8: Insects That Use Plant Defenses for Their Own Protection Check Access

Numerous insects have adapted to feed on plants with chemical defenses and use the defensive compounds for their own protection. Many monophagous and oligophagous insects, particularly moths and butterflies, specific beetles, and some aphid species are connected with host plants that feature distinct toxic compounds. This chapter illustrates the diversity of defensive plant secondary metabolites and mechanisms that allow insects to cope with toxins, and even store them in their systems. Many insects, including monarch butterflies (Danaus plexippus), feed on milkweeds (Asclepias) and ingest their cardiac glycosides (cardenolides). Characteristic structures of cardenolides are shown, with examples of typical plants and their specialized insects. The caterpillars of Heliconius butterflies ingest cyanogenic glycosides by feeding on passion vines (Passiflora), which contain some unusual cyanogenic glycosides. Defensive alkaloids, like aristolochic acid, are the plant defenses that the larvae of pipevine swallowtail butterflies obtain from pipevine plants (Aristolochia). Widespread weedy plants of the genus Senecio contain chemical defenses in the form of hepatotoxic pyrrolizidine alkaloids. Yet the caterpillars of the cinnabar moth (Tyria jacobaeae) and other insects have adapted to them as host plants. Structures of the alkaloids and mechanisms of their action are shown.