34 



BULLETIN 431, U. S. DEPARTMENT OF AGRICULTURE. 



or more should be fed in making an inoculation. The area of 

 brood inoculated may be designated by marking on the brood frame, 

 or by removing the brood from around the area inoculated, thus 

 marking it off. 



MEANS FOR THE DESTRUCTION OF THE VIKtiS OF SACBROOD. 



Although the virus of sacbrood may increase with great rapidity, 

 fortunately it is quite as readily destroyed. Nature supplies many 

 means by which this may be accomplished. While theoretically a 

 sufficient amount of virus may be produced within one month to 

 inoculate all the bees in existence, within another month, if left to 

 natural means alone, practically all such virus would be destroyed. 

 This latter fact constitutes one of the chief reasons for the compara- 

 tively rapid self-recovery of colonies from this disease. 



It was observed in the experiments that larvae dead of sacbrood 

 when left in the brood comb ceased to be infectious in less than one 

 month after death. 



HEATING REQUIRED TO DESTROY SACBROOD VIRUS WHEN SUSPENDED 



IN WATER. 



Approximate results have been published (White, 1914) relative 

 to the heating that is necessary to destroy the -virus of sacbrood 

 when it is suspended in water. In the following table are given 

 some results which have been obtained : 



Table I. — Effect of heating on the virus of sacbrood suspended in water. 1 



Date of inoculation. 



Temperature. 



Time of 

 heating. 



°F. 



°C. 



Minutes. 



122 



50 



30 



131 



55 



10 



131 



55 



20 



135 



57 



15 



136 



58 



10 



136 



58 



10 



138 



59 



10 



140 



60 



15 



142 



61 



10 



149 



65 



15 



158 



70 



15 



167 



75 



15 



176 



80 



15 



Results of inoculation. 



Aug. 6, 1913.. 

 Sept. 10, 1913. 

 Sept. 9, 1913.. 

 Sept. 18, 1913. 

 June 30, 1915. 

 Sept. 10, 1913. 

 Aug. 28, 1915. 

 Sept. 10, 1913. 

 Aug. 28, 1915. 

 Aug. 26, 1913. 



Do 



Do 



Do 



Sacbrood produced. 



Do. 



Do. 



Do. 



Do. 

 No disease produced. 



Do. 



Do. 



Do. 



Do. 



Do. 



Do. 



Do. 



i Fractions will be omitted in this paper, the nearest whole number being given. 



It will be observed from Table I that 138° F. (59° C.) maintained 

 for 10 minutes was sufficient to destroy the virus of sacbrood in the 

 inoculation experiments recorded. Technically, in view of the 

 variable factors which must be considered in experiments of this 

 kind, this result, as representing the thermal death point of the 

 sacbrood virus, should be considered as being only approximate. 

 For practical purposes, however, it is sufficient. 



