TRITROPHIC STUDIES OF RUSSIAN WHEAT APHID, A PARASITOID, AND RESISTANT AND SUSCEPTIBLE WHEAT OVER 3 PARASITOID GENERATIONS

Parasitism of Russian wheat aphid, Diuraphis noxia (Mordvilko), by Dia eretiella rapae (McIntosh) was studied over three parasitoid generatio ns on resistant and susceptible wheat, Triticum aestivum L. Rate of in crease for D. noxia was lower when plants were initially infested with 20 aphids than 10 aphids per plant. Plant damage was similar between the two aphid densities (10 and 20 aphids per plant). Rate of populati on increase for D. noxia was lower on the resistant wheat line (PI 137 739) in all three generations compared with the susceptible wheat cult ivar ('Stephens'). Plant biomass was greater in infested plants of bot h wheat entries exposed to parasitoids than infested plants without pa rasitoids. Percentage emergence, sex ratio, adult longevity, and head width of parasitoids were not changed by plant resistance. Longevity o f female parasitoids was greater when parasitoids emerged from aphids reared on the resistant line. The resistance in PI 137739 was compatib le with D. rapae growth and development. (C) 1998 Academic Press.