To evaluate and monitor insecticide resistance in onion thrips Thrips tabaci on onion (Allium cepa), we conducted a study using three field populations in the Treasure Valley of eastern Oregon and southwestern Idaho using the insecticides Lannate (methomyl) and Exirel (cyantraniliprole). To evaluate these two insecticides, biological assays were conducted to determine which insecticide is effective at controlling onion thrips. To analyze our data, we ran a probit analysis. Our results indicated that the three field populations were more susceptible to the insecticide Exirel than Lannate, as the LC50 values for Exirel were lower than the LC50 values for Lannate. Although the analysis didn’t fit a straight-line model, our slope indicated that as the concentration increased mortality increased, demonstrating a clear relationship between the two variables. It is important to note that onion thrip populations fluctuate throughout the years. It is important to monitor thrips as climate change is on the rise due to their ability to develop resistance at a rapid rate. This ultimately affects onion growers and their ability to control this pest, but it is also essential to integrate different pest management plans that may or may not involve the use of insecticide so running these tests will help learn more about the ecology of onion thrips T. tabaci.