Chalkbrood

Chalkbrood is caused by the fungus Ascosphaera apis.

Originating in Europe, chalkbrood has been detected in all states and territories in Australia except the Northern Territory.

The prevalence of the disease can vary from region to region over time.

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. 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.

In cells, chalkbrood may appear in:

• unsealed cells (as for sacbrood)
• sealed cells—light or dark sunken cell caps, many with perforations (pin holes).

In a heavy infection, brood pattern is scattered.

Chalkbrood symptoms may be mistaken for other brood diseases, such as:

• American foulbrood (AFB)
• Sacbrood
• European foulbrood (EFB)
• white pollen.

Chalkbrood spores remain viable for up to 15 years or more in equipment and soil.

Chalkbrood spreads from one hive to another through:

• infected tools, hives or hive components
• infected bees entering the hive through drift or robbing
• bees visiting water and floral sources where other infected bees have visited.

Stress can trigger chalkbrood disease including:

• high and low temperatures
• wet or dry conditions
• poor nutrition
• failing queen
• poor hive management
• moving hives.

If there are not enough nurse bees to cope with weather extremes (cold clustering and heat fanning), the brood may be left unattended which causes a change in brood-nest temperature. Usually the first larvae affected are those around the edges of the brood where the brood temperature may be higher or lower.

Inspect brood regularly—remove each frame in your brood box and inspect them for signs of disease.

You can send samples to the Biosecurity Sciences Laboratory to determine whether your hives are infected with chalkbrood.

No registered chemicals are available for chalkbrood control.

Use management practices to maintain strong healthy colonies to reduce the effects of chalkbrood:

• remove 'mummies' from bottom boards and around the entrance
• destroy combs containing large numbers of 'mummies'
• supply new combs every 3–4 years
• provide good ventilation in hives
• add young adult bees to hives
• reduce the number of supers on the hive over winter
• feed sugar syrup, fresh uncontaminated pollen or supplements
• maintain strong hives by regular re-queening
• reduce or prevent interchange of hive materials
• do not use the same site each year—if possible shift the apiary site slightly.

Good hygiene also helps:

• change clothes
• disinfect smokers, boots and hive tools using chlorine bleach between apiaries or infected hives.

Some hives are more affected by chalkbrood than others. Most of this variation in susceptibility is due to differences in the ability of bees to uncap and remove diseased brood.

Select or obtain queen bees from hives that show resistance to this disease to reduce the effects of chalkbrood.