Dabbing and shooting of benzo- and naphthoquinone secretions: defensive strategies of bark-inhabiting aleocharine (Col.: Staphylinidae) and tenebrionid (Col.: Tenebrionidae) beetle larvae

The abdominal glands of three bark-inhabiting larvae of genera Bolitochara, Leptusa (Staphylinidae), and Hypophloeus (Tenebrionidae) were studied chemically and morphologically. Behavior of the larvae indicated that secretion is emitted only after severe disturbance of the larvae. These mechanical contacts may also occur incidentally with coinhabiting nonpredatory arthropods when the beetle larvae move within small interstices under bark. Depending on the species, the secretions contained 1,4-benzoquinone derivatives and three 6-alkyl-naphthoquinones dissolved within various alkanes, alkenes, ethyl-, isopropyl-, and isoamylesters. More erratically distributed gland constituents also detected were acetophenone, benzyl propionate, and methyl hydroxybenzoate. In the laboratory, synthetic quinone-containing solutions simulating those found in Leptusa and Bolitochara larvae acted as strong topical irritants and caused further damage to last-stage Calliphora vomitoria larvae if hydrocarbons or esters were used as solvents. The natural secretions of Hypophloeus versipellis elicited considerable mortality in two subcortical sciarid larvae cooccurring with tenebrionid larvae. Bioassay and secretion chemistry of the Staphylinidae/Tenebrionidae larval secretions indicated that they are typical defensive secretions that act topically. Morphological data characterized Bolitocharini larvae as possessing protuberant abdominal tergites supplied with an interiorly situated gland reservoir After mechanical contact, the defensive secretion is topically applied to other arthropods by dabbing this tergal protuberance on targets. The defensive gland of Hypophloeus versipellis is unusual in possessing a movable reservoir opening situated at the anterior border of tergite IX. By this peculiar gland morphology Hypophloeus larvae are capable of shooting secretion droplets frontally from their slightly depressed dorsal abdominal surface.