Honeybee Diseases

Lee S Rosen  –  What are the common Honeybee Diseases

Honeybee Disease - baldbroodwithwax

American Foulbrood is a highly lethal and contagious disease of honey bees, caused by the spore-forming bacteria Bacillus larvae.  The disease causes larvae to die after cells are capped.  Worker bees have difficulty trying to remove the dead larvae, and often contaminate the hive with additional spores.  As the colony weakens and dies out, bees from other colonies (sometimes from several miles away) will be apt to rob out the remaining honey.  As they travel through the hive, they become contaminated as well, and introduce the bacterial spores to their colony as well.  Antibiotics do not kill this bacteria or prevent the disease, but merely hold it off temporarily.  Colonies known to be infected with American Foulbrood must be destroyed by burning to prevent the disease from spreading to a other hives and other nearby apiaries.

Nosema is a condition caused by the microsporidia Nosema apis or Nosema cerana.  This microbe attacks the cells in the wall of a honey bee’s stomach, where it reproduces and attacks repeatedly, eventually destroying the stomach lining.  This cycle of infection takes some time to build up, during which the bee is increasingly unable to digest food.  As a result, the bees become weaker and their hind-guts fill with fecal material.  Nosema disease has traditionally been associated with long-lived overwintering bees, confined in the hive for extended periods of time.  If unable to take periodic cleansing flights (due to cold weather), severe dysentery symptoms may become apparent in the hive and around the entrance.  Housecleaning activities of healthy bees often cause them to ingest spores, initiating their infection.  Typically the disease disappears once spring weather allows for regular cleansing flights and spring pollen plants induce increased brood rearing.  However, new strains appear to be more virulent, and may attack a colony during any time of year, especially if the colony health has been compromised by pesticide exposure or other factors.

Chalkbrood is a brood disease caused by the fungus Ascophaera apis.  Beekeepers typically notice the condition in early spring when workers remove and discard infected larvae near the entrance of the hive.  There is no medical cure for chalkbrood disease, but it is rarely serious to the colony.  As spring brood rearing increases, a colony typically out-grows the condition.

Sacbrood Virus affects only the honey bee larvae, and is mildly contagious within the hive.  Typically, the disease can be stopped by requeening a colony.