Abstract: [Objective] The important pest mites that infest Castanea mollissima,an economic forest species, and Cunninghamia lanceolata, have been considered to be the same mites, Oligonychus ununguis. However, previous studies have shown that reproductive isolation exists between the C. mollissima population from Shandong Province(TSBL) and the C. lanceolata population from Zhejiang Province(ZJSM) of O. ununguis and the reproductive isolation is not caused by geographic isolation and the endosymbionts that can manipulate the reproduction of their hosts. The two populations have been differentiated into two independent species, but whether the differentiation is related to adaptation to different host plants has not been determined. This study was carried out to clarify the differentiation reasons and enrich the speciation theory.[Method] Three female adult mites were randomly selected from the C. mollissima population and the C. lanceolata population respectively which collected previously to be used to hybridization experiment. The genomic DNA was extracted from a single female adult. The 28S rDNA sequences were amplified used the primers designed according to the conserved sequences of the 28S rDNA of other mites in Oligonychus. The amplified products were purified and sequenced. The 28S rDNA sequences of the two populations were compared and the phylogenetic tree of Oligonychus was constructed based on the 28S rDNA sequences. The differentiation reasons of these two populations were analyzed combined with previous studies.[Result] The 28S rDNA sequences of three individuals in each population were identical, without intraspecific variation. The interpopulation sequence identity and the genetic distance between the C. mollissima population and the C. lanceolata population based on 28S rDNA sequences were 98.3% and 1.7% respectively. The phylogenetic tree of Oligonychus based on 28S rDNA sequences showed that O. hondoensis collected from Cryptomeria japonica in Japan was the closest relative of the C. lanceolata population, while O. castaneae collected from Castanea crenata in Japan was the closest relative of the C. mollissima population.[Conclusion] The spider mites on C. mollissima and C. lanceolata are probably two independent species rather than differentiated from the same kind of spider mite because of adaptation to different host plants.

Key words: Oligonychus ununguis, 28S rDNA, Castanea mollissima population, Cunninghamia lanceolata population, species differentiation