The present research represents the first description of a Vespidae species spermatozoon. In Agelaia vicina, the sperm head is composed of an acrosome and a nucleus. The acrosome consists of an acrosomal vesicle, oval shaped in cross sections, and a perforatorium, that projects into the anterior nuclear region. The nucleus is elongated and oval shaped in cross sections. The nucleus-flagellum transition region includes the centriolar adjunct, the nucleus base and the anterior portions of the axoneme and of the large mitochondrial derivative. The centriolar adjunct begins as a thin layer between the nucleus and the large mitochondrial derivative, while just below it acquires a lateral extension partially surrounding the large mitochondrial derivative. In its medial portion, it is triangular shaped, situated laterally to the axoneme and the large mitochondrial derivative, and it finishes in contact with the tip of the small mitochondrial derivative. The flagellum is composed of a 9 + 9 + 2 axoneme, two mitochondrial derivatives and two accessory bodies. The large mitochondrial derivative begins laterally to the nuclear base, and the small one below the centriolar adjunct. Only the large mitochondrial derivative presents a paracrystalline core, situated distally in relation to the axoneme. In the posterior flagellar region, the small mitochondrial derivative finishes first, followed by the large one and both accessory bodies. Although Vespidae belong to the superfamily Vespoidea, as Formicidae, the sperm ultrastructure of A. vicina is phylogenetically more closely related to Apoidea, and curiously very different from that observed for ants. This study supports the use of insect sperm morphology as a tool for phylogenetic analysis, especially in the Hymenoptera order.
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