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Nosema Disease in Bees

Causative Agent


            Nosema disease is caused by one of two fungi named Nosema apis and Nosema ceranae. Nosema are spore forming, fungus-like, intra-cellular parasites 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 penetrate 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 Young queens that become infected are normally superseded within one month.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 away 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 is associated with increased winter loses.


Treating Infected Colonies


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 levels of infection 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 the long term health and vitality of bees. Nozevit Plus is available for purchase on-line 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 Lemongrass Oil


1.         Place above ingredients in 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 are very resistant to the natural elements with the exception of 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 need to 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 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.

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