Horizontal Transmission Of Rickettsia Between Whitefly Bemisia Tabaci And Encarsia Formosa And Its Influence On Their Nutrition And Parasitization-protective Defense Interaction

The whitefly Bemisia tabaci(Gennadius)is one of an important cosmopolitan polyphagous insects,which consist of at least 36 morphologically indistinguished biotypes.The B.tabaci pest can causes severe economic losses due to its directly sucking in phloem sap,honeydew secretion that induce plant mildew stains,and it most destructive damage is transmission of plant viruses.The insect endosymbionts,which is the symbiotic bacteria live in the insect body,play an important role in inset development,reproduction manipulate,genetic evolution and adaptability to environment.On the other hand,Encarsia formosa Gahan,a dominant endoparasitoid of the whitefly B.tabaci,which can efficiently control whitefly pests by parasitizing and feeding on the nymph host.In current study,taking Rickettsia positive,negative populations of B.tabaci(R+ and R-populations,both are B biotype)and its parasitoid E.formosa as research objects.The parasitoid-mediated horizontal transmission of Rickettsia between donor Rickettsia positive B.tabaci,E.formosa and recipient Rickettsia negative B.tabaci was investigated using normal PCR,q RT-PCR and fluorescence in situ hybridization(FISH),including the infection status,titers,localization and homology of Rickettsia endosymbiont in different whitefly and E.formosa hosts;the effects of Rickettsia infection on the nutrition of both whitefly and E.formosa hosts,and on the defensive ability change of whitefly nymphs to the parasitizing of E.formosa wasp.The findings of current study are in followings.1.The infection,retention and distribution of Rickettsia in E.formosa.Parasitoid E.formosa could obtain Rickettsia endosymbiont by parasitizing Rickettsia positive B.tabaci,but it was only kept in the wasp body for a short period,its titer continued to decline and finally tended to zero with the increase of time.The q PCR results revealed that Rickettsia localized in the head,chest and abdomen of new hatched E.formosa from Rickettsia positive B.tabaci,and the relative titer of Rickettsia in the abdomen was much higher than in other parts.The FISH results showed that,Rickettsia mainly persistent in the mouthparts and ovipositors of the 4 d age parasitoid E.formosa,and some can also persistent in the alimentary canal as well as in the chest.2.The infection,retention and homology of Rickettsia in recipient Rickettsia negative B.tabaci.PCR results showed that the recipient Rickettsia negative B.tabaci also can obtain Rickettsia,if they survived from the non-lethal probing or feeds of Rickettsia positive parasitoids E.formosa.The futher q PCR detecton showed that Rickettsia can be vertically transmitted in the F1-F3 generation progenies of recipient Rickettsia negative B.tabaci.The phylognenetic analysis of Rickettsia in the donor Rickettsia positive B.tabaci,E.formosa and Rickettsia negative B.tabaci revealed that,they are 100% in homology based on the 16 S r RNA gene,and they all are clustered into one branch belonging to the Bellii group.3.Effects of Rickettsia on the nutrient contents of B.tabaci and its parasitoids E.formosa.The total amount of protein,soluble sugar,glycogen and trehalose were determined in both Rickettsia positive and negative populations of B.tabaci,Rickettsia carrying and Rickettsia not carrying of E.formosa wasps.Results showed that total amount of soluble sugars,trehalose are significantly increased of the in the Rickettsia positive populations whiteflies and parasitoids,but their proteins and glycogen are not significantly different to each other.4.Effects of Rickettsia on the parasitization defense of B.tabaci host.Rickettsia infection in the B.tabaci hosts,can significantly reduce the parasitism rate and shorten the development period of E.formosa,but no significant effects on their eclosion rate and body size of F1 generation adults.Furthermore,Rickettsia infection in B.tabaci hosts can significant reduce the average parasitism rates of E.formosa,either in laboratory choice experiments or semi-field conditions.