Seedlings from 21 collections of the native North American red raspberry, Rubus idaeus strigosus (Michx.), were screened for reaction to Amphorophora agathonica Hottes, the aphid vector of the red raspberry mosaic virus complex. Sixty-four seedlings from 1,041 screened were selected for resistance to colonization. Three of these were intercrossed and also crossed with 2 cultivars of R, i. vulgatus Arrhen origin to produce F1 progenies. Inheritance of the resistance reaction in the 3 selected seedlings appeared to be controlled by 2 dominant complementary genes. These genes, which are designated Ag2 Ag3, do not appear to give as high a level of resistance to the aphid as gene Ag1, which is of R. i. vulgatus origin and gives virtual immunity. It is suggested that genotypes combining Ag, with Ag2 and Ag3 might be of value in reducing genetic vulnerability if virulent biotypes of A. agathonica appear. Screening for reaction to the aphid under laboratory conditions, prior to field planting, eliminated large numbers of susceptible seedlings. Additional screening in the field the year of planting eliminated more. Segregation ratios, which had been adjusted from the field results, gave better agreements than laboratory screenings alone to the proposed hypotheses.