Beekeeping – Disease
Chalkbrood – a simple guide
Peter Warhurst, Apiary Section, Warwick
Fig. 1 Chalkbrood infected brood comb
Caused by:
a fungus - Ascosphaera apis.
Affects:
unsealed and sealed brood.
Appearance of infection
At first – larvae are covered by a fluffy white fungal (mycelial) growth. This is like white mould on bread or very fine cotton wool. Larvae are swollen inside the cell.
Later – dead larvae dry out to become hard, white or grey/black chalk-like mummies.
Appearance in cells
- May be in unsealed cells (as for sac brood).
- 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.
Confusion
Chalkbrood symptoms may be mistaken for other brood diseases, such as AFB, sacbrood, EFB or even white pollen. However, once identified there is no mistaking the appearance and consistency of the larvae affected by chalkbrood.
Chalkbrood
Larvae – white and mouldy; hard larvae; (mummies) white or grey/black in cells on the floor, or out the front of the hive.
AFB
Larvae – discoloured through to dark brown; unsealed or with perforated sunken discoloured cappings; ropey larvae; hard to remove scales.
EFB
Larvae – twisted around cell wall; white through to discoloured, yellow to dark brown; watery, granular larvae occasionally ropey.
Sacbrood
Larvae discoloured yellow through to black gondola shaped in capped cells or under perforated caps, easily removed.
Housekeeping
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 ten days. Mummies are dropped to the hive floor and later, outside the entrance.
Transmission
Spores are highly infectious and are carried in contaminated pollen, by infected foraging bees leaving spores at floral and water sites, by queens, drifting bees, and drones. Shifting bees on trucks with open entrance causes drift and hence spread of 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.
Stress
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 and moving hives.
Control
There are three means by which the control of the disease has been attempted:
- chemicals
- management practices
- use of ‘disease resistant’ bees.
Chemicals
There is no effective chemical agent that is effective for use against the chalkbrood fungus therefore chemicals are not recommended for the treatment of chalkbrood in Australia.
Management practices
Management practices which reduce the stress on hives also reduces 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 requeening
- 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 affected with chalkbrood more 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 which reduces stress, reduces chalkbrood spores, maintains strong hives, and selects queen bees that show resistance to infection, are currently the main ways to minimise the effects of chalkbrood.
Further information
For more information contact your apiary officer. If you suspect any brood disease or abnormality, it may be a legal requirement in your state to report the occurrence of disease to your nearest apiary officer. Also refer to DPI note Beekeeping – Disease, correct diagnosis.
Fig. 2 Chalkbrood mummies near
the entrance of the hive.
Photos by P. Warhurst DPI Warwick.
Information contained in this publication is provided as general advice only. For application to specific circumstances, professional advice should be sought. The Department of Primary Industries Queensland has taken all reasonable steps to ensure the information in this publication is accurate at the time of publication. Readers should ensure that they make appropriate inquiries to determine whether new information is available on the particular subject matter.
File No: IL0011• February 1998 • Replaces: IL98011
