Genetic relationship between the carmine spider mite Tetranychus cinnabarinus (Boisduval) and the two-spotted mite T-urticae Koch in china based on the mtDNA COI and rDNA ITS2 sequences

The population structure of the Chinese carmine spider mite Tetranychus cinnabarinus (Boisduval) was investigated by amplifying and sequencing a portion of the mitochondrial DNA gene coding for cytochrome oxidase I (COI, 453bp) and a portion in the second internal transcribed spacer (ITS2, similar to 645bp) of rDNA. Nineteen T. cinnabarinus populations of various geographical origins were sampled from all over China. Intraspecific variation analysis showed that 81 nucleotide positions (17.9% of the total length) were found polymorphic in COI sequences, of which 88.9% were silent substitutions. Compared with COI sequences, there were only 11 differences ( five transversions, five transitions and one 2bp insertion/deletion) in the ITS2 sequences among these populations. We argue that the reasons for less ITS2 divergences might be that ancestral polymorphism was generally lower for ITS2 than for COI. From the trees established by MEGA based on Kimura-2-parameter distance, we found that the phylogenetic relationships inferred from COI and ITS2 sequences approximately accorded with their geographical relationships. It has long been considered in China that T. cinnabarinus and T. urticae are two independent species. However, the molecular phylogeny obtained by mtDNA and rDNA analyses indicated that T. cinnabarinus and T. urticae from China were not clearly distinguished from each other.