38 



BULLETIN 780, U. S. DEPARTMENT OF AGRICtTLTURE. 



rays of the sun. The top of the dish was not on during the exposure. 

 After intervals reckoned in hom-s inoculations were made of healthy- 

 colonies, the germs contained in one dish being used. 



Table XIX gives a summary of a set of experiments of this kind. 



Table XIX. — Resistance of Nosema apis suspended in water to the direct rays of the sun. 



Date of inoculation. 



Results of inoculation. 



Aiig. 2, 1915.. 

 July 27, 1915. 

 Aug. 20, 1915. 



Do 



Aug. 26, 1915. 

 Sept. 10, 1915, 

 Aug. 27, 1915. 

 Sept. 11, 1914, 

 Sept. 13, 1915 



Do 



Sept. 14, 1915 

 Sept. 16, 1915. 



Do 



Sept. 17, 1915. 



Nosema infection produced. 



Do. 



Do. 



Do. 



Do. 



Do. 



Do. 



Do. 



Do. 

 No infection produced. 



Do. 



Do. 



Do. 



Do. 



The results in the foregoing table show that NoseTna apis was de- 

 stroyed by the direct rays of the sun in from 37 to 51 hours. It is 

 seen, therefore, that Nosema apis when suspended in water shows a 

 considerable amount of resistance. In the question of the transmis- 

 sion of the disease this resistance may be of considerable importance. 



At the time these experiments were made the intensity of the rays 

 was, as a rule, quite marked and, therefore, favorable for the destruc- 

 tion of germs. The temperature of the aqueous suspension, however, 

 did not reach 136° F. (58° C.) and, therefore, was not sufficient to 

 destroy the virus through heating. Some of the suspensions stood for 

 more than a week in the Petri dishes, thereby introducing the factors 

 of fermentation and putrefaction. The effect of these factors on the 

 results is not known. 



DESTRUCTION IN HONEY. 



In performing the experiments crushed stomachs from about 10 

 Nosema-infected bees were suspended in about 3 ounces of honey in 

 Petri dishes (fig. 7). To prevent robbing by bees the dish was used 

 with the top on. The suspension was exposed to the direct rays of the 

 sun with the dishes resting on a wooden support. After different 

 intervals healthy colonies were inoculated with germs which had 

 been exposed to the sun. 



Even when resting on a wooden support it is not unusual during the 

 summer for the honey of the suspension exposed to the sun to reach a 

 temperature beyond the thermal death pomt of the parasite. To 

 determine facts in regard to the effect of the sun's rays on Nosema 

 apisj therefore, this point in regard to heat must be met by the 

 technique employed. This could have been done quite easUy but 

 for the lack of time. 



