Differentiation of Nosema apis and Nosema ceranae spores under Scanning Electron Microscopy (SEM)

Spores of the microsporidian gut pathogens of honey bees Nosema apis and Nosema ceranae, the causative agents of nosemosis, are difficult to distinguish using the light microscope. This study aimed to find methods which could help to identify N. apis and N. ceranae spores, and to define morphometric parameters in order to distinguish the differences between the spores of the two species. Our observation of spores under Scanning Electron Microscopy (SEM) revealed that N. apis and N. ceranae spores differ in their surface structure. Generally, N. ceranae spores seem to be more sculptured with deeper ornamentation than those of N. apis. Therefore, ornamentation of the spore cell wall with special reference to the width of their exospore furrows and sculpture index allows unequivocal identification of N. apis and N. ceranae species. Whole glands, organs, or various surfaces can be examined under SEM for the presence of spores, and consequently possible reservoirs or niches for storage of Nosema spores can be detected. We observed the results of Nosema spp. infestation on bees' intestines under SEM. Our study revealed that even medium Nosema spp. infection causes the midgut to be completely covered with spores. This spore-made layer can be the cause of bee malnutrition and higher mortality of foragers.