Morphological and ecological traits promoting aphid colonization of the Hawaiian Islands

Species introductions into novel habitats, especially island ecosystems, can have devastating effects on ecosystem function and stability. Though none are native, at least 96 aphid species can now be found on one or more of the Hawaiian Islands. As aphids cause direct feeding damage and transmit plant viruses, it is important to identify the traits that have enabled these particular species to successfully colonize the archipelago. To address this question, nine morphological and ecological traits that may contribute to successful colonization were assessed for aphids present in Hawaii. As a comparative null model, we assessed the same traits for heterospecific congeners which are not present in the archipelago, but are present elsewhere in the world. Here we report that traits with higher frequencies among colonizing aphid species are: small apterae size, broad host range, anholocycly (i.e., permanent parthenogenesis), and presence in continental USA. Small aphids arriving from the mainland US and capable of feeding on numerous plant species may be intercepted less often by plant protection agents. It is also likely that asexually reproducing species are well suited to the Hawaiian subtropical climate, thereby eliminating the need for sexual phases and egg-laying for overwintering. By understanding the traits that enable aphids to successfully colonize remote islands, it is our hope that plant protection efforts may be enhanced, thereby reducing damage to native ecosystems.