Ultrastructural and cytochemical studies of the spermatid and spermatozoon of Culex quinquefasciatus (Culicidae).

Ultrastructural and cytochemical studies were carried out on spermatid and spermatozoon of the mosquito Culex quinquefasciatus. The spermatozoon appeared threadlike, lacking distinct head and tail regions. The nucleus development involved nuclear shape change and chromatin condensation. The acrosome showed two distinct zones and a subacrosomal space. In the sperm tail an axoneme and two mitochondrial derivatives containing crystalline matrix were observed. The axoneme presented a 9+9+'1' microtubule pattern and the accessory microtubules were composed of fifteen protofilaments. The plasma membrane of the spermatozoon was asymmetric, presenting a 30 nm thick surface coat which was not sensitive to the action of pepsin. Carbohydrates were located in the plasma membrane and in the interface basal layer of the coat, by using the periodic acid-thiosemicarbazide-silver proteinate technique. Lectin gold studies revealed mannose, glucose, galactose, N-acetylglucosamine and sialic acid residues on the cell surface. These carbohydrate residues groups randomly occurred on the surface at the head and tail regions. The surface coat disappeared during the sperm storage in the spermatheca before fertilization.