Genetic Diversity And Genetic Structure Of Oriental Fruit Moth, Grapholita Molesta (L.) Analyzed By Microsatellite Markers And DNA Gene Sequences

The oriental fruit moth, Grapholita molesta (L.)(Lepidoptera: Tortricidae) is a keyglobal fruit pest. This pest not only causes damage by feeding on twigs, giving rise to shootdie-back, but also indirectly feeds on fruit, resulting in shedding of fruit, or causes majoreconomic damage every year in the world. G. molesta is characterized by wide rangedistributions, serious damage, abundant host plants and seasonal host switch, and nowdistributes in different continets including Asia, Europe, Americas and Africa. It has beenreported in all provinces of China except Tibet province.Population genetics is an branch of biogogy that provides the mathematical structure forthe study of the process of microevolution, focusing on the of genetic variation within apopulation. Population genetics research, which can provide information about the process ofmicro-evolution, genetic diversity, genetic structure and gene flow, is important to theimplementation of the pest control strategies. In the current study, we selected fivepolymorphic microsatellite loci and two mtDNA genes to examine the effect of geographicisolation, host plants, season change and fruit-bagging on the genetic diversity and geneticstructure of G. molesta populations from two major fruit growing regions of China. Inaddition, the evolutionary relationships of three Tortricidae moths including G. molesta, G.dimorpha and G. funebrana were analyzed based on mtDNA COI gene and COII gene in thisstudy. The results were as follows:We tested the amplification of11microsatellite, which were previously reported in G.molesta and Cydia pomonella populations from Europe, in the samples collected in China.The results showed that five of the11loci were highly polymorphic and can be amplifiedstably. The number of alleles for the five loci ranged from17to35. The number ofheterozygotes was from48to65while the number of homozygotes was from38to70. Themean value of Ho was between0.4063and0.6833, that of He between0.6890and0.8364.The PIC (polymorphic information content) ranged from0.7745to0.9137. The frequency ofnull allele ranged from0.1542to0.2453, which are typical for Lepidopterans. No significantlinkage disequilibrium was found in all the possible combinations, which suggests that the five loci represented independent information across all the samples. We concluded that thefive loci can be used for further analysis.We used the five polymorphic microsatellite loci and mitochondrial COI and COII geneto analyze281G. molesta individuals from12geographic populations sampled in Shandongprovince and Shaanxi province in the same season. The results showed all the populationshave high genetic diversity, which provided for the first time comprehensive empiricalevidence for the assumption that China lies indeed in the range of G. molesta’s origin. Sevenpopulations sampled from Shandong province showed a structure differing from that of fivepopulations sampled Shaanxi province. Populations from Shaanxi province showed similargenetic structure, while significant substructure exsied among populatuons from differentlocations from Shandong province. The mtDNA analysis showed the most commonhaplotypes of COI gene and COII gene were shared by populations from different locations.The COI gene and COII gene haplotypes did not showed any geographical pattern.Grapholita molesta samples were collected from peach, apple and pear host plants inYantai region at the same season to analyze the genetic differentiation of populations fromdifferent host plants. We found the high genetic diversity based on five microsatellite loci andmitochondrial COI gene and COII gene. Populations collected from peach orchards hadsimilar genetic structure, whilst populations from apple and pear had similar genetic structure.However, we found significant genetic variations among populations from peach orchards andpopulations from apple or pear orchards. Subsequently, the most common COI gene and COIIgene haplotypes were shared by the populations from different host plants. The haplotypesdistribution was not related to host plants.Fruit-bagging is being used as a pest management tool to control fruit moths in majorfruit growing areas of China. A total of308G. molesta individuals, collected from threefruit-bagged and two fruit-unbagged apple orchards in Shaanxi province in three seasons wereused to analyze whether the fruit-bagging affect the genetic diversity and genetic structure ofG. molesta populations. Populations from fruit-bagged and unbagged orchards weresignificantly differentiated based on AMOVA of microsatellite data. Genetic structures of G.molesta from the fruit-bagged orchards deviated strongly from those of the unbagged orchardsin June and July. However, the similar genetic structure was found in fruit-bagged orchardsand unbagged orchards, respectively. Interesting, the genetic structure of fruit-baggedorchards and unbagged orchards became similar in August. The common haplotypes of COIand COII gene were shared by populations from both the fruit-bagged and unbagged orchards.The Median-Joining network of all the haplotypes could be divided into three clades based oncombined COI gene and COII gene haplotyes. It is interesting the haplotypes from fruit-bagged and unbagged orchards distributed different clades, respectively. Our resultsshowed fruit-bagging control method had influenced the genetic diversity and geneticstructure of G. molesta.Five microsatellite loci and two mitochondrial genes were used to investigate thevariation of genetic diversity and genetic structure of G. molesta populations sampled in fiveorchards in Shandong province and Shaanxi province in June, July and August. AMOVAanalysis of microsatellite data showed significant variations in populations sampled in each ofthe five orchards. Genetic structure changed with seasons, but the seasonal regular of geneticstructure was different in different orchars populations. Populations from four of the fiveorchards changed the genetic structure. Genetic diversity revealed by microsatellite andmitochondrial gene haplotypes changed changed with seasons.Samples of G. molesta, G. dimorphs and G. funebrana were collected from differentregions of Shaanxi province to analyze the phylogenetic relationship of the three Tortricidaespecies. The genetic distance and phylogenetic trees based on mitochondrial COI gene andCOII gene showed that G. molesta and G. dimorphs had closely evolutionary relationship incomparing with G. funebrana.