Nosema is a microsporidian under the classification of fungus that attacks the gut of the honey bee and is one of the major threats to the honey bee population around the world.There are now two different types of Nosema affecting the European Honey Bee: Nosema apis and Nosema ceranae. Nosema apis has been found in hives since the beginning of the twentieth century but Nosema ceranae was only discovered in the early 2000s. When N. ceranae was first found it was thought to be very similar to N. apis As more research has been conducted and trials performed it has become clear that the two Nosema species are very different. The research group, Bee Doc, has found between 50 and 90 percent of hives throughout Europe, from Scandinavia to Southern France have Nosema. The majority of these hives have N. ceranae.
Nosema apis: Always been a problem
Nosema Apis has been a documented problem for over 100 years. It is particularly a problem when bees are not able to fly for long periods of time, especially the period associated with the colder winter months. This makes N. apis more of problematic for beekeepers working in cooler climates. When bees are prevented from flying they are forced to defecate in the hive due to dysentery caused by N. apis. This allows the disease to spread to other bees who consume the infected spores as they try to clean up. The disease considerably weakens the bees; bees live half as long and hives with Nosema apis have been shown to produce significantly less honey and less bees.When colonies are heavily infected with Nosema apis there can be visible signs such as the inability of bees to fly, excreta on combs, piles of dead or dying bees and the failure of a colony to build up in the spring. However, the majority of N. apis-infected hives will not show any signs and hence it has been nicknamed the 'no-see-um' disease. One way to confirm Nosema is by microscopy, although it is almost impossible to distinguish between N. apis and N. ceranae. While colonies can die from Nosema apis, in general they will survive, albeit weakened and producing less honey and brood. The spores of N. apis are quite resistant to cold but not to heat.
Nosema Ceranae: The new disease you can't see!
Nosema ceranae is different from Nosema apis. It has no obvious symptoms, is more prevalent in warmer climates, its spores are more resistant to heat and are more sensitive to the cold. Importantly, N. ceranae is not as seasonal as N. apis and tends to build up over years.It was only first discovered in the European honey bee in Vietnam in 2004, but it probably transferred across to Europe some time late in the 1990s and has been spreading rapidly since. Although there is no confirmed evidence to show N. Ceranae is the cause of Colony Collapse Disorder (CCD), its prevalence in hives suffering with the problem seems more than coincidental. Recent scientific studies have demonstrated that N. ceranae on its own can be fatal for bees, causing the collapse of hives.
Other scientific research has shown that an additionally worrying problem is the association of N. ceranae with other stresses (for example, diseases, pesticides, drought) in hives. Studies have consistently shown the honey bee is far more vulnerable to pesticides when it has ceranae. It has been demonstrated that it takes 100 times less pesticide to kill a bee with N. ceranae than a bee without the disease.
The link of N. ceranae to viruses is supported by Antúnez et al, when they stated:
“N. ceranae infection seems to suppress the immune response... the present work confirmed the negative impact of Nosema ceranae on bee health as reported previously. Nosema ceranae is a more prevalent and virulent microsporidia than N apis, producing irreversible lesions to the bee ventricular epithelium… favouring the replication of viruses present in a latent state.”
It has also been shown that whenever colonies die from Colony Collapse Disorder that Nosema is nearly always present. Of 30 CCD-affected colonies observed, 100% were positive for Nosema ceranae and 90% for N. apis.Bromenshenk has shown a strong link between a virus, Israeli virus, and Nosema in hives suffering with CCD.
There is still a lot of data emerging on N. ceranae and it is increasingly being shown that whenever there is a problem with hives Nosema ceranae is never far away.