The biology of rice thrips,Stenchaetothrips biformiswas studied on different ages of variety TN1 seed/ings [10‐,20‐30‐day‐old] and the weedEchinochloa colona.The total life span was 20.1, 24.2, 26.2 and 32.5 days on 10‐, 20‐ and 30‐day‐old TN1 seedlings and the weed respectively. The fecundity was 21.4, 21.6, 28.7 and 15.1 eggs respectively on 10‐, 20‐, 30‐day‐old TN1 plants and the weed host. There was lower larval survival, reduced adult longevity, less fecundity and low population growth on the resistant rice variety Ptb 33 compared to the susceptible TN1.