Melissococcus plutonius is a pathogenic bacterium affecting immature stages of the western honey bee (Apis mellifera) and leads to European foulbrood (EFB) disease. Despite EFB outbreaks increasing in frequency in several countries in recent dec-ades, there is little knowledge on the epidemiology of M. plutonius or on the defence mechanisms of honey bees against this pathogen. Mating of honey bee queens with multiple males (polyandry) can be such a mechanism, as it has been shown to be ben-eficial to colony health and fitness. It is hypothesized that a high level of polyandry was selected for in response to pathogen pressure to maximize the probability that at least some patrilines among nestmates in a colony possess a high degree of resistance to specific pathogens, ultimately protecting colonies against infections. We show that M. plutonius infection provokes differential mortality among patrilines of immature honey bee workers. Such differences indicate a genetic origin of resistance against this pathogen—supporting the polyandry hypothesis—and open up avenues to im-prove control of EFB disease via selective breeding.
