Nosema ceranae was discovered in Apis cerana, Eastern honeybee first. Until recently A. cerana has been considered the only host to this parasite. A few years ago N. ceranae was recorded in honey bee Apis mellifera. It appeared that N. ceranae is more pathogenic for A. mellifera than Nosema apis. This parasite can cause significant losses in bee colonies. Bees die without symptoms observed in nosemosis caused by N. apis such as diarrhea.