Common Bee Diseases and Pests

Colony disease is the part of beekeeping where the stakes are highest and the information is most often wrong. This article covers what you can reasonably identify yourself, what requires expert confirmation, and what you must report.

Foulbrood: the serious ones

Foulbrood diseases affect the brood and are the most destructive conditions in beekeeping. There are two forms and they behave very differently.

American foulbrood (AFB)

Caused by the spore-forming bacterium Paenibacillus larvae. Spores remain viable in equipment for decades, which is why AFB is treated so severely. Infected larvae die after the cell is capped, and the capping becomes sunken, darkened and often perforated.

• Sunken, greasy-looking, discoloured cappings with irregular perforations.
• Larvae that die in the upright position and turn brown.
• A ropy consistency when a larva is drawn out with a matchstick — the classic field test.
• A foul odour in advanced cases.
• In the late stage, scales that adhere tightly to the lower cell wall.

European foulbrood (EFB)

Caused by Melissococcus plutonius and typically affects unsealed larvae, which die curled in unusual positions. It is less destructive than AFB and, in some regions, can be managed with husbandry rather than destruction. It is still notifiable in many countries.

• Larvae dying before capping, often in a twisted or displaced position.
• Discoloration from white through yellow to brown.
• A scattered, patchy brood pattern.
• Often no foul odour, which makes field diagnosis harder.

Fungal diseases

Chalkbrood

A fungal infection that turns larvae into hard, white or grey mummies, which are then removed by workers and found on the floor or the landing board. It is usually a stress indicator rather than a primary killer — it appears in chilled, damp or weak colonies and clears when conditions improve.

• Hard, chalky mummies, white at first and darkening to grey or black.
• Mummies visible at the entrance or on the bottom board.
• Usually associated with a chilled nest, poor ventilation or a small population.

Improve ventilation, reduce humidity, and address the underlying colony weakness. Requeening sometimes helps. Chalkbrood rarely requires treatment.

Nosema

A microsporidian infection of the adult bee gut, causing dysentery and shortened lifespan. Signs include faecal staining around the entrance and on the combs, and a colony that dwindles without an obvious cause. It is associated with damp, poor ventilation and long confinement.

Viral diseases

Viral infections in honey bees are mostly managed indirectly, because there is no treatment for the virus itself. The lever you have is the vector.

• Deformed wing virus: crumpled, stubby wings and shortened abdomens. Strongly associated with Varroa, and a sign of high mite pressure.
• Sacbrood: larvae that fail to pupate and become a fluid-filled sac. Usually self-limiting in strong colonies.
• Chronic bee paralysis virus: trembling, hairless, black shiny bees crawling at the entrance. Associated with crowding and stress.
• Black queen cell virus: dark, sunken queen cells. Associated with Nosema and Varroa.

For all of these, the response is the same: control Varroa, relieve stress, and support the colony's ability to cope. A strong, well-fed colony with low mite pressure manages most viruses without intervention.

Pests

Biosecurity: not spreading it yourself

• Never feed honey or honey-derived syrup to bees. It is the classic route for spreading foulbrood spores.
• Never move frames or comb between apiaries without a reason and without knowing the disease status of both.
• Clean tools between hives, and especially between apiaries. Scraping and flaming are both effective for many pathogens.
• Keep a separate hive tool per apiary if you work more than one site.
• Do not put wet supers back on a hive if there is any disease concern.
• Retire old, dark comb on a rotation — it harbours pathogens and pesticide residues.
• Buy colonies and queens from breeders who test and disclose disease status.