Abstract: 【Aim】 This study aims to explore the genetic diversity, genetic differentiation and phylogenesis of Tetranychus truncatus populations in Gansu province, northwestern China. 【Methods】 The mtDNA COI gene in 518 individual samples of T.truncatus, which were collected from 34 populations in 8 different habitats of Gansu province from June to September in 2016, was amplified, sequenced and analyzed. And its sequence variation and genetic differentiation were analyzed using MEGA 7.0, Dna SP 5.0 and other software. 【Results】 The sequenced fragment is 402 bp in length. The average contents of A, T, C and G are 32.2%, 43.2%, 10.5%, 14.0%, respectively. The A+T content (75.4%) was apparently higher than the G+C content (24.6%), with an obvious A/T bias, and the nucleic acid diversity was 0.0328. There were 12 haplotypes in 34 populations, and the haploid type index was 08004. In 12 haplotypes, H2 occurred in the highest number of individuals, which was distributed in 5 ecoregions, appeared 14 times, and occupied 41% in the number of individuals. Five cluster groups were clustered together in the haplotype mediation network diagram. NJ phylogenetic tree showed that 12 haplotypes were divided into four branches, and this result was the same as that of the mediation network diagram. Genetic distance of all the populations was among 0.001-0.08955. UPGMA dendrogram showed that JQ (Jiuquan) population and HS (Heshui) population had higber genetic differentiation with other populations. Mantel test result showed no significant correlation between genetic distance and geographical distance (r=0.043, P>0.05). The genetic differentiation index (Fst) among 34 populations was 0.11995, and the variation proportion among populations was 1.20%. 【Conclusion】 There is no significant correlation between genetic distance and geographical distance among 34 populations of T. truncatus in eight ecoregions of Gansu province. The genetic variation of T. truncatus is mainly within populations, and there is no obvious genetic differentiation among populations.  

Key words: Tetranychus truncatus, mtDNA COI, population genetic, geographical population, genetic differentiation, Gansu