Analysis Of The Factors On Thelytokous-phenotype And Wolbahica Titer In Trichogramma Dendrolimi Matsumura(Hymenoptera:Trichogrammatidae)

Endosymbionts Wolbachia increase their spread by manipulating reproductive phenotype of hosts in various ways,like cytoplasmic incompatibility,thelytoky,feminization and male killing,becoming an important model of studying interaction between bacteria and hosts.Previous researches mainly centered around male killing and cytoplasmic incompatibility,but not thelytoky.Thelytokous Trichogramma have stronger ability to go to fixation in the field as they can produce fertile female offspring without copulation that could control pests.And therefore,Wolbachia-induced thelytokous Trichogramma are generally considered with greater biocontrol potential.Factors like temperatures,antibiotics,hosts' backgrounds and infection time could manipulate the reproductive phenotype of hosts by affecting the expression of Wolbachia.Relative studies about effects of factors on Wolbachia are mainly focused on male killing and cytoplasmic incompatibility,but less are on thelytoky.With thelytokous T.dendrolimi,current study explored the effects of temperature,parasitism form and spawning time on thelytokous phenotype,fitness of T.dendrolimi and Wolbachia titer.The results may lay theoretical foundation for revealing the molecular mechanism of Wolbachia-manipulated thelytoky,and also for the advance of practical application and industrial rear of Trichogramma.Results are listed as follows:1.By continuous four generations' treatments of different temperatures,the effects of thermal experience on thelytokous phenotype and fitness were measured and then analyzed.Results showed that temperature and generation(duration of thermal experience)had significant effects on reproductive phenotype and fitness.Of which,every fitness factor except longevity was significantly better with the generation(thermal experience)but not under 17 ?;fitness was decreased at either high or low temperatures and the optimal developmental condition was 21 ?;Male ratio(except 17 ?)increased with the generation and showed a lowest value under 25 ?.The study also found that number and duration of intersex occurrence was very short(only in the first 1 to 2 days).Results showed that temperature and generation(duration of thermal experience)had significant effects on reproductive phenotype and fitness,the optimal expression of Wolbachia-induced thelytoky is at 25 ?.2.Based on the previous experimental results there above,the effects of two parasitism form,i.e.,singleparasitism and superparasitism on reproductive phenotype and fitness under different temperatures were further investigated.With the help of q PCR,the titer of Wolbachia in maternal wasps from different treatments was detected,aiming to set up the relationship between reproductive phenotype and Wolbachia titer under different temperatures and parasitism forms.Current study found that temperature and parasitism form had significant effects on fitness of thelytokous strain of T.dendrolimi.Either high or low temperature decreased the fitness and wasps from singleparasitism had better fitness than that of those from superparasitism.Wolbachia titer and female offspring ratio were significantly affected by the interaction of temperature and parasitism form: females from singleparasitism showed significant decrease of Wolbachia titer and male offspring with the increase of temperature;the Wolbachia titer and male offspring of females from superparasitism meantime exhibited no correlation with temperature,but a significantly higher Wolbachia titer was found in this one than in those from singleparasitism;intersex proportion was not affected by either temperature or parasitism form;male offspring ratio significantly increased with the age of female adults.The results suggested that temperature and parasitism form are important factors that affected the reproductive phenotype and Wolbachia titer.3.Base on previous studies,the effects of temperature and host background on reproductive phenotype and fitness of thelytokous T.dendrolimi were explored.The study found that T.dendrolimi with different backgrounds had different adaptation abilities to temperature: wasps from Zhangwu county showed good adaptation ability to low temperature while wasps of those from Xifeng county exhibited good adaptation ability to high temperature;temperature was the crucial factor affecting the expression level of T(reproductive phenotype and Wolbachia titer): high temperature significantly decreased the expression level of T in T.dendrolimi,but the effects were slightly different on wasps with different backgrounds: in comparison with those from Xifeng,the wasps coming from Zhangwu were affected much more severely.4.Since oviposition time(female adults' age)was found to be one important factor under continuous oviposition in Chapter three and four,it could be inferred that Wolbachia titer might be affected by the intensity of oviposition.Therefore,current experiment tried to settle the effects pattern of oviposition intensity on reproductive phenotype,Wolbachia titer and fitness through restriction of oviposition time.No significant effects of oviposition time were found on fitness of thelytokous T.dendrolimi;the first 1 d amount of oviposition significantly affect the Wolbachia titer in females wasps and their male offspring ratio.With the increase of oviposition time,the ratio of male offspring significantly increased while the Wolbachia showed an opposite correlation.The results indicated that restriction of oviposition time rendered the thelytokous phenotype of T.dendrolimi more stable but no significant effects were found on fitness.The first 1 d amount of oviposition decided the extent of reproductive phenotype and an irreversible effect on Wolbachia titer in female wasps.