Publisher Summary The structure of invertebrate septate junctions is not exactly the same in the different phyla. It is a peculiarity of the arthropods to possess two types of septate junctions, the distribution of which is dependent on the organs, not on the systematic position. Additionally, the scalariform junctions have only been observed in the arthropods, but are restricted to some (but not all) transporting epithelia. This chapter discusses the functions of septate and scalariform junctions. Among invertebrates, the arthropods have the best-known physiology and a careful examination of the repartition of the junctions and their position and association with other types of junctions or with certain cytoplasmic organelles may throw some light on their functions. A septate junction is constituted by elements of two adjacent cells and appears as a bicellular junction. However, different and very elaborate structures are set up at the line of contact among three cells (abutment of three bicellular junctions); these special features are designated as “tricellular junctions.” Scalariform junctions are characterized by a regular extracellular space of 20 nm wide, crossed by very fine tubular pillars giving in cross section a ladder-like appearance.

Septate and Scalariform Junctions in Arthropods

The MEKRE93 (Methoprene tolerant-Krüppel homolog 1-E93) pathway in the regulation of insect metamorphosis, and the homology of the pupal stage.

Insect Pheromone Research

SEM studies show that the differentiation among Stenus species with respect to the formation of the tarsi (wide bilobed vs. slender tarsomeres) takes place with a considerable augmentation of tarsal ventral setae in wide bilobed tarsomeres. The structural diversity of ventral tarsal setae among and within species is discussed with respect to 1) their different roles as mechanosensilla and tenent setae, respectively, and 2) the different selection pressures in terms of adhesive requirements along the longitudinal tarsus axis. The tarsi are provided with four groups of tarsal mechanosensilla, comprising hair and bristle sensilla, campaniform sensilla, and scolopidia. The tarsus wall is supported by an epidermis, which forms three different types of glands pouring their secretion via different exit paths onto the outer cuticle. The organization and ultrastructure of each of these glands is described. Only one (unicellular) gland is directly associated with the ventral tenent setae and is thus considered to form the main part of the adhesive secretion. The beetles appear to release the tarsal secretion through mediation of the tenent setae, which contains a lipid and a proteinaceous fraction. I propose that the secretion is discharged to the outside via a system of very fine pore canals in the wall of the setal shaft. Gas chromatography and infrared spectroscopy revealed that the lipid fraction of the secretion is a mixture of unsaturated fatty acid glycerides and aliphatic hydrocarbons whose spectra are similar to those of extractions of the superficial lipid coating of the body surface. J. Morphol. 255:24–43, 2003. © 2002 Wiley-Liss, Inc.

Structure of the tarsi in some Stenus species (Coleoptera, Staphylinidae): external morphology, ultrastructure, and tarsal secretion.

A literature survey is provided summarizing the available information on exocrine epidermal glands that produce adhesive secretions in insects. The focus is on both the ultrastructure of the gland cells and the identity and function of the chemical secretion produced by them. Insects employ adhesives for various functions such as tarsal attachment during locomotion, resisting external detachment forces, mating, phoresy and parasitism, egg anchorage, retreat building, self-grooming, prey capture, and active and passive defence. The available studies on the ultrastructure and the secretion of adhesive insect glands cover a broad spectrum of developmental stages and higher taxa, i.e., the Elliplura, the Ephemeroptera, the Polyneoptera, the Acercaria, the Coleoptera, the Amphiesmenoptera, the Hymenoptera, and the Diptera (Table 8.1). Based on this diversity of biological contexts and systematic groups, adhesive structures are found at various tagmata of the body, mainly at the head, the abdomen, and the legs, but also within the thorax in the form of the metapleural glands of ants. Class 1 epidermal cells are the predominant glandular cell type among the adhesive gland systems in insects. With respect to their ultrastructure, the adhesive class 1 cells show features (in terms of their provision with endoplasmic reticulum, Golgi system, free ribosomes, and secretion vesicles and granules) that are either indicative of predominant non-proteinaceous (lipid) or protein secretion. In class 1 cells that are employed in locomotion (i.e., reversible tarsal adhesion to natural substrates such as plant surfaces), lipoidal secretion seems to prevail (although these secretions often appear to be complex mixtures of lipids with proteins and carbohydrates), whereas in the contexts of more permanent body or egg anchorage and of retreat building, protein-based secretion dominates. Oenocyte-like class 2 adhesive gland cells have hitherto only been found in the defence systems of Aphidoidea and Tingidae (both Hemiptera). Adhesive class 3 glands are almost always bicellular, consisting of a terminal secretorily active cell and an adjacent canal cell that surrounds the cuticular conducting duct.

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

Role of a temporary ciliary structure in the morphogenesis of insect glands: An electron microscope study of the tergal glands of male Blattella germanica L. (Dictyoptera, Blattellidae)

L. Sreng

Papers

Role of a temporary ciliary structure in the morphogenesis of insect glands: An electron microscope study of the tergal glands of male Blattella germanica L. (Dictyoptera, Blattellidae)