.