Chalkbrood is a mycosis (a disease caused by a fungus), which affects bee brood.
It is an infectious disease of the larvae, and is caused by a fungus called “Ascosphaera apis”. It looks like pieces of chalk in the comb and is chalky-white initially, but some become dark blue-grey or almost black as in the picture to the right.
The disease mostly occurs in the spring and worsens in the summer, generally disappearing in the autumn when the queen slows down laying. It causes the death and mummification of sealed brood (see the picture to the left) and seriously weakens the colony, affecting honey output and the general health and well-being of your bees. Fortunately, it only very rarely kills a colony.
The larvae in the comb ingest the spores of the fungus with their food, allowing the fungus to get into the intestine of the larvae. The young infected larvae do not usually show signs of disease, but they usually die within two days of being sealed in their cells or die as prepupae. The spread of chalkbrood within the colony is very limited, and the fungus only seems to thrive on honeybee larvae and does not appear to affect the adult bees.
Pieces of Chalkbrood
The fungus grows best when the brood is chilled, so keeping a constant temperature within the hive is a major factor that can help to keep infection at bay. The spread is usually due to the accumulation of mummies (the white chalky remnants of infected bee larvae) and the bees being unable to remove the dead bodies from the hive fast enough.
It is mostly spread between colonies through the activity of the beekeeper, on clothing and tools – another reason why good sanitary practise and careful beekeeping husbandry is essential. The spores can remain dormant for more than 3 years anywhere in the colony, including the wax foundation and frames, this means that the disease can return in previously infected colonies.
Chalkbrood is not just a problem in the UK, but is present on nearly all continents. The only place chalkbrood is not a problem is in Antarctica, and that’s only because there are no bees there! Some beekeepers are lucky enough that their colonies never suffer from chalkbrood, but it can be a harsh and serious problem if one of your colonies does!!
( Article under review )
Signs in the colony
Adult bees will tear down the cappings of the dead larvae to reveal the chalky white mummies. These lie along the length of the cell and often take on the hexagonal pattern.
The bees remove the mummies from the hive and they can often be seen on the hive floor and outside the hive.
The mummies are usually found scattered throughout the brood nest and can reach high numbers.
’Mummies’ on hive floor
The disease often appears in a peak in the late spring/early summer as the colony expands and the brood outnumber the bees. This is because there are insufficient bees to maintain the temperature and control the ventilation (CO2 build-up).
Care needs to be taken to differentiate chalk brood from mouldy pollen but this is usually concentrated around the periphery of the brood nest and tends to be a different colour.
This is done by the typical appearance of the larvae
Chalk brood spores are sticky and will attach to the comb and bees as they remove the infected larvae.
They are also readily transmitted by robbing/drifting bees. The beekeeper can also spread the disease on hive tools and comb transfer.
The disease is considered to be endemic in Britain but levels of infection will vary from colony to colony. The beekeeper has to aim to keep the infection level down.
There are no fungicides available for the larvae and spores on the bees and combs are unreachable.
Combs can be fumigated with acetic acid but heavily affected comb should be destroyed.
Viable spores will still be present on the bees and may be present in honey stores.
In severe cases re-queening from a disease free colony is recommended.
Because of the temperature/ventilation aspect of the disease it is more likely to occur in small colonies or nuclei. Ensuring that there are sufficient bees will reduce the risk.
Some strains of bee are more resistant and queens from these should be selected as part of an integrated breeding policy
Cause: Ascosphaera apis, a fungus. Effect: Chalkbrood disease affects only the brood. The diseased larvae are usually found on the outer edges of the brood nest. Workers, drones, and queens are all susceptible to the disease. Symptoms: The affected larvae are usually found on the outer fringes of the brood area. Brood cells can either be sealed or unsealed. Diseased larvae are stretched out in their cells in an upright condition. Typically, larvae dead from chalkbrood disease are chalk white, hence the name chalkbrood. Sometimes the diseased larvae can be mottled with brown or black spots, especially on the ventral sides. The color variation is from the brown to black color of the fruiting bodies (spore cysts). Transmission: The spores of Ascosphaera apis are ingested with the brood food provided by the nurse bees. The germination of the spores and proliferation of the fungus covers the larva with a white mycelium. Spores of Ascosphaera apis remain viable for years. Consequently, the infection source could be present in the cells used to rear brood. Chalkbrood appears to be most prevalent in the spring when the brood area is increasing. Chalkbrood normally does not destroy a colony. However, it can prevent normal population build-up when the disease is serious. No treatment is presently available for the control of chalkbrood. The disease usually disappears or is reduced as the air temperature increases in the summer.