8 BULLETIN 810, V. S. DEPAETMENT OF AGRICULTURE. 



tered death among brood which has reached the pupal stage. Adult 

 bees are not susceptible to infection. 



/Sex. — ^T^^orker, drone, and queen larvse are all susceptible to in- 

 fection with Bacillus pluton and any of these may die of European 

 foulbrood. 



Bace. — Complete immunity from European foulbrood has not 

 been found among the races of bees studied. Experimental work 

 recorded in the present paper involved the use of at least five 

 colonies of " tested Italians," two of " tested Carniolans," and two 

 of " tested Caucasians." For the most part the bees used were " un- 

 tested Italians," but among the colonies were a few common blacks. 

 In all these strains the disease was readily produced through experi- 

 mental inoculation. The examination of numerous samples of dis- 

 eased brood received from beekeepers throughout the United States 

 suggests that all races commonly kept by American beekepeers are 

 susceptible to European foulbrood. The relative immunity of the 

 different races has not been demonstrated by the studies. These 

 facts, however, do not dispute the observation by practical bee- 

 keepers that some strains of bees show a greater colony resistance 

 than others. 



Climate. — From reports of studies made in Austria by Muck (12), 

 in Denmark by Bahr (1), in England by Cheshire and Cheyne (4), 

 in Germany by Zander (20), and in Switzerland by Burri (3), it is 

 clearly evident that the disease discussed in the present paper occurs 

 in these different countries. It has been encountered also in many 

 sections of the United States and Canada. This distribution shows 

 that the infection can exist under a variety of climatic conditions. 

 The practical import of the fact is that the presence of European 

 foulbrood in any locality can not be attributed entirely to the climate 

 of the region. 



Season. — Beekeepers have observed that European foulbrood oc- 

 curs with greatest severity before midsummer rather than later in 

 the season. The disease, it has been shown experimentally, can be 

 produced, however, at any season of the year at which brood is being 

 reared. Its severity at any given season is to be attributed, there- 

 fore, to environmental conditions rather than to the difference in 

 the susceptibility of larvae during the different seasons. 



Food. — As in American foulbrood it is found that the cause of the 

 disease in the colony is governed very little if at all by the quality 

 of food gathered by bees. Indirectly, however, the quantity present 

 in the hive or obtainable often does influence its course materially. 



EXCITING CAUSE 



That Bacillus alvei may be present in large numbers in brood dead 

 of foulbrood was demonstrated by Cheshire and Cheyne (4) in 1885. 



