Distribution of Nosema ceranae in the European honeybee, Apis mellifera in Japan

The microsporidian species, Nosema apis and Nosema ceranae are both known to infect the European honeybee, Apis mellifera. Nosema disease has a global distribution and is responsible for considerable economic losses among apiculturists. In this study, 336 honeybee samples from 18 different prefectures in Japan were examined for the presence of N. apis and N. ceranae using a PCR technique. Although N. ceranae was not detected in most of the apiaries surveyed, the parasite was detected at three of the sites examined. Further, N. ceranae appears to be patchily distributed across Japan and no apparent geographic difference was observed among the areas surveyed. In addition, the apparent absence of N. apis suggests that N. ceranae may be displacing N. apis in A. mellifera in Japan. Partial SSU rRNA gene sequence analysis revealed the possible existence of two N. ceranae groups from different geographic regions in Japan. It seems likely that these microsporidian parasites were introduced into Japan through the importation of either contaminated honeybee-related products or infected queens. This study confirmed that PCR detection is effective for indicating the presence of this pathogen in seemingly healthy colonies. It is therefore hoped that the results presented here will improve our understanding of the epidemiology of Nosema disease so that effective controls can be implemented.