Nosema ceranae has been recently introduced into the honeybee Apis mellifera as a novel
microsporidian gut parasite. To locate the genetic region involved in N. ceranae infection tolerance, we fed N.
ceranae spores to haploid drones of a F1 hybrid queen produced from a cross between a queen of a Nosemaresistant
bred strain and drones of susceptible colonies. The spore loads of the infected F1 drones were used as
the phenotype to identify quantitative trait loci (QTLs) associated with N. ceranae spore load. One hundred
forty-eight infected drones were individually genotyped with microsatellite markers at an average marker
distance of 20 cM along the genome. Four QTLs were significantly associated with low spore load, explaining
20.4 % of total spore load variance. Moreover, a candidate gene Aubergine (Aub) within the major QTL region
was significantly overexpressed in drones with low spore loads than in those with high spore loads. Our results
confirm the genetic basis of Nosema tolerance in the selected strain and show that both additive effects and
epistatic interactions among the QTLs interfere with the tested phenotype.