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

The defensive secretions of Platyphora kollari beetles (Chrysomelidae) from Brazil contained one oleanene glycoside. This was identified as 3-0-beta - D-glucopyranosyl-(1 --> 4)-beta -D-glucuronopyranosyl-hederagenin (8), by a combination of 1D and 2D NMR methods (COSY, HMQC, HMBC) and SIMS. There we re also several amino acid derivatives, including the known non-protein ami no acid (Z)-2-amino-3,5-hexadienoic acid (1), the new dipeptide L-gamma -gl utamyl-2-amino-(3Z)-hexenoic acid (4), ethanolamine (7), and a mixture of p hosphatidylcholines. Compounds 1 and 7 have already been identified in seve ral leaf beetle taxa. Secretions of Leptinotarsa behrensi contained as majo r triterpene glycoside 3-O-beta -D-glucopyranosyl-(1 -->3)-beta -D-glucuron opyranosyl-oleanolic acid-28-O-beta -D-ghlcopyranoside (9), already isolate d from Platyphora opima. Although the host plants of these beetles were dev oid of these triterpene glycosides, beta -amyrin was shown to be present in three plants on which different species of triterpene-producing chrysomeli ds had been fed (Mikania micrantha, Ipomoea batatas and Convolvulus arvensi s). This suggests that these insects are able to use beta -amyrin from thei r food plant as a precursor to their oleanolic- and hydroxyoleanolic acid g lycosides. The distribution of toxins already identified in leaf beetles su ggests that amino acid derivatives could be a plesiomorphic character, cons idering their wide distribution, whereas the secretion of triterpene saponi ns, probably derived from ubiquitous plant triterpenes, could be an apomorp hic character shared by some Doryphorina. The secretion of cardenolides der ived from ubiquitous plant phytosterols would be another apomorphic charact er shared by other Doryphorina and Chrysolinina.