The volatile compounds emitted from uninfested apple seedlings, cv. Royal Gala, and apple seedlings infested with generalist herbivore Epiphyas postvittana larvae were sampled using headspace collection and analyzed by gas chromatography-mass spectrometry. Nine additional compounds were only detected in infested apple seedlings [including benzyl alcohol, (E)-β-ocimene, benzyl cyanide, indole, (E)-nerolidol, and four unidentified compounds]. Infested apple seedlings produced larger amounts of (Z)-3-hexenyl acetate, linalool, 4,8-dimethyl-1,3(E),7-nonatriene, methyl salicylate, β-caryophyllene, germacrene D, (E,E)-α-farnesene, and (Z)-3-hexenyl benzoate than uninfested plants. Female parasitoids flew exclusively upwind to infested and not to uninfested apple seedlings in wind tunnel choice tests and preferred infested leaflets in still air, even after the removal of larvae. The attraction of a parasitoid to infested apple seedlings in the laboratory and in the field to apple and many other plants in at least six families supports considerable generality of the tritrophic signaling process.