Diminishing fumagillin levels result in hyperproliferation of Nosema ceranae.

Fumagillin is the only approved antibiotic drug to control nosema disease in honey bees and has been extensively used in United States apiculture for more than 50 years. It is known to be toxic to mammals and must be applied periodically and with caution to avoid residues in honey. We show that the current seasonal application protocol for fumagillin may benefit microsporidia, especially Nosema ceranae, allowing hyperproliferation of the pathogens when the drug is diluted to low levels as occurs in hives over the spring and summer. Further investigations suggest that fumagillin continues to alter proteins in the honey bee midgut under very low dosages. N. ceranae is apparently released from the suppressive effects of fumagillin at dosages that continue to impact the bee midgut tissues, resulting in spore production that is significantly higher than in untreated bees. N. apis is likewise released to produce more spores, although not significantly more than in untreated bees, and release occurs at lower dosages than for N. ceranae. Diminishing fumagillin levels in hives may further compromise bees to Nosema spp. infection and proliferation.;