Effect Of Tetracycline And Wolbachia On The Fecundity Of Encarsia Formosa

Encarsia formosa are important parasitic wasps,commonly used in the control of tobacco whitefly(Bemisia tabaci)and greenhouse whitefly(Trialeurodes vaporariorum).However,different strains of the wasps have different control efficiency.E.formosa are widely infected with an intracellular symbiotic bacterium-Wolbachia which inducing parthenogenesis(PI)in the parasitic wasps.It is not yet clear that Wolbachia have positive or negative impacts on the fecundity of the wasps.In order to evaluate the effects of Wolbachia on host,tetracycline is used to remove Wolbachia.However,tetracycline is toxic.It is difficult to distinguish the impacts caused by tetracycline or Wolbachia after feeding.In our study,we amplified the COI and 28S rRNA sequences of E.formosa to compare the genetic backgrounds of them.Meanwhile,we used multilocus sequence typing(MLST)to determine strain of Wolbachia in E.formosa.We treated FO lines of E.formosa with tetracycline of different concentrations to acquire several F1 lines in which Wolbachia titres were decreased,meanwhile,the influences of tetracycline were excluded.In following experiments,Wolbachia were quantified in each E.formosa line.The reproductive effects of tetracycline were indicated on FO wasps,and the effects of Wolbachia on F1 wasps were assessed based on parasitism rates,oocyte load and vitellogenin relative expression levels.Specific results are as follows:(1)Encarsia formosa lines and Wolbachia strainsWe collected E.formosa lines from four laboratories,compared COI and 28S rRNA sequences of these wasps,and typed Wolbachia strain.The results showed that there were two polymorphic sites of mitochondrial COI sequences,and 28S rRNA sequences were basically same in four lines of wasps.We suggested that there was a low level genetic differentiation in four wasp lines.In addition,our results indicated there was a unique Wolbachia strain infected the four wasp lines.(2)Effect of tetracycline on the fecundityNewly emerged wasps were treated for 24 h with tetracycline mixed solution after starved for 24 h,and then were exposed to 3rd-instar B.tabaci nymphs.The parasitism rates of FO lines were significantly affected by tetracycline.Oocyte load per ovariole of the two-day-old treated FO wasps were significantly more than the control line.Compared with control line,relative expression levels of vitellogenin gene of treated lines were significantly higher,and the level of 2-day-age F0-20 was the highest among all lines.To further investigate the toxicity of tetracycline,the FO lines were continuously treated with tetracycline mixed solution till wasps died.Oocyte load and longevity of the control line were significant more than treated lines in following days.Wasps treated with 10 mg/ml tetracycline survived for six days,and their oocyte load decreased significantly day by day.(3)Effect of Wolbachia on the fecundity and the offspring sex ratioThe parasitism rates of nymphs by treated F1 wasps were lower than that by control line.There were also significant differences in oocyte load among F1 lines and control line.The relative expression levels of vitellogenin gene of F1 wasps were not different but lower than that of their control line.After females were fed antibiotic tetracycline,they produced not only female but also male offspring.The female proportion of offspring varied significantly among treated lines.All of the female wasps were infected with Wolbachia,and a few of male offspring were unpredictably infected with Wolbachia.