Phenolic acids and resistance to insect attack in Sorghum bicolor

Glucose and quinic acid esters of several hydroxybenzoic and cinnamic acids were identified in methanolic extracts of leaves of 15-day-old Sorghum bicolor together with two O-glucosides. Some of the phenolic acids were also found to occur as insoluble esters of cell wall polysaccharides. While these derivatives did not affect the feeding of Locusta migratoria on sorghum, the free acids, as a mixture, were markedly inhibitory. It was found that Sorghum contained a mixture of hydrolases which could effect the transformation of “inactive” phenolic esters and glycosides into “active” phenolic acids at a high enough concentration to significantly reduce feeding by Locusta.