Onion is one of the most important vegetable crops commercially grown in the world. In Ethiopia, the production and productivity of onion is low due to high infestation of onion thrips. This experiment was conducted to evaluate the efficacy of insecticide application on onion for the management of onion thrips in Wondo genet district, Sidama Regional State of Ethiopia from January to April 2024. The field experiment was laid out in RCBD with seven treatments and three replications to evaluate the effectiveness of insecticides against onion thrips. The crop was irrigated twice per week for the first four weeks after transplanting and once weekly thereafter. Ten randomly selected pre-leveled onion plants were used to collect data on the number of onion thrips, which was then analyzed using SAS. The infestation and damage status of onion thrips varied depending on the plant's developmental stage. The number of onion thrips per plant was low in early January, but it gradually increased until the peak population in March. The overall onion thrips populations were higher throughout the vegetative development stage but reduced as the plants approached maturity. The result showed onion thrips reduction due to their susceptibility to insecticides. Then Imidacloprid 350 SC and Profenofos 72%EC treatments reduced the population of onion thrips by 56.31% and 56.30%, respectively. Environmental elements (temperature, rainfall and relative humidity), and months The temperature and thrips population in onion showed a significant positive correlation.when rainfall reduced, the number of thrips increased.However, the number of thrips was negatively correlated with relative humidity in onions.Among six tested insecticides against onion thrips, Imidacloprid had the maximum yield of onions (25.17t/ha) achieved. Therefore Imidacloprid 400 ml/ha and Profenofos 600 ml/ha are recommended against thrips in Wondo Genet district. However, as the experiment was done for only one season and a single location, it has to be repeated over seasons and locations to make a conclusive recommendations.