Study On Population Genetics Characteristics Of Aedes Albopictus In Nanjing City

Aedes albopictus is one of Chinese common mosquitoes,which belongs to diptera, Culicidae and category of aedine mosquitoes. Ae. albopictus is widespread, spreading from Hainan Island in the south to Shenyang and Dalian in the north, from Long County and Baoji in the west to Tibet Autonomous Region in the southwest and to most of the districts in the east, which is most common below the 30 degrees north latitude. It is an important vector mosquito of viral transmission of dengue, yellow fever, Chikungunya fever and West Nile Fever.Currently, as there is no special medicine and vaccine for dengue and dengue hemorrhagic fevers, controlling the medium Ae. albopictus is the major means to prevent dengue. As to the prevention of vector mosquito, we should stick to the principle of “Tackling the cause rather than the symptom”, and adopt a comprehensive preventive measure of environmental management and eliminating breeding places”. As chemical control is easy to operate and it can effectively reduce the adult mosquito density and control the epidemic situation, it plays an important role in vector insect control program.Wolbachia is a bacteria found in arthropods that can cause a large number of changes in its host. Most Ae. albopictus are infected with Wolbachia Type A or B; individuals can be infected by just one Type of Wolbachia, or by both types. Mating between Ae. albopictus infected with different Types of Wolbachia does not produce fertile offspring because of cytoplasmic incompatibility(CI). Wolbachia infection can therefore impede gene-flow within Ae. albopictus populations thereby affecting population genetic structure.The continuous and much usage of insecticide lead to the high resistance of vector mosquito. The mechanism of the resistance includes two aspects: the metabolism detoxication and the decline of drone sensibility. Metabolism resistance mainly includes the increase of enzymatic activity of mixed function oxidase(MFO)、 acetylcholinesterase(ACh E)、Glutathione S-Transferase(GSTs) and Esterase(EST). the drones of insecticide mainly include acetylcholinesterase, sodium channel, gamma-aminobutyric acid receptor and juvenile hormone receptor.This study, taking Ae. albopictus in Nanjing as example, we conducts a survey on the breeding place and population density. By collecting Ae. albopictus in the field and measuring lava’s resistance to insecticide, the thesis studies the relationship between metabolic enzymes, resistance drone and resistance to insecticide, and discusses the generation mechanism of the Ae. albopictus’ resistance. By making use of microsatellite DNA markers, the thesis analyzes the population genetic characteristics, discusses the influence of breeding place fragmentation and Wolbachia on genetic differentiation, providing theoretical reference for prevention and control of Ae. albopictus. The research results are as follows:1. The findings of the natural population density of Ae. albopictus are as follows: 29 populations of aedes albopitus in Nanjing were collected between July and September 2013, with 1651 various vessels in total, 696 positive ones. With laboratory morphology and COI sequence, they were all identified as Ae. albopictus. By analyzing the relevance of larva density, breeding spot type, vessel color, vessel size and vessel material, it was found that breeding density was only related to breeding vessel color, without any relation to other factors.2. In the 9 microsatellite locus in this research, the average allele is 7.3265, the average polymorphic information content is 0.56, and the average expected heterozygosity is 0.605. Variation in these nine microsatellites indicates that the 17 Ae. albopictus populations are relatively rich in terms of PIC and have relatively even gene frequency distributions. This approach was a highly effective and reliable way of assessing genetic diversity. These results also indicate that our sample size was more than adequate. The fact that observed heterozygosity was lower than expected in all populations other than ZW and SQ indicates that each of the 17 populations had a relatively high degree of genetic uniformity which may be related to inbreeding and other factors.3. All populations were found to have microsatellite loci that depart from the Hardy-Weinberg Equilibrium, which could be due to differences in Wolbachia infection status within populations. CI caused by Wolbachia infection may cause a serious increase in inbreeding within populations, exacerbated by a combination of anthropogenic and natural factors, such as eradication of breeding habitat, high temperature and decreased rainfall, all of which lead to fragmentation of breeding habitat, reduced population size and therefore increase the likelihood of inbreeding.4. The fixed index of the 17 populations in the 9 microsatellite locus in this research is from 0.013 to 0.141, and the average fixed index of the group is 0.043, showing the panmixia within the group is relatively high and there is no significant genetic differentiation; the genetic differentiation coefficient is from 0.02 to 0.132, and the average genetic differentiation coefficient is 0.04, showing that there is slight genetic differentiation among the 17 Ae. albopictus populations. Analysis of Nei’s Genetic Distance and gene-flow also show that each population’s genetic divergence was relatively low.5. The result in the research shows that there is no significant declining trend in genetic diversity among the 17 Ae. albopictus populations. That means the habitat fragmentation and CI has no significant effect on the genetic differentiation of Ae. albopictus. Through Mantel detection on the genetic distance and geographical distance of 17 populations, the result shows there is no significant correlation between the two variables.6. Wsp gene sequence result caused by the infection with Ae. albopictus Wolbachia is as follows: by carrying out Wolbachia infection detection on 29 Ae. albopictus populations, it is found that only the NQBY population is not infected, and other populations have caught with different degrees of infection whose infection rate ranges from 40% to 100%. By analyzing the sequencing of Wolbachia A population and population, it is found that there exists telegraphy in every population; by randomly selecting and using universal primer to detect the sequencing result infected by Wolbachia, it is found that it is obviously classified into two types, showing that there possibly exist different types of Wolbachia,; by randomly selecting two samples in Group A and Group B infected with Wolbachia in every population, it is found that the sequence of Wolbachia Group A and Group B is basically the same, indicating that Ae. albopictus in Nanjing is infected with a certain type of Wolbachia in Group A and Group B rather than several types of Wolbachia.7.Ae. albopictus’ resistance to common insecticide is as follows: The lab chose propoxur, chlorpyrifos,permethrin and deltamethrin as experiment chemicals to carry out the measure on larva’s resistance. The resistance to propoxur is 2.18 to 5.93 times, the resistance to chlorpyrifos is 1.23 to 2.4 times, the resistance to permethrin is 1.75 to 9.32 times, and the resistance to deltamethrin is 3.03 to 25.83 times. Besides, there exists a linear correlation between the resistance of deltamethrin and the resistance of permethrin.8. The biochemical detection of Ae. albopictus is as follows: by analyzing Ae. albopictus’ resistance to insecticide and the relevance to three kinds of metabolic activities including Ach E, EST and GST, it is found that there is a linear correlation between LC50 and EST activity and GST activity, a linear correlation between chlorpyrifos LC50 and GST activity, without any other correlation; by carrying out a correlation analysis on gene copy number of cytochrome P450 and LC50 of different insecticides, it is found that there is no correlation between the difference of genetic expression quantity and insecticide’ resistance.9. The research results of resistance are as follows: by successfully cloning sodium channel full-length gene and acetylcholine esterase full-length gene, it is found that there is a mutation at 1998 locus of amino acid sequence in sodium channel, which may be related to resistance of deltamethrin; the alternative splicing existing in sodium channel gene may be related to resistance; gene mutation of acetylcholin esterase isn’t found on the sequence.