It was found that a high infestation of greenbug. Toxoptera graminum (Rand.), caused a maximum 55% reduction of wheat plant root systems. Measurements made, to determine at what level of infestation this damage became detectable, were: leaf length gain during infestation, dry leaf weight, dry root weight, and final greenbug count. A varied initial infestation of parental greenbugs plus progeny were maintained on individual plants of Pawnee, Ponca, Bison, and Dickinson wheat. For each criterion measured, the first significant difference between check and in-fested plants on the several varieties generally occurred at different infestation levels. Dry root weight showed a maximum loss of from 32% to 55% compared with the control and was the only measurement in which a susceptible winter wheat, Bison, showed less damage than the resistant spring selection, Dickinson. The results indicate that the root systems and above-ground plant parts were approximately equally damaged.

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