Experiments were carried out to investigate tolerance of various developmental stages to fenitrothion, and susceptibility to 13 insecticides, of 3rd instar nymphs of the bean bug, Riptortus clavatus THUNBERG were tested in the laboratory. The results obtained were as follows; Egg period, nymphal period and adult longevity were 7.5 days,21.8 days and 42.0 days respectively Average number of eggs laid per female were 140.0 eggs. The hatchability of the eggs was 95%. The degree of tolerance was greatly increased by the nymphal development: the relative tolerance to the fenitrothion was 1.4 for the 2nd, 1. 5 for the 3rd, 4.7 for the 4th and 17.8 for the 5th instar. Comparison of LD$_{50}$ values/bug and LD$_{50}$ values/body weight for the 3rd instar of the bean bug to fenitrothion was in good use for insecticide assay. It was found to be highly susceptible to the synthetic pyrethroid compounds tested than any other ones; being the most susceptible to deltamethrin. In case of organophosphates, the LD$_{50}$ of phosphamidon was observed to be 0.0089 $mu extrm{g}$/bug which was the highest susceptible values out of the 6 kinds of the OP compounds; diazinon; 0.0210 $mu extrm{g}$/bug and demeton-S-methyl; 0.0193 $mu extrm{g}$/bug. In carbamate compounds, the LD$_{50}$ values of BPMC and carbaryl was 0.0217 $mu extrm{g}$/bug and 0.0163 $mu extrm{g}$/bug. respectively.ctively.