Evaluation of Fumagilin-B^® and other potential alternative chemotherapies against Nosema ceranae-infected honeybees (Apis mellifera) in cage trial assays

Fumagilin-B® is the only currently registered chemical treatment available to combat nosema disease in apiculture. Fumagillol, the basic hydrolysis product of fumagillin, two semisynthetic fumagillin analogues, and four in-house purely synthetic compounds which were designed to mimic the mode of action of fumagillin against the methionine aminopeptidase type 2 (MetAP-2) enzyme, was observed to exhibit statistically significant biological activity against Nosema ceranae-infected caged bees. None of these compounds were, however, as effective as Fumagilin-B®. The commercially available thymol and enilconazole also exhibited activity against N. ceranae, with thymol being the most promising chemical treatment other than Fumagilin-B®. High cumulative bee mortality was associated with the therapeutic dosage of Fumagilin-B® during our study, suggesting the need for continued investigation.