38 



BULLETIN 431, U. S. DEPARTMENT OF AGRICULTURE. 



Similar preliminary experiments made to determine the amount of 

 drying which the virus of sacbrood will withstand at outdoor tempera- 

 ture and at incubator temperature (about 99° F. [37° C.]) gave results 

 approximately those obtained from drying at room temperature, the 

 time being somewhat less in the case of drying at incubator tempera- 

 ture. 



Preliminary experiments indicate also that when the virus is mixed 

 with pollen and allowed to dry the period for which it remains virulent 

 is increased only slightly. 



RESISTANCE OF SACBROOD VIRUS TO DIRECT SUNLIGHT WHEN DRY. 



In the experiments made to determine the amount of sunlight 

 which the virus of sacbrood is capable of resisting, Petri-dish prepara- 

 tions similar to those made in the drying experiment were prepared. 

 After drying a few hours in the room the uncovered dish is exposed 

 to the direct rays of the sun. At different intervals, measured in 

 hours, inoculations of healthy colonies are made similar to those in 

 the drying experiments. The following results were obtained: 



Table V. — Resistance of the virus of sacbrood, vihen dry, to direct sunlight. 



Date of inoculation. 



Time of 



exposure 



to sun's 



rays. 



Results of inoculation. 



Sept. 17, 1915. 

 July 29, 1915., 

 Sept. 17, 1915. 

 Sept. 16, 1915. 



Do 



Do 



Aug. 25,1915. 

 Sept. 10, 1915. 



Do....... 



Sept. 9, 1915.. 



Do 



Aug. 19, 1915. 

 July 16, 1915. 

 Aug. 20, 1915. 

 Sept. 11, 1915 



Hours. 

 2 

 2A 

 3" 

 4 

 5 

 6 

 6 

 4 



Sacbrood produced. 



Do. 



Do. 



Do. 



Do. 



Do. 



Do. 

 No disease produced. 



Do. 



Do. 



Do. 



Do. 



Do. 



Do. 



Do. 



The results recorded in Table V show that the virus of sacbrood in 

 the experiments made was destroyed in from four to seven hours' 

 exposure to the direct rays of the sun. The results obtained also 

 indicate that much of the virus was destroyed in a 2-hour exposure 

 to the sun. 



It will be readily appreciated that the time that the virus will 

 resist the sun's rays will depend a great deal upon the intensity of 

 the rays at the time of its exposure and the thickness of the layer 

 of the infective larval material in the Petri dish. The drying that 



