Efficacy of Imidacloprid Seed Treatments against Four Wheat Aphids under Laboratory and Field Conditions

Imidacloprid seed treatments are effective at reducing the cohorts of many insect pests on crops such as cotton, corn, and cereals. The effects of imidacloprid seed treatments depend on the aphid species. In China, there are four wheat aphid species—Sitobion avenae (Fabricius), Rhopalosiphum padi (Linnaeus), Schizaphis graminum (Rondani), and Metopolophium dirhodum (Walker)—and for a given region, these four aphid species differ in dominance with changes in cultivation practices and climate. Therefore, it is necessary to evaluate the effects of imidacloprid seed treatments on the four different aphid species. In experiments in the laboratory, imidacloprid seed treatments significantly reduced the survival rates of S. avenae, R. padi, and S. graminum to 57.33 ± 2.86%, 12.67 ± 1.92%, and 20.66 ± 2.33%, respectively, but for M. dirhodum, there was no significant difference between the control (96.33 ± 1.08%) and the treatment (97.00 ± 0.98%). The fecundities of the four aphid species were much reduced, especially for R. padi when feeding on treated wheat plants. For the field survey, only three aphid species were considered because the density of S. graminum was too low to be analyzed. The effects of imidacloprid seed treatment on the three aphid species in the field were consistent with the laboratory results. Imidacloprid seed treatment reduced the population sizes of S. avenae and R. padi at rates of 70.30 ± 3.15% and 87.62 ± 2.28%, respectively, for the whole wheat season in the field. For M. dirhodum, imidacloprid seed treatments were less effective, and the densities of M. dirhodum increased on four sample days. From this study, we confirmed that the effect of imidacloprid seed treatment varied with the composition of aphid species, being especially less effective for M. dirhodum.