MICROBIAL DISEASES OF INSECTS 943 



in the spring of the year show less than 50 per cent of Nosema-infected 

 bees are likely to recover from the infection without treatment. A 

 colony may contain a small percentage of Nosema-infected bees 

 throughout the year and not become heavily infected at any time. 

 Colonies experimentally inoculated in June, July, or August are practi- 

 cally free from the infection within six weeks. This is probably due 

 to the fact that the young bees replace those dying of the infection. 



To the contrary, however, when heavy losses occur among the 

 workers in the spring the colony suffers as there are no young bees to 

 replace those lost as a result of the infection. 



Colonies which die out or become weakened by the disease furnish 

 conditions which invite robbing. Robbing in a certain number of 

 cases probably results in the transmission of the disease but this like- 

 lihood seems not to be nearly as great with Nosema-disease as in the 

 case of the foulbroods. 



Death from Nosema-infection takes place during the active bee 

 season in from two weeks to a month; during winter the disease may run 

 two or three months or even more. Infected drones die sooner than 

 infected workers but infected queens probably live longer. It is quite 

 likely that the age of the bee when infected is not a negligible factor in 

 determining the course of the disease. Whether a bee once infected 

 ever recovers from the infection has not yet been established definitely. 

 From what is known of diseases in man and animals, however, recovery 

 might be expected in a certain percentage of Nosema-infected bees. 

 The data so far indicate that recovery from Nosema-infection among 

 worker bees is comparatively rare. 



METHOD OF CONTROL. Experiments show that brood combs need 

 not be destroyed as no Nosema-infection occurs even when brood-combs 

 from Nosema-infected colonies are inserted immediately into healthy 

 colonies. When medicated diluted honey is fed to Nosema-infected 

 colonies, using different drugs, some drugs prove efficaceous while 

 others have no effect. White states that these latter experiments are 

 altogether too few for definite conclusions as to the extent of their action. 



Two probable sources of infection are the presence of a sluggish 

 body of water near an apiary which is used by bees as a water supply 

 and the robbing of diseased colonies, and these are more or less under 

 control. The disease does not seem to be spread through the medium 

 of flowers, by the hands and clothing of the apiarist, the tools used 



