CHARACTERIZATION OF PLANT-DAMAGE CAUSED BY RUSSIAN WHEAT APHID (HOMOPTERA, APHIDIDAE)

The effect of feeding by the Russian wheat aphid, Diuraphis noxia (Mordvilko), on growth of seedling 'TAM W-101' winter wheat (Triticum aestivum L.) was investigated. A primary response of the wheat plant to aphid feeding involves water imbalances expressed as a loss of turgor and reduced growth. Russian wheat aphids caused substantial reductions in biomass of all plant components measured. When aphids were removed, absolute growth rates quickly recovered as relative growth rates increased. Compared with undamaged controls, recovering plants were more efficient in terms of carbon assimilation, which resulted in higher relative growth rates and compensated for lowered leaf area ratios. Reduction in leaf area ratios results from decreases in specific leaf areas (i.e., a combination of leaf stunting and the inhibition of new-leaf unfolding). As plants recovered, stem weight ratios were substantially reduced, indicating that carbon partitioning to the stem was decreased to compensate for leaf and root growth. The cessation of growth of wheat during infestation by the Russian wheat aphid and ability of the host to recover rapidly when the aphid was removed indicate that the duration of infestation, rather than the level of infestation, may be more important to the host.