Studies On The Biological Characters Of Verticillium Lecanii And Its Infestation To The Tea Aphid, Toxoptera Aurantii

Verticillium lecanii is a worldwide hyphomycete fungus that has been developed as a biocontrol agent against aphids, whiteflies and scales. It also can be applied to the control of the main pest such as tea aphids in the tea trees.Isolation of strains of V. lecanii for different pest plays an important role in improving the pathogenicity of this fungus. Furthermore, the strain is also been applied in experiment for testing the control effective of tea aphids. Four strains of Verticillium lecanii biology and biochemical characters are discussed, in the aspects of morphology and biochemical characters and the infection towards the tea aphid.The results on the biological character of growth speed isolates reveal that strain V07 is the most fast in all the isolates by detecting the diameter of the colony; Strain V23 is the biggest while strain V07 the smallest. Strain V07 is the most in conidia reproduction and strain V08 the least.The biochemical properties include chitinase activity and protease activities, of the four strains were determined. 4 strains of V. lecanii are significant difference in chitinase activity and protease activities. Strain V07 has the highest protease activity and chitinase activity, while strain V08 has the lowest protease activities and chitinase activity.For the pathogenicity of V. lecanii to the tea aphid, twenty experimental colonies were initiated with each inoculated a dose of 5 concentrations of 4 strains fungus, V. lecanii and then were allowed freely for reproduction, fungal infection and mycosis dissemination at the optimal regime of 24℃and 100% RH. The information of percent disease incidence of the epizootic of tea aphid (Toxoptera aurantii), caused by the entomophthoraceous fungus V. lecanii were obtained by rating scale the disease severity of tea aphid experimental colonies, which is usually used for rating plant disease incidence. High level of epizootic occurred in the colonies initiated with initial inoculation of 2×10~7 conidial spore / ml of strain V07．The development of fungal epizootic in each colony was described using a modified Gompertz model, which is usually used for modeling plant epidemic. The initial inoculation dose was highly correlated to R, the apparent infection rate estimated from fitting the model. The conclusion is that the optimum vicinal dosage is 2×10~6 conidial spores/ml.Selecting system which enzyme activity associates the toxicity of strain was set up. The practical operation is more convenient and rapid.