Poison and alarm: the Asian hornet Vespa velutina uses sting venom volatiles as alarm pheromone

In colonial organisms, alarm pheromones can provide a key fitness advantage by enhancing colony defense and warning of danger. Learning which species use alarm pheromone and the key compounds involved therefore enhances our understanding of how this important signal has evolved. However, our knowledge of alarm pheromones is more limited in the social wasps and hornets as compared to the social bees and ants. Vespa velutina is an economically important and widespread hornet predator that attacks humans and honey bees. This species is native to Asia and has now invaded Europe. Despite growing interest in V. velutina, it was unknown if it possessed an alarm pheromone. We show that these hornets use sting venom as an alarm pheromone. Sting venom volatiles were strongly attractive to hornet workers and triggered attacks. Two major venom fractions, consisting of monoketones and diketones, also elicited attack. We used GC-EAD and identified 13 known and three unknown aliphatic ketones and alco...