LAUSR

Eavesdropping is predicted to evolve between sympatric, but not allopatric, predator and prey. The evolutionary arms race between Asian honey bees and their hornet predators has led to a remarkable defence, heat balling, which suffocates hornets with heat and carbon dioxide. We show that the sympatric Asian species, Apis cerana (Ac), formed heat balls in response to Ac and hornet (Vespa velutina) alarm pheromones, demonstrating eavesdropping. The allopatric species, Apis mellifera (Am), only weakly responded to a live hornet and Am alarm pheromone, but not to hornet alarm pheromone. We observed typical hornet alarm pheromone-releasing behaviour, hornet sting extension, when guard bees initially attacked. Once heat balls were formed, guards released honey bee sting alarm pheromones: isopentyl acetate, octyl acetate, (E)-2-decen-1-yl acetate and benzyl acetate. Only Ac heat balled in response to realistic bee alarm pheromone component levels (