Nosema bombi,a microsporidian pathogen of the bumble beeBombus terrestris(L.)

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Abstract
The developmental cycle and morphology of a microsporidian pathogen Nosema bombi Fantham & Porter 1914, of the bumble bee, Bombus terrestris, are described. In experimentally infected bees, spherical meronts were the first stages observed. These varied in size from 2.66 to 7.35 μm, and had 1–4 nuclei. Uninucleate, binucleate, and occasionally tetranucleate sporonts were oval or fusiform in shape, and measured 5.32–8.05 μm × 2.80–4.41 μm. Oval binucleate sporoblasts, measuring 4.64–5.78 μm × 3.03–3.94 μm, appeared in large numbers prior to spore morphogenesis. Spores varied in size from 4.20–5.39 μm × 2.13–3.50 μm in unstained preparations, and were significantly smaller than spores of the honey bee pathogen, Nosema apis (P < 0.001, n = 50). Spores developed primarily in the Malpighian tubules. Electron microscopic examination of spores showed the polar filament to have 14–18 coils, compared with N. apis which has 18–44.