Biotypes, Genetic Differentiation And The Resistant Mechanism To Common Insecticides Of Bemisia Tabaci In China

The tobacco whitefly, Bemisia tabaci (Gennadius) causes severe crop losses in many agricultural systems. The worst of these losses are often associated with the invasion and establishment of specific whitefly biotypes. The B biotype invaded China in the mid-1990s and caused major agricultural losses. Another highly invasive form:the Q biotype was recently identified from some provinces. In order to determine the distribution and genetic diversity of different biotypes of B. tabaci in China, we collected and analyzed a series of field sampling from some provinces in China. In order to discuss the invasion mechanisms of invasive biotypes, the main crops and the dynamics of B. tabaci invasive biotypes were investigated and analyzed in central China during a three-year period. Furthermore, the molecular mechanisms of resistance of B. tabaci to neonicotinoids, pymetrozine and pyrethroids were studied in the laboratory. The results are summarized as follows:The aim of this study was to characterize the biotypes status of B. tabaci in China from 2004 to 2007, by determination of the mitochondrial CO1 gene sequences and cDNA-AFLP polymorphic analysis. All samples of B. tabaci could be divided into six clusters:the B biotypes, the Q biotypes and the 4 indigenous biotypes ZHJ1, ZHJ2, ZHJ3 and FJ. Amplification of the cDNA of 19 B. tabaci populations, the B biotypes of 7 populations showed a higher degree of similarity than the Q biotype. The high level, of genetic diversity has been suggested to be of benefit for the invasion.In a comprehensive survey of biotypes present in central China between 2005 and 2007, we obtained 191 samples of B。tabaci from 19 districts in Hubei province and its surrounds. Biotypes were identified by RAPD-PCR and sequencing mtCO1. We determined that these central Chinese haplotypes included the world's two most invasive B. tabaci biotypes (B and Q) and two indigenous biotypes (ZHJ1 and ZHJ3). By 2007, the Q biotype was dominant over much of Hubei province and appeared to be supplanting all other biotypes although both the invasive and indigenous biotypes existed in sympatry in some regions. The invasion and rapid establishment of the Q biotype in China mirrors events elsewhere in the world, and we suggest that this is a consequence of its reproductive isolation, its polyphagous nature and its broad-spectrum resistance to insecticides. Its dominance has severe implications for the sustainability of some insecticide groups and for the production of a number of crops.Some Q biotypes of B. tabaci from China exhibited strong resistance to the neonicotinoids:imidacloprid, thiamethoxam and acetamiprid (100-300 fold), but only slight resistance to an atypical neonicotinoid:dinotefuran (2-6 fold). The magnitude of resistance displayed by specific strains was strongly correlated with over-expression of the CYP6CM1 gene which is associated with increased oxidative metabolism. That mechanism also appeared to protect B. tabaci against the novel anti-feedant compound, pymetrozine. This is the first time that CYP6CM1 has been correlated with cross-resistance among the neonicotinoids and that the dinotefuran molecule has been shown to be less affected by that mechanism. It is also the first note of the potential cross-resistance that may occur between pymetrozine and the neonicotinoids. These findings have broad applicability to the implementation and design of pest management strategies and the expected spread of Q biotypes expressing high levels of CYP6CM1.Two TaqMan(?) allelic discrimination assays were designed to detect L925I and T929V for analyzing the relationship between two kdr mutations of Q biotype strain and the doses of DDT & pyrethroids. Three compounds were used in discriminating dose leaf-dip bioassays; DDT, deltamethrin, fenfluthrin. The results showed that T929V offers protection against fenfluthrin and DDT as almost all survivors carried this mutation with L925I absent. And T929V should protect against these compounds given its predicted position within the sodium channel. Deltamethrin extends further into the pocket of the sodium channel than the other two compounds and therefore should have a greater interaction with L925I.The population dynamics of Q biotype of B. tabaci and its parasitoids were studied, under the foliar and systemic treatments by imidacloprid. The effects of parasitism by systemic treatment were comparatively lower than foliar treatment. That means foliar treatment may protect parasitoids while imidacloprid is used to control the whiteflies.