Plant species diversity has long been considered a primary driver of arthropod community structure; however, recent ecological research has demonstrated that plant genotypic diversity can also play a major role in influencing the composition of arthropod communities. Genotypic diversity has already been exploited in some agricultural systems to improve disease control and appears to hold promise for managing some insect species as well. To explore the potential for using genotypic diversity within a crop species to help manage insect pests, we used laboratory-based studies to investigate the influence of wheat (Triticum aestivum L.) genotypic diversity on aphid (Rhopalosiphum padi L.) population growth. Increasingly diverse mixtures of wheat genotypes supported lower aphid populations compared with monocultures and were equally productive as single variety plantings. In the absence of aphids, genotypic mixtures were more productive than monocultures. We also analyzed the volatile organic compounds emitted by non-infested genotypic mixtures to provide insight on a possible mechanism influencing aphid populations. Mixtures and monocultures of wheat emitted the same compounds, but mixtures emitted greater amounts of volatile compounds than monocultures. Our results suggest that genotypic mixtures can strongly influence the growth rate and size of aphid populations; therefore, cultivar mixtures appear to hold good potential to be an effective tool for managing insect pests in crop fields.