Aphid landing rates were monitored with horizontal mosaic green pan traps in monocultures of soybean,Glycine max(L.) Merrill, and in additive mixtures of soybean with dwarf or tall isolines of sorghum,Sorghum bicolor(L.) Moench.Rhopalosiphum maidis(Fitch) colonized sorghum whorls and was the major species caught in pan traps. Weekly aphicide spot applications to sorghum whorls, starting at 36 d after planting, did not suppressR. maidiscolonies significantly until after the third application. Landing rates ofR. maidisalatae were similar in treated and untreated crop mixtures. The lack of a significant difference may have resulted from immigration ofR. maidisalatae from outside the experimental field but inefficient colony suppression may have produced similar results. Mixed cropping reduced landing rates ofAphis gossypiiGlover,Aphis helianthicomplex, andLipaphis erysimi(Kaltenbach) on sorghum plants, andR. maidison soybean plants. Generally, landing rates were equally reduced in the mixtures with tall or dwarf sorghum. The percentage of ground covered by vegetation, which was less in monocultures than in mixtures, proved to be more important than crop height in reducing aphid landing rates. All aphid species landed randomly on soybean and sorghum plants within dwarf sorghum mixtures. However, in tall sorghum mixturesAphis neriiBoyer de Fonscolombe andA. gossypiipreferred to land on soybean whereasAphis spiraecolaPatch landed more often on sorghum. LandingR. maidisalatae did not show a preference for sorghum or soybean in the crop mixtures. Different sensitivities to microclimatic conditions may explain these behavioral patterns.