Abstract
The mixed-function oxidases of a polyphagous insect larva (the southern armyworm, Spodoptera eridania) were found to be induced by a diversity of secondary plant substances. The induction proceeds rapidly and in response to a small quantity of secondary substance. Following induction, the larva is less susceptible to dietary poisoning. It is argued that mixed-function oxidases play a major role in protecting herbivores against chemical stress from secondary plant substances.