DNA Barcoding And Molecular Phylogeny Of The Spider Mites In China (Acari: Tetranychidae)

Tetranychid mites that belong to Arachnida. Acari. Acariformes, Tetranychidae, are a kind of world wide economically important pest damaging fruits, vegetables and stove plants. Identification of species in the Tetranychidae is hampered by their closely morphological similarities, especially for species within the genus Tetranychus. In addition, the number of classical mite taxonomists is small and decreasing. The identification of spider mites based on DNA sequences has a special meaning, compared with traditional morphologic identification. It is rapid, simple and reliable. DNA barcoding is a method proposed to classify animals to the species level using nucleotide divergences of molecular markers. We identified nine species from Tetranychidae using the key morphologic characters in this study and sequenced their COI, ITS1, ITS2 and 28S regions. The paper aims to judge whether the four molecular markers as DNA barcodes can identify and determine the relations among 9 spider mite species accurately. What is more, we detected a lot of intraspecific and interspecific nucleotide divergences to analyze their relationships within spider mites.DNA barcoding is a method proposed to classify animals to the species level using a fragment of mitochondrial DNA, usually from the 5'region of COI which is well suited for interspecies identification because of its high degree of polymorphism. Relationships of 9 species from 4 genera in the Tetranychidae were inferred from COI sequences. The results confirm the monophyly of the morphologically defined Tetranychus, Panonychus, Amphitetranychus and Petrobia. However, the phylogeny of T. truncatus, T. cinnabarinus and T. urticae from Tetranychus can not be resolved well. In general. The COI sequence divergences were generally much greater between species than within them, and the genetic distances between genera were much higher. But the genetic distance within T. cinnabarinus can reach 0.1018. Data show that Henan and Yunnan populations are quite different from other five populations from the T. cinnabarinus. which suggests that the existence of cryptic species within this species.Previous studies indicate that the nuclear ribosomal divergences can be used to identify between closely related species, complexes of species and even geographical populations. We chose rDNA ITS1 and ITS2 as markers to explore 23 populations from 9 species 4 genera in the Tetranychidae in China, in order to judge whether ITS region is suited for differentiating spider mites. The sequence divergences based on ITS1 were generally much greater between species than within them, and the genetic distances between genera were much higher. All the interspecific genetic distances were higher than 2%. while sequences of five populations from Petrobia harti were entirely same and the average distance between five populations from T. urticae was 0.018. However, the data indicated that Henan and Yunnan populations are quite different from other populations from T. cinnabarinus. The study based on ITS2 strongly supported the monophyly of the species with the exception of P. ulmi and P. citri at the same clade. However, the genetic distances between two of T. urticae, T. truncates and T. turkestani were lower than 2%, while that of T. cinnabarinus between different populations were higher than 2%. The analysis based on ITS1 and ITS2 indicated that although the phylogeny of T. urticae and T. cinnabarinus has not been solved well, morphologically defined 4 genus and most of species have been differentiated clearly.Relationships of 9 species from 4 genera in the Tetranychidae were inferred from partial D1-D2 region of nuclear 28S-rRNA sequences. The results confirm the monophyly of the morphologically defined Tetranychus, Panonychus, Amphitetranychus, and Petrobia. however, the phylogeny within Tetranychus and Panonychus can not be resolved well. The study based on 28S-rRNA sequences could not identify spider mites to species level, but provide a significant reference to identification of genus level.This study was aimed at identifying 9 familiar species from 4 genera of spider mites in China by using molecular barcodes including mitochondrial COI and nuclear ribosomal ITS1, ITS2 and 28S sequences, analyzing their phylogeny, and providing references to the studies of DNA barcoding of spider mites.