The population dynamics includes quantity dynamics,space dynamics and temporal dynamics. They are interdependent and mutually influential.Fuzzy cluster analysis was carried out with the data of mean densities,indices of patchiness and occupied plot rates of Chorthippus fallax (Zubovsky)on Ganjia High Mountain Grassland in Xiahe County,Gansu Province. The results showed that the population dynamics of this grasshopper could be divided into four distinct periods,i.e.,the initial stage of hatching and the last stage of adult,the peak stage of nymph,the initial stage of adult,and the peak stage of first nymph and the adult. The peak period of nymph was in the middle ten days to the last ten days of July. In this period,the eggs were completely hatched,the population was mainly composed of nymphs of 2 and 3 instars,and the population size was related to the numbers and harmful levels of this grasshopper in the same year.Therefore,this period was the key time for population prediction and chemical control.
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