GERMARIAL STRUCTURE AND OOGENESIS IN BREVICORYNE-BRASSICAE (L) (HEMIPTERA, APHIDIDAE)

The structure and function of the components of the telotrophic ovariole of Brevicoryne brassicae are described, with the aid of transmission electron microscopy. It was of interest to determine the presence of trophic cords in this aphid species. Oöcytes are extruded posteriorly from the germarium and become surrounded by follicle cells which occupy a small region at the base of the germarium. The follicle cells do not contribute yolk to the oocytes and whilst lipid yolk is present within oöcytes, they lack protein yolk. The trophocytes and oöcytes are connected by a nutritive cord which contains many microtubules. Export of rRNA, mitochondria, and possibly lipid from the trophocytes to the oöcytes takes place. Oöcytes emerge from the surrounding layer of follicle cells shortly before nuclear division, and follicle cells do not accompany the embryo down the ovariole. The germarial structure resembles that of other aphids but differs from other hemipterans, which may be a result of the different reproductive strategy of parthenogenetic viviparous aphids. This study confirms the presence in this species of trophic cords within the ovarioles and may indicate this to be a widespread phenomenon in the Aphididae. © 1979.