28 BULLETIN 780, U. S. DEPARTMENT OF AGKICULTUKE. 
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 weaken 
it. The weakness resulting does not occur immediately following the 
infection, however. During the active brood-rearing season the 
you'ng bees reared may exceed the loss from disease and the colony 
will then actually gain in strength. On comparison of colonies that 
are infected with those that are not, however, it will be seen that the 
infected ones 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 different members of the colony. 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 adult 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 under 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 confined. At the end of a week out of 119 bees confined 108 
(91 per cent) had died. On December 15, 1914, the experiments were 
i Small triangular cages devised by Mclndoo (1917, p. 4) in his studies on the honeybee. 
