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.

Structural and tribometric characterization of biomimetically inspired synthetic "insect adhesives"

“…For insect adhesive emulsions, few data are available on the droplet sizes of the inner phase. They are in the range between 100 nanometers and several micrometers [14,20–21] and thus fit well in the range of almost all of our second generation emulsions (cf. Supporting Information File 1, Table S1).…”

“…Adhesive secretions may form both oil-in-water (o/w) [20–22] or water-in-oil (w/o) emulsions [14,23]. Possible functional advantages lie in (i) their increased flexibility towards substrates of different surface energy and polarity, (ii) their possible non-Newtonian viscosity shifts implying adjustable viscosities [24–25] and (iii) the formation of lipoid shields that prevent the aqueous fraction of an adhesive from desiccation and its sticking to the walls of the outlet ductule [4,20,26]. Moreover, within the lipoid fraction itself, both the specific constitution and the mixing ratio of the various hydrocarbon molecules might also largely influence their adhesive performance possibly via viscosity and surface tension effects, molecular re-orientations and the intermolecular attraction of the hydrocarbon chains in the thin liquid films [27].…”

Structure of the tarsi in some stenus species (coleoptera, staphylinidae): External morphology, ultrastructure, and tarsal secretion

“…2 in Delachambre, 1973). They also share many characteristics with the epidermal gland units found in the Stenus head, although the SER and fat globules are well developed, indicating the production of a lipid secretion in the intercalary cells of these units (Kölsch, 2000). Similar gland units have also been described in other insects and are considered to be involved in the formation of the cement layer after ecdysis (e.g., Wigglesworth, 1948;Lai-Fook, 1970;Kendall, 1972;Chapman, 1998).…”

Adhesive Exocrine Glands in Insects: Morphology, Ultrastructure, and Adhesive Secretion

“…In several cases, insects merely use their fore tarsi to clasp their prey. Its general structure and function have been elucidated in several studies (Schmitz, 1943;Weinreich, 1968;Bauer and Pfeiffer, 1991;Betz, 1996Betz, , 1998aKölsch and Betz, 1998;Kölsch, 2000;reviewed in Betz and Kölsch, 2004). In addition, several cases are known in carabid and staphylinid beetles in which other body structures have been modifi ed into highly advanced prey capture organs.…”