The epithelium of the digestive tract serves as the boundary between the organism's internal and external environments. Specifically, the midgut epithelium is essential for digestion, nutrient absorption, and protection from xenobiotics and pathogens. Thus, understanding the structure and differentiation of midgut cells is important for developing plant protection strategies. Stem cells play a key role in intestinal regeneration and can be targets for xenobiotics in food. The spotted-wing drosophila (Drosophila suzukii) and the Colorado potato beetle (Leptinotarsa decemlineata) threaten fruit and crop production. Since the intestinal stem cells of these species were previously unstudied, we used light and transmission electron microscopy to analyze the midgut of adults and larvae in this thesis. In the spotted-wing drosophila, the midgut epithelium consists of absorptive enterocytes, enteroendocrine cells, and stem cells at the base. Stem cells are smaller than specialized epithelial cells, with large spherical nuclei and few organelles. In L2-stage larvae, undifferentiated AMP (adult midgut progenitors) cells are scattered, while in L3-stage larvae, they form small clusters of central spherical cells surrounded by flattened peripheral cells. In adult spotted-wing drosophila, stem cells are found individually or rarely in pairs. Enterocytes and stem cells show morphological differences along the anterior – posterior axis of the midgut. The shape of stem cells becomes more flattened in the posterior section, similar in both L3 larvae and adults. Stem cells vary in ultrastructure and number in different midgut sections. The L3 Colorado potato beetle larvae midgut consists of a single-layered columnar epithelium with stem cell clusters at the base. Unlike the spotted-wing drosophila, the structure and morphology of stem cells in the Colorado potato beetle larvae do not change along the anterior – posterior axis.
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