Nosema ceranae disease of the honey bee (Apis mellifera)

The presence of honey bees in our landscapes has long invoked images of vitality, diligence, and cooperation. Unfortunately, the current state of bee health paints a rather different picture. The survival of honey bees, as well as the livelihoods of those who benefit from their labor, is under threat from several detractors to bee health. Exposure to pesticides, poor forage, mite parasites, and pathogens has resulted in high annual death of colonies in the USA, Europe, and other parts of the world. Among the suspects thought to contribute to bee decline, the fungal pathogen, Nosema ceranae, is found at high prevalence in both healthy and declining colonies. Since N. ceranae is thought to be a recent parasite of Apis mellifera, much remains unknown about its pathology at the individual and colony levels, as well as how infection may interact and synergize with other stressors. A review of research conducted on N. ceranae infection is provided. Attention is given to observations on detection of infection, cytopathology, viability and infectivity of spores, and caste-specific effects to survival, development, physiology, and behavior. Research findings showing effects from interactions with pesticides and viruses are also provided. Comparisons are drawn between N. ceranae and what is known about a similar, long-recognized pathogen of A. mellifera, Nosema apis. When possible, suggestions for future research that could broaden understanding of N. ceranae and ultimately improve honey bee health are offered to link observations on individual bee pathology with pathology observed at the colony level.