Ministry of Agriculture

Apiculture Factsheet #203


General Description

Nosema disease only affects adult honey bees, by parasitizing the cell wall of the midgut.  As a result, infected bees have difficulty to absorb nutrients from ingested food, resulting in weakness and shortened life expectancy.

Field Diagnosis

  • Nosema disease is caused by a spore-forming microsporidian fungus of the genus Nosema.  Most Nosema species are common insect parasites.  Two species parasitize honey bees:  Nosema apis and Nosema ceranae.
  • N. apis has been considered an endemic parasite of the European honey bee in North America.  N. ceranae, a natural parasite of the Asiatic honey bee Apis ceranae, has recently been found to infect the European honey bee.
  • Both Nosema species have been found in British Columbia.
  • Nosema incidence in honey bee colonies peaks in early spring.
  • Infected adult bees suffer from diarrhea. The infection impairs the digestive process and may lead to bee starvation.
  • Beekeepers often fail to detect the disease because affected bees are inside the colony (during winter) or in the field, where they die.
  • In heavy infestations, the outside walls of the hives are smeared with fecal deposits.
  • Nosema is often confused with dysentery which produces similar symptoms.
  • The midgut removal test for visual examination is not sufficiently reliable because discolouration of the midgut occurs in infected and non-infected bees.

Laboratory Diagnosis

For Nosema detection, adult bees are examined microscopically or through PCR testing1.

Standard microscopic detection method:

  • Place 25 dead bees in mortar.  Add 1 ml of water for every bee.
  • Grind up, collect one droplet of solution and place on slide.  Cover with cover slip.
  • Examine slide under 100X power of compound microscope.
  • Nosema spores are large, oblong and highly uniform in shape.

To determine the level of infestation, a haemacytometer can be used to calculate the number of spores per adult bee (see Factsheet #203A - Counting Method of Nosema Spores).

To submit a sample for Nosema identification, collect at least 25 adult bees in tissue paper or paper bag (no plastic), freeze for 24-48 hours, and mail to the Apiculture office.

Control and Treatment

Nosema disease mostly occurs when bees have been confined to the hive for a long time, and when there is moisture build up and poor circulation.

Successful treatment involves antibiotic application to the colony and the cleaning of beehive equipment.

Antibiotic treatment:

The antibiotic fumagillin (trade name Fumagillin-B) offers effective control. Do not feed antibiotic to the colony unless Nosema disease has been confirmed.

Application method is as follows:

  • Dosage:  5 ml (=1 teaspoon) per treatment per colony.
  • Timing:  One treatment in fall and one treatment in spring.
  • Application method:  Applied in syrup only, 5 ml dissolved in 4.5 litres of sugar syrup per colony.  Fumagillin does not dissolve readily in water.  To prepare, add small amounts of warm water (not HOT) to the fumagillin and stir into a paste. Add water gradually and mix into sugar syrup. Mixture can be prepared a day before use. Shake container occasionally. 

The best natural defense against Nosema disease is a strong healthy colony with a prolific queen and sufficient food stores, especially pollen, in a well-ventilated hive body.

Beehive Equipment:

Boxes, inner covers and bottom boards must be scrubbed clean inside and out with hot water and soap. Scrape top and bottom bars.

Equipment can also be sterilized through irradiation at the Iotron facility in Port Coquitlam (

1 PCR = Polymerase Chain Reaction.  This test method identifies organisms by comparing a section of gene material of the test organism with a comparable piece of known composition.  The technique was developed and introduced in the 1990s and has become standard procedure in forensics, medicine and wide range of other disciplines.