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Oeneral Conclusions, — In a stock infected with Nosema apis 

 the behaviour of the bees has in our experience been in striking 

 contrast to that of the members of a colony afflicted with the 

 condition known as " Isle-of-Wight" disease. It is a common 

 experience to find that bees of an infected colony captured 

 entering the hive carrying pollen or nectar are while doing so 

 harbouring very large numbers of the parasite in the spore stage. 

 Loss of flight power has not been found to be a characteristic of 

 Nosema infection until the insect is actually dyinfj. In Isle-of- 

 Wight disease it is usual for this symptom to appear a considerable 

 time before death, if the bees are prevented from sacrificing 

 themselves by crawling and subsequent death from exposure. We 

 have not observed Nosema infected bees to loiter in large numbers 

 about the doorway nor to gather in clusters on the ground, as 

 Isle-of- Wight crawlers do. We have seen them come out, when 

 in extremis, and falling over on the ground, lie upon their backs 

 with feebly moving or trembling legs. Our observations suggest 

 that the course of Nosema disease in a stock may be, first, the initial 

 stage in which workers only are infected. At this stage the disease 

 is not recognisable except on microscopic analysis. The rate of 

 progress appears to depend greatly upon concomitant factors and 

 is not infrequently quite slow. The loss to the stock is to be 

 measured by a shortening of the life of the individual bee and not 

 by a premature cessation of its activities. In the summer the 

 natural increase resulting from the normal egg laying of a healthy 

 queen may greatly outstrip the loss from disease and its presence 

 may be overlooked. At other seasons reduction of the stock from 

 the presence of this parasite is to be expected. Sometimes the 

 parasite appears to die out or to persist in a low proportion of the 

 bees. Survival of the stock in this manner does not imply 

 immunity against Isle-of- Wight disease, and such stocks have been 

 known to succumb later to this disease. A factor of great 

 importance in determining the course of the malady is the infection 

 of the queen. When this occurs, the infection may be expected to 

 spread steadily within the colony as long as she survives. We have 

 shown how potent a disseminator of Nosema an infected queen 

 becomes. The frequency with which loss or death of the queen 

 occurs in Nosema disease, is in striking contrast to her survival in 

 Isle-of Wight disease. 



As regards the occurrence of dysentery in Nosema infection, we 

 have been unable to obtain evidence that this is a primary 

 symptom. Our infected stocks have usually maintained themselves 

 for prolonged periods during which dysentery was not present. 

 We have explained the conditions under which we have been able 

 experimentally to introduce it, with a resultingly increased 

 mortality. 



Our main conclusion from a study of the presence of Nosema 

 apis in bee colonies in this country is that this parasite is always a 

 weakening factor, and in the presence of other adverse conditions 

 favourable to the development of dysentery it may become 

 seriously pathogenic to bee stocks. In ordinary circumstances we 

 have not found it to destroy bee colonies in the rapid and virulent 

 manner common in Isle-of-Wight disease, although at the same 



