Wake Up and Smell the Infected Bees: Volatile Cues of Vairimorpha Infection in Honey Bees

Infection can alter volatile organic compounds (VOCs) across a wide range of taxa, but the effects in adult honey bees remain unexplored. Adult workers are major contributors to colony odour and play a central role in both pathogen transmission and collective disease defence (social immunity). We characterised VOC emissions from Vairimorpha-infected and uninfected worker honey bees over a 14-day infection time series using dynamic headspace sampling and two-dimensional gas chromatography coupled with mass spectrometry (GC × GC-MS). Vairimorpha spp. are globally important gut parasites linked to colony declines. VOC profiles differed significantly between control and infected bees when pooled across all time points, and at days 6 and 12 post-infection, suggesting a 'smell' of infection. Random forest and redundancy analysis identified tetradecane, dodecane, and one unidentified compound as characteristic of early-stage infections, and 3,4-dimethylbenzaldehyde as more abundant during late-stage infections. Our findings provide the first evidence that Vairimorpha spp. infection alters the VOC profile of adult honey bees. We detected robust shifts in VOC profiles that colonies may use to detect disease, which could be harnessed for applied surveillance and/or highlight a potential role for infection odours in regulating social immunity, offering new directions for understanding how parasites interact with host communication systems in social animals.