Introduction

Ascophaera apis, a fungus, causes the disease known as chalkbrood in honeybee larvae.

Infection

 

Spores of the fungus present in brood food if ingested by the bee larva germinate in the hindgut.

Spores of the fungus present in brood food if ingested by the bee larva germinate in the hindgut. However, infection can also occur by growth of the fungus through the cuticle. After the cells are capped, mycelia develop from the fungal spores and eventually engulf the entire larva, giving a white fluffy cotton-wool appearance.

The larval cadaver then shrinks and dries to a white or grey-black chalk-like mummy.

White mummies result from infection with only one sexual type of A. apis while the grey-black mummies indicate invasion by both sexual types.

Larvae are most susceptible to infection at 3-4 days of age and infected larvae die within 2 days of cell capping.

Frames with a high level of chalkbrood “rattle”. Holes in the cell cappings can be used as another diagnosis tool; the nurse bees cut holes in the cappings and later remove the entire cap in order to retrieve and throw out the mummy. In infected colonies, mummies can be found near the hive entrance after being ejected during hive cleaning.
The larval cadaver shrinks and dries to a white or grey-black chalk-like mummy
Contributing Factors

The incidence and spread of chalkbrood infection is difficult to predict. Bee colonies under stress from shortage of space, food or water, poor weather or from other infection will be more susceptible to infection. Spores of A. apis are often transferred in contaminated pollen or on drifting or robbing bees from contaminated hives. Damp cool apiary sites seem to be more prone to attack by chalkbrood and infection appears to vary with geographical region. Queen line genetics plays a part in susceptibility to chalkbrood also as colonies with workers exhibiting a high level of hygienic behaviour do not succumb to chalkbrood infection. Where hygienic behaviour and other factors are negative, colonies can be devastated by the fungus in a very short time.

Treatment

Good husbandry is important; hives should be kept well ventilated and free from damp, with plenty of food. Where persistant chalkbrood infections occur re-queening is advisable.

No commercial treatment for chalkbrood is currently available. However, Apiguard has been shown to have an effect on chalkbrood. See APIGUARD in our product section or click here...

Vita (Europe) Limited are also developing a new natural control agent for this disease, which could be available shortly.