FEEDING AND TOXIC EFFECTS OF FLORAL SESQUITERPENE LACTONES, DITERPENES, AND PHENOLICS FROM SUNFLOWER (HELIANTHUS-ANNUUS L) ON WESTERN CORN-ROOTWORM

Feeding deterrents for adult western corn rootworm, Diabrotica virgifera virgifera LeConte (Coleoptera: Chrysomelidae), some of which were neurotoxic, were isolated from inflorescences of cultivated sunflower by chromatography of ethyl acetate solubles on Toyopearl TSK HW-40F and silica gel. Antifeedants, as measured through a consumption bioassay with treated squash flower disks containing cucurbitacin feeding stimulants for rootworm, were characterized by UV, H-1 and C-13 NMR, and EIMS. Fractionation by these methods gave 15 active principles of which argophyllin A and 3-O-methylniveusin A, both sesquiterpene lactone angelates, were the most potent. Feeding deterrency decreased in the order sesquiterpenes >> diterpenes > flavonoids > dicaffeoylquinic acids. The diterpenoic acid grandifloric acid and its 15-angelate and the flavonoids nevadensin and quercetin-beta-7-O-glucoside were much poorer antifeedants, although more abundant components of sunflower. Synergistic or antagonistic interactions for combinations of deterrents within or between the sesquiterpene, diterpene, and flavonoid classes were not found, indicating sunflower antifeedants act jointly in an additive fashion. The highly active antifeedant germacranolide angelates exhibit structural features and injected symptoms in adult rootworm similar to picrotoxinin, a gamma-aminobutyric acid gated chloride channel antagonist, suggesting a link between sesquiterpene neurotoxicity and GABA.