Abstract: he present study was conducted in Voion county in the region of Kozani, in tobacco fields, involving population monitoring for two years (2004 and 2005), for three insects: Thrips tabaci, Epitrix hirtipennis and Myzus persicae. Two combined insecticides were applied: Tamaron 600SL (methamidophos) and Confidor 200SL (imidachloprid) and a check field (without application) was used. Sampling was conducted at seven periods, with 85 main samples consisted of three plants. Insecticide application reduced insect population about 70-74% and especially thrips population (up to 78%), resulting in double field yield performance of tobacco in comparison to check fields (no application). In the second year, there was a reduction of initial insect population, maybe due to previous effective application of insecticides and environmental conditions. There was a considerable interaction between insecticide application, insect species and sampling period, indicating different effectiveness of insecticides on insect species and differences in seasonal population fluctuation (due to different biological cycles of the insects during the cultivation period). Differences between years were found, indicating different environmental conditions. In general, there were greater populations of thrips or green aphids than flea beetles (about 30%). Second insecticide application was not only indispensable, but also lead to increased efficiency of insecticides. Finally, different environmental conditions, including transplanting period, may affect uniformity of insecticide application in the tobacco fields.