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Chalkbrood Disease 1: What is it and how is it spread?

Chalkbrood Disease in Australia

Australian beehives are “succumbing to the deadly chalkbrood disease at a faster rate than their overseas counterparts, despite having better hygiene practices”, reported the ABC in March this year.

Honey bee nutrition is suspected to be a key aspect, but more research is needed. First, what exactly is Chalkbrood disease?

Chalkbrood disease: What it is and why it’s a problem

  • Chalkbrood disease is a fungal disease that infects and kills honey bee brood (bee larvae), significantly weakening colony numbers
  • It is caused by the fungus Ascosphaera apis, a fast-acting, spore-forming fungus
  • Infected larvae do not usually show signs of disease but will die once sealed in their cells as pupae
  • It takes just days for the fungus to puncture the larvae skin and mummify the larvae
  • It rarely kills entire colonies, but weakened colonies have reduced honey yields and are more susceptible to other bee pests and diseases
  • Chalkbrood disease is confirmed in all Australian states except the Northern Territory

How is Chalkbrood spread?

  • The fungal spores that cause Chalkbrood are tiny and highly infectious.
  • The spores are easily spread between hives through the drifting and foraging of drones and worker bees.
  • This risk is increased when workers rob other hives that are weak and sick.
  • When workers uncap mummies the spores are quickly spread through the hive
  • Infected foraging bees may also leave spores at floral and water sources that other bees then visit
  • However, according to BeeAware, spread of the fungus mostly occurs through the activities of beekeepers.
  • Spores are transferred between apiaries on contaminated equipment, in pollen and in water.
  • Shifting bees on trucks with an open entrance can also spread the fungal spores.
  • The Chalkbrood spores may remain viable for up to 15 years, or even more in equipment and soil

There are conditions that make beehives more susceptible to Chalkbrood. According to BeeAware, the risk is higher when the colony is under stress from cool, wet weather or poor nutrition. According to the Australian Beekeeping Guide, the brood is more susceptible to infection if it is ‘chilled’.

As such, Chalkbrood is more common in the spring when the brood nest is rapidly expanding, since a smaller honey bee workforce cannot maintain brood nest temperature as easily.

Next week we take a look at identifying, treating and managing Chalkbrood in the hive.

chalkbrood disease 1
Brood comb in a frame.

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