Studies On Population Dynamics, Genetic Diversity Of Invasive Bemisia Tabaci And Its Molecular Mechanism Of Resistance To Thiamethoxam

Bemisia tabaci (Gennadius) is an important invasive species that has caused severe damage in the world. B. tabaci was recorded for the first time on cotton in China in 1949, but significant damages caused by this insect had not been noticed until 1990s. In the past several years, the importance of this whitefly in China has increased spectacularly, which has infested in more than 20 provinces in China on cotton, some ornamental plants and most of the vegetable crops, in most of these place, which has resulted in a significant decrease in yields. However, little have been understood about its invasive mechanism and resistant mechanism to insecticide. In this paper, we studied the population dynamics, genetic diversity of invasive B. tabaci and its molecular mechanism of resistance to Thiamethoxam.From 2002-2004, the host plants of B. tabaci have been investigated and identified in Shanxi province, and all the host plants can be divided into 4 grades according to the damage degree caused by B. tabaci. There were 103 species of plant which belong to 27 families as hosts of B. tabaci, of them Cucurbitaceae. Solanaceae, Cruciferae and Leguminosae are the main families of host-plant, and the population density of B. tabaci was higher in south of Shanxi province than in north.The population dynamics of B. tabaci on 12 species of host-plants were studies from 2002 to 2004, which indicated that the infesting time and population densities of B. tabaci on different hosts were significantly different. the density of B. tabaci on different host plants was in the order of sunflower>pumpkin>cotton>soybean>cushaw>eggplant>hechima> tomato>chili>cucumber>kidney> bean>corn. In addition, spatial distributions of B. tabaci in cotton, sunflower and soybean fileds were studied, which indicated that they were collective distribution type.A amplified fragment length polymorphism (AFLP) molecular marker system on B. tabaci was funded by adjusting the DNA density, Mg~2+ density, dosage of dNTP and other reactions parameter etc.AFLP analysis showed that genetic differences exited among and within different host populations, but the difference among populations is bigger that that within populations.Analysis of the genetic diversity among 27 different geographical populations of B. tabaci and determination of biotypes of B. tabaci in China based on AFLP was conducted. The use of 5 primer combinations elected from 64 primer combinations allowed the identification of 229 polymorphic bands (97.03%) from 60 to 500 bp, suggesting abundant genetic diversity among different geographical populations of B. tabaci. Molecular phylogenetic tree based on AFLP analyse revealed the presence in China of at least four different genetic groups of B. tabaci. B biotype, Q biotype and two non B/Q biotype. B biotype was nationwide distributed. Q biotype was present only in local region of China including YunNan province and BeiJing city. Other two non B/Q biotype groups, one was found in ShanDong and HeBei provinces, and another in ZheJiang province.Genetic differences within different geographical populations of B. tabaci, including Zhejiang(ZJl-China),Shandong (SD2-China), Peking(BJ3-China),Shanghai (SH1-China), Shanxi(SX1-China)and Henan (HN-China) were studied using AFLP molecular marker. The results showed that geneticdifference and heterisity of population were lower. Heterisitys of several populations in order were:Peking (BJ3- China) >Shandong (SD2-China)>Zhejiang (ZJ1-China) >Shanghai (SH1-China)>Shanxi (SX1-China)>Henan (HN-China).A 39.96 fold Thiamethoxam-resistant strain of B. tabaci was achieved by the selection with Thiamethoxam.Analysis of the genetic diversity between the resistant and susceptive strains of B. tabaci based on AFLP were conducted. The results showed that a significant genetical differentiation was found between the resistant and susceptive strains of B. tabaci. Additionally, peculiar amplified DNA fragments, the 150bp for resistant strain and the 315bp for susceptive strain were identified using the E-ACT/M-CTG primer, which may serve to...