Selective sequestration of cardenolide isomers by two species of Danaus butterflies (Lepidoptera: Nymphalidae: Danainae)

Several species of milkweed butterflies (Danaini) are known to sequester cardenolides from their milkweed host plants. In adults of Danaus plexippus and D. gilippus, jointly raised on Asclepias curassavica (Asclepiadaceae), two host-plant cardenolides (calotropin and calactin) were found in significantly different ratios: in D. plexippus and the plant, they occurred in roughly equal ratios, but in D. gilippus, calotropin had a 10-12 times lower concentration, suggesting a selective sequestration of calactin. The two Danaus species belong to different subgenera and the results may be relevant to a better understanding of the evolution of cardenolide sequestration in Danaini.