294 



STATE BOARD OF AGRICULTURE. 



CAUSE. 



The cause of American foul-brood is a bacillus called Bacillus larvae 

 (White). This bacillus is very minute in size. It would take nearly 10,000 

 of the organisms placed end to end to cover an inch. The organism can be 

 easily detected in dying or decayed larvae and scales by the use of the micro- 

 scope, and in cases in which beekeepers are doubtful as to the correct diag- 

 nosis, a sample of the diseased material should always be submitted to a 

 laboratory, where examination with a microscope can be made. Samples 

 in which scales are predominant, and which lack the usual characteristic 

 symptoms of either of the foul-broods, should always be examined with the 

 microscope. One of the pecuhar facts concerning American foul-brood is 

 that when sample is examined microscopically it usually contains but one 

 kind of bacteria, Bacillus larvae, whereas samples of European foul-brood 

 may contain any one or all of several different bacteria. 



American foul-brood invades the colony by attacking the young larvae 

 during the time when they are being fed by the nurse bees. These infected 

 larvae usually die just after the cells are capped, although larvae may be 

 found dead of American foul-brood in rare cases still curled up in the end of 

 the cells; on the other hand American foul-brood may kill larvae well advanced 

 in the pupa stage. Adult bees are not affected. 



Larvae of all three classes, i. e., worker, drone, and queen, may become in- 

 fected, although the worker larvae are found diseased most frequently. In 

 fact queen and drone larvae are seldom attacked. The experience of bee- 

 keepers has shown that no race of bees is particularly immune to the ravages 

 of American foul-brood. 



Fig. 1. American foul-brood comb, showing irregular patches of sunken cappings and scales. The 

 position of the comb indicates the best way to view the scales. From Farmers' Bulletin 442, U. S. 

 Department of Agr., Bureau of Entomology. 



