The Significance of Secondary Metabolites for Interactions between Plants and Insects

Several levels of plant/insect-interactions on the basis of secondary compounds are described and illustrated with some examples. Plant secondary substances, originally accumulated for defense, are tolerated by adapted insects. Hence, plants have had to accumulate new secondary constituents during evolution for their protection. Adapted insects are able to use former plant repellents as attractants and, after collection or sequestration, as allelochemicals for several purposes. Some insects produce substances for defense that are structurally typical plant secondary compounds; in one case biosynthesis and uptake from the host of the same substances occurs. It is concluded that secondary metabolites are of great significance for the coexistence and biochemical development of plants and insects.