Structure of ovarioles in adult queens and workers of the common wasp, Vespula germanica (Hymenoptera: Vespidae)

The ovaries of the common wasp, Vespula germanica are polytrophic-meroistic and consist of 2-3 (workers) or 7 (queens) ovarioles. The ovarioles are differentiated into three regions: a terminal filament, a germarium, and a vitellarium. The germaria of both castes consist of two zones: an anterior zone of germ-cell cluster formation and a posterior one of germ-cell cluster differentiation. The vitellaria comprise 4-6 (workers) or 7-10 (queens) ovarian follicles (egg chambers). Each chamber consists of an oocyte and about 60 isodiametric nurse cells (trophocytes). The egg chambers have been arbitrarily classified into four developmental categories: early and late previtellogenic, vitellogenic, and choriogenic. The process of oogenesis in workers proceeds only up to the onset of the late previtellogenesis. Neither vitellogenic nor choriogenic egg chambers were observed in this caste. During early and late previtellogenesis the envelope of the oocyte nucleus proliferates and becomes highly folded. This process leads to the formation of characteristic organelles, termed accessory nuclei (AN). Although AN arise in the oocytes of both queens and workers, their number in the latter caste is always considerably lower. At the onset of the late previtellogenesis AN start to migrate towards the periphery of the oocyte where they reside till the end of oogenesis. The physiological state of the worker ovaries is discussed in the light of the presented results.