| Summary: | Abstract Background Chrysopa pallens is one of the most beneficial and effective natural predators, and is famous for its extensive distribution, wide prey spectrum, and excellent reproductive performance. This study examined the anatomy and fine structure of the C. pallens reproductive system and spermatogenesis. Results The male reproductive system of C. pallens comprises a pair of testes, a vas deferens, seminal vesicles, accessory glands, and short ejaculatory ducts. The testes were already mature on the day of emergence, but the accessory glands did not mature until 5 days post-emergence. In early spermatids, the flagellum had an axoneme on one side of the two mitochondrial derivatives. The nucleus was surrounded by parallel crystalline and paracrystalline materials. The spermatid envelope extends towards the paracrystalline material in a tail-shaped wing. In mature spermatids, the axoneme is located between the two accessory bodies and mitochondrial derivative sets. The parallel-crystalline and paracrystalline materials disappeared. In the testes, the wall of seminal cysts consists of a layer of epithelium, a muscular-connective sheath, and several vesicles of different sizes. The mature seminal cysts contained 128 spermatozoa. The accessory gland is composed of six parts: ventral papilla-like protuberance, anterior glandular lobe, lateral glandular lobe, seminal cyst, posterior kidney-shaped lobe, and posterior papilla-like protuberance. Muscle fibers and secretory granules are extensive. Conclusions This study provides information on the reproductive system of C. pallens and offers a resource for taxonomy and reproductive biology.
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