Prevalence of Nosema ceranae infection in samples of known-age bees (marked) and mixed age background bees.

Shown are mean ± SE Nosema ceranae infection levels of marked bees and background bees at each age group/sampling event. Marked bees were recently emerged bees at the first sampling event, nurse-aged bees at the second sampling event and forager-aged bees when the third sample was taken. Mean infection prevalence between marked (known-age) and background (unknown, mixed-age) bees on corresponding collection days were not significantly different (P > 0.05). Mean prevalence of infection was significantly higher in marked bees sampled on date 3 than on dates 1 and 2, indicated by different letters (P = 0.0043).