> I observed that N. ceranae infection significantly reduced honey bee longevity in the laboratory but did not influence overall colony health or strength in the field. Crucially, a lack of standardized tests to tease apart factors influencing parasite development and virulence have hampered recent efforts due to the diversity of variables selected for in these studies and the conflicting results produced.
> 
> Many stressors limit growth of colony numbers around the world, such as parasites, changes in land-use and climate, insufficient genetic diversity, and socio-economic factors. A lack of understanding about how these factors affect honey bee health has resulted in an inability to mitigate losses. 
> 
> Ultimately, how or if a parasite is managed by beekeepers depends on colony-level effects during typical apiculture scenarios directed towards pollination and honey production. Strategies for preventing and controlling N. ceranae at appropriate times using a variety of methods that target all life stages are required when infection contributes colony mortality or reduced productivity. Conversely, if N. ceranae contributes little to colony vitality, attention should focus on other more economically important parasites.

Geoffrey R. Williams (2013) NOSEMA CERANAE IN WESTERN HONEY BEES (APIS MELLIFERA): BIOLOGY AND MANAGEMENT

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