Numerous assays exist to measure aggressive behaviour in honeybees, most of them using free-flying bees under natural conditions, with results often variable due to environmental factors. Our study describes a novel, laboratory-based Petri dish assay that uses a moving target treated with the alarm pheromone component isoamyl acetate (IAA). In this assay, aggression levels can be measured in individual bees via recording specific behaviours associated with the different stages of aggression. We used this new assay to investigate the modulating effect of the plant odours lavender and Praescent on aggression in bees, as these odours are reported to have a calming effect on animals. Both short-term (5 min) and long-term (48 h) exposure to lavender and Praescent attenuated aggression, even in the presence of the moving target and IAA. Plant odours may thus be an effective treatment for reducing aggressive behaviour in bees.