Mixed viral infections of heterologous viruses such as Potato virus Y (familyPotyviridae, genusPotyvirus, PVY) and Potato leafroll virus (familyLuteoviridae, genusPolerovirus, PLRV) are a regular occurrence in Idaho’s potato,Solanum tuberosum (L.), cropping systems. An increased number of plant samples from Idaho’s potato fields over the past 2 yr has serologically tested positive for both PVY and PLRV via double antibody sandwich enzyme-linked immunosorbent assay (DAS-ELISA) and exhibited more severe symptoms than singly-infected plants (PVY or PLRV). Several studies have extensively examined the mixed infection phenomenon but to the best of our knowledge, none have examined the effect of such infections on vector biology and preference. Laboratory studies were conducted to examine the effect of mixed viral (PVY–PLRV) infection on the fecundity and preference of two of the most efficient PVY and PLRV vectors, the green peach aphid,Myzus persicae (Sulzer), and the potato aphid,Macrosiphum euphorbiae (Thomas) (Hemiptera: Aphididae).M.persicae andM.euphorbiae adults were clip-caged (one adult per cage) to leaflets of PVY, PLRV, PVY–PLRV-infected, and noninfected potato plants. The number of nymphs produced in all four treatments was recorded after 96 h.M.persicae andM.euphorbiae fecundity was significantly higher on mixed infected plants than on singly infected plants or noninfected plants. Preference of alatae and apterae ofM.persicae andM.euphorbiae was determined with the use of settling bioassays. Both alatae and apterae ofM.persicae andM.euphorbiae preferentially settled on PVY–PLRV-infected plants than on singly infected plants (PVY or PLRV) or noninfected plants.