Studies on the cardenolide sequestration in African milkweed butterflies (Danaidae)

Butterflies of the Danaidae family are considered to be toxic or distasteful due to the presence of cardiac glycosides sequestered from their larval food plants. Alcoholic extracts of specimens of Danaus chrysippus aegyptius and Amauris ochlea ochlea from southern Africa (Namibia, S.-Africa, Mozambique) were analyzed by thin-layer chromatography for these cardenolides. But only 4 of 75 specimens of D. chrysippus aegyptius contained trace amounts, all others including 13 specimens of A. ochlea ochlea were negative. Genetic analysis of the ouabain binding site of the Na(+), K(+)-ATPase revealed that both species do not present an amino acid replacement at the position 122, which otherwise makes the enzyme insensitive to cardenolides suggesting that other strategies of toxin tolerance must have been developed.