The experiments were carried out at the experimental farm of Assiut Agricultural Station (Arab-Elawamer) - Abnoub province - during two successive growing seasons 2013 and 2014. The aim is the evaluation of the population trends of onion thrips, Thrips tabaci Lind. (Thysanoptera: Thripidae) and its relation to plant age and certain abiotic factors (temperatures and relative humidity %) that have been evaluated by the direct count on onion plants. Also, flight height activity of this insect pest and it's relation to plant height has been evaluated by sticky traps methodology. By the using of plants direct count three peaks during first January, mid-February and late March in both seasons were recorded. The obtained results revealed that the third peak is equal 1.71 and 1.16 fold of the first and the second peaks, respectively. Thrips peaks were coincided with the optimum (max. and min.) temperatures ^ºC with positive correlation coefficient (r) with the pest populations. However, the relative humidity % (max. and min.) showed a negative (r) with the pest populations during the two studied seasons. Plant age showed positive (r) with the pest populations and appeared as the third factor responsible for T. tabaci population fluctuations. By using both yellow and white sticky traps the pest exhibited two peaks. The first peak showed quietly high numbers at February, 6 while the second peak showed the pest greatest numbers at March, 27 in both seasons. Data revealed that yellow and white sticky traps hanged at 30 cm height, captured the highest numbers at the first peak. However, those hanged at 60 cm height captured the greatest numbers at the second peak. Traps hanged at 90 cm height captured the least numbers at both peaks. Data reported that there were a positive (r) between plant height and thrips populations. It is important to note that the two peaks of T. tabaci recorded by sticky traps were appeared one week before the 2^nd and 3^rd peaks recorded by direct count method. So, sticky traps can be consistently detected thrips earlier than direct count and could be used instead of plant counts to monitor onion thrips populations.