Impact of wheat resistance on Russian wheat aphid and a parasitoid

Impact of wheat, Triticum aestivum L., resistance (resistant PI 137739 and PI 262660, and susceptible 'Stephens') on Diuraphis noxia (Mordvilko), the Russian wheat aphid, and the parasitoid Diaeretiella rapae (M'Intosh), was studied using varying densities of aphids (0, 20, or 40 aphids per plant) and parasitoids (0, 1, or 2 pairs per plant). Resistant lines were less damaged by aphid feeding than Stephens with leaf area, weight, and height reductions observed on Stephens. Plant resistance did not have an adverse affect on percentage of parasitism. Plant quality, indicated by leaf area, weight, and height, was lower when initial aphid density was 40 aphids per plant compared with 20 aphids per plant. Overall, the rate of Russian wheat aphid population increase was lower at 40 aphids per plant compared with 20 aphids per plant. Addition of a 2nd pair of D. rapae increased the percentage of parasitism on plants infested at an initial rate of 20 aphids per plant. Percentage of parasitism was higher when plants were infested initially with 20 aphids per plant than 40 aphids per plant. Plant resistance did not have any adverse effect on emergence time, sex ratio, and adult longevity of D. rapae. Percentage of emergence of D. rapae was greater when emerging from aphids on resistant plants than on the susceptible wheat, Stephens, at 40 aphids per plant. Results indicated that D. rapae parasitism and PI 137739 and PI 262660 resistance were compatible tactics.