Common Bee Diseases and How to Identify Them

Keeping bees healthy requires vigilance against various diseases and pests that can devastate colonies. While varroa mites get most attention, beekeepers must also recognize and manage bacterial, viral, and fungal diseases. Early detection and proper treatment are essential for colony survival. Here's your guide to common bee diseases and how to protect your hives.

American Foulbrood (AFB)

American Foulbrood is the most serious bacterial disease affecting honeybees. Caused by Paenibacillus larvae, AFB is highly contagious and fatal to colonies if left untreated. The bacteria form resilient spores that can survive for decades in equipment, making prevention and early detection critical.

Symptoms include irregular brood pattern with scattered dead larvae, sunken and perforated cappings that appear greasy or darkened, and a characteristic foul smell. The "ropiness test" is diagnostic: insert a small stick into a suspected cell and slowly withdraw it. If the larval remains stretch into a rope-like strand an inch or more, AFB is likely present.

AFB requires aggressive management. In many regions, infected colonies must be destroyed by burning to prevent spread. Some areas allow antibiotic treatment, but this only suppresses symptoms without eliminating spores. Prevention through good hygiene, avoiding used equipment of unknown origin, and regular inspections is essential.

European Foulbrood (EFB)

European Foulbrood, caused by Melissococcus plutonius bacteria, is less severe than AFB but still serious. Unlike AFB, EFB typically affects younger larvae before cells are capped. Symptoms include twisted larvae that appear melted in their cells, a sour smell (less offensive than AFB), and larvae that are easily removed from cells without ropiness.

Strong colonies can sometimes overcome EFB on their own, especially during good nectar flows. Requeening with hygienic stock often helps, as some bee lines show resistance. If treatment is necessary, antibiotics may be used where legal, but improving colony strength and genetics is the long-term solution.

Chalkbrood

Chalkbrood is a fungal disease caused by Ascosphaera apis that affects bee larvae. Infected larvae die and become hard, chalk-like mummies that are white initially, later turning gray or black. You'll find these mummies on the bottom board or at the hive entrance as bees remove them.

Chalkbrood often appears during cool, damp conditions and typically affects weak or stressed colonies. It's rarely fatal but can significantly reduce colony strength. Management focuses on improving hive conditions: ensure good ventilation, reduce moisture, requeen with resistant stock, and strengthen weak colonies through feeding or combining with stronger hives.

Nosema

Nosema is a microsporidian parasite that infects adult bee digestive systems. Two species affect honeybees: Nosema apis and Nosema ceranae. Symptoms include dysentery (brown streaking on hive fronts and frames), reduced colony strength, decreased lifespan of adult bees, and poor spring buildup.

Diagnosis requires microscopic examination of bee samples. Prevention includes ensuring adequate ventilation to reduce moisture, providing good nutrition, and avoiding stress on colonies. Some beekeepers use fumagillin treatment where legal, though its effectiveness against N. ceranae is debated. Strong, well-nourished colonies generally manage nosema better than weak ones.

Deformed Wing Virus (DWV)

Deformed Wing Virus is closely associated with varroa mite infestations. Mites transmit the virus while feeding on bee hemolymph. Infected bees emerge with crumpled, useless wings and shortened abdomens. They cannot fly and typically die within days.

DWV presence indicates varroa mite problems. There's no direct treatment for the virus, so management focuses on controlling mite populations through integrated pest management strategies. Reducing mite loads dramatically reduces DWV incidence and severity.

Sacbrood

Sacbrood is a viral disease affecting larvae. Infected larvae fail to pupate and instead die in their cells, forming a fluid-filled sac. The larva's head turns dark while the body remains light, creating a characteristic gondola or Chinese slipper shape when removed from the cell.

Sacbrood is usually self-limiting in strong colonies with good hygienic behavior. Bees remove infected larvae, and the disease often disappears on its own. Requeening with hygienic stock helps if the problem persists. Maintaining strong, healthy colonies is the best prevention.

Stonebrood

Stonebrood is a rare fungal disease caused by Aspergillus species. Infected larvae become hard and stone-like, covered with fungal growth that may be white, yellow, green, or black depending on the Aspergillus species. The disease is uncommon and usually affects only a few larvae in stressed colonies.

Management involves improving hive conditions, ensuring good ventilation, and reducing stress. Remove affected frames and strengthen the colony. Stonebrood rarely causes serious problems in well-managed apiaries.

Prevention Strategies

Preventing disease is easier than treating it. Maintain strong colonies through good nutrition, adequate space, and minimal stress. Conduct regular inspections to catch problems early. Practice good hygiene by cleaning and sterilizing equipment, especially when moving equipment between hives. Avoid buying used equipment of unknown origin, as it may harbor disease spores.

Select for disease-resistant genetics by requeening with stock known for hygienic behavior and disease resistance. Ensure adequate ventilation to prevent moisture buildup, which encourages fungal diseases. Manage varroa mites aggressively, as they vector multiple viral diseases.

When to Seek Help

If you suspect disease but aren't certain of the diagnosis, contact your local bee inspector, agricultural extension office, or experienced beekeepers. Many regions offer free disease inspection services. Accurate diagnosis is essential for proper treatment and preventing spread to other colonies.

Some diseases are reportable in certain jurisdictions, particularly AFB. Know your local regulations and report suspected cases as required. This protects not only your apiary but the broader beekeeping community.

Record Keeping

Maintain detailed records of inspections, symptoms observed, and treatments applied. These records help you track disease patterns, evaluate treatment effectiveness, and make informed management decisions. Note which colonies show disease resistance, as this information guides breeding and requeening choices.

Disease management is an ongoing aspect of beekeeping. By learning to recognize symptoms early, maintaining strong colonies, and practicing good hygiene, you can minimize disease impact and keep your bees healthy and productive. Prevention and early intervention are always more effective than trying to save severely diseased colonies.