8 DISEASES OF BEES 



American foul brood 



The examination of numerous samples has led to a verification 

 of the fact that the spores of Bacillus larvae are ahnost invariably 

 present in apparently pure culture in the ropy remains and scales 

 of larvae dead of this disease, and further that this organism causes 

 the disease. A number of experiments have been carried out in 

 order to determine the relationship of B. larvae to the cause of 

 American foul brood. It has been found that disease is caused by 

 feeding decaying larvae, dead of American foul brood, to bees of 

 healthy nuclei even when the material is suspended in water and 

 heated for twenty minutes at 85°C (185° F), the spores of the causal 

 organism resisting this temperature readily. Heating under steam 

 pressure at a high temperature killed the spores of B. larvae, and 

 material so treated was no longer capable of initiating disease. 

 After considerable trouble a culture medium upon which B. larvae 

 grew and sporulated readily was evolved : most media upon which 

 this organism grows readily will not support spore formation. 

 Suspensions of the vegetative cells and of the spores of B. larvae 

 were prepared upon this medium and were employed in a series 

 of infection experiments. 



Vegetative cells of B. larvae when introduced into healthy 

 nuclei by feeding the bees, feeding the larvae directly, or spra3dng 

 the bacteria over developing brood, have in no experiment so far 

 produced disease. Thus in two different experiments, approximately 

 170,000 million and 80,000 million vegetative cells prepared on the 

 same medium as that employed for obtaining spores, were sprayed 

 over eggs and developing larvae of healthy nuclei and no disease 

 developed. Toumanoff, working in France, obtained similar results. 

 With spores of B. larvae, obtained from pure cultures of the organism, 

 American foul brood was readily initiated, providing a fairly large 

 dose (mass inoculum) was employed. It was also found that a very 

 much smaller inoculum of spores was effective in producing the 

 disease, when the developing brood of the nucleus was sprayed 

 directly with them than when they were fed to the bees in syrup. 

 In one series of experiments, in which the same spore suspension 

 was employed throughout, nuclei in which the brood was sprayed 

 with approximately 620 million or 62 million spores soon developed 

 American foul brood, while the disease did not develop in a nucleus 

 receiving only approximately 6.2 million spores. When the spores 

 were fed to the bees in syrup instead of being sprayed over develop- 

 ing brood, disease resulted in nuclei receiving approximately 

 62,000 million or 6,200 million spores, but not in those receiving 

 approximately 620 million or 62 million spores. Sturtevant, working 

 in the United States, found that a colony of bees would not develop 

 American foul brood unless it received at least 50 million spores of 

 B. larvae fed to the bees in 1 litre of syrup, the spores used in his 

 experiments being derived from scales of larvae dead of the disease. 

 The above work confirms, in general, his results. The fact that the 



