Tritrophic Relationships of Russian Wheat Aphid (Homoptera: Aphididae), a Hymenopterous Parasitoid (Diaeretiella rapae McIntosh), and Resistant and Susceptible Small Grains

The tritrophic relationships between resistant small grain entries, Russian wheat aphid, Diuraphis noxia (Mordvilko), and Diaeretiella rapae McIntosh were studied. Resistant triticale entries with high levels of antibiosis affected growth and reproduction of both the aphid and the parasitoid. Parasitoid mummies from antibiotic triticale were smaller, took longer to develop, and were fewer in number compared with those from susceptible entries. The sex ratio of parasitoids emerging from the smaller mummies of aphids restricted to the resistant triticale entries was skewed toward females. The protective influence of parasitoids on plants was demonstrated in the experiment. Plants exposed to aphids without parasitoids sustained greater damage and had significantly less biomass than those so protected. A resistant wheat entry showed a reduction in aphid populations and enhanced parasitoid activity due to the fact that its leaves did not roll like those in the susceptible wheat entry. (C) 1991 Academic Press, Inc.