Abstract: To determine the differentiation degree within the spruce spider mites, Oligonychus ununguis（Jacobi）, two populations of the mite on chestnut Castanea mollissima from Shandong Province and on fir Cunninghamia lanceolata from Zhejiang Province were used for analyzing the sequence variation of the second internal transcribed spacer 2 （ITS2） of nuclear ribosomal DNA and part of the mitochondrial cytochrome oxidase I gene （COⅠ）. The reproductive compatibility between the two populations was examined through cross-breeding experiments. The results indicated that ITS2 gene from chestnut and fir individuals is 469 bp and 513 bp in length, respectively. Nucleotide divergence of ITS2 gene was 15.2%-15.7% between the two populations. The mites collected from chestnut differed from those collected from fir by 10.5%-10.8% of the nucleotide divergence in COⅠ sequences. Cross-breeding experiments between the two populations displayed their completely reproductive incompatibility. Therefore, the tested mite populations are probably two different species according to the divergences of DNA sequences and reproductive isolation between them.  

Key words: Oligonychus ununguis, chestnut population, fir population, COⅠ, ITS2, reproductive isolation, cross-breeding experiment