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Résumé :
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Electroantennogram (EAG) responses were recorded from apterous virginoparae of the vetch aphid Megoura viciae Buckton (Homoptera, Aphididae) to more than eighty volatile compounds in order to investigate its sensory ability to perceive plant odours. The response profile of M. viciae reveals a differential sensitivity for the array of plant volatiles tested. The whole group of general green leaf volatiles is very stimulatory. In addition to (E)-2-hexenal, the following compounds of this group elicit large EAG responses: (E)-2-heptenal, 1-octenol-3, hexyl acetate, (Z)-3-hexenyl acetate, hexanol-1,hexanal, 2-heptanone and 3-octanone. Relatively large EAGs are also produced by 4-methoxybenzaldehyde (p-anisaldehyde), hexanonitrile, heptanonitrile, 1,6-hexanedithiol, butyl isothiocyanate, 4-pentenyl isothiocyanate, (-)-(1 S)-beta-pinene, (+)-(S)-carvone, (-)-(R)-carvone, alpha-terpineol, linalool and citronellal. The nitriles are the most effective of all plant volatiles tested. Structure-activity relationships occur in various groups of chemicals and members of the green leaf volatiles, benzaldehydes, isothiocyanates and monoterpenes are ranked accordingly. In the group of green leaf volatiles, aliphatic aldehydes are more stimulating than the corresponding alcohols. EAG responses to series of saturated aliphatic alcohols and aldehydes reveal that C-6 and C-7 compounds are the most stimulatory. Dose-response curves show that the rank order of EAG response amplitudes hardly changes at lower dosages. It is concluded that M. viciae perceives general plant volatiles as well as more-specific components, such as nitriles and isothiocyanates, associated with the odour blends of non-host plant species.
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