The microstructure and ultrastructure of the midgut epithelial cells in Ducetia japonica (Orthoptera: Tettigoniidae)

Tettigoniidae (katydids) represent an important group within Orthoptera and play significant ecological roles, such as serving as a key food source for insectivorous birds and contributing to nutrient cycling through their herbivorous feeding activities. However, detailed knowledge of their digestive tract structure, particularly in relation to physiological function, remains limited. The midgut is the primary site of nutrient digestion and absorption, and its cellular composition directly reflects the digestive strategies and adaptive characteristics of insects. In this study, the midgut morphology and epithelial organization of Ducetia japonica (Orthoptera: Tettigoniidae) were examined using light microscopy, laser scanning confocal microscopy, and transmission electron microscopy. Both light and confocal microscopy were employed to characterize overall tissue architecture, while transmission electron microscopy was used to investigate the ultrastructural features of the epithelial cells. The midgut consists of two bulbous gastric caeca and a tubular ventriculus, with the structure of the gastric caeca being similar to that of the ventriculus. Three types of epithelial cells were identified: columnar cells, endocrine cells, and regenerative cells. Columnar cells, which participate in digestion and absorption, exhibit prominent apocrine secretion, together with possible vesicle trafficking activity suggestive of exocytosis. Endocrine cells, located at the base of the epithelium, exhibit strong immunoreactivity against FMRFamide-related neuropeptides, suggesting their involvement in local paracrine regulation. Regenerative cells, also situated basally, function as intestinal stem cells capable of differentiating into new cells to replace aged or apoptotic cells. These findings provide a cellular and subcellular framework for understanding midgut function in D. japonica and contribute to comparative studies on digestive system evolution in Orthoptera.