The value of defensive compounds as taxonomic characters in the classification of leaf beetles

Abstract

Defensive compounds of the Chrysomelini belong to various chemical classes. They are produced by very distinct biosynthetic pathways (e.g. isoxazolinone and nitropropanoic acid glucosides, a non-proteinous amino acid, cardenolides, polyoxygenated steroid glycosides) or sequestered from their host plant (pyrrolizidine alkaloid N-oxides). Their distribution does not completely match the current classification of Seeno and Wilcox (1982): Colaspidema atra is misplaced in the Chrysomelina; the Chrysolina spp. feeding on Hypericum form a homogenous taxon; the Chrysolinina and the Doryphorina are more closely related to each other than to the other subtribes. Defensive compounds are useful markers to disclose inconsistencies or weaknesses of available classifications but not necessarily to resolve the problems. The precise composition of cardenolide mixtures secreted by Chrysolinina spp. appear to be useful at the specific and infraspecific levels. At these levels, a better estimation of the taxonomic value of the secretions of leaf beetles must await further understanding of their function not only in defense, but also in the reproductive biology of the species.