Morphological changes in the male accessory glands and testes in Vespula vulgaris (Hymenoptera, Vespidae) during sexual maturation


The present study documents the pace of accessory gland and testes degeneration in the wasp Vespula vulgaris by means of a histological and metric approach, that has not been carried out for social wasps so far. To a certain extent, comparison is made with the degenerative processes of the mucus glands of the honeybee drone. In V. vulgaris, no generative tissue is left by the end of 9 d of age, and so degeneration is a fast process. The three different parts of the accessory glands (muscle layer, gland epithelium, and lumen) change with respect to age. The secretory cells of the epithelium reach their maximum activity during the first days of adult life, which results in a maximally filled gland lumen by 9 d. We also provide, for the first time, a histological study of testes degeneration for this species. At eclosion, well-defined cystic structures are still visible, whereas at 9 d, it is no longer possible to distinguish different cystic structures. The diameter of the testes decreases with respect to age. Social insects are well known for their amazing variety of exocrine glands, of which the secretions play a role in numerous aspects of colony organization (Billen & Morgan 1998). As is the case with honeybee drones, male wasps belong to the neglected gender in scientific studies, as is reflected in the few reports on their biology. However, males are also equipped with a number of exocrine glands with variable functions. Examples include sex pheromone production of the mandibular glands in a number of ant species (Hoïldobler & Maschwitz 1965), the territorial scent marks from the labial glands of bumblebee males to attract conspecific females for copu-lation (Kullenberg et al. 1970), and mating sign formation by the secretion of the mucus glands in honeybees (Koeniger 1986, 1991). The male reproductive system consists of paired testes that are responsible for the production of sperm, which is transferred to the females during copulation. Different from mammals, sperm synthesis in males of social hymenopteran species is not continuous, as the testes degenerate before the males become sexually mature. Testes degeneration is actually a remarkable feature in social hymenopterans, although it has never been documented at the histological level in wasps. Zander (1916) and Bishop (1920) mentioned that most of the sperm was found in the seminal vesicle of adult males in honeybees. But in ants, spermatogenesis stops shortly before or after …

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