Tritrophic Studies of Russian Wheat Aphid, a Parasitoid, and Resistant and Susceptible Wheat over Three Parasitoid Generations

Parasitism of Russian wheat aphid,Diuraphis noxia(Mordvilko), byDiaeretiella rapae(McIntosh) was studied over three parasitoid generations on resistant and susceptible wheat,Triticum aestivumL. Rate of increase forD. noxiawas 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 population increase forD. noxiawas lower on the resistant wheat line (PI 137739) in all three generations compared with the susceptible wheat cultivar (‘Stephens’). Plant biomass was greater in infested plants of both wheat entries exposed to parasitoids than infested plants without parasitoids. Percentage emergence, sex ratio, adult longevity, and head width of parasitoids were not changed by plant resistance. Longevity of female parasitoids was greater when parasitoids emerged from aphids reared on the resistant line. The resistance in PI 137739 was compatible withD. rapaegrowth and development.