Discrimination by the potato leafhopper (Hemiptera: Cicadellidae) of host volatiles from resistant and susceptible alfalfa, Medicago sativa L.

Varieties of glandular-haired alfalfa, Medicago sativa L., with resistance to the potato leafhopper, Empoasca fabae (Harris), have been commercially released. To assess the role of volatile organic compounds in leafhopper resistance, stem and leaf volatiles were collected using vacuum steam distillation from the resistant genotype M. sativa G98A and the susceptible M. sativa Ranger. Whole-plant volatiles were collected using head-space analysis. Gas chromatography-mass spectrometry determined that steam distillates from both G98A and Ranger were composed mainly of alcohols and esters, with 1-octen-3-ol, (Z)-3-Hexenyl acetate, and (Z)-3-hexen-1-ol as major components. (Z)-3-hexenyl acetate was the only major component in head-space samples from G98A and Ranger. No volatiles were unique to either G98A or Ranger, but different ratios of volatiles were detected. Two-choice bioassays of leaf steam distillates and head-space samples found significantly more potato leafhoppers oriented toward volatiles from Ranger than G98A. Leafhoppers were attracted to a 0.0001% solution of 1-octen-3-ol, but not to (Z)-3-bexenyl acetate. Instead of producing volatile repellents, resistance of G98A to the potato leafhopper might be based, in part, on decreased attraction.