Study On The Economic Threshold And Ecological Threshold Of Oedaleus Asiaticus Control On Typical Steppe In Inner Mongolia

The work in this dissertation was focused on the indoor intake, the relation between intake and humidity, appetite, the survival rate of the Oedaleus asiaticus , while methods of the field caging and artificial simulation were employed to investigate the interreaction between the feeding of grasshopper and forage yield of grassland, and then to evaluate associative effect in order to confirm the economic threshold (ET) of O. asiaticus. By using Metarhizium anisopliae to control the number of grasshopper within the scope of the economic threshold, while evaluation its protection to the biodiversity of the grassland ecosystem. In terms of the ecological threshold, which was investigated in the typical grassland in Beilike Pasture, Inner Monglia . Where the pasture was destroyed seriously by the grasshopper in 2003. The structure and changes of biologic population in process of restoratation of the pasture were also discussed. The results show as follows: Young grass was intook by low instar O. asiaticus at density less then 30 heads/m2 would lead to an obvious overcompensation to the grass later on, therefore, makeing forage yield increase. It was found that the forage yield within field caging was higher than that measured by using artificial simulation method. With the increase of instar, the grasshopper intake increase, which therefore, leaded to forage yield drops rapidly, the lowest forage yield was achieved when the insect got adult. It is based on to caculate the economic threshold, ET= 6.1182 heads/m~2. The economic threshold ranged between 5 heads/m2 to15 heads/m2 of O. asiaticus at either field caging or artificial simulation experiments. When compensation quantity was 0, control criterion of the O. asiaticus was 7.97 heads/m2 (field caging) or 10.59 heads/m2 (artificial simulation) . According to the principle of the economic threshold (ET), the saving loss = the prevention cost, while the compensate index and vegetation cover as parameters were also considered to builds up the model of ecological threshold of grassland damaged by O. asiaticus. Metarhizium anisopliae as a kind of entomogenous fungis is the function of the long time to control grasshopper communities. There is no difference between chemical control and biological control from the control effect, but biological control has the stability to protect biodiversity of the environment and maintain grassland ecosystem at the same time. Therefore using M. anisopliae to control grasshopper have the developing meaning to the grassland ecosystem.