The Effects of Insect Parasitism on Plant Competition: Greenbugs and Barley

Abstract

Two cultivars of barley (Hordeum vulgare L.) with an isogenic difference in greenbug resistance were grown with and without greenbugs (Schizaphis graminum Rond., Biotype C: Aphididae). Two pots were grown per treatment for a total of 10 pots without aphids at each 2—wk harvest. Two weeks after infestation, total aboveground biomass was greater for both the resistant and susceptible plants with aphids. Four weeks later, biomass was significantly lower for aphid—infested plants compared to plants without aphids. Belowground biomass also declined after 6 wk of infestation. Root—shoot ratios remained statistically the same between harvests and between the control and experimental treatments with aphids. There was 1 exception. Two weeks after infestation, the root—shoot ratio for plants with aphids was significantly < for those without. Analysis of the de Wit replacement series for aboveground biomass showed that plants with aphids differed from control plants in competitive relationships. With aphids, there was a larger disparity in growth of the resistant and susceptible plants and the resistant plants were generally better competitors.