The symptoms of American foulbrood include: (1) a characteristic odor, sometimes described as “of a glue pot”; (2) perforated or sunken brood cappings, darker in color than healthy cappings; and (3) black scales, difficult to remove from the cell because of their stickiness. The scales, residues of pupa digested away by the bacteria, may exhibit adult characters like legs, heads or tongues, which are clearly diagnositic for this particular disease. Any individual larva or pupa that is brown or black, and not glistening white, is immediately suspect. The disease is so feared because the bacterium produces spores, which are highly resistant to environmental stress, and can only be destroyed through burning. It is generally considered as always present, although there have been campaigns to eliminate it totally as in the case of New Zealand.
Diagnosis of American foulbrood takes experience and should be confirmed by a trained bee inspector. Most state laws require periodic bee inspection and notification of the authorities if the disease is suspected. The “ropy” test can be used to make a preliminary diagnosis. A stick or twig is inserted into suspicious cell and then withdrawn; the affected larvae “sticks” tenaciously and the contents can be drawn out into a long string or “rope.”
The Holst Milk Test is another diagnostic tool. An affected pupa or scale is swirled in a weak solution (1%) of skim milk. If the milk clears, American foulbrood is suspected. The enzymes secreted by the Bacillus bacteria will break down the protein in the milk and cause it to precipiate out.
Finally, a brood sample may be sent to the Beneficial Insects Laboratory, USDA/ARS for microscopic diagnosis.
Treatment of American foulbrood because it forms spores is problematic. Most states with inspection services require burning, some may/may not permit feeding with antibiotics, but this is problematic due to resistance issues. Specific cases have been reported in Argentina and Florida.
A recent webinar by Dr. Jim Tew (49 minutes) is certainly worth a look. It contains valuable information, some taken from a classic work on the subject, American Foulbrood, by White, G. F. (Gershom Franklin) published in 1920 by the USDA.
European foulbrood symptoms differ slightly from those of American foulbrood. Because younger larvae are affected, perforated cappings are usually absent. The scales are more easily removed and show no adult structures. The Holst Milk test is negative for European foulbrood and the ropy test results in less “stringiness.” The following table compares symptomology of the two major brood diseases.1
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Table 1. Comparative Symptoms of American and European Foulbrood. |
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American Foulbrood |
European Foulbrood |
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Sealed brood. Discolored, sunken or punctured cappings. Some sealed brood in advanced cases with discolored, sunken, punctured cappings.
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Unsealed brood.
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Usually older sealed larvae or young pupae. Upright in cells. |
Usually young un-sealed larvae. Some older sealed larvae. Typically in coiled stage. |
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Dull white, becoming light brown, coffee brown to dark brown, or almost black. |
Dull white, beccoming yellowish white to brown, dark brown or almost black. |
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Soft, becoming sticky to ropy. |
Watery, rarely sticky or ropy. Granular. |
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Slight to pronounced glue odor to gluepot odor. |
Slightly sour to penetratingly sour. |
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Uniformly lies flat on lower side of cell. Adheres tightly to cell wall. Fine, threadlike tongue of dead pupae may be present. Head lies flat. Brittle. Black. |
Usually twisted in cell. Does not adhere tightly to cell wall.Rubbery. Black. |
1 H Shimanuki and D. Knox, Diagnosis of Honey Bee Diseases, Agriculture Handbook No. 690, USDA Ag. Research Service, April, 1991.
European foulbrood does not produce spores. The treatment, therefore, does not require burning the colony and it can often be cleared up by antibiotics and/or requeening, which creates a break in the brood cycle.
See more about foulbrood and its symptoms as on the World Wide Web.
