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Résumé :
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Plant water stress and aphid resistant barley affects performance of 2 aphids found on barley, Hordeum vulgare L., and plant response to their feeding. Russian wheat aphid, Diuraphis noxia (Mordvilko), and corn leaf aphid, Rhopalosiphum maidis (Fitch), densities were measured on barley resistant, moderately susceptible and susceptible to Russian wheat aphid; the barley was grown under water stressed and nonwater stressed soil conditions. Russian wheat aphid densities increased more under water stressed conditions than nonwater stressed conditions. Conversely corn leaf aphid densities were greater when water was readily available to the plant, indicating that the effect of plant stress need not be consistent among species of herbivores even for insects of apparent similar feeding strategies, such as aphids. Plant resistance status mediated plant stress effects on aphid performance. Russian wheat aphid densities were greater on the moderately susceptible and susceptible barley lines, and water stress enhanced this trend. These trends resulted in corresponding increases in plant damage, But corn leaf aphid densities did not differ significantly among the barley lines, indicating that barley bred for Russian wheat aphid resistance did not result in a parallel trend of resistance to corn leaf aphid. Plant health was much less affected by corn leaf aphid. These results further emphasize that interspecific aphid variation in performance on plants exist. At a very practical level, when Russian wheat aphid resistance is incorporated into commercial lines, the effect of water stress on Russian wheat aphid feeding damage may be largely overshadowed by plant tolerance to the damaging aphid. Water management geared toward optimizing plant health may reduce effects of Russian wheat aphid when using susceptible commercial barley lines, but it should only be considered an aid to other control tactics given the susceptibility of the plant.
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