The Invading Risk Analysis Of Bactrocera Dorsalis Hendel And Solenopsis Invicta Buren In Jiangsu Province Of China

The oriental fruit fly Bactrocera dorsalis Hendel and the red imported fire ant Solenopsisinvicta Buren are two important quarantine pests worldwide. It is believed that B. dorsalishas expanded to occupy more than 20 countries and districts of North America, Oceaniaand Asia and it also has been widely distributed in the provinces of Taiwan, Guangxi,Fujian, Hainan, Hunan, Guizhou, Yunan, Sichuan and Jiangsu of China at present. Withquite indiscoverable carrying pathway, the larva B. dorsalis causes harm to hundreds ofcrops and wild plants such as orange, pomelo, peach, wax apple, durian, guava, mango,banana, lichee, longan and so on, which has become one of the most serious pestsnowadays. S. invicta, an original pest in Parana drainage area, has invaded America, Brazil,Peru, Bolivia, Argentina, Uruguay, Porto Rico, Australia, Malaysia, Antigua, Bahamas,Trinidad and Tobago, and showed quick diffusion tendency worldwide. It is proved that S.invicta has established new populations in Taiwan, Hong Kong, Macao, Guangdong,Guangxi and Hunan in China. S. invicta endangers people's health, havocs ecosystem andpublic utilities, creates great economic lost to Agriculture, and consumes vast sum ofmoney for prevention. Both the two species are ranked in the national and internationalquarantine pests list. Quarantine measurements are mainly adopted for preventing anyaccidental introduction of these two pests to China. It is obvious that Jiangsu Province, thewindow of east China, is facing a great invasive threat by the two pests. In order to find outthe invasive risk of the pests in Jiangsu, we try to apply Arc GIS 8.1 in our study basing onthe biological and ecological characteristics of B. dorsalis and S. invicta. Furthermore, wechoose S. invicta as a model and mitochondrial DNA cytochrome subunit I (mtDNA COI)gene as a genetic maker to examine the interspecific relationship between Solenopsisspecies and the genetic variation of five geographic populations of S. invicta from China atthe molecular level. Our studying result helps people for recognizing the pests' invasionpathways and the break-out mechanisms using both macro and micro visions and aims tolay a consolidated theoretical basis for preventing the further diffusion and detrimentultimately. 1. The risk analysis of invasive B. dorsalis in Jiangsu Province of ChinaIt is known that the temperature is the most important key factor for regulating colonymetabolism and activity, which is therefore used as the primary ecological factor fordetermining the geographic distribution and diffusion tendency of B. dorsalis. Based on thebiological and ecological characteristics of the oriental fruit fly, B. dorsalis, we analyzedthe meteorological data in twenty years from 13 sites in Jiangsu Province using MicrosoftExcel system. The result shows that Jiangsu Province is a potential suitable establishmentarea for the pest. Effective accumulated temperature analysis indicates that the pest mayhave five to seven generations a year in the province. The geographical distribution mapforecasted via the Geographic Information System (Arc GIS 8.1) indicates that regions suchas Changzhou, Liyang, Suzhou, Nanjing and Lvsi, whose altitude fall in 31°N～32°N,show relatively better suitability. The map also indicates that the pest can establish itspopulation or have outbreaks easily from late July to early August.2. The risk analysis of invasive S. invicta in Jiangsu Province of ChinaLifetime female alate production of red imported fire ant, S. invicta is calculated so asto determine whether the colony can exist and develop itself or not. The fact that extremelow temperature will cause lower reproductive rates and winter kill, which gives evidencethat the target area is not suitable for geographic distribution and diffusion. Though heightabove sea level and precipitation amount will affect its suitability to some extent, we deemthat the above two parameters will not limit the geographic distribution and diffusion of S.invicta in Jiangsu Province after the analysis of meteorological data in twenty years from13 sites in the Province. The result shows that Jiangsu Province is a potential suitableestablishment area for the pest. Effective accumulated temperature analysis indicates thatthe pest may have one to three generations a year in the province. The geographicaldistribution map forecasted via the Geographic Information System (ArcGIS 8.1) indicatesthat regions such as Changzhou, Liyang, Suzhou, Nanjing and Lvsi, whose altitude fall in31°N～32°N, show relatively better suitability. The map also indicates that the pest canestablish its population or have outbreaks easily from late July to early August. Quarantineofficials should be vigilant for any accidental introductions of this pest in the susceptibleregions and time.3. The molecular genetic structure of S. invicta populations from China Molecular genetic marker technology has been wildly applied in such entomologicaldomains like classification& determination, systematic evolution, ecological adaptation andpest control, etc. The application of molecular technology presently in Pest Risk Analysis(PRA) are mainly two aspects, classification& determination at individually level andevolution analysis at phylogenetic level. The population phylogeny analysis based on themass information of nucleic sequence gives an insight into the reorganizations of not onlythe interspecific relationship but also the intraspecific heredity & variation, origination,evolution, invasion, establishment, expansion, etc. As mtDNA COI gene is recognized as asuitable genetic marker for analyzing the systematic relationship of the relative species, thesubspecific categories and the geographic populations, in our study we use moleculartechniques to examine the interspecific relationship between Solenopsis species and theintraspecific variation of mtDNA COI sequences among the populations of S. invicta.Samples for the experiment were collected from Wuchuan of Guangdong Province,Beiliu, Cenxi, Luchuan of Guangxi Province, and Zhangjiajie of Hunan Province. GenomeDNA of S. invicta was extracted by using UNIQ-10 Column-shaped Extraction Kit. PartialDNA sequence of mtDNA COI for each population was then PCR amplified using one pairspecial primers. The purified PCR products were subsequently connected with pGEM-Tvector and transformed to susceptive Escherichia coli. After PCR test to the transformantsusing the same primers, the positive clone was screened out for sequencing. The partialmtDNA COI of each geographic population for S. invicta was finally determined by theidentical sequences after three clones at least were randomly sampled for sequencing. Apartial mtDNA COI sequence of 965 bp length was proved to be successfully amplified foreach population in our study. The DNA sequences were then submitted to the GenBankdatabase and then compared online with the published sequences by similarity searchengines such as BLAST in NCBI website then calculated in GeneDoc and aligned usingClustalⅩcomputer program. Twenty foreign mtDNA COI sequences of S. invicta and eightmtDNA COI sequences of Solenosis species as out-group, previously published by otherresearchers, were introduced to our research for the construction of phylogenetic tree.Analysis of genetic and phylogenetic relationship was performed by using MEGA2.1.Genetic relationships among every geographical population were estimated based on thepair-wise matrix of sequence divergences by Kimura-2 Parameter method. Phylogenetictree was constructed by the Neighbor-Joining (NJ) method. Confidence levels for NJ treewere assessed by bootstrapping from 1000 pseudo-replications. We come to a conclusion that the discrimination between the red imported fire ant, S.invicta, and other allied species of Solenopsis can be resolved preferably by using mtDNACOI gene as a molecular genetic marker. We could see from the phylogenetic tree that mostspecies in Solenopsis as an out-group can be separated distinctly from the S. invicta at veryhigh confidence levels and they are located in distinct clades in the tree. The populations ofS. invicta from China ares close with the Argentine populations based on the analysis tomtDNA COI, no matter they are divided into two major clades. Populations from Luchuanand Beiliu of Guangxi Province and Zhangjiajie of Hunan Province are quite relative andthey are in a major clade with some Argentine populations; Populations from Cenxi ofGuangxi Province and Wuchuan of Guangdong based on the analysis to mtDNA COI arecompletely the same and they are in another major clade with some other Argentine S.invicta populations.The introduction history of the exotic pest, S. invicta in China is not too long, whichresults in the delicate molecular evolutional discrepancy between the different geographicpopulations in China. We argue that the Chinese S. invicta are most probablely originatedfrom Argentina accidentally, however the introduction pathway and time maybe differentfrom each other. Generally speaking, the genetic variation between the populations of S.invicta in China is low relatively. We deem that one reason is the short history of the pest inChina, which results in insufficient variation accumulation and lower variation rate, so thepopulations of S. invicta still keeps a close genetic relationship with each other; anotherreason is that the approximate ecological conditions of their habitats bring about the lowerselection pressure. Population variation level sometimes relies on how much the organismsadapt themselves to the environment. If the evolutionary directions and intensities causedby environment are approximately the same, there will not be a distinct variation betweenthe populations in an area.