American Foulbrood: Caused by a bacillus larvae- bacterium. It results in a scattered brood pattern with sunken, perforated, discolored cells with a greasey appearance flat on bottom of cell. Larvae are light brown, dull white, dark brown, eventually coffee to dark brown. It has an unpleasant glue-like odor.
Chalkbrood: Caused by Acosphaera apis, a fungus.. Appears as scattered light or dark, convex cells. It does not have an unpleasant odor.
Chilled brood: Caused by sudden or prolonged low temperature. Results in few or many dead larvae in cells at edge of broodnest. Cells appear light or dark and are sunken and discolored. Has a rotten odor in severe cases.
Sacbrood: Caused by a virus. Cells are scattered, often with many unsealed cells. Often cells appear dark and sunken, many are perforated. Often has a sour odor.
Photos courtesy of the United States Department of Agriculture
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