14 



Position in the cell. Larvae exhibit marked variation in their 

 Dosition according to the age at which they die. Young arvae dying at 

 fhe characteristic^stage while still curled generally ^^.^^^m around as 

 though in pain assuming unnatural positions m the cell. Those aryae 

 that die after capping are larger and lie more uniformly extended in the 

 cell. 



Colour changes. The pearly white colour of healthy larvae changes 

 to greyish yellow. As putrefaction continues the colour deepens to a 

 dark greyish brown mass. 



Consistency of dead larva. After approximately three weeks of 

 decay the larva becomes a sticky, somewhat granular mass. The granular 

 appearance at this stage is contrasted to the smooth glue-like appearance 

 of American Foulbrood. 



Tracheae visible. The tracheae are glistening, silvery air tubes 

 situated below the skin. In many larvae dead of the disease these 

 tracheae may be plainly seen and remain visible during the complete 

 process of putrefaction. The presence of tracheae is an important symp- 

 tom to diiferentiate infection in the advanced larval stage from American 

 Foulbrood. 



European Foulbrood odour. In advanced cases, especially where 

 many larvae die in the capped over stage, there is a very offensive odour. 

 It is described as resembling that of rotten fish. 



Scale formation. The dried larval remains are less brittle and more 

 rubber-like than American Foulbrood scales. They are shrivelled, brown 

 in colour and can easily be removed from the cells. The fact that brood 

 dead of European Foulbrood can be removed by the bees makes it possible 

 for strong colonies to clean up the disease. 



(b) Cause of European Foulbrood 



Bacillus pluton, a non spore former, is considered to be the organism 

 which actually causes the death of the larva. Invariably, however, there 

 are secondary organisms present, the chief of which is Bacillus alvei. 

 When a laboratory diagnosis is made the presence of Bacillus alvei 

 indicates European Foulbrood. 



(c) Methods of Spread 



The organism causing European Foulbrood does not form spores so 

 is unable to live over winter in honey. It is carried over in pieces of dead 

 larvae. From this small beginning in the spring it can spread very 

 rapidly under favourable conditions. If nectar is stored in contaminated 

 cells and fed to larvae they contract the disease. Further spread may be 

 caused by robbing, interchanging combs or drifting nurse bees. 



(d) Immunity to European Foulbrood 



Workers, drones and queens are all susceptible to European Foul- 

 brood. Italian bees, due to their vigorous house cleaning habits, stop the 

 spread of disease and eventually eradicate it. Some strains are far more 

 efficient in cleaning out dead larvae than others. Black bees are very 

 susceptible to the disease. 



