Resistance selection and resistance stability by several insecticides to Aphis gossypii Glover

A general evolution of resistance in A.gossypii to most insecticides has been repor-ted in recent years.Preliminary determinations for LD_(50) were carried out in this laboratory forcomparing resistance differences of A.gossypii treated with imidacloprid,imidacloprid+SV_1,omethoate and fenvalerate.By successive resistance-selection four resistant strains of cottonaphid were set up,R-imidacloprid,R-imidacloprid+SV_1,R-omethoate and R-fenvalerate.Results showed that,the resistance rate of R-imidacloprid and R-imidacloprid+SV_1 strains(after 18 generations of resistance selection)were lower than that of the R-fenvalerate and R-omethoate strains(after 12 generations of resistance selection).The resistance rate reached10.08-fold to imidacloprid in the 18th generation(F_(18)),9.70-fold to imidacloprid+SV_1(F_(18)),28.48-fold to omethoate(F_(12))and 35158-fold to fenvalerate(F_(12))respectively.Whenresistant-selection was suspended in the next successive 12 generations,the resistances ofaphids decreased.