Helopeltis pernicialis damage to a cashew crop was very serious in each of two years, resulting in no harvest unless the trees were protected either by pesticides or biological control agents. A control threshold was determined by a combination of the net income from increased yield and the frequency of insecticide use. A damage level of 1- 5% achieved the highest net profit. A damage level of 6- 10% resulted in yield that was over 73% of the yield of the 1- 5% damage level, but required one third less pesticide application. Therefore, it appears that 6- 10% damage level can be regarded as a control threshold for H. pernicialis. The pre-flowering flush appeared to be the most appropriate time to carry out the monitoring and spray programme to control H. pernicialis. Preliminary results showed that at the time when H. pernicialis caused serious damage to a tree without O. smaragdina nests, a tree with a constant ant population was only slightly damaged, andthe damage level never exceeded the control threshold of 6- 10%. It is suggested that O. smaragdina has high potential as a biological control agent.