There is an update available from the University of Minnesota Honey Bee Diseases and Pests Manual. It's available as a free download from their site here: In the update, they state that "Nosema ceranae has virtually displaced the old species Nosema apis thoughout the U.S. We are still learning about Nosema ceranae, but as of this writing, we DO NOT RECOMMEND THE USE OF FUMAGILLIAN TO TREAT THIS DISEASE."
Has anyone done testing on their hives to confirm this? Randy Oliver states on his website that there are some commercial beeks using Fumigillin to treat Nosema ceranae but using a three fold increase in the dosage. Obviously, off label use.

The update also goes on to state "Research is indicating improper use of fumigillin exacerbates Nosema, making it a bigger problem. We are strongly opposed to unnecessary use of antibiotics to treat bee colonies."

Sounds like it's time to reconsider the profolactic use of Fumagillin altogether.