Observations on the development and transmission of Nosema apis Z. In the ventriculus of the honeybee
The developmental stages of Nosema apis Z. (first merogony, second merogony, sporogony, sporoblasts, spores) in the ventriculus of the honeybee (Apis mellifera L.) are described, based on electron microscopy observations. The invasive process is not demonstrated, but there is no reason to believe that invasion by N. apis should differ from the process of other species in the microsporidian genus, Nosema, where the sporoplasm is injected into the host cell through the polar filament. The development of the parasite is strictly intracellular as in all other microsporidia. Structures within the host cytoplasm indicate a possible intercellular spread of the parasite through extrusion of polar filaments from mature spores still inside the host cell. No proof of secondary vegetative stages invading adjacent cells were found, 'although this possibility cannot be excluded. Four days post infection (p.i.), mature spores were found in the host cytoplasm; 6 days p.i., spores produced in the gut epithelium of the host were found with extruded polar filaments in the ventricular lumen. Meiotic activities or karyogamy were not seen. It is suggested that the life cycle of N. apis could be asexual.