Nosema spp. infection of house bees. A: Percentage of colonies infected by Nosema spp. in each group before and after the interventions in autumn 2007 and spring 2008 based on the PCR analysis of the composite samples of house bees. The experimental groups of colonies were established as follows: group 1 T (treatment in autumn 2007), group 2 T (treatment in autumn 2007 and spring 2008), group 4 T (treatment in autumn 2007, winter, spring and summer 2008), group CS (sugar syrup in autumn 2007, winter, spring and summer 2008) and group C (unmanaged colonies). B: Individual worker analysis (n = 20 house bees) in randomly selected colonies, and the corresponding results when composite samples from the same colonies were analysed (n ≥ 30 house bees). Hyphens indicate no PCR signal for this Nosema species in the individual bees analysed.