46 BULLETIlSr 780, U. S. DEPARTMENT OF AGRICULTURE. 



MODES OF TRANSMISSION OF NOSEMA-DISEASE. 



No problem in the study of Nosema-disease is more important than 

 that of its transmission. The problem is at the same time one of 

 the most difficult for complete solution. While further infoiTaation 

 is still much desired, yet it is possible from the studies which have 

 been made to arrive at certain conclusions concerning the manner 

 in which the disease is spread. The discussions which follow are 

 based chiefly upon observations noted in the foregoing pages. 



It is naturally safe to conclude that the transmission of Nosema- 

 disease depends directly upon the transmission of the parasite that 

 causes it. If the course of Nosema apis in nature were followed 

 completely, therefore, the problem relative to the spread of the disease 

 would be solved. Such a task is difficult, as the possible sources 

 for the parasite and the accompanying conditions are various. 



The fact, determined experimentally, that a suspension of Nosema 

 apis in sirup when fed to bees wiU produce the disease shows quite 

 conclusively that infection takes place through the ingestion of the 

 parasite. At present there is no evidence that it takes place other- 

 wise than by way of the alimentary tract. This leads to the im- 

 portant tentative conclusion that the transmission of the disease is 

 effected through either the food or the water supply of bees, or both. 



On reaching the stomach by ingestion the parasite begins its growth, 

 invades the walls of the organ, multiplies enormously, and forms 

 spores which are shed into the lumen and passed out of the alimentary 

 tract with the excrement. The chances that any single parasite once 

 outside the bee will be ingested and cause infection are very sUght. 

 The immense number that are produced, however, increases the 

 chances very greatly. Again, the chances of infection are very much 

 reduced by the many destructive agencies in nature encountered by 

 the parasite. Among these are drying (p. 31), heat (p. 29), direct 

 sunUght (p. 37), fermentation (p. 33), and putrefaction (p. 35). 



The excrement is voided normally during flight and most often 

 soon after the bee leaves the hive. Should the droppings from in- 

 fected bees fall into a body of water, such water would become 

 thereby contaminated with the Nosema parasite and the use of it 

 by bees would expose them to infection. Should the body of water 

 be a rapidly flowing one, natinally the chances that other colonies 

 of the apiary might become infected from such a source would be 

 less than if it were a sluggish one. Should such contaminated water 

 be exposed to the sun, the rays of the latter would have a tendency 

 to destroy the parasites. The resistance of Nosema apis to the de- 

 structive effects of the sun's rays (p. 38) are sufficiently great, 

 however, that there would still remain a strong likelihood that infec- 

 tion might take place from the water supply. While in the water 



