Abstract: To clear the mechanism of activity differences of azadirachtin A and azadirachtin B, the toxicities of azadirachtin A and azadirachtin B on Trichoplusia ni BTI-Tn-5B1-4 cell line were compared. The results showed that both azadirachtin A and azadirachtin B had excellent inhibitory effect on BTI-Tn-5B1-4 cell proliferation. After T. ni BTI-Tn-5B1-4 cells were treated with azadirachtin A and azadirachtin B for 3 d, their IC50 values were 2.09 μg/mL and 9.85 μg/mL, respectively, suggesting that the toxicity of azadirachtin A was greater than that of azadirachtin B. Under inverted microscope, it was found that both azadirachtin A and azadirachtin B could induce cell deformation, adhesion capacity reduction and vacuole appearance, and azadirachtin A showed obviously greater effect than azadirachtin B. Azadirachtin treated-cells were commonly bigger than the control, and the cells treated with azadirachtin A were bigger than those with azadirachtin B through flow cytometry analysis. Azadirachtin can also change membrane potential of BTI-Tn-5B1-4 cells After BTI-Tn-5B1-4 cells were treated for 3 d, DiBAC₄ (3) fluorescence intensity in azadirachtin A and azadirachtin B-treated cells was 88.12% and 55.37%, respectively, showing that azadirachtin A had greater effect than azadirachtin B. Under fluorescence microscope, it was found that azadirachtin could influence cell nucleus, and azadirachtin B affected more remarkably than azadirachtin A, based on the results that the amount of cells with damaged-nucleus treated with azadirachtin B was larger, and damage in cell nucleus was more severe. The results suggest that there exists mechanism difference between azadirachtin A and azadirachtin B, and provide the clues to explain the mechanism of azadirachtin that inhibits insect growth at the cell level.

Key words: Azadirachtin A, azadirachtin B, Trichoplusia ni BTI-Tn-5B1-4 cell line, cell toxicity, flow cytometry