Chalkbrood : the Mycosis in Honeybees and its Control Measures

Abstract

Chalkbrood is a fungal disease affecting the larvae of western honeybee (Apis mellifera). It is known as one of the notifiable bee infectious diseases legislated by Japanese government. Ascosphaera apis (A. apis), an etiological fungus, is normally present in honeybee habitats. A. apis has extremely strong resistance against low water potential, thus it can survive for long periods in a tough dry environment. There are no approved pharmaceutical products against this disease in Japan. Moreover, few disinfection methods are applicable during the honey harvesting period. Therefore, to keep the number of A. apis low in beehives, it is important to conduct control measures based on risk factors associated with the disease onset. Epidemiologically, most cases of chalkbrood in Japan have been detected in the summer of Hokkaido (northern island of Japan), as the beekeepers in Honshu transfer their swarms to avoid the summer heat stress and to seek an adequate quantity of flowering plants for the nourishment of their bees. In an experimental infection, the larvae exposure to а low-temperature environment increased the chalkbrood incidence. Therefore, changing temperature conditions and summer bee swarm transfer to colder climate areas would be one of the risk factors for the chalkbrood. The identification of A. apis is mostly based on morphological observations. However, as the differentiation between A. apis from the other Ascosphaera fungi by this method is sometimes confusing, it is advisable to use molecular technique alongside. There are many constraints for establishing appropriate control measures against the infectious honeybee diseases including chalkbrood. Therefore, epidemiological studies need to be promoted from the viewpoint of healthy honey production and bee health improvement.