Worker genetic diversity and infection by Nosema apis in honey bee colonies

The hypothesis that parasites and pathogens select for polyandry in eusocial Hymenoptera was tested, using the honey bee Apis mellifera and its microsporidian parasite Nosema apis. Five honey bee colonies with low and five with high worker genetic diversity were infected with N. apis spores. At 54-56 days after inoculation, parasite spores in the workers' midguts were counted to determine whether there was a greater variation of infection intensity (spore counts per worker) in high-diversity colonies than in low-diversity ones. In all colonies there were two discrete sets of workers, with few or many parasite spores. To compare the variations of infection intensity between two colony groups, coefficients of variation were calculated for all workers examined, and for the slightly infected and strongly infected workers. The percentages of slightly infected workers in the low- and high-diversity groups were also compared. None of the comparisons between low- and high-diversity colonies showed significant differences, therefore no relation was found between honey bee workers' genetic diversity and their infection with N. apis.