> very high levels of nosema

The issue is not nosema, but what are you going to do about it. At this point, the only recommended treatment is a potent antibiotic. Fumagillin is not allowed to be used in Europe. Most antibiotics are being outlawed for use on bees in the US. 

Look at Europe: Are their bees suffering more due to the lack of Fumagillin? Because if they aren't there is little justification to use it. Furthermore, studies have shown that the use of antibiotics harms bees, increasing their sensitivity to other chemicals.

> Fumagillin is widely used to treat and prevent Nosema sp. infection of bees in North America, but its use is not permitted in the EU [61]. It is applied to hives in the fall and again in the spring, often in a heavy sugar syrup solution [62].

> Because fumagillin is widely used, most commonly by commercial bee keepers, and is likely an inhibitor of the MDR transporters in bees, it may alone or in combination with other inhibitors create significant sensitivity to otherwise tolerable dosages of pesticides or other toxins which are substrates of the transporters. 

> Johnson et al. [63] also observed increased honey bee sensitivity to tau-fluvalinate following treatment with fumagillin. The seasonal pattern of fumagillin hive treatments coincides with application of oxytetracycline, also shown to sensitize bees to pesticides; also potentially through inhibition of MDR transporters [8]. 

> We show that several compounds commonly encountered by honey bees (fumagillin, Pristine, quercetin) significantly increased honey bee mortality due to ivermectin and significantly reduced the LC50 of ivermectin suggesting that they may interfere with transporter function. These inhibitors also significantly increased honey bees sensitivity to the neonicotinoid insecticide acetamiprid. 

SOURCE:

Guseman, A. J., Miller, K., Kunkle, G., Dively, G. P., Pettis, J. S., Evans, J. D., & Hawthorne, D. J. (2016). Multi-Drug Resistance Transporters and a Mechanism-Based Strategy for Assessing Risks of Pesticide Combinations to Honey Bees. PloS one, 11(2), e0148242.

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