Fungal spores of the causative agent of Chalkbrood, Ascophaera apis, develop into mycelia in capped cells - eventually engulfing the entire larvae giving a fluffy cotton-wool appearance.
The larval cadaver shrinks and dries to form a white or grey-black chalk-like mummy [Fig 1]. Frames with a high level of Chalkbrood rattle, in addition holes in cell cappings are found (cut by nurse bees when retrieving the mummy to discard it) [Fig 2]. These discarded mummies can be found near the hive entrance of infected colonies [Fig 3].
Reducing humidity and condensation by elevating hives and through the use of a ventilated floor can prevent Chalkbrood infestations, as can positioning colonies in bright, sunny areas with low moisture levels [Fig 4]. Old comb is particularly susceptible so frames should be replaced at least every three years.
No commercial treatment specifically targeting chalkbrood is currently available, but Apiguard has been shown to be effective. As ever, good beekeeping practices can help prevent or reduce the impact of chalkbrood and general stress factors should be minimised. Hives should be kept well ventilated and free from damp, with plenty of food. Where persistent chalkbrood infections occur re-queening is advisable. Workers showing a high level of hygienic behaviour are less prone to chalkbrood infection.