Abstract: 【Aim】 Sperm ultrastructure exhibits great variations among insect groups and has important value for species recognition and phylogenetic analysis of  insects. However， spermatogenesis and sperm ultrastructure in Mecoptera have not been sufficiently studied. 【Methods】 The spermatogenesis and sperm ultrastructure of the scorpionfly Panorpa liui Hua were investigated by light and transmission electron microscopy.【Results】 Each spermatogonium undergoes seven successive divisions in a cyst of P. liui， resulting in 128 spermatids that synchronously transform later into spermatozoa. These mature spermatozoa form a sperm bundle， but the number of spermatozoa is normally less than 128 in a bundle. During spermiogenesis， the sperm acrosome is generated by the pro-acrosomal granule material， which originates from Golgi apparatus in the cytoplasm of spermatids. The elongated nucleus is transformed through nucleus elongation and streamlining with a simultaneous condensation of chromatin. The mitochondrial derivatives are transformed from the conspicuous nebenkern， which is formed from mitochondrial aggregation and fusion in the cytoplasm of spermatids. The mature spermatozoon consists of a short head， a neck region， and a long flagellum. The head is composed of the apical bilayered acrosome and the elongated nucleus with two lateral grooves. The neck region mainly consists of the centriole and the electron-dense， sheath-shaped centriolar adjunct. The flagellum is helical and mainly comprises a 9+2 axoneme， two mitochondrial derivatives of different sizes， and two accessory bodies.  【Conclusion】 The phenomenon that the number of sperm in a sperm bundle of P. liui is usually slightly less than 128 is likely associated with the complex process of spermiogenesis and phagocytosis of cells. The mitochondrial derivatives differ distinctly among different groups and likely provide valuable characters for phylogenetic analysis of Mecoptera.

Key words: Mecoptera, Panorpidae, spermiogenesis, mitochondrial derivative, centriolar adjunct, accessory body