The native terrestrial food web of sub-Antarctic islands is dominated by decomposers with rare herbivores and almost no predators. As a consequence of increasing human activities, the number of alien plants and invertebrates species, including phytophagous species, has been dramatically rising on these islands. These repeated introductions seem likely to have a great impact on the ecosystem functioning. This is the first detailed study on species diversity, host range and spatial distribution of aphids on French sub-Antarctic islands. Six cosmopolitan and polyphagous aphid species have been recorded on these islands. Five species have been found in the wild where they colonized native and introduced plants, and one species was confined to a glasshouse. Aphids colonized a littoral band and were limited to below 200 m a.s.l. Their spatial distribution is constrained by host plant distribution and temperature. The two dominant species, Myzus ascalonicus and Rhopalosiphum padi, are obligately parthenogenetic in these islands and have been observed to be active on plants during winter. The other species are also presumably obligate parthenogens because of the absence of host plants where sexual reproduction can occur. We suggest that polyphagy and parthenogenesis are major biological traits that influence colonization success by aphids in a sub-Antarctic environment.
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