Mass spectral characterization of fatty acid amides from alfalfa trichomes and their deterrence against the potato leafhopper

Abstract

A homologous series of N-(3-methylbutyl)amides of normal saturated C 14, C 15, C 16, C 17 and C 18 fatty acids were identified as major components of glandular trichome extracts from Medicago sativa G98A, an alfalfa genotype resistant to the potato leafhopper, Empoasca fabae. A second homologous series of N-(2-methylpropyl)amides of C 14 through C 18 normal fatty acids were minor components. Saturated free fatty acids C 12, C 13, C 14, C 15, C 16, C 17 and C 18 were present in trace amounts, as was the N-(3-methylbutyl)amide of linoleic acid (C 18:2). N-(3-methylbutyl)amides and N-(2-methylpropyl)amides of C 14 through C 18 fatty acids, along with the N-(3-methylbutyl)amide of linoleic acid, were synthesized and bioassayed for leafhopper deterrence by applying the compounds to the surface of a sachet containing an artificial diet. Leafhoppers were then offered a two-way choice between diet surfaces treated with the synthetic amides or an untreated control. N-(3-methylbutyl)amides and N-(2-methylpropyl)amides of C 14 through C 18 fatty acids did not deter leafhopper settling in a dose-dependent fashion. In contrast, when tested singly, N-(3-methylbutyl)amide of linoleic acid exhibited dose-dependent deterrence against leafhopper settling. Fatty acid amides localized in alfalfa glandular trichomes likely contribute to leafhopper resistance.