Which of the following is NOT a symptom of American Foulbrood?

Open cells with curled larvae is not a symptom of American Foulbrood because this particular disease typically presents with specific signs that differ from those associated with other brood diseases. American Foulbrood is characterized by sunken cappings, where the wax cappings over brood cells appear sunken due to disease progression. Additionally, affected larvae often die in a particular way—becoming dark and resulting in a putrid, foul odor, which is explicitly noted as a sign of the disease.

Irregular brood patterns can also be a symptom, as the disease causes issues in normal brood development, leading to uneven and patchy patterns within the hive. Therefore, recognizing these symptoms helps in diagnosing American Foulbrood effectively, while open cells with curled larvae more closely align with other forms of disease, such as European Foulbrood, rather than American Foulbrood itself.