Insect herbivory is often restricted by glucosylated plant chemical defence compounds that are activated by plant
β-glucosidases to release toxic aglucones upon plant tissue damage. Such two-component plant defences are widespread
in the plant kingdom and examples of these classes of compounds are alkaloid, benzoxazinoid, cyanogenic and iridoid
glucosides as well as glucosinolates and salicinoids. Conversely, many insects have evolved a diversity of counteradaptations
to overcome this type of constitutive chemical defence. Here we discuss that such counter-adaptations occur
at different time points, before and during feeding as well as during digestion, and at several levels such as the insects’
feeding behaviour, physiology and metabolism. Insect adaptations frequently circumvent or counteract the activity of
the plant β-glucosidases, bioactivating enzymes that are a key element in the plant’s two-component chemical defence.
These adaptations include host plant choice, non-disruptive feeding guilds and various physiological adaptations as
well as metabolic enzymatic strategies of the insect’s digestive system. Furthermore, insect adaptations often act in
combination, may exist in both generalists and specialists, and can act on different classes of defence compounds. We
discuss how generalist and specialist insects appear to differ in their ability to use these different types of adaptations:
in generalists, adaptations are often inducible, whereas in specialists they are often constitutive. Future studies are
suggested to investigate in detail how insect adaptations act in combination to overcome plant chemical defences and
to allow ecologically relevant conclusions.