CHANGES IN FERULIC ACID AND LIPID-CONTENT IN APHID-INFESTED BARLEY

Aphid infestation reduced the susceptibility of barley cultivars to ne w infestations. The intrinsic growth rate of aphids was lower in the p opulations reared on previously infested plants, than in populations r eared on barley without previous infestation. Changes in the content o f ferulic acid, and other aromatic compounds and lipids, were detected in barley seedlings infested by the aphid, Schizaphis graminum. Ferul ic acid concentration increased from 4 to 14 mu mol kg(-1) fresh wt, a s a function of infestation level by aphids. Survival of aphids reared with diets containing this compound was lower than the controls. Aphi d survival at 24 hours was under 58% and 40% in diets with 10 and 20 m u M ferulic acid, respectively. In diets without the compound, surviva l was 84%. Analysis of alicyclic and aliphatic compounds in extracts o f infested and non-infested barley plants showed differences in the re lative concentrations of compounds. Our results suggest that the incre ase of ferulic acid induced by initial infestation may protect the pla nt against new infestations. Changes in lipid concentrations could be an acclimatization response of the plant to water-stress caused by the aphids.