What are the signs?
When observing the hive, inspecting the entrance and bottom board/mesh you may come across greyish-white pellets or even dark grey to black ( when fruiting bodies are present) the size of larvae. They look like small lumps of chalk and hence the aptly named ‘Chalkbrood’. Closer inspection of the bee frames in the colony may reveal certain cells with the caps removed showing these pellets inside.
The disease is characterised by the infected brood, called ‘mummies’ so named by their appearance. Larvae die of chalkbrood after the cells have been capped.
Chalkbrood initially appears fluffy and swollen, but will shrink and become hard.
Young larvae usually die within a couple of days of having been sealed in their cells, otherwise they die as propupae.
So what is Chalkbrood?
Chalkbrood is a infectious fungal disease which is caused by Ascospaera apis and which appears to be on the increase. Only the larvae of Apis mellifera are particularly susceptible and Ascospaera apis does not multiply in adult bees and rarely kills a colony, but it will weaken a colony and reduce honey yield by up to 30%.
How is it transmitted?
Spores are highly infectious and carried in contaminated pollen by infected foraging bees with spores left at floral and water sites, drifting bees and drones. Ascospaera apis is ingested by the bee larvae with their food. Usually the spread is limited to within the colony. It is known that Ascospaera apis grows best when the brood is chilled, and the correct temperature within the brood box is an important factorin limiting infection. As the disease has a limited ability to spread, most transmission occurs through the activities of beekeepers – exchanging equipment and bees, feeding contaminated honey and using contaminated tools and gloves.
Stressing bees contributes to increasing the susceptibility of Chalkbrood. Changes in brood temperature can trigger the disease. If nurse bee numbers become insufficient to cope with extreme weather conditions the brood may be left unattended. You may observe the first larvae to be affected are those around the edges of the brood where the temperature may be higher or lower. Stress of any kind can cause the Chalkbrood to become apparent.
Common causes of stress are: -