The brown planthopper (BPH), Nilaparvata lugens (Stål), is the most important insect pest of rice in Asia. Host plant resistance is one of the strategies currently used to control BPH. The resistant rice cultivar Rathu Heenati (RH) carrying the BPH3 gene (recently renamed as "BPH32") remains effective despite more than 30 years of deployment. RH has been determined to be resistant against BPH at all growth stages. However, we observed that BPH could feed on panicles but not on the leaf sheaths of RH. The resistance gene BPH32 was introduced into KDML105 through marker-assisted selection, and the introgression line UBN03078 was developed. This rice line was used to observe the patterns of target gene's regulation. A low-level expression of BPH32 on panicles has been hypothesized to cause susceptibility in UBN03078 at the heading stage. Findings from our gene expression analysis support the hypothesis that the resistance gene was down regulated in the uppermost internodes compared with the leaf sheaths of the heading rice plant. This phenomenon may allow BPH to feed on the panicles of the resistant plants, but this requires further investigation.