Abstract: Experiment conducted on large block showed that Aci NPV insecticide were quite effective in the control of the larvae when it was used in the field.It has been proved that once the virus is introduced into the forests,whatever it is sprayed at high, low or even ultra-low volume,or whatever it is applied in air or on ground,epizootic frequency will occur in the larval population. The results of the experiments were quite satisfactory.The larval population reduced rate was 85% to 96% in the year of application.In ground-spraying, the dosage was 3.0 × l011～6.0 × l011 PIB/hm2 with a lowest dosage of 2.03×1011PIB/hm2,while in air-spraying,the dosage of aerial ultra-low spraying was 3.75×l011PIB/hm2 with a lowest dosage of 1.88 ×1011 PIB/hm2.The observation suggests that a strategy of spraying every other line would reduce the cost of operation spray programs 63.8%. The suitable time for spraying was when 80% of the larval population was composed of lst and 2nd instar ones.