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

The resistant wheat plant introductions PI 137739 and PI 262660 and th e susceptible wheat (Triticum aestivum L.) cultivar 'Stephens' were us ed to determine the effects of varying Russian wheat aphid, Diuraphis noxia (Kuvdjumov), population densities (0, 10, and 40 aphids per plan t) 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 param eters measured included height, dry weight, and damage. D. noxia feedi ng damage was determined by counting the number of leaves that were ro lled and were chlorotic. The numbers of live and dead aphids were coun ted to measure D. noxia population development D. noxia densities on s usceptible 'Stephens' wheat were greater than on the resistant accessi ons 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 dens ity, and the reproductive rates were lower on all dates. Plants intial ly infested with 10 aphids supported larger populations on day 15, bec ause of lower mortality, higher aphid reproductive rates, and fewer dy ing plants.