Macroscopic diagnosis

The typical symptoms observed in a colony affected by chalkbrood are irregular wax cappings over the brood and uncapped cells scattered over the brood frames (Fig. 1). The cell capping may also have small holes or appear slightly flattened. Chalkbrood mummies can often be seen in the combs, at the hive entrance or found on the bottom board (Fig. 2). Observation of combs may reveal different stages of the disease; fresh larval cadavers covered with white cotton-like mycelium and desiccated mummies that appear as white, dark or a combination of white and dark solid clumps. White desiccated mummies look like small pieces of chalk giving rise to the name of the disease and dark mummies are coloured by fungal fruiting bodies.

Diagnosis in the field is generally based on the presences of chalkbrood mummies (as described above). Following field diagnosis, a microscopic examination is usually required to confirm the presence of spore cysts in the samples using the microscope slide smear technique. The spores can be mounted on a microscope slide with a drop of distilled water and observed at 100-400 x magnification.

Fig. 1. A brood frame from a honey bee colony with clinical symptoms of chalkbrood and a close up insert of fresh mummies. In many cells chalkbrood mummies have been partly removed by the worker bees.  Photos: F Padilla, J M Flores and A B Jensen.

Figure 1

Fig. 2. Dark and white chalkbrood mummies. The black mummies contain millions of new infective spores. Photo: A B Jensen.

Figure 2