Yolk protein uptake in the oocyte of the Asian tiger mosquito Aedes albopictus (Skuse) (Diptera: Culicidae)

The formation and uptake of the yolk protein in the oocyte of the Asian Tiger, Aedes albopictus mosquito was investigated. Light and electron microscopy of the ovaries at early resting stage as well as the structural changes associated with yolk formation were described 16 h after blood meal. The deposition of the yolk protein in the oocyte was correlated with a 15-fold increase in 138-mu m pit-like depressions on the oocyte surface. These pits result by invagination of the oocyte cell membrane. They have a 20-mu m bristle coat on their convex cytoplasmic side and a layer of protein on their concave extraoocyte space. The pits, by pinching off from the cell membrane become bristle coat vesicles which carry the adsorbed protein into the oocyte. These vesicles lose the coat and then fuse to form small crystalline yolk droplets, which subsequently coalesce to form the large protein yolk bodies of the mature oocyte. Preliminary radioautographs and certain morphological features of the fat body, ovary, and midgut, suggest that the midgut is the principal site of the yolk protein synthesis in A. albopictus.