European Foulbrood

Thursday 26 May 2022


Special Announcements

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Sometimes it can feel like the list of honeybee diseases is never ending, but with the proper control strategies and testing procedures, they can be managed! This week we are focusing on European foulbrood, providing information to help identify and control this disease. We’re also excited to introduce a project, by the Western College of Veterinary Medicine at the University of Saskatchewan, on European foulbrood surveillance.

European Foulbrood

European foulbrood (EFB) is a disease of honeybee brood, caused by the bacteria Melissococcus plutonius. In living larvae, the infections can be seen in the midgut, appearing chalky white instead of the typical yellow-orange. Dead larvae that have been infected by EFB have more distinct symptoms that beekeepers can use to diagnose their bees. The larvae usually die before the cell is capped and can easily be observed. Healthy larvae are white and curled in a “C” shape around the bottom of the cell. Larvae infected with EFB become yellow to brown and are twisted around the cell walls, positioned lengthwise, from the opening to the bottom of the cell. The body cavity darkens and dries into a rubbery scale that can easily be removed from the cell. The death of larvae from EFB will cause a decrease in adult honeybee populations, which will result in reduced colony strength and lower productivity for pollination services or honey production.

Honeybee larvae with EFB symptoms (from

M. plutonius is parasitic and competes for food in the honeybee larvae midgut. When there is an abundance of food for the colony, the larvae usually show no symptoms of disease, and eventually pupate and develop into adult bees. When food is scarce, larvae are not able to compete with M. plutonius and succumb to infection. Some reasons for food scarcity are prolonged bad weather, movement of colonies to poor forage locations, and having a low ratio of nurse bees to brood. For example, at the beginning of a heavy nectar or pollen flow, when the size of a colony’s brood nest outgrows the capability of the nurse bees for feeding larvae. Therefore, symptoms are typically seen in spring and late summer.

Cultural, physical, and chemical strategies should be used as an integrated pest management (IPM) approach to prevent and control EFB and reduce the impact of this disease. Cultural strategies, such as the selection of hygienic breeding stock and supplementing colonies with food, can help. Routinely replacing comb is an important strategy used for EFB, as it may reduce the amount of M. plutonius present in hives. To learn more about comb rotation, please check out our Comb Rotation Factsheet. Chemical strategies are limited to the metaphylactic use of the antibiotic oxytetracycline (OTC). As this is also an important antibiotic for human health, it can only be purchased with a prescription from a veterinarian.

If you are concerned about your hives and see signs of EFB, it is important to test! The Western College of Veterinary Medicine at the University of Saskatchewan is collecting samples of infected larvae for an ongoing European Foulbrood Disease Surveillance Project. We encourage you to read the project brochure found here for details! If you suspect EFB in your colonies, please do not hesitate to contact ATTTA for more information.  We can supply you with sampling kits and instructions for collection to participate in this project.

Written by John MacDonald, ATTTA Seasonal Apiculturist

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