Description of Nosema

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Monomorphic and diplokaryotic but heterosporous in the sense of early and late spores; transmission is per os and transovarial; development at all stages is in direct contact with host cell cytoplasm; merogony with binary fission of diplokaryotic stages and multiple fission of stages with several diplokarya, these possibly reflecting a delay in cytoplasmic fission; sporogony involving binary fission of fusiform diplokaryotic cells; two types of spores are known, those produced early in infection (36 h) are pyriform, thin-walled and with 3-5 coils of the isofilar polar tube, and those produced later (after 54 h) are ovoid, 3-4 x 1.5-2 µm, thick walled and have 10 - 12 coils of the isofilar polar tube; both types are diplokaryotic and apart from the polar tube length are morphologically similar with lamellar polaroplast, centrally placed nuclei and small posterior vacuole; the early spores germinate in situ and are responsible for the spread of infection within the host, while the late spores are responsible for transmission between hosts; type species N. bombycis in all tissues of larvae, pupae and adults of silkworms Bombyx mori (Lepidoptera, Bombycidae) and other Lepidoptera.
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