On farm, trials were carried out at rainfed rice growing areas of West Bengal, India during Kharif(rainy) season 2003-04 and an average population of parasitic nematode Hexamermis sp. counted from the same field during 2003-04 to 2018-19 in Birbhum. A similar set of experiment was conducted during boro(summer) season 2008-09 in Bankura and average population of Hexamermis sp. was also calculated from the same field during 2008-09 to 2018-19. Each trial comprised three treatments viz (i) Natural Biological Control (NBC) with no pesticide application throughout the crop season (ii)Need based protection (NBP)- judged by periodic monitoring of brown planthopper population and (iii) Schedule treatment (ST)- involving application of insecticides following usual package of practices. The study revealed that NBC resulted in maintaining highest level of parasitism of Brown Plant hopper by this parasite Nematode as compared to NBP and ST. Identical results were also obtained from 15 years and 10 years average data from Birbhum and Bankura during kharif (rainy) and boro(summer) season rice respectively..