Insect Sci. Applic. Vol. 20, No. 3, pp. 181-189, 2000 0191-9040/00 $3.00 + 0.00 Printed in Kenya. All rights reserved © 2000 ICIPE IDENTIFICATION OF BEHAVIOURALLY ACTIVE COMPONENTS FROM MAIZE VOLATILES FOR THE STEMBORER PARASITOID COTESIA FLAVIPES CAMERON (HYMENOPTERA: BRACONIDAE) ADELE J. NGI-SONG, PETER G. N. NJAGI, BALDWYN TORTO AND WILLIAM A. OVERHOLT International Centre of Insect Physiology and Ecology (ICIPE) P.O. Box 30772, Nairobi, Kenya {Accepted 20 November 2000) Abstract—In the present study, Y-tube olfactometric assays confirmed that volatiles from maize seedlings infested with Chilo partellus larvae were more attractive to the borer's larval endoparasitoid Cotesia flavipes, than volatiles from uninfested maize. Coupled gas chromatography- electroantennographic detector (GC-EAD) analysis of the volatiles from larvae-infested maize revealed six electrophysiologically active compounds on the antennae of the female parasitoid. These compounds were identified by GC-MS as (Z)-3-hexenyl acetate, linalool, (E)-4,8-dimethy 1-1,3,7- nonatriene, heptanal, (E)-p-ocimene and a C-5 aliphatic compound. (E)-4,8-Dimethyl-l, 3, 7- nonatriene was present in EAG-detectable amounts in the volatiles of uninfested seedlings. In bioassays, a blend comprised of (Z)-3-hexenyl acetate, linalool, (£)-4,8-dimethyl-1,3,7-nonatriene, (E)-P-ocimene and heptanal was significantly attractive to the parasitoid. Of the individual compounds, (Z)-3-hexenyl acetate was attractive at the doses tested while (E)-4,8-dimethyl-l, 3, 7- nonatriene and heptanal showed varying degree of attractiveness to the parasitoid at different doses. Linalool and (E)-p-ocimene were unattractive at the same doses. The significance of these results is discussed. Key Words: Chilo partellus, tritrophic system, Cotesia flavipes, GC-EAD, Zea mays, plant volatiles, Braconidae, Pyralidae Resume—Dans cette etude, des essais olfactometriques en tubes Y ont confirme que les matieres volatiles de jeunes plants de mai's infestes par des larves du foreur de tige, Chilo partellus attiraient plus de larves de Cotesia flavipes un endoparasitoi'de de ce foreur, en comparaison des matieres volatiles du mai's non infeste. L'analyse par chromatographie a phase gazeuse couplee avec un detecteur electro-antennographique des matieres volatiles du mai's infeste de larves a revele six composes avec des activites electro-physiologiques sur les antennes de la femelle du parasitoi'de. Ces composes ont ete identifies par methodes GC-MS comme (Z)-3-hexenyle acetate, linalol, (E)- 4,8-dimethyle-l,3,7-nonatriene, heptanal, (E)-P-ocimene et un autre compose, le C-5 aliphatique. (E)-4,8-dimethyle-l,3,7-nonatriene etait present en quantites detectables par methode EAG, dans les matieres volatiles de jeunes plants non infestes. Au cours des essais biologiques, un cocktail fait de (Z)-3-hexenyle acetate, de linalool, de (E)-4,8-dimethyle-l,3,7-nonatriene, de (E)-P-ocimene et d'heptanal, attirait fortement le parasitoide. Quant aux differents composes pris isolement, (Z)-3- hexenyle acetate etait attrayant aux doses testees tandis que (E)-4,8-dimethyle-l,3,7-nonatriene et heptanal montraient des degres variables d'attractivite a differentes doses. Le linalol et (E)-P-ocimene ne montraient pas d'attrait aux memes doses. L'article discute de la signification des resultats obtenus. Mots Clcs: Chilo partellus, systeme tritrophique, Cotesia flavipes, GC-EAD, Zea mais, matieres volatiles vegetales, Braconidae, Pyralidae Corresponding author: AJN-S. E-mail: angisong@icipe.org 181