Nosema Disease in Bees

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Like all living things, honey bees are subject to various health challenges. One condition beekeepers must watch for is Nosema disease in honey bees. Nosema is one of the most common diseases of adult honey bees. Rather prevalent in many apiaries, it can be a very serious condition and responsible for hive failures.

Beekeeper inspecting bees in hive for nosema disease or other pathogens.

As beekeepers, we have the responsibility to protect our colonies as much as possible. It is not always possible to protect them from everything. However, healthy colonies can deal with various honey bee diseases – so that is a good start.

What is Nosema Disease?

Nosemosis (Nosema disease) is caused by microsporidian parasite (related to fungus). In simplest terms, small things we can’t see with just our eyes. These microscopic fungi can infest a wide range of hosts – including honey bees.

This condition is not specific to honey bees. In fact, grasshoppers, wax moths, bumble bees and locusts can suffer from Nosema disease.

But the type of Nosema is specific to the insect that they attack. The one that harms a grasshopper does not hurt a Bumble Bee.

Species that Affect Honey Bees

There are 2 species of Nosema that affect honey bee colonies. The first to be mentioned in association with honey bees was Nosema “Apis”.

It affects all races or types of European honey bees. For decades, N. apis was the most prevalent form of the disease in the United States.

The second species is Nosema “ceranae” which originated in Asia. Honey bees native to that region developed some resistance to this species of Nosema (those that did not – died out).

This is similar to the situation we have with Varroa Mites in bees today. Bees from Asia show some resistance to them.

Sadly, N. ceranae is widespread in the United States now. It makes up the majority of reported cases. Ceranae is a more virulent strain and kills a colony much faster.

The 2 types of Nosema are very difficult to identify. Their cells look very much alike. True diagnosis requires samples to be sent to the USDA-ARS Bee Research Lab in Beltsville, MD.

Honey bees sharing food or open honey on comb and worker bee sucking up honey and pollen.

How Colonies are Infected

Both types of Nosema disease produces spores. Bees are infected by consuming nosema spores through their mouth.

They can pick up spores from coming into contact with other infected bees or contaminated food or water. Only a few spores are enough to develop into a big problem.

In just a few days, a few spores can multiply to over 30 million in 1 bee. N. apis is more commonly seen in the Spring. After months of Winter confinement the digestive system of the bees is sluggish at best.

Worker bees that function as house bees are contaminated as they attempt to clean the soiled comb. This is the most common way that Nosema disease is spread among colony members.

Buying bees in packages or nucs, even the purchase of a queen may bring nosema spores into your apiary. It can be a serious disease if not controlled.

Some foragers become so weak they can not make it back to the hive. Leaving the beekeeper to wonder where the bees went to suddenly, leaving behind a queen and a few workers.

Life Cycle

In the beginning, the spores of Nosema apis are consumed and enter the gut. Here, they begin to multiply. As spores enter the midgut (between the honey stomach and small intestines), the lining of the midgut is affected.

Proper digestion of food is impaired causing swelling, poor nutrition and sickness. Spores work their way through the digestive system and are expelled from the body in bee feces.

Nosema spores can live up to 1 year in fecal material, in a water source, in pollen and honey or on the surface of honeycomb.

Affects of Nosema Infestations

Having N. apis may not kill your colony but it does weaken them. The hive has an overall look of failure to thrive. According to outward signs, the colony should be growing but it just is not.

  • adults living shorter lives
  • less productive colony
  • more susceptible to other stresses

Infected honey bees do not live as long and their shorter lives and are less productive. The life cycle of the queen bee may be affected. They may not mature to their potential and suffer in pheromone production and reduced egg laying.

In an attempt to correct whatever is wrong, the colony make attempt to supersede the queen in hopes of an improvement.

This leads to a reduced number in the work force – fewer forager bees to go out in the field. Brood rearing suffers because nurse bees are not healthy enough to care for growing young.

Honey production per hive suffers due to weak bees that are unable to digest food properly. The overall condition of the colony declines as its members become weaker and sicker.

Added to this stress, if the colonies are dealing with other problems such as mites, this could be the last straw. That is why routine varroa mite testing is so important.

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Diagnosing Nosema

As with many things, the common symptoms of a Nosema infection are also common to other conditions. Viruses, other diseases, pest and pathogens may include some or all of these symptoms.

Therefore, none of these indicators can be used as a true guide to a diagnosis of nosema disease.

However, if you see several of these issues in your bees – especially in Spring or Fall – it requires a closer look.

  • a colony not eating sugar water when others are
  • bees with swollen abdomens
  • workers trembling and shivering
  • bees unable to fly
  • bees crawling aimlessly around the bottom board or entrance
  • K wing – wings held in various angles and not folded in the hive
  • feces on comb, and outside walls of the hive-dysentery

Note: Not all bees with dysentery have nosema. Not all colonies with nosema have dysentery.

If you have the equipment and desire, you can do a bit of field testing. The Nosema field test inspects the digestive tract of several bees.

Look for a swollen midgut that does not have the normal circular bands. This swelling is more common in N. apis (the less common type) than N. ceranae.

A lab test from the bee lab- is the only way to truly provide a Nosema diagnosis. Not only the presence of the disease but which one you have in your beehive.

Beekeeper finding dysentery inside hive checks for nosema.

Nosema Treatments

For years, the only reliable treatment for Nosema disease in honey bees has been Fumagillin. This is an antibiotic derived from Aspergillus fumigatus sold as fumagilin-B or Fumidil-B.

It has been used in the beekeeping industry for more than 50 years. Killing the active stage of Nosema apis but not the spores, Fumagillin helps control-but not eradicate the disease.

In fact, it was used prophylactically (as a protective measure without evidence of a problem) often. So often that is has caused concern.

Over time, researchers became more concerned about the possibility of chemical residuals in comb and honey. It’s use is banned in several countries.

In the war against Nosema ceranea, fumagilin has not been as effective. This is a real problem due to the fact that most of the disease in the US currently is N. ceranea. However, the treatment may reduce the infestation enough to help the colony recover.

Possible Natural Aids

While there are many “natural” products on the market that claim to aid in controlling Nosema disease in bees, there is no as much evidence to back up their claims.

There is hope that some of these products promoting better bee gut health can help our bees become healthier. This could help them deal with disease and pathogens more effectively.

To this end, I sometimes mix up one of these essential oil recipes for my colonies. And, I try to give them some sugar water with Hive Alive before the end of Fall.

Disinfecting Comb

In colonies that dwindle during Spring to a non sustainable level, the beekeeper may wish to attempt saving the comb.

This can be achieved by fumigating the comb with an acetic acid. But, this is not something attempted by most hobbyists.

Best Prevention Methods

The best prevention against problems with Nosema Disease is good hive management practices. Many colonies experience this disease and recover.

The goal is to have colonies that are as healthy as possible. This helps lessen problems with diseases or pests that are related to stress.


How do colonies become infected with Nosema?

Honey bee colonies become infected by ingesting Nosema spores in food or water. This happens during food transfer between bees or cleaning the comb too.

What are the signs and symptoms of Nosema disease in honey bees?

The signs of Nosema disease in a honey bee colony mirror may other conditions. While swollen abdomens or even dysentery may be a sign – only a lab test is a reliable method to confirm the presence of Nosema.

What treatments are available for Nosema disease in honey bee colonies?

Currently, only the antibiotic fumagillin is approved for treating colonies with Nosema. However, it targets the active stage of the disease and does not kill spores. Some beekeepers experiment with probiotic and other natural feed supplements in an affect to promote bee health overall.

Can Nosema cause colony losses?

Yes, Nosema can definitely be responsible for lost colonies if left unchecked. However, light cases can clear up on their own when conditions improve for the colony.

Final Thoughts

Nosema can and does kill honey bee colonies. However, many colonies have mild cases that resolve themselves when conditions improve. This is similar to EFB (European Foulbrood) which is also a stress disease.

Monitoring the condition of your bees and focusing on good honey bee health is the best way to prevent a loss of bees due to Nosema.

Treating with Fumagillin is one resource available to use if the condition merits. But, this drug is not a silver bullet and should not be over-used.

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