Abstract: Effects of azadirachtin dosages on population dynamics of the diamondback moth (DBM), Plutella xylostella, were investigated in both laboratory and field. The results showed that azadirachtin strongly deterred the adult from laying eggs and significantly inhibited larval feeding on the plant with it. When 0.005 mL/L of azadirachtin was applied, 78.3% of the adults of DBM was kept away from the host plant and larval antifeedant ranged from 62.9% to 71.8%. Total food intake by DBM larva decreased to 59.0% of that in the control. The index of population trend of DBM decreased to 2.4 from 22.0 in the control. The interference index of population control was 0.1079. Based on the space-state equation of cybernetics, models of DBM population dynamics were set up, which indicated the deterrent activity of azadirachtin to the adult egg-laying played a key role in population control.

Key words: azadirachtin, Plutella xylostella, population control, deterrent effect, antifeedant effect