Pheromones are pungent messages, warning interlopers to steer clear and attracting attentive mates from miles around, but now it seems that these scented communications could also sharpen an animal's wits. Martin Giurfa from the University of Toulouse, France, and Patrizia d'Ettorre from the University Paris XIII, France, suspected that pheromones could also alter an animal's responsiveness to experiences. With a lengthy career investigating how insects form memories, Giurfa knew that honey bees would be the ideal insect to test his new theory. Having recently discovered that bees defensively extend their stingers after experiencing a mild electric shock, Giurfa, d'Ettorre and their student Natacha Rossi decided to test how pheromone components alter the bees’ responses.

After gently securing individual insects in tiny harnesses, the scientists administered a series of very mild electric shocks while recording whether the bees extended their stingers in defence. Having established the bees’ responsiveness to the gentle shocks, the team gave the insects a 15 min or 24 h break and then transferred the individuals to a glass chamber where they experienced one of three pheromone components – geraniol (which attracts worker bees), 2-heptanone (which repels intruder bees from invading colonies) and isopentyl acetate (which triggers stinging attacks) – before retesting their response to the gentle shocks.

The bees that experienced both sets of shocks in quick succession (15 min apart) tired and responded less during the second set of tests, so the team was pleased when the bees that had been exposed to isopentyl acetate (which primes defensive stinging) seemed to be as responsive to the second set of electric shocks as they had been initially. And the pheromone was equally effective 24 h later. In contrast, the bees were less likely to extend their stingers after bathing in an atmosphere of geraniol, while the repulsive 2-heptanone did not alter the bees’ responsiveness to the gentle shocks.

‘Our findings underline the role of pheromones as potential modulators of different behaviours’, say Giurfa and his colleagues. The trio suspects that pheromones alter the insect's perception of an experience, although they can't rule out the possibility that the chemical messengers could alter the insects’ ability to extend their stingers, and they suggest that pheromones could also affect the ability of insects and other animals to learn from their experiences.

Pheromones modulate responsiveness to a noxious stimulus in honey bees
J. Exp. Biol.
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