In the present study, spermatozoa of the Prorops nasuta (Hymenoptera: Bethylidae) parasitoid were described morphologically. This is the first publication to describe a species belonging to the superfamily Chrysidoidea. Light and transmission electron microscopy were used. The spermatozoa of P. nasuta are linear, with a mean length of 665microm. The acrosome is composed of an acrosomal vesicle and a perforatorium. The nucleus measures approximately 17microm in length and is circular at its cross-section; however, its anterior extremity is oval. The chromatin is electron-dense and compact, although there are clear areas in the posterior peripheral regions. In the nucleus-flagellum transition region, the cross-section of the centriole adjunct is oval, with a pleated border and an E-PTA-positive peripheral region. The axoneme shows a 9+9+2 microtubule arrangement. The microtubules are E-PTA positive and, at the posterior extremity, the accessories are the last to terminate. The diameters and shapes of the two mitochondrial derivatives are almost identical. One begins beside the nuclear base and the other after the centriole adjunct. Posteriorly, they terminate together, immediately before the axoneme. Both have mitochondrial cristae and a region of paracrystalline material; however, the format and arrangement of this material differs from those of all other species previously studied. The paracrystalline material is more strongly E-PTA positive than the cristae region. Accessories bodies are electron-dense and located between the mitochondrial derivatives and the axoneme. In general, P. nasuta spermatozoa are similar to those of the majority of Hymenoptera; however, they have various exclusive characteristics that may be useful for studying the phylogeny and taxonomy of the superfamily Chrysidoidea and of Hymenoptera in general.
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