The sperm structure and the spermiogenesis of the drugstore beetle Stegobium paniceum (L.) (Coleoptera-Ptinidae-Anobinae)

We describe in this paper the morphology of the male reproductive system, the spermiogenesis and the sperm ultrastructure of the drugstore beetle S. paniceum (L) (Coleoptera, Ptinidae). The male reproductive apparatus has a pair of long testes with six follicles, filled with cysts, each containing 128 germ cells. The sperm is about 480 μm long and is endowed of an apical spiral cylindrical acrosome, 1.7 μm long. The nucleus, 25 μm long, is also cylindrical at maturity. During spermiogenesis the nuclear envelope gives rise to two ovoid membranous structures flanking the nucleus for its whole length. The centriole adjunct material is configurated as concentric electron-dense rings. The flagellar components have a helical array; the axoneme has the typical 9 + 9+2 pattern for most of its length, but in the posterior flagellar region it modifies greatly its ultrastructure and is embedded in an electron-dense material. The two accessory bodies have a crescent-moon shape in the mature sperm, but at the beginning of spermiogenesis they are small structures lateral to the axoneme, later assuming a crescent-moon structure. A flattened cistern located between the axoneme and the plasma membrane is present in the early spermatids, but soon it fuses with the plasma membrane. Two symmetrical, largely crystallized mitochondrial derivatives are present for most of the flagellar length. S. paniceum and Lasioderma serricorne share several sperm structures. Ultrastructural results and molecular data confirm a close relationship between these two species and support their positioning within Ptinidae.