Nosemosis, also known as Nosema, is a common bee disease mainly caused by a parasite Nosema ceranae and Nosema apis. It has invaded many beehives worldwide, commonly European honey bees colonies. The danger of this disease is that it does not present any obvious symptoms however it does result with the hives’ performance productivity and population. During the summer, most populations carry infected bees with little or no effect in the colony. However, when colder weather comes such as early spring or winter, this can present a high hazard for your bees.
Symptoms
It’s hard to tell if bees are infected as they either show no symptoms or none that is specific to this infection. Many symptoms associated with Nosema apply to other diseases of adult bees.
By observation, some key factors are correlated to Nosema. Nosema is a gut disease and can spread in high levels when there is a large bee population confined in the hive, usually during autumn or winter. Observe your hive and see if there are bees on the ground in front of the colony. This also occurs with other bee diseases, so this is not specific to Nosema on its own.
Another symptom is the K-wing. This is exhibited when bees have high nosema spore counts in their body. K-wing is where the forewing and the hind wing come unhooked and is displayed like a letter K. Although this symptom is associated with Nosema, it is not unique to nosema. Usually, on the first warm day after winter, bees will leave the colony to defecate the moment they leave, resulting in stains or streaks of faeces outside the hive. This is usually yellow or brown in colour.
Lastly, observe if there is fecal staining on the colony. This symptom may be one that is exclusive to Nosema disease. When Nosema is built up during winter, bees are more confined within the colony and are unable to defecate outside the colony.
The term ‘spring dwindle’ or rapid dwindling is one of the best indicators of this infection. This can be identified when a few sick or dead bees are found near the entrance and the loss of many adult bees. This should not be confused with normal weakening of colonies caused by natural causes in early spring. Sick or crawling bees at the hive entrance, dead bees on the ground and excreta (dysentery) in the hive are tell-tale signs, however, they may be equally caused by other common diseases and conditions.
Despite these symptoms, it is not 100% accurate that it is associated exclusively to Nosema. The only way to rightly diagnose is to collect a sample of adult bees to send to a lab, mostly associated with your nearest apiary associations.
How does it spread?
When the spores of the parasites are swallowed by bees, they tend to germinate within 30 minutes and penetrates the stomach lining of the bees. It rapidly grows and multiplies in numbers within 6 to 10 days using the cell contents of bees as its food supply. It has the ability to penetrate and infect neighbouring healthy cells and spreads the infection further. Once digested, infected cells are shed into the stomach and release spore-infected enzymes which are then extracted through the bees’ poop.
The infection is not usually spread directly, however, when worker bees clean contaminated combs they become infected. During the summer, most colonies have a few infected bees with no effect on the colony. However, the spores can carry on through the combs in winter and may initiate an outbreak when the climate changes that may cause deaths of bees. This is due to infected bees being confined in the hive due to cold weather, thus they tend to defecate inside the hive causing contamination and spread of infection throughout the colony. Spring outbreaks usually starts in late August or September, when temperatures begin to rise, and last until late spring or early summer.
In these outbreaks, most colonies, even strong ones, may be heavily weakened just before winter. This is due to the loss of population due to massive deaths and would take a long build-up period to repopulate in order to survive the winter. Spores may even contaminate honey or even in pollen. Research shows that worker bees can infect the queen through the mailing cages, queen banks and queen mating nuclei.
Control and Management Practices
Australian beekeepers use management practices to minimise occurrence of the infection. There may be present information regarding chemical treatments to control the Nosema infection, however, this is not registered in Australia for use in honey production beehives. The use of any chemical treatment is illegal and could have detrimental results for the beehive.
Generally, it is always recommended to maintain a regular check of your beehive. This will help you detect any changed behaviour in its early stages. By observation, you can also check whether your bees are producing high levels of honey as preparation for winter. If there are low levels, check any signs of defecation in the hive or if bees are able to collect high levels of pollen. This will ensure a good repopulation of young bees.
During the summer, it is important to regularly check your water sources. Check if its contaminated by faeces or any dead bees. Although bees do like a ‘dirt’ water, it’s better to make sure that there aren’t any present bacteria in the water that can harm them.
Naturally, bees have their own way of fighting the spread of infection. If fewer than 20% of worker bees are infected, there is little to no effect. At 40%, there are signs that the colony build up is slowing down and there is a decrease in honey production. By 60% and high up, poor performance is more obvious and the higher chances that the colony can collapse as it can no longer take care of its brood (Colony Collapse Disorder). The critical issue for the hive is to minimise the contamination to the newly born bees, however, it can be quite complicated to repopulate un-infected bees as pollen may also be contaminated if there is defecation present in the hive due to poor weather conditions. The queen’s strength in this stage is critical, however, she can be contaminated. When colonies sense that their queen is failing, they will find a replacement queen through rearing supersedure cells. Supersedure is a generic response when the colonies are struggling. When successful and better flight weather, the colony may survive the infection and remove the nosema from the hive.
More information is linked here:
http://www.dpi.nsw.gov.au/__data/assets/pdf_file/0003/177519/nosema-disease.pdf
https://www.agrifutures.com.au/wp-content/uploads/publications/08-006.pdf
References:
The Australian Beekeeper. November 2019. “Nosemosis: Part 4”. Vol.121. Jarrah Publishing.
Agriculture Victoria. 2009. Nosema Disease of Honey Bees. http://agriculture.vic.gov.au/agriculture/pests-diseases-and-weeds/animal-diseases/bees/nosema-disease-of-honey-bees
University of Florida. 2012. “Episode 2: Nosema Disease” https://www.youtube.com/watch?v=AMDN7r1SfbY&feature=youtu.be
