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



There is but little danger that the disease will be transmitted by 

 way of flowers visited by bees from sacbrood colonies and later from 

 healthy ones. 



Theoretically, it is possible that the disease may be transmitted 

 through a contamination of the water supply by bees from sacbrood 

 colonies. Whether infection ever takes place in this way, however, 

 is not yet known. If the disease is ever transmitted in this way, it 

 would seem that it is more likely to take place in the spring of the 

 year than at any other season. 



While there is yet much to be learned about sacbrood, it is hoped 

 that by carefully considering these studies the beekeepers will be 

 aided in devising efficient and economical methods for its treatment. 



SUMMARY AND CONCLUSIONS. 



The following summary and statements of conclusions seem to be 

 justified as a result of the investigations recorded in this paper: 



(1) Sacbrood is an infectious disease of the brood of bees. 



(2) Adult bees are not susceptible to the disease. 



(3) The infecting agent causing sacbrood is of such a nature that 

 it passes through the pores of a fine clay filter. It is therefore a 

 filterable virus. 



(4) A colony may be inoculated by feeding it sirup or honey con- 

 taining the virus. 



(5) The quantity of virus contained in a single larva recently dead 

 of the disease is sufficient to produce quite a large amount of sacbrood 

 in a colony. 



(6) The period from time of inoculation to the appearance of the 

 first symptoms of the disease — the incubation period — is approxi- 

 mately six days, being frequently slightly less. 



(7) By inoculation the disease may be produced at any season of 

 the year that brood is being reared. 



(8) The disease is more often encountered during the first half of 

 the brood-rearing season than during the second half. 



(9) It occurs among bees in localities having as wide a range of 

 climatic conditions, at least, as are found in the United States. 



(10) The course of the disease is not greatly affected by the char- 

 acter or quantity of the food obtained and used by the bees. 



(11) Larval remains recently dead of the disease prove to be very 

 infectious when fed to bees. Dead larvag which have been in the brood 

 comb more than one month are apparently noninfectious. 



(12) Colonies possess a strong tendency to recover from the disease 

 without treatment. 



(13) The virus of sacbrood suspended in water and heated to 

 138° F. (59° C.) was destroyed in 10 minutes. Considering the vary- 

 ing factors which enter into the problem, the minimum temperature 

 necessary to destroy this virus when applied for 10 minutes should 



