Brown planthoppers (BPH) damage rice directly through feeding and transmitting two the most dangerous kinds
of virus on rice, i.e. rice ragged stunt and rice grassy stunt virus. This is one of the most dangerous species of insect for rice plant. Therefore, detecting and estimating BPH population in rice fields are concerned recently to support the BPH monitoring. In this research, an approach to detecting and counting BPH in images taken by light traps, the most used device to catch BPH in rice fields, is proposed. This approach uses morphological operations to analyse BPH structure and the sequential region labeling algorithm to count the separate BPH. In addition, an approach to dealing with overlapped BPH is also introduced. The experimental results show that our proposed approach is suited to identify and count the BPH in images. Particularly, our approach can deal with images that contain overlapping individuals.