The spores do germinate normally inside the bee gut. the harpoon like
structure (polar filament) only injects sporoplasm into the host cells. The
nucleus then go through vegetative reproduction to produce more cells, which
then become spores.  Fumagillin disrupts DNA replication (the process of one
become many cells), so no new spores are produced. so the life cycle of
nosema is disrupted. The detailed mechanism is not clear, one paper says it
disrupts DNA/RNA function, another paper mentions another (I do not remember
the details, read about 14 years ago).

Note, however, that fumagillin does not do anything to the spores that are
sitting inside wax, or honey.  It works *ONLY* after the spores are ingested
and germinated inside the bees. It can remove spores (from the pool) only if
bees eat the spores during the period that fumidil is inside the hive (and
available for bees to eat) and stays effective.  Once fumidil loses its
effectiveness, or fumidil-honey is gone, any spores that are still in the
colony can start more infections. 


Zachary Huang, beetographer
http://www.beetography.com

****************************************************
* General Information About BEE-L is available at: *
* http://www.honeybeeworld.com/bee-l/default.htm   *
****************************************************