Patterns of Apis mellifera infestation by Nosema ceranae support the parasite hypothesis for the evolution of extreme polyandry in eusocial insects

We investigated the relationship between infestation levels of Nosema ceranae and patriline membership by sampling individual worker bees from five colonies from both Russian and Italian lineages. Individual workers were tested for N. ceranae infestation level using qPCR, and then genotyped to determine their patriline membership. Levels of N. ceranae infestation differed significantly between lineages and colonies for both Russian and Italian workers. Patriline-based variance was evident only among the Russian workers. There was substantial variation in N. ceranae levels among Italian workers, ranging from 0 to 2 × 109Nosema/bee, but this variation was unrelated to patriline membership. The results for Russian honey bees are congruent with predictions derived from the parasite hypothesis for the evolution of polyandry–patrilinial variance in parasite tolerance contributes to colony level resistance by reducing the probability of catastrophic failure that might occur if a colony was genetically homogeneous.