A distributed-delay simulation model was developed for Frankliniella occidentalis (Pergande) on greenhouse cucumber. The life history parameters used for construction of the model were obtained from published data. The model was validated using population growth data that were obtained by sampling two greenhouse cucumber crops. Predicted population dynamics by the model were in agreement with observed greenhouse population dynamics of F. occidentalis when population densities were <550 adults and larvae per plant. Sensitivity analyses revealed that sex ratio and fecundity by females were the most sensitive parameters in the population model. The simulation model was used to determine the economic thresholds for F. occidentalis based upon previously established economic injury levels. This was done by investigating the population dynamics of F. occidentalis in situations where a pesticide was applied when the population levels exceeded the determined economic thresholds at temperatures of 20 and 25°C. The effects of initial thrips density combined with different thrips invasion rates or temperatures on the population growth of F. occidentalis were also evaluated by the simulation model.