8 



BULLETIN 804, U. S. DEPARTMENT OF AGRICULTURE 



started, the method and degree of house cleaning being watched after 

 the colony had been dequeened, strengthened, and requeened with good 

 Italian stock. Note was also made of any recurrence of disease and 



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Fig. 1. — Method of plotting the location and history of diseased bee larvse in the 

 combs. O Freshly diseased larvse. O Cells that have been cleaned out. 9~Cells 

 that have been cleaned out and filled with nectar. ^ Larvae remaining in the cells 

 more than one observation period. The area of sealed brood was the amount 

 present at the time of infection of the colony. 



apparent reason therefor. In other words, a complete study was 

 made of the cycle of the disease and of the activities of the bees 

 during its course. 



OBSERVATIONS 



COLONY Q 



Race. — ^Hybrid. 



Queen. — 1917, dark and poor. 



Bees. — Workers and drones very dark, almost black, very excitable. 



Condition of colony at time of infection. — ^Brood in four frames, a little 

 less than half sealed, besides two frames of eggs. Bees covering about 

 eight frames, medium strength. Slightly more field bees than nurse 

 bees, because of having divided this colony, old bees returning from the 

 division. 



Date of first infection. — ^May 28, 1918. 



Material used. — Ten diseased larvae from sample No. 5863, macerated in 

 250 c. c. of a 50 per cent sugar sirup. 



First appearance of disease noted. — May 31, 1918, three dayr^ after inocu- 

 lation. 



Age of larvw first attacked. — Three to four days after hatching from the 

 eggs. 



Colony G (fig. 2) , hybrids, soon succumbed to the infection, the first 

 diseased larva appearing three days after infection, the gross diagnosis 

 being confirmed by the finding of Bacillus pluton on microscopic ex- 

 amination. The spread of the disease was rapid, the disease being 

 present in only one comb on the third day and in seven combs on the 

 seventh day. All of this early spread took place in brood unsealed 



