Ascosphaera apis (Aa) is the scientific name for chalkbrood and is experienced by beekeepers world wide. The ascospores (2.7μm to 3.5μm in size) are spread by trophallaxis and nurse bee activities. These ascosphores can remain dormant but viable in the black mummified bodies for up to 15 years.

When consumed by bee larvae the spores germinate in the ventriculus, cross through the peritrophic membrane and penetrate the epithelial gut lining when the mycelium invades all the larval tissue. The larvae become soft whilst in the cells and covered in fluffy white mould. The bees will try to rid the brood of diseased cells. They pull out chalkbrood infected larvae which will be found on the hive floor, The black, older mummies contain ascospores whilst the younger white ones do not. For this reason it is important to remove the mummies as quickly as possible.

Although it is a disease of larvae not pupae the diseased larvae may be capped before the worker bees realise there is an issue. For this reason mummies may be found in cells which have been uncapped.

Colonies may have the ascospores present in the hive but it requires contributing stressor factors for the occurence of overt chalkbrood disease. Keep the hive well ventilated by using an open mesh floor if possible. Fungi need humid conditions to thrive. Other diseases or pests may cause chalkbrood to flourish. Poor apiary hygeine encourages this disease.

If your worker bees do not remove the chalkbrood infected larvae consider replacing the queen with one which produces hygenic bees.
Scientific Beekeeping
A B Jensen (
Research Methods for Fungal Disease in Apis Mellifera