An alarm pheromone in the venom gland of Vespa velutina: evidence revisited from the European invasive population.
Alarm pheromones are major communication signals in animals and major semiochemicals in the colony organisation of social insects. We investigated the composition of venom in Vespa velutina, an invasive hornet species accidentally introduced into Europe a decade ago. Crushed venom glands were applied to seven wild V. velutina nests and induced aggressive responses of workers in all the colonies tested. Then, solvent extracts or headspace Solid Phase Micro Extraction (SPME) were analysed and quantified by gas chromatography coupled with either flame ionization detector or a mass spectrometer, and checked retention times to Kovats indices and Linear retention indices (LRI). We compared our results to those obtained in the same species from its native area in a previous study. Nonan-2-one and the 4, 8-dimethylnon-7-en-2-one were found in large amount in the venom gland. Five other molecules including the heptan-2-one, non-8-en-2-one, undecan-2-one and two unknown molecules were also found. Similar compounds were globally found, however, one unknown compound was present in our European population but absent in native area ones and should be identify. Although pheromones are thought to be species-specific, our results suggest that their composition may vary within species due to population history, thus questioning its value as a taxonomic tool. Although our results are preliminary, we also recommend carefully considering the origin of the Vespa velutina individuals chosen to develop pheromone-based methods (attractants or mating disruption) for pest management.