Chalkbrood is caused by the fungus Ascosphaera apis and it affects both sealed and unsealed brood.
Appearance of infection
At first, larvae are covered with a fluffy white fungal (mycelial) growth that looks like white mould on bread or very fine cotton wool. Larvae become swollen inside the cell. Later, the dead larvae dry out to become hard, white or grey/black chalk-like mummies.
Appearance in cells
- May be in unsealed cells (as for sacbrood).
- May be in sealed cells - light or dark sunken cell caps, many with perforations (pin holes).
Appearance in combs
In a heavy infection, brood pattern is scattered.
Chalkbrood symptoms may be mistaken for other brood diseases, such as American foulbrood (AFB), sacbrood, European sacbrood (EFB) or even white pollen. However, once identified there is no mistaking the appearance and consistency of larvae affected by chalkbrood.
Bees may detect dead larvae under cell caps, chew holes in cappings and remove mummies. A hive with good hygiene habits usually removes mummies within 10 days. Mummies are dropped to the hive floor and later, outside the entrance.
Spores are highly infectious and are carried in contaminated pollen by infected foraging bees with spores left at floral and water sites, by queens, drifting bees, and drones. Shifting bees on trucks with an open entrance causes drift and hence spreads disease. Spores remain viable for up to 15 years or more in equipment and soil. Use of contaminated sites and old equipment could lead to infections. Interchange of equipment by the beekeepers also spreads the disease.
A change in brood-nest temperature can trigger chalkbrood disease. When nurse bee numbers become insufficient to cope with weather extremes (cold clustering and heat fanning), the brood may be left unattended. Usually the first larvae affected are those around the edges of the brood where the brood temperature may be higher or lower. Stress of any kind can cause the signs of the disease to become apparent. Common causes of stress are:
- high and low temperatures
- wet or dry conditions
- poor nutrition
- failing queen
- poor hive management
- moving hives.
The Biosecurity Sciences Laboratory in Brisbane provides a brood-disease identification service. To use this service simply:
- cut a piece of brood comb approximately 10 cm x 10 cm square containing suspect larvae, or
- place a matchstick in the cell of suspect larva, and obtain larval material on one end of the stick. Place the matchstick in a small vial ready to send to the laboratory.
Wrap the comb or vial sample in paper (not plastic) and place in a padded postal bag or small box.
Send the specimen to:
Biosecurity Sciences Laboratory - Specimen receipt
Health and Food Sciences Precinct
PO Box 156
Archerfield BC Qld 4108
You can make personal deliveries to:
Biosecurity Sciences Laboratory
Health and Food Sciences Precinct
Specimen receipt (Loading Block 12)
39 Kessels Road
Coopers Plains Qld 4108
Include a completed Specimen advice sheet: Form A (PDF, 78KB).
With no registered chemicals available for chalkbrood control, the only means of controlling the disease is through management practices and use of disease-resistant bees.
There is no effective chemical agent effective for use against chalkbrood fungus, therefore, chemicals are not recommended for the treatment of chalkbrood in Australia.
Management practices that reduce the stress on hives also reduce the number of chalkbrood spores. Maintaining strong healthy colonies has been demonstrated to reduce the effects of chalkbrood.
Management practices which may reduce the effects of chalkbrood disease are:
- removing 'mummies' from bottom boards and around the entrance
- destroying combs containing large numbers of 'mummies'
- supplying new combs
- providing good ventilation in hives
- adding young adult bees to hives
- not allowing bees to winter in a hive that is over supered
- feeding sugar syrup, fresh uncontaminated pollen or supplements
- maintaining strong hives by regular re-queening
- reducing or preventing interchange of hive materials
- not using the same site each year - if possible shift the apiary site slightly.
Good hygiene will also help. Change clothes and disinfect smokers, boots and hive tools using chlorine bleach between apiaries or infected hives.
Use of disease-resistant bees
Some hives are more affected with chalkbrood than others. Most of this variation in susceptibility is due to differences in the ability of bees to uncap and remove diseased brood. By selecting queen bees or obtaining queen bees from hives that show resistance to this disease, the effects of chalkbrood can be reduced.
A combination of management practices that reduce stress and chalkbrood spores, maintain strong hives and use selection of queen bees that show resistance to infection are the main ways to minimise the effects of chalkbrood.