The Distribution,transmission,and Effects On The Host Reproduction Of Rickettsia In Bemisia Tabaci MED

Bemisia tabaci(Gennadius)is a species complex composed of 35 cryptic species that are morphologically indistinguishable but genetically distinguishable,B.tabaci MED(Q biotype)and B.tabaci MEAM1(B biotype)are notorious invasive species in China.Since 2008,B.tabaci MED has gradually displaced B.tabaci MEAM1 and has become the predominant biotype in most parts of China,of which the facultative symbiont of B.tabaci MED played an important role in terms of spread and invasion.In this study,we chose the facultative symbiont Rickettsia as the research object,explored the influence of Rickettsia to B.tabaci MED from three aspects,which were the qualitative,positioning and quantitative three levels,the vertical/horizontal transmission and biological effect.Firstly,we use the fluorescence in situ hybridization(FISH)techniques to locating Rickettsia in MED with the fluorochrome-labeled specific probe,to clarify the location of Rickettsia in each developmental stage of MED.Secondly,we took the Fluorescence Quantitative PCR on Rickettsia in MED based on Taqman probe and Rickettsia 16 srDNA gene is the target gene,to verify the copy numbers of Rickettsia in each developmental stage of MED.At the same time,three independent ecological experiments are conduct: 1.The vertical transmission of Rickettsia in B.tabaci MED;2.The horizontal transmission of Rickettsia in B.tabaci MED;3.The impact of Rickettsia to the life history of B.tabaci MED.This paper mainly results were as follows:(1)Rickettsia was distributed in all developmental stage of B.tabaci MED.The localization patterns of Rickettsia in adult B.tabaci were divided into two cases: insider the bacteriocytes and outside.The localization in the bacteriocyte was spherical,and the bacteriocyte was a kind of specialized cells in whitefly abdomen.The localization out of the bacteriocyte was main inside the egg.The two localization patterns are accompanied by the distribution of primary symbionts Portiera.The patterns of Rickettsia in forth instar was also divided into two cases: one is the position mainly in vasiform orifice and linguiform projection at the end of the body,the other is the symbionts random distributed at the thorax and head of the nymphs.The positions of thrid instar,second instar and first instar were focused on the vasiform orifice and linguiform projection,of which Rickettsia in the second instar also could insided in the bacteriocytes,and in the first instar also could distributed in the tentacles,trachea and mouthparts and so on.The localization of Rickettsia in eggs was egg pedicle.(2)The copy number of Rickettsia among the different B.tabaci nymphs was difference,but it was relatively stable at adult stage.The content of Rickettsia in the early development stage was gradual increased,up to peak at the second instar nymph,after that,the copy number sharply droped and reached the lowest point at the third instar nymph.At 5 days after emerged,the number reached at the second peak,then kept around the number of the emerged stage.From the point of the entire development process,the copy number of Rickettsia was increased and then decreased under the overall trend.(3)In this study,the vertical transmission of Rickettsia in B.tabaci MED was observed,but the horizontal transmission was not.The rate of vertical transmission of Rickettsia from infected mothers to daughters or sons was approximately 98%,and the rate of horizontal transmission of Rickettsia from infected fathers to uninfected mothers was nearly 0%.Rickettsia could significant increase the development speed during the preadult stage,the development speed of the females harboured Rickettsia was significant higher than the males.Moreover,Rickettsia can drive life history fitness benefits and female bias sex ratios,and the infected female could produced more offspring,Rickettsia could improve the eclosion rate and longevity of B.tabaci MED,but not significant.In this thesis,we explored the location and the copy number of Rickettsia in each developmental stage of B.tabaci MED by using molecular biology techniques,furthermore,we clarified the transmission efficiency and the impact of Rickettsia to the life history of B.tabaci MED,the results improved the understand of the B.tabaci invasion drived by Rickettsia,and showed a new insights for the biological function that secondary symbionts to the insect host.