IDENTIFICATION OF SEMIOCHEMICALS RELEASED DURING APHID FEEDING THAT ATTRACT PARASITOID APHIDIUS-ERVI

Herbivore induced release of plant volatiles mediating the foraging be havior of the aphid parasitoid Aphidius ervi was investigated using th e pea aphid, Acyrthosiphon pisum, feeding on broad bean, Vicia faba. B ehavioral responses were studied using an olfactometer and a wind tunn el. Volatiles obtained by air entrainment of aphid infested plants wer e more attractive to A. ervi than those from uninfested plants, in bot h behavioral bioassays. GC-EAG of both extracts showed a number of pea ks associated with responses by A. ervi, but with some differences bet ween extracts. Compounds giving these peaks were tentatively identifie d by CC-MS and confirmed by comparison with authentic samples on CC, u sing two columns of different polarity. The activity of pure compounds was further investigated by EAG and wind tunnel assays. Results showe d that, of the compounds tested, 6-methyl-5-hepten-2-one was the most attractive for A. ervi females, with linalool, (Z)-3-hexen-1-yl acetat e, (E)-beta-ocimene, (Z)-3-hexen-1-ol, and (E)-beta-farnesene all elic iting significantly more oriented flight behavior than a solvent contr ol. Foraging experience significantly increased parasitoid responses t o these compounds, with the exception of (E)-beta-farnesene. Time-cour se GC analysis showed that feeding of A. pisum on V. faba induced or i ncreased the release of several compounds. Release of two of these com pounds (6-methyl-5-hepten-2-one and geranic acid) was not induced by t he nonhost black bean aphid, Aphis fabae. During the analysis period, production of (E)-beta-ocimene remained constant, but 6-methyl-5-hepte n-2-one, linalool, geranic acid, and (E)-beta-farnesene appeared durin g the first day after A. pisum infestation and increased in concentrat ion with increasing time of aphid feeding.