Resistance in Barley to the Greenbug, Schizaphis graminum.1 1. Toxicity of Phenolic and Flavonoid Compounds and Related Substances2

Abstract

Biotype B greenbugs, Schizaphis graminum (Rondani) (Homoptera: Aphidae), were reared on chemically defined diets containing some commercially available phenolic and flavonoid compounds individually incorporated at 3.75 × 10−4M or less. Compounds having ortho-hydroxyl groups which included catechol, tannic acid, quercetin, chlorogenic acid, and protocatechuic acid, were detrimental to greenbug growth; almost none of the progeny survived when these compounds were included in the diet and the number of progeny was drastically reduced. Cis-caffeic acid at 7.6 × 10−5M greatly reduced growth, and reproduction was nil whereas trans-caffeic acid at 1.9 × 10−4M somewhat reduced weight gain but had no effect on reproduction. Another group of compounds, less toxic but one which effectively reduced the survival of the progeny, were either benzoic or cinnamic acid derivatives having a para-hydroxyl group. There was less than 20% survival of greenbugs feeding on diets that included vanillic, sinapic, syringic, gentisic, or ferulic acids. Many of these compounds are constituents of barley leaves. It is therefore likely that at least part of the resistance to greenbugs of some barley varieties is attributable to the presence of these phenolic and flavonoid substances in quantities sufficient to retard the insect's growth and reproduction.