Sperm ultrastructure of the European hornet Vespa crabro (Linnaeus, 1758) (Hymenoptera: Vespidae)

This study represents the first sperm description of a Vespinae species (Vespa crabro). The acrosome consists of an acrosomal vesicle and a perforatorium. The nucleus has compact chromatin and shows lenticular structures on the nuclear envelope. These structures, which have never been observed in a hymenopteran sperm, could be clusters of nuclear pores. The centriolar adjunct has an asymmetric pattern and shows a structured periphery. The centriole consists of 9 accessory microtubules and 9 doublet microtubules devoid of arms and spokes. The axoneme has a 9 + 9 + 2 microtubule pattern and the accessory microtubules have 16 protofilaments. The mitochondrial derivatives differ in length and diameter. The larger one is adjacent to the nuclear base, while the smaller one begins below the centriolar adjunct. They possess three distinct areas and a large paracrystalline region, which occurs only in the large one. The large mitochondrial derivative ends first, followed by the small one. The axoneme gradually disorganizes: first the central microtubules disappear, then the doublets, which show opened B-tubules, and finally the accessory microtubules. The sperm morphology of V. crabro is very similar to that of the polistine wasp, Agelaia vicina. This can indicate that, in Vespidae, sperm morphology is maintained without important variations among subfamilies and/or that this similarity indicates close phylogenetic relationship between these two subfamilies. Although Vespidae phylogenetically related to Formicidae, these data suggest that the former more closely related to Apoidea than to Formicidae.