Chalkbrood is caused by the ascosphaera apis fungus. The fungus infects larvae and fills them with infectious spores.

Infection method

Spores of the fungus are introduced to larvae by:
  • contaminated food
  • pollen
  • bees carrying the fungus.

Spores can be viable for 15 or more years in contaminated equipment and soil.

Age of brood affected

Larvae 3 to 4 days old are most vulnerable to infection. Both sealed and unsealed brood can become infected.


There are 2 stages of infection:

  1. Larvae take on a white, fluffy appearance. They will swell to the full dimension of the cell.
  2. Larvae change to hard, flat lumps that resemble chalk. They will darken to be a grey or black colour. At this stage the chalky larvae produce infectious spores. Adult bees will clear the chalky larvae out of the cells.


Hives will usually recover from chalkbrood by themselves.

Remove the chalky larvae from the bottom of the hive to help it recover.

To reduce outbreaks:

  • clean hands and equipment between hives
  • keep hives warm and dry
  • do not subject the bees to nutritional stress
  • re-queening.

Diagnosing chalkbrood

Chalkbrood can be diagnosed by sending:

  • chalky larvae
  • comb containing suspected chalkbrood.

Make sure sections of comb are in a waterproof container.

Send samples to:

Apiary Unit
Primary Industries and Regions SA
33 Flemmington Street
Glenside SA 5065

Page Last Reviewed: 22 Feb 2018
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