Distribution of autogenous and host-derived chemical defenses inOreina leaf beetles (Coleoptera: Chrysomelidae)

Abstract

The pronotal and elytral defensive secretions of 10Oreina species were analyzed. Species feeding on Apiaceae, i.e.,O. frigida andO. viridis, or on Cardueae (Asteraceae), i.e.,O. bidentata, O. coerulea, andO. virgulata, produce species-specific complex mixtures of autogenous cardenolides.O. melanocephala, which feeds onDoronicum clusii (Senecioneae, Asteraceae), devoid of pyrrolizidine alkaloids (PAs) in its leaves, secretes, at best, traces of cardenolides. Sequestration of host-plant PAs was observed in all the other species when feeding on Senecioneae containing these alkaloids in their leaves.O. cacaliae is the only species that secretes host-derived PA N-oxides and no autogenous cardenolides. Differences were observed in the secretions of specimens collected in various localities, because of local differences in the vegetation. The other species, such asO. elongata, O. intricata, andO. speciosissima, have a mixed defensive strategy and are able both to synthesize de novo cardenolides and to sequester plant PA N-oxides. This allows a great flexibility in defense, especially inO. elongata andO. speciosissima, which feed on both PA and non-PA plants. Populations of these species were found exclusively producing cardenolides, or exclusively sequestering PA N-oxides, or still doing both, depending on the local availability of food-plants. Differences were observed between species in their ability to sequester different plant PA N-oxides and to transform them. Therefore sympatric species demonstrate differences in the composition of their host-derived secretions, also resulting from differences in host-plant preference. Finally, within-population individual differences were observed because of local plant heterogeneity in PAs. To some extent these intrapopulation variations in chemical defense are tempered by mixing diet and by the long-term storage of PA N-oxides in the insect body that are used to refill the defensive glands.

Chemical defense in Platyphora kollari Baly and Leptinotarsa behrensi Harold (Coleoptera: Chrysomelidae). Hypotheses on the origin and evolution of leaf beetles toxins

“…This paper constitutes the first report of the presence of oleanene glycosides in the defensive secretion of a chrysomelid beetle in the genus Leptinotarsa which, until now, was characterized by the production of amino acid derivatives (Pasteels et al 1988(Pasteels et al , 1994Timmermans et al 1992). Preliminary investigation by mass spectrometry of the secretion of yet another Leptinotarsa species, L. calceata, collected on an Asteraceae species near Tatletela (Mexico), demonstrated without ambiguity the presence of still unidentified triterpene glycosides (unpublished data).…”

“…In the family Chrysomelidae (leaf beetles), the presence of defensive glands located on the elytra and on the pronotum has been reported for adults of four of the nineteen subfamilies (Pasteels et al 1988(Pasteels et al , 1994. Previous work has shown that adults of the subtribe Chrysomelina (subfamily Chrysomelinae, tribe Chrysomelini) produce isoxazolinone glucosides bearing one or several 3-nitropropanoate moieties (Pasteels et al 1982).…”

“…Previous work has shown that adults of the subtribe Chrysomelina (subfamily Chrysomelinae, tribe Chrysomelini) produce isoxazolinone glucosides bearing one or several 3-nitropropanoate moieties (Pasteels et al 1982). In contrast, the subtribe Chrysolinina is generally characterized by the production of cardenolides (Pasteels & Daloze 1977;Daloze & Pasteels 1979), although five Chrysolina species feeding exclusively on Hypericum perforatum secrete polyoxygenated steroid glycosides instead (Daloze et al 1985;Randoux et al 1990; Daloze et al 1991), whereas several Oreina species sequester pyrrolizidine alkaloids from their Asteraceae food plants, either alone (in Oreina cacaliae) or in admixture with cardenolides (see Pasteels et al 1995;Hartmann et al 1997, and references therein). In contrast, in the subtribe Doryphorina sensu Daccordi (Seeno & Wilcox 1982), the genus Leptinotarsa is characterised by defensive secretions containing amino acid derivatives, whereas two Calligrapha species produce cardenolides (Daloze et al 1986;Timmermans et al 1992).…”

Pyrrolizidine alkaloids and pentacyclic triterpene saponins in the defensive secretions of Platyphora leaf beetles

“…For defense, they secrete secondary metabolites stored in elytral and pronotal exocrine glands (review in Pasteels et al 1988Pasteels et al , 1994. Although some of these compounds are wellknown plant metabolites, they are usually not present in their food plants and are synthesized by the insects, e.g.…”

“…Only few Oreina species, specialized on Senecioneae (Asteraceae) are known to sequester toxic pyrrolizidine alkaloids (PAs) from plants (Hartmann et al 1997;Pasteels et al 1995Pasteels et al , 1996and ref. therein).…”