Light and Electron Microscopic Investigations of the Morphology of the Salivary Glands, Digestive Tract and Malpighian Tubules of the Aquatic Bug, <scp> <i>Nepa cinerea</i> </scp> Linnaeus, 1758 (Hemiptera: Nepidae)

The morphological characteristics of the internal systems in insects are considered important for understanding their biology. This research reports the morphological structures of the salivary glands, digestive tract, and Malpighian tubules of Nepa cinerea, an aquatic predatory insect, using light and scanning electron microscopies. The salivary gland is structurally complex and consists of a paired principal and accessory salivary glands and ducts. The former are small anterior and larger posterior lobes. The accessory salivary gland has both vesicular and tubular structures. The digestive system is divided into three main regions: foregut (pharynx, esophagus), midgut (ventriculus 1, 2, 3), and hindgut (ileum, rectum). The foregut is surrounded by a cuticular intima, a single layer of squamous epithelium with flattened nuclei, and a muscle layer. The midgut consists of a single layer of columnar epithelial cells characterized by chromatin-dense nuclei and a striated border. The epithelium is supported by the basal membrane. The muscles are external to the epithelium. Regenerative cells are located in the base of the epithelial folds. The hindgut is lined with an intima, a single layered epithelium and a muscle layer. Four Malpighian tubules connect at the junction between the midgut and hindgut. These structures are composed of cuboidal epithelial cells characterized by secretion granules, densely packed chromatin in the nuclei, and an apical striated brush border. These findings offer valuable baseline data for future morphological, physiological, and phylogenetic studies on aquatic Hemiptera and contribute to a deeper understanding of insect internal anatomy.