Nosema Disease

Causative Agent


Nosema disease is caused by one of two fungi named Nosema apis and Nosema ceranae. Nosema is a spore-forming, fungus-like, intra-cellular parasite of honey bees and other specific hosts (Nosema bombi in bumble bees).


Life Cycle

Bees ingest Nosema spores which germinate in the midgut (digestive tract). The fungus then penetrates a cell in the lining of the midgut and grows by absorbing nutrients from the cell. The fungus grows and divides inside the cell until all the nutrients are absorbed, which triggers sporulation. Some of the spores then germinate inside the cell and pass thru the cell walls to infect other tissues. Other spores pass through the digestive system and are excreted. Damaged cells in the digestive tract of the bees are subject to secondary infections, and dysentery (brown diarrhea spots on the combs, frames, and exterior of the hive) is a common sign of Nosema apis but not N. ceranae.


Effects on Colony


Worker bees, when infected at less than a week of age, do not digest food properly and cannot produce brood food secretions. These bees become foragers at an early age, and their life spans can be reduced by 78%. Young queens that become infected are normally superseded within one month. In climates where winter temperatures prevent supersedure for months, colonies can go queenless and dwindle in spring.




Diagnosis is by laboratory examination using a microscope to compare the guts of normal bees with bees from the hive being tested. Testing can reveal probable numbers of spores in the bee’s guts. One million spores per bee are associated with increased winter losses.


Treating Infected Colonies


The timing of treatment is based on the best time to prevent comb contamination and infection of bees that clean up fecal deposits while expanding the brood nest. Later in summer, when bees are defecating outside, N. apis normally cannot be detected. A few bees are infected all year, but only the late-season bees are of consequence. When late-season bees develop high infection levels, they defecate on the combs in October, November, and December.


Fumagillin is an antimicrobial agent isolated from the fungus Aspergillus fumigatus.  The fungus is found naturally in soil and decaying organic matter. Fumagillin is sold under the brand name Fumidil-B or Fumagilin-B and is fed to bees in syrup. Fumagillin prevents the Nosema spores from reproducing in the honey bee gut but does not kill them.


 Nozevit Plus is an all-natural and organic whole-plant polyphenol honey bee food supplement intended to help maintain honey bee intestinal integrity and promote bees' long-term health and vitality. Nozevit Plus is available for purchase online and thru your bee supplier.


Essential Oil Treatment and Prevention (courtesy of the Fat Bee Man)


1      cup water

2      teaspoons Tea Tree Oil

1      teaspoon Wintergreen Oil

1 – 3   drops of Lemongrass Oil


1.     Place the above ingredients in a glass blender and mix on high for 4 or 5 minutes to emulsify.


2.     To the mixture above, add enough water to make one half gallon total.


3.     To use: Add one cup of the diluted mixture from step two above to one gallon of sugar syrup and feed to each hive three to four times in fall and spring.


Decontamination of Equipment


 Nosema apis spores are susceptible to irradiation or fumigation with glacial acetic acid. The spores resist natural elements except for sunshine and persist for years. Nosema apis spores may be killed by heat. Equipment must be held at or above 120 degrees Fahrenheit for 24 hours or 140 degrees Fahrenheit for 15 minutes. Beeswax melts at 145 degrees Fahrenheit, so you must precisely control the temperature.


Nosema ceranae is susceptible to cold.  The spores of Nosema, all life stages of the greater wax moth, and all stages of the small hive beetle are killed by freezing to 32 degrees Fahrenheit or lower overnight.


Prevention for Nosema


Maintain large colonies going into winter

Provide good ventilation, so hives stay dry

Ensure hives have adequate stores of honey and pollen

Keep hives in a sunny location to encourage cleansing flights

Treat for Varroa mites.  Bees weakened by mites are more susceptible to disease.

Replace old combs with new ones to prevent disease build-up.