Orange/lemon-scented beetles: opposite enantiomers of limonene as major constituents in the defensive secretion of related carabids.

The major constituent in the pygidial gland defensive fluid of the carabid beetle Ardistomis schaumii is (R)-(+)-limonene, whereas that of Semiardistomis puncticollis is (S)-(-)-limonene. This was an unanticipated result, since it is not very common to find the opposite enantiomers of the same compound among the secondary metabolites of related species. Moreover, the glandular liquid of A. schaumii contains 1,8-cineole, and that of S. puncticollis has beta-pinene, beta-phellandrene, sabinene, and p-cymene. Of about 500 carabid species that have been chemically investigated, this is the first report of the presence of such complex mixtures of monoterpenes in their defensive secretions.