macro shot photography of black and yellow bees

What Causes Nosema in Bees and What Treatment is Available?

Nosema is a common disease that affects honeybees.  It is important for beekeepers to know the signs and symptoms of nosema so they can treat and prevent it.  Read on to learn what causes nosema in bees as well as different methods of treatment. 

What is Nosema?

Nosema is a fungal infection that affects honeybees. Nosema apis and Nosema ceranae are the two species that can affect bees. 

Once infected, the fungi invades the honeybee’s gut and damages the intestinal lining.  As a result, bees with nosema experience malnutrition, increased likelihood of contracting other diseases, and ultimately, a shortened lifespan. 

Symptoms of Nosema

  • Diarrhea: Due to damage of the intestinal lining, bees with nosema often experience diarrhea.  You may see brown spots on the front of the hive or inside on the comb. 
  • General weakness: Bees with nosema may appear weak and lethargic.
  • Reduced brood production: Nosema infected bees have a reduced ability to produce brood.  As a result, the population size of the colony will decrease. 
  • Decreased honey production: Bees with nosema are unable to forage as much, which leads to lower honey production. 
  • Shortened lifespan: Because of a decline in overall health, bees infected with nosema have a shortened lifespan.

What Causes Nosema in Bees?

Nosema infection in bees is caused by spore forming fungi.  Poor nutrition, poor hygiene, exposure to pesticides and chemicals, and transmission via contaminated food and water are known causes of nosema. 

Fecal matter in the hive can cause the growth and spread of nosema spores. If the hive does not have proper ventilation, moisture cannot be removed. This causes a damp environment that can easily grow nosema. 

Bees that have been exposed to pesticides and other chemicals tend to have weakened immune systems that leave them susceptible to nosema infection. 

Nosema spores are also transmitted through contact with other infected bees.  Food and water sources can become contaminated with nosema and infect other bees. 

Nosema Treatment

There are a few different methods of treating nosema in bees. Nosema treatment includes proper hive management, antifungal medication, essential oils, probiotics, and replacing old comb. 

Hive Management

Proper hive management is important to promote good hygiene in the hive. Providing a clean and properly ventilated hive, good nutrition, and reducing stress on the bees can help to combat nosema. 

Antifungal Medication

Antifungal medication such as fumagillin is commonly used to treat nosema in bees.  Fumagillin can be mixed into sugar syrup or dusted right onto the bees. 

Essential Oils

Wintergreen and Eucalyptus essential oils have antifungal properties that can treat nosema. To use these oils, add it to sugar syrup or use a vaporizer to disperse it into the hive. 


Adding probiotic supplements to sugar syrup helps to promote the bee’s gut health and improve their immune system.  This is important, as bees with weakened immune systems are especially susceptible to nosema. 

Replace Old Comb

If there is a nosema outbreak in your hive, you may need to replace the old comb. This is because nosema spores can live in old comb for several years. Replacing contaminated or old comb is a good way to reduce the risk of a nosema outbreak in your hive. 

Preventing Nosema

To prevent nosema in bees, it is important to focus on proper hive hygiene, providing adequate nutrition, reducing stress on the colony, and hive inspections to monitor the hive for signs of infection. 

Cleaning the hive regularly ensures that fecal waste will not remain in or around the hive, preventing the growth of nosema spores. Replacing old comb periodically also helps to prevent nosema. 

Good nutrition for honeybees include a varied and balanced diet that boosts their immune system.  They can get this from having access to a diverse range of pollen sources. However, if that isn’t possible, their diets can be supplemented with protein supplements and sugar syrup. 

When the bees are stressed, they are more susceptible to nosema and other diseases.  Therefore, reducing stress factors such as overcrowding and poor ventilation helps to raise healthy bees. 

Regular hive inspections are important to catch signs of disease early.  This ensures that you will be able to quickly detect and treat any problems that may arise. 


Nosema is a common fungal infection that affects honey bees.  Poor hygiene and nutrition, as well as exposure to pesticides and contaminated food and water are known causes of nosema. Treatment of nosema includes antifungal medication, essential oils, probiotics, and replacing old comb.