39 



occurrence of the disease is not governed by climatic 

 conditions. 



The disease is an insidious one, and in its first stages can 

 only be detected by examination with a microscope. For this 

 reason it often becomes well advanced before its presence is 

 suspected. Colonies, apparently healthy, often reveal a high 

 percentage of infection when the bees are subjected to 

 microscopical examination. 



The disease is caused by a microscopic animal parasite 

 consisting of a single cell, which is present in vast numbers 

 in the walls of the chyle-stomach and intestine of diseased 

 bees. This protozoon has been given the name of Nosema 

 Apis, Zand., and, as it belongs to the group called the 

 Microsporidia, the disease has been named Micrasporidiosis . 



During ;ts short life Nosema Apis passes through three 

 stages. Eirst, on emerging from the spore, it is known as a 

 " planont," on account of its capacity to move from place to 

 place; during this stage it wanders in sfearch of a convenient 

 cell in the body of the bee which it can penetrate. As soon 

 as it has entered a cell, the parasite loses its capacity to move 

 and passes into the second stag;e of its life history, when it is 

 called a "meront. " During this stage it feeds, grows, and 

 multiplies enormously, and after a series of changes, each 

 daughter form becomes a spore. The spore is the third form 

 of the Nosema, and it is in this form that the parasite spreads 

 from one colony of bees to another'. The spore has a hard 

 protective coat and is about one-thousandth of the size of a 

 grain of rice, which it resembles in shape. Both planonts 

 and meronts can increase in number by division, though the 

 meronts have a greater capacity in this direction than the 

 planonts. The rate of increase is important since there is 

 reason to believe that the virulence of the epidemic depends 

 on the circumstances which favour the rapid increase or other- 

 wise of the Nosema in the intestine of the bee. Further it 

 should be noted that it is the increase in numbers that causes 

 disease in the infected bee. 



The symptoms of the disease are so variable that until 

 recently Nosema disease has been refeired to under several 

 different names. In its least harmful form it develops slowly 

 and kills very few bees, while the colony is often replenished 

 by the young bees that emerge from the cells. In this form 

 it is commonly termed " spring dwindling," and frequently 

 escapes the notice of all but expert bee-keepers. In other 

 cases the disease is dia,gnosed as " starvation." The loss of 

 foragers ca.us6s a diminution in the income of food supplies, 

 and eventually the colony dies from starvation. It is possible 

 that the combs, if subsequently made use of, may start the 

 disease at indefinite intervals. At other times, especially in 

 the spring, the mortality is so great as to prevent the colony 

 from gathering surplus. 



