Buprofezin treatment of brown planthopper, Nilaparvata lugens Stal. at sub-lethal doses resulted in the survival of individuals with varying reproductive potentials. From this reproductive potential of different stages, population build up of second generation was calculated. Logistic function was found to fit more closely the data on population growth at different concentrations. It could thus serve as a mathematical model for predicting the second generation population build up in a buprofezin treated population.