Defensive secretion of the tenebrionid beetle, Blaps mucronata: physical and chemical determinants of effectiveness.

The primary components of the defensive secretions of Blaps mucronata (Tenebrionidae) are two quinones (methyl-p-benzoquinone and ethyl-p-benzoquinone) and the hydrocarbon 1-n-tridecene. The hydrocarbon is shown, by comparison with longer- and shorter-chain n-alkanes and 1-n-alkenes, to be optimally suited as carrier of the quinones, and as a surfactant that promotes spread of secretion over the beetle's body following discharge from the gland openings at the abdominal tip. As shown from repellency tests with ants (Monomorium pharaonis) and topical irritancy tests with cockroaches (Periplaneta americana), the anti-insectan potency of the secretion derives as much from the hydrocarbon as from the quinones.