European Foulbrood (EFB) is a disease affecting honey bee colonies worldwide, caused by the non-spore-forming bacterium Melissococcus plutonius. This pathogen infects the midgut of honey bee larvae after they consume contaminated food. The bacteria multiply within the larva’s digestive system, competing for nourishment and leading to its starvation. While adult bees are not directly impacted, they can transmit the disease within the hive. The disease is contagious and can persist in equipment, honey, and wax.
Identifying European Foulbrood in the Hive
A primary indicator of European Foulbrood is a spotty or irregular brood pattern, often described as a “shotgun” pattern. This occurs as nurse bees identify and remove sick or dead larvae, leaving empty cells scattered amongst healthy, capped brood. The disease affects young larvae before their cells are capped, so beekeepers will notice these signs in open cells.
Infected larvae undergo a distinct change in appearance. Healthy larvae are pearly white and curled in a ‘C’ shape at the bottom of the cell. Larvae with EFB become twisted or contorted within the cell walls. Their color changes from white to yellow, then progressing to brown as they decompose, and the dead larvae collapse into a semi-liquid mass.
Another diagnostic sign is a potential sour or fishy odor, though this is not always present. As the dead larvae dehydrate, they form a dark brown, rubbery scale. This scale is easily removed from the cell, which is a feature for field diagnosis.
Differentiating from American Foulbrood
Distinguishing European Foulbrood from the more destructive American Foulbrood (AFB) is an important skill for beekeepers. The two diseases are caused by different bacteria; AFB is caused by the spore-forming Paenibacillus larvae. This difference leads to very different signs, and misidentification can lead to improper management and colony loss.
The age of the affected larvae is a major point of contrast. While EFB kills larvae before the cell is capped, AFB infection kills the developing bee after the cell has been capped, during the pupal stage. This results in sunken, darkened, and sometimes perforated cappings not seen with EFB.
The appearance of the larval remains also differs significantly. AFB kills the pupa, which decomposes into a coffee-colored, gooey substance. A common field diagnostic is the “rope test,” where a toothpick inserted into an AFB-infected cell will draw out a mucousy, rope-like thread. This ropiness does not occur with EFB.
Finally, the smell and resulting scale are distinct. While EFB may have a sour odor, AFB is known for a foul smell often compared to a glue pot. The scale formed by AFB is black, hard, and adheres tightly to the cell wall, making it difficult for bees to remove.
Management and Treatment Strategies
European Foulbrood is often a stress-related disease, and its severity can depend on the colony’s overall health. A light infection may resolve on its own if the colony is strong and a good nectar flow begins. Removing stressors such as poor nutrition or hive movement can be enough for the bees to manage the infection without further intervention.
For more persistent infections, the “Shook Swarm” method is an effective non-chemical technique. This involves shaking the adult bees from the infected combs onto new, clean foundation in a sterilized hive body. This process separates the bees from contaminated brood combs, honey, and pollen, breaking the disease cycle. The old combs must be destroyed to prevent re-infection.
Requeening the colony with a new queen from a stock known for hygienic behavior is another recommended strategy. Hygienic bees are more adept at detecting and removing diseased larvae quickly, which helps to control the spread of the bacteria within the hive. This genetic trait can improve a colony’s resistance.
In some regions, antibiotics such as oxytetracycline are used to treat EFB, but this requires a veterinarian’s prescription. It is important to follow dosage instructions and withdrawal times to prevent contamination of honey. Overuse or improper use of antibiotics can also lead to resistant bacterial strains.
Prevention and Hive Health
The most effective approach to EFB is prevention through diligent apiary management. Maintaining strong, populous colonies is a primary defense, as robust hives are better equipped to manage disease. A large workforce of nurse bees can more effectively remove infected larvae before the bacteria circulates widely.
Good nutrition is fundamental to colony health. Beekeepers should ensure their hives have consistent access to diverse pollen and nectar sources. In times of dearth, supplemental feeding with sugar syrup and pollen substitutes can prevent the nutritional stress that makes colonies more susceptible to EFB.
Strict apiary hygiene is another pillar of prevention. This includes not sharing combs or equipment between hives and regularly sterilizing tools. These practices reduce the risk of cross-contamination, as the bacteria can remain viable on equipment.
Reducing colony stress also strengthens a hive’s natural defenses. This can be achieved by minimizing disturbances, ensuring good ventilation, and protecting hives from pests.