European foulbrood

Signs or indications

Unhealthy larvae with yellow streaking leading to brown or blackish discoloration; dead, dying larvae twisted in cell rather than forming the normal C-shape.

Description

European foulbrood (EFB) is a non-spore-forming bacterial brood disease caused by the bacterium Melissococcus plutonius. EFB is considered a stress disease and is most prevalent in spring and early summer, usually disappearing with a nectar flow. Occasionally, the disease remains active throughout the entire foraging season. All bee castes are susceptible to EFB.

EFB needs to be distinguished from American foulbrood (AFB) so colonies or equipment are not needlessly destroyed (only AFB requires destruction of adults and frames).

EFB is characteristic of open brood cells. When dying or dead remains are stirred with toothpick or stick, they do not rope out (although they may be sticky and gooey). The EFB scale does not tightly adhere to the lower cell surface. The odor is a rotting odor which is different from AFB odor but easily confused with the odor of dead and dying brood. These signs are very distinct from AFB disease, which is also caused by a bacterium.

It is possible to confirm an EFB diagnosis with an EFB test kit. If in doubt, consult a local expert for help with diagnosis or send a sample to the USDA Beltsville Bee Lab or to a local bee lab. EFB is treatable; colonies frequently recover as weather improves, resources become more abundant, and colony population grows.

Most closely resembles

AFB; chalkbrood

Resources

Shimanuki H and Knox D. 2000. Diagnosis of Honey Bee Diseases. US Department of Agriculture Agriculture Handbook 690. https://www.ars.usda.gov/is/np/honeybeediseases/honeybeediseases.pdf

MAAREC. 2005. Bee diseases & their control. Mid-Atlantic Apicultural Research & Extension Consortium Publication 4.9. https://canr.udel.edu/maarec/wp-content/uploads/sites/18/2010/03/Diseases_of_Honey_Bees_PM.pdf

Mueller CM, Jack CJ, Mortensen AN, and Ellis J. 2020. Identification and Treatment of European Foulbrood in Honey Bee Colonies. University of Florida/IFAS Extension. Accessed 2023. https://edis.ifas.ufl.edu/publication/IN1272

Wilson M and Skinner J. 2019. European Foulbrood: A Bacterial Disease Affecting Honey Bee Brood. Bee Health. Accessed 2023. https://bee-health.extension.org/european-foulbrood-a-bacterial-disease-affecting-honey-bee-brood/

Snyder R. 2018. 2018 Northern California Update. BeeInformed. Accessed 2023. https://beeinformed.org/2018/07/24/2018-northern-california-update/ 

 Decomposing larvae in several brood cells and twisted larvae in cells in upper right characteristic of EFB; photo by Robert Snyder
Decomposing larvae in several brood cells and twisted larvae in cells in upper right characteristic of EFB; photo by Robert Snyder
 Larvae infected with EFB; photo by Robert Snyder
Larvae infected with EFB; photo by Robert Snyder
 Larvae infected with EFB pathogen; photo by Robert Snyder
Larvae infected with EFB pathogen; photo by Robert Snyder
 EFB yellowish larvae; photo by Robert Snyder
EFB yellowish larvae; photo by Robert Snyder
 Removing EFB-infected larva; no roping occurs; photo by Sarah Scott
Removing EFB-infected larva; no roping occurs; photo by Sarah Scott
 EFB yellowish larvae twisted in cells; photo by Robert Snyder
EFB yellowish larvae twisted in cells; photo by Robert Snyder
 Note yellowing, twisted larvae in cells (.e.g., yellow arrow), and the prominence of trachea (e.g., green arrow); photo by Robyn Underwood
Note yellowing, twisted larvae in cells (.e.g., yellow arrow), and the prominence of trachea (e.g., green arrow); photo by Robyn Underwood
 Twisted larvae characteristic of EFB; photo by Robert Snyder
Twisted larvae characteristic of EFB; photo by Robert Snyder
 Early infestation of EFB; photo by Dewey M. Caron
Early infestation of EFB; photo by Dewey M. Caron
 EFB test kit showing a negative result above, and a positive result below; photo by Dewey M. Caron
EFB test kit showing a negative result above, and a positive result below; photo by Dewey M. Caron
 EFB Test kit; photo courtesy Vita
EFB Test kit; photo courtesy Vita