MICROBIOLOGY OF DISEASES OF INSECTS 653 



spore is formed which does not cause the eiLlargeinent of the rod to any extent. 

 No cultural characteristics are given. 



Importance. — This disease is of no special economic importance. 



Sac Brood, a Disease or Bees 

 Filterable virus — White* 



History and Distribution. — A disease which was similar to, but 

 was not foul brood was noted in 1881 by Doolittle in America, by 

 Jones of Canada in 1883, and by Simmins of England in 1887. The 

 larvae were found to die here and there throughout the brood comb; 

 the disease would disappear entirely or it would reappear the next 

 season; the bees would frequently remove the dead brood and no 

 further trouble would ensue. Simmins found no microscopic evidence 

 of disease in these larvae. In 1892 an editorial in one of the bee jour- 

 nals stated that dead brood had been encountered which did not seem 

 to be infectious and which lacked two decisive symptoms of the real 

 foul brood, i.e., the ropiness and the "glue-pot" odor. In 1902 

 G. F. White of the U. S. Dept. of Agriculture began the study of this 

 diseased brood. This disease was described in Switzerland in 1906 

 and later in 1910. 



The name " sac brood " comes from the fact that many larvae dead of 

 this disease can be removed from the ceU without rupturing their 

 body waU. When thus removed they have the appearance of a small 

 enclosed sac. 



Symptoms. — The. strength of a colony in which sac brood is present 

 is frequently not noticeably diminished. When the brood is badly 

 infected, however, the colony naturally becomes appreciably weakened 

 thereby. The brood dies after the time of capping. The dead larvae 

 are, therefore, almost always found extended lengthwise in the cell and 

 lying with the dorsal side against the lower wall. It is not unusual to 

 find many larvae dead of this disease in uncapped cells. Such brood, 

 however, had been uncapped by the bees after it died. In this disease 

 the cappings are frequently punctured by the bees. Occasionally a 

 capping has a hole through it, indicating that the capping itself had 

 never been completed. A larva dead of this disease loses-its normal 



* White, G. P. Sacbrood. Cir. 169. B. of Ent., U. S. Dept. Agr., 1913. 



