50 BULLETIN 431, U. S, DEPARTMENT OF AGRICULTURE. 



frequently do, contain no diseased brood. Experimentally it is pos- 

 sible to destroy a colony by feeding it repeatedly the virus of sac- 

 brood, and beekeepers report that the disease sometimes destroys 

 colonies in their apiaries. The percentage of colonies, however, that 

 actually die out as a direct result of the disease is small. The weak- 

 ening of the colony in the spring of the year not only reduces or entirely 

 eliminates the profits on it for the season, but may also cause it to 

 be in a weakened condition on the approach of winter. 



Whether a larva once infected ever recovers from the disease is not 

 known. Keasoning from what is known of the diseases of other ani- 

 mals and man, one would expect that a larva may recover from sac- 

 brood infection. It is known that many larvae, both worker and 

 drone, do die. From the information thus far obtained it does not 

 appear that a queenless colon j- would be likely to remain so as a con- 

 sequence of the disease. 



As to the prognosis of the disease in a colony it may be said, there- 

 fore, that it is very favorable for the continued existence of the colony. 

 As to the economic losses to be expected from the disease, the present 

 studies suggest that they may vary from losses that are so light as not 

 to be detected upon examination to losses that may equal the entire 

 profits of the colony for the year. Indeed, at times the death of the 

 colony takes place as a result of the disease. 



RELATION OF THESE STUDIES TO THE TREATMENT OF SACBROOD. 



An earlier paper (White, 190S) contains a brief general discussion 

 of the relation existing between the cause of bee diseases and the 

 treatment of them. The general remarks made in it apply also to 

 sacbrood. No doubt the beekeeper in studying the results given 

 here has already observed relations existing between them and points 

 which should be incorporated in methods for treatment. Mention- 

 ing a few of them here may serve to suggest still others. 



That the weakness resulting in a sacbrood colony is due to the 

 death of worker larvae; that adult bees are not susceptible to the 

 disease; that queenlessness is rarely to be expected as a sequence 

 of the disease; that the disease may be produced with ease at any 

 time of the year that brood is being reared; that it occurs at all 

 seasons, but is more frequently encountered in the spring; that it 

 is found in localities differing widely as to food and climatic con- 

 ditions: and that no complete racial [immunity to the disease has 

 yet been found are facts concerning the predisposing causes of sac- 

 brood which beekeepers will at once recognize as bearing a close rela- 

 tion to the methods by which the disease should be treated. 



As sacbrood can not occur in the absence of its exciting cause 

 (a filterable virus), a knowledge of this cause is of special importance 

 in the treatment of the disease. 



