28 BULLETIN 780, U. S. DEPARTMENT OF AGEICTJLTURE. 



On March 30, 1915, a colony was inoculated, resulting in heavy 

 infection with Nosema apis. On June 17 the inoculation was repeated. 

 Later a swarm was cast. Inoculations were repeated on July 3, 9, 

 17, 24, 31, and August 13. The colony became much weakened and 

 later in the autumn died. 



Beginning on March 22, 1916, a colony was inoculated at irregular 

 intervals thereafter until September. Much brood was being reared 

 in it throughout the season, but its strength in September was about 

 equal to its strength in March. 



The evidence obtained, it will be observed, is sufficient to justify 

 the conclusion that the Nosema infection in a colony tends to vfeaken 

 it. The weakness resulting does not occur immediately following the 

 infection, however. During the active brood-rearing season the 

 youSng bees reared may exceed the loss from disease and the colony 

 will then actually gain in strength. On compsirison of colonies that 

 are infected with those that are not, however, it will be seen that the 

 infected oiies are the weaker. An experimental colony receiving 

 repeated inoculations increases in strength, as a rule, during the first 

 two weeks following the initial feeding through the emergence of 

 young bees, but comparatively little, if any, after the first month. 



The question arises as to whether the weakness is the result of 

 infection in workers, drones, or the queen, or in a combination of 

 these dififerent members of the coloiiy. Brood apparently does not 

 become affected with Nosema apis (p. 10). The weakness in a colony 

 can not be attributed, therefore, to infection of the brood. Infection 

 among drones is rare (p. 11). Loss in strength, therefore, could not 

 be expected to result from infection in the drones. The queen in an 

 infected colony is more often free from the infection than not (p. 11). 

 Weakness from Nosema infection can result, therefore,when the queen 

 is free from infection. By elimination in this way the conclusion is 

 reached that the weakness produced by Nosema infection in a colony 

 is due primarily to infection among the adidt workers. 



Other observations made point to the same conclusion. Workers 

 taken from colonies in which Nosema infection had reached a rather 

 advanced stage were confined in the Mclndoo wire-screen cages * and 

 kept at room temperature. Healthy ones were similarly caged and 

 kept Tmder observation. The relative length of time that the infected 

 and uninfected bees lived under these conditions was noted. 



On December 8, 1914, in each of four cages were placed from 15 

 to 30 bees taken from colonies heavily infected with Nosema apis. 

 By the end of one week, out of 79 bees confined 62 (78 per cent) had 

 died. On the same date bees from another infected colony were simi- 

 larly confibaed. At the end of a week o\it of 119 bees confined 108 

 (91 per cent) had diedj On December 15, 1914, the experiinents were 



1 Small triangular cages devised by Mclndoo (1917, p. 4) in his studies on the honeybee. 



