Abstract: In this paper,Spodoptera exigua from Fuzhou of Fujian Province was continuously selected and bred to test its resistance to cyhalothrin，fenvalerate and alpha-cypermethrin,and to evaluate its realized resistance heritability (h²) and resistance risk.The results showed that after 12,10,and 10 generations,the resistance of S.exigua to cyhalothrin,fenvalerate and alpha-cypermethrin was increased by 18.1,27.6,and 45.4 fold,and the realized resistance heritability was 0.2567,0.3571 and 0.4239,respectively.Assuming that the h² of field S.exigua population was half of these values,it required 9～20 generations for cyhalothrin,6～14 generations for fenvalerate,and 5～12 generations for alpha-cypermethrin to obtain 10-fold increase in resistance under selective pressure of 50%～90% mortality for each selective generation.Of the three pyrethroids,the resistance risk to cyhalothrin was smaller than that to fenvalerate and alpha-cypermethrin.

Key words: Artificial oases, Potential pattern, Actual pattern