Morphology of the female reproductive system and spermatheca in Notonecta maculata Fabricius, 1794 (Heteroptera: Notonectidae).

Notonecta maculata Fabricius, 1794 is an ecologically important freshwater predator of mosquito larvae and other aquatic invertebrates and has potential as a biological indicator of water quality. This study presents the first detailed microscopic anatomical and histological description of the female reproductive system of N. maculata, based on stereomicroscopy, light microscopy, and scanning electron microscopy. The female reproductive system consists of a pair of ovaries, each with seven telotrophic meroistic ovarioles, a spermatheca, and a genital chamber. Each ovariole is differentiated into a terminal filament, germarium, vitellarium, and pedicel. The germarium contains trophocytes, a trophic core, and young oocytes. The vitellarium includes approximately 14 oocytes at previtellogenic, vitellogenic, and choriogenic stages. During vitellogenesis, oocytes accumulate yolk granules, and the germinal vesicle shifts peripherally. In choriogenesis, the follicular epithelium flattens, and the chorion differentiates into endo-, exo-, and extrachorion layers. The pedicel is surrounded by a single-layered columnar epithelium and a thin muscle layer. The spermatheca comprises a reservoir and duct; the reservoir shows cuticular intima, glandular epithelium, and muscle layers, with mature sperm bundles in the lumen. These findings establish a baseline for future comparative, systematic, and reproductive biology studies.