Chalkbrood disease

Chalkbrood disease is an infectious fungal condition affecting honey bee colonies, caused by the ascomycete fungus Ascosphaera apis. It is essential to clarify that this pathogen affects honey bee larvae exclusively, meaning it is a significant veterinary issue in apiculture rather than a botanical plant disease. The fungus invades the larval tissues, leading to death and transforming the larvae into hard, chalk-like mummies.

The primary hosts for this pathogen are honey bees (Apis mellifera). Transmission occurs when bee larvae ingest fungal spores along with their food. Once inside the larval gut, the spores germinate, and the mycelium rapidly consumes the host's body. Eventually, the larva dies and becomes encased in white fungal growth, which later turns gray or black as the fungus produces spores, resembling a piece of chalk.

Clinical symptoms are marked by the presence of white, gray, or black mummified larvae found on the hive floor or within the brood cells. In the early stages, the larva swells and becomes covered with a white, cotton-like mycelium. Worker bees typically attempt to remove infected larvae from the hive, so keepers often see these characteristic mummies at the hive entrance or on the landing board during routine inspections.

The development and spread of Ascosphaera apis are heavily influenced by environmental stressors within the hive. High humidity, poor ventilation, and cold, fluctuating temperatures create an ideal climate for the fungus to thrive. Furthermore, the overuse of antibiotics can suppress the beneficial gut microflora of the bees, making the colony significantly more susceptible to opportunistic fungal infections.

The economic impact of chalkbrood disease is severe, as it causes a decline in colony strength and a substantial reduction in honey production. Untreated, chronic infections can lead to the total collapse of a honey bee colony. Effective protection strategies include:

• Maintaining strong, healthy colonies with young, productive queens.
• Ensuring proper hive ventilation to reduce moisture levels.
• Regular disinfection of beekeeping equipment.
• Applying approved antifungal treatments during active outbreaks.