130 Journal of Agricultural Research voi. xxvm, no. 2 



THE RELATION OF CONTRIBUTING CAUSES TO THE COMPARATIVE 

 DEVELOPMENT OF THE TWO SERIOUS BROOD DISEASES OF 

 BEES 



In order to understand the basis upon which the consideration of this problem 

 has been developed, it is necessary to make a comparative study of certain of 

 the characteristics of the two brood diseases, American foulbrood and European 

 foulbrood, aside from their etiology. It will be apparent from this study that 

 certain contributing causes, although recognized and described, have not been 

 further analyzed to any extent, particularly in relation to specific etiology. 

 The experimental work of the present investigation is concerned primarily 

 with. American foulbrood, however, since the causative organism, Bacillus 

 larvae, can be isolated and grown in pure culture, while as yet no artificial medium 

 suitable for the growth of Bacillus pluton, the cause of European foulbrood, 

 has been devised. 



RACE 



It is an accepted fact that in American foulbrood the race or strain of bees 

 has little or no relation to the development of or the resistance to the disease. 

 This, aside from apparent lack of immunity or resistance of any of the races, 

 may be explained partially by the fact that the decomposed material resulting 

 from the death of the larvae is of such a nature that the bees can not to any 

 extent remove it from the combs after the disease has once become established. 

 The dried-down masses (scales) are practically glued to the cell walls. Bacillus 

 larvae forms resistant spores which allow the disease to be carried and spread 

 almost indefinitely by means of the honey and old scales. 



In European foulbrood, on the contrary, Italian bees seem to have some character- 

 istic which makes them more resistant or vigorous in combating infection under 

 the proper conditions. The results of bacterial decomposition of the diseased 

 remains, even at their worst, are such that, if the colony is able to build up or 

 is made sufficiently strong in worker bees, they are able to remove these remains, 

 thereby removing the infection sufficiently to prevent its further development. 

 Bacillus pluton does not form spores and lives only a comparatively short time 

 under unfavorable conditions for growth, as in honey or on long drying. Fur- 

 thermore, as has been demonstrated by the writer in a previous paper (45), 

 this apparent resistance of the Italian bees was observed to be due largely to 

 the racial characteristic of removing all foreign materials more promptly from 

 the hive than do common black bees or hybrids, rather than to any natural 

 resistance or immunity to the disease. 



STRENGTH OF COLONY 



If a colony of bees has been exposed to infection from American foulbrood, 

 the strength of the colony apparently has no direct relation to the development 

 of the disease, except that strong colonies are usually the ones which rob the 

 weaker infected colonies, thereby spreading the infection through the apiary. 

 As suggested above, European foulbrood attacks primarily the weak colonies 

 which have an insufficient force of bees to remove the infected material. Dis- 

 eased combs from such a colony can be placed in a strong healthy colony of 

 Italian bees with no resulting disease. This would be fatal in the case of Ameri- 

 can foulbrood. 



SEX 



There has been slight mention in the literature of the relation of the sex of the 

 bee larvsB to the development of disease. Phillips (38) states with regard to 

 European foulbrood: "A symptom of greatest importance is the fact that the 



