MICROBIAL DISEASES OF INSECTS 941 



this group there is only one species, Nosema apis, that is constantly present in 

 Nosema-disease. The conclusion is naturally reached, therefore, that Nosema apis 

 is the cause of Nosema-disease. Such a conclusion is in harmony with views 

 generally accepted at the present time in regard to proof necessary to establish the 

 causal relation of such a germ to the disease. 



The spore form of Nosema apis is the form most encountered and most readily 

 recognized in making an examination for the parasite. These spores in unstained 

 (India ink) preparations are small, refractile, more or less oval bodies varying some- 

 what in size, but having an average length of 4.46/1 and an average breadth of 2.44/1. 

 In stained preparations the average length and breadth are 4.15/1 and 2.06/1 respec- 

 tively. The spore is surrounded by a somewhat resistant coat which tends to 

 maintain for it a constant form, but it is not a rigid structure, since, when studied in 

 fresh preparations it will be seen to bend to and fro as it is carried along by a current 

 under the coverglass. A source of confusion in the diagnosis of Nosema apis in 

 adult bees is the fact that starch granules from pollen grains of corn and of most of 

 the cereals closely resemble the spores of Nosema apis. This organism has not 

 been cultivated in pure culture by artificial methods. 



Nosema apis suspended in water is destroyed by heating for ten minutes at 

 58; when suspended in honey, 59 is required for destruction. When dried at room 

 and outdoor temperatures respectively it remained virulent for about two months, 

 at incubator temperature about three weeks, and in a refrigerator about seven and 

 one-half months. When dry, fifteen to thirty-two hours direct exposure to the 

 sun's rays is necessary for total destruction; when suspended in water thirty-seven 

 to fifty-one hours is required, while if suspended in honey, destruction is frequent as 

 the temperature of the honey reaches or exceeds 60, a temperature at which the germ 

 is killed by heat. If placed in honey and shielded from the light Nosema apis 

 remains virulent for two to four months at room temperature. Fermentative 

 processes are destructive to the spores in a 20 per cent honey solution in three days 

 at incubator temperature, and in nine days at outdoor temperature while in a 10 

 per cent sugar solution it is destroyed in from seven to eleven days at room tempera- 

 ture. When subjected to putrefactive processes (suspensions made in a i per cent 

 aqueous peptone solution) Nosema apis resists destruction for five days at incubator 

 temperature, for two weeks at room temperature, and for more than three weeks at 

 outdoor temperature. Nosema apis spores in the bodies of dead bees cease to be 

 virulent in one week at incubator temperature, in four weeks at room temperature, 

 in six weeks at outdoor temperature and in four months in a refrigerator, while if 

 the bodies of the dead bees are lying on the soil virulence ceases in from forty-four 

 to seventy-one days. A i per cent solution of carbolic acid destroys the spores of 

 this organism in less than ten minutes. 



METHODS or INFECTION. In general, the manner in which a bee 

 becomes infected with Nosema apis is as follows: Spores which have left 

 the body of an infected bee with the excrement are ingested by the healthy 

 adult bee. As the excrement is usually voided in flight this influences 

 the chance of infection. The environment within the stomach of 



