Permalink : http://hdl.handle.net/2115/38485

KEYWORDS : Asexual;Host alternation;Disjunct distribution;Refuge;Relict

Gall-forming aphids are highly specific to their host plants, and speciation in galling aphids has proceeded in association with a single species or species group of host plants (primary host). This study firstly aims to revise the associations between galling aphids and their host plants by focusing on historical changes in the distribution of host plants. Aphids of the Eriosomatinae are typically associated with the primary and secondary host plants and alternate host plants seasonally, with sexual reproduction on the primary host plant. However, some species are not host-alternating and are wholly parthenogenetic on the secondary host plant. This study secondly aims to test the possibility of long-term persistence of an aphid species by means of parthenogenesis (relict hypothesis). The eriosomatine genus Colopha is a small aphid group represented by three sexual and three asexual species. The sexual species are associated with two Ulmus sister species distributed disjunctly in Europe and eastern North America. In East Asia, an asexual species, Colopha kansugei, is distributed widely on the secondary host. This study tested whether the relict hypothesis is applicable to C. kansugei by comparing DNA sequences. A high rate of substitution (3.4% at the maximum) was found in the mitochondrial COI sequence between local populations. Available evidence suggests that Colopha kansugei has persisted on the secondary host plant through parthenogenesis, probably following the local extinction of the primary host. Use of molecular techniques might possibly detect much more ancient species among parthenogenetic aphids with disjunct distributions.