| Beauveria bassiana is one of the most widely used entomopathogenic fungi in the world.B.bassiana often shows high virulence against many important insect pests,and leads a fungal epizootic disease in an insect pest population.Quantative effects of humidity,temperature,and initial infection ratio on the fungal infection of B.bassiana against Stephanitis nashi and locusta migratoria manilensis were studied and their models were constructed in the present thesis.Fungal pathogens,insect hosts,and other environmental factors as well as pathogen transmission route are the key factors for a fungal epizootic disease.The temperature and humidity play an important role on conidia germination,hypha growth,and fungal infection of B.bassiana.The comparative effects of humidity and temperature on the fungal infection of B.bassiana against S.nashi and L.migratoria manilensis were observed in the present study.The insects were inoculate with 1.0×107 spores/ml spore suspension of B.bassiana,and kept under 25?.It was observed that the pathogenicity of fungi was increased as the humidity increased and positively effects on mortality of insects which conform by the model of time-humidity-death(THM),a fitting model of the time-dose-death model(TDM).The model can describe the fungal disease development with the humidity and time changed.The THM model showed that,when humidity was more than 85%,the mortality of S.nashi was significantly higher than L.migratoria manilensis.After comparison of the mortalities of S.nashi,the time parameters become maximum on day 6(y6)and the parameters of L.migratoria manilensis become maximum on day 11(?11).S.nashi is more sensitive than L.migratoria manilensis to the change of relative humidity.Results on temperature effects showed,when the environmental relative humidity was over 95%,the fungal infection on the both insects by B.bassiana reached the maximum at 25?,and then followed at 28?.A higher or lower temperature decreased the fungal infection.The result shows that the infection of B.bassiana has an obvious optimum of temperature.Although temperature effect on mortality was not conformed to the TDM model,parameters of logistic model equation under different environmental conditions can express the theory of instantaneous mortality of insects and the cumulative mortality rates.By comparing the value of logistic model parameter,S.nashi is more easily got infection than L.migratoria manilensis with a faster speed and a short infection period.The construction of the THM and logistic models benefits us understanding the effects of relative humidity and temperature on fungal infection to different target insects.The prevalence of the epidemic of B.bassiana was closely related to the initial fungal inoculation ratio to the total population.In the present thesis,four different initial inoculation ratios of 10%,30%,50%,and 70%were set to assess the fungal disease development in the populations of the two tested insects,S.nashi and L.migratoria manilensis,.The results showed:Higher initial inoculation ratio,a higher insect mortality and final infection in the insects' population are expected.With initial inoculation ratios of 70%,50%,30%,and 10%,the cumulative mortalities for L.migratoria manilensis were 100%,85%,75%,and 50%,respectively;whereas the cumulative mortalities for S.nashi were 90%,70%,60%,and 30%at the end of the observation.The fungal disease level in the population of S.nashi was some lower than that of L.migratoria manilensis,which means host species poses some influence on the development of the fungal disease of B.bassiana.Gompertz model was used to clarify the relationships among initial infection ratio,speed of disease development,and final infection level.The parameters K and R in the model respectively expressed the highest infection level and apparent infection ratio.The two parameters are positively related to the initial infection ratio.A linear relationship between the fungal disease and the initial infection ratio(P)was found in the present thesis.Obviously the initial infection ratio by B.bassiana determines the epidemic levels in the two insects' population.Comparison of the two different K values of the two insects showed that the highest prevalence level of L.migratoria manilensis significantly greater than that of S.nashi,The difference may mainly caused by different moving ability of the tested insects.The linear equations for the parameters of K and R were combined into the general Gompertz model to predict temporal development of the fungal disease of B.bassiana..The equation for epidemiology of S.Nashi is x=(0.46p+0.48)e-?e-(0.07p+0.20)t The equation for epidemiology of L.migratoria manilensis is x=(0.85p+0.54)e-?e-(0.07p+0.21)... |
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