Detecting brown plant hopper (BPH) population in images is concerned in recent years to support the insect monitoring application in agriculture. Combination of this research topic and the light trap systems will help to automate the counting of BPH falling in the traps, which is currently done manually. In this paper, a new approach to detecting BPH in images based on morphological operations will be proposed. By applying these operations appropriately, shape structure and size of the BPH in images can be identified and the number of BPH can be counted. This helps to detect BPH in images more effective and accurate, and reduce time and effort in doing this task. In addition, we also propose a method for removing noise (inserts other than BPH) in image based on the weight and color factors. The experimental results show that the proposed approach is suitable for detecting and counting BPH in images.