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Primer pheromones are thought to act in a variety of vertebrates and invertebrates but only a few have been chemically identi¢ed. We report that a blend of ten fatty-acid esters found on the cuticles of honeybee larvae, already known as a kairomone, releaser pheromone and primer pheromone, also act as a primer pheromone in the regulation of division of labour among adult workers. Bees in colonies receiving brood pheromone initiated foraging at signi¢cantly older ages than did bees in control colonies in ¢ve out of ¢ve trials. Laboratory and additional ¢eld tests also showed that exposure to brood pheromone signi¢cantly depressed blood titres of juvenile hormone. Brood pheromone exerted more consistent e¡ects on age at ¢rst foraging than on juvenile hormone, suggesting that the primer e¡ects of this pheromone may occur via other, unknown, mechanisms besides juvenile hormone. These results bring the number of social factors known to in£uence honeybee division of labour to three: worker^worker interactions, queen mandibular pheromone and brood pheromone.

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