300 STATE BOARD OF AGRICULTURE. 



CAUSE. 



The cause of European foul-brood has been practically determined to be 

 Bacillus pluton (White) . Although this organism refuses to grow on artificial 

 media, by process of elimination it has been proved that the other organisms 

 found in larvae infected with European foul-brood are not the exciting cause 

 of the disease. It therefore appears that Bacillus pluton is the exciting 

 cause. Bacillus pluton is smaller than the causal organism of American 

 foul-brood and has a different shape. This difference in size and shape 

 aids the bacteriologist in determining microscopically the kind of foul-brood 

 being examined. There are present in diseased larvae anj^ one or all of 

 several bacteria other than Bacillus pluton. This fact has caused some 

 confusion among investigators. 



European foul-brood attacks the larvae at a much earlier age than does 

 American, usuall^^ at two days of age or older. As the period of sickness 

 has been determined to be two days or more, larvae are at least four days 

 old when they die. In fact it is at this age that larvae are most often found 

 dead of European. However, as larvae dead of the disease are sometimes 

 found in capped cells it is evident that older larvae are also occasionally at- 

 tacked. All three classes of larvae are infected, and unlike American, Euro- 

 pean foul-brood frequently attacks drone and queen larvae. 



Experience has proved that black bees are more susceptible to the disease 

 than are Italian. Furthermore it is possible to develop strains of Italian 

 bees by selection which are more nearly immune to the disease than others. 

 For that reason beekeepers in European foul-brood districts should endeavor 

 to raise their ow^n queens from colonies which show resistance. The disease 

 is most prevalent in the spring time. The coming of the honey flow will 

 often remove all traces of the disease in the colony, while cessation or lack of 

 a honey flow seems to assist in the destruction of the colony. 



SYMPTOMS. 



It has been shown that there are three stages of development at which 

 larvae are attacked by European foul-brood. The early stage at which they 

 are attacked is when they are at least four days old and lie in the bottom of 

 the cell in a C shape, not entirely filling the end of the cell. It is at this 

 stage that European usually attacks larvae. They are also attacked at a 

 slightly later stage of development, at which time they occupy the whole 

 of the end of the cell and have begun to stretch out into the base of the cell. 

 Larvae are frequently fomid dead of European at this stage. European 

 foul-brood also attacks larvae after they have been capped in the cell, and 

 it is from brood found dead at this stage that much of the confusion in dif- 

 ferential diagnosis between European and American is experienced. Healthy 

 larvae in the various stages mentioned are perfectly white in color, sometimes 

 with a shghtly bluish tinge, plump and rigid, and appearing firm. The 

 position occupied in the cell will depend, of course, on the stage of develop- 

 ment. Those in the first stage are still curled up in the end of the cell, while 

 those in the last stage will be stretched out the entire length of the cell and 

 capped over. 



When attacked by the disease the larvae turn color from a healthy white 

 to a yellowish tinge, sometimes more distinct than at others, later turning to 

 a brownish color as decay goes on, and finally becoming a dark brown in the 

 final stage of decay. The brood-nest has the appearance of a pepper box, 



