942 MICROBIAL DISEASES OF INSECTS 



the bee is favorable for the growth and multiplication of the parasite. 

 The digestive fluids are believed to assist in removing the spore coat. 

 The liberated young parasite finds its way to the walls of the stomach 

 and invades the epithelial cells. Within this epithelial tissue it grows 

 and multiplies with great rapidity, giving rise finally to numerous 

 spores. The cells of the epithelium at times seem to become virtually 

 filled with the parasites. That portion of an epithelial cell that is 

 normally shed into the lumen of the stomach in case of infection bears 

 with it many spores. These are liberated gradually from the frag- 

 ments, become mixed with the partially digested food in the stomach, 

 and are carried onward first into the small and then into the large 

 intestines, and finally pass out of the alimentary tract with the excre- 

 ment. Other bees ingesting these spores become infected. This, in 

 brief, is the life cycle through which the parasite passes. 



In infecting the stomach the parasite reaches the basement mem- 

 brane but does not penetrate it. The muscular part of the organ is, 

 therefore, uninvolved. Likewise when found in the Malpighian 

 tubules the infection does not proceed beyond the basement membrane. 

 The protozoon does not infect the pharynx, the oesophagus, the honey 

 sac, the proventriculus, the small or the large intestine organs which 

 possess a pronounced chitinized intima. So far, Nosema apis has not 

 been encountered in the blood, musculature or any of the other tis- 

 sues of the body. 



Infection in apiaries has been found to occur at all seasons of the 

 year but is greatest during the spring. Experimentally, however, it 

 has been found that bees are susceptible to Nosema apis infection the 

 year round. The role played by food in the causation of Nosema- 

 disease is slight, if indeed it contributes at all appreciably to it. 



The fact determined experimentally, that a suspension of Nosema 

 apis in syrup when fed to bees will produce the disease, shows quite 

 conclusively, however, that infection takes place through the ingestion 

 of the parasite. At present there is no evidence that it takes place 

 otherwise than by way of the alimentary tract. The facts which are 

 known concerning Nosema-disease indicate that the disease may be 

 transmitted: (i) From the infected bees of a colony to healthy bees 

 of the same colony, and (2) from the infec ted bees of a colony to heal thy 

 bees of another colony. Under certain circumstances the infection is 

 not readily transmitted within the hive. For example, colonies which 



