Gametogenesis, fertilization and ookinete differentiation of Leucocytozoonsmithi

Development of Leucocytozoon smithi during gametogenesis, fertilization. an d ookinete differentiation was studied by light and electron microscopy. Ga metogenesis occurred rapidly, within 1-2 min after gametocytes were ingeste d by black flies. Usually one axoneme, but not infrequently two, was observ ed in microgametes. The macrogamete nucleus was characteristically elongate d and fragmented, with a convoluted nuclear envelope. Fertilization occurre d within five min after ingestion of gametocytes by the vector. The entire axoneme and nucleus of the microgamete entered the cytoplasm of the macroga mete. Zygote differentiation resembled sporozoite formation in that a thick ened inner membrane and subpellicular microtubules developed beneath the pl asmalemma, followed by cytoplasmic protrusion or evagination to form the an terior end. Extension of the inner thickened membrane continued as the zygo te elongated. Development of sausage-shaped ookinetes was completed within 6-8 h after ingestion of a blood meal by a black fly. Mature ookinetes poss essed a single nucleus, double-layered pellicle, canopy, apical pore, polar ring complex, subpellicular microtubules, micronemes. crystalloids. abunda nt mitochondria. endoplasmic reticulum, and ribosomes. Comparison of develo pment of L. smithi with species of Plasmodium and Haemoproteus ils revealed general similarities in both sexual and asexual development within the ins ect vector. A diagram summarizing life cycle events for L. smithi is includ ed.