Induction and systemic release of herbivore-induced plant volatiles mediating in-flight orientation of Aphidius ervi

In-flight orientation of the braconid Aphidius ervi in response to volatile s released from broad bean plants infested by the pea aphid, Acyrthosiphon pisum, was studied in a no-choice wind-tunnel bioassay. The role of aphid i nfestation level and duration, systemic production of volatiles by "insect- free" parts of the plant, and the specificity of aphid-induced volatiles on the flight behavior of the foraging female parasitoids were investigated. The upper insect-free part of a three-leaved broad bean plant, which was ba sally infested by a population of 40 A. pisum, released synomones detectabl e by A. ervi females after at least 48-72 hr of infestation, resulting in b oth significant increases iii oriented flights and landings on the source c ompared with uninfested control plants. This suggests that volatiles involv ed in host-location by A. ervi are systemically released by broad bean plan ts either in response to circulation of aphid saliva, circulation of saliva -induced bioactive elicitors, or circulation of the synomones themselves. A ir entrainment extracts of volatiles collected from a broad bean plant infe sted by the nonhost Aphis fabae or an uninfested broad bean plant elicited few oriented flights and landing responses by female parasitoids. These ext racts were significantly less attractive than extracts collected from a bro ad bean plant infested by the host A, pisum, indieating the specificity of synomones elicited by different aphid species on the same plant species.