European Foulbrood

The Lesser Foulbrood

European Foulbrood (EFB) often gets confused with its more devastating relative, American Foulbrood (AFB), but the two diseases differ significantly in cause, severity, and management. EFB is caused by Melissococcus plutonius, a non-spore-forming bacterium that infects larvae during the feeding stage before their cells are capped. Because the bacterium does not form endospores, it does not persist in equipment the way AFB does, and infected colonies can recover without equipment destruction.

Symptoms

EFB kills larvae in the open, uncapped stage. Infected larvae change color from pearly white to yellow, then brown. They may appear twisted or displaced from their normal coiled position in the cell (a diagnostic sign called "molten" or "deflated" larvae). The larval remains are usually rubbery rather than ropy (distinguishing them from AFB, which produces the characteristic ropy string test). There may be a sour smell, but it is not the rotten, fishy odor of AFB.

Stress Connection

EFB is strongly linked to colony stress. It typically appears in spring when colonies are rapidly expanding brood production but may lack sufficient nurse bees to keep larvae well-fed. Undernourished larvae are more susceptible to infection. Strong colonies with adequate nutrition and nurse bee populations often overcome EFB naturally without treatment as the colony grows into summer strength.

Management

Requeening with a hygienic queen is the most effective long-term strategy, as hygienic workers detect and remove diseased larvae quickly. Ensuring adequate nutrition (protein from pollen or pollen substitute) supports nurse bee health. In severe cases, oxytetracycline antibiotic treatment may be prescribed by a state apiary inspector. Unlike AFB, EFB does not require burning equipment; thorough cleaning and frame replacement is sufficient.