RUSSIAN WHEAT APHID (HOMOPTERA, APHIDIDAE) POPULATION DEVELOPMENT AND PLANT-DAMAGE ON RESISTANT AND SUSCEPTIBLE WHEAT

The resistant wheat plant introductions PI 137739 and PI 262660 and the susceptible wheat (Triticum aestivum L.) cultivar 'Stephens' were used to determine the effects of varying Russian wheat aphid, Diuraphis noxia (Kuvdjumov), population densities (0, 10, and 40 aphids per plant) on plant growth and aphid population development. Aphid population development and plant growth were evaluated by destructively sampling plants and aphids at 1, 5, 10, and 15 d after infestation. Plant parameters measured included height, dry weight, and damage. D. noxia feeding damage was determined by counting the number of leaves that were rolled and were chlorotic. The numbers of live and dead aphids were counted to measure D. noxia population development D. noxia densities on susceptible 'Stephens' wheat were greater than on the resistant accessions at 5, 10, and 15 d after infestation. The impact of aphid feeding was less on PI 137739 and PI 262660 than on 'Stephens' wheat. When the initial D. noxia density was 40 aphids per plant, the total number of aphids produced was higher at days 5 and 10 than the other aphid density, and the reproductive rates were lower on all dates. Plants intially infested with 10 aphids supported larger populations on day 15, because of lower mortality, higher aphid reproductive rates, and fewer dying plants.