Testis development and spermatogenesis in drones of the honey bee, Apis mellifera L.

Like Apis mellifera queens and different from all other bees, drones also have an exaggerated gonad phenotype, with over 150 serial units in each gonad. Yet, compared with the ovaries of the female castes, little is known about the development of the honey bee testis. Here we present a histological atlas on postembryonic testis development and spermatogenesis. Already in the first instar larvae, the testioles composing each testis can be distinguished. The testioles then grow along their apical-basal axis by mitotic divisions of the spermatogonia, which eventually form germ cell clusters. Meiosis starts when brood cells are capped, and it ends with the appearance of spermatids in red-eyed pupae. Subsequently, spermiogenesis takes place, and all spermatozoa are formed before adult emergence. We also present the first data on juvenile hormone levels in drone larvae. With this, we provide a database for future research on gonad development in honey bee drones.