Nosema Disease in Honey Bees

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Nosema disease is one of the most common diseases of honey bee colonies. It is prevalent in many apiaries – even if the beekeepers does not know about it. Often, nosema causes colonies to perform poorly or not reach their potential – but it can deadly. In this guide, you will learn the basics of honey bee nosema disease and how it might affects your bees.

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

As a beekeeper, I am always on the lookout for problems – including various honey bee diseases. Healthy colonies are productive colonies and they are less work and worry for the beekeeper too!

What is Nosema Disease?

Nosemosis (Nosema disease) is caused by microsporidian parasite (a microsporidian). There are two primary species of nosema that affect honey bees: Nosema apis and Nosema ceranae.

Nosema apis

Nosema apis has traditionally been the most common type of this disease in honey bee colonies – certainly in the United States. It affects all types of European honey bees (Apis melliefera).

It tends to cause hive problems in early Spring or late Fall, causes the bees to experience diarrhea (dysentery), lethargy and reduced foraging.

Nosema ceranae

Nosema ceranae was previously thought to only be a parasite of the Asian honey bee. Now, it has spread across the world and become the most aggressive form of the disease.

Causing problems throughout the year (not just seasonally), Nosema ceranae does not have any easily observable symptoms. This makes it very hard to detect – the colony may already be in major decline before the beekeeper is aware of a problem.

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.

Once inside the digestive tract of the honey bees, nosema spores multiply and damage healthy tissue. The life span of honey bees affected declines and this results in a weakening of the entire colony.

Interestingly, this condition is not specific to honey bees. Grasshoppers, wax moths, bumble bees and locusts can suffer from Nosema diseases that are specific to their species.

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

How Nosema Disease is Spread

Both types of Nosema disease produce spores (I think of them as “disease seeds” 🙂 Spores are tough and can survive quietly for long periods of time in the proper environment.

When spores are ingested by honey bees, the infected bee can transfer them to other bees in the hive or other colonies.

Common Methods of Infection

Oral/Fecal Infection : The most common way honey bees become infected with nosema disease is through contaminated food or water. When an infected honey bee poops (or excretes waste) inside the hive- comb, honey and all surfaces become unsanitary.

Worker bees are responsible for hive hygiene – as they attempt to clean the soiled comb they become infected with spores. In just a few days, a few spores can multiply to over 30 million in 1 bee.

Bee to Bee: Honey bees are sharing insects. Perhaps you have seen two or more bees sharing food before – this is called trophallaxis. Unfortunately, nosema can also be shared through food transfer or mutual grooming.

Buying bees in packages or nucs, even the purchase of a new queen bee may bring nosema into your apiary.

Beekeeping Equipment: Sometimes we beekeepers are responsible for spreading this type of disease. Contaminated frames, super boxes – even an uncleaned hive tool can transfer nosema from hive to hive.

Swarming/Robbing: Honey bee swarming is a natural process where a strong colony splits into two parts. One leaves the home hive with up to half the work force and some honey. They may also take nosema spores with them to their new home.

In situations where robbing honey bees are stealing from a weaker hive – they too may be taking more back to their home than is intended. A few spores can develop into honey bee nosema disease in a short time.

Detecting Nosema in Your Hive

Nosema can be very difficult to diagnose – especially in Nosema ceranae which tends to have fewer overt symptoms. Also, various viruses of honey bees, pests and pathogens may result in some or all of these symptoms.

Therefore, none of these indicators can be used as a true guide to a diagnosis of nosema disease. A lab test is the only way to provide a Nosema disease diagnosis (including which one you have).

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.

Other Signs Beekeepers Watch for:

  • 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.

Beekeeper finding dysentery inside hive checks for nosema disease in the hive.

Treatment Options for Nosema

Prevention of infection is key. Because, there is no treatment plan that will totally remove nosema spores from your hives. However, there are things you can do to limit the harm caused.

Nosema disease tends to be a “stress-disease”. It causes problems for the colony when the hive is weakened or under stress.

Therefore, do what you can to keep your bees happy! Seriously, making sure they are healthy and free from other pests provides a good environment for their well-being.

Chemical Treatment: Fumagilin-B

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.

Killing the active stage of Nosema apis but not the spores, Fumagillin helps control-but not eradicate the disease.

Because it was used prophylactically (as a protective measure without evidence of a problem), there is concern about the possibility of chemical residuals in comb and honey. It’s use is banned in several countries.

Unfortunately, fumagilin has not been as effective against Nosema ceranae. This is a real problem since most of the nosema disease in the US is caused by N. ceranae. However, the treatment may reduce the infestation enough to help the colony recover.

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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 Nosema Disease is good hive management practices. Hives can recover from light infections.

That is my plan in the apiary. I have not treated for Nosema in years and have not lost any colonies to the disease. My goal is to have colonies that are as healthy as possible. This lessens problems with diseases that are related to stress.

FAQs

How do colonies become infected with Nosema?

Honey bee colonies become infected with Nosema by Nosema spores in food or water, bee to bee contact or during hive cleaning.

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

The signs of Nosema disease in a honey bee colony mirrors many 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.

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