EVALUATION OF RUSSIAN WHEAT APHID (HOMOPTERA, APHIDIDAE) DAMAGE ON RESISTANT AND SUSCEPTIBLE HOSTS WITH COMPARISONS OF DAMAGE RATINGS TO QUANTITATIVE PLANT MEASUREMENTS

Resistant and susceptible plant hosts of the Russian wheat aphid, Diur aphis noxia (Mordvilko), were used to evaluate the relationships betwe en damage rating indices and quantitative measurements of plant damage . The degree of association between percentage of leaf chlorosis, leaf rolling, and plant stunting, indicated that these occur independently . Damage ratings based on percentage of chlorosis accurately identifie d highly resistant and highly susceptible entries. When compared with quantitative plant measurements, the most reliable plant damage rating was plant stunting expressed as the percentage of height of a noninfe sted control. No significant relationships between leaf rolling and qu antitative plant measurements were found. However, aphid-caused reduct ions in leaf turgor were closely related to the amount of chlorosis.