Infection Cycle, Transmission Mechanisms, and Management of Nosema ceranae in Apis mellifera Colonies

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Virginia Tech


Nosema ceranae is a recently described, widespread microsporidian parasite of Apis mellifera that has raised concerns as to whether it is contributing to increased colony losses. To better understand this parasite, investigations were made into the seasonality of infections, alternative transmission mechanisms, and potential control approaches. All studies used real-time PCR with specific primers and probes for N. ceranae, as well as traditional spore analysis. Monthly colony monitoring in Virginia showed that N. ceranae was present yearlong with the highest levels observed in April-June and lower levels through the fall and winter. There was no difference in infection levels among bees sampled from different areas of the hive regardless of the time of year. Additionally, N. ceranae infects all castes of the colony. Drones of different ages, including pupae, in-hive, and flying drones, were found to be infected at low levels with infections most prevalent during peak annual levels in April-June. Approximately 5% of flying drones had moderate to high levels of infection indicating that flying drones, which would be the most likely age group to drift, could assist in the horizontal transmission of N. ceranae both within and between apiaries. Immature and mated queens were also found to be infected at low levels. Infection in the ovaries and spermathecae suggests the possibility for vertical transmission. Finally, control of N. ceranae is thought to improve the health of bees and to reduce colony losses. Fall fumagillin treatments and winter stimulative pollen feeding were compared. Neither treatment significantly lowered N. ceranae levels in colonies sampled 3-6 months later, nor did they significantly improve colony survival. Due to the high cost of treatment and the time required, we do not recommend either treatment for N. ceranae infections during the fall. Colony winter losses due solely to N. ceranae seem unlikely because levels of N. ceranae were low. Impacts from N. ceranae infections were also minimal during the summer as productive colonies had some of the highest levels of infection. Although N. ceranae is prevalent throughout hives, it does not seem to be a major cause of colony losses.



Nosema ceranae, Apis mellifera, seasonality, drones, queens