Newly introduced phytophagous insects can affect native and introduced plant species. If the native plant species evolved without undergoing selective pressure from these insects, insectplant interactions may be different for native and introduced plant species. In particular, this difference may involve mechanisms of plant defense against herbivores. If native plants lack such mechanisms, they may be more palatable to insects than exotic plants. On isolated sub-Antarctic islands, native plant species have evolved in the absence of sap-feeding insects, subsequently introduced a few decades ago. In this study, performance of an introduced aphid species, Myzus ascalonicus Doncaster, was experimentally compared on three native [Pringlea antiscorbutica Hook.f, Acaena magellanica (Lam) Vah, and Leptinella plumosa Hook.f.] and three exotic plant species (Taraxacum officinale F.H. Wigg, Cerastium fontanum Baumg., and Senecio vulgaris L.) found on the Kerguelen Islands. Counts and weights of aphid colonies were 2–7 times higher on native plants than on exotic plants depending on experimental conditions. The results are discussed in light of the possibility of an absence or ineffective defense mechanisms in native plants.