What Is Nosema? Research-Backed Advice For Beekeepers

A beekeeper inspecting hives for threats like Nosema disease

Nosemosis, commonly called Nosema disease, is triggered by two fungi: Nosema apis and Nosema ceranae. It affects the bee’s digestive system and can cause severe colony losses in spring and fall.

N. apis originally affected European honey bees, while N. ceranae targeted Asian honey bees. However, N. ceranae has recently begun harming European bees and is more destructive than N. apis.

The infection causes young adult bees to become early foragers, skipping the nursing phase. Their lifespan shortens, and if queens get infected, they lay fewer eggs. Nosemosis harms the bee colony’s health and size, potentially leading to its collapse.

Important: Low numbers of Nosema-infected bees is common in hives. A healthy, thriving colony will usually fight off the disease.

Symptoms of Nosema

Nosema-infected bees typically exhibit no symptoms; any signs can be attributed to other threats. Beekeepers should get a sample of bees laboratory tested for a reliable diagnosis.

A heavily impacted colony may experience adult bee deaths at a rapid rate. Expect minimal dead bees at the hive’s entrance; dying bees will crawl away from the hive.

The colony is impacted my Nosema in several ways, including:

  • Dysentery in adult bees.
  • Life expectancy of infected bees is reduced by up to 50%.
  • Nurse bees are unable to produce royal jelly.
  • Young bees prematurely start foraging or guarding.
  • Queens stop laying eggs and soon die.
A closeup of hive top bars covered in dysentery from bees with Nosemosis
Nosemosis: Dysentery resulting from Nosema apis.

Nosema ceranae vs. Nosema apis – what’s the difference?

Nosema ceranae and Nosema apis are both microsporidian parasites that infect honeybees. Nosema ceranae was initially identified in Asian honeybees but now impacts the Western bee in most parts of the world.

Although knowledge is limited on N. ceranae, most of its characteristics are shared with N. apis. Nosema ceranae has a more severe effect on a bee’s digestive system than Nosema apis.

Nosema Apis was identified over a century ago, while Nosema ceranae wasn’t found until 1994.

Comparison summary table:

 Nosema apisNosema ceranae
First discovered19091994
DetectedMild weatherAll year round
Number of gut cells affectedLessMore
Bee mortality rateLowerHigher
Dysentery symptomsMore pronouncedLess pronounced

Life cycle and spread

Nosema is spread on honey and pollen. When bees ingest Nosema apis spores, they germinate in the stomach within 30 minutes. The organism then invades the stomach cells, proliferating rapidly by consuming cell contents.

In 6-10 days, vast spores form in these cells. The parasite can also infect neighboring cells, spreading the disease.

During digestion, bees naturally shed stomach cells, releasing enzymes. Infected cells, however, release nosema spores instead. These spores can infect other stomach cells or exit with the bee’s feces.

Photograph of Nosema apis viewed under microscope at a magnification of 400x
Nosema apis magnified x400.

Young bees get infected when they consume spores while cleaning tainted combs. In summer, many bee colonies have a few infected bees, but the impact is often minimal.

In fall and winter, spores within the hive may trigger a Nosema outbreak. Bees trapped inside by bad weather may defecate inside the hive, contaminating it with spores.

The infection may result in severe casualties until the weather warms, allowing bees to leave the hive.

Related reading:

Fast facts

  1. Rapidly reducing colony numbers is also referred to as “spring dwindle.”
  2. Common symptoms of Nosemosis, like dysentery and sick crawling bees, are also associated with many other hive problems.
  3. Infected adult bees rarely transmit the disease directly to their brood.
  4. When N. ceranae spores are chilled or frozen, they lose viability.


Beekeepers can help prevent Nosemosis in their apiaries by reducing nutritional stress and pesticide exposure. Research has found these two factors play a huge role in the disease’s impact on bees. Source.

Other preventative measures include:

  • Locating hives in a sunny location away from damp gullies and areas that are wind prone.
  • Keeping prolific queens that lay a lot of eggs.
  • Ensuring there is a large number of young bees as winter approaches.
  • Making sure bees have adequate supplies of honey for winter.
  • Avoiding hive inspections or other disruptions to the hive unless essential.
  • Reducing hive space during winter helps keep the colony warm and reduces the area to guard.
  • Avoiding crushing bees during hive management, as undertaker bees will spread the spores if the deceased bees are infected.
  • Removing the oldest, darkest comb each spring and replace it with fresh, new foundations.

Recommended reading: A practical guide to chalkbrood.

Image of Nosema ceranae magnified 1000 times under a microscope
Nosema ceranae magnified x1000.

Commonly asked questions

How is Nosemosis diagnosed?

Nosema infection is diagnosed using microscopy and nucleic acid technologies; only electron microscopy and PCR reliably differentiate between Nosema Apis and Nosema Ceranae spores.

What is the impact of Nosema on honey bee colonies?

Nosema typically reduces the lifespan of worker bees, decreases honey production, and weakens the overall health of a colony. In severe cases, it contributes to colony collapse.

Is honey from Nosema-infected colonies safe for humans?

The honey produced in hives with Nosema is safe for consumption.

Can Nosema disease affect humans?

Nosema is not transmissible to humans.

An image of a large cluster of dead bees on the hive's floorboard as the result of Nosema infection.
Nosema infection can kill a large number of adult bees.

How to treat Nosemosis

Treatment of Nosema varies by country, and beekeepers should consult local authorities before implementing eradication strategies.

Fumagilin-B is a chemical treatment that is effective against Nosema disease. It is commonly used in the United States; however, the product is prohibited in some countries like Australia. For the most part, this chemical is not authorized in Europe. Source.

Research articles about Fumagillin-B

Click the plus sign to read our quick summary.

Our quick summary:

While fumagillin is effective against Nosema apis, it is toxic to mammals and can leave residues in honey.

The researchers made a surprising discovery during tests. They found that Nosema ceranae increases spore production when exposed to decreasing fumagillin levels – up to 100% more than bees not exposed to the drug.

Even though fumagillin targets a specific enzyme in these pathogens, its current usage might make the N. ceranae infection worse instead of better.

Read the research>

Our quick summary:

Nosema ceranae can harm bee health, reproduction, and productivity. Although fumagillin is commonly used for treatment in some countries, it has side effects.

In one study, researchers treated infected bees with either fumagillin or Agaricus blazei mushroom extract in a controlled environment.

While fumagillin showed positive results in infected bees, it had adverse effects when used as a preventive measure on non-infected bees.

In contrast, the A. blazei extract showed potential benefits without side effects, indicating it might be a viable alternative for Nosema control. Further research is required.

Read the research>

Our quick summary:

Although fumagillin is a standard treatment, its negative impact on bees necessitates alternative treatments.

Alternatives like naringenin can reduce spore count significantly, while certain plant extracts halt microsporidia growth. Combining these treatments might curb bee losses from this infection.

Additionally, better hive management and reduced insecticide use are vital for boosting global bee populations. A holistic “one-health” strategy is essential for restoring bee numbers worldwide.

Read the research>


Image attribution: “Courtesy The Animal and Plant Health Agency (APHA), Crown Copyright”

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