The ultrastructure of glands and the production and function of the secretion in the adhesive capture apparatus ofStenusspecies (Coleoptera: Staphylinidae)

Abstract

The elongated labium of rove beetles of the genus Stenus forms an adhesive capture apparatus that enables them to catch fast-fleeing prey such as Collembola. The adhesion is mediated by a secretion produced in glands within the head capsule and secreted onto the paraglossae. Transmission electron microscopy has revealed that these "adhesive glands" are composed of discrete gland units, each consisting of three cells. Two cells are secretorily active, each producing a different secretion, one proteinaceous and the other lipoid. Consequently, a two-phase secretion can be found on the surface of the paraglossae. Adhesive glands and normal epidermal glands share several characteristics and are therefore considered to be homologous. Structural differences can be functionally interpreted. The long glandular ductules themselves serve as a reservoir for the secretion before it is expressed prior to the predatory strike. Van der Waals forces and both the surface tension and the viscosity of the adhesive secretion are discussed as possible mechanisms of adhesion. The adhesion resulting from the viscosity of the fluid is the strongest and exceeds the force theoretically required for catching collemboles.