Phylogeography of the Asia-Australia geographic group of Bemisia tabaci (Hemiptera: Aleyrodidae) in Taiwan

Bemisia tabaci (Hemiptera: Aleyrodidae) is an important pest and is known to have a high degree of intraspecific genetic diversity. More than 26 biotypes or 12 genetic groups have been designated in Bemisia tabaci. Previous studies showed that the China, Australia, and Asia I genetic groups belong to the Asia-Australia geographic group and the Asia genetic group belongs to Asia II geographic group. These two geographic groups have overlapping distributions in Asia. However, preliminary analyses have only been conducted on the Asia group. In this study, mitochondrial cytochrome oxidase I (mtCO1) and microsatellite loci were used to analyze the phylogeography of the Asia-Australia geographic group. A phylogenetic tree of Bayesian inference using CO1 data indicated that the Asia-Australia geographic group can be divided into four major clades: China, Australia, Far-East Asia and Asia clades. The first two clades respectively belong to the China and Australia genetic groups. The other two belong to Asia I genetic group. The identification of four clades is consistent with the four haplogroups distinguished through a minimum spanning network analysis of CO1 data. Sequence divergences between haplogroups reach 7～11% and provide evidence for cryptic species among and within genetic groups. Collections in Taiwan found the China, Far-East Asia and Asia clades. Samples from the islands of Matsu and Kinmen, located off the southeastern Chinese coast, belong to the China clade. Other samples from the main island of Taiwan belong to the Far-East Asia and Asia clades. On the island of Taiwan, there is high genetic differentiation and little gene flow between the Far-East Asia and Asia clades. Therefore, the hypothesis of multiple origins with different colonization times is proposed, and this was also supported by the geological histories in the island of Taiwan and the evolutionary rate of mtCO1 in insect. Furthermore, the microsatellite loci were used to analyze the population structure of the Asia-Australia geographic group in Taiwan. The Bayesian cluster method defined the Asia-Australia geographic group into four clusters (clusters 1~4). Clusters 1 and 2 respectively match to the China and Asia clades. Clusters 3 and 4 belong to the Far-East Asia clade. FST values and an assignment test revealed high gene flow and almost no genetic differentiation in a small range of < 20 km. When including the entire Taiwanese region, the Far-East Asia and Asia clades have high genetic differentiation as shown by the results of CO1 analysis which reveal that the genetic structure has diverged within the genetic group. The distributions of clusters 3 and 4 overlap in northeastern Taiwan, but FST values and the assignment test indicated high genetic differentiation with little gene flow. This result suggests that clusters 3 and 4 are diverging on Taiwan and biological interaction between geographic groups and topographical isolation may be reasons for this. According to the assignment test, the dispersal history in cluster 1 of the Matsu population reveals a south to north trajectory which reflects the direction of southwest monsoons during the summer. Certain dispersal histories were also found on the main island of Taiwan which relate to the complex topography and interspecific biological interactions. Compared with the phylogeography between the Asia and the Asia-Australia geographic groups, the previous study showed that the former has complicated haplogroups and reveals earlier colonization in Taiwan. Topography, climate, biological interactions, and geological histories may have played important roles in the distribution, gene flow, and dispersal histories of this species in Taiwan.