DISEASES OF BEES 15 



bees taken from brood combs containing large numbers of larvae 

 sick or dead of European foul brood have quantities of bacteria in 

 their rectal ampullae. Among these the secondary invaders found 

 in European foul brood are usually most prominent, especially 

 B. alvei and small rod-shaped bacteria, but B. pluton organisms 

 are frequently present. European foul brood has been produced in a 

 healthy nucleus by spraying an aqueous suspension of the gut 

 contents of six such bees recently taken from an infected colony 

 over the developing brood, but it is not known how long the parasite 

 will remain alive in the gut of the bee. It is extremely doubtful if 

 B. -pluton multip]i<;s in the digestive tract of the bee. All attempts 

 to demonstrate B. pliAton in the pharyngeal, mandibular or salivary 

 glands of nurse or house-cleaning bees taken from infected stocks, 

 either microscopically or by means of infection experiments, have 

 failed. So far no evidence has been obtained which indicates that 

 this organism multiplies elsewhere than in the gut of the young 

 larva. 



Queens from infected stocks have in no instance caused disease 

 when introduced into healthy queenless nuclei. In these experi- 

 ments the queen and 12 young worker bees were removed from the 

 affected stock and were caged from 1-2 days with candy as the 

 sole source of food prior to introduction. These results verify those 

 obtained by Morgenthaler and his associates working in Switzerland. 



European foul brood has been induced in healthy nuclei early 

 in the brood rearing season by suspending in them combs containing 

 large munbers of decomposing larvae artificially infected by feeding 

 them pure cultures of S. apis or B. alvei and subsequently starving 

 them for four days at hive temperature. These results have been 

 obtained in each of two consecutive seasons. It has been found that 

 when the disease is initiated in this manner it never appears as soon 

 as in nuclei infected directly with B. pluton cells taken from the gut 

 of a young infected larva, especially when this organism is sprayed 

 directly on the eggs and young larvae. There seems to be a definite 

 lag period, usually of about three weeks, during which no infected 

 larvae are seen. It might be inferred from these experiments that 

 B. pluton normally exists in colonies of bees waiting for suitable 

 conditions to multiply, and that these conditions can be induced by 

 putting into the colony very large numbers of decomposing larvae 

 which have been artificially infected with secondary invaders found 

 in European foul brood. This is only a suggestion which must be 

 verified by further experiments. So far all attempts to induce 

 European foul brood in healthy nuclei by " artificial weakening " 

 (removing bees or sealed brood and giving a surplus of eggs and 

 young larvae) have failed, but these experiments were not carried 

 out early in the brood-rearing season. Normally European foul 

 brood can only be induced readily in the early part of the brood- 

 rearing season, and, unlike American foul brood, disappears, or 

 tends to disappear, toward the close of the brood rearing. 



