Anthocorid predators learn to associate herbivore-induced plant volatiles with presence or absence of prey

We investigated how the plant-inhabiting, anthocorid predator, Anthocoris nemoralis. copes with variation in prey, host plant and associated herbivore-induced plant volatiles and in particular whether the preference for these plant odours is innate or acquired. We found a marked difference between the olfactory response of orchard-caught predators and that of their first generation reared on flour moth eggs in the laboratory, i.e, under conditions free of herbivory-induced volatiles. Whereas the orchard-caught predators preferred odour from psyllid-infested pear leaves, when offered against clean air in a Y-tube olfactometer, the laboratory-reared first generation of (naive) predators did not. The same difference was found when a single component (methyl salicylate) of the herbivore-induced plant volatiles was offered against clean air. After experiencing methyl salicylate with prey, however, the laboratory-reared predators showed a pronounced preference for this volatile. This acquired preference did not depend on whether the volatile had been experienced in the juvenile period or in the adult phase, but it did depend on whether it had been offered in presence or absence of prey. In the first case, they were attracted to the plant volatile in subsequent olfactometer experiments, but when the volatile had been offend during a period of prey deprivation, the predators were not attracted. We conclude that associative learning is the most likely mechanism underlying acquired odour preference.