The aim of this study was to identify which Nosema species infect those Apis mellifera worker bees performing different functions in the colony. Samples were taken from different places inside and outside the hive, in the honey flow season. In February 2010, winter hive debris from 30 colonies was analyzed, and based on the microsporidian species identified by multiplex PCR. The following bee colonies (none of which displayed clinical symptoms of the disease) were selected for further analyses to determine the occurrence of microsporidian parasites: 1) colony A/C infected with Nosema apis and N. ceranae (mixed infection), 2) colony A infected with N. apis, 3) colony C - infected with N. ceranae, and 4) colony K - the control, which was free of infection. Between April and August, 20 nurse bees from frames of open brood, and 20 forager bees returning to the hive from pollen-collecting trips were randomly selected from each colony at 30-day intervals. The results of the study indicate that the microsporidian species is determined not only by the type of worker bee (sampling site), but also by the period (month) of the sample collection. Our findings also suggest that regardless of the type of initial infection, bees infected by different microsporidian species and bees free from infection can coexist in colonies.
