Aphids (Hemiptera: Aphididae) are well known as micro-insect pests, which are very specific to their host plants, sucking phloem for acquiring nutrients, and most of them have successfully maintained parthenogenetic generations cyclically or permanently. In the world, the approximately 5,000 described aphid species belong to the family Aphididae, which has taxonomically been subdivided into 27 subfamilies in current. The diversification of host plants, especially angiosperms, has played an important role in their evolution. Major questions about aphid evolution include origins of host alternation as well as age and patterns of diversification in relation to host plants. To address these, I did both macroscale (phylogenetics) and microscale (population genetics) researches on aphids. First I reconstructed the phylogeny of the three major aphid groups, Aphidini, Macrosiphini, and Pterocommatinae, which are the most diverse in the world and constitute more than 60% of the total species. These major lineages demonstrate the evolutionary history of aphids interacting with their host plants. I also used molecular dating method to calculate reasonable divergence time on each clade. Based on phylogenetic and dating analyses, most generic divergences in Aphidinae occurred in the Middle Tertiary when primary hosts, mainly Rosaceae, were diverging, whereas species-level divergences were related with diversification of secondary hosts such as Poaceae in the Middle to Late Tertiary. Most generic divergences in Aphidini occurred in the Middle Tertiary, and species-level divergences occurred between the Middle and Late Tertiary. The divergence times of aphid lineages at the generic or subgeneric levels are close to those of their primary hosts. Second I performed population genetics of the polyphagous cotton-melon aphid, Aphis gossypii Glover. I analyzed population genetic structure between 570 aphids collected from 41 plant species of primary and secondary, mostly wild, hosts using 9 microsatellite loci. As results, population structure of A. gossypii revealed that several genetic affinities in common use of some secondary and primary hosts are detected. Host preference in secondary host is higher than that in primary host, and woody plants share same genetic structure. This species might speciated by the related mechanisms such as host alternation and loss of primary host. I will propose macro- and micro-evolutionary patterns of the Aphidini aphids based on integrating phylogenetic and population genetic approaches

Aphid is relatively young group among insects, which radiated contemporaneously with the host plants in angiosperm. Based on recent molecular phylogenetic studies, the tribe Aphidini has been strongly suggested as a primitive group sister to two other tribes, Macrosiphini and Pterocommatini, in the subfamily Aphidinae which is most diversified aphid group. These ideas have been proposed due to the phylogenetic relationships between the groups and the relatively simple morphological characters. Our study is aimed to confirm the evolutionary process of this primitive group in order to understand the diversification of the modern aphids. Firstly, we obtained the phylogenetic relationships for 59 ingroup species plus 10 outgroup species (6 macrosiphine species, 1 hormaphidine species, and 3 adelgids) based on the combined sequences (2,899 bp) of three mitochondrial genes (COI, COII, CytB) and one nuclear gene (EF1α). The optimal tree topology is obtained by the ML analysis in GARLI 0.95b with Kishino-Hasegawa and Shimodaira-Hasegawa tests in PAUP*4b10, and the posterior probabilities on each node were estimated by MrBayes 3.1.1 under the best fit model (GTR+I+G) tested by MrMODELTEST 3.0. Then, the node ages of the obtained tree were calibrated using the relaxed-clock model implemented in BEAST 1.4.8 and its package programs based on one node fixation of 150 MYA (million years ago) for Aphididae+Adelgidae, and two node constraints as 80-100 MYA for Aphididae crown and 50-70 MYA for Aphidinae crown according to the fossil related publications. As results, we found four major facts on their evolution: 1) Aphidini radiated from the early Eocene in the Tertiary, 2) however, most lineages rapidly radiated during the late Eocene, 3) common ancestor of the subtribe Aphidina maybe fed on herbs or shrubs in asterids, 4) host alternation trait was lately acquired on Rosaceae- or Rhamnaceae-feeding aphids.

Multivariate morphomatric analyses were conducted to cluster the morphologically similar group using species units within the tribe Aphidini. Some species of the genus Aphis are morphologically very similar each other and, mentioned by aphid taxonomists as well, possibly grouped by some characteristics. To cluster the morphologically related groups and find some significant characteristics to define morphological groups for 59 Aphidini species, we perform two statistical analyses of 30 morphomatric characters, Principle Component Analysis (PCA; SAS Procedure PRINCOMP) and Canonical Discriminant Analysis (CDA; SAS Procedure CANDISC) using SAS/STAT version 9.1.3 (SAS Institute, Inc., Cary, North Carolina). The results of the morphological clustering analyses were compared with the molecular phylogeny of Aphidini obtained from the previous study using three molecular gene fragments: partial mitochondrial tRNA-leucine + cytochrome oxidase II (tRNA/COII), partial mitochondrial 12S + tRNA-valine + 16S (12S/16S), and nuclear elongation factor-1 alpha (EF1α) (total 3,289bp) for 37 representative species among them. The congruence or difference between morphological and molecular analyses is also discussed in Aphidini group

A phylogeny of the tribe Aphidini (Hemiptera: Aphididae) was reconstructed using three molecular gene fragments: partial mitochondrial tRNA-leucine + cytochrome oxidase II (tRNA/COII), partial mitochondrial 12S + tRNA-valine + 16S (12S/16S), and nuclear elongation factor-1 alpha (EF1α) for a total of 41 species consisting of 37 representative species in Aphidini and 4 outgroup species in the tribe Macrosiphini. Also, to compare with the molecular analyses, a second phylogenetic reconstruction was performed using 41 morphological characters for equally weighted analysis. Minimum evolution, maximum parsimony, maximum likelihood, Bayesian phylogenetic analyses, and Bremer support test were performed for the phylogenetic construction. As our phylogenetic results were compared with the classical taxonomy based on morphological characteristics and biological data, we newly confirmed the following phylogenetic relationships within Aphidini: (1) each monophyletic subtribe of Aphidina and Rhopalosphina was supported by significant P values in the combined analysis, (2) contrary to the classical taxonomic position, Cryptosiphum should be moved to Macrosiphini because it is more closely related to Lipaphis and Brevicoryne in the myzine group of Macrosiphini, (3) The genus Toxoptera was possibly considered as a non-monophyletic group because three species were separately positioned in Aphidina, (4) In Rhopalosiphina, the genus Melanaphis was relatively divergent from three genera, Rhopalosiphum, Schizaphis and Hyalopterus, clustered in a strongly supported clade, (5) in the relationships among four the Aphis species-groups, which are accepted by most aphid taxonomists, most species except for some morphologically distinct species were separated to the two main lineages; the fabae-group was confirmed to be closely related with the spiraecola-group and craccivora-group, but the gossypii-group diverged as a monophyly from those three group.