DSSS - Living with poisons: The successful lives of herbivorous insects

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 of our 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 inhibiting glucose cleavage, by diverting the hydrolysis reaction, and by direct metabolism of the active hydrolysis products.

Under selection pressure, insect herbivores have developed many ways to circumvent the toxic arsenal of their host plants. More knowledge of these adaptations may lead to new approaches to controlling pest insects in agriculture and forestry.