Effect of Imidacloprid on Nonflight Movement of Rhopalosiphum padi and the Subsequent Spread of Barley Yellow Dwarf Virus. C. GOURMET, Department of Agronomy, University of Illinois, Urbana 61801. A. D. HEWINGS, USDA-ARS Crop Protection Research Unit and Department of Plant Pathology, University of Illinois, Urbana 61801; and F. L. KOLB and C. A. SMYTH, Department of Agronomy, University of Illinois, Urbana 61801. Plant Dis. 78:1098-1101. Accepted lor publication 26 August 1994. Copyright 1994 The American Phytopathological Society. DOI: 10.1094/PD-78-1098.

The bird cherry-oat aphid (Rhopalosiphum padi) is an important vector of the barley yellow dwarf luteovirus, BYDV-PAV-11. Insecticides used to reduce the abundance of the vector on small grains can result in an increase in aphid activity and a subsequent increase in disease incidence. The transmission characteristics of viruliferous wingless.(nymphs and apterous adults) R. padi after access to oats treated with different rates of imidacloprid, a seed-treatment insecticide, were compared. After access to treated plants, aphid fecundity was reduced and aphids walked and fed atypically and often abandoned the host plant. The spread of BYDV from a focus of infestation to individual imidacloprid-treated oats planted in a grid was followed by observation of symptoms and by enzyme-linked immunosorhent assay. Aphids transmitted the virus to both treated and untreated plants, but the percentage of infected insecticide-treated seedlings was one-half that of untreated seedlings.