"In colder winter areas, treatment with fumagillin in fall may well help if you've checked to confirm that your colonies are actually infected with nosema."
Recent work on this is equivocal.
See:
Huang, Wei-Fone, et al. "Nosema ceranae escapes fumagillin control in honey bees." PLoS pathogens 9.3 (2013): e1003185. ?
These authors found that fumagillin treatment, while temporarily reducing the numbers of sick bees, actually makes infection worse because the Nosema initially responds to the presence of fumagillin within the bee by increasing spore production. This result is of great concern to me, since what happens in truly cold climates (i.e. months of confinement) is as follows: 1. Treat bees with fumagillin in fall, 2. Bees form cluster, sick bees die, 3. Bees start looking for protein to build brood in late December-early January, also clean up combs a bit to prepare for brood, (meanwhile sub-zero temps prevent beekeeper intervention) 4. Bees eat dead Nosema-infected bees to get protein, 5. Lots of spores in dead bees re-infect colony, 6. Spring dwindle.
Williams, Geoffrey R., et al. "Does fumagillin control the recently detected invasive parasite Nosema ceranae in western honey bees (Apis mellifera)?." Journal of invertebrate pathology 99.3 (2008): 342-344.
Conclusion by these authors is "temporary reduction" in the parasite...not elimination.
Higes, Mariano, et al. "The stability and effectiveness of fumagillin in controlling Nosema ceranae (Microsporidia) infection in honey bees (Apis mellifera) under laboratory and field conditions." Apidologie 42.3 (2011): 364-377.
Found that infection escalates 4 months after treatment.
Higes, Mariano, et al. "The stability and effectiveness of fumagillin in controlling Nosema ceranae (Microsporidia) infection in honey bees (Apis mellifera) under laboratory and field conditions." Apidologie 42.3 (2011): 364-377.
Found that Fumagillin reduces Nosema temporarily, with resurgence after treatment is stopped.
Now this one is a bit of progress:
Maggi, Matías, et al. "Effects of the organic acids produced by a lactic acid bacterium in Apis mellifera colony development, Nosema ceranae control and fumagillin efficiency." Veterinary microbiology 167.3 (2013): 474-483.
They found that feeding bees organic acids (from lactic acid fermentation) supplemental to sugar syrup and fumagillin enhanced the efficiency of fumagillin.
There are many more studies showing that fumagillin doesn't cure a hive of Nosema. You cannot eliminate Nosema from an infected colony, all you can do is temporarily reduce the infection level. That might work well in warmer climates but I question whether it's really helping here as a fall treatment, where it's really cold for months at a time. Requeening may be as effective as using fumagillin and if you raise your own queens it is certainly cheaper. But requeening is risky in the fall unless you know you have a proven queen and she's been well-accepted by the colony.
Christina
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