Light and electron microscopic studies on the development of the ovaries of Culex pipiens quinquefasciatus (Say) (Diptera: Culicidae)

摘要

Christopher's stages of ovarian development are redefined in Culex pipiens quinquefasciatus to provide a more useful description of mosquito physiology. During this ovarian development, seven growing stages of the oocyte are observed in the adult stage. Two distinct periods of egg follicle growth, the previtellogenesis and vitellogenesis, are seen first. The gradual increase in the oocyte size during these phases is attributed to yolk deposition. During vitellogenesis, the oocyte and nurse cell nucleus are similar in size (stage I). Then, the oocyte enlarges and occupies one third of the egg follicle, while the nurse cell (NC) occupies the remaining two thirds. At this phase, the yolk granules (stage III) enlarge, occupying about half of the egg follicle, while the NC contain the other half (stage IV). An increase and accumulation of yolk granules leads to the filling of about three fourths of the egg bulk and makes the oocyte nucleus hardly visible during stage V. The oocyte undergoes a remarkable growth, occupying nine tenth of the length of the follicle in stage VI. Stage VII corresponds to a mature cigar-shaped egg and contains two kinds of yolk globules: a large one and a small one. The oocyte and the NC at all stages are surrounded by a single layer of epithelial cells which increase in number and form the vitelline membrane and the chorion. The mitochondria in the NC, oocyte, and follicular epithelium appear in light microscopy as granules of different sizes. The Golgi apparatus appears in different sizes and shapes, since in the early stages of development, it is restricted to the perinuclear zone. When the development proceeds, it enlarges in size, spreads over the whole cytoplasm, and participates in the formation of the yolk.