Plants are able to defend themselves against herbivory through several means including the production of airborne volatile compounds that attract natural enemies. The pea aphid, Acyrthosiphon pisum, is able to feed on broad bean plants without inducing detectable changes in volatile emission. Additionally, pea aphids inhibit volatile emission normally increased in response to feeding by the beet armyworm caterpillar, Spodoptera exigua. Some of the caterpillar-induced volatiles that are inhibited by aphid feeding are known attractants to the aphid parasitoid Aphidius ervi. These compounds include the terpene (E)-ß-ocimene and the green leafy compounds (Z)-3-hexen-1-ol and (Z)-3-hexenyl acetate. The ability of aphids to inhibit herbivore-induced volatile signals provides insight into a mechanism by which aphids can overcome induced plant defenses that attract parasitoids and predators by manipulating volatile production.