Hi,

At least one reason why Nosema of any kind would increase more rapidly 
during the winter period in colder climates is the fact that the bees 
are forced to stay in the hives for al that time. During that time they 
still have to relief themselves some times so when that is done in the 
hive it will likely contain some Nosema spores. When other bees then try 
to remove some of the excrements they are automatically picking up 
spores and the infective chain is there and soon taking on an explosive 
character. I don't know at which part of the hive the bees tend to 
relief themselves most, but is is bound to finish up everywhere anyway 
later in the winter, since many bees are by then bursting from/with 
Nosema and no longer release it in the most ideal spots, which would 
have been outside the hive.

Ron van Mierlo

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