Effect of infestation by aphids on the water status of barley and insect development

Abstract

To compare the effects of aphid infestation with some effects of wounding and drought-stress, several physiological parameters and metabolite concentrations were measured in infested, mechanically wounded or water-stressed young barley plants (Hordeum vulgare cv Aramir). Barley plants infested with the greenbug (Schizaphis graminum) had lower water potentials and CO2 assimilation than non-infested plants. Abscisic acid content increased by 55% in leaves after 72 hr of infestation. Water potentials and stomatal resistance of barley plants changed only as a consequence of infestation by the greenbug or by drought-stress. Proline concentration increased in leaves subjected to infestation or drought by 11- and 14-fold, respectively. Leaves with artificial damage showed the same reduction in chlorophyll contents as leaves of drought-stressed plants. Greenbug infestation caused higher chlorosis than other treatments. Contents of soluble carbohydrates and proteins decreased 52 and 38% by infestation, 38 and 28% by drought, and 14 and 8% by artificial leaf damage, respectively. To study the influence of these treatments on the quality of barley plants as a food source for the aphids, developmental rates () and the mean relative growth rates (MRGR) of nymphs reared on these seedlings were compared. New Aphids reared on previously infested seedlings had the lowest MRGR and (ca 82 and 68%, respectively) compared to aphids on control plants without previous infestation. Aphids reared on plants subjected to drought also had lower MRGR and (ca 89% and 77%). Greenbugs on wounded leaves had similar MRGR and rates to nymphs reared on control plants. These results show that greenbug infestation of barley produced changes similar to those observed in plants subjected to drought-stress and that aphids feeding on both groups of seedlings had lower developmental and mean relative growth rates. Water-stress caused in barley by aphid infestation or drought would probably affect greenbug development due to the effects of stress on the chemical composition of the plant