Little information exists about pesticide availability and its effect on pest control in rural regions of developing countries. The availability of different insecticidal ingredients in rural areas of Cambodia was determined by inspecting labels on products used by farmers and in retail shops. A large number of products available in markets and used by farmers contained abamectin, emamectin benzoate, cypermethrin, and chlorpyrifos. The effects on the brown planthopper (BPH; Nilaparvata lugens (Stål)) were investigated by comparing the susceptibility of three BPH populations in Cambodia to twelve active ingredients in 2015. All populations showed high susceptibility to abamectin and cypermethrin; however, regional differences in susceptibility were observed for the other ingredients. The implication was that farmers selected the most effective products based on sellers’ opinions. It is important to monitor insecticide use and BPH susceptibility in each region of Cambodia in order to minimize the risk of high BPH population densities.