The effect of soil nitrogen levels and wheat resistance on the Russian wheat aphid, Diuraphis noxia (Homoptera : Aphididae)

These studies looked at the impact of soil nitrogen (N) levels and wheat, T riticum aestivum L., resistance on the Russian wheat aphid, Diuraphis noxia (Mordvilko). In the first experiment, susceptible 'Stephens' and resistant breeding line '10085-5' were grown in the laboratory and fertilized with 1 00%, 10% or 1% of the normal concentration of N in Hoagland's solution (Hoa gland and Aron, 1950). The second experiment was run simultaneously and was similar, except plants in each fertilizer treatment were infested with 15 fourth-instar D. noxia. In the first experiment, 10085-5 was significantly taller and heavier than 'Stephens' at all N levels. Higher N applications h ad a positive effect on plant height and wet and dry weights within a wheat type. In the second experiment, aphid-infested wheat plants weighed less a nd were shorter than wheat in the first experiment. Higher N applications r esulted in taller and heavier plants within a wheat type. Aphid-infested 10 085-5 weighed more than infested 'Stephens' at all N levels. 'Stephens' and 10085-5 did not Significantly differ in height within an N level. D. noxia tolerance in infested 10085-5, as indicated by change in height and final plant dry weight, decreased as N levels decreased. 'Stephens' had significa ntly more aphids than 10085-5 at all N levels tested. However, N level did not have a significant effect on aphid numbers within a wheat variety. Thus , N levels did not affect antibiosis, as measured by aphid numbers.