David L. Dreyer

Feeding deterrency of flavonoids and related phenolics towards Schizaphis graminum and Myzus persicae: Aphid feeding deterrents in wheat

Abstract A number of naturally occurring flavonoids have been tested for their feeding deterrent activity against two aphid species, Schizaphis graminum and Myzus persicae . Most flavonoids, including a number of dihydrochalcones related to phloretin, showed strong deterrency at concentrations well within the range often found in plants. Flavanone and flavone glycosides showed weak feeding deterrency relative to their corresponding aglycones. S. graminum and M. persicae responded similarly towards the compounds tested. The feeding deterrency of wheat extracts towards S. graminum was confined to the phenolic fraction, which included the flavone tricin. The more polar phenolic fraction showed the strongest feeding deterrency towards S. graminum.

Feeding deterrency of some pyrrolizidine, indolizidine, and quinolizidine alkaloids towards pea aphid (Acyrthosiphon pisum) and evidence for phloem transport of indolizidine alkaloid swainsonine

The feeding deterrency of a series of pyrrolizidine, indolizidine, and quinolizidine alkaloids and selected derivatives was measured against the pea aphid (Acyrthosiphon pisum Harris). The indolizidine alkaloid, castanospermine, was intensely active (ED50, 20 ppm) as were the quinolizidine alkaloids, but only modest feeding deterrency was observed with most of the pyrrolizidine alkaloids tested. The insect survival rate of aphids on a castanospermine-supplemented diet over 24 hr was also very low relative to the controls. Castanospermine does not inhibit aphid trehalase. The indolizidine alkaloid swainsonine occurred in the honeydew of pea aphid feeding on the locoweed,Astragalus lentiginosus. Since the pea aphid is a phloem feeder, swainsonine must be transported in the phloem.

PROBING BEHAVIOR OF THE GREENBUG (SCHIZAPHIS GRAMINUM, BIOTYPE C) ON RESISTANT AND SUSCEPTIBLE VARIETIES OF SORGHUM

The probing behavior of biotype C of the greenbug, Schizaphis graminum (Rondani) on susceptible and resistant lines of sorghum, Sorghum bicolor (L.) Moench., was electronically monitored. Waveforms corresponding to salivation, phloem ingestion and non‐phloem ingestion are described. The results of a parallel study revealed that the rate of population growth of S. graminum was significantly greater on susceptible lines of sorghum [i.e., NC + 70X. SC423 (Purple). SC423 (Tan)] than on resistant lines (i.e., TAM 2567, IS 809). Aphids probing the resistant lines of sorghum showed a significantly reduced imbibition of phloem sap compared with those aphids which fed on susceptible varieties. Also, increased numbers of separate probes and increased duration of non‐probing were associated with greenbugs feeding on resistant lines. Greenbugs monitored on the nonhost plant, rice, exhibited non‐phloem ingestion, but not phloem ingestion.

Aphid feeding deterrents in sorghum : Bioassay isolation and characterization.

Improvements in a synthetic diet for use in a bioassay to screen for feeding deterrents againstSchizaphis graminum, greenbug, are reported. Feeding on the synthetic diet was highly pH dependent with maximum feeding occurring at about pH 8.0. The bioassay was used as a guide in the isolation of feeding deterrent substances from aphid-resistant lines of sorghum (Sorghum bicolor). The major greenbug feeding deterrents isolated from sorghum leaves wereP-hydroxybenzaldehyde (ED50 0.13%), dhurrin (ED50 0.16%), and procyanidin (ED50 0.08%).

Citrus bitter principles—V. : Botanical distribution and chemotaxonomy in the rutaceae

Abstract Examination of the limonoids in extracts from seeds of twenty-six Citrus species and hybrids showed limonin to be present in every case, and, with two exceptions, in greater amounts than obacunone and deacetylnomilin. Limonoids have also been shown to occur in the related genera, Poncirus, Microcitrus and Fortunella . New results are presented on the distribution of limonoids in other genera of the Rutaceae, i.e. Casimiroa, Evodia and Calodendrum . The value in chemical taxonomy of these data when combined with previous results is discussed. Comparison is made with limonoids occurring in the Meliaceae, and limonoid degradation products, the simaroubolides, occurring in the Simaroubaceae. In general, the distribution pattern of limonoids and simaroubolides in the Rutaceae, Meliaceae and Simaroubaceae correlates very well with the botanical divisions based upon orthodox taxonomy. Isopimpinellin has been isolated from seeds of Aeglopsis chevalieri Swing. and Bergapten from Cneoridium dumosum (Nutt.) f. Xanthotoxol and alloimperatorin have been isolated from seeds of Poncirus trifoliata .

Evolution of limonoids in the meliaceae

Abstract The structural types of limonoids or meliacins can be characterized in terms of complexity by their position along biosynthetic routes on a biogenetic map, as well as by their basic skeletal specialization and state of oxidation. Genera of the Melioidease, one major subfamily of the Meliaceae, contain meliacins formed along several biosynthetic routes and characterized by relatively low skeletal specializations and oxidation states. Genera of the Swietenioideas, the other major subfamily of the Meliceae, contain meliacins formed along only one biosynthetic route and characterized by relatively high skeletal specializations and oxidation states. Evolutionary trends of meliacin chemistry thus correspond to the morphological division of the Meliaceae.

Grindelane diterpenoid acids from Grindelia humilis: Feeding deterrency of diterpene acids towards aphids

Abstract Two new labdane diterpene acids have been isolated from Grindelia humilis . The spectroscopic properties of the acids and their derivatives, as well as conversion to methyl 6-oxogrindelate, showed that they were the epimeric pair 6α-hydroxy- and 6β- hydroxygrindelic acid. A series of 11 diterpene acids were surveyed for their feeding deterrency towards the aphid Schizaphis graminum . The substances tested showed a wide range of activity.

Further studies on constituents of Thamnosma montana Torr. and Frem. : The structure of thamnosin, a novel dimeric coumarin system

Abstract The structure determination of thamnosin, a minor component obtained from Thamnosma montana Torr. and Frem. is described. Thamnosin (VI) represents a novel dimeric coumarin system which was not previously encountered in nature.

Effect of bioregulator-treated sorghum on greenbug fecundity and feeding behavior: implications for host-plant resistance

Abstract Three commercial and six experimental plant growth bioregulators were surveyed for their effect on aphid reproduction when applied to sorghum. Only CCC and PIX had a significant effect on the greenbug, Schizaphis graminum. Application of the commercial bioregulators CCC and PIXR caused about a 50% decrease in aphid reproduction rate when applied to greenbug susceptible sorghum but had little effect when applied to a greenbug resistant sorghum line. Electronic monitoring of aphid probing behavior on CCC treated, greenbug-susceptible sorghum showed a response pattern which was indistinguishable from that normally observed on greenbug resistant lines and was different from that associated with aphid probing behavior on untreated susceptible lines. The isolated pectin content of the CCC treated susceptible sorghum was twice that of the controls and had twice the methoxy content. These results support the argument that pectin is a barrier to aphid-stylet penetration for phloem feeding aphids which probe intercellularly and that manipulation of pectin content and/or structure can be a major factor in host-plant resistance to sap-sucking insects.

Feeding deterrency of some 4-hydroxycoumarins and related compounds: Relationship to host-plant resistance of alfalfa towards pea aphid (Acyrthosiphon pisum)

A series of 3-acyl-4-hydroxycoumarins, structurally related to dicoumarol, as well as several alfalfa constituents including coumestrol were tested for their feeding deterrency towards the pea aphid. Feeding deterrency of the 3-acyl-4-hydroxycoumarins decreased as the size of the 3-acyl group increased.