The Molecular Identification For Common Thrips Species (Thysanoptera: Thripidae) And Genetic Difference Analysis For Frankliniella Occidentalis Found In 3 Regions Of China

Thrips (Thysanoptera; Thripidae) are small insects(<2mm usually). Of the approximately 5 500 so far described species, scarcely 1% are recorded as crop pests, causing serious damage to crops. Because of their small size, ability to build to high number in difficult circumstances, especially their cryptic behavior, they can not be found until the symptoms are obvious. It is more serious that some thrips also transmit disease to plants or harvestable produces. Identifying thrips by traditional methods is time and labor consuming, some times is difficult especially when thrips are larvae and pupae. It will mislead plant quarantine and pest control if the species identifications slip a cog.Molecular identification based PCR provides new approach for species identification, which offsets the limitation of traditional methods. Recently, the frequent invasion event of thrips makes rapid and exact identification inevitable. In the first part of our study, 433 base pair segment of the mitochondrial gene, cytochrome oxidase subunit I (COI), from 62 individuals of Frankliniella occidentalis (Thysanoptera: Thripidae) and other 8 common thrips species in China are sequenced. The DNA data analysis shows that the average intra-species genetic distance is 0~0.005; there is no significant genetic divergence between the western flower thrips found in Beijing in 2003 and those reported internationally. The average interspecies genetic distance is 0.213. Thrips individuals are successfully clustered by NJ tree. The bootstrap values of the original divergence among intra-species haplotypes amount to 100%. The results show that molecular identification based on PCR and direct sequencing is desirable to identify thrips species.In the second part of study, we sequence the COI 433bp segments of western flower thrips collected from Beijing, Yunnan and Shandong province of China. Besides, the ITS2 segments are sequenced. The results show that the COI sequences are different in some sites among western flower thrips from the three geographic regions, but it is not obvious in ITS2. We studied the phylogeny of thrips based on molecular data from our study and NCBI, the results show that reconstruction of phylogeny based on information from COI 433bp segments can present good cluster of thrips species, but is not perfect in deal with the exact phylogenetic placement of some thrips species.Because not all of labs own the ability to sequence, we tried to design a specific primer to western flower thrips based on ITS2 sequence alignment, and we tested its efficiency in diagnoses. The result shows that the PCR with this primer is positive to western flower thrips only.