Abstract:
Sex-related differences in susceptibility to pathogens are a common phenomenon in animals. In the eusocial Hymenoptera
the two female castes, workers and queens, are diploid and males are haploid. The haploid susceptibility hypothesis predicts
that haploid males are more susceptible to pathogen infections compared to females. Here we test this hypothesis using
adult male (drone) and female (worker) honey bees (Apis mellifera), inoculated with the gut endoparasite Nosema ceranae
and/or black queen cell virus (BQCV). These pathogens were chosen due to previously reported synergistic interactions
between Nosema apis and BQCV. Our data do not support synergistic interactions between N. ceranae and BQCV and also
suggest that BQCV has limited effect on both drone and worker health, regardless of the infection level. However, the data
clearly show that, despite lower levels of N. ceranae spores in drones than in workers, Nosema-infected drones had both a
higher mortality and a lower body mass than non-infected drones, across all treatment groups, while the mortality and body
mass of worker bees were largely unaffected by N. ceranae infection, suggesting that drones are more susceptible to this
pathogen than workers. In conclusion, the data reveal considerable sex-specific differences in pathogen susceptibility in
honey bees and highlight the importance of ultimate measures for determining susceptibility, such as mortality and body
quality, rather than mere infection levels.
