European Foulbrood (EFB) is a bacterial disease that targets honeybee larvae. This infection weakens colonies, leading to significant economic losses for beekeepers. EFB primarily affects the developing brood, disrupting the colony’s ability to replace its workforce and maintain a stable population. Left unmanaged, the disease can become highly contagious, leading to a substantial decline in colony health and, in severe cases, the complete loss of the hive.
The Bacterial Cause and Spread
The pathogen responsible for European Foulbrood is the bacterium Melissococcus plutonius, a non-spore-forming organism that multiplies in the digestive tract of young honeybee larvae. Larvae younger than three days old are the most susceptible to infection after ingesting contaminated food. M. plutonius rapidly proliferates in the larval midgut, competing with the bee for nutrients and causing the larva to die from starvation.
Transmission within the hive occurs when adult nurse bees clean the infected cells and inadvertently contaminate their mouthparts. These contaminated nurse bees then feed the bacteria to other developing brood. The bacteria can persist for years in wax, honey, and hive equipment. Transmission between colonies is facilitated by beekeepers moving contaminated equipment, as well as by natural means like drifting and robbing bees.
Identifying Symptoms in the Brood Nest
Diagnosis of European Foulbrood relies on observing distinct visual symptoms within the brood nest. Healthy larvae are normally pearly white and lie in a curled “C” shape at the bottom of the cell. Infected larvae change color from white to a dull yellow, then brown, losing their plump, segmented appearance. They often adopt twisted, unnatural positions, sometimes stretched out or melted against the cell wall.
The disease characteristically strikes the larvae before the cell is capped, making it a disease primarily of the unsealed brood. In advanced cases, a noticeable sour or stale odor, sometimes described as ammonia-like, may emanate from the hive. When the dead larvae dry out, they form a rubbery scale that is loosely attached to the cell wall and is relatively easy for the bees to remove. This pre-capping death is a crucial diagnostic feature, as American Foulbrood typically kills the larva after the cell has been sealed.
The Effect on Hive Productivity and Survival
The larval infection results in a failure to produce the next generation of adult worker bees, diminishing the overall colony population. Since the larvae die before emerging, the colony’s workforce shrinks, resulting in a “spotty” and erratic brood pattern where healthy and dead larvae are intermingled. A reduced workforce means the colony cannot effectively forage, process nectar, or maintain the hive, drastically cutting down on honey production.
The colony becomes progressively weaker as the season advances and the adult bee population declines. This diminished strength makes the hive more susceptible to other pests and diseases, and less able to withstand environmental stress. A colony severely weakened by EFB often fails to store enough resources to survive the winter, potentially leading to total colony collapse.
Management and Control Strategies
Control strategies for European Foulbrood involve a combination of non-chemical and chemical interventions. A common cultural method is the “Shook Swarm” technique, which involves moving the adult bees onto new, clean equipment and foundation. This process removes the bees from the contaminated comb, forcing them to start fresh and allowing the colony to recover.
Requeening the colony with stock bred for hygienic behavior is another effective long-term approach, as these bees are more likely to detect and remove diseased larvae. Beekeepers must also focus on good sanitation, including regular cleaning of tools and avoiding swapping frames between colonies.
In jurisdictions where permitted, the antibiotic oxytetracycline may be used to suppress the bacterial population and allow the colony to recover. While antibiotics quickly reduce the bacterial load, they do not eliminate the bacteria, which can remain dormant in the hive. Their use requires strict adherence to withdrawal periods to prevent honey contamination.