Toxins in chrysomelid beetles: Possible evolutionary sequence from de novo synthesis to derivation from food-plant chemicals

In the Chrysomelinae, it appears that de novo synthesis of chemicals for defense is the primitive state, and the sequestration of plant chemicals for defense the derived state. The derived state evolved through both the morphological and biochemical preadaptiveness of the homologous defensive glands. In the adults, we discuss one unique case of sequestration in exocrine defensive glands of host-plant pyrrolizidine alkaloids by <i>Oreina cacaliae</i>. However, hypericin is not sequestered either in the glands or elsewhere in the body of <i>Chrysolina</i> spp. feeding on <i>Hypericum</i>, which contradicts an earlier claim. In the larvae, we examine in more detail how the phenolglucoside salicin can be used as the precursor of the salicylaldehyde present in the defensive secretion of <i>Phratora vitellinae</i> and <i>Chrysomela</i> spp. with minimal changes in the biochemical mechanisms involved in the biosynthesis of iridoid monoterpenes in related species.