Nosema ceranae infection disrupts nestmate recognition in honey bees

Social immunity reduces pathogen transmission in eusocial insects by collectively detecting and excluding infected or foreign individuals. In honey bees ( Apis mellifera ), guard workers enforce colony boundaries through nestmate recognition. Here we show that infection with the microsporidian parasite Nosema ceranae weakens this defense. Across 600 behavioral assays, infected workers were 45% less likely to be rejected than uninfected controls. Infection was also associated with modest but significant shifts in cuticular hydrocarbon profiles, the primary cues underlying nestmate recognition. Multivariate analyses revealed modest but significant treatment-associated differences in CHC composition that were not attributable to dispersion effects. These findings demonstrate that infection can degrade the reliability of recognition cues and thereby compromise a core behavioral component of social immunity.