Phylogeny And Population Genetic Of Major Agricultural Spider Mites In China

Understanding the pests occurrence and mechanisms of pest composition is fundamental for establishing integrated pest managements.Spider mites constitute an important agricultural pest group.Under the background of global changes and the increasing resistance of pesticides,crop damage caused by spider mites has also become increasingly serious.The misidentification problem of red pigmented spider mites had been raised frequently because of their small body size.Due to the potential misidentification limited records and potential changing in spider mite composition,the occurrence pattern of spider mites in China’s mainland is still largely unknown.In this study,we summarized the occurrence and distribution pattern of spider mites in China’s mainland based on a long-term survey from 2008 to 2017.Using phylogenetic comparative methods,we tested whether pest occurrence is related the phylogenetic information of spider mites;And we used mitochondrial DNA marker and microsatellites to investigate the population sturucure for three maj or spider mites in China.The main results and conclusions are as follows:1)From a long-term survey during 2008-2017 in China’s mainland,we found Tetranychus truncatus was the most frequently sampled Tetranychus spider mite(48.5%),followed by T.pueraricola(21.2%),T.kanzawai(12.5%),T.urticae(red)(5.7%)and T.urticae(green)(4.5%).Among them,T.truncatus was major mite pest in the north of China T.kanzawai was the dominant species in Middle and Lower Reaches of the Yangtze River Region and T.pueraricola was the most important species in southwest region.Other common and serious pests include Amphitetranychus viennensis(6.8%)and Panonychus citri(3.8%).This pattern was largely different from before,when T.urticae(green and red)was believed to be the most serious mite pest.The factors involved in the change of species composition are not clear and need more exploration.We suggested that the increasing corn planting range may be partly responsible for the conversion of dominant species from other spider mites to T.truncatus.Further research on the mechanisms behind why the dominant species change will help to develop integrated management strategies.2)Phylogenetic information has proved to be useful to detected fundamental patterns and processes in ecology(e.g.species richness,ecosystem function)and conservation biology(e.g.,climate change,species loss).However,most pest risk assessments are calibrated without considering phylogenetic information.In this paper,we used regional(China)and global dataset to investigate occurrence patterns and niches properties of spider mites,a group of pests in many cropping systems worldwide,within a phylogenetic context;and disentangle whether phylogenetic pattern of pest occurrence is related non-random evolution of niche properties using phylogenetically controlled analyses.We found that mite occurrence was non-randomly scattered across the phylogeny both at regional and global scales.Relative abundance of spider mite was positively correlated with niche breadth and these corrections tend to be weaker after controlling for phylogeny.These results provide evidence that pattern of pest occurrence was phylogenetically structured and positively related to niche breadths in spider mites assembly.our study highlights the role of evolutionary history on understanding the current distribution and occurrence of spider mites group.We suggest that phylogenetic information could be taken into consideration in pest risk analysis,especially for groups where a significant divergence in species occurrence and/or niches among clades existed.3)Center-periphery hypothesis(CPH)is one of important hypothesis in biogeography which predicts that genetic diversity,genetic flow and population abundance are highest at the center and decrease near the periphery of species’ geographic distributions.n this research,we defined the CPH using the geographic distance to the center(geography)and ecological suitability using current climate data(ecology)and historical climate data(history)from last glacial maxima for a wide distributed arthropod in eastern China,Tetranychus truncatus(Acari:Tetranychidae).We provided a test of the CPH using population genetic data and relative abundance against three CPH definitions.As expected by CPH,we found statistical support for decreased relative abundance,genetic diversity and increased genetic differentiation from geographic center to periphery.Lower levels of genetic variation,population abundance and higher genetic differentiation were generally corresponding lower levels of historical and contemporary ecological suitability.However,none of three CPH definitions alone can explain the genetic and abundance pattern well.Populations’ relative abundance was more significantly related to ecology than geography and history.Ecology and geography best explain the microsatellite diversity,whereas mitochondrial genetic diversity was only significantly related to history.Overall,this study provides mixed evidence for CPH in different definitions,and more importantly,highlight the effects of ecology and history on the population variation across species’ distribution range.4)Red form of Tetranychus urticae(also considered as T.cinnabarinus)was considered to be a native and dominant pest with high population genetic diversity in China.However,after a long term survey and careful identification,T.urticae(red)was found a very low frequency of occurrence in China.We speculated that the T.urticae(red)in China maybe experienced a recent population decline To verify our hypothesis,five populations from T.urticae were sampled and used for population genetic analysis.We found that all all populations shared only one mitochondrial haplotype and showed quite low genetic diversity[effective alleles(Ne)=1.443±0.055;expected heterozygosity(He)=0.234±0.025]which even lower than the invasive green form of T.urticae in China’s mainland.We didn’t detect significant signals of bottleneck for most populations from T.urticae(red).This suggested T.urticae(red)from China possibly is not native species and T.cinnabarinu maybe not a valid species or a synonym of T.urticae(red),but a species complex contains several other spider mites.5)Tetranychus pueraricola was a newly reported spider mite with high occurrence frequency in China’s mainland.It’s possible that this species was introduced from elsewhere and became a serious pest recently.However,the misidentification problem of red pigmented spider mites has been raised frequently.There was also the possibility that T.pueraricola in China was long identified as its sibling species,T.urticae(red form).To test which scenario was more reliable,fourteen populations from T.pueraricola were sampled and used for population genetic analysis.Unlike a recent invasive species,genetic diversity of T.pueraricola was very high with high mitochondrial genetic diversity(16 haplotypes),high effective alleles(Ne=2.038±0.081)and expected heterozygosity(He=0.395±0.016).Most populations didn’t show significant signals of population bottelenck.hese results suggested T.pueraricola was unlikely to be a recent invasive pest but a species that has existed in China for a long time.It’s probably that T.pueraricola in China was long identified as T.urticae(red).