Life cycle of Amblyospora dyxenoides sp. nov. in the mosquito Culex annulirostris and the copepod Mesocyclops albicans

Abstract

A new species of Microspora, Amblyospora dyxenoides, is described. This parasite has three sporulation sequences: two in Culex annulirostris, the mosquito host, and one in Mesocyclops albicans, the intermediate copepod host. Diplokaryotic meronts in larval oenocytes persist to the adult stage and form binucleate spores in females which are responsible for transovarial transmission to larval progeny. Unlike other described species of Amblyospora, binucleate spores may also form in adult male mosquitoes. Diplokaryotic cells infect the oenocytes of some male and female larvae which hatch from transovarially infected egg batches. These larvae survive to the adult stage after which binucleate spores develop in the females to initiate another transovarially transmitted cycle. In other male and female larvae which hatch from infected egg batches the parasite invades fat body tissue where it undergoes meiosis during a complex sporulation sequence resulting in the formation of eight haploid meiospores within a sporophorous vesicle. Fat body infected larvae usually die in the 4th instar. Larval meiospores are responsible for horizontal transmission to M. albicans copepods in which the parasite develops in ovarian tissue to form another kind of uninucleate spore. These infections ultimately lead to death of the copepods and the spores are infectious per os to C. annulirostris larvae. The first mosquito stages resulting from these infections are small cells with a single large nucleus relative to the cytoplasm. It appears that the parasite then returns to the diploid state by cytoplasmic fusion (plasmogamy) of uninucleate gametes to form binucleate cells which later adopt the diplokaryotic arrangement and invade larval oenocytes to complete the life cycle.