The fungus Ascosphaera apis causes chalkbrood disease in honey bees. The disease occurs in honey bee larvae fed fungal spores by nurse bees. The spores germinate in the gut and the larvae die of starvation, before the fungus grows throughout the larval body turning it into a hard “mummy”.
Chalkbrood is more common in early spring when the adult population is small and brood production is increasing. Stress, such as cool wet weather, poor nutrition, hive movements and poor queens increase the risk of chalkbrood and other brood diseases.
As with other brood diseases, the colony will have a scattered brood pattern. Larvae infected with chalkbrood usually die after capping, turning into off-white to black, hard, shrunken, chalk-like mummies that are now made up of infective fungal material. Cell caps are often perforated, as workers respond to the dead brood by removing it from the colony. The dark mummies are covered in infective spores which can remain viable for up to 15 years.
For ongoing infections you should remove all extra boxes to tighten up the colony, requeen and consider giving frames of healthy brood. In the most severe cases it may be best to euthanize the colony as long-term heavily infested colonies may never produce honey and can dwindle and die out.
Chalkbrood spores can be spread through contaminated equipment, pollen and water, robbing of chalkbrood-affected hives and drifting of drones and workers from chalkbrood-affected hives.
Beekeepers can minimise chalkbrood spread by:
- Implementing a barrier management system
- Managing weak hives and preventing robbing
- Replacing diseased combs
- Cleaning mummies from bottom boards and around the entrance
- Placing hives in a dry area facing the sun
- Regularly requeening their colonies
- Purchasing queens from bee breeders that select for disease resistance or hygienic behaviour
- Ensuring good nutrition
- Moving bees at night with adequate ventilation
- Elevate hives and lean entrance forward to prevent flooding
- Keep hives well ventilated
Beekeeping Basics – How to spot Chalkbrood in your Honeybee colony, Norfolk Honey Co
Chalkbrood disease fact sheet, Plant Health Australia
About the author Nadine Chapman