Characterization And Effects Of Symbionts Wolbachia In Encarsia Formosa

Wolbachia are ubiquitous maternally inherited endosymbionts that are estimated to colonize a wide range of arthropods and nematodes. They are best known for their roles in manipulating reproductive disorders in hosts, such as cytoplasmic incompatibility (CI), thelytokous parthenogenesis, male killing and feminization. Through the above listing modifications to host reproductive biology, Wolbachia guarantee their maintenance in hosts. Wolbachia can be localized in many parts of the host body, especially in the reproductive tissues. Encarsia formosa (Hymenoptera:Aphelinidae), a parasitic wasp used for the biological control of Bemisia tabaci (Gennadius) and Trialeurodes vaporariorum (Westwood), is naturally infected with Wolbachia. Researches have shown that thelytoky in E. formosa is caused by Wolbachia and this mode has become its stable reproductive way. The phylogenetic analysis based on wsp sequences of Wolbachia in E. formosa was performed and MLST technique was used for the sequence typing research.Real-time PCR was used to test the density dynamic of Wolbachia in whole adult and isolated parts (head, thorax and abdomen) of E. formosa as well. We also performed antibiotic treatment to study its elimination efficiency on Wolbachia and researched if there was any reproductive abnormality due to the elimination of Wolbachia in the parent generations.The phylogenetic analysis of Wolbachia based on wsp gene indicated that one Wolbachia strain was harbored by E. formosa and the strain was the same to the previously reported one. MLST technique was used to test the sequences of five housekeeping genes (gatB, coxA, hcpA, ftsZ and fbpA genes), finally the ST value (18) was obtained after comparison to the database. Taken the phylogenetic analysis and MLST result together, we concluded that E. formosa was only infected was one unique Wolbachia strain and no change occurred to the strain, indicating a stable symbiotic relation between them.In order to measure density dynamic of Wolbachia, real-time PCR (qPCR) was performed to study the density change of Wolbachia with the increasing age both in whole adult and isolated parts of E. formosa. The results showed that Wolbachia density dynamic in whole adult wasp was a progress with an initial slow raise, then a quick raise and finally a decrease trend. Also, the density experiment here evidenced that Wolbachia was found in all body parts of E. formosa, including head, thorax and abdomen. This result is correspondent to previous reports that Wolbachia symbionts are generally distributed throughout insect body parts (somatic and germ line tissues), not restricted to the reproductive tissues. Generally, Wolbachia was found at low density in head, moderate density in thorax and high density in abdomen of E. formosa. Prevalent favor in abdomen may be the result of massive accumulation of Wolbachia in ovaries, by which way Wolbachia guaranteed its vertical transmission from one generation to another. Head is relatively solid, so high skeleton may be the reason explaining low density of Wolbachia in this section.To study the effect of Wolbachia on E. formosa, antibiotic treatment was used for elimination of Wolbachia in newly emerged adults, result of PCR detection indicated that elimination efficiency of5.0mg/ml tetracycline treatment was up to90%, indicating a high effectiveness. The number of ovarian tubule remained the same in the parent generations after antibiotic treatment, thus artificial elimination of Wolbachia did not change or impair the existing reproductive system. Second, each offspring of the cured parent generations emerged from the Wolbachia-free whiteflies had six ovarian tubules, two less than the parent adults. Hence, the decrease of ovarian tubule showed that the removal of Wolbachia in the parent generations could bring negative effects to the reproductive system of the offspring generations, causing reproductive defects (loss of ovarian tubule). However, F5generation (offsprings) emerged from Wblbachia-infected whiteflies had an unexpected divergence in the reproductive system. Generations from F1to F4all had six ovarian tubules per individual, when F5generation emerged,60%offsprings tested were found to have eight ovarian tubules, and the rest40%offsprings still suffered reproductive defects. As for the divergence, we inferred that elimination of Wolbachia in the parent generations (F0) could reduce the number of ovarian tubule in the offspring generations, but absorbing new source of Wolbachia from their whitefly hosts during developmental stage may compensate for the inborn loss of Wolbachia and make individuals return to the fully-developed reproductive systems.