Abstract: The spatial distribution pattern of different life stages of T. tabaci Lindeman -a serious pest of ornamentals and vegetables worldwide and a fixed-precision sampling plan for this pest on cucumber was investigated in an experimental greenhouse. For decision-making in IPM information about spatial distribution pattern of this pest is needed as is sampling plans. Therefore, the second objective of this paper was to developing fixed- precision stop lines for decision making for onion thrips on cucumber. Population estimation was made with recording number of different life stages of onion thrips on each side of the cucumber leaves. Taylor’s power law and Iwao’s patchiness regression were used to analyze the data. The spatial distribution was aggregated for 1st instar larvae Taylor’s coefficient (β 1.54) and random, for both 2nd instar larvae and adults (β 1.22 and 1.12, respectively). Based on the collected data, stop lines for decision making at a precision level of 0.1 or 0.25 was calculated to allow easy estimation of thrips population density.