Resistance Mechanisms Of Q Biotype Bemisia Tabaci To Thiamethoxam

Bemisia tabaci (Gennadius) is a serious agricultural pest in many cropping systems. In China, B biotypeB.tabaciwas first reported in 1949, and become serious damage until the introduction of B biotype in the mid-1990s. Then Q biotypeB. tabaciwas first found in 2003in China, has become the dominant species instead of BbiotypeB. tabaciduring the past dacade, andhas caused more serious losses in field agricultural systems. Control of B. tabaci in crop systems worldwide has largely depended on chemical insecticides, especially during the past decade, neonicotinoid insecticide, thiamethoxam have been widely used to control whiteflies in many countries. However, field B. tabaci populations have developed resistance to this insecticide. In this study, we sampled some field B. tabaci, determined the resistance level to thiamethoxam, and maintained the high resistance populations in the greenhouse, then to study the resistance mechanism by a series of physiology, biochemistry, and molecules biology measure.In 2011, we sampled 17 whiteflies populations in China, and determined the inter-sibling species B and Q, the result therefore confirms that B. tabaci Q has become the dominant B. tabaci species in most parts of China. The resistance level of field populations to thiamethoxam and imidacloprid were measured, we found B. tabaci have widely developed differential resistance. Among them, the NKBJ and HZZJ population showed a very high resistance level to neonicotinoid insecticide.We maintained the high resistance level B.tabaci in a greenhouse, and assessed the activities of detoxfiying enzymes between the resistant and susceptible populations. The results exhibited that the activities of P450 and GST were significant hihger in the resistant population. It is the first report of GST involving in the neonitinoid insecticide resistance in whiteflies.A P450 gene, CYP4C64, was cloned in the high resistance population of THQR, and the expressional profile in field populationwas determined, then knockdown the gene by RNAi. The result showed that mRNA expression level were associated with the resistant level to thiamethoxam, and over-expression of the gene of CYP4C64 plays a very important role in thiamethoxam resistance in THQR population.The mRNA expressional model of a P450 gene, CYP4C64 were studied by dual-luciferase reporter gene system. The results showed that the up stream of the gene contain the cis-regulate elements at the site-1/-603. Sixteen transcription factors were cloned and injected in the plasmid of pAC5.1, and expressed in the S2 cell, deteced by dual-luciferase reporter gene system. The results exphibited that these transcription factors could not enhanced expression of CYP4C64 in S2 cell.Twenty GST genes were found in in B.tabaci genome sequencing project. And the GST expressional profiles were compared in thiamethoxam resistant and susceptible population. The results showed that five GST genes were over-expressed in the resistant population. We cloned a GST gene, BtGST11, which is the highest over-expressed in resistanct population, and comfirm it invloving the resistant to thiamethoxam by RNAi in B.tabaciQ.Nicotinic acetylcholine receptors were annotated in B.tabaci genome sequencing project. Eight alpha subunits and one beta subunti were found in B.tabaci Q genome, and exhibitd a conservative and specificity of evolutaion comparing with other insects. The nicotinic acetylcholine receptors sequence information from diverse species, including agricultural pests, disease vectors and pollinating insects, provides a valuable starting point for understanding the interactions of insecticides with their targets at the molecular level, as well as enhancing our understanding of mechanisms causing insecticide resistance, and may prove instructive in the future design and development of improved insecticides with enhanced specificity for pest species.