Bept. 1, 1932 Commercial Honey and Spread of American Foulbrood 263 



1926, 1 out of 3 in 1927, and 1 out of 4 in 1928. It was assumed that 

 the disease was probably not spread by robbing, since no active rob- 

 bing was observed at any time. In practically every case where a 

 control colony became infected, it was so located in relation to the 

 inoculated colonies that drifting of young nurse bees during play 

 flights could account for the spread of the disease, in one or two cases 

 quite definitely so. In 1929 all eight uninoculated colonies, although 

 they were not located with the inoculated colonies but were within 

 robbing range of all, remained free from disease. The prevention of 

 drifting apparently eliminated the casual spread of disease. 



Occasionally a colony of bees affected with American foulbrood will 

 try to clean out the diseased remains, often removing parts of the 

 scales and sometimes actually tearing a comb down to the midrib in 

 order to do this. White (SO, p. 34-35) states: 



There is considerable evidence to support the belief that occasionally in cases 

 of light infection the disease may disappear unaided by treatment. * * * j^ 

 should be emphasized that such a course for the disease, if it occurs at all, is 

 unusual. Although American foulbrood spreads more or less rapidly within an 

 infected colony, the fact remains that it frequently does not. 



Lineburg (16) in 1925 reported that in two colonies which were 

 diseased in the spring the disease apparently disappeared later in the 

 season. Three colonies were divided and used for maldng increase 

 in June and July, but all remained free from disease, at least until the 

 end of that season. Further observations were not reported. Cor- 

 kins (8) in 1928 reported five colonies which were given combs con- 

 taining scales of American foulbrood at the beginning of the honey 

 flow of 1927 and developed no disease up to July 10, 1928. Two 

 other colonies were observed to have cleaned out the disease and 

 remained healthy for an entire season. However, during the several 

 years of his experimental work on American foulbrood, the writer 

 never observed a colony in which the disease was permanently 

 cleaned out until 1927. In that year, of 16 colonies inoculated with 

 various dilutions of spores, 4 colonies, 2 of which received more than 

 the probable minimum dose causing infection, showed no disease 

 during the season. The disease completely disappeared by the end 

 of brood rearing ia 10 of the 12 other colonies that had showed either 

 positive or probable disease some time during the summer. In 1928 

 package bees were placed on the combs of seven qf these colonies 

 that had apparently cleaned out the disease during the previous 

 summer and on two that had been inoculated with presumably a 

 sufiicient number of spores but which had remained healthy. Three 

 of the seven developed disease again the second season, while four 

 remained healthy during the entire season. Neither of the two 

 inoculated colonies that had remained free from disease in 1927 

 developed it in 1928. Of the 11 colonies inoculated in 1928 that 

 developed disease, 4 cleaned up the disease by the end of the brood- 

 rearing season and 2 inoculated colonies showed no disease. In 

 1929, 1 of the 2 colonies developing disease cleaned up by the end of 

 the brood-rearing season, making a total of 15 cases in which the 

 disease was cleaned up by the end of brood rearing. Two of the 

 colonies inoculated with the minimum infectious dose or more showed 

 no disease during that summer. 



It is possible that, in the high altitude of Laramie, and in similar 

 places where the air is very dry, the scales of American foulbrood 

 131772—32 2 



