Chalkbrood disease of honey bees
Chalkbrood is a fungal disease of honey bee brood that infects the gut of the larvae. It is caused by a spore-forming fungus named Ascosphaera apis that is consumed along with larval food. Although chalkbrood disease can affect workers, drones, or queens it most often occurs in workers and drones.
Chalkbrood is frequently seen in late spring when colonies are expanding rapidly, the weather is still cool, and there may not be enough nurse bees to keep the brood warm. It often disappears spontaneously as summer temperatures rise. Although chalkbrood rarely destroys a colony, it can weaken a colony and cause reduced honey production.
What does chalkbrood disease look like?
- Larvae become chalk-white and are often covered with cottony filaments
- The white coloration may eventually give way to a gray or black, depending on the life stage of the fungus
- It often appears at the perimeter of the brood nest
- Infected or dead larvae may be seen at the hive entrance or in pollen traps. The dead and hardened larvae are referred to as “mummies.”
How does the disease enter the hive?
- The disease is transmitted by spores that are readily moved from colony to colony on infected pollen, robbing bees, drifting bees, or beekeeping equipment.
- Since spores remain viable for many years, they can persist in a hive until the conditions become right for growing.
What conditions allow the chalkbrood fungus to grow?
- Excessive moisture in the hive, caused by poor ventilation
- Cool temperatures
- Inadequate colony nutrition (a healthy colony is more apt to keep the hive free of mummies and keep the brood nest warm)
- Colonies weakened by other disease organisms
- Poor genetic resistance
How can chalkbrood be prevented or reduced?
- Increase ventilation in the hive
- Replace old, blackened brood combs as these may harbor chalkbrood spores
- If a colony lacks sufficient food stores, supplement with good-quality feed
- Replace queens with stock bread for hygienic behavior and/or disease resistance
Some reports have indicated that the incidence of chalkbrood disease is increasing. The increased frequency may be related to poor nutrition, higher disease loads, and increased colony stress that seems to be occurring in honey bees around the globe.
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