FUNCTION, CHEMISTRY AND EVOLUTION OF THE ABDOMINAL GLAND SECRETION OF THE ROVE BEETLE GENUS BLEDIUS (COLEOPTERA: STAPHYLINIDAE: OXYTELINAE)

Johannes L. M. STEIDLE
Institut für Zoologie, Angewandte Zoologie/Ökologie der Tiere, Freie Universität Berlin, Haderslebenerstr. 9,12163 Berlin, Germany

The species of the rove beetle genus Bledius (Oxytelinae) are provided with a pair of integumental glands located in the iast abdominal segments. These glands are present in the whole subfamily Oxytelinae.

The biological function of these glands is still an unresolved question [1]. Therefore the function was studied by observing the behaviour of Bledius furcatus OLIV. and B. spectabilis KRAATZ when they encountered natural enemies, namely the ant Cataglyphis bicolor F. and the sandpiper species Calidris alpine L., respectively. In both cases, the survival probability of the beetles was increased by the presence of the secretion. This suggests that the abdominal glands of the genus Bledius and probably of the whole subfamily Oxytelinae is used for defensive purposes.

Bledius species. In all species the secretion contained the solid toxin p-toluquinone and its precursor p-toluhydroquinone dissolved in various solvents. In B. furcatus, B. tricornis and B. dissimilis these solvents were mainly alkenes and lactones, especially 1-undecene and y-dodecalactone (secretion type 1). This secretion type was already known fromr B. spectabilis and B. mandibularis [2]. In addition to alkenes and lactones the secretion of B. opacus and B. subtenaneus contained decanoic acid and 3-methyi-2butenoic acid (secretion type 2). In B. arenarius the quinones were dissolved in octanoic acid and octyloctanoate, exclusively (secretion type 3).

In B. arenarrus and B. opacus the amount of p-toluquinone in the secretion was lower in comparison to the other species. Topical application experiments with ground beetles of the genus Dyschirius, a natural predator of B. arenarius, revealed that the minute amount of quinone in B. arenarius did not result in a lower irritation effrciency of the secretion. This is probably due to the large amount of octanoic acid in the secretion. Octanoic acid has a distinct irritation effect on arthropods [3]. It may act simultaneously as solvent and irritant, thereby replacing the p-toluquinone and reducing the necessary quantity of quinone.

The secretion's chemistry of the Bledius species mentioned above and of other Oxytelinae species [4] was compared to the phylogeny of the whole subfamily [1, 4]. The abdominal gland secretion probably evolved within the subfamily Oxytelinae from isopropyl- and methyl-propylesters in primitive Oxytelinae species via alkenes and lactones in many derived species (including some Bledius species) to acid and esters in the genus Bledius.

Literature
  1. Herman, L.H.: Bull. Am. Mus. Nat. Hist. 184, 1-368 (1986).
  2. Wheeler, J.W., Happ, G.M., Araujo, J., Pasteels, J.M.: Tetrahedron Lett. 46, 46354638 (1972)
  3. Eisner, T., Meinwald, J., Monro, A., Ghent, R.: J. Insect Physiol. 6, 272-298 (1961)
  4. Dettner, K.: Biochem. Syst. Ecol. 21, 757-765 (1993)
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