Annual infection cycle of Nosema ceranae in Virginia honey bee colonies

Virginia winter honey bee losses have averaged 30 percent over the past 10 years. Increases in colony losses are in part due to increased stress on colonies from new pathogens. Nosema ceranae is a newly discovered microsporidian that was found to infect Apis cerana in 1996. In 2005, it was shown to naturally infect A. mellifera. While N. ceranae was initially thought to be an emergent pathogen of honey bees, studies show it has been present in the United States since 1995 and is widespread. Classical detection techniques for Nosema depend on microscopy and the examination of samples for spores; however, the spores of N. ceranae cannot be distinguished from those of N. apis, a microsporidian that has infected honey bees for over 100 years in the United States. To overcome this problem we developed a real-time PCR assay to simultaneously quantify infection levels in honey bees for both species. We used this approach to examine the annual infection cycle of N. ceranae in Virginia. Here we report data from one year of sampling 10 colonies. Each month, workers were sampled from honey supers, the fringe of the brood nest, and the brood nest to ensure that bees of different ages were examined. All hives we analyzed were infected with N. ceranae and infection levels varied by season with higher levels found in the summer. The results have also helped to develop new disease control recommendations for beekeepers.