Sperm ultrastructure of three species of ladybirds (Coleoptera, Coccinellidae)

Abstract

The sperm of three coccinellid species belonging to the subfamilies Chilocorinae, Coccinellinae and Epilachninae were studied under light and transmission electron microscopy. The basic sperm structure of these ladybirds is common to that of the other previously studied species, especially the acrosome in front of the basal body and not the nucleus, with this latter running parallel with the flagellar components. In the Chilocorinae Platynaspis luteorubra (Platynaspidini) the sperm are of the type 1, as in Scymnini and Coccinellini, since they exhibited a cylindrical basal body with 9 + 0 and then 9 + 2, microtubules continuing further in an initial flagellar portion with the only axoneme devoid of accessory structures. The sperm exhibits a thin nucleus and mitochondrial derivatives. Such uniformity of sperm ultrastructure could be indicative of the occurrence of a close relationship between Platynaspidini and Scymnini as also proposed in the previous studies. Conversely, they differ markedly from the sperm of type 3 observed in the Chilocorini Exochomus quadripustulatus. In the Coccinellini Propylea quatuordecimpunctata the sperm are also of the type 1, but they can be easily differentiated from those of the other Coccinellinae studied so far, because of their very short acrosome without the posterior extension, the relatively thicker mitochondrial derivatives and the cylindrical nucleus. Epilachna clandestina sperm resemble those of E. quadripustulatus but differ from them, because they exhibit an elliptical nucleus which is anteriorly very thin, and the asymmetrical mitochondrial derivatives in the anterior extremity, with the greater one starting at the same level of the basal body, rather than at the nucleus level, as it occurs in E. quadripustulatus. Because of the differences observed in the sperm ultrastructure we propose a new sperm type (Type 4) for E. clandestina. This study on ladybird spermatozoon ultrastructure clearly indicates that the current classifications of coccinellids do not reflect the natural history of this well-known insect family.

Keywords: Coccinellidae sperm; Electron microscopy; Insect sperm ultrastructure.