Cardenolide-Mediated Interactions between Plants and Herbivores

Density-Dependent Reduction and Induction of Milkweed Cardenolides by a Sucking Insect Herbivore

“…nerii is a bright yellow, aposematic aphid with a worldwide distribution that is restricted to feeding on plants in the Apocynaceae, especially the subfamily Asclepiadoideae (Patch, 1938;Ismail and Swailem, 1971;Price and Willson, 1979;Malcolm, 1991). This common aphid is found wherever milkweeds and oleander occur and it is known to sequester cardenolides, phloem-mobile host allelochemicals, for use as a chemical defense against natural enemy attack (Rothschild et al, 1970;Pasteels, 1978;Duffey, 1980;Malcolm, 1981Malcolm, , 1986Malcolm, , 1989Malcolm, , 1990Malcolm, , 1992Dixon, 1998).…”

“…This common aphid is found wherever milkweeds and oleander occur and it is known to sequester cardenolides, phloem-mobile host allelochemicals, for use as a chemical defense against natural enemy attack (Rothschild et al, 1970;Pasteels, 1978;Duffey, 1980;Malcolm, 1981Malcolm, , 1986Malcolm, , 1989Malcolm, , 1990Malcolm, , 1992Dixon, 1998). Cardenolides are potent, steroidal Na + /K + -ATPase inhibitors that are toxic to most consumers and are characteristic defenses of plants in the Apocynaceae (Malcolm, 1991). A. nerii feed in the cardenolide-rich internal phloem of host bicollateral vascular bundles (Botha et al, 1977;Malcolm, 1981), and these chemicals are present in A. nerii honeydew and body tissue (Bailey, 1974;Malcolm, 1990).…”

“…Our first objective was to determine whether A. nerii feeding influences cardenolide expression in two milkweed species that vary in constitutive chemical defense investment. Asclepias curassavica L. has high constitutive leaf cardenolide content, while A. incarnata L.,the swamp milkweed, has low constitutive leaf cardenolide content (Roeske et al, 1976;Malcolm, 1990Malcolm, , 1991. Our second objective was to determine whether cardenolide expression in these two host plants differentially impacts A. nerii colony size and biomass.…”

Chemical Defence and Toxins of Plants

“…66 The latex of several plants belonging to Asclepidaceae and Apocynaceae often contains very high concentrations of cardenolides. 66,67 The toxicity of cardenolides resides in their inhibitory activity against Na þ À K þ ATPase (or Na þ À K þ pump) involved in maintenance of ion concentrations in cells and neurotransmission, and thus cardenolides are generally toxic to animals, including insects.…”

“…66,67 The toxicity of cardenolides resides in their inhibitory activity against Na þ À K þ ATPase (or Na þ À K þ pump) involved in maintenance of ion concentrations in cells and neurotransmission, and thus cardenolides are generally toxic to animals, including insects. 66,68 Cardenolides bind specifically to membrane extruding part of Na þ À K þ ATPase; however, several insect species specialized in feeding on cardenolide-containing plants have developed cardenolide-insensitive Na þ À K þ ATPase, which commonly have single amino acid substitutions in target sites (cardenolide-binding sites). 69 4.08.1.2.1(vii)(c) Iridoid glycosides Iridoid glycosides are a group of compounds that have a structure related to iridodial (Figure 11).…”