Chemical defense against predation in butterflies and moths has been studied since nineteenth century. A classical example is that of the larvae of the monarch butterfly Danaus plexippus, which feed on leaves of Asclepias curassavica (Asclepiadaceae), sequestering cardenolides. The adults are protected against predation by birds. Several other substances may be involved in chemical defense, such as iridoid glycosides, cyanogenic glycosides, glucosinolates, pyrrolizidine and tropane alkaloids, aristolochic acids, glycosidase inhibitors and pyrazines. The acquisition of these substances by lepidopterans can be due to sequestration from larval or adult host plants or de novo biosynthesis. Many Lepidoptera are known to be unpalatable, including the butterflies Troidini (Papilionidae), Pierinae (Pieridae), Eurytelinae, Melitaeinae, Danainae, Ithomiinae, Heliconiinae and Acraeinae (Nymphalidae), and Arctiidae moths, but knowledge of the chemical substances responsible for property is often scarce. This review discusses mainly three topics: field and laboratory observations on rejection of butterflies and moths by predators, correlation between unpalatability and chemicals found in these insects, and bioassays that test the activity of these chemicals against predators. Perspectives and future directions are suggested for this subject.
pyrrolizidine alkaloids; tropane alkaloids; aristolochic acids; cardenolides; cyanogenic glycosides; glucosinolates
