Effectiveness of Lacewing Larvae in Reducing Russian Wheat Aphid Populations on Susceptible and Resistant Wheat

The use of resistant plants may enhance or reduce the ability of natural enemies to control pest insects. We conducted a series of experiments to compare the effectiveness of lacewing larvae, Chrysoperla plorabunda (Fitch), in suppressing populations of the Russian wheat aphid, Diuraphis noxia (Mordvilko), on susceptible and resistant wheat. Caged plants were inoculated with the same initial density of aphids, and predators were added to half the plants after nearly two aphid generations. Additional plants were used to estimate aphid densities on resistant and susceptible plants when predators were introduced. In one comparison, the effects of plant resistance and predation were synergistic; lacewing larvae caused a greater proportional reduction in aphid density on a tolerant-resistant line (carrying the Dn4 gene) than on its near-isogenic susceptible parent. Higher predation rates on the resistant line persisted over a wide range of predator/prey ratios. The combined effects of predation and plant resistance were mostly additive in other experiments, including a comparison of an antibiosis-resistant line (possessing the Dn1 gene) and its near-isogenic parent. In no comparison was lacewing effectiveness lower on the resistant line. Our results suggest that even modest reductions in aphid population growth (as might occur on tolerant-resistant plants) can be sufficient to produce a synergistic level of pest suppression.