VOLATILE COMPOUNDS FROM MEDICAGO SPP AS POTENTIAL SIGNALS FOR ALFALFA WEEVIL RESPONSE

Alfalfa weevils (AW), Hypera postica (Gyllenhal), are important pests of alfalfa, Medicago sativa L. Although no resistant cultivars exist, certain wild Medicago species with erect glandular hairs impart repellency to AW. It is felt that leaf and stem volatile compounds work in conjunction with trichomes to produce antixenosis. Our study isolated and tentatively identified volatile compound differences among four alfalfa cultivars and three wild Medicago species using supercritical fluid extraction (SFE) followed by gas chromatography-mass spectrometry. Ninety-six volatile compounds present in the leaves and stems of at least one of the entries were observed. Of these, 17 were unique to the wild species. Three unique compounds, 1-methyl-4-(1-methylethyl)cyclohexanol, (Z)-geraniol, and hexahydrofarnesol are particularly interesting because of their similarity to known insect pheromones. Knowledge of Medicago species volatile compounds should provide a nascent foundation for the pursuit of AW antixenosis.